Download or read book Investigation of Excitonic Electronic and Thermal Properties of Two dimensional and Quasi one dimensional Materials written by Bishwajit Debnath and published by . This book was released on 2018 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: We explore the excitonic, electronic, phononic and thermal properties of low-dimensional materials, specifically the two-dimensional and quasi-one-dimensional transition metal chalcogenides. The possibility of observing Bose-Einstein exciton condensation (BEC) in transition metal dichalcogenides (TMDs) has been analyzed at three different levels of theory. We find that, in the strong coupling regime, mean field theory with either an unscreened or screened interlayer interaction predicts a room-temperature condensate. However, intralayer interactions can essentially renormalize the quasiparticle dispersion, which can be captured by many-body GW formalism. In the strong coupling regime, the improved BEC theory predicts that intralayer interactions have a large impact on the condensate order parameter, as well as on its functional dependencies on effective mass and carrier density. We also explore the thermal properties of 2D materials, specifically in the misoriented bilayer graphene (m-BLG) system, using ab initio density functional theory (DFT) and phonon Boltzmann transport equation (BTE). we find that the lattice thermal conductivity of m-BLG reduces to almost half of its unrotated counterpart. To explain the phonon dynamics, we analyze the phonon dispersions, phonon velocity distributions, occupations, density of states and heat capacity, both before and after misorientation. Detailed calculation of the phonon-phonon scattering lifetime reveals that, the increased umklapp scattering in the acoustic and quasi-acoustic phonon branches is the main reason for the reduced thermal conductivity in m-BLG system. We also explore the thermal conductivity of quasi-1D materials, specifically TaSe3 and NbS3, using ab initio DFT and phonon BTE. We find that both materials exhibit highly anisotropic thermal transport. A thermal conductivity of 6.3 W/mK (70.6 W/mK) is observed for metallic TaSe 3 (semiconducting NbS3) along the chain direction. In-depth study of velocity and lifetime distribution shows that lower scattering and higher phonon velocity in NbS3 are the reasons behind such higher thermal conductivity. The umklapp scattering process is found to be the dominant phonon scattering mechanism in this family of low-dimensional materials. We also investigate the electronic and vibrational properties of different phases of the quasi-1D material NbS3. We find that the dimerized phase NbS3-IV is a semiconductor, whereas the undimerized phase NbS 3-V is a metal. Similarity between the band dispersions of phase-I and phase-IV arises from the similarity in their structures, in spite of some stacking and chiral faults. Both phase-I and phase-IV are dynamically stable, whereas the phonon dispersion in phase-V exhibits instability along the inter-chain and growth direction, indicating a possible charge density wave ground state. Finally, we explore the band alignment properties of different quasi-1D transition metal trichalcogenides (TMTs). From the DFT calculations, we can identify several TMTs as promising candidates for ohmic contacts and tunnel FET devices.

Download or read book Electronic Optical and Thermal Properties of Reduced dimensional Semiconductors written by Shouting Huang and published by . This book was released on 2013 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell NWs. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphenelike system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity ix by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

Download or read book Excitations in Organic Solids written by Vladimir M. Agranovich and published by OUP Oxford. This book was released on 2009-02-12 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the last decade our expertise in nanotechnology has advanced considerably. The possibility of incorporating in the same nanostructure different organic and inorganic materials has opened up a promising field of research, and has greatly increased the interest in the study of properties of excitations in organic materials. In this book not only the fundamentals of Frenkel exciton and polariton theory are described, but also the electronic excitations and electronic energy transfers in quantum wells, quantum wires and quantum dots, at surfaces, at interfaces, in thin films, in multilayers, and in microcavities. Among the new topics in the book are those devoted to the optics of hybrid Frenkel-Wannier-Mott excitons in nanostructures, polaritons in organic microcavities including hybrid organic-inorganic microcavities, new concepts for organic light emitting devices, the mixing of Frenkel and charge-transfer excitons in organic quasi one-dimensional crystals, excitons and polaritons in one and two-dimensional crystals, surface electronic excitations, optical biphonons, and Fermi resonances by polaritons. All new phenomena described in the book are illustrated by available experimental observations. The book will be useful for scientists working in the field of photophysics and photochemistry of organic solids (for example, organic light-emitting devices and solar cells), and for students who are entering this field. It is partly based on a book by the author written in 1968 - "Theory of Excitons" - in Russian. However the new book includes only 5 chapters from this version, all of which have been updated. The 10 new chapters contain discussions of new phenomena, their theory and their experimental observations.

Download or read book Inventory of energy research and development 1973 1975 written by Oak Ridge National Laboratory and published by . This book was released on 1976 with total page 1356 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Two Dimensional Materials in Nanophotonics written by Yuerui Lu and published by CRC Press. This book was released on 2019-10-31 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two-dimensional (2D) materials have attracted tremendous interest since the study of graphene in the early 21st century. With their thickness in the angstrom-to-nanometer range, 2D materials, including graphene, transition metal dichalcogenides, phosphorene, silicene, and other inorganic and organic materials, can be an ideal platform to study fundamental many-body interactions because of reduced screening and can also be further engineered for nanophotonic applications. This book compiles research outcomes of leading groups in the field of 2D materials for nanophotonic physics and devices. It describes research advances of 2D materials for various nanophotonic applications, including ultrafast lasers, atomically thin optical lenses, and gratings to inelastically manipulate light propagation, their integrations with photonic nanostructures, and light–matter interactions. The book focuses on actual applications, while digging into the physics underneath. It targets advanced undergraduate- and graduate-level students of nanotechnology and researchers in nanotechnology, physics, and chemistry, especially those with an interest in 2D materials.

Download or read book Magneto Spectroscopy of Excitons in Two Dimensional Semiconductors written by Zhengguang Lu and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding properties of quasiparticles in novel two-dimensional (2D) semiconductors, such as atomically thin transition metal dichalcogenides (TMDCs) and group-III metal monochalcogenides, is among the most interesting topics in condensed matter physics in recent years. Their distinctive excitonic effects resulting from strong Coulomb interaction in the truly 2D limit, strong light-matter interaction, spin-valley locking (in TMDCs), and the availability of new degrees of freedom (stacking and twisting) for tuning electronic properties make these materials a unique platform for exploring excitonic physics and for potential optoelectronic applications. In this thesis, we use low temperature optical magneto-spectroscopy to probe the fundamental properties of excitons and excitonic complexes in monolayer TMDCs and few-layer InSe. In the first part of this thesis, we identified and characterized the intrinsic spin conserved (bright) and spin-flip forbidden (dark) exciton states as well as their related exciton complexes in monolayer WSe2 and MoSe2. The dark excitons are originated from the spin-orbital coupling splitting of the conduction band. We demonstrate that by applying strong in-plane magnetic fields, one can induce mixing and splitting of bright and dark exciton branches, which enables an accurate spectroscopic determination of their energies. We establish, for the first time, the bright-dark excitons splitting in an archetypal TMDC monolayer semiconductor, MoSe2, which helped to resolve a long-standing puzzle of its surprisingly high valley depolarization. In the second part of the thesis, we examine the optical properties of monolayer MoSe2 away from the charge neutrality point. Monolayer TMDCs have extremely high exciton binding energies, which makes the excitonic effects dominate the optical processes even at high electron densities when the Fermi level is in the conduction band. Here, we study excitons dressed by the Fermi sea of electrons forming new quasi-particles, repulsive and attractive exciton-polarons, as well as their Landau quantization at high magnetic fields. In the third part of the thesis, we study another 2D direct-gap semiconductor, InSe, in the regime where the Fermi energy approaches the exciton binding energy. Due to the high mobility of electrons in the conduction and the flat valence band, few-layer InSe provides a nearly ideal system to study many-body phenomena using optical spectroscopy. In this thesis, we report the observation of Fermi edge singularity, spectroscopic measurements of quantum Hall gaps, and detection of possible signatures of fractional quantum Hall states in InSe.

Download or read book Electronic Excitations in Organic Based Nanostructures written by and published by Elsevier. This book was released on 2003-11-13 with total page 509 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book devoted to a systematic consideration of electronic excitations and electronic energy transfer in organic crystalline multilayers and organics based nanostructures(quantum wells, quantum wires, quantum dots, microcavities). The ingenious combination of organic with inorganic materials in one and the same hybrid structure is shown to give qualitatively new opto-electronic phenomena, potentially important for applications in nonlinear optics, light emitting devices, photovoltaic cells, lasers and so on. The book will be useful not only for physicists but also for chemists and biologists.To help the nonspecialist reader, three Chapters which contain a tutorial and updated introduction to the physics of electronic excitations in organic and inorganic solids have been included.* hybrid Frenkel-Wannier-Mott excitons* microcavities with crystalline and disordered organics * electronic excitation at donor-acceptor interfaces * cold photoconductivity at donor-acceptor interface* cummulative photovoltage* Feorster transfer energy in microcavity* New concepts for LEDs

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Frontiers of High Pressure Research II Application of High Pressure to Low Dimensional Novel Electronic Materials written by Hans D. Hochheimer and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 556 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent interactions with industrial companies it became quite obvious, that the search for new materials with strong anisotropic properties are of paramount importance for the development of new advanced electronic and magnetic devices. The questions concerning the tailoring of materials with large anisotropic electrical and thermal conductivity were asked over and over again. It became also quite clear that the chance to answer these questions and to find new materials which have these desired properties would demand close collaborations between scientists from different fields. Modem techniques ofcontrolled materials synthesis and advances in measurement and modeling have made clear that multiscale complexity is intrinsic to complex electronic materials, both organic and inorganic. A unified approach to classes of these materials is urgently needed, requiring interdisciplinary input from chemistry, materials science, and solid state physics. Only in this way can they be controlled and exploited for increasingly stringent demands oftechnology. The spatial and temporal complexity is driven by strong, often competing couplings between spin, charge and lattice degrees offreedom, which determine structure-function relationships. The nature of these couplings is a sensitive function of electron-electron, electron-lattice, and spin-lattice interactions; noise and disorder, external fields (magnetic, optical, pressure, etc. ), and dimensionality. In particular, these physical influences control broken-symmetry ground states (charge and spin ordered, ferroelectric, superconducting), metal-insulator transitions, and excitations with respect to broken-symmetries created by chemical- or photo-doping, especially in the form of polaronic or excitonic self-trapping.

Download or read book Semiconductor Quantum Dots written by Ladislaus B nyai and published by World Scientific. This book was released on 1993 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductor Quantum Dots presents an overview of the background and recent developments in the rapidly growing field of ultrasmall semiconductor microcrystallites, in which the carrier confinement is sufficiently strong to allow only quantized states of the electrons and holes. The main emphasis of this book is the theoretical analysis of the confinement induced modifications of the optical and electronic properties of quantum dots in comparison with extended materials. The book develops the theoretical background material for the analysis of carrier quantum-confinement effects, introduces the different confinement regimes for relative or center-of-mass motion quantization of the electron-hole-pairs, and gives an overview of the best approximation schemes for each regime. A detailed discussion of the carrier states in quantum dots is presented and surface polarization instabilities are analyzed, leading to the self-trapping of carriers near the surface of the dots. The influence of spin-orbit coupling on the quantum-confined carrier states is discussed. The linear and nonlinear optical properties of small and large quantum dots are studied in detail and the influence of the quantum-dot size distribution in many realistic samples is outlined. Phonons in quantum dots as well as the influence of external electric or magnetic fields are also discussed. Last but not least the recent developments dealing with regular systems of quantum dots are also reviewed. All things included, this is an important piece of work on semiconductor quantum dots not to be dismissed by serious researchers and physicists.

Download or read book Handbook of Polymers in Electronics written by Bansi D. Malhotra and published by iSmithers Rapra Publishing. This book was released on 2001-12-31 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Handbook of Polymers in Electronics has been designed to discuss the novel ways in which polymers can be used in the rapidly growing electronics industry. It provides discussion of the preparation and characterisation of suitable polymeric materials and their current and potential applications coupled with the fundamentals of electrical, optical and photophysical properties. It will thus serve the needs of those already active in the electronics field as well as new entrants to the industry.

Download or read book Hearings Reports and Prints of the Senate Select Committee on Small Business written by United States. Congress. Senate. Select Committee on Small Business and published by . This book was released on 1975 with total page 1440 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1993-02 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Proceedings of 2000 International Conference on Excitonic Processes in Condensed Matter written by Kikuo Ch? and published by World Scientific. This book was released on 2001 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: At Yamada Conference LIII, papers on many novel materials and on novel phenomena in condensed matter physics were presented ? for instance, the achievement of simultaneous creation of excitons and free-electron-hole pairs in rare gas solids, and a low frequency fluctuation of the spectral shift of indirect excitons in GaAs coupled quantum wells. Single molecule spectroscopy is a powerful tool for studying molecules including biological systems; the study of delocalization of excitons in the photosynthetic light harvesting antenna system was also reported. The proceedings thus contain many excellent papers dealing with current research topics on the excitonic processes in bulk, quantum wells, quantum dots and other confined systems. This book will serve as an excellent source of recent references and reviews for a wide range of researchers in physics, chemistry, engineering and biological sciences.The proceedings have been selected for coverage in: ? Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings)

Download or read book Excitonic Processes In Condensed Matter Proceedings Of 2000 International Conference Excon2000 written by Kikuo Cho and published by World Scientific. This book was released on 2001-08-22 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: At Yamada Conference LIII, papers on many novel materials and on novel phenomena in condensed matter physics were presented — for instance, the achievement of simultaneous creation of excitons and free-electron-hole pairs in rare gas solids, and a low frequency fluctuation of the spectral shift of indirect excitons in GaAs coupled quantum wells. Single molecule spectroscopy is a powerful tool for studying molecules including biological systems; the study of delocalization of excitons in the photosynthetic light harvesting antenna system was also reported. The proceedings thus contain many excellent papers dealing with current research topics on the excitonic processes in bulk, quantum wells, quantum dots and other confined systems. This book will serve as an excellent source of recent references and reviews for a wide range of researchers in physics, chemistry, engineering and biological sciences.The proceedings have been selected for coverage in:• Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings)

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 Nonlinear Optics and Laser Spectroscopy written by S. C. Abbi and published by Alpha Science Int'l Ltd.. This book was released on 2001 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume begins with a brief up-date of "Laser Sources" and "Spectroscopic Instrumentation and Practice." Non Linear Optics section contains reviews of the fundamental value concerning "Intense Laser Bean Instabilities" and "Atoms and Molecules in Intense Laser Fields" as well as topics of recent interest including Pattern Formation, Optical Phase Conjugation, Solitonic Propagation and Photo-refractive crystals. Laser Spectroscopy section includes a detailed review of Molecular Spectroscopy principles and concise review of Group Theory. Many topics of contemporary interest include Bosonic Effects in Raman Spectroscopy, Resonant Raman Spectroscopy of Low Dimensional Semiconductors, Dynamic Light Scattering Study of Turbulence and Laser Brillouin from Polymeric Gels and Networks. The class-room type coverage of selected topics would encourage young scientists in taking up challenging research projects in areas of Non-linear Optics and Laser Spectroscopy.