The behaviour of carbon and suiphur on [I 111 and [0071 nickel faces on heating in a vacuum and in oxygen (lo-'-1O-6 torr) has been investigated by means of Auger electron spectroscopy (AES). Carbon disappeared from the surface under investigation in vacua on heating up to 500°C for Ni[ 11 I] and up to 800°C for Ni[OOl].
The amount of sulphur was increased as the samples under investigation were heated in vacua to higher temperatures, reaching its maximum at 800-900°C and above 1000°C it was reduced considerably. These effects were explained as due to the reversible segregation of sulphur to the nickel surface. On prolonged heating of the sample under investigation in oxygen (lo-'-10-6 torr, 800°C) sulphur was removed from the surface and the amount of sulphur inside the sample was reduced. Thus, new superficial contamination of the sample with sulphur could have been removed by heating for several minutes up to 7 100°C. After sulphur removal from the surface, Further heating of the sample was found to lead to other admixtures being segregated to the surface.