Non-equilibrium phonon generation and detection in microstructure devices

J. B. Hertzberg; O. O. Otelaja; N. J. Yoshida; R. D. Robinson

doi:10.1063/1.3652979

A Study of Spatially-Resolved Non-Equilibrium in Laser-Irradiated Graphene Using Boltzmann Transport Equation

Volume 8C: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-66095 ◽

2013 ◽

Author(s):

Ajit K. Vallabhaneni ◽

James Loy ◽

Dhruv Singh ◽

Xiulin Ruan ◽

Jayathi Murthy

Keyword(s):

Thermal Conductivity ◽

Steady State ◽

Laser Irradiation ◽

Density Functional ◽

Boltzmann Transport ◽

Energy Carriers ◽

Spatially Resolved ◽

Scattering Rate ◽

Phonon Generation ◽

Non Equilibrium

Raman spectroscopy is typically used to characterize graphene in experiments and also to measure properties like thermal conductivity and optical phonon lifetime. The laser-irradiation processes underlying this measurement technique include coupling between photons, electrons and phonons. Recent experimental studies have shown that e-ph scattering limits the performance of graphene-based electronic devices due to the difference in their timescales of relaxation resulting in various bottleneck effects. Furthermore, recently published thermal conductivity measurements on graphene are sensitive to the laser spot size which strengthens the possibility of non-equilibrium between various phonon groups. These studies point to the need to study the spatially-resolved non-equilibrium between various energy carriers in graphene. In this work, we demonstrate non-equilibrium in the e-ph interactions in graphene by solving the linearized electron and phonon Boltzmann transport equations (BTE) iteratively under steady state conditions. We start by assuming that all the electrons equilibrate rapidly to an elevated temperature under laser-irradiation and they gradually relax by phonon emission and reach a steady state. The electron and phonon BTEs are coupled because the e-ph scattering rate depends on the phonon population while the rate of phonon generation depends on the e-ph scattering rate. We used density-functional theory/density-functional perturbation theory (DFT/DFPT) to calculate the electronic eigen states, phonon frequencies and the e-ph coupling matrix elements. We calculated the rate of energy loss from the hot electrons in terms of the phonon generation rate (PGR) which serve as an input for solving the BTE. Likewise, ph-ph relaxation times are calculated from the anharmonic lattice dynamics (LD)/FGR. Through our work, we obtained the spatially resolved temperature profiles of all the relevant energy carriers throughout the entire domain; these are impossible to obtain through experiments.

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Non-equilibrium LO and TO phonon generation by electron transport in Terahertz quantum cascade lasers

Conference on Lasers and Electro-Optics 2010 ◽

10.1364/cleo.2010.cthu4 ◽

2010 ◽

Author(s):

Miriam Serena Vitiello ◽

Gaetano Scamarcio ◽

Rita Claudia Iotti ◽

Fausto Rossi ◽

Lukas Mahler ◽

...

Keyword(s):

Electron Transport ◽

Quantum Cascade Lasers ◽

Quantum Cascade ◽

Phonon Generation ◽

Cascade Lasers ◽

Non Equilibrium

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Application of analytical electron microscopy to studies of equilibrium and non-equilibrium segregation in materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130705 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1214-1215

Author(s):

Edward A Kenik

Keyword(s):

Electron Microscopy ◽

Analytical Electron Microscopy ◽

Extended Defects ◽

Probe Diameter ◽

Specimen Holder ◽

Analytical Electron ◽

Scanning Transmission ◽

Solute Atoms ◽

Equilibrium Segregation ◽

Non Equilibrium

Segregation of solute atoms to grain boundaries, dislocations, and other extended defects can occur under thermal equilibrium or non-equilibrium conditions, such as quenching, irradiation, or precipitation. Generally, equilibrium segregation is narrow (near monolayer coverage at planar defects), whereas non-equilibrium segregation exhibits profiles of larger spatial extent, associated with diffusion of point defects or solute atoms. Analytical electron microscopy provides tools both to measure the segregation and to characterize the defect at which the segregation occurs. This is especially true of instruments that can achieve fine (<2 nm width), high current probes and as such, provide high spatial resolution analysis and characterization capability. Analysis was performed in a Philips EM400T/FEG operated in the scanning transmission mode with a probe diameter of <2 nm (FWTM). The instrument is equipped with EDAX 9100/70 energy dispersive X-ray spectrometry (EDXS) and Gatan 666 parallel detection electron energy loss spectrometry (PEELS) systems. A double-tilt, liquid-nitrogen-cooled specimen holder was employed for microanalysis in order to minimize contamination under the focussed spot.

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