Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 53: Organische Dünnschichten V

O 53.2: Talk

Wednesday, March 9, 2005, 11:00–11:15, TU EB420

PE and NEXAFS study of self-assembled bacterial surface-layer proteins — •Denis Vyalikh¹, Alexander Kirchner², Steffen Danzenbächer¹, Michael Mertig², Wolfgang Pompe², Yuriy Dedkov¹, and Serguei Molodtsov¹ — ¹Inst. f. Festkörperphysik, TU Dresden — ²Inst. f. Werkstoffwissenschaft, TU Dresden

Electronic structure of regular bacterial cell wall proteins (S layer) of Bacillus sphaericus was studied by photoemission (PE) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopies [1]. Both the occupied and unoccupied valence electronic states were characterized and found to represent a series of PE and NEXAFS peaks, respectively, related to the molecular orbitals of individual amino acids. It was shown that the NEXAFS data could be interpreted applying a phenomenological "building block" model, whereas understanding of the valence-band PE structures can be achieved on the basis of electronic density-of-states calculations performed for rather small proteins. It was found that the π clouds of aromatic rings contribute both to the lowest unoccupied and the highest occupied molecular orbitals (LUMO and HOMO). The studied S layer reveals semiconductor-like behavior with a gap value of ∼ 3 eV. The Fermi level is pinned close to the bottom of the LUMO.

We expect that the position of the Fermi level can be shifted across the gap by insertion of dopants into the pores in the S layers. First experiments on intercalation of alkali and transition metals into S layer are under way in our cooperation. The obtained results will be reported.

[1] D.V. Vyalikh et al., Phys. Rev. Lett. (2004) in print