The Fritz Haber Institut experimental set-up

This experimental assembly is working at the Fritz Haber Institut in Berlin since 1999 [51]. It is schematically represented on Fig. 3. 

This experimental assembly is much more complex than the preceding one. The oxide surfaces are ultrathin alumina films grown on NiAl(l 1 0) single crystals, in the preparation chamber following a standard procedure [16]. The alumina films are characterized in situ by AES and LEED. The metal clusters are prepared by vacuum condensation at RT of a metal atoms beam generated by an electron bombardment evaporator calibrated by a quartz microbalance. Metal atoms condense only on the sample through an aperture placed closed to it. After preparation the sample is transferred in the reaction chamber. The characterization of the metal clusters is based on STM observations of deposits performed in the same conditions in another UHV chamber [16]. 

During operation of the molecular beam sources infrared measurements in reflection absorption mode (IRAS) are possible. The time resolution per IR spectrum is 38 ms that allows following the variation of coverage during a pulse of reactants (typical duration several seconds). However, to have an acceptable signal/noise ratio it is necessary to accumulate successively around thousand spectra, that needs to have a perfectly periodic beam modulation and a stationary kinetic phenomenon during the total duration of the measurements (typically 20 min at a resolution of 8 cm-1 for 30 spectra on a CO pulse of 1 s). 

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