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Thermal Transport In Low Dimensional Semiconductor Nanostructures
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Book Synopsis Thermal Transport in Low Dimensional Semiconductor Nanostructures by : Jaime Bohórquez-Ballén
Download or read book Thermal Transport in Low Dimensional Semiconductor Nanostructures written by Jaime Bohórquez-Ballén and published by . This book was released on 2014 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have performed a first principles density functional theory (DFT) calculations to study the thermal conductivity in ZnO nanotubes, ZnO nanowires, and Si/Ge shell-core nanowires. We found the equilibrium configuration and the electric band structure of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function method. All ZnO nanostructures studied exhibit semiconducting behavior, with direct bandgap at the Gamma point. The calculated values for the bandgaps were larger than the value of the bandgap of the bulk ZnO. We were able to identify phonon modes in which the motion of Zn atoms is significant when it is compared with the motion of oxygen atoms. The thermal conductivity depends on the diameter of the nanowires and nanotubes and it is dramatically affected when the nanowire or nanotube is doped with Ga. For Si/Ge nanowires, the slope and the curvature of acoustic modes in the phonon dispersion relation increases when the diameter increases. For nanowires with the same number of atoms, the slope and curvature of acoustic modes depends on the concentration of Si atoms. We were able to identify phonon modes in which the motion of core atoms is significant when it is compared with motion of atoms on the nanowire's shell. The thermal conductivity in these nanostructures depends on the nanowire's diameter and on the Si atoms concentration.
Book Synopsis Simulation of Thermal Transport in Semiconductor Nanostructures by : Song Mei
Download or read book Simulation of Thermal Transport in Semiconductor Nanostructures written by Song Mei and published by . This book was released on 2017 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the advancement of nanofabrication techniques, the sizes of semiconductor electronic and optoelectronic devices keep decreasing while the operating speeds keep increasing. High-speed operation leads to more heat generation and puts more thermal stress on the devices. Since the heat conduction in semiconductors is dominated by the lattice (i.e., phonons), understanding phonon transport in nanostructures is essential to addressing and alleviating the thermal-stress problem in these modern devices. In addition to the increased thermal stress, the advanced techniques that have allowed for the shrinking of the devices routinely rely on heterostructuring, doping, alloying, and the growth of intentionally strained layers to achieve the desired electronic and optical properties. These introduce impediments to phonon transport such as boundaries, interfaces, point defects (alloy atoms or dopants), and strain. Phonon transport is strongly affected by this nanoscale disorder. This dissertation examines how different types of disorder interact with phonons and degrade phonon transport. First, we study thermal transport in graphene nanoribbons (GNRs). GNRs are quasi-one-dimensional (quasi-1D) systems where the edges (boundaries) play an important role in reducing thermal conductivity. Additionally, the thermal transport in GNRs is anisotropic and depend on the GNR's chirality (GNR orientation and edge termination). We use phonon Monte Carlo (PMC) with full phonon dispersions to describe two highly-symmetric types of GNRs: the armchair GNR (AGNR) and the zigzag GNR (ZGNR). PMC tracks phonon in real space and we can explicitly include non-trivial edge structures. Moreover, the relatively low computational burden of PMC allows us to simulate samples up to 100 $\mu$m in length and predict an upper limit for thermal conductivity in graphene. We then investigate the thermal conductivity in III-V superlattices (SLs). SLs consist of alternating thin layers of different materials and III-V SLs are widely used in nanoscale thermoelectric and optoelectronic devices. The key feature in SLs is that it contains many interfaces, which dictates thermal transport. As III-V SLs are often fabricated using well-controlled techniques and have high-quality interfaces, we develop a model with only one free parameter---the effective rms roughness of the interfaces---to describe its twofold influence: reducing the in-plane layer thermal conductivity and introducing thermal boundary resistance (TBR) in the cross-plane direction. Both the calculated in-plane and cross-plane thermal conductivity of SLs agree with a number of different experiments. Finally, we study thermal conductivity of ternary III-V alloys. In modern optoelectronic devices, ternary III-V alloys are used more often than binary compounds because one can use composition engineering to achieve different effective masses, electron/hole barrier heights, and strain levels. Ternary alloys are usually treated under the virtual crystal approximation (VCA) where cation atoms are assumed to be randomly distributed and possess an averaged mass. This assumption is challenged by a discrepancy between different experiments, as well as the discrepancy between experiments and calculations. We use molecular dynamics (MD) to study the ternary alloy system as both atom masses and atom locations are explicitly tracked in MD. We discover that the thermal conductivity is determined by a competition between mass-difference scattering and the short-range ordering of the cations.
Book Synopsis Thermal Transport in Low Dimensions by : Stefano Lepri
Download or read book Thermal Transport in Low Dimensions written by Stefano Lepri and published by Springer. This book was released on 2016-04-07 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding non-equilibrium properties of classical and quantum many-particle systems is one of the goals of contemporary statistical mechanics. Besides its own interest for the theoretical foundations of irreversible thermodynamics(e.g. of the Fourier's law of heat conduction), this topic is also relevant to develop innovative ideas for nanoscale thermal management with possible future applications to nanotechnologies and effective energetic resources. The first part of the volume (Chapters 1-6) describes the basic models, the phenomenology and the various theoretical approaches to understand heat transport in low-dimensional lattices (1D e 2D). The methods described will include equilibrium and nonequilibrium molecular dynamics simulations, hydrodynamic and kinetic approaches and the solution of stochastic models. The second part (Chapters 7-10) deals with applications to nano and microscale heat transfer, as for instance phononic transport in carbon-based nanomaterials, including the prominent case of nanotubes and graphene. Possible future developments on heat flow control and thermoelectric energy conversion will be outlined. This volume aims at being the first step for graduate students and researchers entering the field as well as a reference for the community of scientists that, from different backgrounds (theoretical physics, mathematics, material sciences and engineering), has grown in the recent years around those themes.
Book Synopsis Transport Properties of Electron-waves in Low-dimensional Semiconductory Nanostructures by : Zhen-Li Ji
Download or read book Transport Properties of Electron-waves in Low-dimensional Semiconductory Nanostructures written by Zhen-Li Ji and published by . This book was released on 1993 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Thermal Transport in Low-dimensional Materials by : Prabhakar Marepalli
Download or read book Thermal Transport in Low-dimensional Materials written by Prabhakar Marepalli and published by . This book was released on 2015 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent years have witnessed a paradigm shift in the world of electronics. Researchers have not only continued to postpone the long dreaded end-of-Moore’s-law, but have also opened up a new world of possibilities with electronics. The future of electronics is widely anticipated to be dominated by wearable and implantable devices, the realization of which will be made possible by the discovery of new materials. Graphene and hexagonal boron nitride (hBN) are two such materials that have shown promising properties to make these devices possible. It has been shown that an energy bandgap can be opened in graphene by patterning it as a narrow ribbon, by applying an electric displacement field to a bilayer configuration, and by other means. The possibility of tuning the bandgap makes graphene an ideal channel material for future electronics. Similarly, hexagonal boron nitride (hBN) and its ribbon configurations have been shown to be excellent dielectric materials. In addition, the similarities in the atomic configurations of graphene and hBN allow them to conform extremely well to each other, achieving atomically smooth interfaces. Graphene devices on hBN substrates have been shown to have mobilities an order of magnitude larger than graphene devices fabricated on silicon dioxide. In addition to their outstanding electrical properties, graphene and hBN have been shown to have excellent thermal properties compared to their traditional counterparts (silicon and silicon dioxide, respectively). More specifically, these materials have been shown to have size dependent thermal properties which may be used to tune device performance. In this thesis, we study the thermal transport of three important classes of materials – graphene nanoribbons, hBN nanoribbons and graphene-hBN heterostructures using the phonon Boltzmann transport equation in a linearized framework. An exact solution of the Boltzmann transport equation is obtained ensuring that normal and umklapp phonon scattering processes are appropriately treated. In the first part of the thesis, we present a computational technique called method of automatic code differentiation to calculate sensitivities in nanoscale thermal transport simulations. Key phonon parameters like force constants, group velocities, the Gruneisen parameter, etc., which can be expressed as sensitivities or derivatives, are computed using this technique. The derivatives computed using this technique are exact and can be generalized to any order with minimal effort. This technique can be unintrusively integrated with existing first-principles simulation codes to obtain the sensitivities of parameters computed therein to chosen inputs. The next focus is to investigate the thermal properties of three main classes of materials – graphene nanoribbons, hBN nanoribbons,and graphene-hBN heterostructures. For nanoribbons, we consider ribbons of varying widths to investigate the transition of key thermal properties with width. The lattice structure of the ribbon structures considered is fully resolved. An efficient parallelization technique is developed to handle the large number of atoms in a unit cell. The thermal conductivity is obtained by an iterative solution of the linearized Boltzmann transport equation. For graphene and hBN ribbons, we find that the thermal conductivity increases with the ribbon width following a power-law trend. The rate of increase of thermal conductivity with width for hBN ribbons is found to be slower compared to graphene. Flexural phonons are found to contribute to the majority of heat conduction in both the materials. Frequency- and polarization-resolved transport is analyzed for ribbon of all widths. The thermal conductivity of single- and few-layer hexagonal boron nitride is also computed and compared with measured data. It is found that the thermal conductivity of hBN based nanostructures (single-layer, few-layer and ribbons) is around 6-8 times smaller than that for the corresponding graphene-based nanostructure. The effect of strain in both these materials is investigated. We find that the thermal conductivity of single-layer hBN is very sensitive to strain whereas graphene shows relatively less sensitivity for the same strains. Finally, thermal transport in graphene-hBN heterostructures is simulated. Two different structures are considered – single-layer graphene on an hBN substrate, and bilayer graphene on an hBN substrate. Substrates of different thickness are considered. Due to the weak interlayer coupling in these heterostructures, it is found that the phonon dispersion remains largely unchanged from the dispersions of the individual layers. The only difference in dispersion is noticed for flexural phonons, which are the only modes affected by interlayer coupling. The addition of an hBN layer underneath the graphene/bilayer graphene layer is found to drastically reduce the thermal conductivity of the heterostructures. This reduction is due to breakdown of the selection rule for flexural phonons which results in increased scattering channels for these phonons. The thermal conductivity gradually decreases, saturating to a bulk value with an increase in the number of hBN layers. The results presented in this thesis are expected to help guide the design of graphene/hBN based flexible electronics.
Book Synopsis Physics of Semiconductors and Nanostructures by : Jyoti Prasad Banerjee
Download or read book Physics of Semiconductors and Nanostructures written by Jyoti Prasad Banerjee and published by CRC Press. This book was released on 2019-06-11 with total page 413 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a comprehensive text on the physics of semiconductors and nanostructures for a large spectrum of students at the final undergraduate level studying physics, material science and electronics engineering. It offers introductory and advanced courses on solid state and semiconductor physics on one hand and the physics of low dimensional semiconductor structures on the other in a single text book. Key Features Presents basic concepts of quantum theory, solid state physics, semiconductors, and quantum nanostructures such as quantum well, quantum wire, quantum dot and superlattice In depth description of semiconductor heterojunctions, lattice strain and modulation doping technique Covers transport in nanostructures under an electric and magnetic field with the topics: quantized conductance, Coulomb blockade, and integer and fractional quantum Hall effect Presents the optical processes in nanostructures under a magnetic field Includes illustrative problems with hints for solutions in each chapter Physics of Semiconductors and Nanostructures will be helpful to students initiating PhD work in the field of semiconductor nanostructures and devices. It follows a unique tutorial approach meeting the requirements of students who find learning the concepts difficult and want to study from a physical perspective.
Book Synopsis Experimental Investigation of Thermal Transport in Low-dimensional Nanomaterials by : Daniel Josephus Alpas Villaroman
Download or read book Experimental Investigation of Thermal Transport in Low-dimensional Nanomaterials written by Daniel Josephus Alpas Villaroman and published by . This book was released on 2017 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Phonon Thermal Transport in Silicon-based Nanomaterials by : Hai-Peng Li
Download or read book Phonon Thermal Transport in Silicon-based Nanomaterials written by Hai-Peng Li and published by . This book was released on 2018 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this Brief, authors introduce the advance in theoretical and experimental techniques for determining the thermal conductivity in nanomaterials, and focus on review of their recent theoretical studies on the thermal properties of silicon-based nanomaterials, such as zero-dimensional silicon nanoclusters, one-dimensional silicon nanowires, and graphenelike two-dimensional silicene. The specific subject matters covered include: size effect of thermal stability and phonon thermal transport in spherical silicon nanoclusters, surface effects of phonon thermal transport in silicon nanowires, and defects effects of phonon thermal transport in silicene. The results obtained are supplemented by numerical calculations, presented as tables and figures. The potential applications of these findings in nanoelectrics and thermoelectric energy conversion are also discussed. In this regard, this Brief represents an authoritative, systematic, and detailed description of the current status of phonon thermal transport in silicon-based nanomaterials. This Brief should be a highly valuable reference for young scientists and postgraduate students active in the fields of nanoscale thermal transport and silicon-based nanomaterials.
Book Synopsis The Physics of Low-dimensional Structures by : Georgios P. Triberis
Download or read book The Physics of Low-dimensional Structures written by Georgios P. Triberis and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers the field of low dimensional structures, starting from the selectively doped double heterostructures n-A1GaAs/GaAs/n-A1GaAs, and (strained) p-Si/SiGe/p-Si (quantum wells). The behaviour of the sheet electron density, the subband populations and energies as a function of the well width, the spacer thickness and the doping concentration is analysed. The temperature dependence of the bulk electron concentration versus the quasi-2DEG are discussed. In the framework of Boltzmann's transport theory a detailed study of the mobility is presented at low and high temperatures taking into account all the relevant scattering mechanisms. The pseudomorphic Si/SiGe undoped quantum wells are a perfect example for the study of the non-parabolicity of the hole-bands. For the first time in a book an exact solution of the multiband effective mass equation that describes the heavy, light and split-off hole valence bands is introduced, and interband transitions and selection rules are obtained. Reducing dimensionality new aspects concerning optical and transport properties of quantum wires (QWRS) is discussed. Specifically, the photoluminescence and the microphotoluminescence spectra of V-shaped QWRS is theoretically interpreted leading to a realistic cartography of the interface roughness of these systems. A computational approach for the solution of the eigenvalue problem in low-dimensional systems of complex but realistic geometry is also presented for the first time in a book, and transport theoretical considerations will lead to a systematic study of the mobility. As DNA could be considered as a one-dimensional "molecular wire" the study of carrier transport along DNA is discussed in terms of hopping transport. A computational scheme is presented which allows the study of near-field magnetoabsorpsion spectra of Quantum Dots (QD) of any given geometry, under magnetic field of any orientation. The effect of the spatial confinement imposed by the QD dimensions and the magnetic confinement governed by the magnetic field are explored. The influence of the Coulomb interactions between electrons and holes is also discussed. The applicability of the method in actual experiments, i.e. the illumination of a nanostructure with a near-field probe in conjunction with the simultaneous application of an external magnetic field, may become a challenge to experimentalists. Finally, magnetothermoelectic transport in the fractional quantum Hall effect (FQHE) regime is discussed. The theoretical framework for the calculation of the resistivity, the thermopower and the thermal conductivity for two-dimensional electron and hole gases, at low temperatures and strong perpendicular magnetic fields is outlined. The composite fermion picture enables the use of the integer quantum Hall effect and Shubnikov - de Haas conductivity models for a quantitative comparison with experiment. A study on the validity of fundamental physical laws such as the Wiedemann-Franz law in two-dimensional structures is also presented.
Download or read book Journal of Heat Transfer written by and published by . This book was released on 2005 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nanostructured Semiconductors by : Konstantinos Termentzidis
Download or read book Nanostructured Semiconductors written by Konstantinos Termentzidis and published by CRC Press. This book was released on 2017-09-01 with total page 475 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book is devoted to nanostructures and nanostructured materials containing both amorphous and crystalline phases with a particular focus on their thermal properties. It is the first time that theoreticians and experimentalists from different domains gathered to treat this subject. It contains two distinct parts; the first combines theory and simulations methods with specific examples, while the second part discusses methods to fabricate nanomaterials with crystalline and amorphous phases and experimental techniques to measure the thermal conductivity of such materials. Physical insights are given in the first part of the book, related with the existing theoretical models and the state of art simulations methods (molecular dynamics, ab-initio simulations, kinetic theory of gases). In the second part, engineering advances in the nanofabrication of crystalline/amorphous heterostructures (heavy ion irradiation, electrochemical etching, aging/recrystallization, ball milling, PVD, laser crystallization and magnetron sputtering) and adequate experimental measurement methods are analyzed (Scanning Thermal Microscopy, Raman, thermal wave methods and x-rays neutrons spectroscopy).
Book Synopsis Low-dimensional Semiconductors by : M. J. Kelly
Download or read book Low-dimensional Semiconductors written by M. J. Kelly and published by Clarendon Press. This book was released on 1995-11-23 with total page 569 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text is a first attempt to pull together the whole of semiconductor science and technology since 1970 in so far as semiconductor multilayers are concerned. Material, technology, physics and device issues are described with approximately equal emphasis, and form a single coherant point of view. The subject matter is the concern of over half of today's active semiconductor scientists and technologists, the remainder working on bulk semiconductors and devices. It is now routine to design and the prepare semiconductor multilayers at a time, with independent control over the dropping and composition in each layer. In turn these multilayers can be patterned with features that as a small as a few atomic layers in lateral extent. The resulting structures open up many new ares of exciting solid state and quantum physics. They have also led to whole new generations of electronic and optoelectronic devices whose superior performance relates back to the multilayer structures. The principles established in the field have several decades to go, advancing towards the ultimate of materials engineering, the design and preparation of solids atom by atom. The book should appeal equally to physicists, electronic engineers and materials scientists.
Book Synopsis Thermal Transport in Graphene-based Nanostructures and Other Two-dimensional Materials by :
Download or read book Thermal Transport in Graphene-based Nanostructures and Other Two-dimensional Materials written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Thermal Transport in Novel Three Dimensional Carbon Nanostructures by : Jungkyu Park
Download or read book Thermal Transport in Novel Three Dimensional Carbon Nanostructures written by Jungkyu Park and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three-dimensional (3D) nanostructures comprised of one-dimensional (1D) and/or two-dimensional (2D) nanomaterials have several advantages over their base nanomaterials. Due to their dimensionally confined structures, for example, 1D carbon nanotubes (CNTs) and 2D graphene exhibit strong direction-dependent thermal transport properties with extremely inefficient cross-plane properties. However, 3D carbon nanostructures such as pillared graphene structures (PGS) are expected to be efficient in both in-plane and cross-plane thermal transport. The aim of this thesis is providing the detailed understanding of thermal transport in 3D carbon nanostructures comprised of CNTs and graphene. Reverse non-equilibrium molecular dynamics simulations were used to show that PGS and CNT networks can have both high in-plane and high cross-plane thermal conductivities comparable to their base nanomaterials, i.e. CNTs and graphene, and also to show that their thermal properties are tunable through altering their architectures. The results indicate that thermal resistances at CNT-graphene junctions result from the combined effect of phonon scattering at the junctions with distorted carbon-carbon bonds and the change in dimensionality of the phonon transport medium as phonons propagate from CNTs (1D) to graphene (2D) and then again to CNT. Moreover, wave packet analysis on SWCNT networks revealed that SWCNT-SWCNT junctions with lager diameter transmit thermal energy more efficiently than the junctions with smaller diameter, and also revealed that SWCNT-SWCNT T-junctions are more efficient in thermal energy transmission than X-junctions. A new experimental method for thermal conductivity measurements in 2D nanosheets was developed. The new method ensures a 1D heat conduction in a 2D sample by creating a spatially uniform temperature profile on the heated side of the sample, and thus improves the accuracy of the measurement in a 2D structure. A MEMS device that can measure the thermal conductivity of a graphene layer using this method is currently being fabricated for the validation of the method.
Book Synopsis Innovative Thermoelectric Materials: Polymer, Nanostructure And Composite Thermoelectrics by : Howard E Katz
Download or read book Innovative Thermoelectric Materials: Polymer, Nanostructure And Composite Thermoelectrics written by Howard E Katz and published by World Scientific. This book was released on 2016-01-22 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: Power generation from environmentally friendly sources has led to surging interest in thermoelectrics. There has been a move toward alternative thermoelectric materials with enhanced performance through materials and structures that utilize common and safer elements and alternative mechanistic approaches while increasing processing latitude and decreasing cost. This wide-ranging volume examines this progress and future prospects with the new technologies, ease of processing and cost as major considerations, and will benefit active researchers, students and others interested in cutting-edge work in thermoelectric materials. Innovative Thermoelectric Materials incorporates the contributions of a group of recognized experts in thermoelectric materials, many of whom were the first to introduce various materials systems into thermoelectric systems. The perspectives brought to this evolving subject will provide important insights on which those developing the field can build, and will inspire new research directions for the future.
Book Synopsis Dynamical Analysis of Non-Fourier Heat Conduction and Its Application in Nanosystems by : Yuan Dong
Download or read book Dynamical Analysis of Non-Fourier Heat Conduction and Its Application in Nanosystems written by Yuan Dong and published by Springer. This book was released on 2015-10-14 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies the general heat conduction law, irreversible thermodynamics and the size effect of thermal conductivity exhibited in nanosystems from the perspective of recently developed thermomass theory. The derivation bridges the microscopic phonon Boltzmann equation and macroscopic continuum mechanics. Key concepts such as entropy production, temperature and the Onsager reciprocal relation are revisited in the case of non-Fourier heat conduction. Lastly, useful expressions are extracted from the picture of phonon gas dynamics and are used to successfully predict effective thermal conductivity in nanosystems.
Book Synopsis Molecular Low Dimensional and Nanostructured Materials for Advanced Applications by : A. Graja
Download or read book Molecular Low Dimensional and Nanostructured Materials for Advanced Applications written by A. Graja and published by Springer Science & Business Media. This book was released on 2002-04-30 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Research Workshop, held in Poznan, Poland 1-5 September, 2001
