@mastersthesis {Younkin:136,
	title = {Surface studies and microstructure fabrication using femtosecond laser pulses},
	year = {2001},
	pages = {118},
	school = {Harvard University},
	type = {phd},
	abstract = {In the first of the two experiments described in this thesis, we constructed and characterized an apparatus for performing ultrafast surface spectroscopy on Pt (111). A combination of an optical parametric amplifier and a difference frequency generation stage allow us to create optical pulses with wavelengths in the range 550 nm-7.3 m and pulsewidths of approximately 100 fs. We also developed methods for using the infrared output of this apparatus in infrared-visible sum-frequency generation at a Pt-vacuum interface. Our attempts to time-resolve a chemical reaction taking place at this interface were unsuccessful because of power limitations, but the techniques that we developed should be applicable in related experiments. In the second series of experiments, we created arrays of conical microstructures on the surface of silicon by irradiating a silicon wafer with trains of ultrashort pulses in the presence of an ambient gas. The microstructures are typically tens of micrometers high and separated by several micrometers. We showed that the morphology of the structures is highly dependent on the species of ambient gas, the gas pressure, the laser fluence, and the number of laser pulses used.The sharpest structures are made in halogen-containing gases,such as SF6 or Cl 2 .The use of N2 or air results in blunt, rounded structures. In this thesis, I discuss the application of these silicon microstructures in optoelectronics and vacuum microelectronics. I note that surfaces covered with these microstructures have striking optical properties:structures made in SF6 absorb approximately 90\% of incident light with wavelengths between 250 nm and 2.5 m.The sharp conical structures also show high field-emission current. The remarkable and potentially useful optical and field-emitting properties of the structures are the result of the conical morphology of the laser-induced microstructures and the impurities introduced into the silicon.},
	author = {R. J. Younkin}
}
