####################################################
# Laurent Menard <lmenard@uiuc.edu>
# requesting 5 days, at minimum=4 days
# beamline 33BM, Electronic impacts on Au bond lengths in ligand protected and supported Au nanoparticles
# instrument 33BM-B XAFS
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# top:/home/www/beamtime-requests/req00920.txt
# UNICAT Member Beam Time Request  #920
# created Wed Dec 14 12:33:20 CST 2005
####################################################

apsrun:
	2006-01

beamline:
	33BM

collaboration:
	Yes

collaborator_Jenia:
	ON

contact:
	lmenard@uiuc.edu

days:
	5

description:
	Part of these experiments were described in last cycle's request but were not completed due to the fact that our experiments on Pt on Al2O3 prooved to be extremely interesting and we wanted to collect as many data on those systems as possible.

A solution of gold nanoparticles and electrolyte (tetrabutylammonium perchlorate) in methylene chloride will be added to a spectroelectrochemical cell (schematics attached) in a chemical fume hood.  The interfaces between the electrodes and the cell will be sealed with Teflon tape to prevent evaporation of methylene chloride and then transferred to the beamline and mounted in the hutch for transmission/fluorescence measurements.  The solution will be purged with Ar (1 atm, ~1 sccm).

The potential of the electrochemical cell will be controlled by a CH Instruments electrochemical analyzer between +2 and -2 V (microamp currents) while XAFS spectra are scanned.  The electrochemical analyzer will be located inside the hutch and interfaced to a laptop computer outside of the hutch.

These experiments are intended to explore the effects of injecting charge on molecular Au13 clusters.  Electrochemical experiments exhibit multi-electron redox behavior - an effect often associated with dramatic structural changes.  Effects will also be measured on larger Au particles that exhibit quantized charging.  This "coulomb staircase" phenomenon allows us to easily determine how many holes or electrons are injected into the clusters at a given applied potential.

We have also become interested in electron transfer from support materials to metal nanoparticles deposited on the support.  In Pt on Al2O3 samples, this transfer was found to be temperature dependent.  Another system of past interest to us is Au on TiO2.  We plan on investigating the temperature dependent Au-Au bonding (temperature range ~150K - 600 K) in light of recent reports of negative thermal expansion in Au nanoparticles and because of our own findings on Pt on Al2O3.

equipment_required:
	

experiment:
	Electronic impacts on Au bond lengths in ligand protected and supported Au nanoparticles

foreign_nationals:
	Joo Kang

hazards:
	Hazards with methylene chloride and tetrabutyl ammonium perchlorate as described in ESAF  for experiment #30389.

Supported gold experiments require use of liquid nitrogen and cartridge heater for temperature control.

instrument:
	33BM-B XAFS

instrument_other:
	

minimumdays:
	4

name:
	Laurent Menard

nonmembers:
	

submit:
	Submit

unacceptable_dates:
	March 1-12

z34ID_details:
	


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