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Studies on thin films of gold Chaurasia, Hari Krishna

Abstract

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.

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