Date of Award

Summer 2003

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Marek Sosnowski

Second Advisor

Haim Grebel

Third Advisor

Zafar Iqbal

Abstract

Laser ablation is a powerful thin film deposition and material processing technology. In the Nonlinear Nanostructure Lab at NJIT, silicon films deposited by laser ablation have been studied for the potential applications in nonlinear optoelectronic devices. The previous studies have suggested that the deposited silicon has a hexagonal symmetry, being a polymorph of silicon that previously has been obtained only at very high pressure. This thesis is part of the continuous study and characterization of this new structure. The objective of the research was to gain better understanding of the hexagonal silicon properties as well as the mechanism that lead to hexagonal silicon formation.

The laser ablation of the silicon nanostructure was done with nanosecond pulsed 532 nm ultraviolet laser in vacuum chamber. Different substrates of quartz and aluminum-coated quartz were used. The ablated silicon film consists of a smooth featureless matrix embedded with crystalline droplets. The micro-Raman spectra measurements revealed that the droplets have a hexagonal symmetry. The topographical properties were studied with combination of scanning electron microscope and atomic force microscope. And its mechanical properties were investigated by nanoidentation using scanning force microscope. The effects of annealing were studied under different temperature and annealing ambient. The annealing conditions that convert the hexagonal silicon to cubic diamond silicon were established. Based on the study, a tentative mechanism of forming the hexagonal silicon was proposed.

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