Applications of Surface Science最新文献

Optical techniques are widely used as non-destructive methods for determining the thickness and effective optical constants of vacuum deposited thin films. Implicit inmany such analyses is the use of an ideal morphological model of a thin film. The morphology of vacuum deposited thin films, however, may be far from ideal. The influence of morphological features on normal incidence reflectance and transmittance spectra of thin films is discussed. In particular, the interpretation of the non-ideal surface of a thin film as either a region giving rise to scattering of incident light or, by applying effective medium theory, as a region of graded refractive index will be considered. The results of a comparative study of the normal incidence reflectance and transmittance spectra of a number of sputtered thin films using both surface scattering and surface region of graded refractive index models is presented. It is shown that the latter model is preferred for films with surface features with dimensions of up to a considerable fraction of wavelength. The implications of these normal incidence results for ellipsometric measurements are also discussed.

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 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.

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.

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.

A study has been made of the size and spatial distribution of the clusters of atoms which form and contribute to film growth when gold is deposited onto ultrahigh vacuum cleaved NaCl surfaces. The observations are used to investigate the existence of interparticle forces between the clusters, and the role of such forces in producing preferred cluster spacings and coalescence.

CdTe films of 0.7 μm thickness were deposited by a resistive heating onto glass and KBr substrates kept at 200°C. The films were irradiated with laser pulses of various energy densities. A pulsed lase (Nd: YAG) capable of producing 20 ns pulses of wavelength 1.06 μm with varying energy densities (2–50 mJ/cm²) was employed. The films were examined by TEM and X-ray diffraction and found to be polycrystalline. DC conductivity and Hall coefficient measurements were made on the films in the temperature range 77–400 K. The optical energy gap has been calculated using the optical transmission spectra.

A model describing the incorporation of dopants into single crystals films grown by molecular beam epitaxy (MBE) is presented. The model accounts for dopant surface segregation during deposition and allows dopant incorporation probabilities and depth profiles to be calculated as a function of film growth conditions (e.g. deposition rate, dopant beam flux, and growth temperature, T_s). Input data to the model include thermodynamic parameters such as the free energy of segregation and dopant-surface binding energies together with kinetic parameters such as incident fluxes and dopant diffusivities. The model is applied here to the case of thermal doping during MBE with impurities exhibiting strong surface segregation and near-unity incorporation probabilities, σ, as well as those exhibiting both strong segregation and temperature-dependent σ values. In addition, an extension of the model is used to account for accelerated-ion doping during MBE. Calculated values of σ(T_s) and calculated depth profiles were found to agree very well with available experimental results in these cases. Finally, dopant incorporation data for epitaxial semiconductors deposited in glow discharge environments in which the growing film is bombarded by relatively large fluxes of inert gas ions as well as by ionized dopant species are presented and discussed. The results in this case are similar to low flux ion doping in MBE but with the additional effects of preferential sputtering and collisional mixing.

The application of LEED fine structure analysis to the study of the surface potential energy barrier is reviewed. Analysis of data for W(001) and W(110) using a saturated image barrier model demonstrates the adequacy of the model and provides further details of the barrier structure. The computational model and the results of the analysis are compared with recent theories of the metal-vacuum interface. The present evidence suggests that jellium calculations provide a qualitatively correct picture of the barrier on transition metal surfaces. LEED fine structures analysis also appears to be a promising direct method for further studies of surface barriers.