ELECTRONIC STATES AT SURFACES : HREELS-STM STUDY

(1)利用高分辨率电子能量损失谱（HREELS）、扫描隧道显微镜（STM）、HREELS-STM和光电子能谱（PES）的组合测量技术，研究了吸附在Si(111)7x7和Si(100)2x1表面的C60分子的结构、振动激发谱、价带谱和C是核心能级谱。在1 ML和0.25 ML之间，HREELS和PES测量表明，在两个表面上的相互作用与范德华相互作用一样弱。在覆盖率低于0.25 ML时，HREELS和PES的结果有些矛盾。使用HREELS，在Si(111)7x7表面观察到几种振动模式的软化，但在Si(100)2x1表面没有观察到软化的迹象。电荷转移方案很好地解释了软化现象。HIREELS结果表明，Si(111)7x7表面的键合性质为离子键合，Si(100)2x1表面的键合性质为范德华键合。相反，在2.4 eV下，用PES可以清楚地观察到C60分子与Si衬底之间的键合状态。PES测量结果表明，该相互作用在Si(111)7x7表面具有共价性质，在Si(100)2x1表面具有介于共价和离子之间的性质，即不是纯离子或纯共价极限。我们讨论了PES和HREELS-STM测量所显示的相互作用的性质，并将其与吸附在金属表面的C60分子的光谱进行了比较。(2)我们还研究了C60前驱体对碳化硅薄膜的初始生长。(3)讨论了HREELS-STM联合测量系统的适用性和可行性。

(1) We have investigated the structures, vibrational excitation spectra, valence band spectra and C is core level spectra of C60 molecules adsorbed on Si(111)7x7 and Si(100)2x1 surfaces, using a combined measurement of high-resolution electron-energy-loss spectroscopy (HREELS) and scanning tunneling microscopy (STM), HREELS-STM, and a photoelectron spectroscopy (PES). At a coverage between 1 ML and 0.25 ML, HREELS and PES measurements show that the interaction is as weak as the van der Waals interaction on both surfaces. At a coverage lower than 0.25 ML, some contradictory results are obtained by HREELS and PES.With HREELS, the softening of several vibrational modes is observed on the Si(111)7x7 surface, but no indication of softening is observed on the Si(100)2x1 surface. The charge transfer scheme explains the softening well. These results by HIREELS indicate that the nature of the bonding is ionic on the Si(111)7x7 surface and of the van der Waals type on the Si(100)2x1 surface. On the contrary, the bonding states between C60 molecules and Si substrates are clearly observed at 2.4 eV on both surfaces with PES.The PES measurements indicate that the interaction has a covalent character at the Si(111)7x7 surface, and that the nature is in between covalent and ionic characters, i.e. not pure ionic or covalent limit, at the Si(100)2x1 surface. We have discussed the nature of the interaction manifested by PES and HREELS-STM measurements in comparison with the spectra of C60 molecules adsorbed on metal surfaces.(2) We have also investigated the initial growth of silicon carbide film by C60 precursor.(3) We have discussed the applicability and possibility of a combined measurement system of HREELS-STM.