Applications of Surface Science最新文献

Adsorption of ethylene on the (110) surface of palladium at 110 K gives rise to two related but clearly distinguishable types of electron energy loss (EEL) spectra corresponding to low and high coverage. Most features in the spectra in both coverage regimes can be interpreted in terms of a π-complex of ethylene with the metal surface. Analysis of the corresponding ethylene-d₄ EEL spectra and comparison with infrared, Raman and inelastic neutron scattering data for the analogous ethylene complex, Zeise's salt, supports this assignment. The selection rules applicable to dipole and impact scattering both on- and off-specular are employed to determine the orientation of the π-complexes with respect to the surface. At higher coverages additional loss features are observed. These are interpreted in terms of the presence of a small proportion of σ-diadsorbed ethylene complexes bonded to pairs of metal atoms.

High resolution LEED intensity data from Cu(001), showing barrier scattering features within ∼ 3 eV from a beam threshold, have been analyzed with a two parameter “modified image barrier” (MIB) model and a three parameter “saturated image barrier” (SIB) model. It is found that a range of values of z₀, the origin of the image potential tail, in the MIB model can provide a fit of experimental maxima and minima energy locations to within 0.3 eV. With the SIB model, there is a multiplicity of values of z₀ (and corresponding value of U_s, the value of the potential with respect to the vacuum level at the jellium discontinuity), which can provide a fit to that data to 0.3 eV. Fits to within 0.05 eV were also obtained with parameters outside the values determined by previous authors. It is concluded that the validity of each model and the determination of z₀ can only be found from such experimental data if it is fitted to at least 0.05 eV.

Indium tin oxide films have been grown by reactively sputtering an indium/tin metallic alloy target in argon-oxygen mixtures. Growth parameters and annealing conditions have been optimized at low temperatures. Reactively sputtered oxide films were highly insulating and did require a post-deposition annealing treatment in a reducing ambient, to become highly transparent and conducting. A new annealing ambient, cracked ammonia, has been found to be very effective and economical. Films have been characterized for their structure and morphology by electron diffraction and scanning electron microscopy respectively. Relative advantages of annealing in cracked ammonia over nitrogen-hydrogen mixtures employed by other workers have been discussed. Films with preferred orientation, high optical transmission (∼ 95%) and low electrical resistivity (3 × 10⁻⁴ ω cm) have been obtained.

The oxidation of fracture surfaces of a pyrrhotite mineral of composition Fe_0.89S at ambient conditions in air has been studied by X-ray photoelectron spectroscopy (XPS). Fe(2p) and Fe(3p) spectra indicated that iron had diffused from the outermost layers of the mineral lattice to form a hydrated iron(III) oxide or hydro-oxide. The corresponding S(2p) spectrum exhibited a shifted component at a binding energy increasing with time of exposure. It is considered that this component arises from the formation of iron-deficient sulfides with the iron content decreasing with increasing oxidation time.

Dense and complex circuit layouts in integrated circuits often require multilevel interconnecting wiring. At IBM East Fishkill sputtered SiO₂ is used to provide insulation between the wiring levels. Defects in the insulating layers can result in interlevel shorts (ILS). If a projection from one metal layer is inadequately covered with the insulator it may short to the metal layer above. Since the inadequacy of coverage is a result of the non-conformal coating that results from sputter deposition, a relatively thin layer of conformal PECVD Si_xN_y deposited upon the top of the SiO₂ will provide adequate insulation over projections. Electrical testing of special test patterns showed significant improvement in ILS using the structure described.

We have studied the equilibrium shapes of large ⁴He crystals at two different roughening transitions (T_R1 = 1.2 K, T_R2 = 0.9 K) by a simple optical technique. The method used provides the temperature and angular dependences of the surface stiffness. The measured surface stiffness appears to be constant in the close vicinities of the roughening transitions (|T−T_R| ∼ 0.001−0.05T_R, ϕ ∼ 0.005−0.1), in strong disagreement with two current theories, viz., the phenomenological “mean field theory” and the lattice model calculations.

The general applicability of power law forms of the background in electron spectra is pointed out and exploited for background removal from under Auger peaks. This form of B(E) is found to be extremely sensitive to instrumental alignment and to fault-free construction - an observation which can be used to set up analyser configurations in an accurate way. Also, differences between N(E) and B(E) can be used to derive a spectrometer transmission function T(E). The questions of information density in an energy-analysing spatially-resolving instrument are addressed after reliable instrumental characterization has been established. Strategies involving ratio histograms, showing the population distribution of the ratio of a pair of Auger peak heights, composition scatter diagrams and windowed imaging are discussed and illustrated.

The surface compositions of the α/β and γ/γ' phases of different metallographic preparations of Ni-15Cr-24Al and Ni-15Cr-24Al-0.3Zr (at%) alloys are presented. Surfaces investigated include a mechanically polished surface for both alloys, a mechanically polished acid etched surface of the Ni-Cr-Al-Zr both before heating and after heating to 600°C for several hours, and the underlying surface of this latter sample exposed by ball cratering. Both phases of all surfaces considered show depletion of Al. It is concluded that the Al depletion is not an artefact of the sample metallographic preparation or the analytical procedure. This is supported by analysis of the composition of a sample scratched in situ under UHV. It is further concluded that the Al depletion is due to oxidation during bakeout. Cr-rich features in both the α/β and γ/γ' phases are reported. An optimal two dimensionally smoothed Cr Auger image is presented showing these features which are considered to be due to the αCr solid solution particles or clustering of these particles in the α/β phase and the Ni solid solution component in the γ/γ' phase.

Extensive study of the vapour deposition of noble metals onto UHV cleaved alkali halide crystal surfaces has made an important contribution to the development of time-dependent nucleation theory. There nevertheless remain significant inconsistencies between results obtained from different studies of identical systems. The role which the time-dependent kinetic approach to nucleation theory has played in the past and that which it might take in the future are discussed.

Low-temperature experimental results on Ge(111) and Si(111) surfaces prepared by crystal cleavage in ultra-high vacuum (∼ 10^-10 Torr), liquid N₂, and liquid He are presented and briefly discussed. Some of these results are reanalyzed and new interpretations are suggested.