| Summary: | 碩士 === 國立中正大學 === 物理系 === 91 === By depositing Co onto Si(111)-5´2/Au surface at room temperature followed by heating to elevated temperatures, we have observed the effects of Co growth through controlling the surface temperature and the duration of heating period using Scanning Tunneling Microscopy（STM）. We summarize our findings as follows:
(1) By heating a surface up to 300℃ after depositing Co at room temperature, the Au clusters on the original (5×2) structure are destroyed. Part of the surface reveals a (Ö3×Ö3)-R30° reconstruction which is likely the result of the formation of CoSi/Co2Si. As the temperature increases to between 300℃ and 800℃, CoSi2 islands appear while other part of the surface reverts back to (5×2) structure.
(2) By keeping the heating temperature below 800℃ after the deposition of Co at room temperature, two kinds of islands appear on the surface: a dome-shaped island and a hexagonal-shaped island. The relative density of these two kinds of islands varies as the heating condition changes. The size (both the diameter and the height) of the two kinds of islands grows as the temperature and the duration of heating time increase.
(3) As the temperature exceeds 800℃ on the Co covered surface, Au atoms leave the surface. This high-temperature treatment has the same effect as depositing Co onto a clean Si(111)-7×7 surface, which leads to the formation of triangular structure composed of CoSi2.
(4) Through Superconducting Quantum Interference Device (SQUID) measurements, we have reached the conclusion that the CoSi2 islands display the superparamagnetic behavior with a blocking temperature of 50K. The magnetization vs. external fields oscillates about saturation value in a very significant way.
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