Teses / dissertações sobre o tema "(AIGa)N quantum dots"

Les diodes électroluminescentes (LED) sont essentielles dans les technologies modernes, permettant une large gamme d'applications allant de l'éclairage à des usages spécialisés dans les domaines médicaux et environnementaux. Les LED ultra-violettes (UV), basées sur des hétérostructures à base d'alliages de nitrure d'aluminium et de gallium ((Al,Ga)N) avec des émetteurs quantiques, présentent un grand potentiel pour des applications telles que la stérilisation, la purification de l'eau et le diagnostic médical, grâce à leur efficacité énergétique, leur compacité et leur durée de vie plus longue par rapport aux lampes au mercure conventionnelles. Les systèmes à base d'(Al,Ga)N possèdent une bande interdite directe large et ajustable et est comprise entre 3.4 eV et 6.2 eV ce qui équivaut à une longueur d'onde d'émission de 365 nm et 200 nm respectivement. Cela fait rend particulièrement adaptés à l'émission de lumière sur un large spectre de longueurs d'onde dans la gamme UV, tandis que la capacité de dopage du matériau permet de réaliser des régions de type négatif (type n) et de type positif (type p), ce qui est nécessaire pour fabrication des LED. Malgré ces avantages, les LED UV basées sur l'(Al,Ga)N souffrent actuellement d'une efficacité quantique plus faible que à leurs homologues émettant dans le visible, en particulier en raison de la forte densité de défauts, des effets de polarisation de l'émission et de la faible extraction de la lumière. Cette thèse explore différentes voies permettant de remédier à ces problèmes. En particulier, l'utilisation de métasurfaces optiques, c'est-à-dire de réseaux de nanostructures, est envisagée pour améliorer l'émission des hétérostructures (Al,Ga)N. Le chapitre 1 présente l'état de l'art dans ce domaine ainsi que la motivation de ce travail. Le chapitre 2 offre une vue d'ensemble complète des propriétés fondamentales des matériaux (Al,Ga)N, notamment leurs caractéristiques cristallographiques et optiques. Il décrit également la croissance par épitaxie par jets moléculaires des boîtes quantiques (Al,Ga)N utilisées dans ce travail. Au chapitre 3, nous étudions expérimentalement l'influence de la relaxation mécanique des hétérostructures et de la qualité cristalline sur les propriétés optiques des boîtes quantiques émettant dans la gamme UV. Le chapitre 4 examine en profondeur la réponse photonique des matériaux (Al,Ga)N, offrant une analyse théorique et expérimentale des mécanismes d'interaction de la lumière et de la polarisation de l'émission. Enfin, le chapitre 5 traite de l'intégration des métasurfaces avec des émetteurs UV basés sur (Al,Ga)N pour améliorer le contrôle de l'émission et les performances globales du dispositif. L'utilisation de métasurfaces, capables de manipuler la lumière à l'échelle sub-longueur d'onde, est explorée comme une stratégie prometteuse pour augmenter l'extraction de la lumière en dirigeant et contrôlant l'émission dans la gamme UV
Light-emitting diodes (LEDs) are essential in modern technology, enabling a wide range of applications from general lighting to specialized uses in medical and environmental fields. Ultraviolet (UV) LEDs, based on heterostructures of aluminum gallium nitride alloys ((Al,Ga)N) with quantum emitters, hold significant promise for applications in sterilization, water purification, and medical diagnostics due to their energy efficiency, compact form, and longer lifespan compared to conventional mercury lamps.The(Al,Ga)N-based systems have a wide and tunable direct band gap ranging from 3.4 eV to 6.2 eV, which is equivalent to emission wavelengths of 365 nm and 200 nm, respectively. This makes them particularly suitable for light emission over a broad wavelength spectrum in the UV range, while the material doping capability supports both n-type and p-type doping regions, which is necessary for LED fabrication. Despite these advantages, UV LEDs based on (Al,Ga)N currently suffer from lower quantum efficiency compared to their visible-light counterparts, particularly due to high defect densities, emission polarization effects, and overall low light extraction.This work explores these challenges in more detail and also considers the possibility of improving the radiative characteristics of (Al,Ga)N heterostructures by embedding them into a metasurface. Chapter 1 introduces the state of the art in this topic and the motivation for this work. Chapter 2 presents a comprehensive overview of the fundamental properties of (Al,Ga)N materials, including their crystallographic and optical characteristics. It also describes the Molecular Beam Epitaxy growth of (Al,Ga)N quantum dots (QDs) used in this work. In Chapter 3, we experimentally investigate the influence of the mechanical relaxation of the heterostructures and the crystalline quality on the optical properties of the QDs emitting in the UV range. Chapter 4 delves into the photonic response of (Al,Ga)N materials, offering a theoretical and experimental analysis of light interaction mechanisms and emission polarization. Finally, Chapter 5 discusses the integration of metasurfaces with (Al,Ga)N-based UV emitters for improving emission control and overall device performance. The use of metasurfaces, which can manipulate light at the subwavelength scale, is explored as a promising strategy to increase light extraction efficiency by directing and controlling emission in the UV range

This thesis presents an experimental investigation into the properties of highly doped (n_phosphorous ~ 1.4 x 10¹⁹cm^-3) n-type silicon-germanium double quantum dots. The structures are fabricated with a diameter of between 40nm and 70nm by means of electron beam lithography. Their electronic properties are then measured using a variety of cryogenic techniques, including a dilution refrigerator with a base temperature of 20mK. The main results from this investigation are described below. The ‘Coulomb Oscillations’ form a hexagonal lattice as the electrochemical potentials on the two dots are shifted by means of electrostatic gates. This indicates that the double dot is indeed a double well potential, and shows that the electron number on the dots can be independently altered. The elastrostatic gates are shown to have a wide degree of control over not just the electrochemical potential on the dots, but also the shape of the potential well. In this way, the two wells can be induced to coalesce; one of the wells can be merged into its nearby lead; or the coupling parameters between the dots and dots and leads can be altered. A supplementary piece of work, undertaken in collaboration with Paul Cain, is presented in appendix A. This describes an original scheme for quantum computation in which the ammonia molecule is used as the qubit. It is confined within a fullerene and placed on a crystal surface where gates and global microwave pulses manipulate, and interact it with other such encapsulated ammonia molecules. Finally, measurements is performed with an electrometer which has the ability to distinguish the polarisability of the ammonia molecule’s eigenstates.

GaN quantum dots grown by molecular beam epitaxy are examined by micro-photoluminescence. The exciton and biexciton emission are identified successfully by power-dependence measurement. With two different samples, it can be deduced that the linewidth of the peaks is narrower in the thicker deposited layer of GaN. The size of the GaN quantum dots is responsible for the binding energy of biexciton (E^b_XX); E^b_XX decreases with increasing size of GaN quantum dots. Under polarization studies, polar plot shows that emission is strongly linear polarized. In particular, the orientation of polarization vector is not related to any specific crystallography orientation. The polarization splitting of fine-structure is not able to resolve due to limited resolution of the system. The emission peaks can be detected up to 80 K. The curves of transition energy with respect to temperature are S-shaped. Strain effect and screening of electric field account for  blueshift of transition energy, whereas Varshni equation stands for redshifting. Both blueshifting and redshifting are compensated at temperature ranging from 4 K to 40 K.

Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008.
The successful preparation and structural characterization of a number of N,N-dialkyl-N’-benzoyl(thio)selenourea ligands is described; where the intermolecular interactions are characterized by the presence of Resonance Assisted Hydrogen Bonding (RAHB), π- π interactions between neighbouring benzene residues only being evident amongst the longer alkyl chain derivatives. The first structural characterization of an asymmetrically substituted N,N-dialkyl- N’-benzoylselenourea ligand reveals an increased stability of the Z isomer in the solid state, this being reflected by the sulfur analogue. Attempts to synthesise N,N-dicyclohexyl-N’-benzoylselenourea led to the isolation and structural characterization of a novel 1,3,5-oxaselenazine salt and dicyclohexylaminobenzoate. The first structural characterization of a “bipodal” N,N-dialkyl-N’-benzoylselenourea ligand, 3,3,3’,3’-tetrabutyl-1,1’- isophthaloylbis(selenourea), reveals RAHB in the crystal lattice similar to that exhibited by the “monopodal” analogue, N,N-dibutyl-N’-benzoylselenourea. The successful complexation of the N,N-dialkyl-N’-benzoyl(thio)selenourea ligands to a number of different transition metal ions is reported allowing the preparation of several potential single source precursors. Coordination through the O and Se/S donor atoms to Pd(II) results in the formation of square planar metal complexes, with a cis conformation, several of which could be structurally characterized. In particular, the first structural elucidation of an asymmetrically substituted N,N-dialkyl-N’-benzoylselenourea metal complex, cis-bis(N-benzyl-N-methyl-N’- benzoylselenoureato)palladium(II) indicates the increased stability of the EZ isomer in the solid state. Structural elucidation of the novel (N,N-diphenyl-N’-benzoylselenoureato)cadmium(II) reveals a bimetallic complex in the solid state, where the expected 2:1 ligand : metal ratio is maintained, and the two Cd(II) centres are 5 and 6 coordinated, with O and Se donor atoms. Multinuclear Nuclear Magnetic Resonance (NMR) Spectroscopy has been employed in the thorough characterisation of the potential single source precursors, 77Se NMR spectroscopy indicating a decreased shielding of the 77Se nucleus as the “hardness” of the central metal ion increases i.e. Pd(II) > Zn(II) > Cd(II). Use of 113Cd NMR spectroscopy indicates the preferential binding of N,N-diethyl-N’- benzoylselenourea to Cd(II) over that of its sulfur analogue, and initial studies suggest a form of chelate metathesis taking place in solution. 31P NMR spectroscopy is used to gain insight into the formation of cis-bis(N,N-diethyl-N’- benzoylselenoureato)Pt(II). Thermolysis of (N,N-diethyl-N’-benzoylselenoureato)cadmium(II) and its sulfur analogue led to the successful synthesis of CdSe and CdS quantum dots respectively, where thermolysis over a range of temperatures allows a degree of size control over the resulting nanoparticles. The effect of precursor alkyl chain length on nanoparticle morphology was investigated for both the N,N-dialkyl-N’-benzoylthio- and –selenoureas. A correlation between the two for the (N,N-dialkyl-N’-benzoylselenoureato)Cd(II) complexes is described and possible growth mechanisms are discussed. Preliminary investigations into the use of other N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes as single source precursors reveal that both (N,N-diethyl-N’-benzoylselenoureato)Zn(II) and its sulfur analogue show potential as single source precursors for the formation of ZnO and ZnS nanoparticles respectively. Initial studies into the use of N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes as single source precursors for the synthesis of core-shell nanoparticles is briefly described. The Aerosol Assisted Chemical Vapour Deposition (AACVD) of several N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes is reported, where both (N,N-diethyl-N’-benzoylselenoureato)Cd(II) and its sulfur analogue allow the deposition of crystalline CdSe and CdS respectively. The AACVD of (N,N-diethyl-N’- benzoylselenoureato)Zn(II) leads to the deposition of crystalline ZnSe, ZnS being deposited by (N,N-diethyl-N’-benzoylthioureato)Zn(II). The deposition of heazelwoodite (Ni3S2) with varying morphologies results from the AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Ni(II). Thermal annealing of the amorphous material deposited by the AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Pd(II), allows the formation of highly crystalline palladium. The deposition of metallic platinum using cis-bis(N,N-diethyl-N’-benzoylthioureato)Pt(II) is described as well as the deposition of crystalline Pd17Se15 from cis-bis(N,N-diethyl-N’-benzoylselenoureato)Pd(II). This, to the best of our knowledge, is the first time that AACVD has been performed, using the N,N-dialkyl-N’- benzoyl(thio)selenourea metal complexes as single source precursors, in addition, we believe it to be the first time that palladium selenide has been deposited using the AACVD technique.

Orientador: Lisandro Pavie Cardoso
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-17T08:00:52Z (GMT). No. of bitstreams: 1 Menezes_AlanSilvade_D.pdf: 23119383 bytes, checksum: ab5e971a0c297e969fddfdd4a44a73a6 (MD5) Previous issue date: 2010
Resumo: Neste trabalho, a difração múltipla (DM) de raios-X associada com as vantagens da radiação síncrotron configura-se como uma microssonda de alta resolução e é utilizada para obter relevantes contribuições ao estudo das propriedades estruturais de materiais semicondutores, apresentem-se eles como nanosistemas epitaxiais ou implantados com íons. O estudo e detecção de reflexões híbridas (interação camada epitaxial/substrato) coerentes (CHR) negativas nas varreduras Renninger (RS) do substrato é uma das contribuições desta tese. O mapeamento ?:f da condição de difração da reflexão secundária (113)(111) mostra que a CHR negativa que aparece é, na realidade, a interferência destrutiva entre a reflexão secundária da rede da camada e a reflexão primária do substrato. Ressalta-se aqui importância da medida detalhada da condição de difração de reflexões secundárias adequadas da DM. O uso do caso especial da DM denominado difração Bragg-superfície (BSD), cuja reflexão secundária se propaga paralelamente à superfície dos monocristais ou interfaces nas heteroestruturas, quando envolve reflexões secundárias que são sensíveis à simetria da rede cristalina, constitui outra contribuição da tese. O pico na RS para o substrato (GaAs), que representa o caso de quatro-feixes (000)(004)(022)(022) e que se separa em dois picos na RS da camada GaInP por distorção tetragonal foi utilizado como uma nova ferramenta no estudo de deformações tetragonais, mesmo para camadas epitaxiais finas. Além disso, a presença de distorções ortorrômbicas ou até mesmo monoclínicas, pode ser investigada pela medida dos dois pares de picos secundários (022)(022) e (202)(202), também presentes na mesma RS da camada ternária. Outras contribuições desta tese estão na aplicação da DM no estudo de amostras de SiO2/Si(001) implantadas com íons Fe+, que passaram pelo processo de cristalização epitaxial induzida por feixe de íons (IBIEC) e, finalmente, por tratamento térmico. Mapeamentos ?:f do pico BSD (000)(002)(111) forneceram parâmetros de rede e tensões nas direções perpendiculares e paralelas com relação à superfície, para as regiões tensionadas provocadas por formação das nanopartículas da fase ?-FeSi2 produzidas por IBIEC. Para outro conjunto de amostras semelhantes exceto pela ausência do óxido a interessante formação de nanopartículas da fase ?-FeSi2 sob a forma de placas orientadas na amostra IBIEC, que foram observadas por microscopia e confirmadas por curvas de rocking (002) na condição de DM para os picos BSD (111) e (111) e mapeamentos ?:f, provocou tensões anisotrópicas no plano da superfície da amostra IBIEC. Formas esféricas das nanopartículas também detectadas por microscopia introduzem tensões isotrópicas e a caracterização estrutural das amostras foi realizada da mesma maneira mencionada acima. Medidas dos mapeamentos do espaço recíproco (RSM) com reflexões simétricas e assimétricas foram importante para confirmar os resultados obtidos por MD das amostras implantadas, por permitir observar a variação de composição lateral e periódica existente na camada de GaInP, assim como, por confirmar o efeito da altura dos pontos quânticos de InP sobre a camada ternária, no nível de tensão provocado por eles na camada de recobrimento desses pontos, ou seja, quanto maior a altura maior o nível de tensão na camada
Abstract: In this paper, X-ray multiple diffraction (MD) associated with the advantages of synchrotron radiation appears as a high-resolution microprobe and it is used to obtain relevant contributions to the study of structural properties of semiconductor materials, as they present themselves nanosystems epitaxial or implanted with ions. The study and detection of negative hybrid reflections (interaction epitaxial layer/substrate) coherent (CHR) in substrate Renninger scans (RS) is one of the contributions of this thesis. The ?:f mapping, i.e., the scanning of the (113)(111) secondary reflection diffraction condition shows that the CHR negative that appears is, in fact, the destructive interference between the layer secondary reflection and the substrate primary reflection. It is emphasized here the importance of a detailed measurement of the diffraction condition of adequate MD secondary reflections. The use of the MD special case named Bragg-Surface Diffraction (BSD), in which the secondary reflection propagates parallel to the single crystal surface or interfaces in heterostructures, when involves secondary reflections that are sensitive to the crystalline lattice symmetry, is another relevant contribution of this thesis. The substrate (GaAs) RS peak, which stands for the (000)(004)(022)(022) four-beam case that splits into two three-beam peaks GaInP layer RS by tetragonal distortion was used as a novel tool in the study of tetragonal distortions, even for thin epitaxial layers. Moreover, the presence of orthorhombic distortion or even monoclinic one, can be investigated by measuring the two pairs of secondary peaks (022)(022)and (202)(202) also present in the same ternary layer RS. Other thesis contributions are in the application of DM to the study of SiO2/Si(001) crystals implanted with Fe+, which were submitted to Ion Beam Induced Epitaxial Crystallization process (IBIEC) and then, annealed. ?:f mappings of the (000)(002)(111) BSD peak gave rise to perpendicular and in-plane lattice parameters and strains for the stressed regions provoked by the ?-FeSi2 nanoparticles formation provided by IBIEC. For another set of similar samples except for the absence of the oxide, the interesting formation of oriented plate-like ?-FeSi2 nanoparticles, that were observed by TEM and confirmed by (002) rocking curves obtained at MD condition for the BSD (111) and (1 peaks and the ?:f mappings that provided anisotropic in-plane strains in IBIEC sample. Nanoparticles spherical-like also detected by TEM induce isotropic strains and the samples structural characterization was obtained using the same above mentioned manner. Measurements of the reciprocal space mapping (RSM) using symmetric and asymmetric reflections were important to confirm the implanted crystal results obtained by MD by allowing to observe the periodic and lateral composition variation in the GaInP layer as well as, to confirm the effect of the height of InP quantum dots grown on the ternary layer in the strain degree they cause in the ternary cap layer, it means, the greater the height the greater the level of strain in the cap layer
Doutorado
Física da Matéria Condensada
Doutor em Ciências

Les récepteurs glutamatergiques de type N-Méthyl-D-Aspartate (RNMDA) jouent un rôle majeur dans de nombreux processus physiologiques, et leur implication dans la physiopathologie de certains troubles neuropsychiatriques tels que la schizophrénie est suggérée par un robuste faisceau de données cliniques et précliniques. Cependant, les mécanismes cellulaires et moléculaires conduisant à une telle dérégulation des RNMDA restent inexpliqués. La diffusion membranaire, mécanisme de contrôle spatial et temporel de la distribution des RNMDA à la surface des neurones, constitue un puissant régulateur de la transmission synaptique. Mon projet de thèse repose ainsi sur l’hypothèse originale qu’une altération de la diffusion de surface des RNMDA jouerait un rôle central dans l’émergence de troubles psychotiques. Afin d‘explorer cette piste, j’ai étudié l’impact de molécules aux propriétés psychomimétiques (i.e induisant un état psychotique) sur la diffusion de surface des RNMDA. Les résultats obtenus au cours de ma thèse démontrent que des molécules psychomimétiques, aux modes d’action distincts (antagonistes du RNMDA et autoanticorps anti-RNMDA), perturbent la diffusion membranaire ainsi que la localisation synaptique des RNMDA, conduisant à terme à des défauts de transmission glutamatergique. Mon travail de thèse propose donc qu’un défaut de diffusion membranaire des RNMDA conduirait à des altérations fonctionnelles pouvant contribuer à l’émergence de troubles psychotiques. L’ensemble de mon travail apporte ainsi un regard nouveau sur la mécanistique des troubles psychotiques et ouvre la voie à de nouvelles pistes thérapeutiques
Glutamatergic N-Methyl-D-Aspartate receptors (NMDAR) play a key role in many physiological processes, and their implication in the pathophysiology of several neuropsychiatric disorders is now well established. Multiple lines of evidence converge towards a dysregulation of the NMDAR in psychotic disorders such as schizophrenia (SCZ). However, the molecular and cellular deficits underlying NMDAR dysfunction remain misunderstood. By tightly controlling NMDAR synaptic localization, surface trafficking represents a powerful regulator of synaptic transmission. Could an alteration of NMDAR surface trafficking underlie NMDAR dysfunction and contribute to the emergence of psychotic disorders? To tackle this question, my PhD project aimed at investigating the impact of different psychotomimetic molecules on NMDAR surface trafficking. In the first part of my project, I explored the impact of NMDAR autoantibodies (NMDAR-Ab) from SCZ and healthy subjects. My results revealed that NMDAR-Ab from SCZ patients rapidly disturb NMDAR synaptic trafficking and distribution, through a loss of NMDAR-EphrinB2 receptor interaction, eventually preventing the induction of synaptic plasticity. In the second part of my PhD project, I showed that psychotomimetic NMDAR antagonists also alter NMDAR synaptic mobility and localization. Downregulation of PSD proteins expression prevented NMDAR antagonists-induced deficits, suggesting that such alterations ensue from modifications of NMDAR intracellular interactions. Taken together, these results demonstrate that psychotomimetic molecules profoundly impact NMDAR surface trafficking, supporting a pathogenic role of this unsuspected process in the emergence of psychotic symptoms

Dans cette thèse, nous nous intéressons à la croissance de boîtes quantiques par formation de nano-trous in-situ par « droplet-etching » ainsi qu’à la fabrication et caractérisation de dispositifs basés sur ces nanostructures. La thèse comporte sept chapitres. Le premier chapitre est une introduction au sujet et les méthodes expérimentales sont présentées dans le second chapitre. Les méthodes de fabrication ainsi que les résultats expérimentaux obtenus sont discutés dans le troisième chapitre.Nous montrons que l’utilisation in-situ de la méthode de droplet-etching permet de modifier localement l’épaisseur d’un puits quantique à modulation de dopage et créer des boîtes quantiques dans le puits où existe un gaz bidimensionnel d’électrons. Ces nanostructures constituent des diodes n-i Schottky que nous avons étudié. Les effets de ces boîtes quantiques non-contraintes et les fluctuations d’épaisseur à l’échelle nanométrique du puits quantique sur la mobilité du gaz bidimensionnel d’électrons sont discutés dans le quatrième chapitre et cinquième. Le sixième chapitre présente la fabrication d’une jonction p-n latérale basée sur l’échantillon de puits quantique avec des boîtes. Nous discutons les différentes étapes de fabrication et analysons leur influence sur le dispositif, ainsi que leurs propriétés optiques. En particulier, nous démontrons l’électroluminescence d’une boîte unique localisée dans une jonction p-n latérale. Finalement, le dernier chapitre conclue ce travail et en présente les perspectives
In this thesis the formation of quantum dots (QD) via in-situ droplet nanohole etching, the fabrication and characterization of devices based on these nanostructures is described. The thesis consists of seven chapters. In the first chapter an introduction is given to present the topic to the reader. In the second chapter the experimental methods are presented. In the third chapter, the fabrication method is described and the experimental results obtained in this project are discussed. It will be shown the use of in-situ droplet etching to locally modify the thickness of a modulation doped quantum well, to create QDs embedded in a quantum well(QW) where a two dimensional electorn gas (2DEG) is confined by modulation doping and the embedding of these nanostructures in a n-i-Schottky diode. The effect of these strain-free dots, and the related nanoscale thickness fluctuations of the quantum well, on the 2DEG mobility are discussed in the fourth and in particular in the fifth chapter. In the sixth chapter, the fabrication of a lateral p-n junction based on the QW sample with embedded QD is presented. Following describing the fabrication stages and analysing the influence of each stage on the device, the optical properties of the junction will be discussed. In particular, it will be shown the electroluminescence of a single dot located at lateral the p-n junction. Finally, in the last chapter the conclusion of this work and the future projects are presented

Dans cette thèse, nous nous intéressons à la croissance de boîtes quantiques par formation de nano-trous in-situ par « droplet-etching » ainsi qu’à la fabrication et caractérisation de dispositifs basés sur ces nanostructures. La thèse comporte sept chapitres. Le premier chapitre est une introduction au sujet et les méthodes expérimentales sont présentées dans le second chapitre. Les méthodes de fabrication ainsi que les résultats expérimentaux obtenus sont discutés dans le troisième chapitre.Nous montrons que l’utilisation in-situ de la méthode de droplet-etching permet de modifier localement l’épaisseur d’un puits quantique à modulation de dopage et créer des boîtes quantiques dans le puits où existe un gaz bidimensionnel d’électrons. Ces nanostructures constituent des diodes n-i Schottky que nous avons étudié. Les effets de ces boîtes quantiques non-contraintes et les fluctuations d’épaisseur à l’échelle nanométrique du puits quantique sur la mobilité du gaz bidimensionnel d’électrons sont discutés dans le quatrième chapitre et cinquième. Le sixième chapitre présente la fabrication d’une jonction p-n latérale basée sur l’échantillon de puits quantique avec des boîtes. Nous discutons les différentes étapes de fabrication et analysons leur influence sur le dispositif, ainsi que leurs propriétés optiques. En particulier, nous démontrons l’électroluminescence d’une boîte unique localisée dans une jonction p-n latérale. Finalement, le dernier chapitre conclue ce travail et en présente les perspectives
In this thesis the formation of quantum dots (QD) via in-situ droplet nanohole etching, the fabrication and characterization of devices based on these nanostructures is described. The thesis consists of seven chapters. In the first chapter an introduction is given to present the topic to the reader. In the second chapter the experimental methods are presented. In the third chapter, the fabrication method is described and the experimental results obtained in this project are discussed. It will be shown the use of in-situ droplet etching to locally modify the thickness of a modulation doped quantum well, to create QDs embedded in a quantum well(QW) where a two dimensional electorn gas (2DEG) is confined by modulation doping and the embedding of these nanostructures in a n-i-Schottky diode. The effect of these strain-free dots, and the related nanoscale thickness fluctuations of the quantum well, on the 2DEG mobility are discussed in the fourth and in particular in the fifth chapter. In the sixth chapter, the fabrication of a lateral p-n junction based on the QW sample with embedded QD is presented. Following describing the fabrication stages and analysing the influence of each stage on the device, the optical properties of the junction will be discussed. In particular, it will be shown the electroluminescence of a single dot located at lateral the p-n junction. Finally, in the last chapter the conclusion of this work and the future projects are presented

La détection de lumière dans une large gamme de longueur d’onde allant de l’UV au proche infrarouge est réalisée avec une sensibilité importante en utilisant l’effet d’amplification amené par un transistor à effet de champ et la capacité de détection dans une grande gamme de longueur d’onde amenée par des nanoparticules de CdSe et de PbS de diamètres différents. Dans une première partie, un FET utilisant une couche active de nanofils de ZnO est fabriqué. La détection de lumière UV-Vis est assurée en enrobant ces nanofils par un mélange de nanoparticules de CdSe et d’oxyde de graphène. L’oxyde de graphène assure une bonne transition des électrons crées par la lumière dans le CdSe vers le ZnO. La photo-réponse obtenue, supérieure à 104 A/W à 350 nm, a été multipliée par un facteur 100 dans la gamme 200-500nm en utilisant l’oxyde de graphène. Dans une seconde partie, la détection de lumière infrarouge a été assurée par des nanoparticules de PbS incorporées dans un transistor organique de type N utilisant du C60 comme couche active. Les électrodes en argent de ce transistor et son isolant de grille en photorésine SU8 sont déposés par impression. Les nanoparticules sont déposées en solution à l’interface entre le semiconducteur et l’isolant de grille. Ce phototransistor incorporé dans un inverseur a montré l’apparition d’un signal de sortie de 2V dû à l’application d’une lumière de 1050 nm de longueur d’onde et de 250 µw/cm2 de puissance
Detection of light in large wavelength range, from the UV to NIR, is got with high sensitivity by using the amplification of a field effect transistor and the ability of light detection in large range by CdSe and PbS quantum dots with different diameters. In the first part, a FET with ZnO nanowires active layer is fabricated. The light detection in UV-Vis range is insured thanks to CdSe QDs/RGO (Reduced Graphene Oxide) fragments decorating the surface of the ZnO nanowires RGO insures good transfer of photo-electrons induced by the light into the CdSe QDs towards ZnO. The responsivity, higher than 104 A/W at 350 nm, has been improved by 100 in 200-500 nm range by using RGO. In the second part, IR light detection has been insured by using PbS QDs embedded in N-type Organic FET using C60 film as active layer. Silver electrodes of this transistor and its SU8 photoresist gate insulator have been printed. QDs have been deposited in solution at the interface between the semiconducting layer and the gate insulator. This phototransistor has been used in an inverter. The output voltage of the inverter change by 2V under lighting with 1050 nm wavelength and 250 µW/cm2 power

Lors des processus développementaux d'élongation axonale et de synaptogenèse, les protéines d'adhésion telles les cadhérines ou les Ig-CAM jouent des rôles fondamentaux en permettant la formation de contacts entre neurones. Pour étudier la dynamique de ces contacts et leurs rôles dans ces processus, nous avons mis en œuvre des techniques d'imagerie sur des neurones primaires d'hippocampe (clivage thrombine, FRAP, pinces optiques, quantum-dots), ceux-ci étant associés à un système semi-artificiel de microsphères recouvertes de protéines d'adhésion purifiées (N-cadhérine et L1). En utilisant une construction L1 portant une étiquette GFP extracellulaire clivable à la thrombine, j'ai pu précisé l'implication des processus de diffusion membranaire et d'exo- endocytose dans la dynamique des contacts L1-dépendants et obtenir des données quantitatives relatives à l'interaction homophile L1. J'ai également contribué à caractériser la liaison extracellulaire entre N-cadhérine et GluR2, sous-unité des récepteurs AMPA, et l'influence de l'expression de la N-cadhérine sur la mobilité de GluR2. L'interaction entre ces deux protéines pourrait être impliquée dans la formation et/ou la maturation des synapses.

Nous presentons une etude structurale de depots epais de gan sur alumine et d'heterostructures gan / al#xga#1#-#xn de basse dimensionnalite. Les systemes etudies ont ete elabores par epitaxie par jet moleculaire (mbe) ou par depot en phase vapeur d'organo-metalliques (mocvd). La technique d'investigation est la microscopie electronique a transmission, utilisee en modes conventionnel, haute resolution et faisceau convergent. La premiere partie de l'etude traite de la croissance optimisee de couches de gan sur substrat d'alumine. La polarite des depots est le parametre clef de cette croissance. En effet, la presence de domaines d'inversion de polarite ga dans une matrice a polarite n provoque une croissance sous forme d'ilots hexagonaux, tandis qu'une matrice a polarite ga assure une surface de croissance lisse. Les depots realises contiennent tous des dislocations en grande densite (10#+#1#0/cm#2), dont les vecteurs de burgers sont egaux a 1/3 <2,1,1,0>, 1/3 <2,1,1,3> et 0001. Des nanotubes sont formes par l'ouverture locale du coeur de dislocations 0001. Des defauts prismatiques 2,1,1,0 et 0,1,1,0 ont aussi ete observes. Les derniers forment les parois des domaines d'inversion de polarite et introduisent une translation de 1/20001 entre les cristaux de polarites opposees. Dans une seconde partie, differentes heterostructures gan / al#xga#1#-#xn (puits, super-reseaux et boites quantiques) sont etudiees a l'echelle atomique par analyse quantitative des images haute resolution. L'epitaxie de gan sur al#. #1#5ga#. #8#5n reste coherente pour 16 monocouches deposees. Par contre, une relaxation partielle apparait dans un super-reseau gan / aln dont les couches ont une epaisseur superieure a 11 monocouches. Les heterostructures aln / gan sont caracterisees par une faible miscibilite et des interfaces relativement abruptes. Selon la temperature, les couches de gan deposees sur aln adoptent un mode de croissance bidimensionnel ou de type stranski-krastanov. Ce dernier mode de croissance permet le confinement d'ilots de gan dans aln et ouvre la voie a la realisation de boites quantiques.

Ce travail a porte sur la croissance epitaxiale des nitrures d'elements iii gan, aln, et inn, en utilisant l'epitaxie par jets moleculaires assistee par plasma d'azote. Nous avons optimise les premiers stades de la croissance de gan ou aln sur substrat al#2o#3 (0001). Le processus utilise consiste a nitrurer la surface du substrat a l'aide du plasma d'azote, afin de la transformer en aln, puis a faire croitre une couche tampon d'aln ou de gan a basse temperature, avant de reprendre la croissance de gan ou aln a haute temperature (680 a 750c). Nous avons en particulier etudie les proprietes d'une couche de gan en fonction de la temperature a laquelle est realisee l'etape de nitruration. Lorsque les conditions de demarrage de la croissance sont optimisees, nous avons pu observer des oscillations de rheed pendant la croissance de la couche de gan. Nous avons etudie l'effet du rapport v/iii sur la morphologie de surface et les proprietes optiques et structurales de cette couche. Nous avons propose l'utilisation de l'indium en tant que surfactant pour ameliorer ces proprietes. Nous avons ensuite aborde la realisation de superreseaux gan/aln dont nous avons optimise les interfaces. Les mecanismes de relaxation des contraintes de aln sur gan et gan sur aln ont ete etudies. Nous avons egalement elabore les alliages algan et ingan, comme barrieres quantiques dans les heterostructures. Nous avons montre que la relaxation elastique des contraintes de gan en epitaxie sur aln donne lieu a la formation d'ilots de tailles nanometriques, qui se comportent comme des boites quantiques. Leur densite et leur taille dependent de la temperature de croissance, et des conditions de murissement apres croissance. Les proprietes optiques de ces ilots sont gouvernees a la fois par les effets de confinement quantique et par le fort champ piezo-electrique induit par la contrainte dans les ilots.

碩士
國立臺灣大學
電信工程學研究所
102
A model of solar cell embedding quantum dots in the intrinsic layer of a p-i-n solar cell has been presented. With proper selection of material, size and fractional volume, quantum dots can provide an intermediate band between the valence and the conduction bands of the matrix material, which will absorb photons with energy lower than the original bandgap to absorb more incident photons in the otherwise unsed spectral irradiance. The design approach to acquire the highest efficiency of the conventional p-i-n solar cell is presented as a benchmark. Quantum dots are then embedded in the intrinsic region of the reference solar cell to improve its efficiency. InAs is chosen to implement the quantum dots, to be embedded in the p-i-n solar cell made of GaAs. With a more packed arrangement of QD’s from that in the literatures, the simulation results shows that the efficiency of the conventional GaAs p-i-n solar cell can be increased by 1.05%.

碩士
國立中興大學
材料科學與工程學系所
107
In this study, hollow structure of SnO2 nanoparticles (SnO2 HS) have prepared by hydrothermal method. The SnO2/PANI nanocomposites were synthesis by in-situ polymerization and SnO2/PANI/NGQD ternary nanocomposites were successfully synthesis by electrostatic self-assembly approach. The prepared SnO2/PANI/NGQD was used for electrode materials of dopamine (DA) electrochemical sensor. The products of the SnO2、PANI、SnO2/PANI及SnO2/PANI/NGQD nanocomposites were characterized by SEM、TEM、XRD、FTIR . The electrochemical response of dopamine was determined by using cyclic voltammetry and different pulse voltammetry. For the SnO2/PANI system, the result of SEM image shows the particle size of SnO2/PANI nanoparticles decrease when the SnO2 nanoparticles increase. Obviously, the surface area increase when the SnO2 nanoparticles increase. Because of excess SnO2 nanoparticles, the size of SnO2/PANI was increase. In other words, the electrochemical current value of 5wt% SnO2/PANI (5SP) was the largest because it has the smallest size. In cyclic voltammetry, the peak current of PANI is 26μA and the peak current of 5SP is 45μA. In the system of 5SP with n-doped graphene quantum dots (N-5SP), the electrochemical response of DA by using cyclic voltammetry and differential pulse voltammetry in PBS solution. In CV mode, the peak current was increase to 55μA when the modify electrode was N-5SP. In DPV mode, the linear detection ranges for DA are 0.5-200μM (R2=0.98) and the detection limits was 0.42μM (S/N=3). Besides, the electrochemical response of this modify electrode was also determined with dopamine, ascorbic acid and uric acid in PBS solution. In DPV mode, the linear detection ranges for AA, DA and UA are 20-200μM (R2=0.98). The oxidation peak of AA, DA and UA are -50mv, 110mv and 260mv respectively. The separation of the oxidation peak potentials for AA-DA, DA-UA and AA-UA were 160mv, 150mv and 310mv, which shows the ability of anti-interference of the modify electrode. Furthermore, the result shows that the modify material of N-5SP has perfect electro catalytic properties for dopamine.

碩士
國立交通大學
電子物理系
91
Photoluminescence is used to study the optical properties of self-assembled InAs/GaAs quantum dots (QDs) with different N incorporation and InAs deposition thickness. The emission wavelength can be increased to 1344nm by incorporating 1% N into In0.14Ga0.86As quantum well, but PL intensity becomes weaker. Besides, incorporating N into QDs makes the quality much worse. For small deposition of 1.98ML, a large FWHM at 50K is observed, implying a relatively poor confinement for electrons in such small-size QDs. When temperature increase, we observe a significant red shift and a decrease of FWHM due to the transfer of the electrons from relatively small-size to large-size QDs. By increasing the InAs deposition to 2.34ML and 2.7ML, the emission wavelength increases to 1311nm. The small FWHM at 50K and its temperature insensitivity suggest a good electron confinement. However, when the InAs deposition thickness increases beyond 2.7ML, the QD emission wavelength shows no increase, instead, two groups of different wavelength QDs, one emits at 1223nm and the other at 1300nm, are observed. The quality of the short-wavelength QDs is comparable to the 1.98ML sample in which the QDs emit at a similar wavelength. Nevertheless, when the temperature increases beyond 200K, the FWHM drastically increases. We speculate this abnormal increase of FWHM by that the electrons excitation to first excited state at high temperature and undergo a nonradiative recombination through relaxation-induced defect states. Finally, from the relationship between PL intensity and temperature, we can obtain the activation energy which is found to be inverse proportional the emission wavelength. The obtained activation energy is consistent with the energy separation between the ground state and first excited state according Grundmann’s theory. Hence, we conclude that the decrease in intensity with increasing temperature is due to the carrier excitation from the ground state to first excited state.

碩士
元智大學
化學工程與材料科學學系
106
Sulfur and nitrogen co-doped graphene quantum dots (SN-GQDs) were synthesized through an efficient pyrolysis of citric acid, urea and ammonium sulfate and served as a highly selective probe for sensing of Hg2+ ions in aqueous solution. The pyrolysis technique is capable of preparing SN-GQDs and N-doped graphene quantum dots (N-GQDs) within a short period. The bean sprouts and celery grown in SN-GQD solution can emit blue light under 360-nm UV irradiation, indicating the permeation throughout the plant cell with good bio-compatibility. The fluorescence (FL) intensity of both GQDs shows a decreasing function of concentration of Hg2+ ions. The sensitivity of SN-GQD offers 4.23 times higher than that of N-GQD, based on the calculation of Stern-Volmer equation. One inter-band gap structure of SN-GQDs for the detection toward mercury ions is proposed. The S doping can coordinate with phenolic groups on the edge of SN-GQDs (i.e., the formation of (CxO)2Hg2+) and induce the cutting off or alleviation of photon injection paths, thereby leading to significant FL quenching. This work proves that SN-GQD offers a potential feasibility for probing the quality of drinking water.

碩士
元智大學
化學工程與材料科學學系
107
This study adopts an efficient pyrolysis of citric acid and urea to synthesize carbon quantum dots for detection of various metal ions in aqueous solutions. Two kinds of CQDs: N-doped and N-/S-doped CQDs, namely, N-CQD and SN-CQD, are found to emit fluorescence (i.e., blue and green light) under ultraviolet irradiation (360 nm). Both CQDs show a super hydrophilicity and they are thus uniformly dispersed in aqueous solutions. The fluorescence quenching of both CQD suspensions can be viewed in the presence of metal ions, i.e., Na+, K+, Fe2+, and Pb2+. Interestingly, the ratio of fluorescence intensity from NCQD suspension shows a decreasing function of ionic concentration for all metal ions, whereas SN-CQD suspension displays the excellent selectivity and sensitivity toward Fe2+ ions. This improved performance of SN-CQD suspension can be attributed to the presence of S-containing groups that provide a strong affinity interacted with Fe2+ ions, inducing a specific interaction and resulting in the fluorescence quenching. Accordingly, it can be concluded that SN-CQD sample can be considered as a promising candidate to specifically detect industrial and biological wastewater.

碩士
國立交通大學
電子研究所
101
Embedding quantum dots in the i-region of the GaAs p-i-n solar cells(SC), we change the quantum dot parameters one at a time to understand how does quantum dot affect the performance of quantum dot solar cells(QDSC).First, we construct the model of QDSC .By studying the theory of quantum dot absorption coefficient, the fabrication of quantum dot and the device structure, we can conclude that there are six quantum dot parameters: size, volume fluctuation, shape, materials, surface density, and spacer thickness .We alter quantum dot parameters to understand whether the particular parameter will increase the SC efficiency or not .This can also shows that how it changes open circuit voltage, short circuit current, and current density-voltage curve .And we compare the efficiency to the traditional GaAs p-i-n SC .After that, we construct a QDSC model which has quantum dots with two materials .Using the model to study under different conditions what will happen to the SC efficiency. Through the absorption coefficient intensity and absorption wavelength distribution, we analyze the variation on the SC efficiency and compare it to the single type quantum dot SC and the traditional GaAs SC. At last we can sum up that the influence degree of each quantum dot parameter on efficiency is: surface density ≧ size ＞size fluctuation ＞spacer thickness. Besides, to have the maximum efficiency of the two materials quantum dot SC, we need to consider the combination of quantum dot absorption coefficients, the match between the absorption coefficient intensity and the light flux distribution, and we can also increase the stack number of the quantum dots with better absorption.

This thesis presents a novel method for the preparation of quantum dot-thermoresponsive polymer nanocomposite hydrogels. The quantum dots (QD’s) were synthesized in a microwave reactor using a high temperature organometallic synthesis procedure. The initial hydrophobic surface layer on the QD’s was coated with an amphiphilic polymer to enable phase transfer from non-polar solvent to water followed by physical immobilization of the QD’s in the thermoresponsive polymer hydrogel by photopolymerization. Their temperature dependent emission properties were investigated as a function of concentration of the incorporated QD’s. The resultant temperature dependent changes in the position of the peak emission wavelength of the QD-polymer nanocomposite hydrogels were found to be due to the change in the physical environment causing increased interaction between the embedded amphiphilic polymer coated QD’s and/or due to aggregation of QD’s. This change in peak emission position was found to be reversible in the temperature range from 29 to 37 °C.

碩士
國立清華大學
化學系
103
Graphene quantum dots (GQDs) are nano-sized materials having unique properties like the quantum confinement effect and edge effect which has led to its emergence in fluorescence-based applications. The low toxicity, high solubility, chemically inertness, and stable luminescent properties of GQDs must be explored further for its application in sensors and bio imaging studies. A one-pot synthesis of GQDs based on the bottom-up approach has been developed in this study with citric acid and amino acids（glycine、cysteine） precursors to successfully achieve two N-doped Graphene Quantum Dots (N-GQD). In this reaction, amino acid plays dual role of donating both carbon and nitrogen atom. These as-prepared N-GQDs have a high quantum yield of 14（glycine） and 58%（cysteine） as compared to previously reported GQDs. The final product has been characterized using FT-IR, PL, TEM, UV-Vis, XPS, and AFM, which shows successful nitrogen doping as GQDs. These highly fluorescent N-GQDs have been used for faster sensing of tetracycline in honey, making this, a green method as it does not involve the use of any toxic reagent. The detection is based on the on-off mechanism and fluorescent control of N-GQDs. The sensing is primarily based on a π-π stacking interaction between N-GQD and tetracycline by quenching the fluorescence of N-GQDs. Detection of honey has been carried out using a standard addition method. A detection limit of 4 μg·L−1, recovery of 77-112%, and a relative standard deviation of 14.5% is a proof to a highly sensitive detection. Further, rapid detection of 21 commercial honey samples has been carried out, of which, four samples have been found with the presence of tetracyclin.

碩士
國立成功大學
化學工程學系碩博士班
94
Light-emitting diodes (LEDs) have the advantages of no mercury pollution and high emission efficiency. Developments of LEDs not only serve to improve the disadvantages of traditional illuminants but also save the energy and protect the environment of the world. This research is speculation manufacture QD LED. Make use the high performance luminescence and limit the quantum confinement effect to control the luminescence color of QD In this study, n-CdS/p-CdSe QDs are synthesized by sol-gel method assisted with microwave heating. The influences of microwave heating time, using the solution with the different molar ratio S/Cd and Cu-doped on the size of CdS QD were investigated. The QD thin films were fabricated using an electrospray assisted an electrostatic collector from QD/ethanol solution. Particles were collected at a specific location for a specific voltage according to their mobility. The size distribution of QD were analyzed by SMPS (Scanning Mobility Particle Sizer) and TEM. The nanostructure and crystallization of the thin film were analyzed by means of XRD and SEM. In addition, the optical and electric properties were measured by PL and CL. The UV fluorescent was observed emitted lights of QD films.

碩士
國立中央大學
電機工程研究所
97
The main purpose of this thesis is to investigate how to improve the photoresponse of poly-Si TFTs with Ge QDs using SPC of a-Si in channel fabrication. We have successfully demonstrated that the photoresponse of poly-Si TFTs could be enhanced by a factor of 2 by incorporating Ge QDs into the gate oxide. However we know that a polycrystalline silicon film deposited by LPCVD system (as-deposited poly-Si) at 620 oC has smaller grains and more grain boundaries. Grain boundaries in the channel behave like traps to reduce the carrier mobility, and carrier lifetime. Consequently, active carriers excited from Ge QDs under illumination injected into channel are more likely recombined by the trap, leading to a less photocurrent enhancement. In this thesis, we employ a crystallization method, solid-phase-crystallization of amorphous silicon (SPC of a-Si) annealing at 550 oC for 24 hours, to increase the grain size and reduce the numbers of grain boundaries to increase the photocurrent in TFTs incorporating Ge QDs in the top-gate dielectric.

碩士
國立臺灣科技大學
材料科學與工程系
100
In this work, Br-PPO was fabricated through bromination of PPO. Then we used electrospinning to prepare nanofiber structure. Proparyl-PNIPAAm was polymerized by atom transfer radical polymerization (ATRP) and grafted to modified electropsinning fiber with azide group by click chemistry (Copper-catalyzed Azide-Alkyne Cycloaddition, CuAAC). Finally, we synthesized ZnS quantum dots, and PNIPAAm was immersed in the quantum dots. It can form hydrogen bond between both of them. The successful synthesis of Br-PPO, N3-PPO, PPO-PNIPAAm was demonstrated via FTIR and ESCA analysis. Then we used SEM and TEM to observe the diameter of electrocspinning increased from 320 nm to 385 nm. Thus, we verified that the Propargyl-PNIPAAm was grafted to the electrocspinning successfully. the hydrophilic property of PNIPAAm changed contact angle from 130° to 25°. Then we used the thermoresponsive Propargyl-PNIPAAm to absorbed and released ZnS to demonstrate that ZnS was released above LCST from UV-ViS and PL analysis. And we also used SCMS, TEM and EDS mapping to confirmed the distribution of ZnS on the electrospinning. Therefore from this study we fabricated the nanofiber with blue fluorescence successfully.