Photoelectron spectroscopy, with LEED, Auger electron spectroscopy (AES) and secondary electron emission crystal current (SEECC) measurements, has been used to investigate the electronic structure of well-characterized overlayers of Tl, Cr, Mn and Fe on Ag(100) and Fe on Cu(100). The Stranski-Krastanov growth mode has been found for Tl on Ag(100). In the chain structure observed at 70 K, there is no evidence for a Peierls distortion, in contrast to Tl chains on Cu(100). Band-mapping of the Tl 6p band has indicated the absence of an energy gap at the Fermi level, confirming the LEED result that the Peierls distortion has been suppressed. This is believed to be due to commensurability with the substrate. A study of Cr on Ag(100) has revealed epitaxial growth up to two monolayers, with a transition to bilayers before the completion of the first layer. Photoemission measurements of the Cr 3s multiplet splitting indicate an enhanced magnetic moment, which approaches the bulk value with coverage. This enhancement is thought to be a consequence of d-band narrowing, resulting from the reduced dimensionality of the overlayer. A p(1 x 1) surface alloy is initially observed when Mn is deposited on Ag(100), but with a magnetic moment smaller than the bulk Mn value; angle-resolved photoemission measurements indicate significant overlayer- substrate d-d interaction, in contrast to Cr on Ag(100). With further coverage, the magnetic moment increases and when simultaneous multilayer growth occurs on the AgMn surface, the bulk value is attained. Pseudomorphic 1ayer-by-layer growth has been identified for Fe deposited on Cu(100) and the band structure has been determined for Fe coverages of one and seven monolayers. From a comparison with calculated band structures, it is proposed that the monolayer is ferromagnetic, while the thicker fee film may be antiferromagnetic. An Fe monolayer on Ag(100) has also been shown to have ferromagnetic order.

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The penetration of thin aluminum oxide films by liquid bismuth was studied between 350 and 500°C. A correlation was sought between the type and thickness of the oxide film, and the time and nature of the attack. Mechanical and electropolished, and anodized films of different thicknesses were exposed to liquid bismuth either by immersing a plate in the liquid and measuring the contact angle or by melting a drop of bismuth on a specific area of a plate. Electropolished surfaces had no resistance to attack by the bismuth. Pitting and edge attack occurred with all other surface preparations. The anodized films often separated from the aluminum under thermal stresses and allowed the bismuth to spread under the film, sometimes removing it entirely. Attempts were made to control the number and nature of defects in the oxide film, but the difficulty of this is shown by the scatter in the results. No attack on aluminum oxide itself is likely and no diffusion of bismuth through the oxide was found at the temperatures used. The conclusion was reached that the bismuth penetrated the oxide film only at points where there was a high concentration in the film of some impurity oxide (such as nickel or copper oxides) that reacts with bismuth. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

An investigation into the effect of oxygen on the three ultraviolet optical absorption bands in magnesium oxide was carried out. These peaks were located at 5.75, 5.0 and 4.40 eV within the range 212 to 350 mu. The single crystal platelets were heated in air or oxygen for increasing times at various temperatures. It was found that the increase in peak height with time followed a diffusion relation. A mechanism of formation of the centers causing the 5.75 and 4.40 eV peaks was proposed. The mechanism was based on the oxidation of iron and manganese impurities and the diffusion of magnesium to the crystal surface. The absorbing center was defined as (Fe⁺³∙VMg⁺²). From this it was shown that the diffusion process governing both the 5.75 and the 4.40 eV peaks followed the same Arrhenius relation: D=1.7 X 10⁵ e -77,000/RT cm²/sec. over the temperature range of 800 to 1100° C. No similar conclusions could be drawn concerning the 5.0 eV peak. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This paper is a report on the Investigations of the production of metals by the hydrogen reduction of metal chlorides and on the physical properties of the metal produced. The study covers the hydrogen reduction of cobaltous chloride; crystallographic analyses of the cobalt powder produced under conditions of varying reduction temperature and hydrogen flow, and treated under various conditions of cooling and reheating; compacting and sintering of the powder under varying pressures and sintering temperatures; tensile tests on pressed and sintered cobalt bars; tests on growth of single crystals of iron and cobalt; crystallographic orientation of the iron single crystal; and Tukon hardness variation with orientation in the (001) plane of an iron single crystal. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Investigations are made into the properties of 20 - 600 A gold films deposited onto freshly cleaved mica substrates by high vacuum evaporation. An accurate method of determining the equivalent thickness of a film is developed by combining a radio frequency technique employing quartz crystals with direct weighing. It is found that thicknesses as low as 0.5 A can be monitored to within ± 5%. An attempt is made to improve the structure of the gold films by using rapid deposition rates (15 to 20 A per second) and by depositing the gold films on nucleating silver layers of molecular thicknesses. The effect of increasing nucleating layer thicknesses (up to 25 A) is studied by electron microscopy and d.c. resistance measurements. A critical nucleating layer thickness for silver is found to exist between 5 to 7 A. On these critical layers, gold films down to 25 A are found conducting. All the films tested show an irreversible change in conductivity with heating. Without a silver layer, continuous decrease in the conductivity of gold films is observed, the film being destroyed at 450° C. On the other hand, increasingly better conductivities are observed by heating the gold-on-silver films, and an optimum annealing temperature of about 350° C is indicated. Above this temperature the conductivity decreases; however, films are still conducting and continuous at 600° C. These films are, therefore, suitable as heat reflecting windows. D.C, and high frequency measurements (at 9.7 Gc) on gold films are given. In both cases, almost identical values of surface resistance are obtained in the range 10 to 1,000 ohms per square. A method for preparing gold film bolometer elements using interrupted deposition of gold on a nucleating silver layer is discussed. As very thin gold on silver films with high d.c. conductivities are found to have low microwave transmission coefficients, the possible application of visual protection from microwave radiation is discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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