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Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 51: Surface chemical reactions I

O 51.2: Talk

Thursday, March 26, 2009, 16:30–16:45, SCH A01

Real-space investigation of high-barrier diffusion of hydrogen on Si(001) — •M. Dürr1,2, C. H. Schwalb1, and U. Höfer11Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität Marburg, D-35032 Marburg — 2Fakultät Angewandte Naturwissenschaften, Hochschule Esslingen, D-73728 Esslingen

Due to the strong corrugation of Si(001) with its dimer row reconstruction, various diffusion channels exist already on the flat, clean surface. Among the possible processes, diffusion between two dimer rows is associated with the highest diffusion barrier; as a consequence, it has not been observed by means of standard STM experiments up to now.
To probe this high-barrier pathway in real space, we used a combination of STM and nanosecond laser heating [1,2]. STM images taken after different numbers of heating pulses represent snapshots of the surface configurations frozen at various stages of the diffusion process. In this way hydrogen diffusion associated with rates as high as 108 s−1 could be monitored with atomic resolution at 1400 K. We observe that diffusion across the dimer rows is almost as effective as diffusion along the dimer rows. The experiment thus demonstrates the importance of this high-barrier process at elevated temperatures. Considering the large Si–Si distance between the dimer rows, the observed diffusion rate is surprisingly high. It is interpreted in terms of a strong concerted movement of hydrogen and the Si lattice.
[1] M. Dürr et al., Science 296, 1838 (2002).
[2] C. H. Schwalb et al., Phys. Rev. B 75, 085439 (2007).

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