Keywords

Simulations, laser ablation, semiconductors

Abstract

We present a model of laser-solid interactions in silicon based on an empirical potential developed under conditions of strong electronic excitations. The parameters of the interatomic potential depends on the temperature of the electronic subsystem Te, which is directly related to the density of the electron-hole pairs and hence the number of broken bonds. We analyze the dynamics of this potential as a function of electronic temperature Te and lattice temperature Tion. The potential predicts phonon spectra in good agreement with finite-temperature densityfunctional theory, including the lattice instability induced by the high electronic excitations. For 25fs pulse, a wide range of fluence values is simulated resulting in heterogeneous melting, homogenous melting, and ablation. The results presented demonstrate that phase transitions can usually be described by ordinary thermal processes even when the electronic temperature Te is much greater than the lattice temperature TL during the transition. However, the evolution of the system and details of the phase transitions depend strongly on Te and corresponding density of broken bonds. For high enough laser fluence, homogeneous melting is followed by rapid expansion of the superheated liquid and ablation. Rapid expansion of the superheated liquid occurs partly due to the high pressures generated by a high density of broken bonds. As a result, the system is readily driven into the liquid-vapor coexistence region, which initiates phase explosion. These results strongly indicates that phase explosion, generally thought of as an ordinary thermal process, can occur even under strong non-equilibrium conditions when Te > > TL. In summary, we present a detailed investigation of laser-solid interactions for femtosecond laser pulses that yield strong far-from-equilibrium conditions.

Notes

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Graduation Date

2012

Semester

Fall

Advisor

Schelling, Patrick

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Materials Science Engineering

Degree Program

Materials Science and Engineering

Format

application/pdf

Identifier

CFE0004599

URL

http://purl.fcla.edu/fcla/etd/CFE0004599

Language

English

Release Date

December 2012

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Subjects

Dissertations, Academic -- Engineering and Computer Science, Engineering and Computer Science -- Dissertations, Academic

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