Applications of Surface Science最新文献

While the chemical analysis of a surface has become commonplace using a variety of techniques including Auger Electron Spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA), it is often advantageous to differentiate between the chemistry of the surface and the near surface. The method used to make this distinction depends on the thickness of the layers to be differentiated. If the combined thickness of the layers is greater than 100 Å, then the surface must be physically removed by ion bombardment before the subsurface components can be identified. An example of the chemistry revealed by this method is given in a sputter profile of an eight layer, 3000 Å, metal magnetic tape. The internal interfaces show more oxidation than the bulk of the metal layers. If the combined thickness of the layers is less than 100 Å, then the surface and subsurface components can be identified by non-destructive techniques. This is accomplished by using high energy excitation or by angle resolved studies. Examples will be shown of the change in the surface and near surface chemistry of polystyrene as it is treated in H₂ and H₂O plasmas. The degree of oxidation of the polymer surface can be monitored as a function of reaction depth using angle resolved ESCA. Extending the range of angle resolved studies by using Au Mα X-rays is shown for a native oxide on silicon.

The adsorption and reactions of methanol, methyl formate and formaldehyde on clean and oxygen-covered copper (110) surfaces has been studied with EELS, UPS and temperature programmed desorption (TPD). We report spectroscopic data for (a) the condensed multilayers at 90 K, (b) the surface monolayers and (c) the reaction intermediates formate (HCOO) and methoxy (CH₃O) generated by reaction with surface atomic oxygen. On the clean surface methanol and methyl formate bond via the oxygen and carbonyl lone pair orbitals, whereas formaldehyde always polymerizes to surface paraformaldehyde above 120 K. Atomic oxygen generates methoxy by reaction with methanol and formate by reaction with formaldehyde as reported previously. Methyl formate undergoes nucleophilic attack to form both methoxy and formate in the presence of atomic oxygen, in a similar fashion to the reaction on Ag (110). Whereas the oxidation reactions of these molecules on copper catalysts can be explained with reference to the observed intermediates, no evidence is found for the dimerization of formaldehyde or the dehydrogenation of methanol to form methyl formate: reactions which are quite facile under higher pressure conditions.

The chemical deposition method has been employed in the preparation of alloy semiconductor thin films. Thin films of Cd_1−xHg_xS and Cd_1−xPb_xS alloys were deposited onto titanium substrates from thiourea solutions. A monotonic decrease in the bandgaps of the semiconductor alloys was obtained as the Hg and Pb ratio was increased. Bandgap values of 1.8 and 1.6eV were measured for electrodes with a Hg: Cd ratio and a Pb: Cd ratio of 0.18 respectively, considerably lower than the bandgap of pure CdS.

Peculiarities of the photoelectron yield in conditions of X-ray grazing-incidence diffraction are discussed. The high sensitivity of photoelectron emission angular dependence on structural perfection of the crystal subsurface layers is demonstrated. A method for evaluation of the escape depths of photoelectrons with different energies is proposed.

An electron spectrometer with toroidal geometry has been developed which enables angularly resolved spectra to be obtained simultaneously at a large number of angles. This reduces data acquisition times by a factor of 100 and makes accessible many experiments on surfaces and interfaces which involve reactive materials or which require long experiment times. Photoelectron spectra of gases are presented which demonstrate the analyzer's energy and angular resolution showing it to be more than adequate for surface studies.

High dose ion-implantation was used to synthesize stoichiometric TeO₂ layers over tellurium films at 30 keV. Using infrared absorption spectroscopy it was concluded that the stoichiometric layer could be produced with ¹⁶O₂⁺ ions to a fluence of 4.8×10¹⁷ ions cm⁻², which is in close agreement with the estimated oxygen dose.

Gold/silicon binary mixtures are prepared by depositing thin gold films onto Si(111) single crystals and subsequently annealing at various temperatures. The structure of the films is studied in situ with the help of an ultra-high-vacuum X-ray diffraction chamber. After deposition at room temperature the gold films are homogeneous with a plane-parallel morphology. After annealing at 630 K the Au 111 peak suddenly disappears in the X-ray spectrum indicating that a eutectic melt has been formed. Cooling leads to a regeneration of the peak at 590 K. This temperature is distinctly smaller than the eutectic temperature reported in the literature (643 K). Obviously small gold islands are formed which are embedded into the silicon surface.

It was found that the isotope ratios of ⁵⁸Ni/⁶⁰Ni and ⁶³Cu/⁶⁵Cu measured by SIMS changed by a few percent at the initial stage of ion bombardment for well-polished pure metal samples. A similar change was also found for silver, palladium, titanium and chromium targets. The isotope ratios, the light to the heavy, for the fresh surfaces were low at first and increased with time to reach constant values as the ion bombardment continued. It was pointed out that the main process able to induce such a large mass effect would be preferential recoil implantation of isotopes by primary ions.

The technique of surface acoustic wave (SAW) has been applied to doped amorphous GeH films to gain information on the nature of defects. The attenuation of SAW of 300 MHz and 1.5 GHz has been measured in sputtered films of a-GeH doped with P or B at temperatures between 0.5 and 475 K. Sound velocity measurements are also made. A strong absorption maximum at low temperature is observed in a-Ge(H,P) and a-Ge(H,B) films. Distinct effects of annealing on the attenuation and velocity of SAW are observed. These impurity induced features are discussed in the light of acoustoelectric interaction. It is interesting to observe that a-Ge(H,B) film seems to have tunneling states characteristic of glasses.

CdTe thin films formed by compound evaporation onto glass substrates, held at between 40 and 460°C, exhibited abrupt changes of physical properties at ca. 270°C. The resistivity changed from 0.1 ω m to 100 kω m, and a marked increase in crystallinity and absorption edge sharpness was noted. These changes resulted from a decrease in the free tellurium content of the films at ca. 270°C.