Ab Initio Modeling of Noncontact Atomic Force Microscopy Imaging of Benzene on Cu(110) Surface

The imaging of the detailed atomic structure of single organic molecules adsorbed on a Surface is still a challenge for noncontact atomic force microscopy (NC-AFM). To investigate such a NC-AFM imaging process, we performed ab initio calculations to simulate the interaction of clean silicon tips with a benzene molecule adsorbed on a Cu(110) surface. The apex structure of the AFM tip was modeled by Si4H3 and Si4H9 Clusters. These two nanotips were approached on top of three different molecular sites. The forces acting on the Si4H3 nanotip are always repulsive and lead to a displacement of the benzene molecule on the Cu(110) Surface. On the contrary, the forces acting on the Si4H9 nanotip can be attractive or repulsive depending oil the approaching molecular site. In this case, the benzene molecule can bind to the tip and is retracted from the surface. The different behavior of the two nanotips considered in our Study is analyzed in the framework of the frontier orbital theory. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 108: 2803-2812, 2008