[[alternative]]The change of behavior with temperature of Co on Si(111)-7×7 and Co on(√3×√3)Ag/Si(111)surface

[[abstract]]Cobalt atoms can react with the adatoms of Si（111）-7×7 surfaces at the room temperature. The reaction transfers the electric state of Si adatoms. The bright dots change to dark dots under the scanning tunneling microscopy（STM） observation of negative bias. By the statistic method, we find the most of dark dots appear at unfaulted half unit cell（UHUC）center sites. The behavior of Co/Si（111）-7×7 system are observed at low temperatures by using a variable temperature STM. At 100K, we find that Co atoms will not react with silicon but randomly adsorb on the surfaces. As the temperature increasing, the critical temperature of the reaction among 126K and 130K are found by STM observations. We suppose that the Co atoms will diffuse and react with Si（111）-7×7 UHUC center site at higher temperatures. Co atoms which are deposited on the（ × ）-Ag/Si（111）surfaces are simply adsorbed on the surfaces without other reactions. The behaviors of Co atoms at the temperature of 100, 200, 300, 400 and 500℃ are observed by STM. As the temperature rising, the Co atoms congregate as islands, and the islands prefer to condense on the edges of islands. Besides, no any evidence shows the Co atoms react with the Si substrate. As the result we conclude that the （ × ）-Ag buffer layer on Si（111）surface can effectively prevent the reaction between Co and Si atoms.