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

我们用超薄银膜在低温下显示出不同的表面结构，测量了一氧化碳吸附Si（111）表面的热解吸光谱（约120-1000 K）。我们得到了以下有趣的结果。测定了Si(111) 7x7清洁表面161k时NO的脱附，168k时0_2、N_2和N_2O的脱附。另一组报道了在~ 150k下N_2、NO和N_2O的脱附，但我们的工作发现(i) O_2也有脱附，（ii）由于两个不同的脱附峰，存在两种不同的脱附过程。我们的结果与之前报道的峰值温度不同是由于温度监测位置、NO覆盖范围和温度升高速度的不同。因此，下列结果在相对温度下是可以比较的。Si(111)√<3x>√<3> -Ag表面的解吸光谱形状与dean表面相似，但前者的解吸收率约为后者的1/10。结果表明，NO气体在√<3>-Ag表面几乎不发生吸附和解吸，其性质与硅表面或银表面有很大的不同。测定了在146 K、210 K和325 K条件下对N_2、N_2O和NO的脱附。单晶Ag（111）表面在180 K和380 K下分别有N_2O和NO的脱附。我们发现还原反应为N_2的脱附，而不是在单晶表面进行，而是在Ag（111）纳米晶岛上进行。

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.