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O: Oberflächenphysik
O 10: Rastersondentechniken (I)
O 10.2: Talk
Monday, March 27, 2000, 16:30–16:45, H44
Single molecule identification with Inelastic STS. — •J.I. Pascual, J. Jackiw, H. Conrad, and H.-P. Rust — Fritz-Haber-Institut der Max-Planck Gesellschaft, Faradayweg 4-6, D-14195 Berlin
Vibrational Spectroscopy on single molecules is a powerful technique for the characterisation of the chemical environment of adsorbates. In this presentation we explore the capabilities of this recent [1] technique in the study of adsorption processes of benzene on a Ag(110) surface. At 4 K we found that a weak bounded state, presumably physisorbed, is mostly populated. Molecules adsorbed in this state are imaged as featureless maxima and show mobility long the [0,0,1] direction. Small quantities of other features, depressions in STM images, were also observed after this low temperature deposition, although its origin was not possible to elucidate from STM data. To identify them, we acquired vibrational spectra at these depressions and reproducible low energy peaks, associated with the onset of inelastic tunnelling channels were obtained. The spectra is identical to the ones measured at benzene molecules chemisorbed at step edges after dosing at 66 K. Therefore, we can identify the low temperature depressions as C6H6 in that chemisorbed state, and the peaks measured, as due to excitations of vibrational modes presumably associated with the molecule-substrate bond. The saturation of one monolayer at 4 K was also performed. Molecules in the physisorbed state reorganize to form a dense hexagonal overlayer, with a clear vibrational fingerprint different from that measured in the chemisorbed state.
[1] B.C. Stipe, M.A. Rezaei and W. Ho. Science 280, 1732 (1998).