A. Kade

Spectroscopic studies of the electronic properties of regularly arrayed two-dimensional protein layers

Photoemission (PE) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy were applied to characterize electronic properties of the regular two-dimensional bacterial surface protein layer (S layer) of Bacillus sphaericus NCTC 9602, which is widely used as a protein template for the bottom-up fabrication of advanced metallic and hybrid nanostructures. PE and NEXAFS at the C 1s, O 1s, and N 1s core levels show similar chemical states for each oxygen atom and also for each nitrogen atom, while carbon atoms exhibit a range of chemical environments in different functional groups of the amino acids. A series of characteristic NEXAFS peaks were assigned to particular molecular orbitals of the amino acids by applying a phenomenological building-block model. It was found that the π clouds of aromatic rings make the main contribution to both the lowest unoccupied and highest occupied molecular orbitals. The two-dimensional protein crystal shows a semiconductor-like behaviour with a gap value of ~3.0 eV and the Fermi energy close to the bottom of the LUMO.

X-ray Damage in Protein—Metal Hybrid Structures: A Photoemission Electron Microscopy Study

Bacterial surface layer protein sheets (S layer) coated with an ultrathin cobalt or silver film were studied by means of laterally resolved near-edge X-ray absorption fine structure spectroscopy performed by photoemission electron microscopy. Comparison with results obtained on pristine S layers allowed us to characterize both chemical interaction and X-ray damage in these protein-metal hybrid systems. In particular, we found that besides direct damage upon exposure to X-ray radiation the biomolecules experience additional contribution of the deposited metals, by low-energy electron generation in the metal particles.

Detecting the parity of electron wave functions in solids by quantum-well states of overlayers

We present an approach to monitor the parity of wave functions of electronic states of bulk solids, which was elaborated on the model Ag/W(110) system. The dispersion of quantum-well (QW) states formed in the thin Ag layer was examined by means of angle-resolved photoemission. The obtained experimental data were compared with results of layer Korringa–Kohn–Rostoker calculations. We found that around k points, where the two-dimensional QW bands cross the projected bulk bands of the W substrate of the same symmetry, broad hybridization gaps in the QW distributions are observed. Careful analysis based on a symmetry approach for the electronic bands in the Ag monolayer and the W substrate suggests that respective gaps may generally be taken as a fingerprint for the interaction with substrate states of even parity with respect to the emission plane. We anticipate that QW states may be used as a probe for symmetry properties of strongly correlated states in systems like heavy-fermion compounds that are difficult to access theoretically within an ab initio approach.