#
# arev:/usr/local/unicat/unireq/beamreq/req00110.txt
# UNICAT Member Beam Time Request  #110

# created Fri Mar 31 11:30:51 CST 2000
#

collaboration:
	No

days:
	6

description:
	Metal epitaxy on a crystalline substrate with a general 
	crystallographic orientation can sometimes lead to conflicts
	between competing orientations of the resulting overlayer.
	This occurs because of the symmetry breaking effect of the steps
	or virtual steps on the miscut substrate.
	
	The specific example we are interested in is Cu_3Au(111) exitaxy on
	Nb(110) grown on miscut sapphire.  The Nb buffer layer preserves
	a memory of the miscut sapphire in such a way as to generate an
	asymmetric population of Cu_3Au crystal grains.  The 'majority'
	population has (111) orientated along the surface normal, and (1-10)
	along the positive step direction.  The 'minority'
	population has (111) orientated along the surface normal, and (1-10)
	along the negative step direction.  This results in alternately
	strong and weak (1-11) reflections resulting in three-fold symmetry 
	as the sample is rotated about the surface normal.
	
	At the end of our last run, we fount that Coherent X-ray Diffraction 
	(CXD) was well-suited to imaging these minority grains.  In samples
	with a 200:1 asymmetry, the minority grains were found to be about
	0.5 microns in size and sufficiently separated that diffraction
	could be recorded separately from each grain.  During the time
	available we looked at two other samples which were found to have
	different grain sizes.
	
	We now propose to examine a systematic series of samples, as a
	function of asymmetry ratio, and as a function of position on
	the sample, to evaluate the trend.  The samples will be provided
	by R. Appleton and C. P. Flynn.
	

equipment+required:
	Huber Diffractometer

experiment:
	Shapes of minority domains in Cu_3Au thin films

hazards:
	No unusual hazards

name:
	Robinson

new+request:
	on

nonmembers:
	

station:
	33ID-D

unacceptable+dates:
	4-9 July
	



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