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1
Halpert, Jonathan E. "Design and synthesis of nanocrystal heterostructures for optoelectronic applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43764.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.Vita.
Includes bibliographical references.
Colloidal semiconductor nanocrystals can be used for a variety of optoelectronic applications including light emitting devices (LEDs) and photovoltaics. Their narrow emission spectra make them excellent fluorophors for use in red, green and blue emitting organic LEDs and have been shown to achieve external quantum efficiencies as high as 2.7%, 1.8% and 0.4% respectively. Better synthetic methods have produced nanocrystal emitters with higher quantum yield, boosting efficiency, while a better understanding of QD-OLED function has led to improved organic transport materials. These QD-OLED devices can also be redesigned using inorganic hole and electron transport materials to produce inorganic QD-LEDs (QD-ILEDs) with EQE as high as 0.1%. Inorganic transport layers are more robust to solvents and oxygen, and are expected to greatly increase the device lifetime of QD-LEDs over devices employing organic materials. New QD deposition techniques using an inorganic hole transport layer include inkjet printing and Langmuir-Shaeffer dip-coating. Greater synthetic control of the II-VI nanocrystals has also yielded type-II CdSe/CdTe nanobarbells capable of internal exciton separation for photovoltaic applications. Although efficient solar cells using this material could not be produced, the material has given us several insights into the physics and future designs of bulk heterojunction photovoltaic devices. Finally, nanocrystal heterostructures formed using J-aggregate dyes electrostatically bound to QDs, have shown potential for use in LCD or lasing device applications.
by Jonathan E. Halpert
Ph.D.
2
BRUNI, FRANCESCO. "NOVEL MATERIAL DESIGN AND MANIPULATION STRATEGIES FOR ADVANCED OPTOELECTRONIC APPLICATIONS." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/151660.
Full textAbstract:
Il mio progetto di dottorato è stato focalizzato sui semiconduttori organici per applicazioni fotovoltaiche e di fotorivelazione. Inizialmente ho lavorato sul controllo morfologico di blende binarie di molecole organiche e fullereni usando la cosiddetta strategia dei pigmenti latenti. In particolare ho lavorato sull'ingenierizzazione dello strato attivo di celle solari organiche a eterogiunzione. Ho dimostrato una nuova strategia per controllare la segregazione di fase in film sottili di molecole elettron donatrici e fullereni, introducendo nel sistema un network di legami di idrogeno attivato termicamente. Successivamente ho studiato i processi di accumulazione di carica all’interfaccia tra acqua e un semiconduttore polimerico per applicazioni biomediche per mezzo di nanocristalli colloidali biemissivi con alta sensibilità verso agenti elettronattrattori. In fine, ho dedicato l’ultima parte del mio lavoro all’approfondimento delle possibili applicazioni di questa classe di nanocristalli come sensori raziometrici di pH intracellulare e come vernici per il monitoraggio ottico della pressione.My PhD has been focused on organic semiconductors for photovoltaics and photodetecting applications. Initially, I worked on the control of the morphology in binary blends of small organic molecules and fullerenes using the so called latent pigment approach. Subsequently, I investigated the charge accumulation and polarization effect occurring at the interface between water and a polymeric semiconductor used as optical component in retinal prosthesis by means of inorganic colloidal nanocrystals featuring a ratiometric sensing ability for electron withdrawing agents. As a last part of the work, I focalized on the applications of these nanocrystals as ratiometric sensors for intracellular pH probing and pressure optical monitoring. Specifically, during the first part of my PhD, I worked in the field of organic photovoltaics on the morphology engineering of the active layer of small molecules bulk-heterojunction solar cells. I demonstrated a new strategy to fine tune the phase-segregation in thin films of a suitably functionalized electron donor blended with fullerene derivatives by introducing in the system a post-deposition thermally activated network of hydrogen bonds that leads to improved stability and high crystallinity. Moreover, this process increases the carrier mobility of the donor species and allows for controlling the size of segregated domains resulting in an improved efficiency of the photovoltaic devices. This work revealed the great potential of the latent hydrogen bonding strategy that I subsequently exploited to fabricate nanometric semiconductive features on the film surface by using a very simple maskless lithographic technique. To do so, I focalized a UV laser into a confocal microscope and used the objective as a “brush” to thermically induce a localized hydrogen bonding driven crystallization with diffraction limited resolution. My work on organic semiconductors continued with a study on the surface polarization driven charge separation at the P3HT/water interfaces in optoelectronic devices for biologic applications. In this work, I probed the local accumulation of positive charges on the P3HT surface in aqueous environment by exploiting the ratiometric sensing capabilities of particular engineered core/shell heterostuctures called dot-in-bulk nanocrystals (DiB-NCs). These structures feature two-colour emission due to the simultaneous recombination of their core and shell localized excitons. Importantly, the two emissions are differently affected by the external chemical environment, making DiB-NCs ideal optical ratiometric sensors. In the second part of my PhD, I, therefore, focalized on the single particle sensing application of DiB-NCs. Specifically, I used them to ratiometrically probe intracellular pH in living cells. With this aim, I studied their ratiometric response in solution by titration with an acid and a base. Subsequently, I internalized them into living human embryonic kidney (HEK) cells and monitored an externally induced alteration of the intracellular pH. Importantly, viability test on DiB-NCs revealed no cytotoxicity demonstrating their great potential as ratiometric pH probes for biologic application. Finally, I used DiB-NCs as a proof-of-concept single particle ratiometric pressure sensitive paint (r-PSP). In this application, the emission ratio between the core and the shell emission is used to determine the oxygen partial pressure and therefore the atmospheric pressure of the NC environment.
3
Dong, Shuping. "Effects of acid hydrolysis conditions on cellulose nanocrystal yield and properties: A response surface methodology study." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78102.
Full textAbstract:
Cellulose nanocrystals (CNCs) are frequently prepared by sulfuric acid hydrolysis of a purified cellulose starting material. CNC yields, however, are generally low, often below 20%. This study employs response surface methodology to optimize the hydrolysis conditions for maximum CNC yield. Two experimental designs were tested and compared: the central composite design (CCD) and the Box–Behnken design (BBD).
The three factors for the experimental design were acid concentration, hydrolysis temperature, and hydrolysis time. The responses quantified were CNC yield, sulfate group density, ζ-potential, z-average diameter, and Peak 1 value. The CCD proved suboptimal for this purpose because of the extreme reaction conditions at some of its corners, specifically (1,1,1) and (–1,–1, –1). Both models predicted maximum CNC yields in excess of 65% at similar sulfuric acid concentrations (~59 wt %) and hydrolysis temperatures (~65 °C).
With the BBD, the hydrolysis temperature for maximum yield lay slightly outside the design space. All three factors were statistically significant for CNC yield with the CCD, whereas with the BBD, the hydrolysis time in the range 60–150 min was statistically insignificant. With both designs, the sulfate group density was a linear function of the acid concentration and hydrolysis temperature and maximal at the highest acid concentration and hydrolysis temperature of the design space. Both designs showed the hydrolysis time to be statistically insignificant for the ζ-potential of CNCs and yielded potentially data-overfitting regression models. With the BBD, the acid concentration significantly affected both the z-average diameter and Peak 1 value of CNCs.
However, whereas the z-average diameter was more strongly affected by the hydrolysis temperature than the hydrolysis time, the Peak 1 value was more strongly affected by the hydrolysis time. The CCD did not yield a valid regression model for the Peak 1 data and a potentially data-overfitting model for the z-average diameter data. A future optimization study should use the BBD but slightly higher hydrolysis temperatures and shorter hydrolysis times than used with the BBD in this study (45–65 °C and 60–150 min, respectively).Master of Science
4
Lin, Stephanie J. "Bioreneweable polymer nanocomposites: A study of the design space available for cellulose nanocrystal/poly(3-hydroxybutyrate) nanocomposites." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52214.
Full textAbstract:
This research is directed toward determining the design space that is available for cellulose nanocrystals /poly(3-hydroxybutyrate)(CNC/PHB) composites. In order to develop this understanding, the processing-structure-properties relationships of CNC/PHB nanocomposites were examined at several different steps in a stepwise processing method. The as-processed morphology of solvent cast (SC) and anti-solvent compression molded (ASCM) samples were examined using DSC, optical microscopy and ATR-FTIR and the effect of processing and CNC addition on the isothermal and nonisothermal crystallization was examined using DSC, hot stage microscopy, and a novel fast scanning chip calorimeter, the Flash DSC. Results show that the addition of water during SC processing significantly reduced the rate of crystallization at both isothermal and nonisothermal conditions. This reduction in crystallization rate was due to the presence of water suppressed the intramolecular hydrogen bonding. Results from the experimenters performed also indicated CNCs act as a nucleating agent. Even though the overall kinetics of crystallization was increased with CNC addition, the growth rate of the spherulites was reduced with the addition of CNCs. Mechanical characterization of the ASCM and SC-EtOH samples showed that the differences in viscoelastic behavior with CNC addition for the ASCM samples but not the SC-EtOH samples. Also the strain to failure of both processing methods was increased with CNC addition. The knowledge that was obtained from this work can be used when designing processing protocols and heat treatments for PHB-based nanocomposites materials to allow greater control over crystallization processes and mechanical properties expanding opportunities for materials design.
5
Eley, Clive William. "The rational design of photocatalytic semiconductor nanocrystals." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ee29c922-857c-432a-8316-a7e04c822b1d.
Full textAbstract:
This thesis reports the successful rational design of three highly active photocatalytic semiconductor nanocrystal (SNC) systems by exploiting morphology effects and the electronic properties of type II semiconductor heterojunctions. Novel architectures of colloidal SNCs are produced with the aim of suppressing exciton recombination and improving charge extraction for the successful initiation of desirable redox chemistry. Rod-shaped niobium pentoxide Nb2O5 nanocrystals (NCs) are shown to exhibit significantly enhanced activity (10-fold increase in rate constant) relative to spherical-shaped NCs of the same material. The increase is attributed to Nb5+ Lewis acid site rich (001) surfaces, present in higher proportions in the rod morphology, which bind organic substrates from solution resulting in direct interaction with photogenerated charges on the surface of the NC. Building on the insights into morphology-activity dependence, type II semiconductor heterojunctions are exploited for their ability to increase exciton lifetimes and spatially separate charges. Two novel II-VI heterostructured semiconductor nanocrystals (HSNCs) systems are investigated: a series of CdX/ZnO (X = S, Se, Te) HSNCs and ZnS/ZnO HSNCs capped with two different surface ligands. In the first case, substantial photocatalytic activity improvement is observed for HSNCs (relative to pure ZnO analogues) according to the following trend: CdTe/ZnO > CdS/ZnO > CdSe/ZnO. The observed trend is explained in terms of heterojunction structure and fundamental chalcogenide chemistry. In the second case, both ZnS/ZnO HSNCs exhibit activity enhancement over analogous pure ZnO, but the degree of enhancement is found to be a function of surface ligand chemistry. Photocatalytic activity testing of all the materials investigated in this work is performed via the photodecomposition of methylene blue dye in aerated aqueous conditions under UVA (350 nm) irradiation. The synthetic techniques employed for the synthesis of colloidal SNCs investigated in this thesis range from chemical precipitation and solvothermal techniques to several different organometallic approaches. A wide variety of analytical techniques are employed for the chemical, structural and optical characterisation of SNC photocatalysts including: XRD, XPS, TEM, UV-vis absorption, PL spectroscopy and FTIR. Atom Probe Tomography (APT) is employed for the first time in the structural characterisation of II-VI heterojunctions in colloidal HSNCs. Overall, this thesis provides a useful contribution to the growing body of knowledge pertaining to the enhancement of photocatalytic SNCs for useful applications including: solar energy conversion to chemical fuels, the photodecomposition of pollutants and light-driven synthetic chemistry.
6
Sayevich, Uladzimir. "Synthesis, Surface Design and Assembling of Colloidal Semiconductor Nanocrystals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-209074.
Full textAbstract:
The work presented in the thesis is focused on the synthesis of diverse colloidal semiconductor NCs in organic media, their surface design with tiny inorganic and hybrid capping species in solution phase, and subsequent assembling of these NC building units into two-dimensional close-packed thin-films and three-dimensional non-ordered porous superstructures.
7
Cordero, Hernández José Manuel. "Synthesis of derivatizable semiconductor nanocrystals through rational ligand design, and applications thereof." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107554.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-145).
Over the last decade, the synthesis methods of colloidal nanocrystals have advanced at an astonishing rate, producing particles that are chemically stable, monodisperse, and, in the case of semiconductor quantum dots (QDs), immensely bright. Inorganic nanocrystals linked to functional organic or biological molecules have recently emerged as a new class of nanomaterials for generating highly efficient devices, and sensing agents for a broad range of advanced applications. A key step in the synthesis of these constructs involves transforming the chemistry of the surface from that generated by the nanocrystals synthesis conditions (high boiling-point and hydrophobic solvent environment) to one possessesing the appropriate functional groups for derivatization and that is compatible with the intended final application. Here, we describe the synthesis of a series of organic ligands that modify the surface in that manner. The first ligand exhibits a norbornene functional group and binds strongly to the surface of colloidal nanocrystallites during particle synthesis, eliminating the need for ligand exchange and enabling large-scale production of high quality derivatizable nanomaterials. This ligand is compatible with state-of-the-art synthesis methods of a large variety of semiconductor nanocrystallites, including PbS, CdSe/CdS, and InAs/CdSe/CdS core/shell nanoparticles. Applications that make use of the norbornene click-chemistry functionality will be presented, along with efforts to preserve the high quantum yield and colloidal stability in water. We also introduce a bidentate carboxylate-based ligand as part of an effort to enhance the quality of QDs through the chelate effect. This ligands enhances the PLQY at high temperature, as a result of surface-related trap state passivation. Finally, we describe the synthesis of a new functional group for generating derivatizable-QDs that can be easily copolymerized with the polyimidazole ligand (PIL), and that is reactive with tetrazine and, upon thermal activation, with thiols to form stable bioconjugates.
by José Manuel Cordero Hernández.
Ph. D.
8
Sun, Qingbo. "Defect Design, Chemical Synthesis and Associated Properties of Multifunctional TiO2-Based Nanocrystals." Phd thesis, Canberra, ACT : The Australian National University, 2017. http://hdl.handle.net/1885/139617.
Full textAbstract:
Local defect structures are significant to determine material
properties since defects introduced into host materials would
affect the local/average crystal environments and thus lead to a
change of macroscopic physicochemical performances. The
intentional design of specific local defects not only depends on
the selected synthesis method and preparation process but also
relies on the selected dopant or co-dopant ions. A deep
understanding of the intrinsic relationships between local defect
structures, chemical synthesis and associated properties is
thought as one major framework of material genome plan. It also
pushes the design, development and application of novel
multifunctional materials.
Based on local defect structural design coupled with new
synthesis strategies, indium and niobium co-doped anatase
titanium oxide nanocrystals are synthesized. It is experimentally
demonstrated that the dual mechanisms of nucleation and diffusion
doping are responsible for the synergistic incorporation of
indium difficult-dopants and niobium easy-dopants, and
theoretically evidenced that the local defect structures created
by indium, niobium co-dopants, reduced titanium and oxygen
vacancies are composed of defect clusters and defect pairs. These
introduced local defect structures act as nucleation centres of
baddeleyite- and lead oxide-like metastable polymorphic phases
and induce an abnormal trans-regime structural transition of
co-doped anatase titanium oxide nanocrystals under high pressure.
Furthermore, these small co-doped nanocrystals can be used as raw
materials to manufacture titania-based ceramic capacitors
designed in terms of electron-pinned defect dipole mechanism. The
sintering temperature is thus lowered to 1200 °C, which conquers
the technological bottleneck using this material.
To develop the third generation of high-efficient visible light
catalysts, nitrogen and niobium co-doped anatase titania
nanocrystals are synthesized. Experimental and theoretical
investigations demonstrate that the formation of highly
concentrated defect-pairs is key to significantly enhance visible
light catalytic efficiency. In further combination of local
defect structural design and the exploration of new synthesis
strategies, anatase nanocrystals containing nitrogen and reduced
titanium ions are synthesized. The formation of local defect
clusters is demonstrated to play an important role on the obvious
enhancement of Rhodamine B degradation efficiency under only
visible light illumination. It is thus unveiled that a
fundamental understanding of the functions of local defect
structures and a well-controlled synthetic strategy are critical
to develop highly efficient visible light catalysts with
unprecedented photocatalytic performances.
Through these systematic investigations, it is concluded that
local defect structures generated by introduced co-dopants are
complicated in strong-correlated titania systems and differ from
case to case. A major difficulty to efficiently introduce
difficult-dopant ions such as nitrogen and indium at high
concentrations is solved. Two high-efficient visible light
catalysts are achieved for environmental remediation by using the
clean and renewable solar energy; and one raw material for
manufacturing new ceramic capacitors and new metastable
polymorphic phases is provided. The discussion on the doping
mechanisms, the defect formation and their associated impacts on
material performances will not only benefit the future
development of physical chemistry, material science and defect
chemistry, but also opens a new route to design novel
multifunctional materials based on local defect structure
design.
9
Muley, Amol. "Synthesis and characterization of nanostructured metallic zinc and zinc oxide." Thesis, Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39101538.
Full text
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Guhrenz, Chris, Vladimir Sayevich, Florian Weigert, Eileen Hollinger, Annett Reichhelm, Ute Resch-Genger, Nikolai Gaponik, and Alexander Eychmüller. "Transfer of Inorganic-Capped Nanocrystals into Aqueous Media." American Chemical Society, 2017. https://tud.qucosa.de/id/qucosa%3A33352.
Full textAbstract:
We report on a novel and simple approach to surface ligand design of CdSe-based nanocrystals (NCs) with biocompatible, heterobifunctional polyethylene glycol (PEG) molecules. This method provides high transfer yields of the NCs into aqueous media with preservation of the narrow and symmetric emission bands of the initial organic-capped NCs regardless of their interior crystal structure and surface chemistry. The PEG-functionalized NCs show small sizes, high photoluminescence quantum yields of up to 75%, as well as impressive optical and colloidal stability. This universal approach is applied to different fluorescent nanomaterials (CdSe/CdS, CdSe/CdSCdxZn1–xS, and CdSe/CdS/ZnS), extending the great potential of organic-capped NCs for biological applications.
11
Marchetti, Marco <1980>. "Design, synthesis and Chemical-physical characterization of photocatalytic inorganic nanocrystals for technological applications." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5737/2/marchetti_marco_tesi.pdf.
Full textAbstract:
This work was based on the synthesis and characterization of innovative crystals for biomedical and technological applications.
Different types of syntheses were developed in order to obtain crystals with high photocatalytic properties.
A hydrothermal synthesis was also processed to correlate the chemical-physical characteristics with synthesis parameters obtaining synthesis of nanoparticles of titanium dioxide with different morphology, size and crystalline phase depending on the variation of the synthesis parameters.
Also a synthesis in water at 80 °C temperature and low pressure was developed from which anatase containing a small percentage of brookite nanoparticles were obtained, presenting a high photocatalytic activity. These particles have been used to obtain the microcrystals formed by an inorganic core of hydroxyapatite surface covered by TiO2 nanoparticles.
Micrometer material with higher photocatalytic has been produced.
The same nanoparticles have been functionalized with resorcinol oxidized in order to increase the photocatalytic efficiency. Photodegradation test results have confirmed this increase.
Finally, synthetic nanoparticles with a waterless synthesis using formic acid and octanol, through esterification "in situ" were synthesized. Nanoparticles superficially covered by carboxylic residues able to bind a wide range of molecules to obtain further photocatalytic properties were obtained.
12
Marchetti, Marco <1980>. "Design, synthesis and Chemical-physical characterization of photocatalytic inorganic nanocrystals for technological applications." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5737/.
Full textAbstract:
This work was based on the synthesis and characterization of innovative crystals for biomedical and technological applications.
Different types of syntheses were developed in order to obtain crystals with high photocatalytic properties.
A hydrothermal synthesis was also processed to correlate the chemical-physical characteristics with synthesis parameters obtaining synthesis of nanoparticles of titanium dioxide with different morphology, size and crystalline phase depending on the variation of the synthesis parameters.
Also a synthesis in water at 80 °C temperature and low pressure was developed from which anatase containing a small percentage of brookite nanoparticles were obtained, presenting a high photocatalytic activity. These particles have been used to obtain the microcrystals formed by an inorganic core of hydroxyapatite surface covered by TiO2 nanoparticles.
Micrometer material with higher photocatalytic has been produced.
The same nanoparticles have been functionalized with resorcinol oxidized in order to increase the photocatalytic efficiency. Photodegradation test results have confirmed this increase.
Finally, synthetic nanoparticles with a waterless synthesis using formic acid and octanol, through esterification "in situ" were synthesized. Nanoparticles superficially covered by carboxylic residues able to bind a wide range of molecules to obtain further photocatalytic properties were obtained.
13
Levchuk, Ievgen [Verfasser], Christoph [Gutachter] Brabec, and Rainer [Gutachter] Hock. "Design and optimization of luminescent semiconductor nanocrystals for optoelectronic applications / Ievgen Levchuk ; Gutachter: Christoph Brabec, Rainer Hock." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1139171550/34.
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Schnitte, Manuel [Verfasser]. "Catalysts and Process Design for Living Aqueous Polymerization to Ultra High Molecular Weight Polyethylene Nanocrystals / Manuel Schnitte." Konstanz : KOPS Universität Konstanz, 2021. http://d-nb.info/1229837639/34.
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Liu, Wenhao Ph D. Massachusetts Institute of Technology. "Design and synthesis of biocompatible fluorescent semi-conductor nanocrystals for in-vivo and in-vitro imaging/sensing applications." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/58397.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.Vita. Cataloged from PDF version of thesis.
Includes bibliographical references.
Quantum dots (QD) are unique materials in which their optical properties are decoupled from their solution properties via the tunability of surface ligands. The primary focus of this thesis is the design and synthesis of new ligand coatings to render QDs water soluble, pushing the boundaries of QD applications in biology both in-vivo and in-vitro. On the in-vivo front, ultrasmall QDs (-5 nm hydrodynamic diameter) were synthesized via the use of Cysteine as a zwitterionic ligand coating to generate the smallest biocompatible QDs known to date, allowing for the first time collection of quantitative in-vivo renal clearance data of inorganic nanoparticles in a mouse as a model for design of future clearable nanoparticle in-vivo probes and drug delivery vehicles. On the in-vitro front, a suite of multifunctional ligands were synthesized to produce QDs that exhibit low non-specific binding to cells, small hydrodynamic diameter (HD), tunable surface charge, high quantum yield, and good solution stability across a wide pH range. These ligands feature dihydrolipoic acid for tight binding to the QD surface, a short poly(ethylene glycol) (PEG) spacer for water solubility and biocompatibility, and an amine or carboxylate terminus for covalent derivatization. We successfully demonstrated covalent attachment of energy acceptor dyes to enable sensing applications via Forster Resonance Energy Transfer (FRET), and attachment of proteins to enable high-affinity cell labeling and single particle tracking. In addition, QDs solubilized with these ligands could be derivatized via metal-affinity driven conjugation chemistry with polyhistidine-tagged proteins, which facilitated the purification of monovalent QDs for the first time via gel electrophoresis. Further improvement on ligand stability focused on addressing the problem of thiol oxidation, and a new class of multifunctional polymer ligands were developed featuring multiple imidazole moieties for multidentate interactions with the QD surface. The polymers are synthesized via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization to produce molecular weight controlled monodisperse random copolymers from three types of monomers that feature imidazole groups for QD binding, polyethylene glycol (PEG) groups for water solubilization, and either primary amines or biotin groups for derivatization.
by Wenhao Liu.
Ph.D.
16
Sayevich, Uladzimir Verfasser], Alexander [Akademischer Betreuer] [Gutachter] Eychmüller, and Eike [Gutachter] [Brunner. "Synthesis, Surface Design and Assembling of Colloidal Semiconductor Nanocrystals / Uladzimir Sayevich ; Gutachter: Alexander Eychmüller, Eike Brunner ; Betreuer: Alexander Eychmüller." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1114068004/34.
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Saari, Jonathan. "Unravelling the excitonics of semiconductor nanocrystals an effort in guiding the design of novel structures for optoelectronic applications through spectroscopy." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121387.
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The optical modulation of the multiexitonic multiplicity of CdSe/ZnS nanocrystals (NC) through state-specific excitation demonstrated the potential of NCs as a novel platform for all-optical logic and switching with modulation rates reaching 1 THz, as dictated by Auger recombination. An optical pumping scheme demonstrating all-optical AND gating through CdSe/ZnS NCs made use of the unique multiexcitonic interactions of colloidal nanocrystals. State resolved pump-probe spectroscopic techniques were applied to study the relative excitonic environments of freshly synthesized and aged CdTe NC. These experiments reveal fast electron trapping for aged CdTe NC from the single excitonic state (X). Pump fluence dependence with excitonic state-resolved optical pumping enables directly populating the biexcitonic state (XX) which produces further accelerated electron trapping rates. This increase in electron trapping rate triggers coherent acoustic phonons by virtue of the ultrafast impulsive timescale of the surface trapping process. The observed trapping rates were discussed in terms of electron transfer theory.The subtleties of the excitonic couplings within NCs motivated the development of a novel two-dimensional electronic spectrometer with active carrier-envelope phase stabilization, capable of both collinear and non-collinear geometry. Pulse-generation was achieved through synched acousto-optic programmable dispersive filters. Phase stability was measured through spectral interferometry and found to be in excess of λ/300 for over an hour. The highly phase-stable design allowed for complete polarization control through pulse-pair recombination in a beam-splitter. Polarization control was achieved through sweeping the relative phases of the shaped pulses and demonstrated through a Mueller ellipsometer. Both one- and two-colour proof-of-principle experiments were performed on CdSe NCs.La modulation optique de la multiplicité multi-excitonique des nano-crystaux CdSe/ZnS obtenue par excitation d'états spécifiques démontre le potentiel d'application de ces matériaux dans le domaine de la logique optique, atteignant des taux de modulation de l'ordre de 1ThZ comme dicté par le taux de recombinaison d'Auger. Grâce à une méthode de pompage optique, une fonction « ET » a été réalisée avec des nanocrystaux de type CdSe/ZnS, mettant ainsi à profit les interactions multi-excitoniques uniques de ces nanocrystaux colloïdaux. Des techniques spectroscopiques pompe/sonde résolues en états quantiques ont été appliquées afin d'étudier les différences d'environnements excitoniques entre des points quantiques CdTe fraîchement synthétisés et ayant vieilli. Dans le cas des points quantiques âgés, ces expériences révèlent une rapide capture de l'électron par l'état excitonique simple (X). Le fait que la nature de l'état excitonique optiquement excité dépende de la fluence de la pompe permet de directement peupler l'état bi-excitonique (XX), ce qui a pour effet d'accélérer le taux de capture d'électrons. Cette augmentation du taux d'électrons capturés provoque l'émission de phonons acoustiques en vertu des dynamiques ultrarapides des processus de capture à la surface des nanocrystaux. Les taux de capture observés lors de ces expériences ont été discutés dans le cadre de la littérature sur le transfert de charge. Les subtilités des couplages excitoniques au sein des nanocrystaux a motivé le développement d'un spectromètre bi-dimensionnel dans le domaine du visible, pourvu d'un mécanisme de stabilisation de la phase de l'enveloppe des pulses et capable d'opérer en géométries colinéaires et non-colinéaires. La génération des pulses a été obtenue grâce à des filtres dispersifs accousto-optiques programmables. La stabilité de la phase a été mesurée par interférométrie spectrale et une valeur supérieure à λ/300 a été obtenue sur plus d'une heure. Ce montage, possédant une grande stabilité des phases, permet de contrôler la polarisation des pulses excitant l'échantillon en combinant une paire de pulses dans un miroir semi-réfléchissant. Le contrôle de la polarisation a été obtenu en balayant les phases relatives des pulses et en les observant dans un ellipsomètre de Müller. Des expériences à une et deux couleurs ont été réalisées sur des nanocrystaux de type CdSe, établissant ainsi la preuve du concept.
18
Ye, Wei. "Nano-epitaxy modeling and design: from atomistic simulations to continuum methods." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50304.
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The dissertation starts from the understanding of dislocation dissipation mechanism due to the image force acting on the dislocation. This work implements a screw dislocation in solids with free surfaces by a novel finite element model, and then image forces of dislocations embedded in various shaped GaN nanorods are calculated. As surface stress could dramatically influence the behavior of nanostructures, this work has developed a novel analytical framework to solve the stress field of solids with dislocations and surface stress. It is successfully implemented in this framework for the case of isotropic circular nanowires (2D) and the analytical result of the image force has been derived afterwards. Based on the finite element analysis and the analytical framework, this work has a semi-analytical solution to the image force of isotropic nanorods (3D) with surface stress. The influences of the geometrical parameter and surface stress are illustrated and compared with the original finite element result. In continuation, this work has extended the semi-analytical approach to the case of anisotropic GaN nanorods. It is used to analyze image forces on different dislocations in GaN nanorods oriented along polar (c-axis) and non-polar (a, m-axis) directions. This work could contribute to a wide range of nanostructure design and fabrication for dislocation-free devices.
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Quach, Ashley Dung. "Design and Development of Nanoconjugates for Nanotechnology." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/130.
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Nanotechnology builds devices from the bottom up with atomic accuracy. Among the basic nano-components to fabricate such devices, semiconductor nanoparticle quantum dots (QDs), metal nanocrystals, proteins, and nucleic acids have attracted most interests due to their potential in optical, biomedical, and electronic areas. The major objective of this research was to prepare nano-components in order to fabricate functional nano-scale devices. This research consisted of three projects. In the first two projects, we incorporated two desirable characteristics of QDs, which are their abilities to serve as donors in fluorescence energy transfer (FRET) and surface energy transfer (SET) as well as to do multiplexing, to engineer QD-based nanoconjugates for optical and biomedical applications. Immobilizing luminescent semiconductor CdSe/ZnS QDs to a solid platform for QD-based biosensors offers advantages over traditional solution-based assays. In the first project, we designed highly sensitive CdSe/ZnS QD SET-based probes using gold nanoparticles (AuNPs) as FRET acceptors on polystyrene (PS) microsphere surfaces. The emission of PS-QD was significantly quenched and restored when the AuNPs were attached to and then removed from the surface. The probes were sensitive enough to analyze signals from a single bead and for use in optical applications. The new PS-QD-AuNP SET platform opens possibilities to carry out both SET and FRET assays in microparticle-based platforms and in microarrays. In the second project, we applied the QD-encoded microspheres in FRET-based analysis for bio-applications. QDs and Alexa Fluor 660 (A660) fluorophores are used as donors and acceptors respectively via a hairpin single stranded DNA. FRET between QD and A660 on the surface of polystyrene microspheres resulted in quenching of QD luminescence and increased A660 emission. QD emission on polystyrene x microspheres was restored when the targeted complementary DNA hybridized the hairpin strand and displaced A660 away from QDs. The third project involved fabrication of different nanoconjugates via self-assembly of template-based metal nanowires and metal nanoparticles using oligonucleotides as linkers. These nanoconjugates can serve as building blocks in nano-electronic circuits. The template method restricted the oligonucleotides attachment to the tip of the nanowires. Nanowires tagged with hybridizable DNA could connect to complementary DNA-modified metal crystals in a position-specific manner.
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Guzzetta, Fabrizio. "Rationale Design of Up-Converting Nanoparticles Towards Advanced Optical Applications." Doctoral thesis, Universitat Jaume I, 2018. http://hdl.handle.net/10803/662815.
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The thesis aims to shed some light on the massive production of up-converting nanocrystals through solvothermal conditions. Solvothermal route allows to prepare larger quantities of these nanomaterials, as compared to normal glassware-based routes, and increase yield of nanomaterials per synthesis. The synthetic route was optimized through thorough analysis of several parameters
Then, the produced nanomaterials were used to propose new optical applications in both biological (encapsulation of the nanomaterials within vesicles based on glicolypids under different pH conditions) and technological fields (the solids were entrapped within a soft-matter matrix that, under a critical temperature, underwent a sol-gel transition and permitted in a low-temperature range (below water boiling point) the modulation of matrix emissions).
Lastly a microwave - assisted synthesis was studied, as alternative to solvothermal route, to understand the formation of up-converting nanocrystals, which allowed a versatile post-synthetic coating for further applications of the crystals.La tesis abarca un problema general de producción a gran escala de los nanomateriales. Condiciones solvotermales permiten optimizar el rendimiento de producción de materiales, y por lo tanto esta ruta de síntesis ha sido elegida para su producción masiva. El proceso ha sido optimizado a través el analísis de diferentes parametros de reacción. Se han producido también aplicaciones ópticas avanzadas tanto en ámbito biológico (atrapando los sólidos en vesiculas preparadas por medio de glicolípidos a diferente pH) cuanto en ámbito tecnologico (los solidos venián atrapados en sistemas fibrilares que a raíz de una temperatura critica en la transición sol-gel permitía modulación de las emisiones de la matríz órganica). En fin se ha estudiado y analizado la formación de sistemas cristalinos por medio de la sintesis a microondas, como sistema alternativo al solvotermal, que ha resultado en la formación de nanorods con posibilidad de recubrimiento post-síntesis.
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Dussert, Fanny. "Vers des quantum dots moins toxiques, une approche "safer by design"." Thesis, Université Grenoble Alpes, 2020. https://thares.univ-grenoble-alpes.fr/2020GRALV028.pdf.
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Les quantum dots (QD) sont des nanocristaux semi-conducteurs fluorescents aux propriétés optiques exceptionnelles, ce qui les rend particulièrement attractifs dans les domaines de l’optoélectronique et pour les applications biomédicales. Cependant, au cours de leur cycle de vie, le vieillissement des QDs peut conduire à la dégradation de ces composés, induisant la libération d'éléments toxiques. Même si les études de toxicité sur les QDs à base d'indium sont peu nombreuses, certaines révèlent une toxicité intrinsèque plus faible que les QDs contenant des métaux lourds comme le Cd. Dans ce contexte, notre laboratoire synthétise différents QDs d’InP recouverts de coquilles, conçus par une approche « safer by design », dans le but de produire des QDs moins toxiques avec de meilleures propriétés optiques. Ces QDs sont constitués d'une structure cœur/coquille de InZnP/Zn (Se,S) qui est recouverte, ou non, d'une couche additionnelle de ZnS, épaisse ou mince. Dans cette étude, des kératinocytes primaires humains, issus de chirurgies mammaires, sont exposés aux QDs, après synthèse ou après vieillissement environnemental simulé. Dans un premier temps, les transformations physico-chimiques des QDs au cours du vieillissement sont caractérisées et mettent en évidence d’importantes modifications photophysiques et structurales ainsi que la formation de produits de transformation. Néanmoins, les résultats montrent que les transformations physico-chimiques des QDs sont ralenties par la présence de la double coquille, notamment lorsqu’elle est épaisse. Dans un second temps, l’évaluation de la toxicité des QDs est effectuée et de nouveaux tests sont dévelopés en criblage à haut contenu (HCS) sur un microscope automatisé. Alors que les QDs non vieillis se sont révélés relativement stables et peu toxiques pour les cellules, il n’en fût pas de même pour leurs produits de dégradation. L’exposition des cellules aux QDs vieillis a mis en évidence une forte toxicité à faibles concentrations, modifiant l’expression de certains gènes et protéines essentiels à l’homéostasie cellulaire. Ces résultats montrent que les nouvelles générations de QDs sont plus sûres. Cependant, il est important de continuer à améliorer leur photostabilité puisque leur dissolution et le relargage d’éléments toxiques en fin de vie sont inévitables pour le momentQuantum dots (QDs) are fluorescent semiconductor nanocrystals with exceptional optical properties, which make them particularly attractive in optoelectronic fields and for biomedical applications. However, during their life cycle, the aging of QDs can lead to the degradation of these compounds, inducing the release of toxic elements. Even if toxicity studies on indium-based QDs are still limited, they show a lower intrinsic toxicity in comparison to the heavy metal containing Cd-based QDs. In this context, our laboratory synthetizes different InP QDs with different shell designs, following a safer by design approach, with the aim of producing less toxic QDs with better optical properties. These QDs are composed of a InZnP/Zn(Se,S) core/shell structure which is covered or not by a thick or a thin additional ZnS layer. In this study, primary human keratinocytes which come from breast surgeries, were exposed to these QDs, either pristine or after simulating environmental weathering. First, the physico-chemical transformations of QDs during aging are characterized. Significant photophysical and structural modifications are highlighted and transformation products are identified. However, the results show that these physico-chemical transformations are slowed down by the presence of a double shell, especially when it is thick. Then, the evaluation of QDs toxicity are performed and new assays are developed via high content screening (HCS) on an automated microscope. While pristine QDs were relatively stable and not very toxic to cells, it was not true for their degradation products. Exposure of cells to aged QDs demonstrated high toxicity at low concentrations and modifyed the expression of some genes and proteins essential for cellular homeostasis. These results show that new generations of QDs are safer. However, it’s important to keep improving their photostability since their dissolution and the release of toxic elements at the end of their life are still inevitable
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Crnkic, Edin. "Geometry guided phase transition pathway and stable structure search for crystals." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44760.
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Recently a periodic surface model was developed to assist geometric construction in computer-aided nano-design. This implicit surface model helps create super-porous nano structures parametrically and support crystal packing. In this thesis, a new approach for pathway search in phase transition simulation of crystal structures is proposed. The approach relies on the interpolation of periodic loci surface models. Respective periodic plane models are reconstructed from the positions of individual atoms at the initial and final states, and surface correspondence is found using a Simulated Annealing-like algorithm. With geometric constraints imposed based on physical and chemical properties of crystals, two surface interpolation methods are used to approximate the intermediate atom positions on the transition pathway in the full search of the minimum energy path. This hybrid approach integrates geometry information in configuration space and physics information to allow for efficient transition pathway search. The methods are demonstrated by examples of FeTi, VO2, and FePt. Additionally, two new particle swarm optimization (PSO) algorithms are developed and applied to crystal structure relaxation of the initial and final states. The PSO algorithms are integrated into the Quantum-Espresso open-source software package and tested against the default Broyden-Fletcher-Goldfarb-Shanno relaxation method.
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Griveau, Lucie. "Emulsion polymerization in the presence of reactive PEG-based hydrophilic chains for the design of latex particles promoting interactions with cellulose derivatives." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1329/document.
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Dans cette thèse, des particules de polymère fonctionnalisées en surface avec des groupes poly (éthylène glycol) (PEG) ont été synthétisées pour favoriser leur interaction avec les dérivés cellulosique via liaisons hydrogène intermoléculaires. Deux voies de synthèse ont été proposées pour obtenir ses composites cellulose/latex.La première voie est basée sur l'auto-assemblage induit par polymérisation (PISA) pour former des nanoparticules fonctionnalisées avant leur adsorption sur un substrat cellulosique. La PISA tire profit de la formation de copolymères blocs amphiphiles dans l'eau en combinant la polymérisation en émulsion avec les techniques de polymérisation radicalaire contrôlées (RDRP). Ces dernières sont utilisées pour synthétiser des polymères hydrophiles agissant à la fois comme précurseur pour la polymerization en émulsion d'un monomère hydrophobe, et comme stabilisant des particules de latex obtenues. Deux techniques de RDRP ont été étudiées : les polymérisations RAFT et SET-LRP. Des polymères hydrophiles à base de PEG de faible masse molaire ont été synthétisés en utilisant ses deux techniques qui sont ensuite utilisés pour la polymérisation d'un bloc hydrophobe dans l'eau. Le transfert de l'agent de contrôle au site de la polymérisation était difficile en utilisant la SET-LRP en émulsion, conduisant à la formation de larges particules. En utilisant la RAFT en émulsion, des particules nanométriques ont été obtenues, avec un changement morphologique observé en fonction de la taille du segment hydrophobe, puis adsorbées sur des nanofibrilles de cellulose (CNF).La seconde voie utilise la polymérisation en émulsion classique réalisée en présence de nanocristaux de cellulose (CNC) conduisant à une stabilisation Pickering des particules de polymère. L'interaction cellulose/particule est assurée grâce à l'ajout d’un comonomère à type PEG. Une organisation a été visualisé dans laquelle plusieurs particules de polymère recouvrent chaque CNCIn this thesis, polymer particles surface-functionalized with poly(ethylene glycol) (PEG) groups were synthesized to promote their interaction with cellulose derivatives via intermolecular hydrogen bond. Two synthetic routes were proposed to obtain such cellulose/latex composites.The first route was based on the polymerization-induced self-assembly (PISA) to form functionalized polymer nanoparticles prior to adsorption onto cellulosic substrate. PISA takes advantage of the formation of amphiphilic block copolymers in water by combining emulsion polymerization with reversible-deactivation radical polymerization (RDRP) techniques. The latter were used to synthesize well-controlled hydrophilic polymer chains, acting as both precursor for the emulsion polymerization of a hydrophobic monomer, and stabilizer of the final latex particles. Two RDRP techniques were investigated: reversible addition-fragmentation chain transfer (RAFT), and single electron transfer-living radical polymerization (SET-LRP). Low molar mass PEG-based hydrophilic polymers have been synthesized using both techniques, used for the polymerization of a hydrophobic block in water. The transfer of controlling agent at the locus of the polymerization was challenging for SET-LRP in emulsion conditions leading to surfactant-free large particles. Nanometric latex particles were obtained via RAFT-mediated emulsion polymerization, with morphology change from sphere to fibers observed depending on the size of the hydrophobic segment, which were then able to be adsorbed onto cellulose nanofibrils (CNFs).The second route used conventional emulsion polymerization performed directly in presence of cellulose nanocrystals (CNCs) leading to Pickering-type stabilization of the polymer particles. Cellulose/particle interaction was provided thanks to the addition of PEG-based comonomer. Original organization emerged where CNCs were covered by several polymer particles
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Cho, Minjung. "Biomedical Nanocrystal Agents: Design, Synthesis, and Applications." Thesis, 2013. http://hdl.handle.net/1911/71938.
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In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2~22 nm) and iron based magnetic nanocrystals (4 ~33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3~4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.
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Cheng, Yen-Tse, and 鄭硯澤. "Design and Fabrication of cellulose nanocrystal sensors for potential wearable application." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/eedbxw.
Full textAbstract:
碩士國立清華大學
奈米工程與微系統研究所
106
This thesis presents a series of studies in the development of cellulose nanocrystals (CNCs) nanofiber for sensors application. In the first study, a CNC microfiber was designed and fabricated to demonstrate humidity sensing. The sensor is made of a cellulose composite fiber. The device monitors humidity via a humidity induced electrical impedance change. The compact, efficient design of the fiber makes it ideal to incorporate into textile for applications such as body fluid monitoring and other biometrics. Preliminary result shows that the sensor has a 2% accuracy and 20 to 80% RH range. The electrical impedance changes relative linearly with relative humidity. The sensor also shows a relatively fast response (~4s) compare to current commercial available humidity sensors. In the second study, a method for fabricating yarn structure made of nanofiber was developed for the application of electronic textile. Concept of electrically self-twisting behavior was proven in the fabricating of PEDOT:PSS/PVA/CNC fiber composite. The two factors including the electric field and conductive treatment were found to be dominant factors for triggering the yarn formation. Moreover, the working parameter and material combination was also discussed.
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Lee, Seung Soo. "Synthesis and design of nanocrystalline metal oxides for applications in carbon nanotube growth and antioxidants." Thesis, 2013. http://hdl.handle.net/1911/71983.
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Synthesis of size tunable nanomaterials creates distinct chemo-physical properties. Recently, the popularity of magnetic iron oxide and cerium oxide (CeO2) nanocrystals enables researchers to use magnetic iron oxides (magnetite and ferrites) in size dependent magnetic separation and CeO2 as an automobile exhaust gas catalyst. This research shows production of diameter-controlled monodisperse magnetic iron oxide (ranging from 3 to 40 nm in diameter) and CeO2 (from 3 to 10 nm in diameter) nanocrystals with exceptional narrow diameter distribution (σ<10%). The morphology and composition of the nanocrystals were varied by use of diverse metal precursors, reaction temperature, time, cosurfactants, and molar ratio between metal salt and surfactant. Now the narrow diameter distributions of preformed magnetic iron oxide nanocrystals made it possible to grow diameter controlled uniform CNTs. The correlation between aluminum ferrite nanocrystal diameter and CNT diameter was nearly one. Additionally, we could synthesize the highest percentage (60%) of single walled CNTs from the smallest aluminum ferrite nanocrystals (4.0 nm). Because of the synthesis of uniform nanocrystalline CeO2, we could study diameter dependent antioxidant properties of nanocrystalline CeO2; antioxidant capacity of CeO2 was nine times higher than a known commercial
standard antioxidant, Trolox. In addition, the smallest CeO2 nanocrystal (4 nm) decreased the oxidative stress of human dermal fibroblasts (HDF) exposed to hydrogen peroxide. These works suggest better understanding of monodisperse nanocrystal synthetic mechanism and potential uses of the materials, such as high quality CNT growth using magnetic iron oxides as precursor catalysts and the reduction of oxidative stress in cells using monodisperse CeO2 nanocrystal as an antioxidant for reactive oxygen species in biological media.
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Winkenwerder, Wyatt August 1981. "Surface chemistry of FeHx with dielectric surfaces : towards directed nanocrystal growth." 2008. http://hdl.handle.net/2152/17825.
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The surface chemistry of GeH[subscript x] with dielectric surfaces is relevant to the application of germanium (Ge) nanocrystals for nanocrystal flash memory devices. GeH[subscript x] surface chemistry was first explored for thermally-grown SiO₂ revealing that GeH[subscript x] undergoes two temperature dependent reactions that remove Ge from the SiO₂ surface as GeH₄ and Ge, respectively. Ge only accumulates due to reactions between GeH[subscript x] species that form stable Ge clusters on the SiO₂ surface. Next, a Si-etched SiO₂ surface is probed by GeH[subscript x] revealing that the Si-etching defect activates the surface toward Ge deposition. The activation involves two separate reactions involving, first, the capture of GeH[subscript x] by the defect and second, a reaction between the captured Ge and remaining GeH[subscript x] species leading to the formation of Ge clusters. Reacting the defect with diborane, deactivates it toward GeH[subscript x] and also deactivates intrinsic hydroxyl groups toward GeH[subscript x] adsorption. A structure is proposed for the Si-etching defect. The surface chemistry of GeHx with HfO₂ is studied showing that the hafnium germinate that forms beneath the Ge nanocrystals exists as islands and not a continuous film. Annealing the hafnium germinate under a silane atmosphere will reduce it to Ge while leading to the deposition of hafnium silicate (HfSiO[subscript x]) and silicon (Si). Treating the HfO₂ with silane prior to Ge nanocrystal growth yields a surface with hafnium silicate islands on which Si also deposits. Ge deposition on this surface leads to the suppression of hafnium germinate formation. Electrical testing of capacitors made from Ge nanocrystals and HfO₂ shows that Ge nanocrystals encapsulated in Si/HfSiO[subscript x] layers have greatly improved retention characteristics.text
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Gupta, Gaurav Ph D. "Design of novel catalysts by infusion of presynthesized nanocrystals into mesoporous supports." 2008. http://hdl.handle.net/2152/17857.
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Traditionally, supported metal catalysts have been synthesized by reduction of precursors directly over the support. In these techniques, it is challenging to control the metal cluster size, composition and crystal structure. Herein, we have developed a novel approach to design catalysts with controlled morphologies by infusing presynthesized nanocrystals into the supports. High surface area mesoporous materials, including graphitic carbons, have been utilized for obtaining a high degree of metal dispersion to enhance catalyst stabilities and activities. Gold and iridium nanocrystals have been infused in mesoporous silica with loadings up to 2 wt % using supercritical CO₂ as an antisolvent in toluene to enhance the van der Waals interactions between nanocrystals and the silica. The iridium catalysts show high catalytic activity and do not require high temperature annealing for ligand removal, as ligands bind weakly to the iridium surface. To further enhance metal loadings to >10 % in the catalysts, short-ranged interactions between the metal nanocrystals and the support are further strengthened with weakly binding ligands to expose more of the metal surface to the support. For pre-synthesized FePt nanocrystals, coated with oleic acid and oleylamine ligands, high loadings >10 wt % in mesoporous silica are achieved, without using CO₂. The strong metal-support interactions favor FePt adsorption on the support and also enhance stability against sintering at high temperatures. High resistance to sintering favors formation of the FePt intermetallic crystal structure with <4 nm size upon thermal annealing at 700 °C. The fundamental understanding of the metal-support interactions gained from these studies is then utilized in the design of highly stable Pt and Pt-Cu electrocatalysts with controlled size, composition and alloy structure supported on graphitized mesoporous carbons for oxygen reduction. The resistance of the graphitic carbons to oxidation coupled with strong metal-support interactions mitigate nanoparticle isolation from the support, nanoparticle coalescence, Pt dissolution and subsequent Ostwald ripening and thus enhance catalyst stability. The control of the Pt nanocrystal morphology with high concentrations of highly active (111) surface leads to 25% higher activities than commercial Pt catalysts. Furthermore, the catalyst activities obtained for Pt-Cu catalysts are 4-fold higher than Pt catalysts due to strained Pt shell generated from electrochemical dealloying of copper from the nanoparticle surface.text
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Arora, Vikas. "Design and synthesis of semiconductor nanocrystals to modify their optical and electronic properties." Thesis, 2018. http://localhost:8080/iit/handle/2074/7563.
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Chen, Huei-Siou, and 陳慧修. "Design and Synthesis of TiO2 Nanocrystals with Tunable Structure for Photovoltaic Application." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/a2x6p9.
Full textAbstract:
博士國立臺北科技大學
有機高分子研究所
99
The potential application of TiO2 nanoparticles in most of the fields such as photocatalysis, sensors, solar cells, and memory devices are of great interest due to their unique properties. With the increasing demand in alternative energy sources, solar energy has been considered as one of the most promising renewable energy source. Amongst solar cells, dye sensitized solar cell (DSSC) plays a prominent role owing to its low cost and comparable efficiency. TiO2 electrode is one of the major concerns in DSSCs since the TiO2 phase, surface composition, and morphology of TiO2 films affect the dye adsorption, electron transport, and electrolyte diffusion in the cell as well as the DSSCs performance. Synthesis of TiO2 nanoparticles with different morphology and crystal phase by hydrothermal-based chemical method is the first focus of this work. Pure phase anatase TiO2 nanoparticles with size of ~ 20 nm [1], rutile TiO2 nanobars with size of 30-50 nm [2], rutile TiO2 nanoflowers with size of 200-400 nm, and anatase TiO2 nanocubes with size of ~ 50 nm were successfully prepared and demonstrated the effective properties in both photocatalytic reaction and DSSC applications. The second focus of this thesis is to develop a new dye structure for DSSC application through the cooperation with Professor Wen-Ren Li in Chemistry Department at National Central University. The N-heterocyclic carbene-pyridine-based ruthenium sensitizers have been demonstrated to have superior photoelectric conversion efficiency compared to traditional N719 dye [3-4].
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Chang, Li-Wei, and 張立偉. "Design and Performance Studies of Fabrication, Structure, and Optoelectronic Characteristics in Low Dimensional Oxide/Nitride Nanocrystals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/24483860286769089994.
Full textAbstract:
博士國立清華大學
材料科學工程學系
99
Low dimensional oxide/nitride nanocrystals were synthesized by thermal chemical vapor deposition, e.g. gallium, titanium, nitrogen atoms doped into the nanocrystals in this study. Four particular optoelectronic nanomaterials were studied, they are: Ga-doped ZnO nanowires fabricated by two-step co-evaporation methods; ZnO nanowires implanted with Ti ions by using a vapor vacuum arc (MEVVA) ion implanter; N-doped β-Ga2O3 nanowires synthesized via nitrogen plasma and nitrogen mixed method, and zigzag Ga2O3/GaN fabricated by controlling a switch (on/off = 10 min per each) of ammonia (NH3) gas process. Transformation of microstructure before and after doping, promoting electronic property, and modulation of optical property were then investigated. The self-aligned high density Ga-doped ZnO nanowires can be applied in electron field emission properties by using a two-step co-evaporation method to obtain a turn-on field of 3.4 V/um at a current density of 10 μA/cm2, a threshold field of 5.4 V/um at a current density of 1 mA/cm2, and a field-enhancement factor β of 5945 which is far better than the metallic emitter. The optoelectronic performance from the Ti-doped ZnO nanowires showed that the cathodoluminescence (CL) spectra display a blue-shift in the spectrum with increasing the dopant (Ti) concentration. Furthermore, the energy of the bandgap increases with the electron carrier density increase via the effect of Burstein-Moss. In addition, the electrical transport properties of a single Ti-doped ZnO nanowire were evaluated in a four-probe FE-SEM system and found that the resistivity decreases with increasing Ti content. More importantly the conductance of the Ti-doped ZnO nanowires was made to be dropped significantly with the increasing of mechanical bending, that is to exhibit a piezoelectronic character. The relevant electron concentration, resistivity, and electron mobility of a single Ti-doped ZnO nanowire are respectively 2.7 × 10 18 cm-3, 84.1 Ω cm, and 2.75 × 10-2 cm2V-1s-1 with the M-S-M model. The β-Ga2O3 nanowires can be doped with nitrogen atoms effectively by nitrogen plasma treatment and controlling a switch of (NH3) gas process to observe the modulation of light emission via CL measurement at low temperature. The defects like vacancies could result in a shift of the bandgap at the CL spectra with increasing the nitrogen dopant, thereby affecting the variation of the modulation of the excitation characteristics significantly. Finally, the design pattern for nanowires in the devices have been successfully fabricated, for instance, the p-n nanowire junctions and nitric oxide gas sensors to accommodate the low dimensional oxide/nitride nanocrystals on the development and application of semiconductor industry in the future.
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Lesnyak, Vladimir. "Colloidal Semiconductor Nanoparticles as Functional Materials: Design, Assembly and Applications." 2021. https://tud.qucosa.de/id/qucosa%3A73651.
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This work summarizes results of about ten years of the author’s own research activities in the field of colloidal synthesis of semiconductor nanoparticles, their postsynthetic chemical modification, assembly, and applications. I attempted to provide a concise yet comprehensive overview presenting my own results as a part of the knowledge framework created in close collaboration with many colleagues from all over the world. This habilitation thesis consists of an introduction, explaining the motivation of the research accomplished, followed by a main part which briefly presents key achievements of the author with links to appropriate annexes, i.e. original published articles in peer review journals which are attached to this cumulative script, and completed by conclusions.
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Norman, Zachariah Mitchell. "Structure and Transport in Nanocrystalline Cadmium Selenide Thin Films." Thesis, 2015. https://doi.org/10.7916/D8JQ10RG.
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This thesis explores colloidal semiconductor nanocrystal solutions as a feedstock for creating thin film semiconductor materials through printing processes. This thesis will span the synthesis of nanocrystals, ligand exchange chemistry, solution phase characterization methods, thin film device fabrication, thin film characterization methods, and device characteristics. We will focus extensively relating the structure of nanocrystals in solution and in thin films to their chemistry, optical properties and electronic properties.
By way of introduction, the origin and nature of semiconductor nanocrystals will be explored. This discussion will place semiconductor nanocrystals in their historical context, namely the oil-shocks of the 1970s. The interest in II-VI semiconductor materials stemmed from a desire find photochemical synthetic routes to reduce the use of fossil fuels. As a result, II-VI semiconductor nanocrystal are far more developed synthetically. Additionally, our understanding of II-VI semiconductor nanocrystals is couched in the language of solid state physics rather than chemistry. This will lead into a discussion of their electronic structure and the iterative nature of nanocrystal synthetic development and our theoretical understanding of nanocrystals.
The first chapter will discuss nanocrystal synthetic methods in a broad context, finally narrowing in on the synthesis chosen for this work. Following a description of the synthesis, we will then describe the ligand chemistry and the reactions which may be performed in the ligand shell. The final sections of the chapter will describe the synthetic routes to the three nanocrystal materials used in the rest of this work, namely CdSe-CdCl2/PBu3, CdSe-CdCl2/NH2Bu, and CdSe/NH2Bu.
The second chapter will introduce the crystal structure of II-VI semiconductor nanocrystals and describe how the structure is measured. This will lead in to a discussion of pair distribution function analysis of X-ray data and examples of its application to the solution phase structure of semiconductor nanocrystals. Some size dependent structural properties, namely stain, will be demonstrated by PDF. At the end evidence for surface reconstruction in solution as ligands are removed will be presented.
In the final chapter, techniques for film formation and ligand dissolution with be presented. Annealing of films produces electronic and structural changes which can be observed in the absorbance spectrum, electron microscopy, and X-ray scattering. I propose a three phase annealing model which includes 1) reversible desorption of the organic ligands, 2) irreversible particle fusion, and 3 ripening of grains. The temperature at which ripening occurs depends sensitively on the sample content, which increase chloride concentration decreasing the temperature at which ripening occurs. The ripening process is found to correlate with a phase transition from zinc blende to wurtzite, which indicates that grain boundary mobility is an important part of the ripening process.
Finally thin film transistors are characterized electronically. Fused grains show superior electron mobility as high as 25 cm2/(Vs) and on/off ratios of 10\up5 and less than 0.5 V hysteresis in threshold voltage without the addition of indium. Surprisingly, the ripened grains show poorer transport characteristics. The manuscript concludes by noting the importance of the sintering process in achieving conductivity in thin films and discussing future directions to build upon this work.
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Fangsuwannarak, Thipwan Photovoltaic & Renewable Energy Engineering UNSW. "Electronic and optical characterisations of silicon quantum dots and its applications in solar cells." 2007. http://handle.unsw.edu.au/1959.4/44340.
Full textAbstract:
In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.