Oxygen thermal desorption spectra

Figure 5.3. Oxygen thermal desorption spectra after electrochemical O2 supply to Pt/YSZ at 673 K (I = +12 pA for 1800 s) followed by isothermal desorption at the same temperature at various times as indicated on each curve.4,7 Reprinted from ref. 7 with permission from Academic Press.

The existence of various temperature intervals characterized by predominant manifestation of one of above interactions can be detected from thermal desorption spectra. For instance, the thermal desorption spectrum obtained in [71] for a cleaved ZnO (1010) monocrystal following its interaction with oxygen (Fig. 1.4) indicates the availability of such typical temperature intervals as interval of physical adsorption (a), chemisorption (b), interval of formation of surface defects (c) and, finally, the domain of formation of volume defects (d). 

Fig. 5. Left Thermal desorption spectra of oxygen by Lambert et al.l (Reproduced with permission from Journal of Catalysis). Right Calculated thermal desorption spectrum resulting from recombinative desorption of the surface oxygen, using the rate coefficient expressed by Eq. 16. The heating rate used is 3 Ks-i.

In practice, asymmetric O Is peaks are often found for oxide systems, and these find their explanation in the coexistence of a surface spectrum and a bulk spectrum. The contribution of the surface spectrum for polar systems and in the presence of water strongly bound via hydrogen bridges (and thus not pumped away in a normal XPS system without thermal desorption) may then be larger than the estimated 15% and could amount to a clearly visible structure. The contribution of the -yl species, however, is frequently not easily detectable, as its abundance is strictly limited to a maximum of one monolayer, being sub-stoichiometric with respect to a close packed metal layer as it saturates two dangling coordinations per oxygen atom. 

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