#
# top.uni.aps.anl.gov:/home/www/beamtime-requests/req00197.txt
# UNICAT Member Beam Time Request  #197

# created Thu Sep 20 08:34:26 CDT 2001
#
beamline:
	33ID

collaboration:
	Yes

collaborator+Hawoong:
	on

contact:
	ikr@uiuc.edu

days:
	6

description:
	Nanoscale crystalline solids are predicted to deviate significantly from bulk materials.  We plan to investigate two important surface phenomena associoated with the nanoscale: Depression of freezing point and the possible coexistence of a moulten layer at the surface of a crystal.
	Our recent success in imaging nanocrystals of Au can be extended to the case of Pb, where the surface effects are probably more pronounced.  The crystalline part of a nanoparticle close to its melting point should appear SMALLER by virtue of the surface melting.
	We plan to do UHV CXD imaging experiments in the 33IDE station.  Nanometer-sized Pb crystals will be prepared by evaporation onto a non-wetting surface, the SiO_2 film on a Si wafer.  Once crystallized, the single grains from the film will be studied by measuring the CXD distribution around the 111 Bragg peaks.  These will be inverted into images of the grains.  It is expected that the shapes will change dramatically close to the Pb melting point of 600K.
	We will need to attach a long X95 detector arm to the UHV diffractometer to carry our CCD detector.  We will place our roller-blade slits in the entrance flight path just in front of the Be window.  These procedures have been discussed with Hawoong Hong.
	We would consider it advantageous to have two short 3 day running periods a week apart to allow for bakeouts in the middle of the run.

equipment+required:
	UHV diffractometer.

experiment:
	Surface melting of Lead Nanocrystals

foreign+nationals:
	

hazards:
	No known hazards

minimumdays:
	5

name:
	Ian Robinson

new+request:
	on

nonmembers:
	

unacceptable+dates:
	Week of thanksgiving through 11/26.
	After 12/20.


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