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O: Oberflächenphysik

O 40: Halbleiteroberflächen und -grenzflächen

O 40.7: Vortrag

Donnerstag, 11. März 2004, 17:15–17:30, H45

Si addimer nanowires on SiC(001) surfaces — •J. Pollmann and P. Krüger — Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster

In recent years it has been observed by scanning tunneling microscopy that particular reconstructions of the SiC(001) surface show Si addimer nanowires. Their occurrence depends crucially on preparation conditions. To explain the physical origin of such nanowires we scrutinize current reconstruction models of various SiC(001) surfaces. Analysing the energetics of the c(4×2), 3×2, 5×2 and 7×2 reconstructions, as resulting from our first-principles DFT-LDA calculations of the formation energy, we find that the higher N×2 reconstructions can be formed by two basic building blocks, the c(4×2) and the (3×2) unit. This finding allows us to set up a simple model which extrapolates to all possible N×2 reconstructions. First, the model reveals in excellent agreement with experiment that neither a 4×2 nor a 6×2 reconstruction should occur. Second, it predicts that all higher reconstructions with N≥ 7 are possible. This is in contrast to an earlier notion that only odd reconstructions (with N odd) were to be expected. In fact, the more recent observations of the above mentioned Si nanowires have been made at a SiC(001)-(8×2) surface. This structure directly derives from our model as consisting of one c(4×2) and two 3×2 units per 8×2 unit cell revealing the origin of the experimentally observed Si addimer nanowires. In general, all kinds of Si nanowire arrangements can be achieved depending sensitively on the distribution of the two structural building blocks at the SiC(001) surface.