Thick Polycrystalline Films Research Articles

Electrical transport properties in calcium films

Polycrystalline calcium films obtained by thermal evaporation onto a cooled silica substrate at low temperature in an ultrahigh vacuum system were studied in situ. The temperature was increased to room temperature and then up to 400 K. The electrical resistance of the films was measured by the four-point probe method and the variation with temperature was found to be reversible, indicating that lacunar defects had been eliminated and the structure of the film had been stabilized. The slope of the linear resistivity-temperature plot depends on the film thickness; at greater thicknesses ( d > 170 nm) the resistivity is constant with large values characteristic of a polycrystalline material. An attempt to explain these large values was made in terms of Mayadas and Shatzkes theory. A spherical Fermi surface was found to be a good approximation to explain the electrical conductivity at room temperature. The temperature dependence of the mean free path in the grains was determined. It was found that the resistivity of the thick polycrystalline films is given mainly by the grain boundary scattering and depends also on the background scattering but not on electron-surface scattering.

Reflection X-ray topography of ZnO thin films on non-orienting substrates

Thin or moderately thick polycrystalline films of ZnO with preferentially oriented crystallites deposited on non-orienting substrates can in some cases be investigated using conventional X-ray topography. Examples of such reflection topographs are presented and their characteristic features are discussed. In particular, it is often possible to observe the texture, the film inhomogeneity and the influence of the deposition conditions on the preferred orientation.

Exact and approximate expressions for the temperature coefficient of resistivity of polycrystalline films using the Mayadas-Shatzkes model

Starting from the Mayadas-Shatzkes equations for film conductivity, exact analytical expressions for the temperature coefficient of resistivity for monocrystalline and polycrystalline films were calculated. The temperature coefficient of resistivity for an infinitely thick polycrystalline film and a tabulated function were introduced into the linearized expression for the polycrystalline film; good agreement with previous experiments was obtained.

Grain Size Dependence of the Gauge Factor of Thin Metallic Films

The combined effects of grain boundary, external surface and background scattering (Mayadas and Shatzkes model) are considered. Theoretical expressions of the transverse and longitudinal strain coefficient of resistance of monocrystalline and polycrystalline films are calculated. These general formulae agree with those previously proposed for infinitely thick polycrystalline films.

Work function measurements on (100) and (110) surfaces of silver

(100) and (110) single crystals of silver were cleaned by electron and argon-ion bombardment in ultra-high vacuum. The work functions of the bulk crystals, and of silver films formed upon them by autoepitaxy, were determined photoelectrically. The bulk crystals had work functions of (4.64 ± 0.02) eV and (4.52 ± 0.02) eV respectively. The effect of the deposition of silver films was to reduce the work function, but continued cycles of deposition and annealing at 500 to 600 K caused the work function to return to a value very close to that of the bulk crystal. An annealed film of silver deposited in stages on a mica substrate at 425 K had a work function of (4.72 ± 0.02) eV, corresponding to that of the (111) silver surface. If the mica remained at room temperature during deposition, the work function was about 4.5 eV. The work function of a thick polycrystalline film of silver on quartz was (4.26 ± 0.02) eV. The results support the Smoluchowski correlation of work function with surface atom density. (100)- und (110)-Silbereinkristalle werden mit Elektronen- und Argon-Ionen-Bombardement im Ultra-Hochvakuum gereinigt. Die Austrittsarbeit der Volumenkristalle und der Silberschichten, die auf ihnen auto-epitaktisch aufgebracht wurden, wurden photoelektrisch bestimmt. Die Volumenkristalle zeigten Austrittsarbeiten von (4,64 ± 0,02) eV bzw. (4,52 ± 0,02) eV. Der Einfluß der Aufbringung der Silberschichten bestand in der Verringerung der Austrittsarbeit, jedoch verursachte ein fortgesetzter Zyklus von Aufbringung und Temperung bei 500 bis 600 K, daß die Austrittsarbeit zu einem Wert zurückkehrte, der sehr nahe an dem der Volumenkristalle lag. Eine getemperte Silberschicht, die stufenweise auf einem Glimmersubstrat bei 425 K aufgebracht wurde, zeigte eine Austrittsarbeit von (4,72 ± 0,02) eV entsprechend der der (111)-Silberoberfläche. Wenn die Glimmerunterlage während der Aufbringung auf Zimmertemperatur gehalten wurde, lag die Austrittsarbeit bei ungefähr 4,5 eV. Die Austrittsarbeit von dicken polykristallinen Silberschichten auf Quarz betrug (4,26 ± 0,02) eV. Die Ergebnisse bestätigen die Korrelation von Smoluchowski zwischen der Austrittsarbeit und der Atomdichte an der Oberfläche.