Mode-Wise Phonon Properties of Bismuth Telluride

2012 ◽  
Author(s):  
Yaguo Wang ◽  
Xianfan Xu
Keyword(s):  
Bismuth Telluride ◽  
Thermal Transport ◽  
Phonon Dispersion ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Mode Analysis ◽  
Phonon Modes ◽  
Time Resolved ◽  
Transport Control ◽  
Phonon Properties

Thermal transport properties and thermal transport control are important for many materials, for example, low thermal conductivity is desirable for thermoelectric materials. Knowledge of mode-wise phonon properties is crucial to identify dominant phonon modes for thermal transport and design effective phonon barriers for thermal transport control. In this paper, we adopt the normal mode analysis to investigate spectral phonon properties, and to calculate phonon dispersion relations and phonon relaxation times in bismuth telluride. Our results agree with previously reported data for long-wavelength longitudinal acoustic phonon and A1g optical phonon obtained from ultrafast time-resolved measurements. By combing the frequency dependent anharmonic phonon group velocities and lifetime, mode-wise thermal conductivities are predicted to reveal the contributions of heat carriers with different polarizations and wavelength.

Mode-Wise Thermal Conductivity of Bismuth Telluride

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Yaguo Wang ◽  
Bo Qiu ◽  
Alan J. H. McGaughey ◽  
Xiulin Ruan ◽  
Xianfan Xu
Keyword(s):  
Thermal Conductivity ◽  
Bismuth Telluride ◽  
Thermal Transport ◽  
Phonon Dispersion ◽  
Relaxation Times ◽  
Phonon Modes ◽  
Time Resolved ◽  
Transport Control ◽  
Reported Data ◽  
Phonon Properties

Thermal properties and transport control are important for many applications, for example, low thermal conductivity is desirable for thermoelectrics. Knowledge of mode-wise phonon properties is crucial to identify dominant phonon modes for thermal transport and to design effective phonon barriers for thermal transport control. In this paper, we adopt time-domain (TD) and frequency-domain (FD) normal-mode analyses to investigate mode-wise phonon properties and to calculate phonon dispersion relations and phonon relaxation times in bismuth telluride. Our simulation results agree with the previously reported data obtained from ultrafast time-resolved measurements. By combining frequency-dependent anharmonic phonon group velocities and lifetimes, mode-wise thermal conductivities are predicted to reveal the contributions of heat carriers with different wavelengths and polarizations.

Mode-Resolved Thermal Conductivity of Freestanding and Supported Bismuth Telluride Quintuple Layer

2016 ◽  
Author(s):  
Cheng Shao ◽  
Hua Bao
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Bismuth Telluride ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Phonon Transport ◽  
Mode Analysis ◽  
Underlying Mechanisms ◽  
Dynamics Simulations ◽  
Phonon Properties

The successful exfoliation of atomically-thin bismuth telluride quintuple layer (QL) attracts tremendous interest in investigating the electron and phonon transport properties in this quasi-two-dimensional material. While experimental results show that thermal conductivity is significantly reduced in Bi2Te3 QL compared to the bulk phase, the underlying mechanisms for the reduction is still unclear. Also in some measurements, the Bi2Te3 QL is usually supported on the substrate and the effect of the substrate on heat transfer in Bi2Te3 QL is unknown. In this work, we have performed molecular dynamics simulations and normal mode analysis to study the mode-wise phonon properties in freestanding and supported Bi2Te3 QL. We found that the existing of substrate will decrease the phonon relaxation times in Bi2Te3 QL in the full frequency range. Thermal conductivity accumulation function for both freestanding and supported Bi2Te3 QL are constructed and compared. We found that half of heat transfer in freestanding Bi2Te3 QL contributed from phonons with mean free paths larger than 16.5 nm, while in supported Bi2Te3 QL this value is reduced to 11 nm. In both cases phonons with MFPs in the range of 10–30 nm are the dominate heat carriers, which contribute to 55% and 53% of thermal conductivity in freestanding and supported cases.

Predicting Phonon Transport in Two-Dimensional Boron Nitride-Graphene Superlattices

2014 ◽  
Author(s):  
Carlos da Silva ◽  
Julia Sborz ◽  
David A. Romero ◽  
Cristina H. Amon
Keyword(s):  
Boron Nitride ◽  
Normal Mode Analysis ◽  
Phonon Transport ◽  
Mode Analysis ◽  
Spectral Energy ◽  
Phonon Modes ◽  
Support Engineering ◽  
Group Velocities ◽  
Phonon Properties

The synthesis of boron nitride (BN) - graphene hybrid materials is now a reality that has opened opportunities for creation of new nanostructures with enhanced mechanical, electronic and thermal properties, of particular interest for nanoelectronics applications. Properties of these materials are still not well understood, and modelling approaches are needed to support engineering design of these novel nanostructures. In this work, we study thermal transport in BN-graphene superlattices from a phonon transport perspective. We predict phonon properties (phonon group velocities and phonon lifetimes) using normal mode analysis based on phonon spectral energy density (SED) in these superlattices, with especial emphasis on the role of the orientation of the atoms at the BN - graphene interfaces. We consider various superlattices compositions with two highly symmetric orientation, i.e., zig-zag and armchair. Our results show that phonon group velocities are higher for the zig-zag interface orientation. We also found that phonon modes at small frequencies are more sensitive to the superlattice configurations.

Predicting Phonon Thermal Transport in Two-Dimensional Graphene-Boron Nitride Superlattices at the Short-Period Limit

2015 ◽  
Author(s):  
Carlos da Silva ◽  
Fernan Saiz ◽  
David A. Romero ◽  
Cristina H. Amon
Keyword(s):  
Boron Nitride ◽  
Density Functional ◽  
Phonon Dispersion ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Mode Analysis ◽  
Two Dimensional ◽  
Boltzmann Transport ◽  
Short Period ◽  
Thermal Conductivities

Two-dimensional superlattices are promising alternatives to traditional semiconductors for manufacturing power-dissipating devices with enhanced thermal and electronic properties. The goal of this work is to investigate the influence of the superlattice secondary periodicity and atomic interface orientation on the phonon properties and thermal conductivity of two-dimensional superlattices of graphene and boron nitride. We have employed harmonic lattice dynamics to predict the phonon group velocities and specific heats, and molecular dynamics to extract the relaxation times from normal mode analysis in the frequency domain. Density functional perturbation theory is applied to validate the phonon dispersion curves. The Boltzmann transport equation under single relaxation time approximation is then used to predict the thermal conductivities of the superlattices in the zigzag and armchair orientations with periodicities between one and five. Our results showed that the thermal conductivities increased by 15.68% when reducing the superlattice period from two to one. In addition, thermal conductivities parallel to the interface increase by 20.15% when switching the orientation from armchair to zigzag.

THZ-FREQUENCY SPECTROSCOPIC SENSING OF DNA AND RELATED BIOLOGICAL MATERIALS

2003 ◽  
Vol 13 (04) ◽  
pp. 903-936 ◽  
Author(s):  
T. GLOBUS ◽  
D. WOOLARD ◽  
M. BYKHOVSKAIA ◽  
B. GELMONT ◽  
L. WERBOS ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Biological Materials ◽  
Mode Analysis ◽  
Resonance Structure ◽  
Terahertz Frequency ◽  
Dna Molecules ◽  
Phonon Modes

The terahertz frequency absorption spectra of DNA molecules reflect low-frequency internal helical vibrations involving rigidly bound subgroups that are connected by the weakest bonds, including the hydrogen bonds of the DNA base pairs, and/or non-bonded interactions. Although numerous difficulties make the direct identification of terahertz phonon modes in biological materials very challenging, recent studies have shown that such measurements are both possible and useful. Spectra of different DNA samples reveal a large number of modes and a reasonable level of sequence-specific uniqueness. This chapter utilizes computational methods for normal mode analysis and theoretical spectroscopy to predict the low-frequency vibrational absorption spectra of short artificial DNA and RNA. Here the experimental technique is described in detail, including the procedure for sample preparation. Careful attention was paid to the possibility of interference or etalon effects in the samples, and phenomena were clearly differentiated from the actual phonon modes. The results from Fourier-transform infrared spectroscopy of DNA macromolecules and related biological materials in the terahertz frequency range are presented. In addition, a strong anisotropy of terahertz characteristics is demonstrated. Detailed tests of the ability of normal mode analysis to reproduce RNA vibrational spectra are also conducted. A direct comparison demonstrates a correlation between calculated and experimentally observed spectra of the RNA polymers, thus confirming that the fundamental physical nature of the observed resonance structure is caused by the internal vibration modes in the macromolecules. Application of artificial neural network analysis for recognition and discrimination between different DNA molecules is discussed.

Effect of Rotation to a Half-Sapce in Magneto-Thermoelasticity with Thermal Relaxations

2007 ◽  
Vol 353-358 ◽  
pp. 3018-3021
Author(s):  
Ying Pan ◽  
Zi Hou Zhang ◽  
Li Hou Liu
Keyword(s):  
Magnetic Field ◽  
Half Space ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Generalized Thermoelasticity ◽  
Mode Analysis ◽  
Two Dimensional ◽  
Induced Magnetic Field ◽  
Coupled Problem ◽  
Analytical Expressions

Based on Green and Lindsay’s generalized thermoelasticity theory with two relaxation times, a two-dimensional coupled problem in electromagneto-thermoelasticity for a rotating half-space solid whose surface is subjected to a heat is studied in this paper. The normal mode analysis is used to obtain the analytical expressions for the considered variables. It can be found electromagneto-thermoelastic coupled effect in the medium, and it also can be found that rotation acts to significantly decrease the magnitude of the real part of displacement and stress and insignificantly affect the magnitude of temperature and induced magnetic field.

Perturbed normal-mode analysis of induction times, relaxation times, and reaction rates in unimolecular reactions

1979 ◽  
Vol 57 (13) ◽  
pp. 1723-1730 ◽  
Author(s):  
Andrew W. Yau ◽  
Huw O. Pritchard
Keyword(s):  
Normal Mode ◽  
Transition Probabilities ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Normal Modes ◽  
Reaction Rates ◽  
Mode Analysis ◽  
Decomposition Reactions ◽  
Induction Times ◽  
Network Relationship

A perturbed normal-mode analysis is presented of the induction (or incubation) time, the relaxation rate, and the reaction rate of a diluted unimolecular system. At high temperature, the unimolecular rate approaches the Lindemann behaviour and the low-pressure rate is related to the normal modes of relaxation of the reactive states in a simple manner. In a step-ladder model system, the network relationship between the normal modes and the microscopic transition probabilities leads to explicit theoretical correlations between the respective experimental quantities. Illustrative calculations of such correlations are presented for the decomposition reactions of N2O and CO2 diluted in Ar at shock wave temperatures, and are compared with experiment.

scholarly journals First-principles interpretation of electron transport though single-molecule junctions using molecular dynamics of electron attached states

2021 ◽  
Author(s):  
Dávid P. Jelenfi ◽  
Attila Tajti ◽  
Péter G. Szalay
Keyword(s):  
Molecular Dynamics ◽  
Electron Transport ◽  
Single Molecule ◽  
Transition Probabilities ◽  
Normal Mode Analysis ◽  
Mode Analysis ◽  
Bending Vibrations ◽  
Time Resolved ◽  
State Models

The electron transport through the single-molecule junction of 1,4-Diaminobenzene (BDA) is modeled using ab initio quantum-classical molecular dynamics of electron attached states. Observations on the nature of the process are made by time-resolved analysis of energy differences, non-adiabatic transition probabilities and the spatial distribution of the excess electron. The role of molecular vibrations that facilitate the transport by being responsible for the periodic behaviour of these quantities is shown using normal mode analysis. The results support a mechanism involving the electron's direct hopping between the electrodes, without its presence on the molecule, with the prime importance of the bending vibrations that periodically alter the molecule{electrode interactions. No relevant differences are found between results provided by the ADC(2) and SOS-ADC(2) excited state models. Our approach provides an alternative insight into the role of nuclear motions in the electron transport process, one which is more expressive from the chemical perspective.

Effect of rotation and gravity on generalized thermo-viscoelastic medium with voids

2018 ◽  
Vol 14 (2) ◽  
pp. 322-338 ◽  
Author(s):  
Mohamed I.A. Othman ◽  
Montaser Fekry
Keyword(s):  
Viscoelastic Material ◽  
Viscoelastic Medium ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Mode Analysis ◽  
Content Type ◽  
Analysis Technique ◽  
Effects Of Rotation ◽  
Physical Quantities ◽  
Coupled Theory

PurposeThe purpose of this paper is to study the effect of rotation and gravity on a homogeneous, isotropic, and generalized thermo-viscoelastic material with voids. The problem is studied in the context of the coupled theory, Lord-Shulman theory with one relaxation time, and Green-Lindsay theory with two relaxation times.Design/methodology/approachThe analytical method used was the normal mode analysis technique.FindingsNumerical results for the physical quantities were analyzed and presented graphically. The graphical results indicated that the effects of rotation and gravity were observable physical effects on the thermo-viscoelastic material with voids. Comparisons were made between the results obtained in the absence and presence of rotation and gravity.Originality/valueIn the present work, the authors investigated the effect of rotation and gravity on thermo-viscoelastic medium with voids. Comparisons were also made between the three theories in the absence and the presence of rotation and gravity. Such problems are very important in many dynamical systems.

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