Photochemical reaction at metal cluster surfaces as revealed by ultrafast vibrational spectroscopy

超快振动光谱揭示金属簇表面的光化学反应

基本信息

批准号：
10640570
负责人：
WATANABE Kazuya
金额：
$ 2.24万
依托单位：
The Graduate University for Advanced Studies (1999)Okazaki National Research Institutes (1998)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

We have investigated how intermediate species with excess energy contribute to various surface chemical reactions. We have mainly focused on the following topics :1. Reaction of carbon dioxide during the oxidation process of silicon surface :Carbon dioxide is known as a very stable molecule in gas phase. However, we have found that it is readily converted to carbonate species when it is adsorbed on silicon surface at low temperature and a surface oxidation procedure is conducted.2. Photodesorption of rare gas atoms on silicon surfacesRare gas atoms (Kr, Xe) weakly adsorb on a Si(100) surface. We found for the first time that these adsorbates are desorbed by the irradiation of photos whose wavelength range from near infrared to uv. It is revealed that the desorption occurs via energy transfer from surface hot phonon which is excited by charge recombination of photocarriers at surface states. We also found that the desorption mechanism changes to that involves charge transfer state between the substrate and the adsorbate by surface modification with oxygen or deuterium.3. Photochemistry of oxygen adsorbed on Ag(110)Photochemistry of oxygen atoms on Ag(110) has been investigated. The chemisorbed oxygen atoms are removed by uv light irradiation. It is found that slight amount of carbon atom in the surface region is necessary for the reaction. Wavelength dependence of photo-yield indicates that the phtogenerated hot-electron plays a crucial role in this reaction.4. Development of the light source for time resolved vibrational spectroscopyTHz electro-magnetic field radiation from femtosecond laser irradiated InAs surface has been investigated. Under an ultra-high vacuum condition, an effect of the surface cleanness and a temperature dependence of the THz radiation were examined. It was found that the THz radiation intensity was enhanced up to two-times by surface cleaning and up to 4 times by temperature lowering to 50 K compared to that at room temperature in air.

我们研究了具有过剩能量的中间物质如何促进各种表面化学反应。我们主要关注以下主题：1．硅表面氧化过程中二氧化碳的反应：二氧化碳被认为是气相中非常稳定的分子。然而我们发现，当它在低温下吸附在硅表面并进行表面氧化过程时，很容易转化为碳酸盐物质。 2．硅表面上稀有气体原子的光解吸稀有气体原子（Kr、Xe）在Si（100）表面上弱吸附。我们首次发现这些吸附物通过波长范围从近红外到紫外的光照射而解吸。研究表明，解吸是通过表面热声子的能量转移而发生的，表面热声子是由表面态光载流子的电荷重组激发的。我们还发现，通过氧或氘的表面修饰，解吸机制转变为涉及基质和吸附物之间的电荷转移状态。 3． Ag(110) 上吸附氧的光化学研究了 Ag(110) 上氧原子的光化学。通过紫外线照射去除化学吸附的氧原子。发现表面区域的少量碳原子对于该反应是必要的。光产率的波长依赖性表明光生热电子在该反应中起着至关重要的作用。 4．研究了飞秒激光照射 InAs 表面的时间分辨振动光谱太赫兹电磁场辐射光源的开发。在超高真空条件下，检查了表面清洁度的影响和太赫兹辐射的温度依赖性。研究发现，与室温空气中相比，表面清洁后太赫兹辐射强度提高了两倍，温度降低至 50 K 时太赫兹辐射强度提高了四倍。