Real-space observation on standing configurations of phenylacetylene on Cu (111) by scanning probe microscopy**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0202300 and 2018YFA0305800), the National Natural Science Foundation of China (Grant Nos. 61888102, 61474141, and 21661132006), the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11604373), the Outstanding

Abstract

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.