School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
Phys Chem Chem Phys. 2012 Mar 14;14(10):3323-8. doi: 10.1039/c2cp23871c. Epub 2012 Feb 1.
We have studied the orientational ordering of the second layer of C(60) molecules on Au(111) using scanning tunnelling microscopy (STM) at 77 K. The orientation of individual molecules within the second layer follows a regular pattern, giving rise to a 2 × 2 superlattice. The long-range order of the 2 × 2 lattice depends on the structure of the first molecular layer with the best ordering found inside the R14° domain. The second layer formed on top of the contrast-disordered R30° domain consists of patches of bright and dim molecules. The contrast between bright and dim patches shows a clear dependence on the sample bias. This bias-dependent contrast is explained by considering the contributions to tunnel current from HOMO and LUMO mediated electron transfer processes. Scanning tunnelling spectroscopic measurement reveals the narrowing of the HOMO-LUMO gap for the layer of molecules in direct contact with the Au(111) substrate.
我们使用扫描隧道显微镜（STM）在 77 K 下研究了 C(60)分子第二层在 Au(111)上的取向有序性。第二层中单个分子的取向遵循规则模式，导致出现 2×2 超晶格。2×2 晶格的长程有序性取决于第一层分子层的结构，在 R14°畴内发现了最佳有序性。在对比度无序的 R30°畴上形成的第二层由亮分子和暗分子的斑块组成。亮斑和暗斑之间的对比度明显取决于样品偏置。通过考虑 HOMO 和 LUMO 介导的电子转移过程对隧道电流的贡献，可以解释这种依赖于偏置的对比度。扫描隧道光谱测量显示，与 Au(111)基底直接接触的分子层的 HOMO-LUMO 能隙变窄。
