AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM8
Experimental and Theoretical STM Imaging of Molecules on Metal Surfaces@footnote 1@

Friday, October 29, 1999, 10:40 am, Room 607

Session: Adsorption on Metals and Silicon
Presenter: D.N. Futaba, University of California, Davis
Authors: D.N. Futaba, University of California, Davis
C.A. Pearson, University of Michigan
A. Loui, University of California, Davis
S. Chiang, University of California, Davis
D.M. Jaramillo, University of California, Davis
D.P. Land, University of California, Davis
Correspondent: Click to Email
We have imaged the surface structure of benzene coadsorbed with carbon monoxide (CO) on the Pd(111) surface in ultrahigh vacuum using a low temperature (90K) scanning tunneling microscope (STM). In conjunction with low-energy electron diffraction, three distinct overlayer structures have been observed to form as a function of various dosing conditions: two hexagonal structures when predosed with CO, (2@sr@3x2@sr@3)R30° and (3x3), and one rectangular structure. We are currently studying the mechanism by which one hexagonal layer transforms into the other as the benzene coverage increases. Our models of the structure give an overall molecular coverage of 1/3 for both hexagonal structures, suggesting molecular place exchange. We have performed laser induced thermal desorption and thermal desorption spectroscopy measurements to calibrate relative amounts of CO and benzene for the different structures. We also use a simple computational method, based on extended Hückel theory, to calculate STM images expected for the dehydrogenation of cyclohexene to benzene on Pd(111). Based on the proposed bonding geometry by Hunka et al.,@footnote 2@ we expect to see significant differences between the chemisorbed cyclohexene molecules and the resultant benzene molecules. Our calculated images of paraxylene and metaxylene on Rh(111) showed good agreement with existing experimental STM data by Cernota et al.@footnote 3@ Therefore, we expect good agreement between our calculations of orthoxylene on Pd(111) and our experiments in progress. @FootnoteText@ @footnote 1@ Funded by NSF (CHE-95-20366) and CLC Program of Univ. of California. @footnote 2@ D.E. Hunka, T. Picciotto, D.M. Jaramillo, D.P. Land, Surf. Sci., 421, L166 (1999). @footnote 3@ P.D. Cernota, H.A. Yoon, M. Salmeron, G.A. Somorjai, Surf. Sci., 415, 3511 (1998).