One-dimensional and hierarchical nanostructures have acquired tremendous attention in the past decades due to their possible application. In spite of the rapid emergence of new morphologies, the underlying growth mechanism is still not well understood. The lack of effective p-type or n-type doping is another obstacle for many semiconducting nanomaterials. A deeper investigation into these structures and new methods to fabricate devices are of significant impact for nanoscience and nanotechnology. Motivated by a desire to understand the growth mechanism of nanostructures and investigate novel device fabrication method, the research described in this thesis carried out on the synthesis, characterization, and device fabrication of semiconducting nanostructures. The main focus of the research was on ZnO, SnO2, and Zn3P2 for their great capability for fundamental phenomena studying, promising applications in sensors and optoelectronics, and the potential generalization of results to other materials. Within this study the following goals have been achieved: 1) Improved understanding of polar-surface-induced growth mechanism in wurtzite-structured ZnO and generalization of this growth mechanism with the discovery and analysis of rutile ¨Cstructured SnO2, 2) observation of the significance of the transversal growth, which is usually ignored, in interpenetrative ZnO nanowires, 3) rational design and growth control over versatile nanostructures of ZnO and Zn3P2, and 4) conjunction of p-type Zn3P2 and n-type ZnO semiconducting nanostructures for device fabrications. The framework for the research is reviewed first in chapter 1. Chapter 2 gives the detailed experimental setup, synthesis procedure, and common growth mechanism for nanostructure growth. A detailed discussion on the growth of ZnO nanostructures in chapter 3 provides more insight into the polar-surface-induced growth, transversal growth, vapor-solid growth, and vapor-liquid-solid growth during the formation of nanostructures. Polar-surface-induced growth is also confirmed in the growth of SnO2 nanostructures, which is also included in chapter 2. Chapter 3 presents Zn3P2 nanostructures from the newly designed experiment setup and the device fabrication from ZnO and Zn3P2 crossed nanowires.

To date, the search efforts have shifted from the toxic II-VI, III-V and IV-VI semiconductors to more environmentally friendly materials. Among Group II-V semiconductors, Zn3P2 has shown to be a more benign option, similar to Group IV (Ge, Si) materials, for future applications in photovoltaics and optoelectronics. This work is dedicated to the development of wet-chemical synthetic routes of (1) Zn3P2 and (2) Group IV (Ge, Si, Si1-xGex) nanocrystals with precise control over composition, crystal structure, size and dispersity by adjusting different reaction parameters such as temperature, time and solvent composition. Different characterizations will also be employed to probe the size- and composition-dependent physical and optical properties of resulting products. The first part of this work illustrates the synthesis of luminescent Zn3P2 nanocrystals, an earth-abundant and a direct-gap semiconductor possessing high absorption coefficient and long carrier diffusion length, which uphold promising potential in many optoelectronic applications. A hot injection method by using highly reactive P and Zn precursors (P[Si(CH3)3]3 and diethyl zinc) in hexadecylamine and octadecene was developed to prepare a series of alkyl-amine-passivated tetragonal Zn3P2 crystallites with varying size sizes. Substantial blue shifts in the absorption onsets (2.11−2.73 eV) in comparison to the bulk counterpart (1.4−1.5 eV) and a clear red shift with increasing particle size indicates the quantum confinement effects. This is also consistent with the photoluminescent studies with the size-tunable maxima in the visible region (469−545 nm) as a function of growth temperature and time. The phase purity and alkyl-amine passivation of the nanocrystals were determined by structural and surface analysis, confirming the presence of N–Zn and N–P bonds on the tetragonal Zn3P2 crystallites. The second part of this works focuses on the development of a colloidal synthetic strategy of alkyl-amine capped Si1-xGex nanocrystals with control over size- and composition-dependent optical properties. Despite their high miscibility at all compositions, developing a wet-chemical synthesis of Si1-xGex alloys in the nanoscale remains a challenging task, owing to the difference of their crystallization temperatures and the high surface oxidation of Si. Thus an adapted colloidal method is utilized to fabricate single-element Ge and Si nanocrystals. Powder X-ray diffraction indicates successful production of cubic crystalline Ge and amorphous Si nanoparticles individually in oleylamine/octadecene (surfactant/solvent) mixture at 300°C. Absorption onset values of 1.28 eV and 3.11 eV are obtained for resulting Ge and Si colloids, respectively. By alloying these two materials in their nano-regime, tunable optical properties can be achieved throughout the visible to the near IR region by simply varying their elemental compositions. The success of this bandgap engineering process offers more options for new material design by taking advantage of unique properties from each component material.

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Ce travail de thèse porte sur la synthèse organo-métallique de nanoparticules (NPs) semi-conductrices colloïdales de phosphures d’indium (InP), de zinc (Zn3P2) et de structures cœur/coquille obtenues par la croissance d’une couche de sulfure de zinc (ZnS) à la surface des NPs. Les objectifs consistent à comprendre et maîtriser la synthèse dans le but de décaler les longueurs d’onde d’absorption et d’émission vers le proche infra-rouge, domaine spectral intéressant pour l’imagerie biomédicale.Le premier chapitre présente l’état de l’art sur les nanocristaux (NCx) d’InP et d’InP/ZnS. Un bref rappel sur les propriétés physico-chimiques des NCx semi-conducteurs est présenté et différentes synthèses sont décrites. Une attention toute particulière a été portée sur la taille des NCx, le décalage de l’émission de fluorescence vers les plus grandes longueurs d’onde et l’optimisation des rendements quantiques. Les potentialités offertes par ces objets soit pour les diodes électroluminescentes (LED) blanches soit pour l’imagerie biomédicale montrent l’intérêt d’utiliser les NCx de type InP/ZnS plutôt que d’autres matériaux à base d’éléments toxiques (Cd, Pb, …).Le deuxième chapitre porte sur une synthèse à partir des carboxylates d’indium connue de la littérature. Le but est alors de caractériser la structure des NPs pour comprendre le déroulement de la synthèse et de l’enrobage. Des mesures par résonance magnétique nucléaire (RMN) en phase solide et spectroscopie photo-électronique par rayons X (XPS) révèlent l’oxydation des NPs d’InP. La couche d’oxyde qui se forme durant la synthèse des NPs d’InP s’épaissit lors de l’enrobage. Cette oxydation provient d’un couplage décarboxylant des acides carboxyliques à haute température en présence des NPs. Elle serait à l’origine de l’inhibition de croissance des objets, ce qui limiterait les gammes de longueurs d’onde atteignables.Le troisième chapitre concerne une nouvelle synthèse à partir d’amidinate d’indium au lieu des carboxylates d’indium. L’intérêt de cette approche est la possibilité d’abaisser considérablement la température de réaction (150°C au lieu de 280°C) et ainsi d’éviter la réaction secondaire de décarboxylation. Un enrobage à basse température (150°C) est aussi mis en place. La synthèse induit également une oxydation de la surface des NPs d’InP. Un nouveau couplage a lieu entre les ligands, l’acide palmitique et l’hexadécylamine, et donne de nouvelles conditions oxydantes. Le jeu sur les ratios des ligands montre qu’en bouleversant le milieu réactionnel, les NPs d’InP ne présentent pas de réponse en luminescence concluante. La synthèse et l’enrobage sont alors réalisés sous atmosphère de dihydrogène (H2) en réacteur Fisher-Porter dans le but de contrer ces conditions oxydantes. La synthèse et l’enrobage donnent des tailles de NPs de l’ordre de 3,4 nm (condition nécessaire pour s’approcher d’une émission dans l'infra-rouge) et un rendement quantique de 18-20 %, résultats encore jamais atteints lors de cette thèse.Le dernier chapitre est consacré à une étude exploratoire sur les NPs de Zn3P2. Le phosphure de zinc est un matériau prometteur du fait de l’abondance de ses constituants non toxiques et des longueurs d’onde potentiellement accessibles. Différents paramètres de synthèse sont étudiés et les propriétés structurales et optiques sont caractérisées. Des résultats préliminaires sur l’enrobage montrent des difficultés liées à la stabilité des NPs de Zn3P2. L’utilisation de l’oxyde de trioctylphosphine (TOPO) semble permettre la passivation de ces NPs à l’air et en travaillant sous H2 une meilleure stabilité est envisageable / Résumé de la thèse en anglais : This PhD investigation focuses on organometallic synthesis of indium phosphide (InP), zinc phosphide (Zn3P2) colloidal semiconductor nanoparticles (NPs) and core/shell structures which were obtained by the growth of a layer of zinc sulfide (ZnS) on the surface. The objectives are to understand and control the synthesis in order to shift the absorption and emission wavelengths to the near infra-red range, interesting for biomedical imaging.The first chapter presents the state of the art on the InP and InP/ZnS nanocrystals (NCx). A brief recall on the physical and chemical properties of semiconductor NCx is presented and various syntheses are described. Particular attention was paid to the size of NCx, the shift of the fluorescence emission to higher wavelengths and the optimization of quantum yields. The potential of these objects for white light emitting diodes (LED) or biomedical imaging shows the value added of using InP/ZnS NCx rather than other materials based on toxic elements such as cadmium, lead elements…The second chapter focuses on a synthesis from indium carboxylates known in the literature. The goal is to characterize the structure of NPs to understand the procedure of the synthesis and the coating. Measurements by Nuclear Magnetic Resonance (NMR) in solid state and Photoelectronic X-ray spectroscopy (XPS) revealed the oxidation of InP of the NPs. This oxide layer increases during the coating. This originates from a decarboxylating coupling of carboxylic acids at high temperature in the presence of NPs. This oxidation is believed to inhibit the growth of the object, which restricts the attainable range of wavelengths.The third chapter provides a novel synthesis from indium amidinate instead of indium carboxylate. The advantage of this approach is the potential to lower significantly the reaction temperature (150°C instead of 280°C) and to avoid secondary decarboxylation reaction. A coating with ZnS at low temperature (150°C) is also developed. The synthesis of InP NPs also causes an oxidation of the surface. A coupling takes place again between the ligands, palmitic acid and hexadecylamine providing new oxidizing conditions. The study of different ratios of ligands shows that when the reaction medium is modified, the InP NPs do not exhibit a conclusive luminescence response. Synthesis and coating are carried out under an atmosphere of hydrogen (H2) in Fisher-Porter reactor in order to counter these oxidizing conditions. NPs with diameters of the order of 3,4 nm (a necessary condition to approach the infra-red emission) and a quantum yield of 18-20% are thus obtained. These had never been observed before during this thesis.The last chapter is devoted to an exploratory study on Zn3P2 NPs. Zinc phosphide is a promising material because of non-toxic and abundant constituents, and potential access to near infra-red wavelengths. Different synthesis parameters are studied and the structural and optical properties are characterized. Preliminary results on the coating show instabilities of the Zn3P2 NPs. The use of trioctylphoshine oxide (TOPO) appears to allow the passivation of the NPs in the air and a better stability is possible under an atmosphere of H2