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.

通过使用可变的扫描隧道显微镜（STM），研究了乙烯（C_2H_2）的热分解过程（C_2H_2）。通常，C_2H_2被脱氢以在PT（111）表面形成乙基乙烯。由于C_2H_2只有两个氢原子，因此无法通过分子内氢的重排发生乙基肾形成，并且预计将同时发生几个反应步骤。高分辨率电子损失光谱研究表明，C_2H_2稳定直至300 K，然后加热至370 K的较高温度导致形成乙基乙烯。另一方面，总频率生成研究表明，即使在120 K时，C_2H_2也将其更改为乙烯基，并且在120-350 K的温度范围内通过几个步骤转换为Ethlidyne。这一点。在30 K时，C_2H_2分子随机分布在Pt（111）表面上，并且没有给出以下1个单层以下的所有覆盖范围的有序结构。观察到将C_2H_2饱和表面加热到120 K，局部2x2有序区域。加热至220 K，表面被2x2结构覆盖，带状结构与斑块之间的边界相对应。 2x2结构中出现较大的突起，并且通过退火到更高的温度来增加它们的数量。另一方面，对于低覆盖范围，在120 K处未观察到有序结构。通过加热220 K，可以观察到2x2岛。因此，在120 K和220 K处观察到的物种之间存在排斥和有吸引力的相互作用。这表明在120 K处观察到的物种与220 k时的物种不同。因此，当前的STM结果支持基于SM频率产生研究的后一种反应模型。