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Author: Jebum Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 120
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Book Description
This thesis describes the results of measurements of the transient response of quantum point contacts (QPCs), and shows strong effects of heating due to optical-phonon emission. By changing the gate voltage that controls the confinement potential of the QPC, we observed three different regimes of transient response - the 2-D, multi-mode 1-D, and few mode 1-D regimes, respectively. With the QPC properly formed, the transient voltage is dropped almost entirely across it and we observe clear evidence of heating in the transient response when the QPC is in the multi-mode 1-D regime. The heating is strongly suppressed in few-mode 1-D limit, however, where the current can be carried by only a small number (1 or 2) of subbands. Accompanying the suppression of heating, we find that the non-linear conductance inferred from the transient pulses becomes pinned near 2 e2 /h over a wide range. Further experiments shows that the suppression of heating cannot be explained simply as arising as the current in the QPC drops below some critical threshold value. Motivated by these observations, I have developed a theoretical model to explain our key experimental results. The key feature of the model is that it considers how strong electron-phonon coupling within the QPC can modify the structure of its subbands. Through a phenomenological treatment of the electron-phonon coupling in the QPC, our calculations how that virtual fluctuations of optical phonons allow the lowest subband to become "protected" from scattering under strong bias, as it becomes split-off in energy from the other subbands. Under this condition, only the lowest subband can be accessed for transport through the QPC, allowing us to explain the pinning of the conductance near 2 e2 /h. The demonstration of this protected 1-D mode is a completely new result, and we attribute its discovery to the fact that our transient studies provide us with the ability to image heating directly, in real time, something that is not possible for DC measurements. Since the phonon coupling mechanism that we have considered is quite generic, the protected mode that we have identified may also play a role in determining the operation of scaled MOSFETs as they are pushed progressively towards the regime of ballistic transport.
Author: Jebum Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 120
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Book Description
This thesis describes the results of measurements of the transient response of quantum point contacts (QPCs), and shows strong effects of heating due to optical-phonon emission. By changing the gate voltage that controls the confinement potential of the QPC, we observed three different regimes of transient response - the 2-D, multi-mode 1-D, and few mode 1-D regimes, respectively. With the QPC properly formed, the transient voltage is dropped almost entirely across it and we observe clear evidence of heating in the transient response when the QPC is in the multi-mode 1-D regime. The heating is strongly suppressed in few-mode 1-D limit, however, where the current can be carried by only a small number (1 or 2) of subbands. Accompanying the suppression of heating, we find that the non-linear conductance inferred from the transient pulses becomes pinned near 2 e2 /h over a wide range. Further experiments shows that the suppression of heating cannot be explained simply as arising as the current in the QPC drops below some critical threshold value. Motivated by these observations, I have developed a theoretical model to explain our key experimental results. The key feature of the model is that it considers how strong electron-phonon coupling within the QPC can modify the structure of its subbands. Through a phenomenological treatment of the electron-phonon coupling in the QPC, our calculations how that virtual fluctuations of optical phonons allow the lowest subband to become "protected" from scattering under strong bias, as it becomes split-off in energy from the other subbands. Under this condition, only the lowest subband can be accessed for transport through the QPC, allowing us to explain the pinning of the conductance near 2 e2 /h. The demonstration of this protected 1-D mode is a completely new result, and we attribute its discovery to the fact that our transient studies provide us with the ability to image heating directly, in real time, something that is not possible for DC measurements. Since the phonon coupling mechanism that we have considered is quite generic, the protected mode that we have identified may also play a role in determining the operation of scaled MOSFETs as they are pushed progressively towards the regime of ballistic transport.
Author: Joseph Albert Sulpizio
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 171
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Book Description
One-dimensional (1D) electronic nanostructures comprise a class of systems that boast tremendous promise for both technological innovation as well as fundamental scientific discovery. To fully harness their potential, it is crucial to understand transport through 1D systems at the most fundamental, quantum level. In this thesis, we describe our investigations down three avenues of quantum transport in 1D: (1) ballistic transport in quantum wires, (2) quantum capacitance measurements of nanostructures, and (3) tunneling measurements in carbon nanotubes. First, we discuss measurements and modeling of hole transport in ballistic quantum wires fabricated by GaAs/AlGaAs cleaved-edge overgrowth, where we find strong g-factor anisotropy, which we associate with spin-orbit coupling, and evidence for the importance of charge interactions, indicated by the observation of "0.7" structure. Additionally, we present the first experimental observation of a predicted spin-orbit gap in the 1D density of states, where counter-propagating spins constituting a spin current are accompanied by a clear signal in the conductance. Next, we present the development of a highly sensitive integrated capacitance bridge for quantum capacitance measurements to be used as a novel probe of 1D systems. We demonstrate the utility of our bridge by measuring the capacitance of top-gated graphene devices, where we cleanly resolve the density of states, and also present preliminary measurements of carbon nanotube devices, where we ultimately aim to extract their mobility. Finally, we discuss a set of transport measurements in carbon nanotubes designed to probe interactions between fermions in 1D in which top gates are used to introduce tunable tunnel barriers.
Author:
Publisher:
ISBN: 9789085932079
Category :
Languages : en
Pages :
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Book Description
Author: Joseph Albert Sulpizio
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
One-dimensional (1D) electronic nanostructures comprise a class of systems that boast tremendous promise for both technological innovation as well as fundamental scientific discovery. To fully harness their potential, it is crucial to understand transport through 1D systems at the most fundamental, quantum level. In this thesis, we describe our investigations down three avenues of quantum transport in 1D: (1) ballistic transport in quantum wires, (2) quantum capacitance measurements of nanostructures, and (3) tunneling measurements in carbon nanotubes. First, we discuss measurements and modeling of hole transport in ballistic quantum wires fabricated by GaAs/AlGaAs cleaved-edge overgrowth, where we find strong g-factor anisotropy, which we associate with spin-orbit coupling, and evidence for the importance of charge interactions, indicated by the observation of "0.7" structure. Additionally, we present the first experimental observation of a predicted spin-orbit gap in the 1D density of states, where counter-propagating spins constituting a spin current are accompanied by a clear signal in the conductance. Next, we present the development of a highly sensitive integrated capacitance bridge for quantum capacitance measurements to be used as a novel probe of 1D systems. We demonstrate the utility of our bridge by measuring the capacitance of top-gated graphene devices, where we cleanly resolve the density of states, and also present preliminary measurements of carbon nanotube devices, where we ultimately aim to extract their mobility. Finally, we discuss a set of transport measurements in carbon nanotubes designed to probe interactions between fermions in 1D in which top gates are used to introduce tunable tunnel barriers.
Author: David K. Ferry
Publisher: Cambridge University Press
ISBN: 1139480839
Category : Science
Languages : en
Pages : 671
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Book Description
The advent of semiconductor structures whose characteristic dimensions are smaller than the mean free path of carriers has led to the development of novel devices, and advances in theoretical understanding of mesoscopic systems or nanostructures. This book has been thoroughly revised and provides a much-needed update on the very latest experimental research into mesoscopic devices and develops a detailed theoretical framework for understanding their behaviour. Beginning with the key observable phenomena in nanostructures, the authors describe quantum confined systems, transmission in nanostructures, quantum dots, and single electron phenomena. Separate chapters are devoted to interference in diffusive transport, temperature decay of fluctuations, and non-equilibrium transport and nanodevices. Throughout the book, the authors interweave experimental results with the appropriate theoretical formalism. The book will be of great interest to graduate students taking courses in mesoscopic physics or nanoelectronics, and researchers working on semiconductor nanostructures.
Author: Jianhua Zhou
Publisher:
ISBN:
Category : Electron transport
Languages : en
Pages :
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Author: Klaus D. Sattler
Publisher: CRC Press
ISBN: 1000497429
Category : Science
Languages : en
Pages : 371
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Book Description
This up-to-date reference is the most comprehensive summary of the field of nanoscience and its applications. It begins with fundamental properties at the nanoscale and then goes well beyond into the practical aspects of the design, synthesis, and use of nanomaterials in various industries. It emphasizes the vast strides made in the field over the past decade – the chapters focus on new, promising directions as well as emerging theoretical and experimental methods. The contents incorporate experimental data and graphs where appropriate, as well as supporting tables and figures with a tutorial approach.
Author: Tianyou Zhai
Publisher: John Wiley & Sons
ISBN: 1118310365
Category : Technology & Engineering
Languages : en
Pages : 857
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Book Description
Reviews the latest research breakthroughs and applications Since the discovery of carbon nanotubes in 1991, one-dimensional nanostructures have been at the forefront of nanotechnology research, promising to provide the building blocks for a new generation of nanoscale electronic and optoelectronic devices. With contributions from 68 leading international experts, this book reviews both the underlying principles as well as the latest discoveries and applications in the field, presenting the state of the technology. Readers will find expert coverage of all major classes of one-dimensional nanostructures, including carbon nanotubes, semiconductor nanowires, organic molecule nanostructures, polymer nanofibers, peptide nanostructures, and supramolecular nanostructures. Moreover, the book offers unique insights into the future of one-dimensional nanostructures, with expert forecasts of new research breakthroughs and applications. One-Dimensional Nanostructures collects and analyzes a wealth of key research findings and applications, with detailed coverage of: Synthesis Properties Energy applications Photonics and optoelectronics applications Sensing, plasmonics, electronics, and biosciences applications Practical case studies demonstrate how the latest applications work. Tables throughout the book summarize key information, and diagrams enable readers to grasp complex concepts and designs. References at the end of each chapter serve as a gateway to the literature in the field. With its clear explanations of the underlying principles of one-dimensional nanostructures, this book is ideal for students, researchers, and academics in chemistry, physics, materials science, and engineering. Moreover, One-Dimensional Nanostructures will help readers advance their own investigations in order to develop the next generation of applications.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Liang Yin
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This dissertation presents experimental and computational study of thermal and electrical transport in one-dimensional nanostructures. Synthesizing materials into one-dimensional nanowire has been proved very effective for suppressing the phonon contribution due to scattering at the wire boundaries. Three one-dimensional nanostructured thermoelectric candidates - SiGe nanowires, SrTiO3 nanowires, and ZnO nanowires - were presented and discussed in this dissertation. SiGe nanowires are successfully synthesized on a cleaned n-type (100) Si substrate coated with gold thin film as a catalytic metal, via the vapor-liquid-solid (VLS) growth method. The thermoelectric properties of SiGe nanowires with different diameter, Ge concentration, and phosphorus doping concentration were measured using a MEMS micro-device consisting of two suspended silicon nitride membranes in the temperature range of 60 K ~450 K. The experimental results were obtained by "simultaneously" measuring thermal conductivity, electrical conductivity, and thermopower. The ZT improvement is attributed to remarkable thermal conductivity reductions, which are thought to derive from the effective scattering of a broad range of phonons by alloying Si with Ge as well as by limiting phonon transport within the nanowire diameters. An improved model based on Boltzmann transport equation with relaxation time approximation was introduced for estimating thermoelectric properties of phosphorus heavily doped SiGe nanowires from 300 to 1200 K. All the electron and phonon scatterings were comprehensively discussed and utilized to develop the new model for estimating electrical conductivity, thermopower, and thermal conductivity of SiGe nanowires. As thermoelectric materials, oxide nanowires have great advantages comparing to other semiconductors. Two nanostructured materials, SrTiO3 nanotubes and ZnO nanowires, are introduced and successfully synthesized by simple methods. Thermal conductivity of ZnO nanowires with different diameter were characterized from 60 K to 450 K. In order to measure thermoelectric properties of one-dimensional nanostructures at temperature up to 800 K, a new temperature vacuum system was carefully designed and built from scratch. The thermal conductivity of ZnO nanowires with different diameters at high temperature were measured from 300 K to 800 K. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151175
