Surface states on GaAs(110)

The electronic structure of the (110) surface of GaAs is recalculated using the relaxation geometry recently obtained from analyzing elastic low-energy electron diffraction intensity data and a self-consistent ab initio pseudopotential approach. Better agreement is found for the occupied surface states compared with photoemission data, giving support for the new structural model. The influence of convergence of the plane-wave expansion and relativistic effects on the surface states is also examined.     

Valence surface electronic states on Ge(001)

The optical, electrical, and chemical properties of semiconductor surfaces are largely determined by their electronic states close to the Fermi level (E{F}). We use scanning tunneling microscopy and density functional theory to clarify the fundamental nature of the ground state Ge(001) electronic structure near E{F}, and resolve previously contradictory photoemission and tunneling spectroscopy data. The highest energy occupied surface states were found to be exclusively back bond states, in contrast to the Si(001) surface, where dangling bond states also lie at the top of the valence band.     

Method for calculating the contribution of inelastic electron-electron scattering lifetimes of electronic states on (110) noble metal surfaces

A method for calculating the decay rate of surface states on the (110) noble metal surfaces within the GW approximation is described in detail. The band structure is described by a two-dimensional pseudo-potential model. As an example, the calculated lifetimes of surface states at the [`(Y)] \bar{Y} point on Cu(110) are presented. The calculated lifetime of the occupied state is approximately 2 times greater than that of the unoccupied state. The result obtained for the occupied surface state is in good agreement with the photoemission data.     

Electrostatic response and surface electron states of a Ca(001) face-centered cubic film

The electron response of a Ca(001) face-centered cubic film to an external electrostatic field is calculated. The results of calculations are compared with the previously obtained data on the electron response of a Cu(001) film. The energy location of occupied and unoccupied excited surface states of the Ca(001) film is determined.     

A very low energy electron reflection study of hydrogen adsorption on W(100) and W(110) surfaces

Experimental results of the elastic backscattering of electrons with energies between 0 and 20 eV from the surface systems H/W(100) and H/W(110) are reported and interpreted on the basis of the Darwin model. On W(100) the adatom distance from the reconstructed substrate is found to be different from that on the relaxed surface. Large vertical displacements of the substrate atoms during reconstruction can be excluded. On W(110) the results indicate two different binding states which are occupied sequentially and which differ significantly in their distances from the surface. Work function change data are also reported for both systems.     

On different mechanisms of electron-phonon scattering of electron and hole excitations on an Ag(110) surface

We present the results of a detailed theoretical study of the electron-phonon scattering of electron and hole excitations in the unoccupied and occupied surface states on an Ag(110) surface. We show that the electron-phonon coupling parameter λ in the unoccupied surface state is approximately three times smaller than that in the occupied one, because the scattering of these states is determined by different phonon modes. The difference in the phonon-induced decay mechanisms of electron and hole excitations is determined by different spatial localizations of the unoccupied and occupied surface states at the $ \overline Y $ \overline Y point of the two-dimensional Brillouin zone.     

Si(100)表面电子态的总电流谱研究

用自制的总电流谱仪研究了Si(100)2×1清洁表面以及H原子饱和吸附后的Si(100)1×1-2H双氢化相表面的电子态。在清洁表面上测得的空电子态位于价带顶以上0.7eV处,而占有电子态则在价带顶以下0.25,8.4和近12eV处。在双氢化相表面上还观测到处于价带顶以下两个诱导表面态。 关键词：     

Surface states,local bonding,and surface reconstruction: Na on Cu(110)

Occupied and unoccupied surface states on Na/Cu(110) have been investigated by photoemission and inverse photoemission. By measuring surface state positions at the same adsorbate coverage on the reconstructed and the unreconstructed surface it is demonstrated that the surface states contribute to the total energy balance of the Na induced missing row reconstruction. During the onset of the reconstruction an up-shift of the surface states depopulates an initially occupied CuCu bonding surface state and consequently destabilizes the topmost Cu atoms. The surface state wavefunctions are qualitatively analyzed in a thight-binding LCAO picture.     

Electronic surface states of Cu(1 1 0) surface

Surface states are a unique and important class of quantum states that shave an important effect on the electronic properties of Cu(1 1 0) surface. The Cu(1 1 0) surface has been studied using ultraviolet photoemission spectroscopy (PES), inverse photoemission spectroscopy (IPES), and reflection anisotropy spectroscopy (RAS), and shows a resonance in the RAS spectra at 2.1 eV due to a transition between occupied and unoccupied surface states. The unoccupied surface state involved in the RAS transition at an energy of 1.7 eV at the point of the surface Brillouin zone has been investigated using IPES and the occupied surface state is seen in PES spectra at 0.45 eV below the Fermi level. The energy difference of the surface states, 2.15 eV, is a good match to the transition energy found in the RAS experiments.     

Size-dependent surface states of strained cobalt nanoislands on Cu(111)

Low-temperature scanning tunneling spectroscopy over Co nanoislands on Cu(111) showed that the surface states of the islands vary with their size. Occupied states exhibit a sizable downward energy shift as the island size decreases. The position of the occupied states also significantly changes across the islands. Atomic-scale simulations and ab initio calculations demonstrate that the driving force for the observed shift is related to size-dependent mesoscopic relaxations in the nanoislands.     

CO与Cs在Ru(101-0)表面上的共吸附研究

CO与Cs在Ru（101－0）表面上共吸附的高分辨电子能量损失谱研究结果表明：CO在有Cs覆盖的Ru（101－0）表面上有两种吸附状态，除了与CO在清洁表面上相似的一种吸附状态以外，还有一种新的吸附状态，它的C—O伸缩振动频率比前者低得多．在CO暴露过程中，CO分子首先吸附在低C—O伸缩振动频率的状态，随着CO覆盖度的增加，两种吸附状态的C—O伸缩振动频率都向高频方向移动．两种吸附状态的C—O伸缩振动频率也与Cs的覆盖度有关．当CO覆盖度饱和后，在Cs覆盖度较高的表面上两种吸附状态的C—O伸缩振动频率相对 关键词：     

Dependence of the intrinsic line width of surface states on the wave vector: The Cu(111) and Ag(111) surfaces

The dependence of the intrinsic line width Γ of electron and hole states due to inelastic scattering on the wave vector k _∥ in the occupied surface state and the first image potential state on the Cu(111) and Ag(111) surfaces has been calculated using the GW approximation, which simulates the self-energy of the quasiparticles by the product of the Greens’s function and the dynamically screened Coulomb potential. Different contributions to the relaxation of electron and hole excitations have been analyzed. It has been demonstrated that, for both surfaces, the main channel of relaxation of holes in the occupied surface states is intraband scattering and that, for electrons in the image potential states, the interband transitions play a decisive role. A sharp decrease in the intrinsic line width of the hole state with an increase in k _∥ is caused by a decrease in the number of final states, whereas an increase in Γ of the image potential state is predominantly determined by an increase of its overlap with bulk states.     

CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states

We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage.     

Progressive changes in atomic structure and gap states on Si(0 0 1) by Bi adsorption

From ab initio studies employing the pseudopotential method and the density functional scheme, we report on progressive changes in geometry, electronic states, and atomic orbitals on Si(0 0 1) by adsorption of different amounts of Bi coverage. For the 1/4 ML coverage, uncovered Si dimers retain the characteristic asymmetric (tilted) geometry of the clean Si(0 0 1) surface and the Si dimers underneath the Bi dimer have become symmetric (untilted) and elongated. For this geometry, occupied as well as unoccupied surface states are found to lie in the silicon band gap, both sets originating mainly from the uncovered and tilted silicon dimers. For the 1/2 ML coverage, there are still both occupied and unoccupied surface states in the band gap. The highest occupied state originates from an elaborate mixture of the p_z orbital at the Si and Bi dimer atoms, and the lowest unoccupied state has a ppσ* antibonding character derived from the Bi dimer atoms. For 1 ML coverage, there are no surface states in the fundamental bulk band gap. The highest occupied and the lowest unoccupied states, lying close to band edges, show a linear combination of the p_z orbitals and ppσ* antibonding orbital characters, respectively, derived from the Bi dimer atoms.     

Spectral density of surface states: Clean W(001) surface

The transfer matrix approach is applied to calculate the spectral density of electronic states for the W(001) surface. We use a tight-binding hamiltonian with a nine function basis: 6s, 6p and 5d. Results for $\text{k}$ points along the Σ and ? symmetry lines are presented for occupied states. Both surface and bulk features of the spectral density are in good agreement with angularly resolved photoemission spectra.     

FeS2(100)表面原子几何与电子结构的理论研究

采用密度泛函理论研究了FeS2(100)表面原子几何与电子结构.理论计算结果表明:FeS2(100)表面无弛豫、无重构,是体相原子几何的自然终止.与体相电子结构相比,FeS2(100)表面电子特性明显不同,禁带中央产生新的表面态,且表面态局域性强,主要由Fe原子的3d分波贡献.配位场理论定性分析表明:FeS2(100)完整晶面表面态产生机制是Fe原子的配位数减少、局部对称性下降所致 关键词： 密度泛函理论 表面电子结构 FeS2     

Surface states of a semi-infinite diamond crystal limited by the (100) plane

Two kinds of surface states with energies lying in the gap between the valence and the conductive zone, were found for a semi-infinite diamond crystal, limited by the (100) plane, using the MO LCAO method, in which the molecular orbits are expressed as linear combinations ofsp ³ hybrid orbits of carbon atoms. One of these zones of surface states is completely occupied, the other completely unoccupied. The nature of these surface states is discussed and it is shown that the (100) surface of the diamond behaves similarily as if each surface atom had a free electron pair.     

Si(111)理想、弛豫及2×1重构表面的声子谱研究

本文利用微扰的方法考虑了占据态与空态间的耦合对能带能量的影响,给出延展键轨道近似下半导体力常数的解析表达式.利用这些表达式求出Si(111)的理想、1×1弛豫及2×1Haneman模型重构表面的声子色散曲线及其表面振动的振幅分布.不同表面结果的比较显示弛豫及重构对表面声子性质具有决定性的影响.同时,分析表明Haneman的2×1表面重构模型不足以满意地解释有关实验结果.     

Surface-state depopulation on small Ag(111) terraces

The dependence of the local density of states near the Fermi energy E(F) on the width of terraces T is investigated by tunneling scanning spectroscopy on Ag(111) at 7 K. With decreasing T, the electronic density in the occupied surface state shifts monotonically towards E(F), leading to a depopulation at T=3.2 nm in quantitative agreement with a Fabry-Pérot model. Depopulation coincides with a switch from confinement by terrace modulation to step modulation.     

Ab-initio calculations and STM observations on tetrapyridyl and Fe(II)-tetrapyridyl-porphyrin molecules on Ag(1 1 1)

We modelled the adsorption of tetra-pyridyl-porphyrin (TPyP) and Fe(II)-tetra-pyridyl- porphyrin (Fe-TPyP) molecules on Ag(1 1 1). TPyP adsorbs in a flat geometry at a distance of 5.6 Å from the surface. The dihedral angle of the pyridyl rings is found to be 70°. The molecular structure remains largely unaffected by the adsorption. The structure of the molecular adlayer should thus be determined mainly by lateral intermolecular interactions. These conclusions are confirmed by scanning tunnelling microscopy observations. Upon metalation spin-polarized states with strong Fe d-character appear in Fe-TPyP near the centre of the gap between the highest occupied and the lowest unoccupied states of a TPyP molecule. We find also that the gap is widened in the presence of Fe. This implies a shift of 0.3 eV of unoccupied states as identified by scanning tunnelling spectroscopy simulations and confirmed by experimental data.