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Dissertations / Theses on the topic 'Infrared nanocrystals'
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1
Geyer, Scott Mitchell. "Science and applications of infrared semiconductor nanocrystals." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62053.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.Vita. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 149-158).
In this work we study several applications of semiconductor nanocrystals (NCs) with infrared band gaps. In the first half, we explore the physics of two systems with applications in NC based photovoltaics. The physics of mixed films of CdTe and CdSe NCs is studied in chapter 2 as a model for NC based bulk heterojunction photovoltaics. We demonstrate that the presence of an active electron trap on the CdTe dramatically reduces the electron mobility in mixed films. The trapping state is linked to oxidation of the CdTe NCs. A cadmium oleate treatment is shown to reduced the oxidation rate. In chapter 3, we present a method to switch the carrier type of InAs NCs deposited in a thin film from p-type to n-type by the addition of cadmium. This provides a stable pre-deposition technique to control the NC carrier type and is a step towards pn homojunction based NC devices. We discuss the role that surface passivation and substitution doping may play in determining the carrier type. The second half explores the use of NCs for photodetector applications. Chapter 4 presents our efforts to move from a single pixel, proof of principle PbS NC infrared detector to a large area infrared imaging camera. A method to control the resistivity of the NC film through oxidation and re-treatment with ethanedithiol is presented. This allows for integration of our NC film with existing read out technology. The noise spectrum is shown to be dominated by 1/f noise and the dependence of the noise on the bias and channel length is determined. The detectivity is found to be determined by the carrier lifetime and dark current carrier density. In chapter 5, we demonstrate efficient UV-IR dual band detectors based on luminescent down conversion. In this design, NCs absorb UV light and re-emit the light in the infrared band of an InGaAs detector. The high quantum yields of infrared nanocrystals and unique absorption profile are shown to provide a significant advantage over organic dyes. The bandwidth of the detectors is measured and the effect of the down conversion layer on the spatial resolution is characterized.
by Scott Mitchell Geyer.
Ph.D.
2
Liyanage, Geethika Kaushalya. "Infrared Emitting PbS Nanocrystals through Matrix Encapsulation." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1403953924.
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Kriegel, Ilka. "Near-infrared plasmonics with vacancy doped semiconductor nanocrystals." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-164558.
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Plasmonics with heavily doped semiconductor nanocrystals (NCs) is an emerging field in NC science. However, impurity doping of NCs remains far from trivial and is, as yet, dominated by a low chemical control over the incorporated dopant atoms. An appealing alternative is vacancy doping, where the formation of vacancies in the structure is responsible for an increased carrier density and elegantly circumvents the issues related to impurity doping. Due to high carrier densities of around 10^21cm^(-3) localized surface plasmon resonances (LSPRs) in the near infrared (NIR) are expected, and as such highlighted to close the gap between conventionally doped NCs and noble metal nanoparticles. Copper chalcogenide NCs, namely copper sulfide (Cu2-xS), copper selenide (Cu2-xSe), and copper telluride (Cu2-xTe), are an attractive example of vacancy doped semiconductor NCs, with spectra dominated by intense NIR resonances. Within this study thorough experimental evidence has been given to prove the plasmonic nature of those NIR resonances. By presenting typical plasmonic characteristics, such as refractive index sensitivity of the LSPR, its intrinsic size dependence, plasmon dynamics, or interparticle plasmon coupling, the LSPRs in copper chalcogenide NCs have unambiguously been identified. The chemical nature of vacancy doping turns out to deliver an additional, highly attractive means of control over the LSPR in vacancy doped copper chalcogenide NCs. Through chemical tailoring of the copper vacancy density via controlled oxidation and reduction, as shown in this study, a reversible tuning of the LSPR over a wide range of frequencies in the NIR (1000-2000 nm) becomes feasible. This highlights copper chalcogenide NCs over conventional plasmonic materials. Notably, the complete suppression of the LSPR uncovers the excitonic features present only in the purely semiconducting, un-doped NCs and reveals the unique option to selectively address excitons and highly tunable LSPRs in one material (bandgap Eg~1.2 eV). As such, copper chalcogenide NCs appear to hold as an attractive material system for the investigation of exciton plasmon interactions. Indeed, a quenching of the excitonic transitions in the presence of the developing LSPR is demonstrated within this work, with a full recovery of the initial excitonic properties upon its suppression. A theoretical study on the shape dependent plasmonic properties of Cu2-xTe NCs reveals a deviation from the usual Drude model and suggests that the carriers in vacancy doped copper chalcogenide NCs cannot be treated as fully free. On the other hand, the Lorentz model of localized oscillators appears to account for the weak shape dependence, as observed experimentally, indicating an essential degree of localization of the carriers in vacancy doped copper chalcogenide NCs.
Taken together, this work delivers a huge step toward the complete optical and structural characterization of plasmonic copper chalcogenide NCs. The advantages of semiconductor NC chemistry have been exploited to provide access to novel plasmonic shapes, such as tetrapods that have not been feasible to produce so far. A precise size, shape and phase control presents the basis for this study, and together with a thorough theoretical investigation delivers important aspects to uncover the tunable plasmonic properties of vacancy doped copper chalcogenide NCs.
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Panthani, Matthew George. "Colloidal Nanocrystals with Near-infrared Optical Properties| Synthesis, Characterization, and Applications." Thesis, The University of Texas at Austin, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3572875.
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Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices.
Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa 1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSe XS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.
The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.
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Lox, Josephine F. L., Zhiya Dang, Volodymyr Dzhagan, Daniel Spittel, Beatriz Martín-García, Iwan Moreels, Dietrich R. T. Zahn, and Vladimir Lesnyak. "Near-Infrared Cu-In-Se-Based Colloidal Nanocrystals via Cation Exchange." ACS Publications, 2019. https://tud.qucosa.de/id/qucosa%3A36557.
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We developed a three-step colloidal synthesis of near-infrared active Cu-In-Se (CISe)/ZnS core/shell nanocrystals (NCs) via a sequential partial cation exchange. In the first step binary highly copper deficient Cu2‒xSe NCs were synthesized, followed by a partial cation exchange of copper to indium ions yielding CISe NCs. In order to enhance the stability and the photoluminescence (PL) properties of the NCs, a subsequent ZnS shell was grown, resulting in CISe/ZnS core/shell NCs. These core/shell hetero-NCs exhibited a dramatic increase in size and a restructuring to trigonal pyramidal particles. The reaction parameters, e.g. the Cu:Se-ratio, the temperature and the time were carefully tuned enabling a distinct control over the size and the composition of the NCs. By varying only the size of the CISe/ZnS NCs (from 9 to 18 nm) the PL spectra could be tuned covering a wide range with maxima from 990 nm to 1210 nm. Thus, in these experiments we demonstrate a clear dependence of the optical properties of these materials on their size and extend the PL range of CISe-based nanoparticles further to the infrared part of the spectrum. Furthermore, the relatively large size of these NCs allows their detailed structural analysis via electron microscopy techniques, which is particularly challenging in the case of small particles and especially important to relate the size, composition and crystal structure to their optoelectronic properties.
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Xiang, Hengyang. "Colloidal nanocrystals applied for short-wave infrared photodetectors with fast response." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS423.
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L'infrarouge à ondes courtes (SWIR) désigne généralement les photons dans la plage de longueurs d'onde allant de 1 à 3 micromètres. Les applications dans cette fenêtre de longueur d'onde exploitent divers avantages tels qu’une grande longueur de pénétration dans le tissu biologique, la couverture spectrale pour la vision nocturne atmosphérique et l'énergie d'excitation caractéristique de certains modes de vibration moléculaire. Les photodétecteurs SWIR sont donc les composants technologiques essentiels pour la communication optique, la détection de gaz dans l’environnement, le biodiagnostic et la vision nocturne passive. Les technologies SWIR actuelles reposent principalement sur des semi-conducteurs composés à faible bande interdite, tels que InGaAs, InSb, PbS et HgCdTe. Alors que les photodétecteurs SWIR classiques présentent une excellente détectivité, ils sont coûteux (en raison de la croissance requise par l'épitaxie) et / ou présentent un risque environnemental car impliquant des éléments hautement toxiques. Par conséquent, des efforts continus en matière de recherche et de développement concernant des systèmes de matériaux alternatifs et des méthodes de fabrication permettant d'élargir le champ des applications de la photodétection SWIR sont en cours. Ces dernières années, de nombreux nouveaux matériaux ont été proposés, notamment les nanocristaux de phosphore noir, de graphène, de MoS2 et de PbS colloïdal. Ils sont très prometteurs en termes de fonctionnement à des fréquences de modulation élevées et avec une excellente sensibilité. Cependant, certains inconvénients les éloignent toujours du marché: processus de production difficile (faible reproductibilité), non-adaptabilité à la fabrication à grande échelle, préoccupations de sécurité lors de la production en usine (en raison de l’utilisation d’éléments hautement toxiques). Alternativement, les nanoparticules colloïdales traitées en solution, telles que les nanorods d’or colloïdal (Au NR) et les nanoparticules fonctionnant par up-conversion (UCNP), présentent des caractéristiques intéressantes permettant de surmonter ces inconvénients: capacité de synthèse et de production à grande échelle et à faible coût, haute stabilité, faible toxicité biologique et bonne absorption optique des photons SWIR. Cette thèse a pour objectif d'appliquer ces nanoparticules colloïdales à la fabrication de photodétecteurs SWIR et d’étudiere des possibilités d’application dans le domaine de la photodétection. Quelques photodétecteurs SWIR (Au-NRs / Thermistance, photodétecteur Au-NRs / Pt et photodétecteur UCNPs / Polymers) ont été développés dans ce travail, montrant une sensibilité élevées. De plus, la fabrication de ces dispositifs est un procédé peu coûteux et évolutif vers la production de masse au niveau de la fois à la synthèse des matériaux et de la fabrication des composants, et ouvre une nouvelle voie sur le marché de la prochaine génération de photodétecteursShort-wave infrared (SWIR) typically refers to the photons in the wavelength range from 1 to 3 micrometers. Applications in this wavelength window exploit various advantages such as long penetration length in biological tissue, spectral coverage of the atmospheric nightglow, and the characteristic excitation energy of certain molecular vibration modes. SWIR photodetectors are thus the key technological components to achieve optical communication, environmental gas sensing, biodiagnostics, and passive night vision. Current SWIR technologies mainly rely on low-bandgap compound semiconductors, such as InGaAs, InSb, PbS, and HgCdTe. While classical SWIR photodetectors exhibit excellent detectivity, they are costly (due to epitaxial growth requirement) and/or environment unfriendly involving highly toxic elements. There are, therefore, continuous research and development efforts for alternative material systems and fabrication methods to expand the scope of applications of SWIR photodetection. In recent years, many new materials have been proposed, including black phosphorus, graphene, MoS2, and colloidal PbS nanocrystals. They show great promise in terms of operation at high modulation frequencies or high sensitivity. But some disadvantages still keep them away from the market: rigorous production process (poor reproducibility), non-adaptability to scale-up fabrication, manufactory safety and security concerns (due to the use of highly toxic elements). Alternatively, solution-processed colloidal nanoparticles, such as colloidal gold nanorods (Au NRs) and upconversion nanoparticles (UCNPs), exhibit interesting characteristics possible to overcome these disadvantages: capability of scaling-up synthesis, solution-processability adaptable to low-cost fabrication, high stability, low biological toxicity, and good optical absorption for SWIR photons. This PhD thesis aims to apply these colloidal nanoparticles to fabricate SWIR photodetectors and verifies their possibilities for new generation of photodetection. A few SWIR photodetectors (Au-NRs/Thermistor, Au-NRs/Pt photodetector and UCNPs/Polymers photodetector) were developed in this work, showing high responsivity and sensitivity. In addition, the preparation of these devices is a low-cost and scalable up to mass production process both in the materials synthesis and device fabrication, opening a new and convenient path to the next-generation SWIR photodetectors
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Livache, Clément. "Quantum-confined nanocrystals for infrared optoelectronics : carrier dynamics and intraband transitions." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS216.
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Les nanocristaux colloïdaux sont des objets cristallins obtenus par voie chimique. Ces objets étant confinés, leurs propriétés optiques dépendent de leur taille, et peuvent donc être ajustées à la demande. Les nanocristaux de tellurure de mercure et de séléniure de mercure possèdent notamment des propriétés d’absorption dans l’infrarouge: l’énergie de bande interdite (interbande) des nanocristaux de HgTe peut-être variée du SWIR au MWIR, tandis que les nanocristaux de HgSe, grâce à un auto-dopage électronique dégénéré, présentent des transitions intrabande ajustables du MWIR au LWIR. Un contrôle fin de la chimie de surface de ces objets permet de les intégrer dans des dispositifs électroniques et de créer des détecteurs infrarouge à bas coût. Dans mon travail de thèse, je me suis intéressé à différentes manières de sonder la dynamique des porteurs dans ces dispositifs, soit via la mesure du photocourant, soit par des observations directes de la relaxation des porteurs photogénérés. A partir d’études sur la dynamique dans HgSe, j’ai identifié les limitations apportées par le fort dopage de ces nanocristaux : le transport est dominé par la forte densité électronique, conduisant à des faibles performances pour la détection IR. En reprenant les concepts développés pour les hétérostructures de semi-conducteurs III-V, je propose différentes approches fructueuses pour découpler les propriétés optiques et le transport de charges dans des dispositifs de détection MWIR à base de nanocristaux de HgSeColloidal nanocrystals are crystalline objects grown by colloidal chemistry approaches. Thanks to quantum confinement, their optical properties depend on their size, and can then be tuned accordingly. Using mercury selenide and mercury telluride, we grow infrared-absorbing nanocrystals. While HgTe nanocrystals interband gap can be tuned from the NIR to the MWIR, HgSe nanocrystals display self-doping and intraband transitions in the MWIR to LWIR. With a careful control of their surface chemistry, those nanocrystals can be integrated into electrical devices to create cheap infrared photodetectors. In my PhD work, I am interested in probing carrier dynamics in those devices using various time-resolved techniques, either based on photocurrent measurements or on direct observation of the photocarriers relaxation. From dynamic study of HgSe intraband devices, I identify the issue brought by the degenerative doping level of those nanocrystals: transport is driven by the doping of this material, resulting in very poor IR-sensing performances. By taking inspiration from the III-V semiconductor developments, I propose several successful approaches to uncouple optical and transport properties in HgSe-based, MWIR detectors
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Gencer, Imer Arife. "Si Nanocrystals In Sic Matrix And Infrared Spectroscopy Of In A Dielecric Matrix." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611778/index.pdf.
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This study focuses on various aspects of nanocrystals embedded in a dielectric matrix. In the first part of this work, a new approach with the use of Fourier Transform Infrared spectroscopy (FTIR) in the nanocrystal analysis was developed and presented. Si and Ge nanocrystals embedded in SiO2 matrix were mainly studied. This new approach is based on the analysis of structural variations of SiO2 matrix during the formation of semiconductor nanocrystlas. It is shown that the chemical and structural variations of the host matrix are directly related to the precipitation of nanocrystals in it. This correlation provides valuable information about the presences of nanocrystals in the matrix.
In the second part of this work, fabrication of SiC films with and without Si nanocrystals inclusions was studied. With this aim, stoichiometric SiC and Si rich SiC thin films were fabricated by using magnetron co-sputtering and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques. For SiC films, the structural and optical analyses were performed. For Si rich SiC films, the formation conditions of Si nanocrystals were investigated. Post annealing studies were carried out to track the evolution of the SiC matrix and formation of Si nanocrystals at different temperatures. Chemical and structural properties of the SiC host matrix were investigated with FTIR spectroscopy. Optimum conditions for the fabrication of stoichiometric SiC layers were determined. The crystallography of the nanocrystals was investigated by X-Ray Diffraction (XRD). The variation of the atomic concentrations and bond formations were investigated with X-Ray Photoelectron Spectroscopy (XPS). Raman spectroscopy and Transmission Electron Microscopy (TEM) were used to verify the formation of Si nanocrystals. We have shown that both single and multilayer Si nanocrystals can be fabricated in the amorphous SiC matrix for applications such as light emitting diodes and solar cells.
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Kriegel, Ilka [Verfasser], and Jochen [Akademischer Betreuer] Feldmann. "Near-infrared plasmonics with vacancy doped semiconductor nanocrystals / Ilka Kriegel. Betreuer: Jochen Feldmann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1046503316/34.
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Chen, Yue Ph D. Massachusetts Institute of Technology. "Syntheses of biocompatible luminescent nanocrystals for visible and short-wave infrared imaging applications." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115798.
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Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references.
The primary focus of this thesis is to synthesize biocompatible luminescent nanocrystals for visible and short-wave infrared (1-2 [mu]m, SWIR) imaging applications. Quantum dots (QDs) have been promising fluorescent probes for biomedical imaging due to their high quantum yield (QY), narrow photoluminescence spectra, and excellent photostability. However, challenges remain to be solved to transfer the as-synthesized hydrophobic QD to aqueous solutions while maintaining the high QY and a compact size. This study involves the design and synthesis of a novel ligand that can be introduced to the established QD synthesis, producing norbornene functionalized QDs that can be readily phase transferred into water via norbornene/tetrazine click chemistry, meanwhile allowing flexible functionalization of the QDs by incorporating a functional group on the hydrophilic chain. This ligand system can be applied to a variety of carboxylic-ligand-stabilized QDs, with emission spectra spanning the visible and the SWIR region. The resulting water-soluble QDs exhibit a high QY, a small hydrodynamic diameter (HD), and excellent colloidal stability and pH stability. Further in vitro cell labeling experiments using azido-functionalized QDs demonstrates their potential for cell targeting applications. As in vivo imaging in the SWIR range has further reduced background noise from tissue scattering compared to traditional visible and near infrared (0.7-1 tm, NIR) imaging, images of higher contrast and better resolution can be readily obtained. The next challenge is to develop SWIR emitters that have high quantum efficiency and minimal toxicity, which is of critical importance in order to promote this technology for clinical applications. Our study found that the emission of luminescent gold nanoclusters can be tuned from the visible to the SWIR region by proper selection of ligands and post ligand modifications. The SWIR-emitting gold nanoclusters have a good QY, a HD that is small enough that they exhibit a rapid renal clearance, and images taken in the SWIR region show better resolution of the blood vessels than in the NIR region.
by Yue Chen.
Ph. D. in Physical Chemistry
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Wu, Mengfei Ph D. Massachusetts Institute of Technology. "Infrared-to-visible upconversion in hybrid thin films of colloidal nanocrystals and organic molecules." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/122872.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018Cataloged from PDF version of thesis.
Includes bibliographical references (pages 152-163).
Photon upconversion is a process where two or more low-energy photons are converted into a single higher-energy photon. Upconversion that turns infrared photons into visible ones is particularly useful, having potential applications in photovoltaics, infrared sensing, and biological imaging. In this thesis, I present a solid-state thin-film device that converts infrared photons with wavelength up to 1.1 [mu]m into visible wavelengths around [lambda] = 610 nm. The device consists of a monolayer of lead sulfide colloidal nanocrystals (NCs) and a thin film of rubrene mixed with emissive DBP molecules. Upconversion is realized via triplet-triplet annihilation (TTA) in rubrene sensitized by the NCs. We demonstrate that compared to the previous all-molecular upconverting systems, the use of inorganic NCs helps extend the excitation wavelength into the infrared and offers simple wavelength tunability.
However, a monolayer of NCs has low infrared absorption, severely limiting the upconversion efficiency and necessitating a high excitation intensity. Here, by adding a silver back reflector with an optical spacer to the device structure, we achieve a five-fold increase in the NC absorption due to optical interference effects and an eleven-fold enhancement in the up-converted output. To extend the idea, we further introduce a distributed Bragg reflector at the front of the device. A resonant microcavity is formed with the NCs placed at the peak of a drastically enhanced optical field. The upconversion efficiency is improved by another order of magnitude, with threshold excitation intensity falling to 13 mW/cm² , which is below the available solar flux. At resonance, the device converts (0.06±0.01)% of incident photons at [lambda] = 980 nm into emitted higher-energy photons. In addition, we improve the upconversion efficiency by shortening the surface ligands on NCs.
With faster triplet transfer, the upconverting device attains higher intrinsic efficiency, converting (7±l)% of the absorbed photons at [lambda] = 808 nm into higher-energy emissive excitons in rubrene. This thesis demonstrates the feasibility of NC-sensitized infrared-to-visible upconversion in solid thin films under low excitation intensities comparable to the solar flux, and paves the way toward the practical utilization of TTA-based upconversion in photovoltaics, imaging, and sensing technologies.
by Mengfei Wu.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Gonzalez, Reinaldo J. "Raman, Infrared, X-ray, and EELS Studies of Nanophase Titania." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30605.
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Sol-gel titania particles were investigated, primarily by optical techniques, by systematically varying synthesis, sample handling, and annealing variables. The material phases investigated were amorphous titania, anatase TiO2, and rutile TiO2. Annealing-induced phase transformations from amorphous TiO2 to anatase to rutile were studied by Raman scattering, infrared reflectivity, infrared absorption, x-ray diffraction, and electron energy-loss spectroscopy (EELS). Detailed experiments were carried out on the effects of annealing on the Raman and infrared spectra of anatase nanocrystals. The frequencies of the zone-center transverse optical (TO) and longitudinal-optical (LO) phonons of anatase were determined and were used in analyzing the results obtained on composites consisting of annealed solgel particles.
The TO and LO frequencies of anatase were obtained from polarization-dependent far-infrared reflectivity measurements on single crystals. These results, which determined the dielectric functions of anatase, were used to explain infrared (IR) reflectivity spectra of titania nanoparticles pressed into pellets, as well as the grazing-incidence IR reflectivity observed for titania thin films. Because of the polycrystalline character of the titania nanoparticles, the surface roughness of the pressed pellets, and the island-structure character of the thin films, effective-medium theories (appropriate for composites) were used, along with the anatase dielectric functions, to interpret the experimental results.
The titania nanoparticles were prepared by the hydrolysis/condensation of Ti(OC2H5)4. A polymeric steric stabilizer was used in the sol-gel synthesis in order to prevent continued agglomeration during the condensation process. This yielded particles with a relatively narrow size distribution. The amount of water used in the reaction determines the final particle size. Particles as small as 80 nm and as large as 300 nm were used throughout this work. From the colloidal suspension, loose powders, pressed pellets, and thin films were formed. These samples were subjected to different annealing processes at temperatures ranging from room temperature up to 1000 C. Two different annealing atmospheres were used: air (oxygen-containing) and argon (no oxygen).
The amorphous to anatase transformation was followed by in-situ IR transmission measurements carried out during annealing. The particles as prepared are amorphous and the anatase phase could be detected, using this sensitive IR technique, at temperatures as low as 150 C. This phase transition was shown to be particle size dependent. It was also shown that introducing the stabilizer by means of the alkoxide flask instead of the water flask (during the sol-gel synthesis) decreases the anatase to rutile transformation temperature. Loose powders were found to transform more readily than dense pellets, while island-structure films were found to be the hardest to transform. Even at 1000 C, most of these films did not transform to rutile.
X-ray diffraction experiments were used to determine nanocrystal sizes in anatase samples obtained by air and argon anneals at temperatures from 300 to 800 C. A correlation was found between Raman band shape (peak position and linewidth) and crystallite size, but this correlation was different for air anneals and for argon anneals. These experiments called for an interpretation based on a stoichiometric effect rather than a finite size effect. Based on this interpretation, the as-prepared particles are slightly oxygen-deficient, with a stoichiometry corresponding to TiO1.98.
In the electron energy-loss experiments, a special data-analysis technique was used to extract the EELS spectrum of the titania nanoparticles from the observed substrate-plus-particles signal. This technique successfully resolved the titania absorption-edge peak. Which was found to be momentum independent. For low electron momentum, the results were consistent with the reported optical absorption edge.Ph. D.
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Smith, Kristen Colleen. "Surface processes ruthenium film growth, silicon nanocrystal synthesis, and methylene partial oxidation /." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035980.
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Izquierdo, Eva. "Synthèse et caractérisation d'homostructures et d'hétérostructures de nanoplaquettes de chalcogénures de mercure." Electronic Thesis or Diss., Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLET028.
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Dans un contexte de développement de photo-détecteurs et lasers dans le domaine de l’infrarouge, les nanocristaux colloïdaux de chalcogénures de mercure sont des candidats prometteurs pour l’imagerie infrarouge à bas coût. Des nanoplaquettes de chalcogénures de cadmium sont développées depuis 10 ans. Ces nanoparticules 2D présentent des propriétés optiques originales dans le visible, du fait de leur confinement quantique limité à une di-mension. L’objectif de cette thèse est de syn-thétiser des nanoplaquettes à base de chalco-génures de mercure afin d’obtenir des proprié-tés optiques fines dans l’infrarouge. Pour cela, nous avons utilisé l’échange cationique au mercure sur des nanoplaquettes de chalcogé-nures de cadmium, la synthèse directe n’étant pas encore démontrée.Dans une première partie, ce manuscrit expose la synthèse et la caractérisation de nanopla-quettes fines de 2 et 3 monocouches de HgTe et HgSe. Les nanoplaquettes de HgTe présen-tent des propriétés optiques exceptionnelles dans le proche infrarouge (largeur à mi-hauteur de 57 meV pour une émission aux alentours de 1,5 eV).Par la suite, l’échange cationique sur des na-noplaquettes plus épaisses de CdSe a été étu-dié. La limitation de la diffusion des atomes de mercure sur 2 plans cationiques dans l’épaisseur permet d’obtenir des hétérostruc-tures cœur/coque de CdSe/HgSe présentant des propriétés optiques et électroniques décor-rélées.Pour finir, cet échange cationique a été utilisé pour créer de nouvelles hétérostructures cœur/coque de HgTe/CdS et cœur/couronne HgSe/HgTe permettant de jouer sur la délocali-sation des fonctions d’onde des porteurs de chargeIn a context of detectors and lasers develop-ment in infrared range, mercury chalcogenides colloidal nanocrystals are promising candi-dates for low-cost IR imaging. For 10 years, cadmium chalcogenides semiconductors na-noplatelets are developed. These two-dimensional nanoparticles present great novel optical features in visible range, due to exciton confinement along one direction. The purpose of this thesis is to synthesize mercury chalco-genides-based nanoplatelets in order to obtain nanoparticles with narrow infrared optical fea-tures. To this end, we used cation exchange with mercury on cadmium chalcogenides na-noplatelets, because of the direct synthesis isn’t demonstrated yet.In a first part, this manuscript presents the syn-thesis and the characterization of 2 and 3 monolayers HgTe and HgSe nanoplatelets. HgTe nanoplatelets present exceptionally nar-row near-infrared optical features (57 meV for an emission around 890 nm).The impact of the thickness of CdSe nano-platelets on the cation exchange process was subsequently studied. The limited diffusion of mercury atoms over 2 cationic plans in the thickness direction allows to obtain CdSe/HgSe core/shell heterostructures. The optical and transport properties are decorrelated.Finally, this cation exchange was used to formed new mercury-based heterostructures: HgTe/CdS core/shell and HgSe/HgTe core/crown. These materials present new opti-cal properties in infrared range thanks to the electron and hole confinement in a same or different part of the heterostructure
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Khalili, Lazarjani Adrien. "Advancing Nanocrystal-based Infrared Imaging : Exploring Novel Strategies in the Design and Characterization." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS379.
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L’infrarouge est une région spectre électromagnétique avec des longueurs d'onde plus longues que celles de la lumière visible. Cette gamme spectrale fournit des informations complémentaires au domaine visible, et trouve des applications dans divers domaines tels que la défense, l'astronomie, et les technologies civiles émergentes dont le LiDAR dans les véhicules autonomes, ou la reconnaissance faciale dans nos smartphones. Alors que la technologie de détection à base de silicium règne sur le marché du visible, son équivalent reste à développer dans l'infrarouge. Les nanocristaux colloïdaux offrent une voie prometteuse pour la réalisation de capteurs infrarouges performants et économiques. Ces objets cristallins synthétisés chimiquement présentent des effets de confinement quantique, qui permettent d’ajuster leurs propriétés optiques avec leur taille. Parmi les nanocristaux absorbant l'infrarouge, j'ai utilisé des nanocristaux de chalcogénures de mercure (HgX) qui peuvent adresser toute la gamme infrarouge du visible à la région THz. Au cours de ma thèse, j'ai exploré des concepts innovants liés à la fois aux propriétés matérielles des nanocristaux et à la conception de géométries de dispositifs complexes avec un couplage lumière-matière exalté. En particulier, j'ai proposé différentes approches pour découpler les propriétés optiques et de transport dans les photodétecteurs à base de nanocristaux HgX, afin d’atteindre des performances de détection de pointe. De plus, j'ai entrepris une nouvelle approche en utilisant des mesures in-operando, axées sur l'étude du matériau dans le contexte du dispositif lui-même, plutôt que de les considérer comme des entités distinctesThe infrared region is a part of the electromagnetic spectrum with wavelengths longer than those of visible light. This spectral domain provides complementary information to the visible range, and finds application in various fields such as defense, astronomy, and emerging civilian technologies including LiDAR in autonomous vehicles, or face recognition in our smartphones. While the silicon-based sensing technology rules over the visible market, its equivalent has yet to be developed in the infrared. Colloidal nanocrystals offer a promising avenue for the realization of high-performance and cost-effective infrared sensors. These chemically synthetized crystalline objects exhibit quantum confinement effects, resulting in size-tunable optical properties. Among infrared absorbing nanocrystals, I have specifically used mercury chalcogenides (HgX) nanocrystals that can address the entire infrared range from the visible to the THz region. Over the course of my thesis, I have explored innovative concepts relating to both the material properties of nanocrystals and the design of complex device geometries with enhanced light-matter coupling. In particular, I have proposed different approaches to uncouple optical and transport properties in HgX-based photodetectors, aiming to achieve state-of-the-art sensing performances. Furthermore, I have pursued a novel strategy based on in-operando measurements, which focus on studying the material within the context of the device itself, rather than regarding them as separate entities
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Nemchinov, Alexander. "Using Colloidal Nanocrystal Matrix Encapsulation Technique for the Development of Novel Infrared Light Emitting Arrays." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1339806993.
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Lian, Zichao. "Photo-Induced Carrier Transfer in Heterostructured Semiconductor Nanocrystals for Solar Energy Conversion." Kyoto University, 2018. http://hdl.handle.net/2433/235053.
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Leubner, S., R. Schneider, A. Dubavik, S. Hatami, N. Gaponik, U. Resch-Genger, and A. Eychmüller. "Influence of the stabilizing ligand on the quality, signal-relevant optical properties, and stability of near-infrared emitting Cd1₁₋ₓHgₓTe nanocrystals." Royal Society of Chemistry, 2014. https://tud.qucosa.de/id/qucosa%3A36257.
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Bright and stable near-infrared (NIR) and infrared (IR) emitting chromophores are in high demand for applications in telecommunication, solar cells, security barcodes, and as fluorescent reporters in bioimaging studies. The best choice for wavelengths >750 nm are semiconductor nanocrystals, especially ternary or alloy nanocrystals like CdHgTe, which enable size and composition control of their optical properties. Here, we report on the influence of growth time and surface chemistry on the composition and optical properties of colloidal CdHgTe. Up to now, these are the only NIR and IR emissive quantum dots, which can be synthesized in high quality in water, using a simple one-pot reaction. For this study we utilized and compared three different thiol ligands, thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and glutathione (GSH). Aiming at the rational design of bright NIR- and IR-emissive alloy materials, special emphasis was dedicated to a better understanding of the role of the surface ligand and adsorption–desorption equilibria on the photoluminescence quantum yield and stability. In this respect, dilution and protonation studies were performed. Our results show that with this simple synthetic procedure, strongly fluorescent CdHgTe colloids can be obtained with MPA as stabilizing ligand revealing quantum yields as high as 45% independent of particle concentration.
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Qu, Junling. "Colloidal semiconductor nanocrystals for optoelectronic applications : photodetectors and light emitting diodes." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS021.
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Les nanocristaux dont la dimension est inférieure à leur rayon de Bohr excitonique peuvent fournir des propriétés optoélectroniques accordables avec la taille. Cela permet d’obtenir des propriétés électroniques à façon. En particulier, le développement de la synthèse par voie colloïdale des nanocristaux en fait des briques élémentaires prometteuses pour des applications optoélectroniques à bas coût. Ma thèse cible deux aspects des dispositifs à base de nanocristaux: les photodétecteurs infrarouges et les diodes électroluminescentes (LED). Ma thèse est d'abord centrée sur la photodétection infrarouge sans métaux lourds utilisant soit la transition intrabande d'Ag2Se, soit des nanocristaux plasmoniques ITO. J'ai étudié leurs propriétés optiques et de transport ainsi que leur spectre électronique. J’ai ensuite testé leurs performances pour la photodétection infrarouge. Les performances obtenues sont mises en perspective par rapport à leurs homologues contenant des métaux lourds. Dans une seconde partie de ma thèse, je me focalise sur les LEDs à base de nanocristaux avec des longueurs d’onde visées à la fois dans le visible et le proche infrarouge. La LED visible conçue à l'aide de nanoplaquettes CdSe/CdZnS montre une faible tension de fonctionnement et la durée de vie la plus longue obtenue pour les LED à base de nanoplaquettes. Ensuite, cette LED est couplée à un photodétecteur PbS maison pour réaliser pour la première fois une communication de type LiFi tout nanocristal. Pour les LED proche infrarouge, j’ai utilisé HgTe comme matériau optiquement actif. En formant une hétérojonction à partir de HgTe / ZnO, une LED infrarouge lumineuse capable d'imagerie active est obtenueNanocrystals with a dimension below their excitonic Bohr radius can provide size-tunable optoelectronic properties, enabling on-demand tailoring of properties for specific applications. Especially, the advance of wet chemistry synthesis of colloidal nanocrystals makes them promising building blocks for the next-generation solution-processible low-cost optoelectronics such as light emitting, sensing, and harvesting. My thesis targets two aspects of the nanocrystal-based devices: infrared (IR) photodetector and light emitting diode (LED). My thesis is first focused on the heavy-metal-free IR photodetection using the intraband transition of self-doped Ag2Se or the plasmonic resonance of remotely doped ITO (tin doped indium oxide) nanocrystals. Before integrating them to photoconductive devices, I study their optical and transport properties as well as their energy spectra. I then test their IR photodetection performance and rationalize their weak performance compared with their heavy metal counterparts. In the second part of my thesis, I advance to the all-solution nanocrystal-based LEDs in the visible and SWIR, with an emphasis on their practical applications. The designed visible LED using CdSe/CdZnS nanoplatelets (NPLs) shows the lowest turn-on voltage and the longest lifetime for NPL-based LED. I also provide insights on the origin of efficiency droop. Then, this LED is coupled with a homemade PbS broadband photodetector to achieve, for the first time, an all-nanocrystal based LiFi-like communication setup. For SWIR LEDs, HgTe is used as IR emitter. By forming a HgTe/ZnO bulk heterojunction in the emitting layer, a bright SWIR LED capable of active imaging is obtained
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ROSINA, IRENE. "Exploiting Cation Exchange Reactions in Doped Colloidal NIR Semiconductor Nanocrystals: from synthesis to applications." Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1019427.
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Colloidal quantum dots (CQDs) have tunable optical properties through manipulation of their size, shape, and surface chemistry. Among pholuminescent QDs, near-infrared (NIR) emitting ones are of particular interest since they can be used in several applications, from the labeling in living tissues, to the integration in commercial optoelectronic devices, like photovoltaics for solar energy conversion or photodetectors from visible to the near-infrared and mid-infrared. In addition, the exciting promise of CQDs is that is associated with easy and low-cost device fabrication process. In fact, solution-based techniques like spin-coating, dip coating and ink-jet printing are typically used for solution CQDs readily to be used in large-area processing techniques.
Thus, to obtain an ink solution of nanocrystals (NCs) ready to be used in device fabrication process, in this thesis, cation exchange (CE) reactions have been used as a convenient tool to finely transform NCs directly in solution or deposited as thin films. These reactions allow to substitute a fraction or all “host” metal cations of pre-synthesized NCs with new “guest” cations while preserving both NCs’ size, shape and, typically, crystal structure. Depending on the miscibility of the reactant and product materials, and on the kinetics of the CE reaction, different types of nanostructures can be accessed ranging from alloy NCs, doped systems, dimers, core@shell (or core@graded-shell) heterostructures even with elaborated architectures (i.e., quantum wells, multiple-cores@shell). Unlike ion substitution in solids, cation exchange at nanoscale results in fast reaction rate and an easy modulation of the thermodynamics through selective ion coordination in solution.
This study provides an overview of the CE on semiconductor NCs, in particular on II-VI, I-III-VI2 and III-VI compounds. We first explore the exchange between cadmium chalcogenides and mercury ions to produce Cd1-xHgxTe CQDs which can be potentially employed in NIR photodetectors and photovoltaic devices. Our developed synthesis is a result of a wide systematic investigation process, in which we varied specific physical parameters, such as the reaction temperature, the feed molar ratio of the precursor and the solvent. More specifically, these aspects were studied to have control on the size, shape, surface composition and crystalline phase after mild conditions of annealing into stable connected crystals. This peculiarity could be exploited to boost the photogenerated charges diffusion in polycrystalline photoconducting films fabricated by means of an ink of NCs solution.
Additionally, another aspect studied was the surface passivation of Cd1-xHgxTe colloidal NCs, in order to understand how to optimize the charge transfer efficiency among the nanocrystals. The carrier transport in QD devices differs fundamentally from band transport in bulk semiconductors. In nanocrystal film it is of fundamental relevance to improve the mobility of the photogenerated charges. Noteworthy, the granularity of the system and the consequent coupling between adjacent dots can produce additional physical parameters, as charge recombination. The carrier diffusion length can be limited by trapping sites1. To overcome these limitations, post-synthetic strategies that couple the high quality NCs solutions with ideal properties (band gap, absorption, monodispersivity) and high-quality films (quantum dot packing, passivation, and absorptive/conductive properties) are necessary. Indeed, to improve the inter-NCs conductivity in a NC film, ligand exchange and stripping procedures are widely used, with the aim of replacing insulating surfactants with more conductive species. These procedures have some drawbacks, for example metal cations can desorb from the surface of the NCs during the stripping. On the contrary, here we will show how our nano heterostructures (NHCs) enable to avoid the post-process ligand stripping and to perform the final annealing step in milder conditions.
Above these considerations, CE can be exploited to address NCs solution through surface uniformity from the nano- to the macroscopic scale. This is the first step toward electronic coupling between the separate building blocks of nanocrystals.
Apart from III-V QDs, we shifted our research activity on valid alternative material which do not contain toxic heavy metals such as Cd, Pb, As or Hg, and that offer a high flexibility for tuning band gap in the NIR window. In chapter 5, the results about the study of a III-V system are reported. Thus, we studied InP system, which is probably the only one that could provide a compatible emission color range similar to that of Cd-based QDs but without intrinsic toxicity. Nevertheless, the synthesis of III-V NCs, due to their covalent-bond character, is limited by long reaction times or an uncontrollably fast nucleation that may lead to the formation of amorphous or bulk compounds. The role of our work is to explore the reported InP synthesis and to further improve the luminescent properties of these systems Here we study the effect of different parameter (molar concentration in reaction mixture, the use of different phosphorous precursors) to enhance the control over the particle size and size distribution. After that, we studied different Sulphur source precursors to obtain InP@ZnS core@shell NCs with high quantum Yield (QY).
In the last chapter, we describe also I-III-VI2 system as CuInS2 for photoluminescence modulation. In this Chapter Copper Indium Sulfide nanocrystals are prepared using a single-step heating up method relying on the low thermal stability of ter- dodecanethiol used as stabilizing agent, solvent, and sulfur precursors. The obtained particles exhibit an emission varying from 710 to 940 nm. This range depends on the extent of the heating time (pre-heating) before the threshold temperature of 230°C for the growth process of ternary semiconductor NCs such as of CIS nanocrystals. Afterwards we report on the procedure for the growth of a ZnS shell, which enables a blueshift of the PL emission wavelength with respect to those of their parent CIS, due to the widening of the band gap for the entrance of zinc ions into the CIS structures.
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Moghaddam, Nicolas. "Synthèse de nanoplaquettes épaisses de chalcogénures de cadmiumet étude des propriétés électroniques de nanoplaquettes de tellure de mercure." Electronic Thesis or Diss., Université Paris sciences et lettres, 2021. http://www.theses.fr/2021UPSLS090.
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Les nanoplaquettes de chalcogénures de cadmium sont des semiconducteurs de la famille II-VI, dont l’épaisseur est contrôlée à la monocouche atomique près, permettant ainsi un contrôle fin de leurs propriétés optiques. Ces matériaux peuvent s’étendre sur une centaine de nanomètres et présenter une épaisseur de quelques nanomètres.Lorsque les nanoplaquettes de CdSe 3 monocouches sont passivées par des ligands halogénures à température ambiante grâce à un précurseur de CdX2 (X = Cl, Br, I), l’énergie surfacique diminue. En chauffant (160 °C), des monomères de CdSe se dissolvent des bords des nanoplaquettes pour cristalliser sur les grandes faces. Ici, les nanoplaquettes servent elles-mêmes de réservoir de chalcogénure La modification de la chimie de surface permet donc l’obtention d’objets plus épais jusqu’à 9 monocouches et monodisperses. La versatilité de cette méthode a été prouvée sur d’autres chalcogénures de cadmium.De plus, la compréhension du mécanisme de dissolution/recristallisation a permis de développer un outil de croissance de coque, d’épaisseur contrôlée. La synthèse d’homo- et hétérostructures originales a ainsi été effectuée. Pour la première fois, une couche de CdTe a pu être synthétisée sur des nanoplaquettes de CdSe et CdTe. Enfin, des nanoplaquettes de CdSe à marches au comportemet uniqueont aussi été synthétisées. Ces dernières constituent le premier exemple de semiconducteurs avec un confinement induisant un alignement de bande de type I intraparticulaire et sans contrainte structurale.Un autre aspect de mon travail s’est porté sur la compréhension de la structure électronique des nanoplaquettes de HgTe. Nous avons systématiquement exploré leurs diagrammes de phase en fonction du confinement, de la pression et de la température. Nos résultats montrent qu’en fonction de la pression, les nanoplaquettes (confinement fort) et les nanocristaux (confinement plus faible) de HgTe ont un comportement similaire au massif: la largeur de bande interdite augmente avec la pression. En revanche, en fonction de la température, le régime de confinement est déterminant. En diminuant la température de 300 K à 10 K, la largeur de bande interdite diminue pour les nanocristauxs les plus gros.Cette diminution est de moins en moins importante pour les nanocristauxs les plus confinés, jusqu’aux nanoplaquettes pour lesquelles la largeur de bande interdite augmente. La modélisation de cet effet a permis de mettre en évidence le rôle de la seconde bande de conduction, qui pour les nanoplaquettes, modifie la courbure de la première bande de conduction lorsque la température diminueCadmium chalcogenide nanoplatelets II-VI semiconductors. Their thickness is controlled at the atomic scale with extreme narrow optical features. These materials are few hundreds of nanometers in length and wide with a few nanometers thickness.When passivated by halides, using a CdX2 (X = Cl, Br, I) precursor at room temperature, the CdSe 3 monolayers nanoplatelets surface energy decreases. On heating at mild temperature (160 °C), CdSe monomers dissolve from the edges and recrystallize on the wide facets. Here, nanoplatelets become a chalcogenide reservoir. The modification of the surface chemistry allows then to obtain thickernanoplatelets up to 9 monolayers and monodisperse. The versatility of the method has been proven on other cadmium chalcogenides. Thanks to the comprehension of the dissolution/recrystallization process we developed a new tool to grow shells with controlled thickness. Homo- and heterostructures have been grown by this method. For the very first time, a CdTe layer has been grown on CdSe andCdTe core NPLs. Unique stepped nanoplatelets have also been synthesized. These amazing materials are the first exemple of stress free semiconductors homostructures with confinement-induced intraparticle type I energy level alignment.The comprehension of the electronic structure of HgTe nanoplatelets was also addressed. We systematically studied the phase diagram in function of the confinement, pressure and temperature. Our results show that with pressure, nanoplatelets (strong confinement) and nanocrystals (weaker confinement) of HgTe have a similar behavior than the bulk : the gap increases with the pressure.However, the confinement regime becomes a key factor in function of temperature. When it is decreased from 300 K to 10 K, the gap decreases for large nanocrystals. This trend is less important when nanocrystals are smaller. The gap even decreases for the most confined materials which are the nanoplatelets. The modelisation of this effect showed that the second conduction band bends the firstone when the temperature is decreased
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Martinez, Bertille. "Étude des propriétés optoélectroniques de nanocristaux colloïdaux à faible bande interdite : application à la détection infrarouge." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS254.
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Les nanocristaux colloïdaux de semiconducteurs sont des nanomatériaux synthétisés en solution. En deçà d’une certaine taille, ils deviennent confinés : leurs propriétés optiques et électroniques sont alors dépendantes de leur taille. Le développement de ces nanocristaux a atteint une grande maturité dans le visible. L’enjeu est maintenant d’étendre la gamme accessible et d’obtenir des nanocristaux ayant des propriétés dans l’infrarouge. Parmi les candidats, on trouve les nanocristaux de tellure de mercure, HgTe, et de séléniure de mercure, HgSe. L’objectif de ce doctorat est d’approfondir la connaissance des propriétés optoélectroniques et de transport de ces matériaux afin de concevoir un système de détection infrarouge. Pour y parvenir, la structure électronique de ces matériaux est mesurée pour différentes tailles et différents ligands. Nous pouvons alors déterminer les énergies des niveaux électroniques et quantifier le niveau de dopage. Nous montrons que ce dopage dépend de la taille des cristaux, qu’il devient de plus en plus n quand la taille du cristal augmente. Dans le cas de HgSe, cette évolution du dopage avec la taille se traduit par une transition semiconducteur-métal. Le contrôle du dopage est ensuite étudié en fonction de la chimie de surface. En utilisant des effets dipolaires ou des transferts d’électrons via des ligands oxydants, nous montrons une modulation du dopage sur plusieurs ordres de grandeur. Ces études nous permettent de proposer un détecteur infrarouge à base de HgTe, fonctionnant à 2.5 µm, dont la structure permet de convertir les photons absorbés en courant. Nous obtenons une réponse de 20 mA/W et une détectivité de 3 × 10 9 JonesColloidal semiconductor nanocrystals are nanomaterials synthesized in solution. Below a certain size, these nanocrystals acquire quantum confinement properties: their optoelectronic properties depend on the nanoparticle size. In the visible range, colloidal nanocrystals are quite mature. The next objective in this field is to get infrared colloidal nanocrystals. Mercury selenide (HgSe) and mercury telluride (HgTe) are potential candidates. The goal of this PhD work is to strengthen our knowledge on optical, optoelectronic and transport properties of these nanocrystals, in order to design an infrared detector.To do so, we studied the electronic structure of HgSe and HgTe for different sizes and surface chemistries. We can then determine the energies of the electronic levels and the Fermi energy, quantify doping level … We show that the nanocrystal size has an influence on doping level, which gets more and more n-type as the nanocrystal size gets larger. We even observe a semiconductor-metal transition in HgSe nanocrystals as the size is increased. The doping control with surface chemistry is then investigated. By using dipolar effects or oxidizing ligands, we show a doping control over several orders of magnitude. Thanks to these studies, we are able to propose a HgTe based device for detection at 2.5 µm, which structure allows to convert effectively the absorbed photons into an electrical current and to get a high signal over noise ratio. We get a photoresponse of 20 mA/W and a detectivity of 3 × 10 9 Jones
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Mushonga, Paul. "Fabrication of type-I indium-based near-infrared emitting quantum dots for biological imaging applications." University of the Western Cape, 2013. http://hdl.handle.net/11394/8271.
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Doctor Scientiae - DScSemiconductor nanocrystals or quantum dots (QDs) are fluorescent nanometer-sized particles which have physical dimensions that are smaller than the excitonic Bohr radius, large surface area-to-volume ratios, broad absorption spectra and very large molar extinction coefficients. Biomedical applications of QDs are mainly based on II-VI QDs containing cadmium, such as CdSe/ZnS. These cadmium-based systems are associated with high toxicity due to cadmium. As a result, potential replacements of cadmium-based QDs in biological applications are needed. In this study, InP/ZnSe QDs were synthesized for the first time using a one-pot hot injection method. Furthermore, a growth-doping method was used for silver, cobalt and iron incorporation into the InP core. Water compatibility was achieved through ligand exchange with 3- mercaptopropionic acid. In vitro cytotoxicity and imaging/internalization of the as-prepared MP A-InP/ZnSe and MP A-capped CdTe/ZnS QDs were evaluated. InP/ZnSe QDs were successfully synthesized with ZnSe shell causing a 1.4 times reduction in trap-related emission.
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Gréboval, Charlie. "Étude et contrôle de la densité de porteurs dans des nanocristaux à faible bande interdite : application à la détection infrarouge." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS221.
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Les nanocristaux de semiconducteur colloïdaux sont des objets cristallins synthétisés par voie chimique. En raison du confinement quantique présent dans ces objets, leur propriétés optiques dépendent de leur taille et peuvent être ajustés lors de leur synthèse. Connus principalement pour leur photoluminescence dans le visible, ils peuvent également absorber le rayonnement infrarouge. Parmi les matériaux absorbant dans l’infrarouge, j’ai utilisé pendant ma thèse le tellurure de mercure dont l’énergie de bande interdite peut être ajustée continument sur l’ensemble de la gamme infrarouge. Ces nanocristaux peuvent être déposés sous forme de films sur des électrodes afin de réaliser des photodétecteurs infrarouges. L’objectif est d’utiliser ces photodétecteurs dans des caméras infrarouges à bas coût. Avant cela il est nécessaire d’avoir une connaissance complète de ces matériaux. Je me suis intéressé à plusieurs moyens permettant de sonder la nature et la dynamique des porteurs majoritaires et minoritaires dans des nanocristaux de HgTe. Cela passe par des mesures de photoémission mais également par la réalisation de transistors à effet de champ. J’ai développé de nouvelles technologies de grille pour ces transistors et je présente des exemples d’intégration de ces transistors dans des photodétecteurs. L’ajout d’une grille permet un meilleur contrôle de la densité de porteurs et permet dans certaines conditions d’améliorer la séparation des charges par la formation d’une jonction p-n dans le canal. Cela permet une augmentation significative du rapport signal-sur-bruit des détecteurs et donc de meilleures performancesColloidal semiconductor nanocrystals are chemically synthetized crystalline objects. Quantum confinement occurring in these objects give them size-dependent tunable optical properties that can be adjusted during their synthesis. They are mostly known for their bright photoluminescence in the visible range they can also absorb infrared light. Among infrared absorbing materials, I used mercury telluride which bandgap can be tuned across the entire infrared range. These nanocrystals can then be deposited as thin films onto electrodes to build infrared photodetectors. The goal is to use these photodetectors as sensors in cheap infrared cameras. Before that, a full understanding of their properties is needed. I developed different means to probe both nature and dynamics of the majority and minority carriers in HgTe nanocrystals. This is done through photoemission measurements but also by building field effect transistors. I developed new gating technologies for these transistors, and I show some examples of their integration in photodetectors. The addition of a gate allows a better control of the carrier density and can even lead to a better charge separation induced by the formation of a p-n junction within the channel. This enables a strong enhancement of the signal-to-noise ratio leading to improved performance
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Ouma, Linda Achiengꞌ. "Synthesis, optical and morphological characterization of pbse quantum dots for diagnostic studies: a model study." Thesis, University of the Western Cape, 2013. http://hdl.handle.net/11394/3975.
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>Magister Scientiae - MScIn this study PbSe quantum dots (QDs) were successfully synthesized via the organometallic and aqueous routes. Optical characterization was carried out using photoluminescence (PL) spectroscopy, structural and morphological characterization were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDS) was used to determine the composition of the QDs. All the synthesized QDs were found to have emissions within the near-infrared region of the spectrum (≥1000 nm) with most of them being less than 5 nm in size. The aqueous synthesized QDs had a perfect Gaussian emission spectrum with a FWHM of ~23 nm indicating pure band gap emission and narrow size distribution respectively. The QDs were determined to have a cubic rock-salt crystal structure consistent with bulk PbSe. The aqueous synthesized QDs were however not stable in solution with the QDs precipitating after approximately 48 h. The organometallic synthesized QDs were transferred into the aqueous phase by exchanging the surface oleic acid ligands with 11-mercaptoundecanoic acid ligands. The ligand exchanged QDs were however stable in solution for over two weeks. The effects of reaction parameters on the optical and structural properties of the organometallic synthesized QDs were investigated by varying the reaction time, temperature, ligand purity, lead and selenium sources. It was observed that larger QDs were formed with longer reaction times, with reactions proceeding faster at higher reaction temperatures than at lower temperatures. Varying the ligand purity was found to have minimal effects on the properties of the synthesized QDs. The lead and selenium sources contributed largely to the properties of the QDs with lead oxide producing spherical QDs which were smaller compared to the cubic QDs produced from lead acetate. TBPSe was seen to produce smaller QDs as compared to TOPSe. The cytotoxity of the synthesized QDs was determined following the WST-1 cell viability assay with the QDs being found to be non-toxic at all the tested concentrations
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Chu, Audrey. "Couplage lumière-matière au sein de détecteurs infrarouges à base de nanocristaux colloïdaux." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS082.
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Les nanocristaux colloïdaux sont des nanoparticules dont la croissance se fait en solution. Lorsque la taille de ceux-ci est suffisamment faible, des effets de confinement quantique apparaissent et leurs propriétés optiques deviennent ajustables avec leur taille. Ces nanocristaux sont en particulier utilisés pour leur luminescence dans le visible mais peuvent aussi être utilisés pour réaliser de la photodétection dans la gamme infrarouge. Les nanocristaux de HgTe et PbS présentent des propriétés d’absorption dans l’infrarouge. Le mécanisme de transport au sein d’un film de nanocristaux induit leur utilisation sous forme de couches minces, réduisant l’absorption et conduisant à des performances modestes. L’objectif de mon doctorat est d’augmenter le couplage lumière-matière au sein de film de nanocristaux afin d’augmenter l’absorption et donc la réponse. En particulier je démontrerai la possibilité de nanostructurer les électrodes afin d’induire des résonances de modes guidés pour des films de nanocristaux. L’utilisation de ces nanoélectrodes induit une augmentation de la réponse de deux à trois ordres de grandeur grâce à une augmentation de l’absorption et du gain photoconducteur. L’utilisation de telles résonances est une méthode versatile puisqu’elle peut être appliquée à différents matériaux, à différentes longueurs d’onde et pour différentes géométries. Enfin dans une dernière partie je présenterai un dispositif permettant d’exalter les propriétés de transport au sein d’un film de nanocristaux. Ce dispositif atteint une détectivité de 1012 Jones à 2.5 µm, 1 V et à 200 K, ce qui est comparable avec des détecteurs conventionnelsColloidal nanocrystals are nanoparticles grown in solution. When their dimension is reduced below the Bohr radius, quantum confinement appears: optical properties depend on the size of the crystal. These nanocrystals are currently used for their visible emission properties but can also be applied for infrared photodetection. Mercury and lead chalcogenide (and in particular HgTe and PbS) absorb in the infrared. The hopping transport associated with nanocrystal array induced the use of thin film. The absorption of such film remains low and so does their performance. My work consists in induce light-matter coupling within a nanocrystal array in order to boost the absorption and the responsivity. Using nanostructured electrodes, it is possible to induce guided mode resonances within nanocrystal thin films. The responsivity of such devices presents an increase of a factor 102 – 103 compared to a film on conventional electrodes due to an enlargement of the absorption and the photoconductive gain both. This method is versatile and can be used for different materials, at different wavelengths and for different device geometries. In a last part, I will show a device that improve transport properties in a nanocrystal film. This device has a detectivity of 1012 Jones at 2.5 µm, 1 V and 200 K, which is comparable with commercial detectors
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Chang, Tung-Wah Frederick. "Luminescence and energy transfer excitation of infrared colloidal semiconductor nanocrystals /." 2006. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=442439&T=F.
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Koleilat, Ghada. "Efficient, Stable Infrared Photovoltaics based on Solution-Cast PbSe Colloidal Quantum Dots." Thesis, 2008. http://hdl.handle.net/1807/17189.
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Half of the sun’s power lies in the infrared. As a result, the optimal bandgaps for solar cells in both the single-junction and even the tandem architectures lie beyond 850 nm. However, progress in low-cost, large-area, physically-flexible solar cells has instead been made in organic and polymer materials possessing absorption onsets in the visible. Recent advances have been achieved in solution-cast infrared photovoltaics through the use of colloidal quantum dots. Here we report stable solution-processed photovoltaic devices having 3.6% power conversion efficiency in the infrared. The use of a strongly-bound bidentate linker, benzenedithiol, ensures device stability over weeks. We investigate in detail the physical mechanisms underlying the operation of this class of device. We find that diffusion of electrons and holes over hundreds of nanometers through our PbSe colloidal quantum dot solid is chiefly responsible for the high external quantum efficiencies obtained in this new class of devices.
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Panthani, Matthew George. "Colloidal nanocrystals with near-infrared optical properties : synthesis, characterization, and applications." 2011. http://hdl.handle.net/2152/19825.
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Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices.
Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSeXS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.
The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.text
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王耀霆. "Near Infrared Photodetectors Based on Solution – Phase Synthesis of FeS2 Nanocrystals." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/94134269647258036240.
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碩士國立臺灣師範大學
化學系
98
In this thesis, the near infrared photodetectors based on FeS2 nanocrystals were studied. We used FeS2 nanocrystals as the active layer and ZnO as blocking layer for the devices. FeS2 is a indirect band gap semiconductor which has a narrow band gap of 0.95 eV with high absorption to the light even near-infrared range, and the advantage in using the FeS2 nanocrystals is because they are low-cost, abundant and non-toxic materials. The well dispersed FeS2 nanocrystals were synthesis by Solution –phase methods, furthermore, we could control the shapes of FeS2 nanocrystals by adjust the ratio of surfactant to solvent, then the crystal morphology and structure were identified by TEM and XRD. In conclusion, the photodetectors based on FeS2 nanocrystals response in both the visible and infrared ( λ > 715 nm) have been demonstrated by Current density–voltage characteristics and temporal photocurrent response of the devices.
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Hsu, Yi-Husan, and 徐憶瑄. "Synthesis and characterization of near-infrared light triggered lanthanide-doped upconversion nanocrystals." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/08626558123607409893.
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碩士中山醫學大學
應用化學系碩士班
103
This study mainly discusses the synthesis of NaYF4/LiYF4 nanoparticles containing Tm3+/Yb3+. The upconversion efficiency of these nanoparticles correlated to the equivalent of activator or base during the syntheses is also demonstrated. The TEM images of the particles prepared by autoclave under lower temperature show that most of the particles are irregular (AC7 and AC14). In the meantime, the particles could not show the upconversion efficiency under 980 nm excitation. In order to improve the diameter and the upconversion efficiency of the nanoparticles, we used the heating mantle for the synthesis of the nanoparticles. The nanoparticles with upconversion efficiency and diameter less than 100nm are successfully synthesized. To study the relationship between the equivalent of the activator / base and the upconversion efficiency of the nanoparticles, we increased the equivalent of the activator. The result indicated that the upconversion efficiency was not enhanced by increasing the equivalent of the activator. However, the increasing the equivalent of the base ( LiOH / NaOH) during the synthesis resulted in the enhanced upconversion efficiency of the nanoparticles. The further addition of Y(CH3CO2)3 and base (LiOH / NaOH) to the synthesized NaYF4/LiYF4:Yb,Tm nanoparticles by the heating mantle led to the formation of new nanoparticles. The TEM images of the nanoparticles show that the shapes of the nanoparticles transformed from hexagon to rod (L1S、L3S、N1S、N3S). The analysis of the length-to-width (aspect ratio, AR) of the rod (L1S (AR=3.90), L3S (AR= 3.77); N3S (AR=3.73), N1S (AR=2.64)) showed that the rod with the higher AR value exhibited the effective upconversion efficiency.
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Anumol, S. "A Study of Synthesis and Optoelectronics of Copper Iron Chalcogenide Nanocrystals." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4984.
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Copper iron chalcogenides constitute a promising class of optoelectronic materials courtesy of their narrow bandgaps and earth abundant constitution. However, they are yet to receive the attention they deserve due to the lack of easy synthetic protocols and poorly understood material properties. Discordant narratives in the literature regarding their optoelectronic properties has also prevented them from being used for device-based applications. This thesis is aimed at rectifying a few of these issues. The objective of this thesis is to synthesize and study the properties of copper iron chalcogenide nanocrystals viz., CuFeS2 and CuFeSe2, and to explore their utility in the context of optoelectronic devices.
Chapter 1 provides a brief introduction to the fundamental concepts related to the work described in this thesis. The chapter further discusses the scope and motivation behind the work carried out in this thesis.
Chapter 2 describes our efforts to assign the nature of a feature in the optical absorption spectrum of CuFeS2 nanocrystals occurring at ~500 nm. Using a combination of steady-state and time-resolved optical spectroscopy as well as transport measurements we assign the feature to be a localized surface plasmon resonance and attribute the peculiar properties exhibited by CuFeS2 nanocrystals to this feature. Further, the transport measurements revealed that films of these nanocrystals can support a photoresponse.
Chapter 3 describes the fabrication and characterization of a broadband photodetector based on CuFeS2 nanocrystals. Briefly, we fabricated heterojunctions of CuFeS2 nanocrystals with bulk n type silicon and demonstrated a broadband photoresponse from 460 nm-2200 nm with response time of the order of microseconds. The photodetector was further found to possess a photothermal response that is bolometric in nature, which allows the device to sense hot objects at room temperature.
Chapter 4 describes our efforts to synthesize and study the optoelectronic properties of CuFeSe2 and CuFeSe2-CdS core-shell nanocrystals. We synthesized CuFeSe2 nanocrystals and studied their properties using structural, optical and electrical characterization techniques. The nanocrystals were found to have a very narrow bandgap of 0.11 eV and were also found to exhibit a plasmon resonance at ~410 nm. We further found that the films of these nanocrystals exhibited a photoresponse in the MIR, thus making them a promising candidate for infrared photodetection. We further synthesized highly luminescent CuFeSe2-CdS core-shell nanocrystals and found that the energetic position of their emission is greatly dependent on the sequence in which the shell growth precursors are added to the reaction mixture. Using optical and structural characterization techniques, we find that there are two different core-shell variants that result from the synthesis and their formation is determined by which one of the shell growth precursors is added to the reaction mixture first. The key difference between the two variants were found to be the presence of an interfacial CdSe layer which occurs whenever the cation precursor is added to the reaction mixture first.
Chapter 5 describes the synthesis of CuFexGa1-xS2 nanocrystals, a hitherto unknown composition of nanocrystals. Using alloying as a strategy, we synthesized CuFexGa1-xS2 nanocrystals corresponding to different Fe:Ga ratios. The properties of the resulting nanocrystals were found to be greatly dependent on their composition.
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Sreeshma, D. "Investigations on deep-level defects in HgTe nanocrystals-based photovoltaic devices using a novel instrumentation for Deep Level Transient Spectroscopy." Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6161.
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Colloidally produced nanocrystals (NCs) arranged in thin films hold promise for next-generation semiconductors. These NCs offer tunability in semiconductor properties due to their size, shape, composition, and surface characteristics. However, the performance of NC-based optoelectronic devices still lags behind theoretical predictions. This is primarily attributed to electronic deep-level trap states, which act as recombination centres and limit effective mobility. The large surface area, hybrid nature, and disordered structure of NCs contribute to the abundance of trap states. To improve device performance, it is crucial to identify these defects and understand their impact on electrical characteristics. This work employs Deep Level Transient Spectroscopy (DLTS) to identify deep-level defects in NCs and NC-based photovoltaic devices. DLTS allows for determining defect level energy, concentration, capture cross-section, and differentiation between minority and majority carrier traps. This technique is highly sensitive, capable of detecting low defect concentrations, and resolves signals from various traps.
The conventional DLTS system suffers from drawbacks, including the need for multiple temperature cycles, which can lead to poor device contact and thin film adhesion. Additionally, maintaining a consistent temperature environment for each measurement is challenging, resulting in low-quality data. To address these issues, we develop a microcontroller-based DLTS system. This system utilizes a capacitance meter and electronic circuits controlled by an Arduino-Due microcontroller. We have used Arduino-Due to generate the filling pulse, monitor the capacitance, temperature, data acquisition, timing control and signal processing. By conducting measurements within a single temperature scan, our system saves time, improves accuracy, and reduces experimental failures. We validate the innovative instrumentation using a gold-doped silicon p-n junction sample. Furthermore, we apply this microcontroller-based DLTS system to study deep-level defects in Mercury Telluride (HgTe) nanocrystal-based photovoltaic devices.
We fabricate photovoltaic devices based on HgTe NCs/TiO2 and employ capacitance-voltage (C-V) and DLTS techniques to investigate and collect quantitative data on deep-level trap states. DLTS confirms the presence of interface trap states, while frequency-dependent capacitance measurements support the influence of charge storage in these nanocrystal-based heterostructures, offering insights for advanced device development. Using DLTS, we measure trap energy, capture cross-section, and concentration. These traps in the photovoltaic devices can act as recombination centres and effectively interact with valence and conduction bands. Poor device responsiveness is observed in the ITO/TiO2/HgTe/Au configuration due to inefficient photo charge extraction.
To enhance device performance, we optimize hole and electron extractions by introducing a Molybdenum Oxide (MoO3) hole extraction layer. We investigate the effect of this contact layer on trap level formation in the FTO/TiO2/HgTe/MoO3/Au photovoltaic device using low-temperature I-V, C-V, C-F, and microcontroller-based DLTS measurements. The obtained trap energy levels are comparable to those of the ITO/TiO2/HgTe/Au device, indicating the presence of trap levels at the TiO2/HgTe interface and no significant impact of the MoO3 contact layer on trap formation. Our microcontroller-based DLTS system proves to be an efficient tool for determining defect levels in heterojunctions based on nanocrystals. Surface states at the HgTe nanocrystals and oxygen vacancies in TiO2 are identified as the main contributors to trap levels, primarily located at the TiO2/HgTe interface. To further confirm the origin of trap states, we fabricate an ITO/HgTe/Al Schottky junction and measure the defect level energy using low-temperature I-V and C-F measurements. The obtained energy values support trap levels resulting from surface reconstruction at the TiO2/HgTe heterojunction interface. Passivating these trap states is crucial for improving device effectiveness.
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Abel, Keith Alexander. "Synthesis and characterization of colloidal lead chalcogenide quantum dots and progress towards single photons on-demand." Thesis, 2011. http://hdl.handle.net/1828/3481.
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Nanometer-sized semiconductor crystals, termed ‘quantum dots’, are of fundamental interest because of their size-tunable properties. Three-dimensional quantum confinement of charge carriers by the small crystal size results in discrete atomic-like electronic states. This dissertation describes the synthesis and in-depth characterization of lead chalcogenide colloidal quantum dots for forthcoming applications as near-infrared single photon emitters. An efficient single photon source that operates at telecommunication wavelengths (between 1.3 and 1.6 µm) is a basic requirement for many photonic quantum technologies, such as quantum computing and quantum cryptography.
Chapters 1 and 2 of this work provide an introduction to colloidal quantum dots and their use as single photon emitters. It includes a description of photonic crystal microcavities and their ability to enhance the spontaneous emission rate of quantum dots. The synthesis and basic characterization of PbSe and PbS quantum dots is then discussed in chapter 3. In particular, a new synthetic method for the preparation of highly photoluminescent PbS quantum dots is presented. PbSe/CdSe core/shell quantum dots prepared by a cation exchange reaction are also described and a significant improvement in photo-stability is shown. Chapter 3 concludes with a description of three different surface modification techniques. PbSe core and PbSe/CdSe core/shell materials are investigated further in chapter 4 by advanced characterization techniques that include high-angle annular dark field (HAADF) imaging, energy-filtered transmission electron microscopy (EF-TEM) imaging, energy-dependent X-ray photo-electron spectroscopy (XPS), small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The information obtained from these techniques is combined to form a structural model of the PbSe core and PbSe/CdSe core/shell quantum dots with greater complexity than previously reported. In chapter 5, the temperature-dependent photoluminescence from PbSe and PbSe/CdSe core/shell quantum dots is discussed and a thermal model is presented that accounts for the large (non-trivial) temperature dependence of the Stokes shift and photoluminescence lineshape over the entire temperature range (4.5 to 295 K). Chapter 6 examines two scalable methods to integrate the colloidal quantum dots into silicon two-dimensional photonic crystal slab microcavities (a requirement for efficient single photon emission). Finally, conclusions and possible future work are discussed in chapter 7.Graduate
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Chen, Chi-Feng, and 陳啟峰. "Infrared Spectroscopic Studies of Nanocrystal Diamonds." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/27075145598143235967.
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碩士國立東華大學
材料科學與工程研究所
89
This research investigated the nanometer-sized diamond particles created from both High temperature/High pressure and detonation methods by using Fourier Transform Infrared Spectroscopy (FTIR). Nanodiamonds were hydrogenated/etched via microwave plasma or hot filament generated atomic hydrogen, and C-H vibrational spectra on the surfaces were measured. Cycloaddition reactions on diamond surfaces conducted with the addition of organic gases. The resulting spectra were compared to the Unidentified Infrared Emission Bands (UIBs) that observed in the interstellar medium. Size-dependent IR spectra revealed that these spectra were independent on the size of the nanodiamonds. This investigation wish to provide unambiguous evidence that nanodiamonds particles exist in the interstellar medium, and its IR spectra were similar to that of 100 nm diamonds that were observed in the laboratory.
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Johnston, Keith. "Solution-processed Schottky-quantum Dot Photovoltaics for Efficient Infrared Power Conversion." Thesis, 2008. http://hdl.handle.net/1807/11145.
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Solar energy harvesting demands low-cost energy conversion in the infrared from 1 – 2 μm. However, solution-processed photovoltaic devices have remained relatively inefficient in this spectral region. Herein, lead sulfide colloidal nanocrystal quantum dots are used to facilitate efficient infrared power conversion. Solution-cast nanocrystal films are employed in a simple metal/semiconductor/metal architecture to produce a photovoltaic effect. It is shown that a Schottky barrier is induced, which is responsible for the charge separating action. Through optimization of chemical processes and device fabrication, the photovoltaic response is maximized. The infrared power conversion efficiency reaches 4.2%, which sets a new precedent for solution-processed photovoltaic cells. Furthermore, the devices exhibit efficient broadband solar power conversion and show promise for multijunction cell architectures. Carrier drift through a large depletion region near the Schottky contact is determined to be the dominant transport mechanism.