Unoccupied Surface State Band Research Articles

Surface state lifetime in quasi-one-dimensional oxygen stripes on Cu(1 1 0)

Scanning tunneling spectroscopy data on the lifetime and bottom energy of a surface state band in quasi-one-dimensional stripes are presented as a function of stripe width. The adsorbate system Cu(1 1 0)-p(2 × 1)O has been used to prepare a two-dimensional adsorbate layer and almost defect free quasi-one-dimensional stripes with a width of 3–15 CuO rows, respectively. The onset of an unoccupied surface state band (at 0.56 eV above Fermi-energy on the fully covered surface) has been analyzed with respect to the quasi-particle lifetime at the crossover from two to one dimension. A drastic increase of the onset-width with decreasing stripe width is observed. It can be explained by a decrease of quasi-particle lifetime using a Fabry–Pérot-like model. We obtain a reduction of lifetime from 37 ± 8 fs on the two-dimensional adsorbate layer to 5 ± 1 fs on a three CuO rows wide stripe.

Atomic and electronic structure of the Si(0 0 1)2 × 1–Li chemisorption system at 1.0 monolayer coverage

Ab initio plane-wave pseudopotential density functional theory (DFT) calculations have been performed to determine the atomic and electronic structure of the Si(0 0 1)2 × 1–Li adsorption system at 1.0 monolayer (ML) coverage. Chemisorption of the lithium atoms is found to result in a minimum energy configuration characterized by symmetric Si dimers in agreement with the results of high-resolution core-level photoelectron spectroscopy. The transition from the asymmetric Si dimers of the clean Si(0 0 1) surface to the symmetric dimers of the Li chemisorbed surface is due to charge transfer from the Li adatoms to the substrate. The dispersion of the occupied electronic surface state bands is found to be in good agreement with the angle-resolved photoemission data. The nature of the lowest energy unoccupied surface state band suggests that silicide formation may occur at coverages greater than 1.0 ML.

Atomic and electronic structure of theSi(001)2×2−Lichemisorption system at 0.5 monolayer coverage

Ab initio plane-wave pseudopotential density functional theory $(\mathrm{DFT})$ calculations have been carried out to determine the atomic and electronic structure of the $\mathrm{Si}(001)2\ifmmode\times\else\texttimes\fi{}2\text{\ensuremath{-}}\mathrm{Li}$ adsorption system at 0.5 monolayer $(\mathrm{ML})$ coverage. The minimum energy configuration is found to be characterized by alternating symmetric and asymmetric $\mathrm{Si}\text{\ensuremath{-}}\mathrm{Si}$ dimers along each dimer row independently of the details of the $\mathrm{Li}$ adatom topology. This is due to virtually all of the $\mathrm{Li}$ charge being transferred to just one of the dimers in each $2\ifmmode\times\else\texttimes\fi{}2$ surface unit cell, leaving the second dimer essentially unchanged. The nature and dispersion of the theoretically predicted occupied electronic surface state bands are found to be in good agreement with the angle-resolved photoemission data and little dependent on the actual $\mathrm{Li}$ adatom geometry. The composition of the second and third lowest unoccupied surface state bands, however, clearly depends on the $\mathrm{Li}$ adatom topology. The nature of the lowest energy unoccupied surface state band suggests that the $\mathrm{Si}(001)\text{\ensuremath{-}}\mathrm{Li}$ chemisorption system at $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{ML}$ coverage will exhibit a reactivity similar to that of the clean $\mathrm{Si}(001)$ surface.

Atomic and electronic structure of the Si(001)2×1–K surface

Abstract The plane-wave pseudopotential density functional theory method has been used to study the Si(0 0 1)2 × 1–K adsorption system for 0.5 and 1.0 monolayer coverage. The minimum energy atomic configuration for 0.5 monolayer coverage was found to correspond to the potassium atom in each 2 × 1 surface unit cell occupying the valley bridge site. A double-layer model was determined to be the optimised geometry of the Si(0 0 1)2 × 1–K chemisorption system for 1.0 monolayer coverage. The geometry of this double-layer model was found to be in good agreement with the current experimental data. A detailed analysis of the electronic structure of this double-layer model has also been performed. The overall dispersion of the occupied and unoccupied surface state bands has been shown to be in excellent agreement with the angle-resolved and inverse photoemission data. The nature and dispersion of the surface states of the double-layer model in the vicinity of the energy gap provide evidence of strong interactions, both between the two inequivalent potassium atoms in each 2 × 1 surface unit cell, and between these adatoms and the underlying substrate.

Electronic structure of theSi(111)3×3R30°−Bsurface

The plane-wave pseudopotential density functional theory (DFT) package FHI98MD has been used to optimize the geometry of the $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}R30\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}\mathrm{B}{(S}_{5})$ configuration. The resultant geometry has been found to be in excellent agreement with recent experimental results. By calculating the band structure for the $\mathrm{B}{(S}_{5})$ configuration and carefully analyzing the nature of the wave functions in the vicinity of the Fermi energy, we have been able to identify the surface states along the various symmetry directions of the surface Brillouin zone (SBZ). The overall dispersion of both the occupied and unoccupied surface state bands is found to be in excellent agreement with the angle-resolved photoemission data. The theoretical calculations also predict the occurrence of two occupied surface state bands at the $\ensuremath{\Gamma}$ and M points of the SBZ. The splitting of these bands is predicted to be 0.27 eV and 0.35 eV, respectively, in good agreement with experiment.

Angle-resolved inverse photoemission of the (2×1)-reconstructed 3C-SiC(0 0 1) surface

We have investigated the two-domain (2×1)-reconstructed 3C-SiC(0 0 1) surface using angle-resolved inverse photoemission. An unoccupied surface state band at E SS=2.0 eV with respect to the valence band maximum (VBM) at the Γ point is completely located within the bulk band gap. Further, an unoccupied surface resonance at E SR=3.6 eV above VBM is observed. Both surface structures show no dispersion in Γ J and Γ J ′ directions, respectively. The energetic position of both is in good agreement with LDA surface band structure calculations. However, LDA calculations predict a dispersion of about 0.8–1.0 eV for the surface state band and about 0.5–0.8 eV for the surface resonance band, while experimentally no dispersion in Γ J and Γ J ′ directions is observed.

Occupied and unoccupied surface states on the single-domain Si(100):Sb-2 x 1 surface.

Angle-resolved photoelectron spectroscopy and k-resolved inverse photoemission have been used to study the electronic structure of the Si(100):Sb-2\ifmmode\times\else\texttimes\fi{}1 surface. For both techniques, one occupied and one unoccupied surface-state band has been mapped along the [010] and [011] directions. The surface shows semiconducting behavior with an estimated minimum band gap of 1.45 eV along the [010] direction.

Unoccupied surface-state bands on the single-domain Si(100)2 × 1 surface

We have studied the unoccupied surface bands of single-domain Si(100)2 × 1 surfaces with angle-resolved inverse photoemission (IPE). Two surface states are present near the Fermi level (EF) with flat energy dispersions at 1.1 and ∼ 0.4 eV above EF along the Γ-J direction, while along the Γ-J′ direction these state are dispersive with an apparent crossing at about halfway towards J′. Both surface bands are assigned to the empty dangling-bond states. As only one empty dangling-bond band is expected for a 2 × 1 reconstruction, we attribute the appearance of two branches to domains of asymmetric dimers on the surface, arranged into local p(2 × 2) or c(4 × 2) periodicities. These findings are analogous to the results of recent angle-resolved (direct) photoemission studies of the filled dangling bonds on the 2 × 1 and the cooled c(4 × 2) surfaces.

Unoccupied surface-state band on Si(111) 2×1

Employing k-resolved inverse-photoemission spectroscopy, we have measured the dispersion of the unoccupied electronic surface-state band of cleaved single-domain Si(111) 2\ifmmode\times\else\texttimes\fi{}1 along the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}--J\ifmmode\bar\else\textasciimacron\fi{} and \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}--J\ifmmode\bar\else\textasciimacron\fi{}' symmetry directions. The energy dispersion and general shape of the measured surface-state band agree well with the calculated band of the \ensuremath{\pi}-bonded chain model.

Inverse photoemission from an unoccupied surface state band on Ag(110)

Inverse photoemission from an unoccupied surface state band on Ag(110)

Inverse photoemission from an unoccupied surface state band on Ag(110)

We report the first experimental observation of an unoccupied surface state on a metal surface, i.e. Ag(110), by means of angle-resolved inverse photoemission. It is a Shockley-type surface state which lies within the sp hybridization gap at 1.7 eV above the Fermi level and is placed at the X point of the surface Brillouin zone.