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The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ~100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.
RNase P processes the 5'-end of tRNAs. An essential catalytic RNA has been demonstrated in Bacteria, Archaea and the nuclei of most eukaryotes; an organism-specific number of proteins complement the holoenzyme. Nuclear RNase P from yeast and humans is well understood and contains an RNA, similar to the sister enzyme RNase MRP. In contrast, no protein subunits have yet been identified in the plant enzymes, and the presence of a nucleic acid in RNase P is still enigmatic. We have thus set out to identify and characterize the subunits of these enzymes in two plant model systems. Expression of the two known Arabidopsis MRP RNA genes in vivo was verified. The first wheat MRP RNA sequences are presented, leading to improved structure models for plant MRP RNAs. A novel mRNA encoding the central RNase P/MRP protein Pop1p was identified in Arabidopsis, suggesting the expression of distinct protein variants from this gene in vivo. Pop1p-specific antibodies precipitate RNase P activity and MRP RNAs from wheat extracts. Our results provide evidence that in plants, Pop1p is associated with MRP RNAs and with the catalytic subunit of RNase P, either separately or in a single large complex.