Thermal desorption structure sensitivity

Adsorption at Low Pressure (P < 10" Torr). The adsorption of propene has been studied with thermal desorption spectroscopy (TDS) on all of the different forms of the (100) and (111) surfaces and under several different conditions of exposure. For exposures at low pressure (P< 10 Torr), no selective oxidation is observed. For small exposures (< 5 L) at low-temperature (100K-120K), four propene desorption states are observed from the Ci O(lll) surface comparecf to two desorption states from the Cu9O(100)-Cii surface. These TDS results are shown in Figure 3, and give a cfear indication of a structure-sensitive interaction of propene with Cu20. 

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

Energetic analysis using temperature-programmed desorption (TPD), also called thermal desorption spectroscopy (TDS), on a well-defined surface makes it possible to determine the structure sensitivity and the heights of the energy barriers of the surfece processes. It was shown that the role of the substrate surface orientation in the population of subsmface sites is crucial. On the reconstmeted (110) faces of Ni and Pd or on more open faces [8,83,84], subsurface sites are populated at temperatures as low as 100 K and low H2 pressures (10 Pa), whereas higher temperatures and pressures are necessary with the more densely packed planes [8]. 

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