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Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

Jin Jimmy Wang

Title:
Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation
Author(s):
Wang, Jin Jimmy
Thesis Advisor(s):
Im, James Sungbin
Date:
Type:
Theses
Degree:
Ph.D., Columbia University
Department(s):
Materials Science and Engineering
Persistent URL:
Abstract:
This thesis examines melting in superheated silicon films in contact with SiO₂ under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO₂ interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO₂ interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO₂ interface can be superheated by at least 220K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 10¹⁰ K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO₂ interface at temperatures estimated to be over 300K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO₂ interface.
Subject(s):
Excimer lasers
Thin films
Thin films--Effect of radiation on
Thin films--Thermal properties
Silicon oxide films
Materials science
Chemistry, Physical and theoretical
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332
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Suggested Citation:
Jin Jimmy Wang, , Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation, Columbia University Academic Commons, .

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