Site-specific electronic structure of bacterial surface protein layers

We applied resonant photoemission and X-ray absorption spectroscopy for a detailed characterization of the valence electronic structure of the regular two-dimensional bacterial surface protein layer of Bacillus sphaericus NCTC 9602. Using this approach, we detected valence electron emission from specific chemical sites. In particular, it was found that electrons from the π clouds of aromatic systems make large contributions to the highest occupied molecular orbitals.     

Formation and manipulation of regular metallic nanoparticle arrays on bacterial surface layers: an advanced TEM study

The template-directed formation of regular nanoparticle arrays on two-dimensional crystalline protein layers after their treatment with metal salt complexes was studied by transmission electron microscopy. For these investigations, bacterial surface layers (S layers), recrystallized in vitro into sheets and tube-shaped protein crystals with typical dimensions in the micrometer range, were used as the template. As identified by electron holography and scanning force microscopy, the S-layer tubes form alternating double layers when deposited onto a solid substrate surface. Two distinct pathways for the metal particle formation at the templates have been found: the site-specific growth of metal clusters by chemical reduction of the metal salt complexes, and the electron-beam induced growth of nanoparticles in the transmission electron microscope. Both mechanisms lead to regular arrays with particle densities > 6×10¹¹ cm ^-2. Nanoparticle formation by electron exposure takes exclusively place in the flat-lying double-layered protein tubes, where a sufficient amount of metal complexes can be accumulated during sample preparation. Received 6 December 2000     

Electronic surface resonances and crystal surface structure

A new method of determination of the lateral structure of crystal surfaces is presented. The method is based on earlier work showing the existence of resonances in the elastic scattering of low-energy electrons at crystal surfaces. The method consists of: (a) Measurement of the surface resonance band structure Ek_∥E, k_∥ respectively denote the electron energy and surface-parallel momentum for which resonances occur) and (b) Interpretation of E(k_∥) to determine the lateral variation of the effective potential acting on electrons at the surface.The surface resonance band structure is measured by a net-current electron reflection method. The measurement method is basically the same as used previously but here its precision is greatly enhanced by the use of digital methods of data handling including a digital filter to remove background due to inelastic and non-resonance elastic scattering. The surface resonance band structure is interpreted by a two-dimensional nearly-free electron scheme. In this scheme the interaction elements are Fourier coefficients of an effective potential which is an average of a pseudopotential with respect to the depth distribution of electron density in a surface resonance — the surface-weighted pseudopotential. Experimental surface resonance band structure for Ni(001), Ni(001) p(2 × 2)O and two different Ni(001) c(2 × 2)O surfaces (one of them with an oxygen-saturated Ni substrate) are presented for E = 1–30 eV and k_∥ running halfway from $\text{}\text{?}$gG towards H? in the surface Brillouin zone for Ni(001). The experimental results are fitted, using the nearly-free electron scheme, to determine the Fourier coefficients of the surface-weighted pseudopotential. Surface potential variations synthesized from the above data are discussed in comparison with the atomic arrangements known from LEED. It is demonstrated that the new method can give a correct picture of the lateral structure of surfaces. It is emphasized that these results are obtained without costly equipment or computations called for by other methods.     

Electronic structure and interactions in well-defined coadsorbate layers

A synopsis of results and models for weakly and strongly interacting, well-defined coadsorbate systems is presented. Some experimental examples are given for various adsorbates on Ni(111) representing weak (different N₂ states, Ar/Xe+N₂) as well as strong (N₂+K) interaction. Models for coadsorbate interaction, in particular between molecules (CO, N₂) and alkali atoms, are discussed.     

Electronic structure of the SiAu surface

The electronic density of states of the SiAu surface is calculated using a continued fraction technique. The geometric structure of the surface alloy Au₄Si is generated by molecular dynamics. The local density of states on Si atoms in a metallic environment differs qualitatively from the sp spectrum of a typical semiconductor. The calculated densities of p states of Si are in good agreement with recent X-ray spectra of Si in a metallic environment.     

Specific features of light propagation in a periodic structure with regular arrangement of defect layers

Specific features of light propagation in a periodic structure with a large number of identical regularly arranged defect layers are considered. Rigorous analytical formulas for the transmittance and reflectance of the structures are derived. It is shown that the presence of periodically arranged inclusions may give rise to new photonic band gaps, with their positions controlled by the dielectric properties and thickness of the defect layers.     

Electronic structure of the surface of rare Earth metals

A qualitative model describing the surface of rare earth metals with an uncompleted 4f electron shell (Ce-Yb) and the process of thermal evaporation from this surface is proposed. The model is based on a correlation established between the energies of the lowest-lying levels of the 4f^N?15d6s² configuration and the temperatures of equal saturated-vapor pressures of these metals.     

LaNi5晶体表面态的计算研究

用"团簇埋入自洽计算法"对LaNi5晶体表面进行了全电子、全势场、自旋极化的从头计算.在原子纵向坐标充分弛豫的条件下,得到处于最低基态总能量下LaNi5晶体的非平整表面空间结构及其电子结构.LaNi5晶体最表面La原子向外凸出,Ni原子向里收缩,凹凸不平的表面层增加了表面原子与氢原子的接触面积;而表面层的有效体积增大了约9%,有利于氢原子的进入.LaNi5晶体表面态的费米能量大大高于体材料的费米能量.在费密面上主要是Ni的3d电子,价带未填满,显示金属性.LaNi5晶体表面第一、第二层有1.15个电子从La原子向Ni原子转移,这两层有反向的微小自旋磁矩,从而使表面显示顺磁性.得到了LaNi5晶体表面的价带电子态密度.用过渡态方法计算了LaNi5晶体表面的电离能和电子亲和势.所有计算结果显示:LaNi5晶体表面的性质与体性质显著不同,而与氢化物LaNi5H7的性质非常相近.这说明LaNi5晶体的表面结构有利于氢原子的吸收.     

Electronic structure of the Cu(111) surface

Self-consistent electronic structure calculations are reported on bulk Cu, and 3- and 5-layer Cu films. These yield a size insensitive work function, φ = 5.0±.1 eV, and a surface energy of 0.75 eV, in agreement with experiment. Good size convergence of the film potential permits the construction of a self-consistent potential for an 11-layer Cu(111) film, whose spectral properties we studied. A prominent p-like surface band was found within 0.1 eV of experiment, serving as a check on the surface potential.     

Electronic structure of epitaxial graphene layers on SiC: effect of the substrate

A strong substrate-graphite bond is found in the first all-carbon layer by density functional theory calculations and x-ray diffraction for few graphene layers grown epitaxially on SiC. This first layer is devoid of graphene electronic properties and acts as a buffer layer. The graphene nature of the film is recovered by the second carbon layer grown on both the (0001) and (0001[over]) 4H-SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. Hence the graphene is doped and a gap opens at the Dirac point after three Bernal stacked carbon layers are formed.     

Electronic structure theory of surface, interface and thin-film magnetism

Low dimensional magnetic systems including surfaces, interfaces and thin-films, have attracted a great amount of attention in the past decade because, as expected, the lowered symmetry and coordination number offer a variety of opportunities for inducing new and exotic phenomena and so hold out the promise of new device applications. Local spin density functional (LSDF) ab initio electronic structure calculations played a key role in the development of this exciting field by not only providing a clearer understanding of the experimental observations but also predicting new systems with desired properties. Extensive calculated results reviewed here demonstrate that (1) weakened interatomic hybridization at clean surfaces or interfaces with inert substrates give rise to strong magnetic enhancement and (2) the strong interaction with nonmagnetic transition metals diminishes (entirely in some cases) the ferromagnetism and usually stabilizes the antiferromagnetic configuration. Surprisingly, experimentally observed surface (interface) magnetic anisotropy can be reproduced correctly in the theoretical calculations, although the anisotropy energy is only 10⁻⁴−10⁻⁵ eV.     

Au钝化Si(100)表面的电子特性

用TB-LMTO方法研究单层的Au原子在理想的Si(100)表面的化学吸附.计算了Au原子在不同位置的吸附能,吸附体系与清洁Si(100)表面的层投影态密度, 以及电子转移情况.结果表明, Au原子在吸附面上方的A位(顶位)吸附最稳定, Au钝化Si(100)表面可以取得明显的钝化效果, 这一结论与实验事实相符合.     

The structure of titanium nickelide surface layers formed by pulsed electron-beam melting

X-ray structure analysis technique has been developed for a material heterogeneous over the depth. The structure of the TiNi intermetallide subjected to surface modification by an electron beam has been investigated. The following three layers differentiated in the microcrystalline structure have been singled out: (i) the external sharply textured layer 1–3 μm in thickness with a texture in the [100] B2 direction and a lattice periodicity parameter reduced by 1% in the direction of the normal, (ii) the intermediate gradient-stressed layer 10–15 μm in thickness with the texture of the initial ingot, and (iii) the original material. The crystal lattice of the surface as well as of the intermediate layer is in a state stretched along the surface and compressed along the normal to it. This lattice distortion is maximal in the surface layer and decreases towards the bulk of the material.     

Characterization of regular periodic surface structure by multi-pulse laser irradiation of a Zinc target

The circular-like sidewall and trench around the periphery of the crater are obtained on Zinc metal surface subjected to fewer than 200 cumulative pulses laser ablation.These patterns can be attributed to the higher secondary heating by regular plasma spherical pressure.The 600 pulses laser ablation,however,results in the formation of undesirable bulk wrinkles of super-heated liquid at the side of the trench.These features may be applied in micro-manufacturing of high localizability and selectivity using laser zone texturing.