c(2 x 2)CO ON Ni(100): Photoemission orientation determination

Angular resolved photoemission studies of c(2 x 2)CO adsorbed on Ni(100) show that the molecule is bound to the surface with the molecular axis normal to the surface. The uncertainty of this determination is approximately 15°, which is consistent with the expected angular broadening due to vibrational modes. This is in distinct contrast to a bend of 34° proposed to explain LEED data on this system.     

Metastable (2S) helium atom scattering from NiO(100) and Cu(100) surfaces

The scattering of metastable 2³S He atoms (He*) from cleaved NiO(100) as well as from clean and CO-covered Cu(100) surfaces has been studied. For these varied surfaces, which were characterized in situ by ground state He atom scattering, only broad He* angular distributions without any diffraction peaks were observed. For metastable He atoms scattered from the clean Cu(100) surface a total survival probability of 1×10⁻⁶ was determined. For NiO(100) and the CO-covered Cu(100) surface values of about 1×10⁻⁵ were obtained. Time-of-flight spectra of the surviving He* atoms revealed a substantial energetic broadening which increases with the substrate temperature. This behaviour indicates a large well depth for the He*–surface interaction potential and is discussed in terms of an enhanced multiphonon excitation and/or trapping probability upon the scattering.     

Antibacterial properties of composite UHMWPE/mathrm {TiO}_{2-{it x}} surfaces

Due to the diffusion of severe pathogens, everyday life is exposed to the risks of contracting severe diseases. For this reason, efficient antimicrobial surfaces are of paramount importance. In this work we present the first evidences of a new technique to obtain an antibacterial ultra high molecular weight polyethylene based on a non-stoichiometric, visible light responsive, titanium oxide coating. The coating was obtained through a process in which titanium ions, resulting from laser ablation of a corresponding target, were accelerated and implanted on the samples. The samples were tested against a Staphylococcus aureus strain, in order to assay their antimicrobial efficacy. Results show that this treatment strongly discourages bacterial colonization of the treated surfaces.     

Angle-of-incidence dependence in angle-resolved photoemission from chemisorbed molecules: c(2 × 2)O,c(2 × 2)5, and CO on Ni(100)

We have measured the angular distribution of photoemitted electrons from c(2 × 2)O, c(2 × 2)S, and CO adsorbed on a Ni(100) substrate for various independently set angles of incidence of unpolarized light at 21.2 eV. We have found that these systems have very different dependence on angle of incidence, depending upon which components of the vector potential of the light ($\text{A}$) are responsible for emission. Because the incident and reflected light combine to form a standing wave at a metal surface, the phase relationships between components of $\text{A}$ parallel and perpendicular to the surface play an important role in determining the effective orientation and magnitude of A at the emission site. We compare our measurements with macroscopic $\text{A}$ fields, calculated via the Fresnel relations, which lead to a general understanding of the effects. We further propose a method for expediting photoemission calculations by projecting out components of $\text{A}$ which preserve their phase relationships.     

Electron energy-loss spectroscopy of UHV-cleaved NiO (100) surfaces

Electron energy-loss spectroscopy of ～ 200 eV electrons has been applied to the study of the electronic states of clean NiO (100) surfaces. Initial attempt has been made on the identification of observed peaks, and they are attributed to the one-electronic transitions (O^2-2p → Ni²⁺3d, 4s and 4p; Ni²⁺3d → 4p, 3p → 3d and 4s), and the collective excitations (bulk plasmons of O^2-2p, Ni²⁺3d electrons, and coupled 2p and 3d electrons).     

Anomalous bismuth-stabilized (2x1) reconstructions on GaAs(100) and InP(100) surfaces

First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2x1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2x1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.     

Fast leed intensity measurements from Ni(100)c(2 × 2)CO

The Ni(100)c(2 × 2)CO surface structure has been investigated by very fast LEED intensity measurements using a computer controlled television method. It turns out that the intensity spectra are strongly influenced by intolerably long measuring times during which the primary electron beam impinges onto the surface. The spectra have been taken within 16 sec at 100 K immediately after termination of the adsorption process for all beams simultaneously. They are compared with other measurements and with Pendrys model calculations for a CO molecule bonded linearly on top of a Ni atom with straight molecular axis normal to the surface. Using the r-factor formalism for theory-experiment comparison the bond length results to be 1.15 ± 0.1 Å for CO and 1.80 ± 0.1 Å for NiC. This is in agreement with the results of other methods and removes some discrepancies with those of earlier LEED experiments.