Guo Haiming, Wang Yeliang, Du Shixuan, Gao Hong-jun
Institute of Physics, Chinese Academy of Sciences, PO Box 603, Beijing 100190, People's Republic of China.
J Phys Condens Matter. 2014 Oct 1;26(39):394001. doi: 10.1088/0953-8984/26/39/394001. Epub 2014 Sep 12.
We review our achievements in exploring the high resolution imaging of scanning tunneling microscopy (STM) on the surface and adsorbates in a ultra-high vacuum system, by modifying the STM tip or introducing a decoupled layer onto the substrate. With an ultra-sharp tip, the highest resolution of Si(1 1 1)-7 × 7 reconstruction can be achieved, in which all the rest atoms and adatoms are observed simultaneously with high contrast. Further functionalization of STM tips can realize selective imaging of inherent molecular states. The electronic states of perylene and metal-phthalocyanine molecules are resolved with special decorated tips on metal substrates at low temperature. Moreover, we present two kinds of buffer layer: an organic molecular layer and epitaxially grown graphene to decouple the molecular electronic structure from the influence of the underlying metallic substrate and allow the direct imaging of the intrinsic orbitals of the adsorbed molecules. Theoretical calculations and STM simulations, based on first-principle density function theory, are performed in order to understand and verify the mechanism of high-resolution images. We propose that our results provide impactful routes to pursue the goal of higher resolution, more detailed information and extensive properties for future STM applications.
我们回顾了在超高真空系统中，通过修饰扫描隧道显微镜（STM）针尖或在衬底上引入解耦层来探索STM对表面和吸附物的高分辨率成像方面所取得的成果。使用超尖针尖，可以实现Si(1 1 1)-7 × 7重构的最高分辨率，其中所有其余原子和吸附原子都能以高对比度同时被观察到。STM针尖的进一步功能化能够实现对固有分子态的选择性成像。在低温下，通过在金属衬底上使用特殊修饰的针尖，可以分辨苝和金属酞菁分子的电子态。此外，我们还展示了两种缓冲层：有机分子层和外延生长的石墨烯，以将分子电子结构与底层金属衬底的影响解耦，并允许直接成像吸附分子的本征轨道。基于第一性原理密度泛函理论进行了理论计算和STM模拟，以理解和验证高分辨率图像的形成机制。我们认为，我们的结果为未来STM应用追求更高分辨率、更详细信息和广泛特性的目标提供了有效的途径。
