Makoto Takemori1 and Teiichi Homma2
1Graduate Student, University of Tokyo, Tokyo
Surface Segregation of sulfur is often observed, when metals and alloys are annealed in vacuum. Though this phenomenon has been thought to be pretty reproducible, it recently has come to be realized that the reproducibility is not quite well and many factors are important to control this phenomenon. The fact is that, when the surface is exposed to oxygen at room temperature, the sulfur segregation is often enhanced during subsequent vacuum annealing. In order to know where the sulfur comes from during the enhanced segregation annealing, and to know about the mechanism of this enhancement, a sulfur-doped nickel polycrystalline specimen and a sulfur-containing Fe-18Cr polycrystalline alloy were used and examined by an Auger analyzer. After repeating a series of vacuum annealing and sputtering, or combined oxidation and annealing treatment, little sulfur segregated from the bulk for both specimen surfaces. Exposure to oxygen or air at room temperature enhanced the segregation in each case. Auger analyses before and after annealing, and residual gas analyses during annealing showed that the enhanced sulfur segregation originated form the bulk, not from gas atmospheres. The Fe-18Cr specimen showed a remarkable recovery of segregation, accompanied by a strange phenomenon, perhaps exoelectron emission. It can be suggested that not only the topmost-surface but the bulk of some depth might be affected by oxygen adsorption at room temperature.
surface segregation, sulfur, preadsorption, oxygen, vacuum anneal, nickel, iron-chromium alloy
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