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

我们测量了具有不同表面结构的超薄银膜吸附一氧化氮的Si（111）表面在低温下的热脱附谱（约120-1000 K）。我们得到了以下有趣的结果。1.测量了Si（111）7 × 7清洁表面在161 K时NO的脱附，168 K时O_2、N_2和N_2O的脱附。另一组在150 K时有N_2、NO和N_2O的脱附，但我们的研究发现：（i）O_2也有脱附，（ii）由于有两个不同的脱附峰，存在两个不同的脱附过程。结果表明，温度峰值与前人报道的不同是由于温度监测位置、NO覆盖范围和温度上升速度的不同造成的。因此，在相对温度下，下列结果是可以比较的. Si（111）面<3x>的<3>脱附谱与dean面的脱附谱形状相似，但前者的脱附率是后者的1/10。结果表明，NO气体在Ag-Ag表面几乎没有吸附和脱附<3>，具有与硅或银表面截然不同的性质. Ag（111）岛与Si（111）表面的原子单分子层在146 K、210 K和325 K分别测定了N_2、N_2O和NO的脱附。在单晶Ag（111）表面上，N_2O在180 K时脱附，NO在380 K时脱附。还原反应以N_2脱附的形式进行，但在Ag（111）纳米晶岛上进行，而不在单晶表面进行。

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.