Morphological aspects of surface reactions. Progress report, March 1993--March 1994

摘要

This work focuses on substrate morphology and on fragments synthesized by thermal, electron, and photon activation. The following work is complete: (1) Low energy electron diffraction, Auger electron spectroscopy and scanning tunneling microscopy were used to determine the local morphology of rhodium films on titania. (2) A new tool was developed for diagnosing surface reactions that involve C-H bond cleavage -- predosed oxygen TPD (POTPD), a technique based on scavenging surface H(a) by small amounts of preadsorbed 0(a) to form water. (4) For (pi)-bonded benzene on Ag(111), exposure to low energy electrons results in selective decomposition Of C(sub 6)D(sub 6)(a) to surface D atoms and phenyl fragments, which recombine and desorb as biphenyl between 275-390 K. Similarly, vinyl fragments have been prepared from ethylene. These fragments open the way for kinetic and spectroscopic characterization of interesting hydrocarbon reactions on transition metals. (5) Using Fourier transform infra-red spectroscopy, we have studied how coadsorbates, particularly carbon monoxide, inhibit the decomposition of ethylidyne. The experiments were done in an ambient pressure of CO in order to maintain a sizable coverage into the temperature regime where ethylidyne normally decomposes. One aspect of our present work involves morphological studies of Rh on planar TiO(sub 2) surfaces using scanning tunneling microscopy and scanning electron microscopy. The objective is to measure, in some cases in real-time, how the surface morphology changes as oxidation and reduction processes are carried out. In another interesting project, we are preparing spectroscopically significant and reasonably pure concentrations of methyl groups on Pt(111) by exposing physisorbed methane to controlled doses of low energy electrons.