AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS-MoP

Paper SS-MoP7
Chemical Contrast by Funtionalized Tips and Movement of Highly Excited "Hot" Adsorbates: LT-STM Experiments with CO on Cu(111)

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: L. Bartels, Paul-Drude-Institut, Germany
Authors: L. Bartels, Paul-Drude-Institut, Germany
G. Meyer, Freie Universität Berlin, Germany
K.-H. Rieder, Freie Universität Berlin, Germany
Correspondent: Click to Email
Chemical Contrast between species looking otherwise very similar in STM images (like CO and oxygen on Cu(111), both of which image as circular indentations) can be achieved by controlled in-situ functionalization of the STM tip apex with a single molecule: Electrons tunneling from a STM-tip to a CO molecule on Cu(111) at a sample bias exceeding 2.4V@footnote 1@ can lead to the excitation of the addressed molecule resulting in its hopping either to the tip apex or to a nearby site on the substrate with approx. 1:3 probability. Thus, tips bearing a CO molecule on their apex can be produced. As putting down the CO molecule from the tip apex is easily accomplished using inverted bias, this technique can be used for a whole range of new manipulation (transfer) experiments. Additionally, imaging with a CO tip the apparent shape of CO molecules is inverted to a protrusion, while the shape of oxygen (and several other molecules) remains unchanged, thus allowing for easy discrimination between them@footnote 2@. It could be shown that the transfer of the CO molecule is achieved by single electron attachment to the CO 2@pi@* level, leading after electronic deexcitation to highly vibrational excited CO molecules. Thus, events, in which the CO molecule does not jump onto the STM tip but ends up on the substrate surface, can be used to study the diffusion of highly excited ("hot") adsorbates. We found, that their diffusion is limited in 2/3 of the cases to one adsite distance. In case of longer diffusion distance, scattered movement dominates. A Monte-Carlo simulation of the measured distribution of diffusion paths, however, allows to estimate that in 1/3 of the cases an adsite is transgressed, it is transgresses without scattering the movement of the "hot" molecule.@footnote 3@ @FootnoteText@ @footnote 1@ L. Bartels, G. Meyer, K.-H. Rieder, D. Velic, E. Knoesel, A. Hotzel, M. Wolf, G. Ertl, Phys. Rev. Lett. 80, 2004 (1998) @footnote 2@ L. Bartels, G. Meyer, K.-H. Rieder, Appl. Phys. Lett. 71, 213 (1997) @footnote 3@ L. Bartels, M. Wolf, G. Meyer, K.-H. Rieder, submitted to Chem. Phys. Lett. (1998)