Environmental Engineering Reference
In-Depth Information
Figure 14.1
Scheme of the electrochemical flow cell used in the UHV-STM/EC transfer
system.
facilities for the reversible sample transfer between UHV and electrochemical cell.
The UHV system contained two metal evaporators for Pt and Ru evaporation, a cylind-
rical mirror analyzer (Physical Instruments) for Auger electron spectroscopy (AES),
and a quadrupole mass spectrometer (Balzers QMS 112) for residual gas analysis.
The single-crystal sample, which was shaped as a flat “hat,” was mounted onto a tan-
talum or molybdenum sample holder with an outer diameter of 18 mm (see Fig. 14.1),
which in turn was held in a precision sample manipulator. Sample heating was poss-
ible by radiation heating from a filament behind the sample or by electron bombard-
ment, accelerating electrons from the filament to the sample. The latter allowed to
flash anneal the sample to temperatures of up to 1900K (heating rate
100 K s
21
).
The temperature was measured by an infrared pyrometer (Impac Infratherm IGA
140). For STM measurements, the sample was transferred from the manipulator to
the STM by two wobble sticks.
14.2.2 Sample Preparation
The Ru(0001) surface was prepared by cycles of Ar
þ
ion bombardment (sputtering)
and annealing to temperatures .1100K, followed by oxygen adsorption/desorption
cycles and final annealing to about 1750K to remove residual adsorbed oxygen
[Buatier de Mongeot et al., 1998; Diemant et al., 2003]. After this treatment, the
surface is characterized by atomically smooth terraces of 100 - 200 nm width separated
by monolayer steps (see also Fig. 14.5a). Surface contamination was below the
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