Catalyst Preparation and Transfer

A schematic sketch of the sample deposition setup is shown in Fig. 3.12. After mass selection by means of the QMS (see Sect. 3.1.2) the clusters leave the QMS trough an exit lens attached to the QMS body. In an UHV chamber cross (2 x 10 mbar without deposition, 5 x 10 mbar during deposition) the cluster beam is then guided through aAfo shield (5) with an aperture of 9 mm (fixed on a grounded Cu feedthrough 

The steep angle results in a mtiximal electric field perpendicular to the surface (p-component) and therefore the largest absorption of the adsorbed molecules. 

For IR spectroscopy in general selection rules apply, i.e. which require for a molecule to be detected a dynamic dipole momentum which changes during the vibration. 

The cooled detector minimizes absorption by background carbon dioxide, water vapor and H-bonded water. 

The holders in Fig. 3.13a, b can hold a sample (XPS, INPS or u-reactor) and a TEM grid at the same time with both samples being centro-symmetric. This allows one to deposit a sample of the mentioned type and a TEM sample without breaking the vacuum, changing the deposition conditions and at the same position by simply rotating the manipulator by 180°. This results in comparable deposition condition for the two samples. 

---

The experimental chapter consists of three parts, covering first the cluster synthesis (formation, mass selection and deposition). In a second part, the UHV setup and the procedures for experiments followed by a short introduction to each of the used techniques along with some experimental details is given. Third, the approach for catalyst preparation and transfer and the used techniques for ambient experiments are presented, including explanations of the methods. 

All procedures of catalyst preparation and transfer into the reactor or into the spectrometer cell were performed under vacuum. 

---