Adsorption and electron properties of thin nickel films on W(110) surface

The evolution of the properties of ordered nickel films with thicknesses increasing from one to three atomic monolayers (ML) adsorbed on the W(110) single crystal surface is studied under ultrahigh vacuum conditions by the methods of reflection-absorption infrared spectroscopy (RAIRS) and ultraviolet photoelectron spectroscopy (UPS). The film structure corresponds to that of the Ni(111) single crystal face. The RAIRS technique is used to study the vibrational properties of the probing NO molecules adsorbed on the nickel films studied. In the course of the nickel film growth, whereby its thickness increases from 1 to 3 ML, both the vibrational and photoelectron spectra exhibit significant variation, which is indicative of a change in the adsorption and electron properties of the film. Stabilization of the IR and photoelectron spectra at a film thickness of 3 ML indicates that this thickness corresponds to the formation of the main adsorption and electron properties of the deposit. At the same time, the vibrational spectra of NO molecules adsorbed on a monoatomic nickel film exhibit features typical of adsorption on the W[110] surface of a massive tungsten crystal.     

Formation of spectra of quantum well states in thin Al layers on W(110)

Quantum well states of sp-type in thin metal layers of aluminum on the W(110) surface were experimentally studied by angle-resolved photoelectron spectroscopy depending on the layer thickness in a range of about 1–15 monolayers. It is shown that the aluminum layer is formed in accordance with the Kurdyumov-Sachs orientation relationship. Modification of the quantum well state spectra is observed with the increase in the layer thickness. The changes of the energy of quantum well states with the formation of each new monolayer have a stepwise character. This behavior can be used to calibrate the thickness of the deposited film with an accuracy within fractions of a monolayer. To confirm the reliability of the calibration, the thickness of the formed layers was tested using the attenuation of the W4f _7/2 peak intensity.     

Metastable surface structureof the W(110) face

The observation of a new metastable phase on the (110) tungsten surface contaminated with carbon is reported with an explanation based on a model of surface deformation in the (110) plane. The transition from the stable C1 structure to the metastable C2 structure is reversible and this cycle is reproducilbe.     

Comparison between Rydberg surface resonances on W(001) and W(110)

Comparison is made between high-resolution LEED measurements of electronic surface resonances in the (00) beam from W(001) and W(110). The study of W(110) extended to several polar angles of incidence provides new information that helps to explain the data obtained on W(001) at a fixed angle.     

Analysis of the possibility of the spin-orbit origin of surface state splitting in thin Mg(0001) layers on W(110) and Mo(110)

A set of magnesium films ranging in thickness from submonolayer to a few tens of atomic layers grown on single-crystal W(110) has revealed film-thickness dependent splitting of states localized energywise close to the magnesium surface state. Literature refers to several models describing the origin of this splitting; in one case, it is treated as substrate-induced spin-orbit splitting, and in another, as due to formation of nondegenerate pairs of even and odd surface states penetrating deep into the film bulk. The proposed models draw upon studies of films more than five monolayers thick. A comparative investigation of the Mg/W(110) and Mg/Mo(110) systems has been carried out for magnesium films of different, starting from submonolayer, thicknesses, which did not substantiate the spin-orbit origin of this splitting and suggests instead formation on the substrate-film interface of hybridized states, with their variation with thickness being assigned to variation in the contribution due to the magnesium surface states. Original Russian Text ? A.M. Shikin, D.E. Marchenko, N.A. Vinogradov, G.V. Prudnikova, A.G. Rybkin, V.K. Adamchuk, O. Rader, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 572–583.     

Long jump rates in surface diffusion: W on W(110)

We have reexamined the diffusion of W adatoms on W(110) using the field ion microscope. The diffusivity is in good agreement with previous results and reveals no unusual features, but from observations of the distribution of displacements, corrected for diffusion during temperature transients, we have for the first time been able to measure the temperature dependence of rates for nearest-neighbor and double jumps, as well as for vertical and horizontal transitions. Activation energies and frequency factors for all the long jumps are significantly larger than for single jumps, and a simple model is proposed to account for our observations.     

Atomic structure of antiphase domain boundaries of a thin Al2O3 film on NiAl(110)

Line defects of a thin alumina film on NiAl(110) have been studied on the atomic level with scanning tunneling microscopy at 4 K. While boundaries between two reflection domains do not expose a characteristic structure, antiphase domain boundaries are well ordered. The latter boundaries result from the insertion of a row of O atoms, as atomically resolved images of the topmost oxygen layer show. The insertion occurs only in two of the three characteristic directions of the quasihexagonal O lattice. Depending on the direction, either straight or zigzagged boundaries form. An atomic characterization of line defects on the oxide surface is a first step to correlate their topographic structure and chemical activity.     

有机半导体perylene和tetracene在Ag(110)表面上有序薄膜的结构与电子态研究

利用紫外光电子能谱(UPS)和低能电子衍射(LEED)对银(110)表面上perylene与tetracene的生长进行了研究.LEED的结果表明：一个分子单层的perylene在银(110)表面上会形成C(6×2)的有序结构；一个分子单层的tetracene，观察到的则是C(4×2)的有序结构.根据UPS的测量，与perylene分子轨道有关的4个特征峰分别位于Frimi能级以下35，48，64和85eV处，与tetracene分子轨道有关的4个特征峰的结合能分别为3．4，49，59和94eV.角分辨紫外光电子能谱(ARUPS)的测量表明，表面附近的perylene和tetracene分子平面平行于银衬底表面，tetracene分子的长轴可以确定沿［110］晶向. 关键词： 有机半导体材料 紫外光电子能谱 结构和电子结构     

Structure of ultra-thin Ti film on the Al(001) surface

The atomic structure of sub-monolayer amounts of Ti deposited on the Al(001) surface at room temperature has been investigated using low-energy electron diffraction (LEED) and low-energy ion scattering spectroscopy (LEIS). The Ti coverage was determined using Rutherford backscattering spectroscopy (RBS). Though a crisp LEED image is inherently difficult to obtain, the symmetry of the observed c(2 × 2) LEED images allows us to infer a structure which places Ti atoms in every other Al lattice site. Analysis of the LEIS azimuth- and polar-angle scan spectra has been done to determine the best structural model which supports the c(2 × 2) symmetry of the LEED image as well as LEIS experimental data. It was concluded that the best model consistent with the experimental data, puts Ti preferentially below the surface of the Al substrate at every other lattice site for sub-monolayer coverage of Ti on Al(001). As Ti coverage increases, the presence if Ti atoms in the surface layer also increases. Results of this study are relevant to research pertaining to the possible use of Ti as a catalyst in sodium alanate (NaAlH₄) in hydrogen storage applications.     

Spectra of quantum states in thin metal films and their modification: Al/W(110) system

The modification of spectra of quantum well states of sp-type in thin Al films on the W(110) surface was experimentally investigated by angular-resolved photoelectron spectroscopy both during deposition and in dependence of the detection angle. Quantum well states are observed for the partially filled band of valence states in the range of binding energies from 4.4 eV to the Fermi level. An Al film with a thickness of 11 monolayers exhibits a jump of the dispersion relations of quantum well states in the local W(110) band gap in the ΓS direction and splitting of these relations due to the effect of substrate electronic structure on the formed spectrum of quantum states and their possible spin polarization.     

The ferromagnetic monolayer Fe(110) on W(110)

Ferromagnetic order in the pseudomorphic monolayer Fe(110) on W(110) was analyzed experimentally using Conversion Electron Mössbauer Spectroscopy (CEMS) and Torsion Oscillation Magnetometry (TOM). The monolayer is thermodynamically stable, crystallizes to large monolayer patches at elevated temperatures and therefore forms an excellent approximation to the ideal monolayer structure. It is ferromagnetic below a Curie-temperatureT _c,mono, which is given by (282±3) K for the Ag-coated layer, (290±10) K for coating by Cu, Ag or Au and ≈210 K for the free monolayer. For the Ag-coated monolayer, ground state hyperfine fieldB _hf (0)=(11.9±0.3) T and magnetic moment per atom μ=2.53 μ_B could be determined, in fair agreement with theoretical predictions. Unusual properties of the phase transition are detected by the combination of both experimental techniques. Strong magnetic anisotropies, which are essential for ferromagnetic order, are determined by CEMS.     

Growth of germanium thin films on the W(100) surface

The growth of Ge thin films on the surface of a textured predominantly (100)-oriented tungsten ribbon is studied by thermal desorption spectrometry at different substrate temperatures over a wide range of coverages. The mechanism of growth of the Ge films at T = 300 K is similar to a layer-by-layer mechanism. For T > 300 K, the films grow through the Stranski-Krastanov mechanism, according to which the completion of the monolayer coverage is followed by the formation of three-dimensional crystallites; as a result, the desorption kinetics changes. For small coverages (i.e., in the absence of lateral interactions), the activation energy of Ge desorption from W(100) is E = 4.9 ± 0.2 eV. In a monolayer, this activation energy decreases to E = 3.9 ± 0.2 eV due to the repulsive lateral interactions. The energy of pairwise lateral interactions is determined to be ω = 0.3 eV.     

Adsorption of silicon atoms on the surface of the Au/W(110)

The possibility of formation of an ordered silicene-like structure on Au/W(110) surface has been considered using angle-resolved photoelectron spectroscopy and X-ray photoelectron spectroscopy. It is shown that the addition of silicon atoms results in a considerable distortion of the electron structure of the initial substrate, and the resulting electron structure cannot be attributed to silicene. The configuration of reflections in the low energy electron diffraction pattern indicates the formation of two-dimensional ordered silicon structures with a large number of multidirectional domains.