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DTSTAMP:20261019T095215Z
LAST-MODIFIED:20180806T175813Z
DTSTART:20180807T150000Z
DTEND:20180807T160000Z
UID:event1957@bu.edu
URL:http://physics.bu.edu/internal/events/show/1957
SUMMARY:Nano-Patterning by Ion Bombardment
DESCRIPTION:Featuring Mahsa Mokhtarzadeh\n\nPart of the PhD Final Oral Exam
	s.\n\nExamining Committee:  Karl Ludwig\, Rama Bansil\, David Campbell\, An
	atoli Polkovnikov\, Lee Roberts\n\nAbstract:\n\nThe bombardment of surfaces
	 by ions can lead to the spontaneous formation of\nnano-structures. Dependi
	ng on the irradiation conditions\, smoothening or roughening\nmechanisms ca
	n be the leading order in pattern formation which can result in the\ncreati
	on of dots\, ripples or ultra-smoothening effects. Because ion bombardment 
	is\nalready ubiquitous in industrial settings\, and is relatively inexpensi
	ve compared to\nother surface processing techniques\, self-organized patter
	ning by ion bombardment\ncould enable a simple\, economical means of induci
	ng well-defined nanoscale structures\nin a variety of settings. Understandi
	ng the fundamental behavior of surfaces during\nion bombardment is therefor
	e a vital goal; however\, a complete understanding of\nphysical processes g
	overning surface pattern formation has not been reached yet.\nIn order to a
	ddress this issue\, my thesis research has utilized three primary approache
	s.\nFirst\, I have done real-time non-coherent X-ray scattering experiments
	 at\nCornell High Energy Synchrotron Source (CHESS) for studying kinetics o
	f structure\nformation of Silicon undergoing Ar+  bombardment over a range 
	of wavenumbers 4-5\ntimes larger than has previously been obtained. From ou
	r data\, we were able to\nextract values of the angle-dependent thickness o
	f the amorphous layer that forms\nunder ion bombardment\, the ion-enhanced 
	fluidity within that film\, the magnitude\nof the stress being generated by
	 the ion beam\, and the strength of prompt atomic displacement mechanisms.\
	nSecond\, to further deepen our knowledge of surface dynamics\, I have perf
	ormed\ncoherent X-ray studies of Ar+  bombardment of SiO2 at the Advanced P
	hoton Source\n(APS) for investigating the dynamics more profoundly than can
	 be done with traditional\ntime-resolved experiments. When using a focused 
	ion beam\, an inhomogeneous\nripple motion was generated\, this phenomenon 
	reflected as an oscillatory behavior in\nthe two-time and corresponding g2(
	t) correlation functions. By fitting the oscillations\nin the g2(t) correla
	tion function\, we have determined the surface ripple velocity on\nSiO2 dri
	ven by Ar+  sputter erosion.\nFinally\, to support the results of coherent 
	X-ray experiments\, simulations of\ngrowth models such as linear Kuramoto-S
	ivashinsky (KS) and Kardar-Parisi-Zhang\n(KPZ) have been carried out in ord
	er to compare the simulated temporal correlation\nfunctions of the scattere
	d intensity with those obtained from the coherent x-ray\nscattering experim
	ents.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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