Adsorption and desorption of active gases on Si(111) surfaces with ultra-thin Ag films

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We have measured thermal desorption spectrum (approximately 120-1000 K) from nitric monoxide adsorbed Si(111) surfaces with ultra-thin silver films displaying different surface structures at low temperature. We obtained the following Interesting results.1. Si(111) 7x7 clean surfaceDesorption of NO at 161 K, and 0_2, N_2 and N_2O at 168 Kwas measured. According to the other group, the desorption of N_2, NO and N_2O was reported at 〜150 K However, our work found (i) the desorption of O_2 also, and (ii) the existence of two different desorption processes because of two different desorption peaks. The different peak temperatures between our results and the previous report arise from the differences of temperature monitoring position, coverage of NO, and temperature increasing speed. Thus, the following results can be comparable at relative temperatures.2. Si(111) √<3x>√<3> -Ag surfaceThe shape of the desorption spectrum was similar to that of the dean surface, however, the desorption yield from the former was 〜1/10 of that from the latter. The result indicates that NO gases hardly adsorb and desorb on the √<3>-Ag surface, and it has very different characters from silicon or silver surfaces.3. Ag(111) islands with a few atomic monolayers/Si(111) surfaceDesorption of N_2 at 146 K, N_2O at 210 K, and NO at 325 K, was measured. On the single crystal Ag (111) surface the desorption of N_2O at 180 K, and NO at 380 K. We found the reduction reaction as N_2 desorption, which never proceeds on the single crystal surface, instead, at Ag(111) nano-crystalline islands.