J. Beynon

Evaluation of the composition of reactively evaporated GeOx thin films from optical transmission and XPS data

Computer simulations of germanium 3d core spectra obtained with reactively evaporated GeOx thin films (0 ⩽x 2) have been developed using a modified Sanderson approach, in which five basic sub-units are produced by the conversion of germanium atoms in the primary coordination sphere into either -GeOx groups or -OGeOx groups on oxidation. The relative proportion of the five sub-units are adjusted until the best agreement with the experimental XPS spectra is obtained. The volume fraction of germanium in GeOx obtained using an optical transmittance model is compared with the number fraction obtained from XPS data over a range of oxygen partial pressures.

Thermoelectric power and d.c. conductivity of co-evaporated Mn/SiOx cermet thin films

Abstract The thermoelectric power and d.c. conductivity of Mn/SiOx thin films containing 10 at.% Mn have been measured between 278 and 578 K as a function of substrate temperature (293–418 K). Thermoelectric power and d.c. electrical conductivity measurements suggest that over the temperature range 278–500 K, conduction is due to delocalised electrons at the Fermi level and electrons in donar localised states. For temperatures above 500 K, hole conduction takes place via extended states.

On the optical properties of Mn/SiO and SiO thin films

The ultraviolet, visible and infrared properties of unannealed and annealed amorphous Mn/SiO cermet thin films (300 to 1000 nm thick) prepared by vacuum evaporation at 5.0×10−4 Pa are investigated. The ultraviolet and visible results are analysed assuming optical absorption by indirect transitions. A systematic reduction of the optical energy gap and an increase in the width of the band-tail region is observed with increasing metallic content. The effects of the ratio deposition rate/residual pressure and substrate temperature on the optical properties of SiOx (1

Effects of composition and substrate temperature on the a.c. properties of co-evaporated Mn/SiOx thin films

Capacitance, a.c. conductance and loss factor have been measured in Cu-Mn/SiOx-Cu sandwich structures with compositions 1, 3, 5 and 10 at% Mn in the frequency range 10–106 Hz between temperatures of 110 and 500 K. The capacitance has a weak minimum at 1.0 MHz for all temperatures, whilst the a.c. conductance increases between four and eight orders of magnitude for temperatures of 150 and 473 K, respectively. Various a.c. conduction models have been considered, and it has been concluded that correlated barrier hopping best describes the results. The Goswami-Goswami model was used to describe the variation of loss factor with temperature and composition.

Hall effect and magnetoresistance in Au/SiOx thin films

Abstract Measurements of the temperature dependence in the range 300–520 K of the Hall coefficient and magnetoresistance of thin films of SiO containing 2 and 5 at.% Au are reported. The derived carrier density values are combined with earlier measurements of electrical conductivity to determine the temperature variation in mobility; the mobility increases with increasing temperature in the lower part of the range, as expected for a carrier hopping conduction mechanism, but decreases with increasing temperature in the higher range in accordance with the expectations of free-band conduction. Variations in the parameters with magnetic induction up to 130 mT are discussed. The free-carrier density is substantially constant with temperature, as expected for an amorphous or highly disordered material.

Thermopower measurements on SiO x thin films

Thermopower and d.c. electrical conductivity measurements have been carried out between 125 and 625 K on SiOx thin films, 130 nm thick, deposited on to Corning 7059 substratesin vacuo ≃ 1 mPa at 1.5 nm sec−1. The thermopower, d.c. conductivity and their respective activation energies are fitted to a polynomial expression in 1/T. Below 400 K, the thermopower is negative, at 400 K the thermopower activation energy is approximately zero and the dominant current carriers are holes at the valence band edge, between 400 and 470 they are polaronic holes, between 470 and 590 K non-polaronic holes, and above 590 K electrons. Energy band diagrams are proposed for each temperature range studied.

Effect of composition on optical properties of co-evaporated Mn/SiOx, Cr/SiOx and Cu/SiOx cermet thin films

Optical absorption spectra of amorphous Mn/SiOx, Cr/SiOx, and Cu/SiOx cermet films, 300 nm thick, with compositions from 0 to 25 at% Mn, Cr and Cu, respectively, prepared by co-evaporation at 293 Kin vacuo have been investigated. The linearity of (αħω)1/2 versusħω graphs in the high absorption region for all the cermet films indicates that indirect photon transitions in k-space are involved in the absorption process. Taues rule is also confirmed. In all cases the optical energy gap decreases significantly with increasing metallic content of the films and the width of the tail of localized states increases.

Film-thickness effects on the optical and electrical properties of Cu-GeO2 thin cermet films

The effect of film thickness on the optical and electrical properties of Cu-30 wt % GeO2-70 wt % thin cermet films prepared by electron-beam deposition at about 10−3 Pa and at a substrate temperature of 300 K is reported. The ultraviolet, visible and direct current (d.c.) conductivity results are analysed with the aim of determining the optical band gap,Eopt, the width of the band tails,Ee, and the d.c. thermal activation energy,Ea. It was found that the optical energy gap increases with increasing thickness and that the absorption was due to indirect transitions ink-space. The general feature of the absorption edge remains similar for both unannealed and annealed films, but annealing has the effect of decreasingEopt. The d.c. conductivity results show thatEa decreases with increasing thickness. From a knowledge ofEopt andEa, a probable model of the electronic band structure in Cu-GeO2 thin films has been suggested.

Effects of thickness and deposition rate on the optical absorption properties of co-evaporated Mn/SiOx, Cr/SiOx and Cu/SiOx thin films

Abstracts are not published in this journal

Scanning electron microscopy and electron microprobe analysis of Au-GeOx-Cu and Au-AlOx-Cu sandwich structures

Direct observations of the counter-electrode surface of electroformed Au-I-Cu sandwich structures (where I is reactively evaporated AlOx or GeOx) were carried out using scanning electron microscopy. Electron microprobe analyses of surface defects in electroformed samples, after etching the copper counter-electrode, tended to confirm the presence of copper. Surface defects are identified as the terminations of filament bundles, which supports the filamentary model of conduction.