The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
Haider Ali - One of the best experts on this subject based on the ideXlab platform.
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Chapter 5 – Analytical Treatment of Phonon Transport in Thin Films
Heat Transport in Micro- and Nanoscale Thin Films, 2018Co-Authors: Bekir Sami Yilbas, Saad Bin Mansoor, Haider AliAbstract:The radiative phonon transport equation is critically important to assess the energy transport characteristics in a thin film. In this chapter, analytical treatment of the radiative transport equation is presented, and the formulation of heat transport due to thermal excitation of the thin film is introduced. The closed form solution for the radiative transport equation is presented with the appropriate boundary conditions for the one-dimensional heating situation. In addition, the closed form solution of the hyperbolic heat equation derived from the electron kinetic theory approach is presented, incorporating the thermal disturbance due to laser short-pulse irradiation of the metallic substrates. Since the metallic materials thermally separate under the nonequilibrium heating situations, thermal coupling in terms of the electron–phonon coupling parameter is introduced for the energy transport across the electron and Lattice Subsystems. The radiative transport equation is modified for thin metallic films, and thermal coupling across the electron and Lattice Subsystem is incorporated. The limitations of the two-equation model in micro/nanoscale heating are also discussed.
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Non-equilibrium energy transport and entropy production due to laser short-pulse irradiation
Canadian Journal of Physics, 2016Co-Authors: Haider Ali, Ahmad Y. Al-dweikAbstract:Laser short-pulse heating of a nano-size wire is considered and entropy generation rate is predicted during the heating pulse. The analytical solution of the heat equation is obtained using the Lie point symmetry for the laser short-pulse heating. The nano-size wire is assumed to be symmetric along its y-axis. Laser pulse intensity is considered to be Gaussian at the irradiated surface while the exponential decay of the laser pulse is incorporated in the time domain. It is found that surface temperature variation in the Lattice Subsystem almost follows the laser pulse intensity distribution at the surface. Entropy generation rate attains low values along the symmetry axis and it increases considerably in the region of the nano-size wire edges. This behavior is associated with the temperature gradient, which attains high values in the region close to the nano-size wire edge.
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Effect of Film Thickness on Energy Transport Characteristics in Aluminum Thin Film
Journal of Thermophysics and Heat Transfer, 2015Co-Authors: Haider Ali, Bekir Sami YilbasAbstract:Energy transfer in an aluminum thin film is considered due to a temperature disturbance at the film edges. Temperature oscillation is introduced at the high-temperature edge of the film, and the thermal response of the film is assessed through use of an equivalent equilibrium temperature. Transient frequency-dependent and frequency-independent solutions of the Boltzmann equation are obtained for phonon intensity distributions in the Lattice Subsystem. An electron–phonon coupling parameter is incorporated in order to account for the thermal communication between electrons and Lattice Subsystems in the film. The dispersion relations are used in the solution of the frequency-dependent Boltzmann equation. The study is extended to include the effect of film thickness on energy transport characteristics. It is found that oscillation of the equivalent equilibrium temperature takes place within the film because of temperature oscillation at the high-temperature film edges and, as the film thickness increases, the...
Evgeny Yakovlev - One of the best experts on this subject based on the ideXlab platform.
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Influence of accumulation effects on heating of silicon surface by femtosecond laser pulses
Applied Surface Science, 2015Co-Authors: I. V. Guk, G. D. Shandybina, Evgeny YakovlevAbstract:Abstract In this paper we present numerical evaluations of influence of accumulation effects on the heating of silicon surface by femtosecond laser pulses at low repetition rate in the regimes of formation of laser-induced periodic surface structures. Numerical evaluations were made using combined method, where photoexcitation process of semiconductor is described by diffusion equation of nonequilibrium carriers, electron Subsystem and Lattice Subsystem heat is calculated using two-temperature model and the cooling of semiconductor between the pulses is described by analytical solution of the heat equation. The change of silicon absorptivity during the pulse, the change of the absorptivity between the pulses due to the formation of the periodic structures and a contribution of recombination processes is taken into the account. A comparison of the results with experimental data on the evolution of the microstructures during femtosecond laser irradiation of silicon is made.
Yuwen Zhang - One of the best experts on this subject based on the ideXlab platform.
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Electron-Phonon Coupled Heat Transfer and Thermal Response Induced by Femtosecond Laser Heating of Gold
Journal of Heat Transfer, 2017Co-Authors: Yuwen ZhangAbstract:Ab initio simulation is one of the most effective theoretical tools to study the electrons evolved heat transfer process. Here, we report the use of finite-temperature density functional theory (DFT) to investigate the electron thermal excitation, electron–phonon coupled heat transfer, and the corresponding thermal response induced by energy deposition of femtosecond laser pulse in gold. The calculated results for cases with different scales of electron excitations demonstrate significant electron temperature dependence of electron heat capacity and electron–phonon coupling factor. Bond hardening of laser-irradiated gold and structural variation from solid to liquid are observed. The obtained results shed light upon the ultrafast microscopic processes of thermal energy transport from electron Subsystem to Lattice Subsystem and serve for an improved interpretation of femtosecond laser–metal interaction.
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continuum atomistic simulation of picosecond laser heating of copper with electron heat capacity from ab initio calculation
Chemical Physics Letters, 2016Co-Authors: Yuwen ZhangAbstract:Abstract On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron Subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron Subsystem to the Lattice Subsystem is modeled by including the electron–phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provides a general way that is accessible to other metals in laser heating.
I. V. Guk - One of the best experts on this subject based on the ideXlab platform.
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Role of the heat accumulation effect in the multipulse modes of the femtosecond laser microstructuring of silicon
Semiconductors, 2016Co-Authors: I. V. Guk, G. D. Shandybina, E. B. YakovlevAbstract:The results of quantitative evaluation of the heat accumulation effect during the femtosecond laser microstructuring of the surface of silicon are presented for discussion. In the calculations, the numerical–analytical method is used, in which the dynamics of electronic processes and Lattice heating are simulated by the numerical method, and the cooling stage is described on the basis of an analytical solution. The effect of multipulse irradiation on the surface temperature is studied: in the electronic Subsystem, as the dependence of the absorbance on the excited carrier density and the dependence of the absorbance on the electron-gas temperature; in the Lattice Subsystem, as the variation in the absorbance from pulse to pulse. It was shown that, in the low-frequency pulse-repetition mode characteristic of the femtosecond microstructuring of silicon, the heat accumulation effect is controlled not by the residual surface temperature by the time of the next pulse arrival, which corresponds to conventional concepts, but by an increase in the maximum temperature from pulse to pulse, from which cooling begins. The accumulation of the residual temperature of the surface can affect the microstructuring process during irradiation near the evaporation threshold or with increasing pulse-repetition rate.
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Influence of accumulation effects on heating of silicon surface by femtosecond laser pulses
Applied Surface Science, 2015Co-Authors: I. V. Guk, G. D. Shandybina, Evgeny YakovlevAbstract:Abstract In this paper we present numerical evaluations of influence of accumulation effects on the heating of silicon surface by femtosecond laser pulses at low repetition rate in the regimes of formation of laser-induced periodic surface structures. Numerical evaluations were made using combined method, where photoexcitation process of semiconductor is described by diffusion equation of nonequilibrium carriers, electron Subsystem and Lattice Subsystem heat is calculated using two-temperature model and the cooling of semiconductor between the pulses is described by analytical solution of the heat equation. The change of silicon absorptivity during the pulse, the change of the absorptivity between the pulses due to the formation of the periodic structures and a contribution of recombination processes is taken into the account. A comparison of the results with experimental data on the evolution of the microstructures during femtosecond laser irradiation of silicon is made.
Zoran Ivić - One of the best experts on this subject based on the ideXlab platform.
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Soliton-induced modification of the speed of sound in quasi-one-dimensional molecular crystals
Journal of Physics: Condensed Matter, 1998Co-Authors: Jasmina Tekić, Zoran Ivić, Zeljko PrzuljAbstract:The influence of the anharmonic vibron-phonon coupling, arising on account of a `dressing' effect, on the characteristics of the Lattice Subsystem in quasi-one-dimensional molecular crystals was examined within the `pseudo-harmonic' phonon approximation. It was found that solitons could induce specific modifications of the speed of sound which shows a temperature dependence quite different to that in the case of the linear excitations. The possibility of an indirect experimental verification of the existence of solitons in molecular chains is suggested on the basis of these predictions.
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Soliton-phonon interaction in anharmonic quasi-one-dimensional ferromagnetic crystals: Soliton-induced modification of the speed of sound.
Physical review. B Condensed matter, 1994Co-Authors: Jasmina Tekić, Zoran IvićAbstract:The influence of the spin-phonon coupling on soliton characteristics and the soliton response on the Lattice Subsystem in a quasi-one-dimensional magnetic chain is examined. It was found that, in the case of the ferromagnetic coupling, these correlations may induce reduction of the effective exchange integral which, in the temperature range where one-dimensional ordering prevails, may be maximally about 1%. Consequently the soliton energy and width suffer the negligible modification, too. On the other hand, the magnetic Subsystem may have a certain impact on elastic Subsystem characteristics, the speed of sound in particular. The character of these changes depends strongly on the type of the excitations of the magnetic Subsystem---solitons or magnons.