We study the observed inhomogeneous band bending effects on cleaved MoS2(0001) single-crystal surfaces. Both Mo 3d and S 2p core levels were found to shift to lower binding energy in regions of the MoS2 crystal with high step densities, as suggested by spot splitting of the LEED (low energy electron diffraction) pattern. Surface electronic band structure measurements also reveal a rigid shift of the valence bands in these regions, resulting from local Fermi level pinning effects. A surface electric field gradient on the MoS2 crystals caused by the charged dislocations from the regions of high step densities generated by the cleaving process is found to explain most of the experimental observations.

http://iopscience.iop.org/article/10.1088/0953-8984/24/30/305502/pdf

Inhomogeneous band bending on MoS2(0001) arising from surface steps and dislocations

The incorporation of Li atoms into Si(111) is studied with the aid of density functional theory (DFT). We find that Li adsorption removes the (1 × 2) reconstruction on this surface. For the whole range of chemical potential values of Li at which Li adsorption occurs, only a high coverage structure (1 ML) is stabilized on unreconstructed Si(111). We find for this surface that the simultaneous penetration of two or more Li atoms into the subsurface is very unfavorable. However, the penetration barrier for a single Li atom into the subsurface on 1 ML-Li/Si(111) is very similar to that on clean Si(111). The present work can help us to better understand the process of Li insertion into Si anodes of Li-ion batteries.

Theoretical studies of Li incorporation into Si(111)

Theoretical optical spectroscopy of complex systems

The degree of 1D character of surface chains at group IV (111)-2 × 1 reconstructed surfaces is established by surface sensitive optical spectroscopy. Optical experiments on a diamond C(111)-2 × 1 surface show that the absorption peak related to dangling-bond transitions exhibits a marked blueshift upon oxygen exposure of the clean surface. Such behaviour is analogous to that observed on a clean Si(111)-2 × 1 surface. For both surfaces the experimental finding is interpreted in terms of quantum confinement of surface electrons in quasi-one-dimensional π-bonded chains, whose length decreases with oxygen uptake. A different behaviour is observed in Ge(111)-2 × 1, where only a very slight blueshift of the surface-state optical transition is detected upon oxidation. The almost negligible blueshift in Ge(111)-2 × 1 is consistent with a significant coupling between the π-bonded chains resulting in a much less pronounced one-dimensional character of Ge(111)-2 × 1 surface electrons compared to diamond and silicon reconstructed surfaces.

Confinement effects in π-bonded chains at group IV semiconductor (111) surfaces.

http://nano-bio.ehu.es/files/articles/C._Violante_SS_2014_922.pdf

Si(111)2 × 1 surface isomers: DFT investigations on stability and doping effects

A long-standing puzzle regarding the $\mathrm{Si}(111)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface has been solved. The surface energy gap previously determined by photoemission on heavily $n$-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results.

https://www.cmu.edu/physics/stm/publ/94/isomers111_2x1.pdf

K. H. Rieder

Papers

Coexistence of negatively and positively buckled isomers on n+-doped Si(111) − 2 × 1.