Upcoming Seminars

"Atomic Structure of Carbon and Nitrogen on the Pt(111) Surface," Michael Trenary, University of Illinois at Chicago, hosted by Tijana Rajh

Abstract: The structure and reactivity of elemental carbon and nitrogen on transition metal surfaces are important to a variety of problems in heterogeneous catalysis. Many of the surface chemical properties of both carbon and nitrogen can be deduced through studies that employ techniques that average over monolayers, while scanning tunneling microscopy (STM) can provide direct information on the structure of surface layers, often with atomic resolution. The techniques of reflection adsorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and low-energy electron diffraction (LEED) have been used to study the formation of carbon and nitrogen on Pt(111) through dehydrogenation reactions.

In the case of carbon, the dehydrogenation of acetylene and ethylene was found to first produce ethylidyne (CCH₃), which then decomposes to form C_xH_y clusters of various sizes as observed with room-temperature STM. At higher temperatures, these clusters would undergo further dehydrogenation to form graphene islands. Under conditions that resulted in complete coverage of the Pt(111) surface with graphene, various rotational domains of graphene were observed. The boundaries between graphene domains provide nucleation sites for the growth of Pt nanoclusters when Pt is deposited onto the graphene covered Pt(111) surface. In the case of nitrogen, it was found that reaction between ammonia and molecularly adsorbed O₂ would result in the formation of H₂O, which desorbs below 200K to leave behind a well-ordered p(2×2)-N layer on Pt(111). This N layer readily reacts with H₂ to form NH molecules on the surface, as observed with RAIRS. Through collaborative research with a group in Japan, a low-temperature STM operated at 5K was used to obtain atomically resolved images of the p-(2×2)-N layer and of its hydrogenation to NH.