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Thin metal films have received widespread attention for technical applications like conducting connections in microelectronics, optical elements tailored with desired spectral properties or supported adsorbents in heterogeneous catalysis. The electrical resistivity is an easily accessible and informative quantity to characterise the material.

The scattering hypothesis is based on the assumption that Matthiessen’s rule can be applied, i.e. all scattering contributions compose additively [1] according

The electrical resistivity of polycrystalline metal films usually decreases during an annealing treatment. Figure 3.1 shows a typical example measured for silver films deposited at 77 K on a glass substrate and subsequently annealed for 1 h at the temperature (filled circles [1]). Measuring temperature was always 77 K.

The structure properties of thin gold films deposited on glass substrates are in principle similar to the silver films described in the last chapter. The main difference, however, is the fact that the crystal growth as well as the island formation occur at higher temperatures for gold films. First, we will concentrate on gold films deposited at room temperature and then annealed for 1 h at higher temperatures, all other preparation parameters have been kept as comparable as possible to the case of silver.

The scattering hypothesis predicts that gas adsorption on thin metal films always leads to an increase in resistivity Eq. (2.1b). Exceptions are expected only for a bridging of surface roughness by the adsorbed gas molecules [1, 2], for chemical reactions at the surface [3] or for rather high coverages [4].

In this chapter we will deal with other adsorption systems where each of them shows strong peculiarities with respect to the resistivity properties. We start with the discussion of Xenon adsorption on silver and gold films. Here, a noble gas is adsorbed on noble metals and so the adsorption bond should be extremely weak. A reconstruction of the surface can be excluded in this case, and both systems should provide an excellent basis for the application of Eq. (2.8). On the other hand, CO adsorption on silver and gold films exhibits more complicated features because the molecules are adsorbed with the molecule axis perpendicular to the film surface [1] and so a strong lateral interaction is to be expected [2].

In the last chapter we have briefly mentioned the CO oxidation on ultrathin Pd films deposited on gold substrates. The oxidation of CO is one of the most important and best-studied catalytic reactions. The application must be mainly seen in the exhaust gas decontamination, for example for automobiles.

The electrical resistivity of thin silver [1] and gold [2] films deposited at room temperature on glass and silicon substrates was previously studied mainly with respect to the thickness dependence. The results were explained with the help of the so-called scattering hypothesis where grain boundary scattering is the decisive process for polycrystalline films while surface scattering becomes effective for single-crystal films, in particular at the metal/silicon transition.