Study into laser short-pulse heating of a layered structure

2009 ◽  
Vol 224 (5) ◽  
pp. 1099-1111
Author(s):  
B S Yilbas
Keyword(s):  
Seebeck Coefficient ◽  
Temperature Rise ◽  
Layered Structure ◽  
Lattice Site ◽  
Pulse Heating ◽  
Short Pulse ◽  
Silicon Layer ◽  
Theory Approach ◽  
Seebeck Coefficients ◽  
Lead Layer

Laser short-pulse heating of a lead—silicon—gold-layered structure is considered and non-equilibrium equation in the lattice and electron subsystems is formulated using the electron kinetic theory approach. The Seebeck coefficient in the metallic and silicon layers is also formulated. Electron and lattice site temperature rise in the subsystems and the Seebeck coefficients are computed for time exponentially decaying pulse. The study is extended to include the influence of the first layer (lead layer) thickness on temperature rise and the Seebeck coefficients. It is found that the lattice site temperature across the interface of the lead and silicon layers increases sharply. The Seebeck coefficient predicted in the silicon layer is higher than in the metallic layers in the structure.

Laser short-pulse heating: A theoretical analysis of electron excess energy dissipation in the early heating period

2006 ◽  
Vol 220 (1) ◽  
pp. 95-102
Author(s):  
B S Yilbas ◽  
K Boran
Keyword(s):  
Energy Dissipation ◽  
Laser Pulse ◽  
Electron Temperature ◽  
Temperature Rise ◽  
Lattice Site ◽  
Pulse Heating ◽  
Short Pulse ◽  
Gold Surface ◽  
Excess Energy ◽  
Heating Period

Laser short-pulse heating of a gold surface is considered. In order to examine the influence of electron-phonon collision on electron and lattice temperature rise, two cases are accommodated in the analysis. In case 1, excess energy dissipation through electron—phonon collision is omitted during the initiation of the laser pulse and the electron—phonon collision time, and in case 2, electron excess energy dissipation from the initiation of the laser pulse is accommodated in the analysis. It is found that electron temperature rise is higher while lattice site temperature is lower for case 1 than that corresponding to case 2. However, the electron temperature difference due to case 1 and case 2 is small, particularly during late heating periods.

Laser short-pulse heating with time-varying intensity and thermal stress development in the lattice subsystem

2005 ◽  
Vol 219 (1) ◽  
pp. 73-81 ◽  
Author(s):  
B S Yilbas ◽  
A F M Arif
Keyword(s):  
Thermal Stress ◽  
Lattice Site ◽  
Energy Transport ◽  
Pulse Heating ◽  
Short Pulse ◽  
High Stress ◽  
Surface Region ◽  
Substrate Material ◽  
Temperature Gradients ◽  
Stress Levels

Laser short-pulse heating of solid surfaces results in non-equilibrium energy transport in the region irradiated by the laser beam. Owing to the large temperature gradients in the lattice subsystem, high stress levels develop in the surface region of the substrate material. In the present study, temperature and stress fields in the substrate material are presented for the case of the laser short-pulse heating of gold. Electron kinetic theory and a two-equation heating model are introduced to account for non-equilibrium energy transport during the laser heating pulse. Laser pulses exponentially decaying with time are accommodated in the simulations. It is found that lattice site temperature gradients attain high values inspite of the low magnitude of the lattice site temperature. This, in turn, results in high stress levels in the surface region of the substrate material. Thermal stress is compressive owing to high thermal strain development and low displacement of the surface.

Laser short-pulse heating: Three-dimensional consideration

2001 ◽  
Vol 215 (9) ◽  
pp. 1123-1138 ◽  
Author(s):  
B. S. Yilbas
Keyword(s):  
Kinetic Theory ◽  
Energy Transport ◽  
Pulse Heating ◽  
Short Pulse ◽  
Three Dimensional ◽  
Gold Surface ◽  
Equation Model ◽  
Three Dimensions ◽  
Theory Approach ◽  
Energy Transfer Mechanism

Non-equilibrium energy transport takes place in solids once the laser pulse duration reduces to picoseconds or less. It is this energy transfer mechanism that defines the laser interaction process and therefore the rate at which the material is heated through the collisional process. In the present study, laser short-pulse heating of a gold surface is considered. An electron kinetic theory approach is introduced to model the energy transport process in three dimensions. The governing equation of energy transport is solved numerically, and the electron and lattice site temperatures are predicted. In order to validate the electron kinetic theory predictions, a two-equation model is employed to compute the temperature field in the substrate material. It is found that energy transport due to the diffusional process is unlikely during the heating period considered at present. The predictions of electron kinetic theory agree well with the results obtained from the two-equation model.

Electron kinetic theory approach for sub-nanosecond laser pulse heating

2000 ◽  
Vol 214 (10) ◽  
pp. 1273-1284 ◽  
Author(s):  
B S Yilbas ◽  
S Z Shuja
Keyword(s):  
Laser Pulse ◽  
Kinetic Theory ◽  
Temperature Rise ◽  
Pulse Heating ◽  
Equation Model ◽  
Nanosecond Laser Pulse ◽  
Nanosecond Laser ◽  
Level Energy ◽  
Theory Approach ◽  
Heating Model

Laser short-pulse heating initiates non-equilibrium thermodynamic processes in the surface vicinity of solid substrates that are subjected to the pulse heating. The Fourier heating model, however, overestimates the temperature rise in this region. Consequently, it becomes essential to consider a heating model employing a microscopic level energy exchange mechanism in the surface vicinity. In the present study, electron kinetic theory, Fourier theory (one-equation model) and a two-equation model are introduced for sub-nanosecond laser heating pulses. The effect of laser pulse intensity on the temperature rise is also considered. The equations resulting from the models are solved numerically for gold and chromium substrates. The predictions are validated for a triangular pulse and a silicon substrate. It is found that electron kinetic theory and a two-equation model both predict lower temperatures in the surface vicinity at early heating times. As the pulse heating progresses, the predictions of both models converge to the result of a one-equation model.

Entropy Production During Laser Picosecond Heating of Copper

2002 ◽  
Vol 124 (3) ◽  
pp. 204-213 ◽  
Author(s):  
Bekir Sami Yilbas
Keyword(s):  
Entropy Production ◽  
Energy Transport ◽  
Pulse Heating ◽  
Short Pulse ◽  
Surface Region ◽  
Irreversible Processes ◽  
Heating Process ◽  
Theory Approach ◽  
Lattice Systems ◽  
Nonequilibrium Energy

Nonequilibrium energy transport taking place in the surface region of the metallic substrate due to laser short-pulse heating results in entropy production in electron and lattice systems. The entropy analysis gives insight into the irreversible processes taking place in this region during the laser short-pulse heating process. In the present study, entropy production during laser shortpulse heating of copper is considered. Equations governing the nonequilibrium energy transport are derived using an electron kinetic theory approach. The entropy equations due to electron and lattice systems and coupling of these systems are formulated. The governing equations of energy transport and entropy production are solved numerically. Two pulse shapes, namely step input intensity and exponential intensity, are employed in the analysis. It is found that entropy production due to coupling process attains higher values than those produced due to electron and lattice systems. The effect of pulse shape on the entropy production inside the substrate material is significant.

DIELECTRIC CONSTANT AND SEEBECK COEFFICIENT FOR SEMICONDUCTORS: THERMODYNAMIC AND DFT STUDIES

2013 ◽  
Vol 12 (06) ◽  
pp. 1350057 ◽  
Author(s):  
HSIU-YA TASI ◽  
CHAOYUAN ZHU
Keyword(s):  
Boundary Condition ◽  
Dielectric Constant ◽  
Seebeck Coefficient ◽  
Gas Phase ◽  
Present Method ◽  
Dielectric Constants ◽  
Semiconductor Materials ◽  
Electronic Polarizability ◽  
Seebeck Coefficients ◽  
Good Agreement

Dielectric constants and Seebeck coefficients for semiconductor materials are studied by thermodynamic method plus ab initio quantum density functional theory (DFT). A single molecule which is formed in semiconductor material is treated in gas phase with molecular boundary condition and then electronic polarizability is directly calculated through Mulliken and atomic polar tensor (APT) density charges in the presence of the external electric field. This electronic polarizability can be converted to dielectric constant for solid material through the Clausius–Mossotti formula. Seebeck coefficient is first simulated in gas phase by thermodynamic method and then its value divided by its dielectric constant is regarded as Seebeck coefficient for solid materials. Furthermore, unit cell of semiconductor material is calculated with periodic boundary condition and its solid structure properties such as lattice constant and band gap are obtained. In this way, proper DFT function and basis set are selected to simulate electronic polarizability directly and Seebeck coefficient through chemical potential. Three semiconductor materials Mg 2 Si , β- FeSi 2 and SiGe are extensively tested by DFT method with B3LYP, BLYP and M05 functionals, and dielectric constants simulated by the present method are in good agreement with experimental values. Seebeck coefficients simulated by the present method are in reasonable good agreement with experiments and temperature dependence of Seebeck coefficients basically follows experimental results as well. The present method works much better than the conventional energy band structure theory for Seebeck coefficients of three semiconductors mentioned above. Simulation with periodic boundary condition can be generalized directly to treat with doped semiconductor in near future.

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