ELECTRONIC STATES AT SURFACES : HREELS-STM STUDY

(1)利用高分辨电子能量损失谱(HREELS)和扫描隧道显微镜(STM)、高分辨电子能量损失谱(HREELS-STM)和光电子能谱(PES)相结合的方法，研究了吸附在Si(111)7x7和Si(100)2x1表面的C60分子的结构、振动激发光谱、价带光谱和C is芯能级光谱。在1ML到0.25ML的覆盖率范围内，HREELS和PES测量表明，两个表面上的相互作用都和范德华相互作用一样弱。在覆盖率小于0.25ML时，HREELS和PES得到了一些相互矛盾的结果。在HREELS中，在Si(111)7x7表面上观察到了几个振动模的软化，而在Si(100)2x1表面上没有观察到软化的迹象。电荷转移机制很好地解释了软化现象。HIREELS结果表明，在Si(111)7x7表面上的成键性质是离子的，而在Si(100)2x1表面上的成键性质为van der Waals类型。与之相反，在2.4 eV的PES测量表明，C60分子与Si衬底之间的相互作用在Si(111)7×7表面具有共价性质，而在Si(100)2×1表面的性质介于共价和离子性质之间，即不是纯离子或共价极限。通过与金属表面吸附的C60分子光谱的比较，讨论了PES和HREELS-STM测量所表现出的相互作用的本质。(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能性。

(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.