1,721,010 research outputs found
Heat transport across a SiGe nanowire axial junction: Interface thermal resistance and thermal rectification
No full textWe study thermal transport in SiGe nanowires by means of nonequilibrium molecular dynamics simulations. We calculate the axial interface thermal resistance (ITR) of realistic models of SiGe nanowires that are obtained in different experimental conditions. We study thermal rectification, finding that heat transport from Si to Ge is favored, particularly in sharp junctions, and that this behavior can be explained in terms of the different temperature dependence of the thermal conductivity of the pristine nanowires
Interface driven thermal rectification in a graphene-bilayer graphene junction from nonequilibrium molecular dynamics
No full textCrystal Phase Effects in Si Nanowire Polytypes and Their Homojunctions
No full textRecent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Driven by this promising evidence, we use first-principles methods based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of hexagonal-diamond and cubic-diamond Si NWs as well as their homojunctions. We show that hexagonal-diamond NWs are characterized by a more pronounced quantum confinement effect than cubic-diamond NWs. Furthermore, they absorb more light in the visible region with respect to cubic-diamond ones and, for most of the studied diameters, they are direct band gap materials. The study of the homojunctions reveals that the diameter has a crucial effect on the band alignment at the interface. In particular, at small diameters the band-offset is type-I whereas at experimentally relevant sizes the offset turns up to be of type-II. These findings highlight intriguing possibilities to modulate electron and hole separations as well as electronic and optical properties by simply modifying the crystal phase and the size of the junction
A review on III-V core-multishell nanowires: Growth, properties, and applications
No full textThis review focuses on the emerging field of core-multishell (CMS) semiconductor nanowires (NWs). In these kinds of wires, a NW grown vertically on a substrate acts as a template for the coaxial growth of two or more layers wrapped around it. Thanks to the peculiar geometry, the strain is partially released along the radial direction, thus allowing the creation of fascinating heterostructures, even based on lattice mismatched materials that would hardly grow in a planar geometry. Enabling the unique bridging of the 1D nature of NWs with the exciting properties of 2D heterostructures, these novel systems are becoming attractive for material science, as well as fundamental and applied physics. We will focus on NWs made of III-V and III-V-based alloys as they represent a model system in which present growth techniques have reached a high degree of control on the material structural properties, and many physical properties have been assessed, from both the theoretical and experimental points of view. In particular, we provide an overview on the growth methods and structural properties of CMS NWs, on the modulation doping mechanisms enabled by these heterostructures, on the effects of a magnetic field, and on the phononic and optical properties typical of CMS NWs. Moreover, we review the main technological applications based on these systems, such as optoelectronic and photovoltaic devices
Structural and electronic properties of Si1-xGex alloy nanowires
No full textWe present first-principles density-functional calculations of Si1-xGex alloy nanowires. We show that given the composition of the alloy, the structural properties of the nanowires can be predicted with great accuracy by means of Vegard’s law, linearly interpolating the values of a pure Si and a pure Ge nanowire of the same diameter. The same holds, to some extent, also for electronic properties such as the band-gap. We also assess to what extend the band-gap varies as a function of disorder, i.e., how it changes for different random realization of a given concentration. These results make possible to tailor the desired properties of SiGe alloy nanowires starting directly from the
data relative to the pristine wires
Thermal rectification by design in telescopic Si nanowires
Full text linkWe show that thermal rectification by design is possible by joining/growing Si nanowires (SiNWs) with sections of appropriately selected diameters (i.e., telescopic nanowires). This is done, first, by showing that the heat equation can be applied at the nanoscale (NW diameters down to 5 nm). We (a) obtain thermal conductivity versus temperature, κ(T), curves from molecular dynamics (MD) simulations for SiNWs of three different diameters, then (b) we conduct MD simulations of a telescopic NW built as the junction of two segments with different diameters, and afterward (c) we verify that the MD results for thermal rectification in telescopic NWs are very well reproduced by the heat equation with κ(T) of the segments from MD. Second, we apply the heat equation to predict the amount of thermal rectification in a variety of telescopic SiNWs with segments made from SiNWs where κ(T) has been experimentally measured, obtaining r values up to 50%. This methodology can be applied to predict the thermal rectification of arbitrary heterojunctions as long as the κ(T) data of the constituents are available
Thermal boundary resistance in semiconductors by non-equilibrium thermodynamics
Full text linkWe critically address the problem of predicting the thermal boundary resistance at the interface between two semiconductors by atomistic simulations. After reviewing the available models, lattice dynamics calculations and molecular dynamics simulation protocols, we reformulate this problem in the language of non-equilibrium thermodynamics, providing an elegant, robust and valuable theoretical framework for the direct calculation of the thermal boundary resistance through molecular dynamics simulations. The foundation of the method, as well as its subtleties and the details of its actual implementation are presented. Finally, the Si/Ge interface showcase is discussed as the prototypical example of semiconductor heterojunction whose thermal properties are paramount in many front-edge nanotechnologie
Silicon−Germanium Nanowires: Chemistry and Physics in Play, from Basic Principles to Advanced Applications
No full textCONTENTS
1. Introduction 1371
2. Growth Techniques, Morphology, and Structural
Properties 1373
2.1. Alloyed Nanowires 1373
2.2. Axial Heterostructures 1375
2.3. Radial Heterostructures 1377
3. Chemical and Physical Properties 1379
3.1. Electronic Properties 1379
3.1.1. Modulation of the Electronic Properties
by Composition Control 1379
3.1.2. Interfaces at Work: Strain, Band-Offset,
and Carrier Gases 1381
3.1.3. Doped Nanowires 1384
3.2. Thermal and Thermoelectric Properties 1385
4. Theoretical Modeling 1389
4.1. Electronic Structure 1390
4.1.1. Quantum Confinement Effect and Band
Offset 1391
4.1.2. Size Effects 1393
4.1.3. Alloying and Interface Effects 1394
4.1.4. Strain Effects 1395
4.1.5. Addition of Impurities 1395
4.1.6. Electronic Transport 1396
4.1.7. Optical Properties 1397
4.2. Phonons and Thermal Conductivity 1398
4.2.1. Breakdown of Fourier’s Law at Nanoscale 1398
4.2.2. Numerical Simulations of Thermal Properties
1398
5. Devices and Applications 1402
5.1. High-Performance Nanoelectronic Components
1403
5.1.1. Si1−xGex Alloy Nanowire Transistor 1403
5.1.2. Si-Shell Ge-Core Nanowire Transistor 1404
5.2. From Quantum Transport to Superconductivity:
SiGe Nanowires As Platforms for
Fundamental Physics Studies 1405
6. Conclusions and Perspectives 1405
Author Information 1406
Corresponding Authors 1406
Notes 1406
Biographies 1407
Acknowledgments 1408
References 140
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