Synthesis and characterization of II-IV quantum dots and their assembly into 3D quantum dot superlattices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1995.Includes bibliographical references (p. 160-161).by Christopher Bruce Murray.Ph.D

Nanoparticle Engineering for Chemical-Mechanical Planarization

Increasing reliance on electronic devices demands products with high performance and efficiency. Such devices can be realized through the advent of nanoparticle technology. This book explains the physicochemical properties of nanoparticles according to each step in the chemical mechanical planarization (CMP) process, including dielectric CMP, shallow trend isolation CMP, metal CMP, poly isolation CMP, and noble metal CMP. The authors provide a detailed guide to nanoparticle engineering of novel CMP slurry for next-generation nanoscale devices below the 60nm design rule. This comprehensive text also presents design techniques using polymeric additives to improve CMP performance

Colloidal Synthesis of Lead Halide Perovskite Nanocrystals for Optoelectronic Application

Colloidal Synthesis of Lead Halide Perovskite Nanocrystals for Optoelectronic Applicatio

Optical and Structural Studies of Shape-Controlled Semiconductor Nanocrystals and Their Self-Assembled Solids

Colloidal nanocrystals are prominent candidates to displace current electronic active layers in solid-state device technologies and offer a body of physics which diverges from those of bulk materials and discreet molecules. Realizing the potential of colloidal nanocrystals may transform the costs and performance of common technologies, but understanding of the relationship between particle size, shape, uniformity, and composition and outputs like physical properties or device performance is often incomplete. This work uses the controlled synthesis of anisotropic colloidal nanocrystals to implement characterization techniques including X-ray diffraction and simulation, which allows an ensemble-level description of particle structure, as well as polarized and time-resolved spectroscopy, which demonstrates subtle synthetic control over the properties of quantum-mechanical wavefunctions. Time- and temperature-resolved optical spectroscopy is employed to analyze the behavior of nanocrystal samples under more realistic device operating conditions and to determine the structure/property relationships that underpin improved performance. Highly-uniform samples of colloidal nanocrystals are self-assembled into large-area thin films. Discussion of self-assembly is placed within the context the fundamentals of self-assembly processes and the roadmap to high-performance devices based upon colloidal nanocrystals. X-ray diffraction and microscopic analysis are performed to analyze and qualify the structure of self-assembled films. These measurement techniques provide figures of merit for nanocrystal assemblies including the sample crystallinity and purity, surface coverage, homogeneity. Diffraction analysis is further used to measure alignment of nanocrystal assemblies with respect to a substrate and the orientation of individual particles within assemblies. Monodisperse anisotropic building blocks encode the unique optoelectronic properties of isolated nanocrystals into solid state materials with long-range structural orientation

Croissance catalysée de nanofils de ZnSe avec boîtes quantiques de CdSe

Des nanofils de ZnSe catalysés avec de l'or ont été synthétisés pour la première fois sur pseudo-substrats de ZnSe déposé sur GaAs. La nucléation de l'or a été étuidiée en détails. Des nanoparticules d'or de diamètres homogènes ont été produites. Ces nanoparticules conduisent à la création de nanofils de diamètres de l'ordre des diamètres de Bohr des excitons dans le ZnSe et dans le CdSe. Les très basses densités de nanoparticules d'or obtenues permettent la croissance de nanofils de ZnSe dans un mode non-compétitif. La croissance a été étudiée en fonction de la variation de certains paramètres. Un rapport de flux élevé de Se:Zn~4, ainsi qu'une température aux alentours des 400C donnent lieu aux nanofils les plus droits. Les nanofils résultant de ces conditions sur ZnSe (001) s'orientent selon deux axes. La vitesse de croissance des nanofils peut être modélisée par la diffusion d'adatoms vers l'interface de croissance du nanofil. Il est démontré à l'aide d'observations RHEED que la croissance se déroule dans un mode vapeur-solide-solide (VSS), c'est à dire, avec un catalyseur à l'état solide. Une croissance dans le mode ALE produit des nanofils orientés selon un seul axe. L'incorporation de BQ de CdSe à été étudiée en détails par le biais de plusieurs techniques expérimentales. Il est possible d'obtenir des BQ de CdZnSe de quelques nanomètres de long, avec des hétérojonctions abruptes et contenant aux alentours de 50% de Cd. L'étude optique de ces BQ montre de fines raies excitoniques. L'émission de photons uniques a été mesurée sur la raie biexcitonique jusqu'à la température ambiante. À cause de la présence d'une émission discrète du substrat des nanofils, ceux-ci doivent être transférés sur un substrat non-luminescent pour les études optiques.Growth of Au-catalysed ZnSe NWs has been successfully achieved on ZnSe peudo-substrates grown on GaAs substrate for the 1st time. Nucleation of the gold catalyst nanoparticles was studied in details. Au nanoparticles with homogeneous diameters are achieved. The nanowire diameter that results from these nanoparticles is in the range of the Bohr diameter of excitons in ZnSe and CdSe. Ultralow density achieved for Au nanoparticles makes it possible to grow nanowires in a non-competitive mode. Study of the influence of the growth parameters was done in details. A high Se:Zn~4 flux ratio and a growth temperature in the low 400C range are found to yield the straightest NWs. Homogeneous NWs with two main orientations are obtained on (001) ZnSe. The nanowire growth rate can be modeled by a kinetic mass-transport model of impinging adatoms flowing to the nanowire growth front. ZnSe NW growth was identified as taking place in the VSS mode, that is, with a solid catalyst, by in-situ RHEED observations. A growth of NWs by ALE yields only a single NW orientation. Incorporation of CdSe QDs was studied in details with numerous experimental techniques. It is possible to obtain CdZnSe QDs with a length of a few nanometers with compositionally sharp heterojunctions and a composition in Cd of about 50%. The optical study of such NWs shows sharp excitonic lines. Single photon emission on the biexciton was measured up to room temperature. A limitation comes from the fact that the NWs must be detached from the surface to be studied due to the presence of a discreet background emission originating from the substrate.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Scalable Synthesis of Less-Toxic Colloidal Copper Indium Sulfide Quantum Dots and Application to Optoelectronic Device Architectures

The consequences of mankind’s extravagant energy consumption has loomed over humanity for much of the twenty-first century. As societies realize the increasing urgency of transitioning to renewable energy sources, solar energy has been progressively adopted worldwide. Like most electronic devices, solar cells, photodetectors, and other commercial light sensing and management devices are primarily based on silicon. Due to disadvantageous intrinsic traits, silicon is inefficient at optoelectronic applications. Significant efforts have been exerted towards the discovery and implementation of alternative semiconductor materials. However, due to its abundance and compatibility with established manufacturing processes, silicon has proved difficult to dethrone. In the last two decades, application of nanomaterials have become a particularly notable topic among device and electrical engineers. For solar cells, the utility of nanomaterials occupy an area known as “Third Generation” solar cells, which is defined by the use of novel architectures and materials to overcome the intrinsic limits of bulk semiconductor materials. Among nanomaterials applied for light management devices, quantum dots (QDs) are one of the most significant areas of research. High-performance photovoltaic (PV), photodetector, light emitting, and other light management devices have been achieved from QDs, which have now graduated from the realm of research devices to commercial application. Early successes were primarily achieved using Cd- and Pb-based QDs. Still to this day, the best performance benchmarks in photovoltaics and photodetectors have been set by PbS QDs. However, the known toxicity of these elements poses significant controversy in their adaptation, precluding their commercialization. This thesis explores the application of less-toxic copper indium sulfide (CIS) QDs for photovoltaic and photodetector device architectures. Although less investigated than binary QD materials, cupric chalcopyrites display significant optical and structural properties that are flexibly tuned for a variety of applications. In this work, a low-temperature, one- pot, non-injection, temperature-ramped method is presented for high-throughput synthesis of CIS QDs. Exploration of cationic stoichiometry and temperature conditions yielded a comprehensive model to explain the properties and behaviours displayed by the QDs during synthesis and application. CIS/ZnS core/shell QDs were developed from these QDs, resulting in increased tunability, higher stability, and enhanced emission intensity and life- time. This synthesis procedure reliably yielded QDs tunable from visible to near-infrared (544-800 nm), with photoluminescence quantum yield (PLQY) of up to 20% for core/shell QDs. Furthermore, a synthesis process is presented for zinc copper indium sulfide (ZCIS) QDs, a more stable quaternary variant of CIS QDs incorporating Zn passivation within the core. As the Type I core/shell configuration formed by the CIS/ZnS QDs poses issues with carrier confinement and transport, it cannot be utilized for device purposes. Inspired by the benefits of zinc incorporation for core CIS QD stability, zinc alloying was devised as a method to leverage the benefits of zinc incorporation. A similar one-pot, low-temperature ZCIS synthesis procedure was developed, which reliably produced almost 1 g of intensely emissive ZCIS QDs. Cationic stoichiometry and overcoating were investigated to elucidate their effect on the QD lattice and subsequent parameters. A ligand-exchange process is presented, allowing the functionalization of the as-synthesized, solution-dispersed colloidal QDs for compatibility with film formation. Long, non-polar 1-dodecanethiol (DDT) ligands, which are critical to the scalable one-pot synthesis, were exchanged for short, polar 3-mercaptopropionic acid (MPA) ligands, which allowed the formation of uniform QD solids onto ZnO surfaces. This ligand functionalization is integral to the utility of the QDs in the advantageous metal oxide/QD heterojunction device structure. QD film formation methods were further explored to determine film formation parameters and practices that would best aid in the production of uniform, regular CIS QD solids of sufficient thickness. Sputtered and sol-gel ZnO films were also investigated for enhancement of the ZnO/CIS QD interface. ZnO/CIS QD diodes were fabricated to evaluate the results of the film development processes. Devices with diodic I-V behaviour and response to illumination were achieved. The key to silicon’s persistent presence in the optoelectronics industry is the fabrication processes and techniques utilized in device production, which have evolved to be insepara- ble from its use. Although many novel materials and architectures have been developed for photovoltaic and photodetector devices, their inability to depose silicon stems from their incompatibility with existing manufacturing practices. For nanomaterials and QDs, the nonchalant manner in which they are applied to device fabrication in research and prototyping environments draws doubt of their performance, leading to reluctance for commercial acceptance. Therefore, the establishment of repeatable, reliable, standard fabrication procedures for nanomaterial devices is a significant tenet of this thesis work. Through photolithography and shadow mask patterning, small, regular, 5 μm-diameter device areas were defined onto standard 2.2 × 2.2 cm2 substrates. All steps of the fabrication process were designed to be compatible with existing industry fabrication technologies, paving a smoother transition to commercial production. This work yielded small-area ZnO/CIS QD heterojunction devices on standard substrates, with strong response to illumination. The processes and technologies developed in this work are applicable in the investigation and formation of a variety of nanomaterials-based electronic and optoelectronic devices, amenable to the realization of commercially feasible nanodevices

Production of graphene and two dimensional crystals based functional electrodes for lithium ion batteries

Produzione di elettrodi in grafene e cristalli bidimensionali per batterie a ioni di liti

Formation of Colloidal Semiconductor Nanocrystals

The present work describes different techniques to control some ma jor parameters of colloidal nanocrystals. The individual techniques rely on the manipulation of the nucleation event. The sensitive control of the nanocrystals’ size and shape is discussed. Furthermore the formation of hybrid nanocrystals composed of different materials is presented. The synthesis technique for the production of the different samples involves organic solvents and surfactants and reactions at elevated temperatures. The presence of magic size clusters offers a possibility to control the size of the nanocrystals even at very small dimensions. The clusters produced comprise ca. 100 atoms. In the case of CdSe, nanocrystals of this size emit a blue fluorescence and therefore extend the routinely accessible spectrum for this material over the whole visible range. Samples fluorescing in the spectral range from green to red are produced with standard recipes. In this work a reaction scheme for magic size clusters is presented and a theoretical model to explain the particular behaviour of their growth dynamics is discussed. The samples are investigated by optical spectroscopy, transmission electron microscopy, X-ray diffraction and elemental analysis. Shape controlled nanocrystals might be of interest for a variety of applications. The size dependent properties of nanocrystals are dominated by their smallest dimension. Therefore anisotropically shaped nanocrystals exhibit similar optical and electronic properties as spherical nanocrystals with a compatible diameter. This makes nanorods and nanowires an appealing object for electronics. Another possible application for these materials is to incorporate them into synthetic materials to influence their mechanical stability. Here, a method to form branched nanocrystals is discussed. It turned out that the presence of small impurities in the reaction vessel triggers the formation of branching points. Furthermore this synthesis technique offers some insights into the architecture of the branching point. The branching point is analysed by high resolution transmission electron microscopy and proves for the occurrence of a multiple twinned structure are strengthened by simulation of the observed patterns. Incorporation of a second material into a nanocrystal adds different functionality to the entire ob ject. Ideally both materials contribute with their own functionality and they are not affected by the presence of the other material. Two different techniques to generate nanocrystals of this type are presented. The first relies on a seeded growth approach in which the nucleation of the second material is allowed only on defined sites of the seeds. Anisotropic nanorods show a reactivity that varies for the individual facets. Using such nanorods as seeds dumbbell structures are formed. The second technique uses the tips of pre-formed nano-dumbbells as sacrificial domains. The material on the tips is replaced by gold. In any of the processes a different aspect of the nucleation event or the earliest stage of the growth is of relevance. In the growth of the magic size clusters the nucleation event itself is slowed down to a pace at which the experimenter can follow any step. The occurrence of branching can be traced down to the emergence of defects in the crystalline structure in the earliest stage of the growth. Hybrid materials are formed by a seeded-growth mechanism. Pre-formed nanocrystals provide the nucleation sites for the second material