A Study of the Effectiveness of the Standard Surface Cleaning Techniques as Applied to Ni(111), Ni(100), and Ni Sheet Using Auger Electron Spectroscopy (AES)
An investigation of the standard surface cleaning techniques, e.g., oxygen reaction at high temperatures and argon ion bombardment, has been carded out with special reference to Ni(111), Ni(100), and Ni sheet using Auger electron spectroscopy (AES) to monitor surface conditions. Carbon, sulphur, chlorine, nitrogen, and oxygen are observed as impurities on these surfaces. On Ni(111) a heavy carbon deposit (> 10 Å thick) is noted. Argon ion bombardment is not effective in removing this layer. High temperature reaction (> 700°C) with oxygen is required to eliminate the surface carbon. The kinetics of this reaction are recorded by monitoring the rate of production of carbon monoxide dNCO/dt which obeys the relationship dNCO/dt=kPO20.9±0.1 exp−(32±2 kcal mol−1)/RT in the temperature range 663–917°C and oxygen pressure range 1.0×10−8 to 5.9×10−7 Torr. After this carbon removal the sulphur and chlorine impurities are eliminated using argon ion bombardment. Reaction with oxygen at 1100°C and 10−6 Torr is also effective in removing these latter impurities. At this point only a small carbon peak due to slow diffusion from the bulk is present on the surface. However, a short anneal to 700 °C for <1 min caused small amounts of sulphur and chlorine to reappear. This effect is discussed in terms of diffusion and support effects. The minimum attainable coverage (θs) of sulphur on the Ni(111) was θs=0.1. For Ni(100) and Ni sheet a much smaller carbon peak compared to Ni(111) is observed. This may be “removed” by heating alone. Some reaction of surface carbon and oxygen takes place to give gaseous carbon monoxide. Some carbon diffuses into the bulk. On cooling, carbon slowly diffuses to the surface. Sulphur and chlorine impurities may be removed by argon ion bombardment. Removal of these impurities by oxygen reaction at high temperatures is unsatisfactory. Oxidation occurs. Hydrogen reduction is not particularly successful, although this oxygen can be removed by prolonged argon ion bombardment.