Reduction of thin oxide layer on Fe 60Ni 40 substrates in hydrogen plasmas

Abstract

The method of low temperature reduction of thin oxide layers in hydrogen plasmas is described. Samples made of Fe 60Ni 40, alloys were picked from the production line for housings of electronic devices. During thermal treatment a layer of brownish oxide was formed on the surface. The thickness of the oxide layer was estimated from AES depth profiles of the samples and it was about 30 nm. Samples were fixed on small thermocouples and exposed to hydrogen plasmas with a density of 8 × 10 15 m −3, an electron temperature of 6 eV, and the dissociation degree of the hydrogen molecules of 30%. Samples were treated in hydrogen plasmas for different periods. During the treatment, the temperature of samples was raised to about 185 °C, then was dropped to 30 °C, and then remained constant for as long as the RF generator was on. The appearance of the maximum temperature coincided with the change of the sample colour. After plasma treatment, the samples were analyzed with AES. Depth profiles of the samples exposed to the plasma for less than 17 s showed hardly any change in surface composition. The AES depth profiles of samples exposed to plasmas for more than 20 s, however, showed no presence of oxygen, The composition of the surface layer was the same as that of the bulk material, 60% iron and 40% nickel. Complete reduction of the oxide layer on the samples therefore occurred in a short time (less than 3 s) after 17s exposure of the samples to the hydrogen plasma.