Download or read book Relationships Between Processing Structure And Properties Of Nanocrystal Quantum Dots And Superlattices written by Kaifu Bian and published by . This book was released on 2015 with total page 421 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystal quantum dots are novel materials of great scientific and technological interests. The attractive features of quantum dots include size-tunable optoelectronic properties, high optical absorption cross section and ease of synthesis and deposition. These unique features qualify quantum dots as a promising material platform for emerging technological applications such as photovoltaic devices, sensors, light emitting diodes and bioimaging. In most of the proposed applications, individual quantum dots cannot be utilized until they form macroscopic assemblies. Under proper conditions quantum dots self-assemble into periodical superlattices. The properties and performance of quantum dot assemblies depend on not only the intrinsic properties of isolated dots but also their spatial arrangement or ordering. Consequently the relationships between processing, structure and properties of quantum dots and superlattices are of great importance in guiding the design and fabrication of novel nanomaterials with advantageous features using quantum as building blocks. In this dissertation, I present my graduate research studying such trilateral relationships in lead chalcogenide quantum dot systems. The first half of this dissertation discusses the relationship between processing and structure of self-assembled superlattices. An overview of how the ligand-ligand interaction as the major driving force along with factors including particle size, shape, ligand morphology, solvents and interfaces determine superlattice morphology is provided and followed by specific examples. (1) By tuning surface ligand morphology of PbS quantum dots and growth conditions, the effective particles shape was altered and therefore different symmetries (fcc, bcc and bct) of superlattice were achieved. (2) The translational and orientational orderings in an fcc superlattice of cuboctahedron PbS quantum dots was decoded by small and wide angle x-ray scatterings. The dots showed two distinct orientations as a result of the interplay between particle shape and ligand attractions. (3) Study of the nucleation, orientational alignment and symmetry transformations of PbS nanocubes at solvent-air and solvent-substrate interfaces is presented to demonstrate the role of interfaces as templates in guiding superlattice formation. Presented in the second half of this dissertation are my research works using high pressure, which efficiently tunes both superlattice and atomic structures without altering chemistry, to probe the relationships between structure and properties of quantum dots systems. (1) Difference in the pressure-induced atomic phase transition pressure indicated that dots in bcc superlattice are more mechanically stable than those in fcc due to translational and orientational orderings. (2) Elastic stiffness of PbS quantum dots were found to show size-dependence which is explained by a core-shell model. (3) Size-dependent variation of band gap of PbS quantum dot under elevated pressure was observed and correlated to changes of atomic structure. (4) Quantum dots were innovatively used as a nano-scaled tool to uniaxially compress organic molecule chains and measure the force-length relationship of single molecules.
Download or read book Semiconductor Nanocrystal Quantum Dots written by Andrey Rogach and published by Springer Science & Business Media. This book was released on 2008-09-02 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first book to specifically focus on semiconductor nanocrystals, and address their synthesis and assembly, optical properties and spectroscopy, and potential areas of nanocrystal-based devices. The enormous potential of nanoscience to impact on industrial output is now clear. Over the next two decades, much of the science will transfer into new products and processes. One emerging area where this challenge will be very successfully met is the field of semiconductor nanocrystals. Also known as colloidal quantum dots, their unique properties have attracted much attention in the last twenty years.
Download or read book Nanocrystal Quantum Dots as Building Blocks for Artificial Solids and Their Applications in Optoelectronic Devices written by Joshua Jongwoo Choi and published by . This book was released on 2012 with total page 251 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystal quantum dots exhibit size-dependent optoelectronic properties and provide intriguing scientific and technological opportunities. Most proposed technologies based nanocrystals depend on macroscopic functional assemblies of nanocrystals in which the nanocrystals interact with each other to give rise to new collective properties - also called as artificial solids. As in the analogous atomic crystals, the optoelectronic properties of artificial solids are governed by (1) the energy levels of nanocrystals, (2) electronic coupling between nanocrystals, and (3) the symmetry of the nanocrystal superlattice. These issues add many levels of complexity to the design of artificial solids and, for the successful development of nanocrystal based technologies, it is crucial to gain deep understanding on the structure-property relationship of nanocrystals on multiple length scales. In this dissertation, I will present studies that show insights into the three governing factors of the optoelectronic properties of artificial solids mentioned above. (1) Nanocrystal energy levels: a direct correlation between interfacial energy level offsets between lead chalcogenide nanocrystals and ZnO layers with photovoltaic device performance is presented. Based on obtained insights on the size dependent photovoltaic properties of lead chalcogenide nanocrystals, first demonstration of solution processed nanocrystal tandem solar cells was achieved. (2) Inter-nanocrystal electronic coupling: rates of photogenerated exciton dissociation in nanocrystal assemblies as a function of inter-nanocrystal spacing are probed. The results show that excitons dissociate via tunneling induced delocalization among neighboring nanocrystals. Based on insights obtained from this work, drastically improved performance of solution processed nanocrystal infrared light emitting diodes is demonstrated. (3) Nanocrystal superlattice symmetry: interaction between ligand molecules on the surface of nanocrystals play critical roles in self-assembly process. Differences in the coverage of surface ligands bound to nanocrystals can be exploited to tune the shape of nanocrystal interaction potential during the self-assembly. Denser ligand coverage causes nanocrystals to interact as spheres and face-centered cubic structure is formed. In contrast, sparse ligand coverage amplifies the aspherical shape of the core crystallite and can cause non-close packed structures such as body-centered cubic.
Download or read book Nanocrystal Quantum Dots written by Victor I. Klimov and published by CRC Press. This book was released on 2017-12-19 with total page 584 pages. Available in PDF, EPUB and Kindle. Book excerpt: A review of recent advancements in colloidal nanocrystals and quantum-confined nanostructures, Nanocrystal Quantum Dots is the second edition of Semiconductor and Metal Nanocrystals: Synthesis and Electronic and Optical Properties, originally published in 2003. This new title reflects the book’s altered focus on semiconductor nanocrystals. Gathering contributions from leading researchers, this book contains new chapters on carrier multiplication (generation of multiexcitons by single photons), doping of semiconductor nanocrystals, and applications of nanocrystals in biology. Other updates include: New insights regarding the underlying mechanisms supporting colloidal nanocrystal growth A revised general overview of multiexciton phenomena, including spectral and dynamical signatures of multiexcitons in transient absorption and photoluminescence Analysis of nanocrystal-specific features of multiexciton recombination A review of the status of new field of carrier multiplication Expanded coverage of theory, covering the regime of high-charge densities New results on quantum dots of lead chalcogenides, with a focus studies of carrier multiplication and the latest results regarding Schottky junction solar cells Presents useful examples to illustrate applications of nanocrystals in biological labeling, imaging, and diagnostics The book also includes a review of recent progress made in biological applications of colloidal nanocrystals, as well as a comparative analysis of the advantages and limitations of techniques for preparing biocompatible quantum dots. The authors summarize the latest developments in the synthesis and understanding of magnetically doped semiconductor nanocrystals, and they present a detailed discussion of issues related to the synthesis, magneto-optics, and photoluminescence of doped colloidal nanocrystals as well. A valuable addition to the pantheon of literature in the field of nanoscience, this book presents pioneering research from experts whose work has led to the numerous advances of the past several years.
Download or read book Colloidal Quantum Dot Optoelectronics and Photovoltaics written by Gerasimos Konstantatos and published by Cambridge University Press. This book was released on 2013-11-07 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.
Download or read book A Computational Study of the Molecular and Electronic Structure of Self assembled Nanocrystal Superlattices written by Ananth Prakash Kaushik and published by . This book was released on 2013 with total page 596 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystalline solids have become the subject of intense study due to their unique optical properties and their capacity to form self-assembled superlattices making them suitable for use in a variety of applications such as solar cells, light-emitting devices, etc. In this thesis, we have used atomically and molecularly explicit Molecular Dynamics simulations to create a fundamental understanding of these systems. We have shown that size of the nanocrystal and the grafting density of ligands can affect the morphology of the ligand corona. We have studied the links between processing conditions and the resultant symmetry of the superlattice, whether face-centered cubic (fcc) or body-centered cubic (bcc) structures. Our results for the free energies of the system provide definitive proof of a clear dependence of preferred superlattice symmetry on the ratio of ligand length to nanocrystal size. We also provide a fundamental understanding regarding the effect of microstructural details on the electronic structure and charge transfer properties in nanocrystal superlattices. Specifically, we have shown that the charge transfer rate between nanocrystals depends on the shape and ratio of the areas of the different facets on the nanocrystal core. The impact of this kind of study is the provision of key insights into molecularscale information about the relative roles of surface-bound ligands and nanoparticle cores that are very difficult to determine experimentally. This insight, we hope, can be leveraged to ably guide future experimental studies.
Download or read book Process Dependent Properties in Colloidally Synthesized Giant Core Shell Nanocrystal Quantum Dots written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to their characteristic bright and stable photoluminescence, semiconductor nanocrystal quantum dots (NQDs) have attracted much interest as efficient light emitters for applications from single-particle tracking to solid-state lighting. Despite their numerous enabling traits, however, NQD optical properties are frustratingly sensitive to their chemical environment, exhibit fluorescence intermittency ('blinking'), and are susceptible to Auger recombination, an efficient nonradiative decay process. Previously, we showed for the first time that colloidal CdSe/CdS core/shell nanocrystal quantum dots (NQDs) comprising ultrathick shells (number of shell monolayers, n,> 10) grown by protracted successive ionic layer adsorption and reaction (SILAR) leads to remarkable photostability and significantly suppressed blinking behavior as a function of increasing shell thickness. We have also shown that these so-called 'giant' NQDs (g-NQDs) afford nearly complete suppression of non-radiative Auger recombination, revealed in our studies as long biexciton lifetimes and efficient multiexciton emission. The unique behavior of this core/shell system prompted us to assess correlations between specific physicochemical properties - beyond shell thickness - and functionality. Here, we demonstrate the ability of particle shape/faceting, crystalline phase, and core size to determine ensemble and single-particle optical properties (quantum yield/brightness, blinking, radiative lifetimes). Significantly, we show how reaction process parameters (surface-stabilizing ligands, ligand:NQD ratio, choice of 'inert' solvent, and modifications to the SILAR method itself) can be tuned to modify these function-dictating NQD physical properties, ultimately leading to an optimized synthetic approach that results in the complete suppression of blinking. We find that the resulting 'guiding principles' can be applied to other NQD compositions, allowing us to achieve non-blinking behavior in the near-infrared. Lastly, in addition to realizing novel light-emission properties by refining nanoscale architectures at the single-NQD level, we also investigate collective properties by assembling our core/shell NQDs into larger scale arrays.
Download or read book Structural and Compositional Properties of Semiconductor Quantum Dots and Nanocrystals written by Reza Jalilikashtiban and published by . This book was released on 2010 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Controlling the Electronic Structure in II VI Core shell Nanocrystal Quantum Dots Toward Tuned Optical Properties written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Semiconductor Superlattices Growth And Electronic Properties written by Fernando Agullo-rueda and published by World Scientific. This book was released on 1995-04-17 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book surveys semiconductor superlattices, in particular their growth and electronic properties in an applied electric field perpendicular to the layers. The main developments in this field, which were achieved in the last five to seven years, are summarized. The electronic properties include transport through minibands at low electric field strengths, the Wannier-Stark localization and Bloch oscillations at intermediate electric field strengths, resonant tunneling of electrons and holes between different subbands, and the formation of electric field domains for large carrier densities at high electric field strengths.
Download or read book Physical And Chemical Processing Methods For Producing Nanocrystal Films With Properties By Design written by Benjamin Edward Treml and published by . This book was released on 2016 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: As quantum dot (QD) synthesis techniques and device architectures advance, it has become increasingly apparent that new ways of connecting QDs with each other and the external environment are required in order to realize the considerable potential of QDs for optoelectronic applications. Throughout my PhD studies at Cornell, I have worked to establish the scientific and engineering foundation for processing techniques to produce designer materials from QD building blocks. Specifically, I have investigated two general processing methods, thermal annealing and solution based chemical treatments to remove or replace the insulating native ligands and produce electronically coupled thin films. In a series of studies on thermal annealing of QD films across 10 orders of magnitude in time, I show how nonequilibrium laser annealing over ns and [mu]s can be used to precisely control the structure of QD thin films to increase electronic coupling while maintaining quantum confinement, how in situ studies of QDs arranged in a periodic nanoreactor can shed light on QD fusion at the second to minute time scale, and how spatial temperature gradients during nonequilibrium laser annealing can be exploited to reveal that QD sintering is a thermally activated process with a constant activation energy over two orders of magnitude of QD growth rate. My work on chemical processing of QD films focuses on low temperature solution processing methods. I demonstrate how simultaneous cation and ligand exchange at the surface of QDs can electronically couple and passivate QD films in a single step, leading to a 4 fold increase in Förster resonant energy transfer rate and order of magnitude reduction in trap density. Through controlled removal of ligands and post assembly QD growth, I show how building epitaxial bonds among QDs in a long range ordered assembly can lead to a ~3 order of magnitude increase in the mobility of carriers in QD films. This work is an illustration of how detailed understanding of the processing-structureproperty relationships in QD assemblies over multiple length scales can produce functional thin films with properties by design. Further advances that build on this work and others will take full advantage of the unprecedented flexibility provided by the size tunable properties of QDs to expand the periodic table into another dimension and drive materials innovation.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2540 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Materials for Solid State Lighting and Displays written by Adrian Kitai and published by John Wiley & Sons. This book was released on 2017-03-06 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: LEDs are in the midst of revolutionizing the lighting industry Up-to-date and comprehensive coverage of light-emitting materials and devices used in solid state lighting and displays Presents the fundamental principles underlying luminescence Includes inorganic and organic materials and devices LEDs offer high efficiency, long life and mercury free lighting solutions
Download or read book Core Shell Quantum Dots written by Xin Tong and published by Springer Nature. This book was released on 2020-07-01 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book outlines various synthetic approaches, tuneable physical properties, and device applications of core/shell quantum dots (QDs). Core/shell QDs have exhibited enhanced quantum yield (QY), suppressed photobleaching/blinking, and significantly improved photochemical/physical stability as compared to conventional bare QDs. The core-shell structure also promotes the easy tuning of QDs’ band structure, leading to their employment as attractive building blocks in various optoelectronic devices. The main objective of this book is to create a platform for knowledge sharing and dissemination of the latest advances in novel areas of core/shell QDs and relevant devices, and to provide a comprehensive introduction and directions for further research in this growing area of nanomaterials research.
Download or read book Silicon Nanocrystals written by Lorenzo Pavesi and published by John Wiley & Sons. This book was released on 2010-02-02 with total page 648 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique collection of knowledge represents a comprehensive treatment of the fundamental and practical consequences of size reduction in silicon crystals. This clearly structured reference introduces readers to the optical, electrical and thermal properties of silicon nanocrystals that arise from their greatly reduced dimensions. It covers their synthesis and characterization from both chemical and physical viewpoints, including ion implantation, colloidal synthesis and vapor deposition methods. A major part of the text is devoted to applications in microelectronics as well as photonics and nanobiotechnology, making this of great interest to the high-tech industry.
Download or read book Electronic Structure of Quantum Confined Atoms and Molecules written by K.D. Sen and published by Springer. This book was released on 2014-09-19 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present volume is a collection of review articles highlighting the fundamental advances made in this area by the internationally acclaimed research groups , most of them being pioneers themselves and coming together for the first time.
Download or read book Ellipsometry at the Nanoscale written by Maria Losurdo and published by Springer Science & Business Media. This book was released on 2013-03-12 with total page 740 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents and introduces ellipsometry in nanoscience and nanotechnology making a bridge between the classical and nanoscale optical behaviour of materials. It delineates the role of the non-destructive and non-invasive optical diagnostics of ellipsometry in improving science and technology of nanomaterials and related processes by illustrating its exploitation, ranging from fundamental studies of the physics and chemistry of nanostructures to the ultimate goal of turnkey manufacturing control. This book is written for a broad readership: materials scientists, researchers, engineers, as well as students and nanotechnology operators who want to deepen their knowledge about both basics and applications of ellipsometry to nanoscale phenomena. It starts as a general introduction for people curious to enter the fields of ellipsometry and polarimetry applied to nanomaterials and progresses to articles by experts on specific fields that span from plasmonics, optics, to semiconductors and flexible electronics. The core belief reflected in this book is that ellipsometry applied at the nanoscale offers new ways of addressing many current needs. The book also explores forward-looking potential applications.
