A variance analysis of broadened X-ray diffraction lines from evaporated thin films of aluminium

Abstract

Thin films of aluminium evaporated onto glass substrates under ultra-high vacuum conditions (∼ 10⁻⁹ torr) have been examined by x-ray diffraction and found to consist of randomly arranged polycrystals with moderate to strong [111] fibre texture. Two films evaporated simultaneously onto substrates at 25°c and –196°c have been examined in detail using copper K_α radiation and variance as a measure of diffraction line breadth. It is shown that the breadths of the lines studied cannot be interpreted solely in terms of particle size and strain but that some contribution from mistakes must be admitted. Suggestions for dealing with this additional complexity are given and shown to lead to plausible magnitudes for r.m.s. strain, namely 1–3 × 10⁻³. These two films were subsequently annealed in vacuum at 230°c and their line profiles redetermined and analysed again. Both sets of profiles showed a shift to higher angles (∼ 0.1° 2Θ for 111) and the variance analysis indicated a reduction in strain and smaller mistake contribution for the room temperature deposited film and the converse for the low temperature deposited one. The behaviour of the room temperature deposited film is in good agreement with electron microscope observations of the behaviour of dislocation loops containing a stacking fault in quenched and annealed aluminium foils. The apparently contradictory behaviour of the low temperature deposited film is discussed.