| Summary: | 碩士 === 國立臺灣師範大學 === 化學系 === 102 === The adsorption and thermal reactions of thiophenol (C6H5SH) and phenol (C6H5OH) on Ge(100) surface were studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) using synchrotron radiation. The desorbed products of thermal reactions could be measured by TPD, and the XPS was utilized to identify the surface species.
Most of the thiophenol adsorbed on Ge(100) at 105 K dissociated into surface C6H5S(a) and H(a). The thiophenoxy group lay flat in the low-exposure regime and stood upright upon higher exposures. The chemsorbed and physorbed thiophenol appeared on the Ge(100) at larger exposures.
The desorption products of C6H5SH were C6H5SH(g), H2(g), GeS(g), H2S(g), and C6H6(g). At 575K, the desorption of thiophenol resulted from the recombination of C6H5S(ad) and H(ad). The surface C6H5S(a) cleaved the carbon-sulfur bond to release the C6H5 bond and reacted with H to desorb benzene. According to the TPD spectra, we propose that benzene has two adsorption states. The desorption of hydrogen with recombination of H(ad) + H(ad) and some hydrogen reacted with surface S to become H2S(g).At 690K, GeS(g) desorbed from the surface due to the cleavage of the Ge-Ge bond.
The adsorption features of phenol and thiophenol are almost the same, but the thermal decomposition reactions are different because the carbon-oxygen bond is stable. Phenoxy group cleaves the carbon-oxide bond to produce GeO(g) at higher temperature in the TPD spectra. Three desorption peaks in TPD spectra are observed due to recombination reactions. According to the experimental data and computational result, we propose the reactions mechanisms of C6H5SH and C6H5OH thermal reaction on Ge(100).
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