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Maake, Popoti Jacqueline. "Photovoltaic and gas sensing applications of transitional metal nanocomposites of poly(3-hexylthiophene)-titanium dioxide." University of Western Cape, 2021. http://hdl.handle.net/11394/8240.
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>Magister Scientiae - MScThis thesis starts with the reviewing of studies on the loading of noble metals and nanostructured metal oxides into bulk heterojunction organic solar cell device architectures. The reviews focused on the innovative developments in the use of various fullerene derivatives as electron acceptors in organic solar cells. It additionally reflected on the effect of metallic nanoparticles (NPs), such as gold (Au) and silver (Ag), on the performance of organic solar cells. Besides the metallic NPs, the effect of metal oxide nanoparticle loading, e.g. CuO, ZnO and TiO2, on the organic solar cell performance, and the use of noble metals doped TiO2 on the gas sensing application were reviewed.
2024
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Perino, Mauro. "Characterization of plasmonic surfaces for sensing applications." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424012.
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My research activity during the Ph. D. period has been focused on the simulation and the experimental characterization of Surface Plasmon Polaritons (SPP).
Surface Plasmon Polaritons are evanescent electromagnetic waves that propagate along a metal/dielectric interface. Since their excitation momentum is higher than that of the photons inside the dielectric medium, they cannot be excited just by lighting the interface, but they need some particular coupling configurations. Among all the possible configurations the Kretschmann and the grating are those largely widespread.
When the SPP coupling conditions are reached, abrupt changes of some components of the light reflected or transmitted at the metal/dielectric interface appear. Usually this resonances are characterized by a minimum of the reflectance acquired as a function of the incident angle or light wavelength. Several experimental methods are available to detect these SPP resonances, for instance by monitoring the light intensity, its polarization or its phase.
Changes in the physical conditions of the metal/dielectric interface produce some changes of the SPP coupling constant, and consequently a shift in the resonance position. If these changes derive from a molecular detection process, it is possible to correlate the presence of the target molecules to the resonance variations, thus obtaining a dedicated SPP sensor.
I focused the first part of my Ph.D. activity on the simulation of SPP resonances by using several numerical techniques, such as the Rigorous Coupled Wave Analysis method, the Chandezon method, and the Finite Element Method implemented through Comsol v3.5.
I simulated the SPP resonance in the Kretschmann coupling configuration for plane and nano-grating structured metal/dielectric interfaces. Afterward, I calculated the SPP resonance behaviour for grating and bi-dimensional periodic structures lighted in the conical configuration. Furthermore, I analysed the correlations between the grating coupling method and the Kretschamann coupling method.
Through all these simulations, I studied the sensitivity of the different SPP resonances to the refractive index variation of the dielectric in contact with the metal. In this way, I was able to find a new parameter suitable for describing the SPP resonance, i.e., the azimuthal angle. By considering this particular angle, the sensitivity of the SPP resonances could be properly set according to the experimental needs and, even more important, noticeably increased to high values.
Experimentally I used two opto-electronic benches, one for the Kretschmann configuration and one for the conical mounting configuration. I have performed experimental measurements, in order to compare the experimental data with the simulations. In particular the following conditions were tested:
• Plane interface, Kretschmann configuration
• Nanostructured grating, Kretschmann configuration
• Nanostructured grating, Conical configuration
I focused my attention on the nano-structured grating in conical mounting configuration. I found an innovative way to characterize its SPP resonances, by measuring the transmitted signal as a function of the incident and azimuthal angles. The transmittance and the azimuthal sensitivities were characterized with the gratings in both air and water.
In order to study the experimental azimuthal sensitivity, I changed the liquid refractive index in contact with the grating by using different water/glycerol solutions. Moreover, I functionalized the surface by using thiolated molecules that form Self Assembled Monolayer onto the metallic layer. In this way, I was able to change the SPP coupling constants and detect the corresponding azimuthal resonance shifts. I also detected the immobilization of an antibody layer onto the metallic surface of the plasmonic interface.
All the devices I used in the experimental measurements were produced by the University spin off Next Step Engineering.Durante il mio periodo di dottorato in Scienza e Tecnologia dell’Informazione l’attività di ricerca principale è stata focalizzata sulla caratterizzazione, simulativa e sperimentale, dei plasmoni di superficie. I plasmoni di superficie sono onde elettromagnetiche evanescenti che si propagano all’interfaccia tra un mezzo metallico ed un mezzo dielettrico. Il loro vettore d’onda è più elevato rispetto a quello della luce nel mezzo dielettrico. Per poter quindi generare l’eccitazione si devono utilizzare particolari tecniche di accoppiamento. I due metodi più diffusi sono l’accoppiamento Kretschmann e l’accoppiamento tramite reticolo. Una volta raggiunte le condizioni di accoppiamento dei plasmoni di superficie, si realizza il fenomeno della risonanza plasmonica, la quale si manifesta attraverso brusche variazioni nelle componenti della luce riflessa o trasmessa dalla superficie. Tipicamente si può registrare un minimo della riflettanza in funzione dell’angolo di incidenza della luce sulla superficie. Esistono, tuttavia, anche altre modalità per registrare e misurare queste risonanze, come ad esempio monitorando intensità, polarizzazione o fase della luce trasmessa e riflessa dalla superficie, in funzione della sua lunghezza d’onda o dei sui angoli di incidenza. Le variazioni chimico/fisiche che avvengono all’interfaccia metallo/dielettrico, modificando la costante di accoppiamento plasmonica, cambiano le condizioni di risonanza. Nel caso in cui le variazioni all’interfaccia siano dovute ad un processo di riconoscimento molecolare è possibile rilevare le molecole d’interesse valutando i cambiamenti della risonanza plasmonica, fornendo così l’opportunità per l’implementazione di sensori specifici. L’attività di dottorato è stata focalizzata innanzitutto sullo studio teorico del comportamento della risonanza plasmonica, utilizzando varie tecniche di simulazione numerica: il metodo RCWA (Rigorous Coupled Wave Analysis), Il metodo di Chandezon ed il metodo agli elementi finiti, implementato tramite Comsol v3.5. Ho poi affrontato lo studio, tramite simulazioni, delle risonanze di superficie in configurazione Kretschmann, sia per interfacce metallo/dielettrico piane sia per interfacce nano-strutturate. Considerando una configurazione conica, ho simulato le risonanze di superficie per nano-strutture reticolari e per nano-strutture bi-dimensionali periodiche. Inoltre ho analizzato il legame tra le modalità di accoppiamento grating e Kretschmann. Tramite queste simulazioni mi è stato possibile valutare e studiare la sensibilità delle varie risonanze plasmoniche alla variazione di indice di rifrazione, quando essa avviene all’interfaccia metallo/dielettrico. È stato così possibile identificare un nuovo parametro per descrivere la risonanza plasmonica e la sua sensibilità, ossia l’angolo azimutale, definito come l’angolo tra il vettore del grating ed il piano di scattering della luce. Considerando questo particolare angolo, la sensibilità del sensore può essere controllata con un’opportuna regolazione degli altri parametri coinvolti nell’eccitazione plasmonica, consentendole di raggiungere valori molto elevati. Successivamente, grazie all’utilizzo di due banchi, uno per la configurazione Kretschmann ed uno per la misura di reticoli nano-strutturati in configurazione conica, ho realizzato delle campagne di misure sperimentali. E’ stato così possibile confrontare i risultati sperimentali con le simulazioni numeriche per le seguenti condizioni: • Interfaccia piana, configurazione Kretschmann • reticolo nano-strutturato, configurazione Kretschmann • reticolo nano-strutturato, configurazione conica L’attività sperimentale si è particolarmente focalizzata sul reticolo nano-strutturato, sia per l’innovativa modalità di caratterizzazione delle sue risonanze plasmoniche (valutazione del segnale trasmesso in funzione dell’angolo di incidenza e dell’angolo azimutale), sia per l’elevata sensibilità ottenuta valutando la variazione dell’angolo azimutale. La caratterizzazione è stata effettuata sia per il reticolo esposto all’aria che per il reticolo immerso in un liquido (tipicamente acqua). Per poter verificare il comportamento della sensibilità azimutale ho variato l’indice di rifrazione del liquido in contatto con la superficie utilizzando soluzioni miste di acqua e glicerolo. Inoltre, tramite tecniche di funzionalizzazione della superficie, ovvero applicando delle molecole thiolate che vengono adsorbite sulla parte metallica dell’interfaccia, mi è stato possibile variare le costanti di accoppiamento plasmonico, in modo da verificare la capacità del dispositivo di rilevare l’avvenuta creazione di uno strato molecolare sulla superficie. Inoltre ho positivamente verificato la capacità di immobilizzare uno strato di anticorpi sulla superficie plasmonica. Tutte le misure sperimentali che ho svolto in questa tesi sono state effettuate su sensori con superfici piane o nano-strutturate prodotte dallo spin-off universitario Next Step Engineering, con il quale ho collaborato durante il percorso di ricerca.
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Ahmadivand, Arash. "Plasmonic Nanoplatforms for Biochemical Sensing and Medical Applications." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3576.
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Plasmonics, the science of the excitation of surface plasmon polaritons (SPP) at the metal-dielectric interface under intense beam radiation, has been studied for its immense potential for developing numerous nanophotonic devices, optical circuits and lab-on-a-chip devices. The key feature, which makes the plasmonic structures promising is the ability to support strong resonances with different behaviors and tunable localized hotspots, excitable in a wide spectral range. Therefore, the fundamental understanding of light-matter interactions at subwavelength nanostructures and use of this understanding to tailor plasmonic nanostructures with the ability to sustain high-quality tunable resonant modes are essential toward the realization of highly functional devices with a wide range of applications from sensing to switching.
We investigated the excitation of various plasmonic resonance modes (i.e. Fano resonances, and toroidal moments) using both optical and terahertz (THz) plasmonic metamolecules. By designing and fabricating various nanostructures, we successfully predicted, demonstrated and analyzed the excitation of plasmonic resonances, numerically and experimentally. A simple comparison between the sensitivity and lineshape quality of various optically driven resonances reveals that nonradiative toroidal moments are exotic plasmonic modes with strong sensitivity to environmental perturbations. Employing toroidal plasmonic metasurfaces, we demonstrated ultrafast plasmonic switches and highly sensitive sensors. Focusing on the biomedical applications of toroidal moments, we developed plasmonic metamaterials for fast and cost-effective infection diagnosis using the THz range of the spectrum. We used the exotic behavior of toroidal moments for the identification of Zika-virus (ZIKV) envelope proteins as the infectious nano-agents through two protocols: 1) direct biding of targeted biomarkers to the plasmonic metasurfaces, and 2) attaching gold nanoparticles to the plasmonic metasurfaces and binding the proteins to the particles to enhance the sensitivity. This led to developing ultrasensitive THz plasmonic metasensors for detection of nanoscale and low-molecular-weight biomarkers at the picomolar range of concentration.
In summary, by using high-quality and pronounced toroidal moments as sensitive resonances, we have successfully designed, fabricated and characterized novel plasmonic toroidal metamaterials for the detection of infectious biomarkers using different methods. The proposed approach allowed us to compare and analyze the binding properties, sensitivity, repeatability, and limit of detection of the metasensing devices
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Prasad, Janak [Verfasser]. "Sensing applications of biofunctionalised plasmonic gold nanoparticles / Janak Prasad." Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/1070108898/34.
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Hajebifard, Akram. "Plasmonic Nano-Resonators and Fano Resonances for Sensing Applications." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/41616.
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Different types of plasmonic nanostructures are proposed and examined experimentally and theoretically, with a view towards sensing applications. First, a self-assembly approach was developed to create arrays of well-ordered glass-supported gold nanoparticles (AuNPs) with controllable particle size and inter-particle spacing. Then, a periodic array of gold nano-disks (AuNDs) supported by a Bragg reflector was proposed and examined in a search for Fano resonances in its optical response. Arrays of heptamer-arranged nanoholes (HNH) in a thin gold film were also proposed and explored theoretically and experimentally, revealing a very rich spectrum of resonances, several exhibiting a Fano lineshape.
A commercial implementation of the vectorial finite element method (FEM) was used to model our plasmonic structures. Taking advantage of the periodic nature of the structures, a unit cell containing a single element was modelled. The transmittance, reflectance or absorbance spectra were computed, and the associated electromagnetic fields were obtained by solving the vector wave equations for the electromagnetic field vectors throughout the structures, subject to the applicable boundary conditions, and the applied source fields. The sensing performance of the structures, based on the bulk sensitivity, surface sensitivity and figure of merit (FOM) was calculated.
First, a novel bottom-up fabrication approach was applied (by our collaborators) to form a periodic array of AuNPs with controllable size over large areas on SiO2 substrates. In this method, self-assembly of block copolymer micelles loaded with metal precursors was combined with a seeding growth route to create ordered AuNPs of desired size. It was shown that this new fabrication method offers a new approach to tune the AuNP size and edge-to-edge inter-particle spacing while preserving the AuNP ordering. The optical characteristics of the AuNP arrays, such as their size, interparticle spacing, localized surface plasmon resonance (LSPR) wavelength, and bulk sensitivity, were examined, numerically and experimentally. This proposed novel fabrication method is applicable for low-cost mass-production of large-area arrays of high-quality AuNPs on a substrate for sensing applications.
Then, we proposed and examined the formation of Fano resonances in a plasmonic-dielectric system consisting of uncoupled gold nano-disk (AuND) arrays on a quarter-wave dielectric stack. The mechanism behind the creation of Fano resonances was explained based on the coherent interference between the reflection of the Bragg stack and the LSPPs of the AuNDs. Fano parameters were obtained by fitting the computational data to the Fano formula. The bulk sensitivities and figure of merit of the Fano resonances were calculated. This plasmonic structure supports Fano resonances with a linewidth around 9 nm which is much narrower than the individual AuND LSPP bandwidth ( 80 nm) and the Bragg stack bandwidth ( 100 nm). Supporting Fano resonances with such a narrow linewidth, the structure has a great potential to be used for sensing applications. Also, this metallic-dielectric nanostructure requires no near-field coupling between AuNDs to generate the Fano resonances. So, the AuNDs can be located far enough from each other to simplify the potential fabrication process.
The optical properties of HNH arrays on an SiO2 substrate were investigated, numerically and experimentally. Helium focused ion beam (HeFIB) milling was applied (by Dr. Choloong Hahn) to fabricate well-ordered and well-defined arrays of HNHs. Transmittance spectra of the structures were obtained as the optical response, which exhibits several Fano resonances. Then, the mechanism behind the formation of the Fano resonances was explained, and the sensing performance of the structure was inspected by measuring the bulk sensitivities. This array of nanohole cluster is exciting because it supports propagating SPPs and LSPPs, and also Wood’s anomaly waves, which makes the optical response very rich in excitations and spectral features. Also, as a periodic array of sub-wavelength metallic nanoholes, the system produces extraordinary optical transmission - highly enhanced transmission through (otherwise) opaque metallic films at specific wavelengths, facilitating measurement acquisition in transmission.
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Pasquale, Alyssa Joy. "Engineering photonic-plasmonic devices for spectroscopy and sensing applications." Thesis, Boston University, 2012. https://hdl.handle.net/2144/32043.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The control of light on the nano-scale has driven the development of novel optical devices such as biosensors, antennas and guiding elements. These applications benefit from the distinctive resonant properties of noble metal thin films and nanoparticles. Many optimization parameters exist in order to engineer nanoparticle properties for spectroscopy and sensing applications: for example, the choice of metal, the particle morphology, and the array geometry. By utilizing various designs from simple monomer gratings to more complex engineered arrays, we model and characterize plasmonic arrays for sensing applications. In this thesis, I have focused on the novel paradigm of photonic-plasmonic coupling to design, fabricate, and characterize optimized nanosensors. In particular, nanoplasmonic necklaces, which consist of circular loops of closely spaced gold nanoparticles, are designed using 3D finite-difference time-domain (FDTD) simulations, fabricated with electron-beam lithography, and characterized using dark-field scattering and surface-enhanced Raman spectroscopy (SERS) of p-mercaptoaniline (pMA) monolayers. I show that such necklaces are able to support hybridized dipolar scattering resonances and polarization-controlled electromagnetic hot-spots. In addition, necklaces exhibit strong intensity enhancement when the necklace diameter leads to coupling between the broadband plasmonic resonance and the circular resonator structure of the necklace. Hence, these necklaces lead to stronger field intensity enhancement than nanoparticle monomers and dimers, which are also carefully studied. Furthermore, by embedding a dimer into one or more concentric necklace resonators, I am able to efficiently couple radiation into the dimer hot-spot by utilizing first- and second-order far-field coupling. This nanolensing leads to an order of 6-18 times improvement in Raman enhancement over isolated dimers, which is a promising platform for compact on-chip sensors. Additionally, I have fabricated and experimentally characterized devices that were designed in my group for SERS of pMA using an optimization algorithm. The algorithm confirms that the best arrangement of nanoparticles to increase near-field intensity enhancement in a single hot-spot is to embed a dimer into particles that couple light into the hot-spot via far-field photonic radiation. These genetically optimized nanoantennas show improvement in Raman enhancement 10 times that of nanoparticle dimers, and 100 times the enhancement of optimized two-dimensional monomer diffraction gratings.
2031-01-02
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Robinson, Jendai E. "Fabrication and Characterization of Plasmonic and Electrochemical Devices Towards Sensing Applications." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1490351933726863.
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Buchholt, Kristina. "Nanostructured materials for gas sensing applications." Doctoral thesis, Linköpings universitet, Tillämpad Fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69641.
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In this Thesis I have investigated the use of nanostructured films as sensing and contact layers for field effect gas sensors in order to achieve high sensitivity, selectivity, and long term stability of the devices in corrosive environments at elevated temperatures. Electrochemically synthesized Pd and Au nanoparticles deposited as sensing layers on capacitive field effect devices were found to give a significant response to NOx with small, or no responses to H2, NH3, and C3H6. Pt nanoparticles incorporated in a TiC matrix are catalytically active, but the agglomeration and migration of the Pt particles towards the substrate surface reduces the activity of the sensing layer. Magnetron sputtered epitaxial films from the Ti-Si-C and the Ti-Ge-C systems were grown on 4H-SiC substrates in order to explore their potential as high temperature stable ohmic contact materials to SiC based field effect gas sensors. Ti3SiC2 thin films deposited on 4H-SiC substrates were found to yield ohmic contacts to n-type SiC after a high temperature rapid thermal anneal at 950 ºC. Investigations on the growth mode of Ti3SiC2 thin films with varying Si content on 4H-SiC substrates showed the growth to be lateral step-flow with the propagation of steps with a height as small as half a unit cell. The amount of Si present during deposition leads to differences in surface faceting of the films and Si-supersaturation conditions gives growth of Ti3SiC2 films with the presence of TiSi2 crystallites. Current-voltage measurements of the as-deposited Ti3GeC2 films indicate that this material is also a promising candidate for achieving long term stable contact layers to 4H-SiC for operation at elevated temperatures in corrosive environments. Further investigations into the Ti-Ge-C system showed that the previously unreported solid solutions of (Ti,V)2GeC, (Ti,V)3GeC2 and (Ti,V)4GeC3 can be synthesized, and it was found that the growth of these films is affected by the nature of the substrate.
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Sil, Devika. "SYNTHESIS AND APPLICATIONS OF PLASMONIC NANOSTRUCTURES." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/364016.
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ChemistryPh.D.
The localized surface plasmon resonance (LSPR), arising due to the collective oscillation of free electrons in metal nanoparticles, is a sensitive probe of the nanostructure and its surrounding dielectric medium. Synthetic strategies for developing surfactant free nanoparticles using ultrafast lasers providing direct access to the metallic surface that harvest the localized surface plasmons will be discussed first followed by the applications. It is well known that the hot carriers generated as a result of plasmonic excitation can participate and catalyze chemical reactions. One such reaction is the dissociation of hydrogen. By the virtue of plasmonic excitation, an inert metal like Au can become reactive enough to support the dissociation of hydrogen at room temperature, thereby making it possible to optically detect this explosive gas. The mechanism of sensing is still not well understood. However, a hypothesis is that the dissociation of hydrogen may lead to the formation of a metastable gold hydride with optical properties distinct from the initial Au nanostructures, causing a reversible increase in transmission and blue shift in LSPR. It will also be shown that by tracking the LSPR of bare Au nanoparticles grown on a substrate, the adsorption of halide ions on Au can be detected exclusively. The shift in LSPR frequency is attributed to changes in electron density rather than the morphology of the nanostructures, which is often the case.
Temple University--Theses
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Angiola, Marco. "Gas sensing properties of carbon nanostructures." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424809.
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This work is aimed to evaluate the optical gas sensing properties of carbon nanomaterial. In particular it is focused on two materials, Carbon Nanotubes (CNTs) and Graphene Oxide
(GO).
The comprehension of the mechanisms of interaction of these materials with the gas molecules is fundamental for a future application of these materials as sensors targeted to a
specific specie or capable to distinctly detect several dangerous species. On this purpose nanostructures based on GO and CNTs have been produced and tested as optical gas sensors toward oxidizing/reducing gases (H2, CO, NO2) and aromatic volatile Organic Compounds (benzene, toluene, xylene).
Gold nanoparticles (Au NPs) have been used as optical probe thanks to the peculiar Localized Surface Plasmon Resonance feature in the visible range, which is extremely
sensitive to the variation in optoelectronic properties of the surrounding media, such as refractive index and the variation in charge carrier involved in plasmonic excitation in the Au NPs.
Not only amplify the Au NPs the variation in optoelectronic properties of the layer of carbon nanomaterial, but also the electromagnetic coupling with carbon nanomaterials may induce
an enhancement in response and a lowering of the limit of detection of the sensors to the target species.
Moreover, the GO and CNTs are provided of a large possibility of functionalization, which can be used to tailor the gas sensing properties of the nanostructures toward specific species.
CNTs have been combined with the Au NPs, Pd NPs, Ni NPs and fullerenes. Pd and Au NPs increase the response toward H2
, meanwhile Ni NPs and fullerenes appear specific to CO. It
is also suggested the opportunity to monitor the features of the absorbance plot of fullerenes and CNT in the NIR as optical probes, with the carbon nanomaterials playing both the role
of sensing element and optical probe.
The presence of the different functional groups in GO was investigated. The increase in sp2conjugation has a profitable effect for the sensing of H2. Instead, the removal of the oxidized
functional groups hinder the response of the films toward CO and NO2.
The reduction and functionalization of the GO with para- Phenylene Diamine induces the detection of NH3without Au NPs as optical probe. The sensors produced are characterized by high transparency in the visible range and may be incorporated as non-invasive sensors on transparent surfaces.
Most of the sensors worked at 150°C and 300°C. Test of gas sensing have been conducted at low temperatures, at 80°C for CNTs in fullerene matrix and good results were achieved. The
possibility of sensors active at room temperature is suggested by the positive tests conducted with CMG, paving the way for future developments in active optical material sensitive to
gases at room temperature.Il presente lavoro è focalizzato sullo studio di sensori ottici basati su nanomateriali di carbonio, nell’ottica di un’applicazione di questi materiali come sensori di gas. Il lavoro prende in analisi due materiali, i nanotubi di carbonio (CNTs) e il grafene ossido (GO). La comprensione dei meccanismi di interazione di questi materiali con le molecole di gas è fondamentale per le applicazioni future di questi materiali nel rilevamento di diverse specie nocive di gas. A tal proposito, nanostrutture a base di GO e CNTs sono state sviluppate e studiate come sensori ottici verso gas ossidanti-riducenti (H2, CO, NO2) e nei contronti di composti volatili organici aromatici (benzene, toluene, xylene). Le nanoparticelle di oro sono state utilizzate come sonde ottiche grazie alla loro peculiare caratterista di risonanza plasmonica di superficie localizzata, la quale è estremamente sensibile alle variazioni di proprietà ottico-elettroniche del mezzo che le circonda, come l’indice di rifrazione, e alle variazione di densità di portatori di carica che sono coinvolti nell'eccitazione plasmonica nelle nanoparticelle di oro. Quindi, le nanoparticelle di oro, non solo amplificano le variazioni optoelettroniche del film di nanomateriali di carbonio a cui sono state accoppiate, ma interagiscono con questi inducendo un miglioramento della risposta ai gas e un abbassamento del limite di rilevamento ai gas in analisi. Inoltre, GO e CNTs presentano una vasta gamma di possibili funzionalizzazioni, che, possono essere sfruttate per una progettazione mirata delle proprietà di gas sensing delle nanostrutture di carbonio. I CNTs sono stati abbinati a nanoparticelle di Au, Pd, Ni e a fullereni. Pd e Au portano ad un miglioramento delle prestazioni dei sensori verso il gas H2, nanoparticelle di Ni e fullereni sembrano avere un’azione specifica verso il gas CO. In questo lavoro viene anche suggerita la possiblità di monitorare le proprietà di assorbanza di fullereni e CNTs nel range del vicino IR. I CNTs, in tal caso, avrebbero la duplice funzione di sonde ottiche e di materiale sensibile. Oltre all'effetto delle nanoparticelle di oro sulle proprietà di gas sensing del GO, è stata valutata l’influenza dei diversi gruppi funzionali. L’estensione dei domini sp2 sembra favorire il rilevamento di H2, mentre una forte rimozione di gruppi funzionali inibisce la risposta del GO verso CO e NO 2.
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Starke, Thomas. "Gas sensing applications of phthalocyanine thin films." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312313.
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TAMVAKOS, ATHANASIOS. "ZnO-Based nanostructures for gas sensing applications." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2598561.
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Metal oxide chemical sensors based on nanomaterials are gaining popularity and finding extensive use in automotive industries, process control and environmental monitoring. ZnO, a semiconducting metal oxide has attracted great interest over the years for its sensitivity to a variety of gases. Nanostructured sensing materials, such as thin films, nanowires, tetrapods, nanoflackes offer an inherently high surface area, reducing operating temperatures and increasing sensitivity to low concentrations of analytes. In this thesis, ZnO nanostructures have been tested as chemical sensors and a detailed study on the effect of different process parameters such as grain size, roughness, surface-to-volume ratio, depletion layer, temperature, gas concentration and material properties on gas sensitivity is presented. Initially, ZnO nanodevices were prepared with a variety of techniques, such as RF sputtering, electrodeposition, hydrothermal growth, chemical vapour deposition, thermal evaporation and controlled oxidation. The structural characterization of the nanodevices
has been done by a FEI QUANTA 3D dual beam SEM/FIB machine and by a Dimension 3100 Atomic Force Microscope (AFM) (Digital Instruments) in tapping mode. X-ray diffraction (XRD) spectra were recorded on an AXS D8 diffractometer (Bruker) with a Cu Kα X-ray tube. The gas sensor substrate based on alumina consisted of Pt
grid of 50nm thickness and golden contacts of 200nm thickness creating an alumina patterned substrate. The sensor deposition area was coated with ZnO nanostructures to form the sensing material. Sensing measurements are performed in a closed steel
chamber where air and tested gases have been inserted. ZnO based nanostructures’ response was measured in different concentrations of Ethanol, CO and NO2.
Initially the role of grain size and roughness has been investigated in several thin film based nanodevices. Grain size is decreasing with increasing RF sputtering power and increasing by post-annealing treatment. Roughness instead is increasing with both the increasing of RF sputtering power and post-annealing treatment. High response was observed for those films with smaller grain size, while the roughness seems to influence very little the response of the sensor. For all thin films, the response is increasing with ii temperature and gas concentration. Recovery time and response time seem to follow a
non-linear behavior with the above parameters.
Extended studies have investigated the role of surface-to-volume ratio and depletion layer in the sensing performance. It has been observed that the increase of surface-to volume ratio has an important effect on the sensitivity, increasing, more than twice the response of such a device in respect to another that is based on a ZnO thin film. On the
other hand, the dimensions of a nanostructure play the most crucial role in the depletion layer width in respect to the sensing properties. The diameter of a nanowire should be comparable with its depletion layer width. In this case the depletion layer has strong effect, which makes the sensor’s response depend also on it.
The sensing properties of all fabricated structures have been compared to find the optimum sensor that could face the demands of automotive industries. All fabricated structures have been compared in different configurations to find out which one presents the best sensing performance. To that direction sensors based on thin film,
tetrapods, nanowires, nanoflackes have been tested in same environmental conditions.
Advanced nanostructures present better sensing properties. Sensing response of every advanced nanostructure presents more than double sensing response than every thin film-based nanostructure. Comparing the advanced nanostructures with each other, tetrapods based sensor has higher response and recovery time, while the sensitivity is slightly higher for the nanowires-based sensor.
Theoretical studies have been performed by ab-initio simulations in NO2 environment.
They have revealed that the sensing mechanism is driven almost exclusively by competitive adsorption between NO2 and atmospheric oxygen mediated by temperature change. The influence of the NO2 on the electronic properties of ZnO has been assessed and it is in accordance with the experiments.
Our future work is the investigation of other materials for the development of sensing nanodevices targeting to develop more sensitive nanosensors in the same or lower cost. Additionally, the investigation of other growth techniques that could develop more
complicated structures in low cost is another point of interest for the future.
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Hutter, Tanya. "Plasmonic and photonic nano-structures for applications in SERS and chemical sensing." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648334.
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Kravets, Vira V. "Optical Properties of Plasmonic Nanostructures for Bio-Imaging and Bio-Sensing Applications." Thesis, University of Colorado at Colorado Springs, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10282081.
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Kravets, Vira V. (Ph.D., Physics) Optical properties of plasmonic nanostructures for bio-imaging and bio-sensing applications Dissertation directed by Associate Professor Anatoliy Pinchuk. ABSTRACT This dissertation explores the physics of free electron excitations in gold nanoparticle chains, silver nanoparticle colloids, and thin gold films. Electron excitations in nanostructures (surface plasmons, SP) are responsible for unique optical properties, which are applied in bio-sensing and bio-imaging applications. For gold nanoparticle chains, the effect of SP on resonance light absorption was studied experimentally and theoretically. Mainly, how the spectral position of the absorption peak depends on inter-particle distances. This dependence is used in ?molecular rulers?, providing spatial resolution below the Rayleigh limit. The underlying theory is based on particle interaction via scattered dipole fields. Often in literature only the near-field component of the scattered field is considered. Here, I show that middle and far fields should not be neglected for calculation of extinction by particle chains. In silver nanoparticles, SP excitations produce two independent effects: (a) the intrinsic fluorescence of the particles, and (b) the enhancement of a molecule?s fluorescence by a particle?s surface. The mechanism of (a) is deduced by studying how fluorescence depends on particle size. For (b), I show that fluorescence of a dye molecule on the surface of a nanoparticle is enhanced, when compared to that of the free-standing dye. I demonstrate that the dye?s fluorescent quantum yield is dependent on the particle?s size, making labeled silver nanoparticles attractive candidates as bio-imaging agents. Labeled nanoparticles are applied to cell imaging, and their bio-compatibility with two cell lines is evaluated here. Finally, in gold films under attenuated total internal reflection (ATR) conditions, the SP create a propagating wave (SP-polariton, SPP) when coupled with the incident light. Because of the sensitivity of SPPs to the medium adjacent to the gold film surface, they are widely applied in bio-sensing applications. A toolbox for the description of sputter-deposited gold films is presented here: it employs three experimental techniques (ATR, transmittance and atomic force microscopy) in combination with the effective medium theory for double-layered film model. Our findings have allowed for the avoidance of superficial fitting parameters in our model.
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Jiménez, Gallardo Ismael. "Tungsten oxide nanocrystalline powders for gas sensing applications." Doctoral thesis, Universitat de Barcelona, 2003. http://hdl.handle.net/10803/1507.
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This doctoral dissertation deals with the study of nanocrystalline tungsten oxide-based powders for gas sensing applications. Gas monitoring is receiving increasing attention due to environmental and safety reasons. Gas sensors based on heated semiconducting metal oxides are appreciated as they can detect low concentrations of certain gases by a variation of conductance of the metal oxide layer. Among the different metal oxides proposed, tungsten oxide (WO3) is considered one of the most promising materials for the detection of ammonia (NH3), hydrogen sulphide (H2S) and nitrogen dioxide (NO2). The first chapter of this dissertation presents the general framework where this investigation is placed. It includes a brief overview of chemical sensors, metal oxide-based gas sensors and the reported properties of WO3 for gas sensing applications. Finally, motivation and main targets of this investigation, as well as the organisation of this dissertation, are presented and argued. Chapter 2 presents the experimental details of this study. It discusses the preparation of WO3 nanocrystalline powder, the experimental techniques used to analyse the structural properties of the WO3 powders and the implementation and test of gas sensor devices. For this work, XRD, Raman spectroscopy, TEM-EELS, XPS, EPR, TPD and DRIFTS have been used. Thick-film screen-printed gas sensors based on WO3-powders were tested.
The target of Chapter 3 is to present an investigation into the structural and spectroscopic properties of pure and catalysed nanocrystalline WO3 powder. Firstly, the characterisation of pure nanocrystalline WO3 powder is considered. The main parameter analysed is the influence of the annealing treatment on the structural properties. Structural and spectroscopic properties of catalysed WO3 are also reported here. In this case, the emphasis lays on the characterisation of catalytic centres, rather than on bulk WO3. The catalytic additives introduced were copper (Cu), vanadium (V) and chromium (Cr).
Results concerning gas sensors based on WO3 nanocrystalline powders for the detection of the previously mentioned gases are reported in Chapter 4. The purpose of this investigation was to evaluate the sensing properties of thick-film gas sensors based on WO3 obtained from tungstic acid and to determine the effect of different additives on sensor response to NH3, H2S and NO2. Interference of humidity on the detection of these gases was also evaluated. A tentative interpretation of the reported results based only on the test data presented is also provided.
The aim of Chapter 5 is to explore the implementation of real condition characterisation techniques to WO3-based nanopowders in order to study surface species and reactions involved in gas sensing. By real condition, we refer to a characterisation under controlled conditions of temperature and gas concentration on the sample, as similar to test conditions as possible. These studies, which are standard in the field of catalysis, are not so common for gas sensors. This is still a key point in the field of gas sensors at the moment: to obtain a deeper understanding of what occurs on the surface of the sensing material. The chapter has two main parts, corresponding to the results of DRIFTS and TPD techniques. By means of DRIFTS it is possible to identify surface species that present infrared vibrations. By TPD, the desorption of adsorbed target gases is analysed.
Finally, Chapter 6 aims at discussing the results previously presented as a whole, as well as presenting the main conclusions that can be drawn from this investigation and some proposals for a future research grounded on the present work.
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Hoel, Anders. "Electrical Properties of Nanocrystalline WO3 for Gas Sensing Applications." Doctoral thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4051.
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Tungsten trioxide is a material with a variety of application areas. For example, the material is used within thin film technologies as electrochromic material in smart windows, as electrochemically functional material in thermal control applications or as active layer in gas sensing application. Metal-oxide semiconductor gas sensors are of significant interest to detect toxic and hazardous gases. The use of small and cheep sensors is preferable since a large number of sensors easily can be placed at different sites to monitor the concentration of different species without involving huge investments. In this work, WO3 nanoparticle films were produced using an advanced gas deposition unit for gas sensing applications. The structure of the WO3 nanoparticle films was determined using X-ray diffraction, neutron scattering, X-ray photoelectron spectroscopy, elastic recoil detection analysis and electron microscopy. The as deposited films consist of sub-stoichiometric WO3 and exhibit a large degree of porosity, which together with the small particle size of about 5 nm results in a large surface area and therefore excellent prospects for gas sensor applications. Investigations on the optical properties and temperature dependence of the resistance indicate hopping conduction in the WO3 films. The bandgaps for tetragonal and monoclinic WO3 were found to be direct, which is in accordance with band structure calculations. Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at fixed operating temperatures as well as on temperature modulated sensors. The films of WO3 showed excellent sensitivity to H2S gas and selectivity to other gases. The responses of temperature modulated sensors were further analyzed using mathematical transformations and pattern recognition methods whereby different gases could be distinguished. We also present a sensing technique using conduction noise as a tool for detection of alcohol vapor. The relative change of the noise, due to the inserted alcohol, can be as large as two orders of magnitude.
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Vaitiekus, Deivis. "Development of quantum cascade lasers for gas sensing applications." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/13916/.
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Quantum cascade lasers (QCLs) are capable of high power, tunable wavelength and single mode emission at room temperature in the mid-infrared wavelength region. These capabilities make them perfect light sources for laser based gas spectroscopy. The work described in this thesis focuses on development of QCLs suitable for selective gas sensing applications. The thesis starts with the description of different changes to the QCL active region design. These changes were studied in order to improve laser performance while keeping the emission wavelength fixed. The proposed modifications were performed on short mid-infrared wavelength (lambda=3-4um) quantum cascade lasers based on InGaAs/AlAsSb and InAs/AlSb material systems. The focus of this work is then moved to the description of a single mode quantum cascade laser with a third order unilateral grating. The previously unreported grating architecture that was used to achieve distributed feedback (DFB) in a QCL, as well as grating design and laser characterization are detailed in Chapter \ref{chap:uni}. The reported laser generates single mode emission with 30 dB side mode suppression ratio and a linewidth of 0.4cm^(-1). The simplified fabrication process for a third order DFB grating is developed for lambda=3.3-3.6um emission wavelength. A different approach to achieve single mode emission in a QCL is described in Chapter 6. An external cavity QCL setup combined with the Fabry-Perot (FP) reflector is reported for the first time. The FP reflector is used to provide selective feedback that is controlled by the separation distance between two FP reflector mirrors. This external cavity arrangement allows generation of a wide spectral range and the rapid wavelength tuning capability. Finally, the thesis is concluded with sensitive gas detection experiments. The direct absorption technique is utilized to demonstrate the 160ppmv detection of methane with the ro-vibrational absorption line located at lambda=3.3um and 1ppmv detection of nitric oxide with the absorption line located at lambda=5.3um. The experiments were performed using single mode lasers that were designed and fabricated in Sheffield.
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CICIOTTI, FULVIO. "Oscillator-Based CMOS Readout Interfaces for Gas Sensing Applications." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241089.
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Il rilevamento di gas tossici e pericolosi è sempre stato necessario per motivi di sicurezza. Negli ultimi anni, in particolare, l’attenzione per lo sviluppo di sistemi portatili e a basso costo per il rilevamento dei gas è aumentata notevolmente. Questa tesi presenta circuiti CMOS versatili, veloci, ad alta precisione e basso consumo per applicazioni portatili di rilevamento di gas. I sensori target sono i Metal Oxide Semiconductor (MOX). Questi sensori sono ampiamente utilizzati per la loro intrinseca compatibilità con le tecnologie MEMS integrate. Le tipologie di lettura scelte sono basate su un oscillatore controllato dalla resistenza del sensore stessa, in modo da ottenere una conversione resistenza-tempo. Ciò garantisce un ampio range dinamico, una buona precisione e la capacità di far fronte alle grandi variazioni di resistenza del sensore MOX. Quattro diversi prototipi sono stati sviluppati e testati con successo. Sono state anche eseguite misurazioni chimiche con un vero sensore SnO2 MOX, validando i risultati ottenuti. Le misure hanno mostrato come il sensore e l’interfaccia sia in grado di rilevare fino a 5ppm di CO in aria. Gli ASIC sono in grado di coprire 128 dB di DR a 4Hz di output data rate digitale, o 148 dB a 0.4Hz, garantendo un errore relativo percentuale sempre migliore dello 0,4% (SNDR> 48 dB). Le prestazioni target sono state raggiunte con aggressive strategie di progettazione e ottimizzazione a livello di sistema. È stata utilizzata una tecnologia CMOS a 130nm fornita da Infineon Technologies AG. La scelta di un nodo tecnologico così scalato (rispetto alle tipiche implementazioni in questo settore) ha consentito di ridurre ulteriormente i consumi fino a circa 450 μA. Inoltre, questo lavoro introduce la possibilità di utilizzare la stessa architettura basata su oscillatore per eseguire la lettura di sensori capacitivi. I risultati delle misurazioni con sensori capacitivi MEMS hanno mostrato 116 dB di DR, con un SNR di 74 dB a 10Hz di velocità di trasmissione dati digitale. Le architetture sviluppate in questa tesi sono compatibili con gli standard moderni nel settore del rilevamento del gas per dispositivi portatili.Detection of toxic and dangerous gases has always been a need for safety purpose and, in recent years, portable and low-cost gas sensing systems are becoming of main interest. This thesis presents fast, high precision, low-power, versatile CMOS interface circuits for portable gas sensing applications. The target sensors are Metal Oxide Semiconductor (MOX) sensors which are widely used due to their inherent compatibility with integrated MEMS technologies. The chosen readout typologies are based on the time-domain Resistor-Controlled Oscillator. This guarantees wide dynamic range, good precision and the ability to cope with the large MOX sensor resistance variations. Four different prototypes have been successfully developed and tested. Chemical measurements with a real SnO2 MOX sensor have also been performed to validate the results, showing a minimum CO detection capability in ambient air of 5 ppm. The ASICs are able to cover 128 dB of DR at 4 Hz of digital output data rate, or 148 dB at 0.4 Hz, while providing a relative error always better than 0.4% (SNDR >48 dB). Target performances have been achieved with aggressive design strategies and system-level optimization, and using a scaled (compared to typical implementations in this field) 130nm CMOS technology provided by Infineon Technologies AG. Power consumption is about 450 μA. Moreover, this work introduces the possibility to use the same oscillator-based architecture to perform capacitive sensors readout. Measurement results with capacitive MEMS sensors have shown 116 dB of DR in CSENS mode, with an SNR of 74 dB at 10 Hz of digital output data rate. The architectures developed in this thesis are compatible with the modern standards in the portable gas sensing industry.
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Marinov, Dilyan. "Laser spectroscopic trace-gas sensing with medical and environmental applications /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17281.
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Li, Sheng. "Design, fabrication and testing of micronozzles for gas sensing applications." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3389.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Newton, Andrew. "Optical properties of Langmuir-Blodgett films in gas sensing applications." Thesis, Coventry University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309773.
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Tanvir, Nauman Bin [Verfasser], and Gerald A. [Akademischer Betreuer] Urban. "Investigation of metal oxide nanomaterials for CO2 gas sensing applications." Freiburg : Universität, 2017. http://d-nb.info/1138195316/34.
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Breivik, Magnus. "Fabrication of mid-infrared laser diodes : for gas sensing applications." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23859.
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Mid-infrared laser diodes have been fabricated and tested, and semiconductor materials related to mid-infrared lasers have been characterized by X-ray diffraction (XRD). The temperature dependent lattice constant of Al0.9 Ga0.1AsySb1−y, GaSb, AlSb and InSb have been examined using XRD measurements. For Al0.9Ga0.1AsySb1−y, GaSb and AlSb, the lattice constants were measured for temperatures up to 546°C, while for InSb it was examined up to 325°C. For AlSb, also the temperature dependent Poisson ratio was determined. It was found that the thermal expansion of Al-containing layers above room temperature was higher than previously reported. An expression for the lattice matching condition for Al0.9Ga0.1AsySb1−y epilayers on GaSb substrates as a function of temperature was presented. For GaSb, it was found that the work of Bublik et al. [1] provided accurate data for the temperature dependent lattice constant, and either our data or Bublik et al. [1]’s data should be used. The measurement technique was validated by measuring the lattice constants of Si and GaAs, where our measured values were found to be in agreement with previously published values. For AlSb it was found that the thermal expansion was larger than previously reported in the literature. For InSb it was found that the lattice constant near room temperature was larger than previously reported, and the thermal expansion above 100°C was larger than previously reported. Laser material was grown using molecular beam epitaxy (MBE). The grown samples were processed into Y-junction laser diodes. The lasers were etched using inductively coupled plasma reactive ion etching (ICP-RIE) and photoresist (PR) ma-N 440 was spun on and baked for use as electrical insulation. The insulation layer was etched using reactive ion etching (RIE) to uncover the top of the etched lasers for contacting. It was found that a O2/CF4 etch gave the best uniformity of the insulation layer. The lasers were contacted and tested. The Y-junction lasers were characterized using power measurements for optical power, multimeters for diode voltage, Fourier transform infrared (FTIR) for spectral measurements, and an infrared camera for near and far field measurements. The measurements suggested that the curved waveguide did not guide the light, most likely due to a low refractive index contrast. This was later supported by scanning electron microscope (SEM) measurements, which showed an etch depth of 1.4 μm, much lower than the etch target of 1.9 μm. The Y-junction waveguides were simulated using the beam propagation method (BPM). Based on 2D BPM simulations, it was found that an effective refractive index contrast of at least 0.03 is required for guiding light in a curved waveguide for our dimensions, and that waveguide roughness due to processing is less important. The simulations support the findings from the laser measurements, and further suggest that a deeper etch is required for functioning Y-junction laser diodes. Suggestions for improvements to the manufacturing mid-infrared laser diodes are presented.
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Davies, Edward. "Optical fibre sensors with applications in gas and biological sensing." Thesis, Aston University, 2011. http://publications.aston.ac.uk/15800/.
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This thesis describes the study of various grating based optical fibre sensors for applications in refractive index sensing. The sensitivity of these sensors has been studied and in some cases enhanced using novel techniques. The major areas of development are as follows. The sensitivity of long period gratings (LPGs) to surrounding medium refractive index (SRI) for various periods was investigated. The most sensitive period of LPG was found to be around 160 µm and this was due to the core mode coupling to a single cladding mode but phase matching at two wavelength locations, creating two attenuation peaks, close to the waveguide dispersion turning point. Large angle tilted fibre gratings (TFGs) have similar behaviour to LPGs, in that they couple to the co-propagating cladding modes. The tilted structure of the index modulation within the core of the fibre gives rise to a polarisation dependency, differing the large angle TFG from a LPG. Since the large angle TFG couple to the cladding mode they are SRI sensitive, the sensitivity to SRI can be further increased through cladding etching using HF acid. The thinning of the cladding layer caused a reordering of the cladding modes and shifted to more SRI sensitive cladding modes as the investigation discovered. In a SRI range of 1.36 to 1.40 a sensitivity of 506.9 nm/URI was achieved for the etched large angle TFG, which is greater than the dual resonance LPG. UV inscribed LPGs were coated with sol-gel materials with high RIs. The high RI of the coating caused an increase in cladding mode effective index which in turn caused an increase in the LPG sensitivity to SRI. LPGs of various periods of LPG were coated with sol-gel TiO2 and the optimal thickness was found to vary for each period. By coating of the already highly SRI sensitive 160µm period LPG (which is a dual resonance) with a sol-gel TiO2, the SRI sensitivity was further increased with a peak value of 1458 nm/URI, which was an almost 3 fold increase compared to the uncoated LPG. LPGs were also inscribed using a femtosecond laser which produced a highly focused index change which was no uniform throughout the core of the optical fibre. The inscription technique gave rise to a large polarisation sensitivity and the ability to couple to multiple azimuthal cladding mode sets, not seen with uniform UV inscribed gratings. Through coupling of the core mode to multiple sets of cladding modes, attenuation peaks with opposite wavelength shifts for increasing SRI was observed. Through combining this opposite wavelength shifts, a SRI sensitivity was achieved greater than any single observed attenuations peak. The maximum SRI achieved was 1680 nm/URI for a femtosecond inscribed LPG of period 400 µm. Three different types of surface plasmon resonance (SPR) sensors with a multilayer metal top coating were investigated in D shape optical fibre. The sensors could be separated into two types, utilized a pre UV inscribed tilted Bragg grating and the other employed a post UV exposure to generate surface relief grating structure. This surface perturbation aided the out coupling of light from the core but also changed the sensing mechanism from SPR to localised surface plasmon resonance (LSPR). This greatly increased the SRI sensitivity, compared to the SPR sensors; with the gold coated top layer surface relief sensor producing the largest SRI sensitivity of 2111.5nm/URI was achieved. While, the platinum and silver coated top layer surface relief sensors also gave high SRI sensitivities but also the ability to produce resonances in air (not previously seen with the SPR sensors). These properties were employed in two applications. The silver and platinum surface relief devices were used as gas sensors and were shown to be capable of detecting the minute RI change of different gases. The calculated maximum sensitivities produced were 1882.1dB/URI and 1493.5nm/URI for silver and platinum, respectively. Using a DFB laser and power meter a cheap alternative approach was investigated which showed the ability of the sensors to distinguish between different gases and flow rates of those gases. The gold surface relief sensor was coated in a with a bio compound called an aptamer and it was able to detect various concentrations of a biological compound called Thrombin, ranging from 1mM to as low as 10fM. A solution of 2M NaCl was found to give the best stripping results for Thrombin from the aptamer and showed the reusability of the sensor. The association and disassociation constants were calculated to be 1.0638×106Ms-1 and 0.2482s-1, respectively, showing the high affinity of the Aptamer to thrombin. This supports existing working stating that aptamers could be alternative to enzymes for chemical detection and also helps to explain the low detection limit of the gold surface relief sensor.
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Farcau, Cosmin [Verfasser]. "Ordered Plasmonic Nanostructures: from Fabrication to Relevant Applications in Optical Spectroscopy and Sensing / Cosmin Farcau." Munich : GRIN Verlag, 2015. http://d-nb.info/1097463818/34.
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Wilson, Rachel Lyndsey. "Deposition of ultra-thin metal oxide films for gas sensing applications." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/10040158/.
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The aim of this research project was to investigate the use of Atomic Layer Deposition (ALD) and Chemical Vapour Deposition (CVD) to deposit n- and p-type metal oxide thin films for use in gas sensing applications, with the long term goal to identify the materials which provide maximum sensitivity and selectivity. Two ALD reactors have been designed and constructed specifically for this project. N-type TiO2 thin films have been deposited by ALD of titanium(IV) isopropoxide and water, where film growth was shown to proceed via a self-limiting mechanism. Films were characterised using AFM, XRD, XPS and Raman, which confirmed anatase phase on the film surfaces. TiO2 films of various thickness were deposited onto gas sensor substrates and exposed to a range of test gases in order to evaluate their gas sensitivity at operating temperatures of 350 °C and 480 °C at several different relative humidity’s. Electrical resistance changes were observed for a 50 nm TiO2-coated sensor in response to NH3, where the sensor response was found to decrease with increasing relative humidity. However for a 10 nm film, whose thickness was most consistent with reported literature values of the Debye length for TiO2 was the not the most sensitive. Attempts to deposit p-type NiO films via ALD were less successful. However two novel nickel complexes were synthesised: [Ni(dmamp)2] and [Ni{(NiPr2)2CNEt2}2], whose volatility was greater than some of the other commonly used nickel precursors for ALD and CVD applications. These precursors, along with [Ni(thd)2] and [Ni(Cp)2], have been screened for their use in the deposition of NiO thin films via ALD with water. However, XPS analysis confirmed nickel metal and/or Ni(OH)2 on the film surfaces, which has been attributed to both a lack of reactivity between the nickel precursors and water and issues with the reactor design. Separate CVD experiments performed with [Ni(dmamp)2] and [Ni{(NiPr2)2CNEt2}2] resulted in the deposition of NiO films, as confirmed by XRD and XPS. Under the CVD conditions used, film growth could be controlled relatively easily, as compared to other conventional CVD methods.
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Ni, Liang. "Silicon nanowires synthesized by VLS growth mode for gas sensing applications." Rennes 1, 2012. http://www.theses.fr/2012REN1S010.
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Ce travail de recherche a consisté à réaliser de dispositifs microélectroniques à partir de nanofils de silicium (SiNWs) synthétisés par la méthode VLS (Vapor Liquid Solid). La croissance de ces nanofils a été effectuée par dépôt LPCVD (Low Pressure Chemical Vapor Deposition) à l’aide d’un catalyseur métallique (or). Le dopage in-situ de type N (à partir de phosphore) des nanofils de silicium a été démontré pour une gamme comprise entre 2. 1016 et 2. 1020 at. Cm-3. Les propriétés électriques des nanofils ont été étudiées en fonction du dopage et de la température. Deux dispositifs différents à base de nanofils de silicium ont été réalisés à partir i) de peignes inter-digités et ii) de cavités en « V ». Des premières mesures électriques qualitatives des résistances à base de SiNWs ont démontré une forte sensibilité à la fumée. Des mesures quantitatives dynamiques ont mis en évidence des performances élevées sous exposition à une faible concentration de gaz ammoniaque (350 ppm de NH3/N2), la sensibilité relative (Sg) pouvant atteindre 740%. Ce travail de recherche a permis de démontrer la faisabilité de dispositifs électroniques à partir de nanofils de silicium présentant des applications potentielles comme capteurs de gaz aux performances prometteusesThis research work mainly focused on realization of microelectronic devices based on silicon nanowires (SiNWs) synthesized by VLS (Vapor Liquid Solid) method. The growth of these nanowires was carried out by LPCVD (Low Pressure Chemical Vapor Deposition) using a metal catalyst (gold). The N-type in-situ doping (from phosphorus) levels of the VLS silicon nanowires were demonstrated for a range varying from 2. 1016 to 2. 1020 at. Cm-3. The electrical behaviors of nanowires were studied in function of doping and temperature. Two different devices based on silicon nanowires were fabricated, i) inter-digital comb-shaped devices and ii) V-shaped groove devices. The first static measurements upon the SiNWs based resistor showed their high sensitivity under exposure to smoke. The quantitative dynamic measurements under exposure to a low concentration of ammonia gas (350 ppm NH3/N2) were carried out, which demonstrated high performances of the SiNWs based resistors. The relative sensitivity (Sg) can reach 740 %. This research work demonstrated the feasibility of electronic devices from silicon nanowires with potential applications as gas sensors with promising performances
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Ahsan, Mohammed. "Thermally evaporated tungsten oxide (WO3) thin films for gas sensing applications." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/53124/1/Mohammed_Ahsan_Thesis.pdf.
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In this thesis, the author proposed and developed gas sensors made of nanostructured WO3 thin film by a thermal evaporation technique. This technique gives control over film thickness, grain size and purity. The device fabrication, nanostructured material synthesis, characterization and gas sensing performance have been undertaken. Three different types of nanostructured thin films, namely, pure WO3 thin films, iron-doped WO3 thin films by co-evaporation and Fe-implanted WO3 thin films have been synthesized. All the thin films have a film thickness of 300 nm. The physical, chemical and electronic properties of these films have been optimized by annealing heat treatment at 300ºC and 400ºC for 2 hours in air.
Various analytical techniques were employed to characterize these films. Atomic Force Microscopy and Transmission Electron Microscopy revealed a very small grain size of the order 5-10 nm in as-deposited WO3 films, and annealing at 300ºC or 400ºC did not result in any significant change in grain size. X-ray diffraction (XRD) analysis revealed a highly amorphous structure of as-deposited films. Annealing at 300ºC for 2 hours in air did not improve crystallinity in these films. However, annealing at 400ºC for 2 hours in air significantly improved the crystallinity in pure and iron-doped WO3 thin films, whereas it only slightly improved the crystallinity of iron-implanted WO3 thin film as a result of implantation. Rutherford backscattered spectroscopy revealed an iron content of 0.5 at.% and 5.5 at.% in iron-doped and iron-implanted WO3 thin films, respectively. The RBS results have been confirmed using energy dispersive x-ray spectroscopy (EDX) during analysis of the films using transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) revealed significant lowering of W 4f7/2 binding energy in all films annealed at 400ºC as compared with the as-deposited and 300ºC annealed films. Lowering of W 4f7/2 is due to increase in number of oxygen vacancies in the films and is considered highly beneficial for gas sensing. Raman analysis revealed that 400ºC annealed films except the iron-implanted film are highly crystalline with significant number of O-W-O bonds, which was consistent with the XRD results. Additionally, XRD, XPS and Raman analyses showed no evidence of secondary peaks corresponding to compounds of iron due to iron doping or implantation. This provided an understanding that iron was incorporated in the host WO3 matrix rather than as a separate dispersed compound or as catalyst on the surface.
WO3 thin film based gas sensors are known to operate efficiently in the temperature range 200ºC-500 ºC. In the present study, by optimizing the physical, chemical and electronic properties through heat treatment and doping, an optimum response to H2, ethanol and CO has been achieved at a low operating temperature of 150ºC. Pure WO3 thin film annealed at 400ºC showed the highest sensitivity towards H2 at 150ºC due to its very small grain size and porosity, coupled with high number of oxygen vacancies, whereas Fe-doped WO3 film annealed at 400ºC showed the highest sensitivity to ethanol at an operating temperature of 150ºC due to its crystallinity, increased number of oxygen vacancies and higher degree of crystal distortions attributed to Fe addition. Pure WO3 films are known to be insensitive to CO, but iron-doped WO3 thin film annealed at 300ºC and 400ºC showed an optimum response to CO at an operating temperature of 150ºC. This result is attributed to lattice distortions produced in WO3 host matrix as a result of iron incorporation as substitutional impurity. However, iron-implanted WO3 thin films did not show any promising response towards the tested gases as the film structure has been damaged due to implantation, and annealing at 300ºC or 400ºC was not sufficient to induce crystallinity in these films.
This study has demonstrated enhanced sensing properties of WO3 thin film sensors towards CO at lower operating temperature, which was achieved by optimizing the physical, chemical and electronic properties of the WO3 film through Fe doping and annealing. This study can be further extended to systematically investigate the effects of different Fe concentrations (0.5 at.% to 10 at.%) on the sensing performance of WO3 thin film gas sensors towards CO.
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Rivera, Ivan Fernando. "RF MEMS Resonators for Mass Sensing Applications." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5817.
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Sensing devices developed upon resonant microelectromechanical and nanoelectromechanical (M/NEMS) system technology have become one of the most attractive areas of research over the past decade. These devices make exceptional sensing platforms because of their miniscule dimensions and resonant modes of operation, which are found to be extremely sensitive to added mass. Along their unique sensing attributes, they also offer foundry compatible microfabrication processes, low DC power consumption, and CMOS integration compatibility. In this work, electrostatically and piezoelectrically actuated RF MEMS bulk resonators have been investigated for mass sensing applications. The capacitively-transduced resonators employed electrostatic actuation to achieve desired resonance mode shapes. These devices were fabricated on silicon-on-insulator (SOI) substrates with a device layer resistivity ranging from 0.005 Ω cm to 0.020 Ω cm. The electrode-to-resonator capacitive gap was defined by two different techniques: oxidation enabled gap reduction and sacrificial atomic layer deposition (ALD). For oxidation enabled gap reduction, a hard mask composed of silicon nitride and polysilicon is deposited, patterned, and defined using standard MEMS thin-film layer deposition and fabrication techniques. The initial lithographically-defined capacitive gap of 1 μm is further reduced to ~300 nm by a wet furnace oxidation process. Subsequently, the reduced gap is transferred to the device layer using a customized dry high-aspect-ratio dry etching technique. For sacrificial approach, a ~100 nm-thin ALD aluminum oxide sidewall spacer is chemically etched away as the last microfabrication step to define the ~100 nm capacitive gap. Small capacitive gaps developed in this work results in small motional resistance (Rm) values, which relax the need of the read-out circuitry by enhancing the signal transduction. Piezoelectrically-actuated resonators were developed using thin-film bulk acoustic resonant (FBAR or TFBAR) and thin-film piezoelectric-on-substrate (TPoS) technologies with reported Q factors and resonant frequencies as high as 10,638 and 776.54 MHz, respectively, along with measured motional resistance values as low as 169Ω. To the best of our knowledge, this work is the first one that demonstrated TPoS resonators using LPCVD polysilicon as an alternative low loss structural layer to single-crystal silicon with Q factors as high as ~3,000 (in air) and measured motional resistance values as low as 6 kΩ with an equivalent acoustic velocity of 6,912 m s-1 for a 7 μm thick layer. Polysilicon based TPoS single devices were measured with the coefficient of resonant frequency of -3.77 ppm/°C, which was the lowest ever reported for this type of devices. Also a novel releasing process, thin-piezo on single crystal reactive etched (TPoSCRE), allows us to develop of TPoS resonators without the need to SOI wafers. The fabricated devices using this technique were reported with Q factor exceeding ~1,000 and measured motional resistance values as low as 9 kΩ.
The sensitivity of a fourth-order contour mode ZnO-on-SOI disk resonator based mass sensor was determined by performing multiple depositions of platinum micro-pallets using a focus ion beam (FIB) equipped with gas injection system on strategically-chosen locations. It was found out that the sensitivity of the resonator on its maximal and minimal displacement points was of 1.17 Hz fg-1 and 0.334 Hz fg-1, respectively. Also, the estimated limit of detection of the resonator was found to be a record breaking 367 ag (1 ag = 10-18g) compared to devices with similar modes of resonance. Lastly, a lateral-extensional resonator was used to measure the weight of HKUST-1 MOF crystal cluster. The weight of it was found to be 24.75 pg and 31.19 pg by operating two lateral resonant modes, respectively.
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Jarro, Sanabria Carlos Andrés. "GROWTH OF SILVER NANOPARTICLES ON TRANSPARENT SUBSTRATES FROM LIQUID PRECURSORS: IMPROVEMENTS AND APPLICATIONS." UKnowledge, 2013. http://uknowledge.uky.edu/ece_etds/38.
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Interest in controlling the synthesis of silver nanoparticles in colloidal solutions has increased during the last two decades. There is also growing interest in forming layers of silver nanoparticles on substrates, particularly for surface-enhanced Raman spectroscopy applications. However, methods to grow silver nanoparticles directly on substrates have not been studied extensively, and there are few techniques for controlling the size, shape, density, and location of the particles. This work presents a simple and reliable method to photodeposit silver nanoparticles onto transparent substrates. The size, shape and deposition density of the nanoparticles are influenced by the precursor solution, light intensity, and surface modification of the substrate. This allows control of the optical and electrical properties of the nanoparticle films. Furthermore, the particles can be patterned using direct laser exposure, scanning probe methods, and electron-beam lithography. Applications and advantages of this deposition method are proposed and explored.
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Zhao, Jun [Verfasser], and Harald [Akademischer Betreuer] Giessen. "Large-area low-cost fabrication of complex plasmonic nanostructures for sensing applications / Jun Zhao. Betreuer: Harald Giessen." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2015. http://d-nb.info/1069533262/34.
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Parthangal, Prahalad Madhavan. "Synthesis and integration of one-dimensional nanostructures for chemical gas sensing applications." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6881.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hoel, Anders. "Electrical Properties of Nanocrystalline WO3 for Gas Sensing Applications." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4051.
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Lai, Khue Tian. "Optical characterisation of quantum well infrared photodetectors (QWIPs) for gas sensing applications." Thesis, University of Hull, 2004. http://hydra.hull.ac.uk/resources/hull:5592.
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Although much work has been done on λ∼5-12 μm quantum well infrared photodetectors (QvWPs), the distinctive feature of this project is the use of strain compensated materials on InP substrates, AIAs (tensile) and InGaAs (compressive), to achieve shorter wavelengths and higher temperature operation. Stepped wells, high thin barriers, and strained layers have been used to achieve λ∼2-5 μm and also enhanced normal incidence absorption. These structures also give an additional degree of freedom to control the position of the excited states in the QWIPs conduction band. The strain-balancing allows the use of Indium (In) concentrations up to 84% and hence deep wells with a large band offset relative to the outer barrier (which predominantly controls the dark current). The conduction band offset (ΔEc) for these structures (with respect to the wide InAlAs barrier) is estimated to be ∼675 meV. In the course of this work, we have also been able to estimate the subband nonparabolicity (m* and α) from absorption spectra in highly doped quantum wells (QWs). In this thesis, the main results which I present are on a comparative study of the intersubband absorption in a series of double barrier QW (DBQW) structures grown on GaAs substrates (Chapter 5) and InP substrates (Chapter 6). The background and theory of QWs is given in Chapter 1. In Chapter 2, the experimental procedure is detailed, while the theoretical model to calculate the conduction band profile and energy levels and the comparison of this model with literature values are presented in Chapter 3. Early results are discussed in Chapter 4. Finally, a summary and future work are outlined in Chapter 7.
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Adnan, Rohul. "Gold-based Nanomaterials: Spectroscopy, Microscopy and Applications in Catalysis and Sensing." Thesis, University of Canterbury. Chemistry, 2015. http://hdl.handle.net/10092/10507.
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The birth of nanotechnology era has revolutionized materials science, catalysis and field of optoelectronics. Novel and unique phenomena emerge when material dimensions are reduced to ultra-small size regime and enter nanometre (2-100 nm) realm. Such novel materials are expected to replace bulk materials, offering lower cost of manufacturing and enabling progress in many areas such as solar cell, drug delivery, quantum communication and computing, catalysis and sensing applications. With the progress in nanomaterial synthesis and fabrication, the need for the state-of-art characterization techniques became obvious; such techniques help to establish a complete understanding of the nature and interactions of nanosized materials.
In this thesis, the first part focuses on the synthesis of gold and ruthenium clusters, namely Au8, Au9, Au101, Ru3, Ru4 and AuRu3, using the well-established synthetic protocols in the literature. Apart from the standard lab-based characterization techniques such as nuclear magnetic resonance (NMR), UV-visible spectroscopy (UV-vis) and Fourier Transform Infra-red (FTIR), a less explored but useful technique far infra-red (far IR) spectroscopy, available at the Australian Synchrotron (AS), was employed to investigate the vibrational modes in these clusters. Peaks in the experimental far IR spectra were assigned unambiguously to specific vibrations by comparing with the ones generated via DFT calculations with the help of collaborators, group of Professor Gregory Metha, University of Adelaide. For the Au9 cluster, three significant gold core vibrations are observed at 157, 177 and 197 cm-1 in the experimental spectrum. In the case of the Ru3 cluster, only a single ruthenium core vibration is identified within the spectrum, at 150 cm-1 with the calculated force constant, k = 0.33 mdyne/Å. The Ru4 cluster exhibits two metal core vibrations at 153 and 170 cm-1 with force constants of 0.35 and 0.53 mdyne/Å, respectively. Substitution with a gold atom yielding a mixed metal AuRu3 cluster shifts the core transitions toward higher wavenumbers at 177 and 299 cm-1 with an increase in force constants to 0.37 and 1.65 mdyne/Å, respectively. This is attributed to the change in chemical composition and geometry of the metal cluster core. A combination of the DFT calculations and high quality synchrotron-based experimental measurements allowed the full assignment of the key transitions in these clusters.
Next, these clusters were fabricated into heterogeneous catalysts by depositing on different metal oxide nanopowders. Synchrotron X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were performed at the Australian Synchrotron and the Photon Factory synchrotron in Japan to investigate the electronic structure of Au8, Au9 and Au101 on TiO2 catalysts. The XPS analysis reveals that “as-deposited” Au8 and Au9 retain some un-aggregated clusters while Au101 show bulk-like gold. These findings are in line with TEM observations, where the aggregates (large particles, > 2 nm) of Au8, Au9 and Au101 are hardly seen under HRTEM. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) studies show the absence of localised surface plasmon resonance (LSPR) peaks in these “as-deposited” clusters, suggesting they are below 2 nm in size. Importantly, the XAS spectrum of “as-deposited” Au9 clusters estimates that 60% of pure, un-aggregated Au9 clusters and 40% of bulk gold in the sample. Upon calcination under O2 and combined O2 and H2 (O2-H2), Au8, Au9 and Au101 clusters form larger nanoparticles (> 2 nm) with the appearance of LSPE peak in UV-vis DR spectra. In addition, majority of the phosphine ligands (that stabilise the gold core) dislodge and form phosphine oxide-like species by interacting with oxygen on the TiO2 surface.
The third part focused on testing the catalytic performance of the supported Au8, Au9, Au101, Ru3, Ru4 and AuRu3 clusters on different TiO2, SiO2, ZnO and ZrO2 in benzyl alcohol oxidation. Au101-based catalysts display the highest catalytic activity with a turn-over frequency (TOF) up to 0.69 s-1. The high catalytic activity is attributed to the formation of large Au nanoparticles (> 2 nm) that coincides with the partial removal of capping ligands. Au8 and Au9 clusters which contain NO3- counter anions are found to be inactive in benzyl alcohol oxidation. Further work shows that the presence of NO3- species diminishes the catalytic activity. Monometallic ruthenium clusters, Ru3 and Ru4, are found to be inactive yet the bimetallic AuRu3 clusters are active in benzyl alcohol oxidation, suggesting the synergistic effect between ruthenium and gold metal. Investigation of catalytic testing parameters reveals that tuning selectivity of the product is possible through manipulating the reaction temperature.
Finally, a joint experiment with Prof. Wojtek Wlodarski’s group at RMIT, Melbourne was undertaken to test the sensing ability of Au9 clusters for hydrogen detection. Au9 clusters were deposited onto radio-frequency (RF) sputtered WO3 films at two different concentrations; 0.01(S1) and 0.1(S2) mg/mL. It was found that the optimal temperatures for sensor S1 and S2 were 300 °C and 350 °C, respectively. The sensor with lower Au9 concentration (S1) displays a faster response and recovery time, and a higher sensitivity toward H2. HRTEM studies reveal that the sensor S1 contain a significant population of sub-5 nm Au nanoparticles which might be responsible for a faster rate of H2 adsorption and dissociation. The key finding in this study suggest that the addition of catalytic layer such as ultra-small Au9 clusters results in improved sensitivity and dynamic performance (response and recovery time) of H2 sensors.
In summary, this thesis demonstrated that cluster-based nanomaterials have wide range of applications spanning from catalysis to sensing. Further improvements in material synthesis and use of multiple complimentary characterization techniques allowed better understanding of the nature of the key active species (metal nanoparticles) assisting design of catalysts and sensors with enhanced performance.
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Evans, G. P. "Single-walled carbon nanotube networks and related composite materials for gas sensing applications." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10046785/.
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In this thesis, the gas sensing properties of single-walled carbon nanotube (SWCNT) networks and SWCNT-Zeolite composite materials were investigated in a variety of environmental conditions. The aim of the project was to establish the effect that adsorbed water vapour had on the electrical properties of SWCNT networks, along with any subsequent impact on the NO2 sensing responses of SWCNT-based chemiresistors. Motivated by these investigations, the sensitivity of the SWCNT networks to water vapour was exploited to develop the water-assisted regeneration (WAR) method, enabling the improved recovery of the baseline sensing signal. Zeolites, known as molecular sieves due to their selective adsorption properties, were utilised in SWCNT-Zeolite composite sensing layers to reduce the cross-sensitivity of functionalised SWCNTs to water vapour. Functionalisation of the SWCNTs with a range of anionic, cationic and nonionic surfactants to aid solution processing was found to enhance the conductancehumidity effect, in some cases by a factor of 10. An interesting bi-directional switch in conductance change was observed when anionic (conductance decrease) vs cationic (conductance increase) were used. Under experimental conditions, fluctuations in atmospheric humidity levels were shown to alter the gas sensing characteristics of the SWCNT networks. Formed from interconnected metallic and semiconducting SWCNTs, the chemiresistive sensors demonstrated increased response magnitudes, adsorption rates and recovery rates at higher levels (A 50% RH) of relative humidity. Raman spectroscopy, UV-Vis-NIR spectroscopy, electron microscopy and electrical characterisation techniques were used in conjunction with gas sensing experiments to study changes in the properties of the sensing elements, helping to elucidate potential mechanisms. Extraction of key sensing parameters was facilitated by the application of a model for completely irreversible adsorption of NO2, whilst a model based on partially reversible desorption was found to best describe the sensing data.
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KIPTIEMOI, KIPRONO KORIR. "ZnO nanowires for energy harvesting and gas sensing applications: a quantum mechanical study." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2539901.
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The research activity related to my PhD project is focused on providing a better understanding on energy harvesting capabilities and gas sensing mechanism of ZnO nanowires.
Nanowires made of materials with non-centrosymmetric crystal structures are expected to be ideal building blocks for self-powered nanodevices due to their piezoelectric properties, yet a controversial explanation of the effective operational mechanisms and size effects still delays their real exploitation. To solve this controversy, we propose a methodology based on Density Functional Theory (DFT) calculations of the response of nanostructures to external deformations that allows us to distinguish between the different (bulk and surface) contributions: we apply this scheme to evaluate the piezoelectric properties of ZnO [0001] nanowires, with a diameter up to 2.3 nm. Our unified approach allows for a proper definition of piezoelectric coefficients for nanostructures, and explains in a rigorous way the reason why nanowires are found to be more sensitive to mechanical deformation than the corresponding bulk material.
Gas-sensing mechanism of ZnO nanowire is investigated using ethanol as our prototype gas. In particular, we show that in the case of ethanol, it has larger binding energy to the ZnO surface compared to oxygen gas, hence able to remove pre-adsorbed oxygen molecules on the surface, and leads to release of trapped electrons to conduction band. Therefore, ZnO sensing is strongly linked to oxygen removal from the surface.
Furthermore, in this work oxygen vacancies distribution and concentration in ZnO nanostructures, which is still a question of debate is investigated using combined DFT and Climbing-Image Nudged Elastic Bands (CI-NEB) approach.
This work has successfully addressed some of the unanswered questions related to application of ZnO nanowires in field of energy harvesting and gas sensing, and may invaluable in fine-tuning nano-devices to attain enhance performance.
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Mangu, Raghu. "NANOSTRUCTURED ARRAYS FOR SENSING AND ENERGY STORAGE APPLICATIONS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/207.
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Vertically aligned multi walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst, were integrated into a resistive sensor design. The steady state sensitivities as high as 5% and 10% for 100 ppm of NH3 and NO2 respectively at a flow rate of 750 sccm were observed. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH3 and NO2 flow rates. An equivalent circuit model was developed to understand the operation and propose design changes for increased sensitivity.
Multi Walled Carbon NanoTubes (MWCNTs) – Polymer composite based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO2 substrates via xylene pyrolysis using chemical vapor deposition technique. Polymers like PEDOT:PSS and Polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-Propanol and Ethylene Glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100ppm) of gases like NH3 and NO2. Effect of various solvents on the sensor response imparting selectivity to CNT – Polymer nanocomposites was investigated extensively. Sensitivities as high as 28% was observed for a MWCNT – PEDOT:PSS composite sensor when exposed to 100ppm of NH3 and -29.8% sensitivity for a MWCNT-PANI composite sensor to 100ppm of NO2.
A novel nanostructured electrode design for Li based batteries and electrochemical capacitor applications was developed and tested. High density and highly aligned metal oxide nanowire arrays were fabricated via template assisted electrochemical deposition. Nickel and Molybdenum nanowires fabricated via cathodic deposition process were converted into respective oxides via thermal treatments and were evaluated as electrodes for batteries and capacitor applications via Cyclic Voltammetery (CV). Several chemical baths were formulated for the deposition of pristine molybdenum nanowires. Superior electrochemical performance of metal (Ni and Mo) oxide nanowires was observed in comparison to the previously reported nano-particle based electrodes.
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Adeyemo, Adedunni D. "Interaction of Metal Oxides with Carbon Monoxide and Nitric Oxide for Gas Sensing Applications." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1332475552.
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Thabethe, Sibongiseni Stanley. "Growth and characterization of FeSi nanowires by chemical vapor deposition for gas sensing applications." Thesis, University of the Western Cape, 2014. http://hdl.handle.net/11394/4239.
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>Magister Scientiae - MScFeSi nanowires were synthesized via a chemical vapor deposition method. Anhydrous FeCl3 powder in this case served as the Fe source and was evaporated at a temperature of 1100oC to interact with silicon substrates which served as the silicon source. The nanowires followed the vapor solid (VS) growth mechanism, which does not require the use of a metal catalyst; the native silicon oxide layer on the silicon substrates played the role of the catalyst in the growth of these nanostructures. A second growth mechanism, involving the use of a metal catalyst to assist in the growth of the nanowires was attempted by depositing a thin film of gold on silicon substrates. The reaction yielded SiOx nanowires; these results are discussed in detail in Chapter 5. All the nanostructures were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Photoluminescence Spectroscopy (PL), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR).
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Emamjomeh, Seyed Mahmoud. "Nanoscale sensors based on "D TMDs and nanostructured Metal Oxides for gas sensing applications." Doctoral thesis, Università degli Studi dell'Aquila, 2018. http://hdl.handle.net/11697/165111.
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Chemical gas sensor is an electronic functional device to warn us about dangerous gases in human environment. Its function and reliability can save human health, lives and environment from diseases and disasters and control the air pollution. Thus, it can be said the human generation is closely related to the function ability and properties of gas sensors that could be counted sensitivity, selectivity and stability.
To improve these features, in recent decades there has been an increased attension for the development of nanomaterials which provide high structural and morphological control, high efficiency and miniaturization of gas sensors.
The work presented in this thesis is focused on the synthesis of mono-few layered 2D TMDs semiconductors and metal oxide nanomaterials for manufacturing gas sensors for toxic gas sensing measurements. A wide range of gas sensors have been realized, starting from the synthesis of various semiconductors such as metal oxides and Transition Metal Dichalcogenides and using various deposition techniques. In particular, electrospinning, spin coating and ball milling assisted ultra sound probe sonication were utilized to obtain one-dimensional (1D) nanofiber metal oxides and two-dimensional (2D) TMDs respectively.
Morphological characterization of materials was carried out by means Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Transmission Electron
Microscope (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Xray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The electrical
characterizations were carried out by a laboratory equipment. Target gases such as H2, CO, NO2 with concentrations like those found in polluted environments were investigated.
Fabricated gas sensors have shown excellent results and performances suggesting the use of nanomaterials-based devices for commercial purposes.
This PhD work has developed through relationships with various research groups including the Departments of Physics and Industrial Engineering of the University of
L'Aquila, the Department of Industrial Engineering of the University of Padova, the Department of Chemistry of the University of Pavia, School of Chemical Sciences of the
University of Auckland in New Zealand; and School of Chemical and Physical Sciences of Victoria University of Wellington in New Zealand.
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Tarttelin, Hernandez P. "Modification of n-type and p-type metal oxide semiconductor systems for gas sensing applications." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1549841/.
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This thesis investigates the modification of three metal oxide semiconductor gas sensors with zeolite materials for the purposes of detecting trace concentrations of gases that have an effect on health, security, safety and the environment. SnO2, Cr2O3 and Fe2O3 were chosen as the base materials of interest. Zeolites HZSM- 5, Na-A and H-Y were incorporated into the sensing system either as admixtures with the base material or as coatings on top of it. The aim of introducing zeolites into the sensing system was to improve the performance of the otherwise unmodified sensors. Twenty-two novel zeolite-modified sensor systems are presented for the detection of a range of hydrocarbons and inorganic gases. Whilst sensors based on SnO2 systems were more responsive to gases, some sensors were also found to provide a greater degree of variability among repeat tests, particularly at lower operating temperatures i.e. 300 °C. Cr2O3 sensors modified by admixture with zeolite H-ZSM- 5 were seen to be poorly sensitive to most analytes. Cr2O3 sensors modified by admixture with zeolite Na-A and by overlayer of zeolite H-Y provided very promising sensitive and selective results towards toluene gas. Sensors based on the zeolite modification of Fe2O3 were not found to be promising candidates as gas sensors at this stage. Sensors were purposely exposed to gases that had similar molecular structures or kinetic diameters to assess the true capability of the sensors to discriminate among analytes. An array of four sensors based on n-type and p-type systems was subsequently chosen to see whether machine learning classifiers could be used to accurately discriminate among nine analytes. Using an SVM SMO classifier with a polykernel function, the model was 94.1% accurate in correctly classifying nine analytes of interest just after five seconds into the gas injection. Using an RBF kernel function, the model was 90.2% accurate in correctly classifying the data into gas type. These are very encouraging results, which highlight the importance of furthering research in this field; a sensing array based on zeolite-modified metal oxide semiconductor sensors may benefit a number of research domains by providing accurate results in a very fast and inexpensive manner.
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Shehata, Nader. "Design of optical characteristics of ceria nanoparticles for applications including gas sensing and up-conversion." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/49574.
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This thesis investigates the impact of doping on the optical and structural characteristics of cerium oxide (ceria) nanoparticles synthesized using chemical precipitation. The dopants selected are samarium and neodymium, which have positive association energy with oxygen vacancies in the ceria host, and negative association lanthanides, holmium and erbium, as well as two metal dopants, aluminum and iron. Characteristics measured are absorption and fluorescence spectra and the diameter and lattice parameter of ceria. Analysis of the characteristics indicates qualitatively that the dopant controls the O-vacancy concentration and the ratio of the two cerium ionization states: Ce+3 and Ce+4. A novel conclusion is proposed that the negative association lanthanide dopants can act as O-vacancies scavengers in ceria while the O-vacancy concentration increases in ceria doped with positive association lanthanide elements. Doped ceria nanoparticles are evaluated in two applications: dissolved oxygen (DO) sensing and up-conversion. In the first application, ceria doped with either Sm or Nd and ceria doped with aluminum have a strong correlation between the fluorescence quenching with the DO concentration in the aqueous solution in which the ceria nanoparticles are suspended. Stern-Volmer constants (KSV) of doped ceria are found to strongly depend upon the O-vacancy concentration and are larger than some of the fluorescent molecular probes currently used to measure DO. The KSV measured between 25-50oC is found to be significantly less temperature dependent as compared to the constants of commercially-available DO molecular probes. In the second application, up-conversion, ceria nanoparticles doped with erbium and an additional lanthanide, either Sm or Nd, are exposed to IR radiation at 780 nm. Visible emission is only observed after the nanoparticles are calcinated at high temperature, greatly diminishing the concentration of O-vacancies. It is concluded that O-vacancies do not play a dominant role in up-conversion, unlike that drawn for down-conversion, where the fluorescence intensity is strongly correlated with the O-vacancy concentration. Correlations between annealing temperatures, dopant, and dopant concentrations with the power dependence of up-conversion on the pump and the origin of the intensities of the visible emission are presented. These studies show the promise of doped ceria nanoparticles.Ph. D.
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Strauß, Ina Carina [Verfasser], and Jürgen [Akademischer Betreuer] Caro. "Metal-organic frameworks for gas and vapour-sensing applications / Ina Carina Strauß ; Betreuer: Jürgen Caro." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2020. http://d-nb.info/1215427255/34.
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Schulz, Marcel [Verfasser], and Peter [Akademischer Betreuer] Behrens. "Reactive metal-organic-frameworks for highly selective gas sensing applications / Marcel Schulz ; Betreuer: Peter Behrens." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2020. http://d-nb.info/1213445817/34.
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Renard, Laëtitia. "Nanostructured tin-based materials : sensing and optical applications." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14183/document.
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Des matériaux hybrides de classe II ont été préparés à partir de précurseurs bis(tripropynylstannylés). Deux familles de précurseurs sol-gel incluant des espaceurs hydrocarbonés et thiophénique ont été obtenues et conduisent à des matériaux hybrides auto-organisés où les plans d’oxyde sont séparés par les espaceurs organiques. Ainsi l’espaceur rigide a donné lieu à une structure pseudo-lamellaire montrant une bande d’émission monomère avec un assez faible décalage vers le rouge par rapport à l'émission des précurseurs en solution. En revanche, alors que les xérogels thiényle plus désordonnés conduisent à une large émission caractéristique de la formation d’excimères ou de dimères. Par ailleurs, des films minces contenant les espaceurs alkylène et arylalkylène ont été préparés et ont montré une morphologie "pseudoparticulaire" poreuse et un ordre à courte distance contenant des réseaux SnOx. De façon inattendue, ces films minces hybrides détectent le dihydrogène dès une température de 50 °C dans la gamme 200-10000 ppm. A partir de ces films hybrides minces, le dioxyde d'étain cristallin (SnO2) a été préparé par un post-traitement thermique. Comme prévu, ces films SnO2 cassitérite détectent le dihydrogène et, dans une moindre mesure le monoxyde de carbone avec une température optimale de fonctionnement comprise entre 300 et 350 °CClass II hybrid materials were prepared from ditin hexaalkynides. Two families of precursors, including either hydrocarbon or oligothiophene-based spacers, were obtained and led by the sol-gel process to self-assembled organotin-based hybrid materials made of planes of oxide separated by organic bridges. Thus, the rigid thienyl spacer gave rise to a “pseudo-lamellar” structure that showed a monomer emission band with a rather small red-shift compared with to the emission of the precursor in solution. However more disordered thienyl xerogels led to broad emission features assigned to excimer or dimer formation. Moreover, thin films containing alkylene- and arylalkylene bridged have been prepared and showed a “pseudoparticulate” porous morphology and a short-range hierarchical order in the organic-inorganic SnOx pseudoparticles. Unexpectedly these hybrid thin films detect hydrogen gas at a temperature as low as 50 °C at the 200-10000 ppm level. From these hybrid thin films, crystalline tin dioxide (SnO2) were prepared by a thermal post-treatment. As expected, cassiterite SnO2 films detected H2 and to a less extent CO with a best operating temperature comprised between 300 and 350 °C
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Arsat, Rashidah, and rashidah arsat@student rmit edu au. "Investigation of Nanostructured Thin Films on Surface Acoustic Wave and Conductometric Transducers for Gas Sensing Applications." RMIT University. Electrical and Computer Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091002.094407.
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In this thesis, the author proposed and developed nanostructured materials based Surface Acoustic Wave (SAW) and conductometric transducers for gas sensing applications. The device fabrication, nanostructured materials synthesis and characterization, as well as their gas sensing performance have been undertaken. The investigated structures are based on two structures: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). These two substrates were chosen for their high electromechanical coupling coefficient. The conductometric structure is based on langasite (LGS) substrate. LGS was selected because it does not exhibit any phase transition up to its melting point (1470°C). Four types of nanostructured materials were investigated as gas sensing layers, they are: polyaniline, polyvinylpyrrolidone (PVP), graphene and antimony oxide (Sb2O3). The developed nanostructured materials based sensors have high surface to volume ratio, resulting in high sensitivity towards di¤erent gas species. Several synthesis methods were conducted to deposit nanostructured materials on the whole area of SAW based and conductometric transducers. Electropolymerization method was used to synthesize and deposit polyaniline nanofibers on 36° YX LiTaO3 and 64° YX LiNbO3 SAW substrates. By varying several parameters during electropolymerization, the effect on gas sensing properties were investigated. The author also extended her research to successfully develop polyaniline/inorganic nanocomposites based SAW structures for room temperature gas sensing applications. Via electrospinning method, PVP fibres and its composites were successfully deposited on 36° YX LiTaO3 SAW transducers. Again in this method, the author varied several parameters of electrospinning such as distance and concentration, and investigated the effect on gas sensing performance. Graphene-like nano-sheets were synthesized on 36° YX LiTaO3 SAW devices. This material was synthesized by spin-coating graphite oxide (GO) on the substrate and then exposin g the GO to hydrazine to reduce it to graphene. X-ray photoelectron spectroscopy (XPS) and Raman characterizations showed that the reduced GO was not an ideal graphene. This information was required to understand the properties of the deposited graphene and link its properties to the gas sensing properties. Thermal evaporation method was used to grow Sb2O3 nanostructures on LGS conductometric transducers. Using this method, different nanoscale structures such as nanorods and lobe-like shapes were found on the gold interdigitated transducers (IDTs) and LGS substrate. The gas sensing performance of the deposited nanostructured Sb2O3 based LGS conductometric sensors was investigated at elevated temperatures. The gas sensing performance of the investigated nanostructured materials/SAW and conductometric structures provide a way for further investigation to future commerciallization of these types of sensors.
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Wierzbowska, Katarzyna Barbara. "Studies of electronic and sensing properties of epitaxial InP surfaces for applications in gas sensor devices." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2007. http://tel.archives-ouvertes.fr/tel-00926562.
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Cette thèse est consacrée à l'étude de la physico-chimie des structures électroniques et microélectroniques à base de phosphure d'indium (InP). Le contexte scientifique de cette étude est d'abord abordé dans une description de la pollution atmosphérique ainsi que de sa métrologie. Les propriétés physico-chimiques et électroniques de InP sont particulièrement détaillées. Les structures des capteurs de gaz en cours de développement pour cette application sont ensuite répertoriées. Les méthodes de caractérisation chimique (spectroscopie de surface XPS et Auger, microscopie à force atomique AFM) et électronique (Van der Pauw) ainsi que l'analyse théorique des propriétés électroniques des couches minces sont également présentées. Enfin, des mesures en laboratoire à température et concentration variables de NO2 proches de celles rencontrées dans une atmosphère urbaine sont présentées. Les résultats obtenus suite à l'analyse théorique et aux différentes expériences ont montré le rôle prédominant des oxydes natifs présents à la surface de InP sur les réponses des capteurs. Ces derniers interviennent également sur la stabilité de la réponse aux gaz, tout comme leurs propriétés physico-chimiques. Les résultats des caractérisations électroniques et chimiques corroborent les résultats des essais des capteurs et permettent une modélisation de l'action du gaz sur InP
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González, Fernández Ernesto. "Low-power techniques for wireless gas sensing network applications: pulsed light excitation with data extraction strategies." Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/672792.
Full textAbstract:
Aquesta tesi està enfocada en dues línies d'investigació. La primera aborda el desenvolupament d'una metodologia
basada en llum polsada per modulació de sensors químic-resistius per a l'extracció d'informació del senyal transitòri, i
la segona planteja la implementació d'una xarxa sense fils de sensors (WSN) basada en tecnologia LoRa per al
monitoratge de la qualitat de l'aire (AQM) i la detecció d'esdeveniments de fuita de gasos. Aquest document està
estructurat en quatre capítols organitzats de la següent manera: el Capítol 1 presenta l'estat de l'art, una introducció
als mecanismes de millora de l'comportament dels sensors químic-resistius, així com una introducció a la
implementació de xarxes sense fils de sensors per a la monitorització de la qualitat de l'aire; el Capítol 2 està compost
pels dos articles publicats relacionats amb la metodologia basada en la modulació utilitzant llum polsada per a
l'extracció d'informació del senyal transitòria de sensors químic-resistius; el Capítol 3 presenta l'article publicat
relacionat amb la implementació d'una WSN per a AQM; el Capítol 4 presenta les conclusions derivades dels resultats
obtinguts durant el desenvolupament de el projecte de tesi i les recomanacions per al treball futur associat a la
continuïtat dels principals resultats d'aquesta tesiLa presente tesis está enfocada en dos líneas de investigación, La primera aborda el desarrollo de una metodología basada en luz pulsada para modulación de sensores químico-resistivos para la extracción de información de la señal transitoria; y la segunda plantea la implementación de una red inalámbrica de sensores (WSN) basada en tecnología LoRa para la monitorización de la calidad del aire (AQM) y la detección de eventos de fuga de gases. Este documento está estructurado en cuatro capítulos organizados de la siguiente forma: el Capítulo 1 presenta el estado del arte, una introducción a los mecanismos de mejora del comportamiento de los sensores químico-resistivos, así como una introducción a la implementación de redes inalámbricas de sensores para la monitorización de la calidad del aire; el Capítulo 2 está compuesto por los dos artículos publicados relacionados con la metodología basada en la modulación utilizando luz pulsada para la extracción de información de la señal transitoria de sensores químico-resistivos; el Capítulo 3 presenta el artículo publicado relacionado con la implementación de una WSN para AQM; el Capítulo 4 presenta las conclusiones derivadas de los resultados obtenidos durante el desarrollo de el proyecto de tesis y las recomendaciones para el trabajo futuro asociado a la continuidad de los principales resultados de esta tesis.
The present thesis project is focused in two different yet related research lines. The first one addresses the development of a pulsed light-based chemiresistive sensor modulation methodology for transient information extraction. The second research line developed deals with the implementation of a LoRa-based portable, scalable, low-cost, and low power Wireless Sensor Network (WSN) for Air Quality Monitoring (AQM) and gas leakage events detection. This document is structured in four Chapters organized as follows: Chapter 1 presents the state of the art, an introduction to sensing performance enhancement and transient data extraction methods, as well as an introduction to the implementation of WSN for AQM; Chapter 2 is composed of the two published paper related to the pulsed light modulation methodology for transient information extraction; Chapter 3 presents the published paper related to the implementation of a LoRa-based WSN for AQM; Chapter 4 states the conclusions derived from the results obtained during this thesis project and the recommendations for the future work associated to the continuity of this thesis findings.
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Sturaro, Marco. "Synthesis and characterization of transparent conductive oxides for gas sensing, solar control and transparent electrode applications." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3426751.
Full textAbstract:
My thesis is focused on the synthesis of thin films of transparent conductive oxides (TCOs) by colloidal approach for gas sensing applications, solar control and transparent electrode.
The work is mainly divided in three different parts.
In the first place on the development of nanoparticles of doped conductive oxides and transparent by colloidal synthesis. In particular nanoparticles were synthesized using heat up synthesis that do not require high temperature injection: doped ZnO with trivalent metals such as aluminum and gallium, or doped with tetravalent elements such as Silicon and Germanium, and Niobium doped TiO2 nanoparticles. Free electrons introduced into the crystal by dopants lead to the development of peculiar optoelectronic properties, in particular the formation of a LSPR in the near infrared. In the first part such nanoparticles are also characterized by different techniques and are faced in particular the variations in their morphology and the optical properties as a result of different concentrations of doping.
The second part examination was focused on the deposition of TCOs colloidal suspensions and the characterization of TCOs thin film. One of the primary objectives was to obtain functional thin films (such as transparent electrodes or coatings for solar control) using mild heat treatments and through different approaches, using UV lamps or organic acids attacks in order to eliminate most of the organic residues. In this way, by combining heat-up synthesis easily scalable, depositions via spray coating or spin coating (which does not therefore require the use of vacuum or expensive equipment) and heat treatments that do not require excessive temperatures, it is possible to pave the way to an industrialization of the process.
The last part focuses on the use of such films for sensor applications, in particular for the detection of H2 and NO2. LSPR is sensitive to changes of the dielectric constant in the neighborhood of the particles, and to variation of charge density, allowing to monitor the gases that interact with the oxide resulting in a shift in the wavelength of the LSPR peak. Optical gas sensing and electrical gas sensing measurements were performed to evaluate different behavior of different dopant concentrations. Measurements in the presence of blue LEDs were also carried out, investigating the role of this radiation in the desorption kinetics of adsorbed molecules. Finally Platinum nanoparticles influence on the detection of hydrogen was also evaluated in order to improve the sensitivity of the sensor exploiting Pt catalytic activity.Il mio lavoro di tesi si è focalizzato sulla sintesi di film sottili di ossidi trasparenti e conduttivi (TCOs) per via colloidale per applicazioni di gas sensing, solar control ed elettrodo trasparente. Il lavoro è suddiviso principalmente in tre diverse parti. La prima parte si concentra sullo sviluppo di nanoparticelle di ossidi dopati conduttivi e trasparenti per via colloidale. In particolare sono stati sintetizzate, utilizzando sintesi heat-up che non richiedono iniezione ad alta temperatura, nanoparticelle di ZnO dopato con metalli trivalenti come Alluminio e Gallio, oppure dopato con elementi tetravalenti come Silicio e Germanio, e nanoparticelle di TiO2 dopata con Niobio. Gli elettroni liberi introdotti nel cristallo in seguito al drogaggio portano allo sviluppo di peculiari proprietà optoelettroniche, in particolare alla formazione di una LSPR nel vicino infrarosso. Tali nanoparticelle sono state caratterizzate mediante diverse tecniche che permettono di investigare in particolare le variazioni della loro morfologia e delle proprietà ottiche a seguito di diverse concentrazioni di dopante. Nella seconda parte vengono invece approfonditi gli aspetti legati alla deposizione delle sospensioni colloidali ottenute e alla caratterizzazione dei film sottili prodotti. Uno degli obiettivi primari è ottenere film sottili funzionali (ad esempio come elettrodi trasparenti o per rivestimenti solar control) utilizzando blandi trattamenti termici e attraverso diversi approcci, tra cui irraggiamento UV o attacchi con acidi organici in modo da eliminare gran parte dei residui organici. In questo modo, combinando sintesi heat up “non injection” facilmente scalabili, deposizioni tramite spray coating o spin coating (che non richiedano quindi l’uso di vuoto o apparecchiature costose) e trattamenti termici che non richiedano temperature eccessive, è possibile aprire la strada ad una industrializzazione del processo. L’ultima parte si focalizza sull’utilizzo di tali film per applicazioni sensoristiche, in particolare per la rilevazione di H2 e NO2. La LSPR è sensibile ai cambiamenti della costante dielettrica nell’intorno delle particelle ed alla variazione di densità di carica: ciò permette di monitorare i gas che interagiscono con l’ossido analizzando lo spostamento in lunghezza d’onda del picco plasmonico. Sono stati effettuate misurazioni di gas sensing ottico ed elettrico per valutare le diverse performance dei TCOs a diversa concentrazione di dopante. Misurazioni in presenza di LED blu sono state inoltre eseguite, investigando il ruolo di tale radiazione nella cinetica di desorbimento delle molecole adsorbite. Infine è stata anche valutata l’influenza di nanoparticelle di Platino sulla rilevazione di idrogeno al fine di migliorare la sensibilità del sensore sfruttando l’attività catalitica di tali nanoparticelle.