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Performance of A New High Pressure STM
P. Thostrup, L. жsterlund, P. B. Rasmussen E. LФgsgaard, I. Stensgaard, F. Besenbacher
CAMP and Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark

Au(111) Abstract
A long-term goal of surface science is to understand and predict surface processes occurring at technologically relevant conditions. We have designed a new High Pressure (HP) STM which enables atomic-scale imaging up to atmospheric pressures. Thus, we are able to bridge the so-called pressure gap between UHV and high pressure studies. Here we present results of such measurements of Au(111) and Cu(110) in a H2 atmosphere. Results from post-exposure experiments in the HP cell of dispersed metal particles on various oxides are also shown.
Size: 32 x 31 е It = + 3.37 nA Vt = +2.0 mV
2

(1x1)

Cu(110)

UHV

UHV (1x2)

Size: 75 x 73 е It = +1.42 nA Vt = +105.0 mV

2

Chamber and STM design
Gate valve

0.85 bar
Suspension Reactor vessel STM

Size: 32 x 31 е It = + 2.65 nA Vt = +1.0 mV

2

1 bar

Size: 75 x 73 е It = +1.55 nA Vt = +29.3 mV

2

UHV chamber

Top window

L. жsterlund et al, to be published

Linear transfer rod

Valve Main manipulator STM To pump Sample and sample support Cantilever Massive block

Real system - Complex

Studying model catalysts
Model system - Simple
Single crystal model catalyst - Active material

Sample holder Outer housing Inner housing Scanner tube - inchworm assembly

Supported model catalyst - Clusters of active material (nano crystals) on support material

Bridging the pressure gap
- Prepare sample in UHV - Transfer sample to reactor vessel - Expose to desired reaction conditions (p,T)
Quench and look approach
In situ investigation

Au/TiO2(110) High O2 pressures

Small island D=14 е, h=2.5 е

Pt/Al2O3/NiAl(110) High H2 pressures
355 е x 403 е 0.78 nA/0.25 V Pt: 15min@9.4 Amps

Incorporate reaction vessel into UHV system

451 е x 502 е 1.6 nA/0.9 V Au: 5min@11 Amps +annealing 10 min @850 K

D=30 е h=12 е

Study sample during exposure

861 е x869 е 1.3 nA/1.8 V Au: 2 min/11.5 Amps + exposure to 10 Torr O2 for 30 min

355 е x 403 е -0.78 nA/-1.25 V Pt: 15 min/9.4 Amps + exposure to 10 Torr H2 for 5 min

- Evacuate reaction vessel - Transfer sample back into UHV - Post reaction analysis with all available techniques.

Only large Au islands! Metal/oxide interaction weak

No crystallisation Metal/oxide interaction strong