#
# arev:/usr/local/unicat/unireq/beamreq/req00022.txt
# UNICAT Member Beam Time Request  #22

# created Mon Jul 27 12:12:21 CDT 1998
#

days:
	6

description:
	CDWs have been reported in two surfaces, Sn/Ge(111) and Pb/Ge(111), with a 3x3 symmetry superimposed on the native rt3xrt3 structure.
	X-ray studies of the Sn/Ge(111) system found extremely weak diffraction of a few counts/hour, implying an exceedingly small structural displacement.
	The published results might also be interpreted in terms of a direct probing of the modified electron density associated with the CDW.
	I believe there may be a significant enhancement of the 3x3 signal at resonance with atomic transitions in the adsorbate.
	I have attempted a resonant experiment at the Pb LIII edge in Pb/Ge(111) at NSLS, but did not have enough flux at 13keV.
	I would like to try the experiment at APS therefore.
	
	The sample prepartion is a little trickier than Sn/Ge(111).
	There are other rt3 phases than the required single-atom-per-cell phase.
	It is necessary to monitor the structure factors during the preparation to get this right.
	The experience at NSLS will be very useful in this regard.
	The Pb evaporator is also well-calibrated from that earlier run.
	
	This would be a collaboration with Hawoong Hong and TC Chiang, who have also expressed interest in the expt.

equipment+required:
	Hawoong's chamber with LN2 sample cooling.
	

experiment:
	Charge density wave in Pb/Ge(111)

hazards:
	

name:
	Ian Robinson

new+request:
	on

nonmembers:
	

station:
	33ID-E

unacceptable+dates:
	Only good dates for me are Sept 1-9 and 22-26.
	Other dates might also work if collaborators are on hand.
	The schedule must suit Hawoong also, since it can't be done without him.
	



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