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Scanning Tunneling Microscopy study of the dynamical processes of atoms and molecules on transition metal surfaces

扫描隧道显微镜研究过渡金属表面原子和分子的动力学过程

基本信息

批准号：
11640505
负责人：
TAKAGI Noriaki
金额：
$ 1.6万
依托单位：
The Graduate University for Advanced Studies
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

The thermal decomposition processes of acetylen (C_2H_2) on the Pt(111) surface have been investigated by the use of variable-temperature Scanning Tunneling Microscopy (STM). Generally, C_2H_2 is dehydrogenated to form ethylidyne on the Pt(111) surface. Since C_2H_2 has only two hydrogen atoms, ethylidyne formation cannot occur by an intramolecular hydrogen rearrangement and the several reaction steps are expected to occur simultaneously. High resolution electron energy loss spectroscopy studies indicate that C_2H_2 is stable until 300 K and furthermore heating to higher temperature of 370 K leads to the formation of ethylidyne. On the other hand, sum frequency generation study says that C_2H_2 is changed to vinylidene even at 120 K and is converted to ethlidyne by several steps at the temperature range of 120-350 K.Our STM investigation has been made in order to make clear about this point. At 30 K, C_2H_2 molecules are randomly distributed on the Pt(111) surface and do not give ordered structure for all the coverage regime below 1 monolayer. Heating the C_2H_2-saturated surface to 120 K, local 2x2 ordered regions are observed. Heating to 220 K, surface is covered with the 2x2 structure with the band-like structures which correspond to the boundaries between the patches. Larger protrusions in the 2x2 structure appear and the number of them is increased by furthermore annealing to higher temperatures. On the otherhand, no ordered structure is observed at 120 K for a low coverage regime. By heating 220 K, 2x2 islands are observed. Therefore, repulsive and attractive interactions exist between the species which are observed at 120 K and 220 K, respectively. This indicates that the species which are observed at 120 K are different from the ones at 220 K.Therefore, present STM results support the latter reaction model based on the sm frequency generation study.

采用变温扫描隧道显微镜（STM）研究了乙炔（C_2H_2）在Pt（111）表面的热分解过程。通常，C_2H_2在Pt（111）表面脱氢生成乙炔。由于C_2H_2只有两个氢原子，乙炔的生成不可能通过分子内氢原子重排而发生，而几个反应步骤可能同时发生。高分辨电子能量损失谱研究表明，C_2H_2在300 K之前是稳定的，进一步加热到370 K的高温会形成乙炔。另一方面，和频生成研究表明，C_2H_2在120 K时也会转化为偏乙炔，并在120 ~ 350 K的温度范围内经过几个步骤转化为乙炔。我们进行STM调查是为了弄清楚这一点。在30 K时，C_2H_2分子在Pt（111）表面随机分布，在1层以下的所有覆盖区都没有有序结构。将c_2h_2饱和表面加热至120k，观察到局部2x2有序区。加热至220 K，表面覆盖2x2结构，其带状结构对应于斑块之间的边界。在2x2结构中出现较大的突起，并且通过进一步退火到更高的温度，它们的数量增加。另一方面，在低覆盖率下，在120 K时没有观察到有序结构。通过加热220 K，观察到2x2个岛。因此，在120 K和220 K下观察到的两种物质之间存在排斥和吸引相互作用。这表明在120 K下观察到的物种与在220 K下观察到的物种是不同的。因此，目前的STM结果支持基于sm频率生成研究的后一种反应模型。