Comparative studies on the thin films of dicyanoanthracene grown on metal and semimetal surfaces

Abstract

The interactions between molecules and substrates play an important role in growing organic thin films. The metallic and semimetallic substrates, owing to the different electronic structures, can have distinct interactions with molecular films. Here we make a comparative study on the two-dimensional (2D) self-assemblies of dicyanoanthracene (DCA) molecules on the metallic Cd(0001) and semimetallic Bi(111) surfaces. It is found that the DCA thin film grown on Cd(0001) surface at low temperature exhibits a three-dimensional (3D) growth mode, with the monolayer islands, two-layer islands, and three-layer islands coexisting on the Cd(0001) surface. When deposited at room temperature, the DCA molecules exhibit a 2D growth mode, where the monolayer DCA adopts the 4×<inline-formula><tex-math id="Z-20230308215342">\begin{document}$\sqrt {13} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222197_Z-20230308215342.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222197_Z-20230308215342.png"/></alternatives></inline-formula> reconstruction with respective Cd(0001). The commensurate epitaxy indicates that there is strong interaction between DCA molecules and Cd(0001). In clear contrast, the DCA molecules deposited on the semimetallic Bi(111) surface at low temperature exhibit a 2D growth mode. Furthermore, a moiré pattern with the periodicity of 2.6 nm is observed in the DCA monolayer, indicating the incommensurate epitaxy of DCA monolayer on Bi(111). This can be explained by the weak interaction between DCA and Bi(111) substrate. These results demonstrate that both of the electronic structure of substrates and substrate temperatures can be used to adjust the structures of morphology of DCA films.