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Thermal Transport Across Interfaces Two Dimensional Materials And Iii V Ternary Alloy Superlattices
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Book Synopsis Thermal Transport Across Interfaces, Two-dimensional Materials, and III-V Ternary-alloy Superlattices by : Gabriel Jaffe (Ph.D.)
Download or read book Thermal Transport Across Interfaces, Two-dimensional Materials, and III-V Ternary-alloy Superlattices written by Gabriel Jaffe (Ph.D.) and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements of the thermal conductivity across thin films and interfaces are crucial for efforts to build a predictive model of thermal conductivity at sub-micron length scales. This thesis will cover cross-plane thermal conductivity measurements of InAlAs/InGaAs superlattices where phonon interface scattering plays an important role in determining the thermal conductivity of the heterostructure. Thermal measurements are performed using the three-omega method. This method typically requires long straight heating wires to be fabricated across the sample of interest. In many cases, obstructions on a sample's surface prevent straight wires from being made. We demonstrate both experimentally and numerically that heating wires in variety of shapes can be used for three-omega experiments without introducing significant systematic error.
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 0 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 Understanding Heat Transport at Interfaces for Thermal Management of Electronics by : Lenan Zhang
Download or read book Understanding Heat Transport at Interfaces for Thermal Management of Electronics written by Lenan Zhang and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery and development of two-dimensional (2D) materials offer new opportunities for high-performance nanoscale electronics. However, new material systems involve new device architectures, which leads to new challenges on both the electronic and thermal design. While significant progress has been made to understand and engineer the electrical properties of 2D devices, the thermal problems remain relatively poorly understood. Since many 2D electronics can reach very high-power density (>104 W/cm2 ), the dense vertical integration of multilayers within a few nanometers leads to a significant temperature rise (>150 °C), which becomes the bottleneck of device performance. These thermal challenges are associated with two critical thermophysical properties of 2D materials, i.e., the thermal expansion and the interfacial thermal transport. In addition, to address the thermal management of 2D electronics, novel cooling approaches with insights gained from 2D thermal interfaces are in high demands. This thesis performed a systematic study on the thermal expansion and thermal transport of the van der Waals (vdW) bonded 2D interfaces, and developed highly efficient thermal management solutions based on two-phase cooling. First, we developed for the first time a pure experimental approach to accurately measure the thermal expansion coefficients(TECs) of various 2D materials. Our measurements confirmed the correct physical range of 2D monolayer TECs and hence addressed the more than two orders of magnitude discrepancies in literature. Second, we investigated the thermal transport across various 2D interfaces. In particular, we elucidated the role of vdW interaction in the anisotropic thermal transport of substrate-supported 2D monolayers and identified an optimal vdW interaction toward the maximum total heat transfer. On the other hand, we explored the twist-angle dependence of 2D interfacial thermal transport. We observed that depending on different material systems, the thermal transport of 2D materials can exhibit both strong and weak twist-angle dependences, which creates a new degree of freedom to manipulate heat at the atomic level. Lastly, with fundamental understanding of 2D thermal interfaces, we designed and optimized a liquid-vapor thin film evaporator based on microstructured surfaces, enabling high-performance thermal management of 2D electronics. This thesis provides a holistic understanding for the fundamental thermal properties of 2D materials and interfaces, which are critical to address the thermal crisis of 2D electronics. We believe the simulation, experimental, and design approaches developed in this thesis can serve as a guideline for the next-generation 2D electronics with unprecedented reliability and performance.
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Thermal Transport in Materials and Structures Pertinent to Quantum Cascade Lasers by : Carlos Perez
Download or read book Thermal Transport in Materials and Structures Pertinent to Quantum Cascade Lasers written by Carlos Perez and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since their initial demonstration in 1994, quantum cascade lasers (QCLs) have undergone enormous advancements. However, inefficient dissipation of heat can hinder the performance of QCLs. The complex structure of QCL devices creates a difficult thermal problem. The multilayer and multi-material nature of QCL designs results in a highly resistive thermal pathway to the heatsink due to various phonon-scattering mechanisms. Given the large proportion of electrical pump power that dissipates as heat within these arrays, the thermal design needs to be optimized to minimize the temperature increase within the array and avoid thermal issues, such as reduced maximum power output, decreased wall-plug efficiency, thermal lensing, and increased lasing threshold current. To maintain the advancement of QCLs, the thermal dissipation issues of these devices must be addressed. It is necessary to characterize the different scattering mechanisms that affect the thermal conductivity of materials and structures, such as superlattices (SLs), relevant to these devices. In this work, time-domain thermoreflectance was used to measure the thermal properties of SLs, silicon-doped indium phosphide (Si-InP), iron-doped indium phosphide (Fe-InP), InGaAs, and InAlAs at various temperatures, concentrations, interface densities (# interfaces/total thickness), and thicknesses. In this work, the thermal conductivity of thin films of Si-InP and Fe-InP from 80 to 450 K was measured. The phonon gas model and sensitivity analysis were used to characterize the role of various scattering mechanisms in Si-InP and Fe-InP. The effect of film thickness on the thermal conductivity of these materials was quantified. In addition, the thermal conductivity of In0.63Ga0.37As/In0.37Al0.63As SLs with interface densities ranging from 0.0374 to 2.19 nm-1 in the temperature range of 80--450 K was measured. Time-domain thermoreflectance measurements of the thermal conductivity of III-V alloy SLs as a function of interface density demonstrate the presence of a minimum, which is an indication of a crossover from incoherent to coherent phonon transport as the interface density increases. This minimum continues with increasing temperature, showing the continued dominance of the temperature-independent interface and alloy disorder scattering over the temperature-dependent three-phonon scattering in thermal transport through III--V alloy SLs. The In0.5275Ga0.4725As measurements indicate that thermal conductivity decreases as thickness decreases, primarily due to boundary scattering, until a critical thickness of ~100 nm is reached, below which the thermal conductivity appears to flatten out at ~2.75 W m-1 K-1. The In0.521Al0.479As measurements seem to be insensitive to sample thickness, similar in some ways to what has been shown in amorphous materials such as SiO2, where the effects of thin film size are nonexistent. This study fills the knowledge gap regarding the thermal properties of materials and structures important to QCLs.
Book Synopsis Novel Physical Phenomena in Oxide Superlattices by : Ajay Kumar Yadav
Download or read book Novel Physical Phenomena in Oxide Superlattices written by Ajay Kumar Yadav and published by . This book was released on 2016 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is historically proven that artificial heterostructures are of paramount importance for both fundamental research and technological application. One distinguishable example is superlattices and quantum-well heterostructures of conventional semiconductors (III-V). Several fundamental observations such as two-dimensional electron gas, quantum confinement effect, quantum Hall effect and fractional quantum Hall effect, were first realized in artificial heterostructures of conventional semiconductors. On the technological front, artificial heterostructures of conventional semiconductors were found to revolutionize optoelectronic and high-speed electronic industry. Given the capability of artificial heterostructures to enable new physical phenomena, with an appropriate choice of material system, these heterostructures hold the potential to uncover hidden physical phenomena and exotic phases, which are otherwise not observed in bulk systems. One choice of such a system could be a strongly correlated material where the presence of strong electronic correlations has been known to enable unique electronic and magnetic properties. Complex oxides, in particular, are known to exhibit a strong interaction between various degrees of freedom available such as spin, charge, orbital and lattice degree, and thus offer a suitable choice of material system. In literature, one can find plenty of examples from different areas of research such as superconductivity, magnetism, ferroelectricity and thermoelectricity, where artificial superlattices led to the observation of fundamentally different behavior, compared to bulk superlattice constituents. These artificial superlattices and heterostructures continue to be the most promising candidate for exploring new phenomena and enhancing physical properties in complex oxide material systems. In this dissertation, artificial superlattices of complex oxides were synthesized in a thin-film geometry to enable the observation of fundamentally new physical phenomena, compared to their bulk counterparts, in few selected areas of investigation. First, I will present the experimental results on heat transport across superlattice structures composed of insulating perovskite oxides. The measured thermal conductivity of these artificial superlattices exhibited a unique phonon transport, i.e. coherent phonon transport, phenomenon that is extremely rare to observe in bulk form. The key element for enabling the coherent transport of phonon in these superlattice systems is the range of phonon wavelengths, which carry most of the heat in the material. The critical range being between 1-3 nanometers, the size of the system needs to reduce to this length scale in order to observe the effect of the wave nature of phonons on heat transport. Thus, superlattice structures offer an ideal candidate to search for this novel phenomenon. Several theoretical studies predicted the existence of these phenomena, but the experimental evidence of their existence remained largely absent or inconclusive. By synthesizing the superlattice of perovskite oxides, I’ve observed unambiguous evidence of the coherent transport of phonons at short-period superlattices of SrTiO3-CaTiO3 and BaTiO3-SrTiO3. In contrast to conventional heat conduction mechanisms, where phonon transport can be described by energy-carrying particles, the uniqueness of this phenomenon is highlighted by the fact that the wave aspect of phonons needs to be invoked to understand their transport behavior. After observing the wave nature of phonons in dictating heat conduction across periodic superlattices, other artificial heterostructures were studied to understand the nature of coherent phonon transport at the superlattice interfaces. Designed superlattice-like sequences, where the structural order can be controlled from a periodic sequence to a completely random sequence, were synthesized to further understand the role of the coherent scattering of phonons in thermal transport across superlattice structures. Next, I will discuss the experimental observation of another unique phenomenon, which was enabled by artificial superlattices of complex oxides in a different subject of research, i.e. ferroelectricity. Several theoretical studies on nanostructured ferroelectric systems such as nanodisc, nanocomposites, superlattices etc., predicted the stabilization of novel ferroelectric ground states. A number of different topologies of electrical polarization such as vortices and skyrmions, were predicted in ferroelectric nanostructures, which showed a strong resemblance to spin topologies such as skyrmion, merons etc. found in magnetic systems. Experimental confirmation for the existence of these exotic polarization states, however, remained absent. By leveraging the competition among charge, orbital and lattice degrees of freedom in superlattices of a paraelectric (SrTiO3) and ferroelectric (PbTiO3) material, vortex-antivortex structures of electrical polarization were stabilized in ferroelectric (PbTiO3) layers of PbTiO3-SrTiO3 superlattice. Only for a narrow range of superlattice periods, the polarization vortices are stabilized with a balance between one gradient energy associated with the non-uniform polarization profile of the vortex structure and the other’s electrostatic and elastic energies associated with depolarization fields and epitaxial constraints from the substrate, respectively. In the last section, I will describe unique and unusual phenomena associated with the existence of polarization vortices in paraelectric/ferroelectric superlattices. Superlattices of PbTiO3-SrTiO3 with varying periodicity showed a rich spectrum of characteristically different ferroelectric domains. Specifically, in the short-period regime, domain size was observed to evolve with a negative scaling coefficient, which is unusual for typical ferroelectrics. When the superlattice periodicity was increased, the average domain size decreased, suggesting an opposite behavior to the universal Kittel’s Law, where in the latter, an increase in ferroelectric thickness leads to an increase in the average domain size. Second, I will present intriguing results on the fundamental characteristics of polarization vortices as revealed from X-ray circular dichroism studies. The finite difference in absorption spectra of left-circular vs. right-circular polarized light from vortex structures, suggested that vortex-antivortex arrays are chiral in nature. The presence of chirality in polarization vortex structures is a characteristically different behavior compared to bulk ferroelectric systems where uniformly polarized regions are expected to exhibit a linear X-ray dichroism (i.e. a difference in the absorption spectra of linearly polarized light in a direction parallel and perpendicular to ferroelectric order). Lastly, a possibility of manipulating phonon dispersion using vortex ordering or vortex “lattice” is discussed, along with a hypothesis of inducing localization in propagative phonons.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1989 with total page 992 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physics Briefs written by and published by . This book was released on 1992 with total page 1812 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Nuclear Science Abstracts written by and published by . This book was released on 1975 with total page 1550 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis 2D Monoelemental Materials (Xenes) and Related Technologies by : Zongyu Huang
Download or read book 2D Monoelemental Materials (Xenes) and Related Technologies written by Zongyu Huang and published by CRC Press. This book was released on 2022-04-19 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monoelemental 2D materials called Xenes have a graphene-like structure, intra-layer covalent bond, and weak van der Waals forces between layers. Materials composed of different groups of elements have different structures and rich properties, making Xenes materials a potential candidate for the next generation of 2D materials. 2D Monoelemental Materials (Xenes) and Related Technologies: Beyond Graphene describes the structure, properties, and applications of Xenes by classification and section. The first section covers the structure and classification of single-element 2D materials, according to the different main groups of monoelemental materials of different components and includes the properties and applications with detailed description. The second section discusses the structure, properties, and applications of advanced 2D Xenes materials, which are composed of heterogeneous structures, produced by defects, and regulated by the field. Features include: Systematically detailed single element materials according to the main groups of the constituent elements Classification of the most effective and widely studied 2D Xenes materials Expounding upon changes in properties and improvements in applications by different regulation mechanisms Discussion of the significance of 2D single-element materials where structural characteristics are closely combined with different preparation methods and the relevant theoretical properties complement each other with practical applications Aimed at researchers and advanced students in materials science and engineering, this book offers a broad view of current knowledge in the emerging and promising field of 2D monoelemental materials.
Book Synopsis Comprehensive Dissertation Index by :
Download or read book Comprehensive Dissertation Index written by and published by . This book was released on 1989 with total page 1016 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Government Reports Annual Index by :
Download or read book Government Reports Annual Index written by and published by . This book was released on 1994 with total page 1744 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Journal of the Optical Society of America by :
Download or read book Journal of the Optical Society of America written by and published by . This book was released on 1986 with total page 1152 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis American Doctoral Dissertations by :
Download or read book American Doctoral Dissertations written by and published by . This book was released on 1991 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nanomaterials for Hydrogen Storage Applications by : Fatih Şen
Download or read book Nanomaterials for Hydrogen Storage Applications written by Fatih Şen and published by Elsevier. This book was released on 2020-09-09 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanomaterials for Hydrogen Storage Applications introduces nanomaterials and nanocomposites manufacturing and design for hydrogen storage applications. The book covers the manufacturing, design, characterization techniques and hydrogen storage applications of a range of nanomaterials. It outlines fundamental characterization techniques for nanocomposites to establish their suitability for hydrogen storage applications. Offering a sound knowledge of hydrogen storage application of nanocomposites, this book is an important resource for both materials scientists and engineers who are seeking to understand how nanomaterials can be used to create more efficient energy storage solutions. Assesses the characterization, design, manufacture and application of different types of nanomaterials for hydrogen storage Outlines the major challenges of using nanomaterials in hydrogen storage Discusses how the use of nanotechnology is helping engineers create more effective hydrogen storage systems
Book Synopsis International Aerospace Abstracts by :
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 934 pages. Available in PDF, EPUB and Kindle. Book excerpt:
