Real-space observation on standing configurations of phenylacetylene on Cu (111) by scanning probe microscopy

The adsorption configurations of molecules adsorbed on substrates can significantly affect their physical and chemical properties. A standing configuration can be difficult to determine by traditional techniques, such as scanning tunneling microscopy (STM) due to the superposition of electronic states. In this paper, we report the real-space observation of the standing adsorption configuration of phenylacetylene on Cu (111) by non-contact atomic force microscopy (nc-AFM). Deposition of phenylacetylene at 25 K shows featureless bright spots in STM images. Using nc-AFM, the line features representing the C-H and C-C bonds in benzene rings are evident, which implies a standing adsorption configuration. Further density functional theory (DFT) calculations reveal multiple optimized adsorption configurations with phenylacetylene breaking its acetylenic bond and forming C-Cu bond(s) with the underlying copper atoms, and hence stand on the substrate. By comparing the nc-AFM simulations with the experimental observation, we identify the standing adsorption configuration of phenylacetylene on Cu (111). Our work demonstrates an application of combining nc-AFM measurements and DFT calculations to the study of standing molecules on substrates, which enriches our knowledge of the adsorption behaviors of small molecules on solid surfaces at low temperatures.