生长在Cd(0001)和Bi(111)上的二氰基蒽分子薄膜的对比

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

分子与衬底之间的相互作用在有机薄膜的生长过程中起着非常重要的作用.对于金属衬底和半金属衬底来说,由于不同的电子结构,二者与分子薄膜之间的相互作用会有明显的差异.本文利用扫描隧道显微镜对比研究了二氰基蒽(DCA)分子在金属衬底Cd(0001)和半金属衬底Bi(111)上的薄膜生长.实验发现,在Cd(0001)衬底上,低温沉积的DCA薄膜表现出三维生长模式,而室温沉积的DCA薄膜表现出二维生长模式.特别是DCA分子单层具有斜方对称的4×√13公度结构,表明DCA与Cd(0001)之间存在较强的相互作用.与此形成鲜明对比的是,在半金属Bi(111)衬底上,低温沉积的DCA薄膜表现出二维生长模式,在分子单层中有莫尔条纹出现,表明DCA单层是一种非公度结构,DCA与Bi(111)之间的相互作用较弱.通过上述的对比研究可以看出,衬底材料的电子结构和沉积温度均可影响DCA分子薄膜的结构和生长模式.

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×√13 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 moirépattern 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.