Wednesday, December 4, 2019

Copper phthalocyanine molecules on an InSb(001) c(8 × 2) surface studied by ultra-high-vacuum STM and non-contact AFM

The surface ordering of copper phthalocyanine (CuPc) molecules deposited onto an InSb(001) c(8 ×2) reconstructed surface has been studied using scanning tunneling microscopy (STM), non-contact atomic force microscopy (nc-AFM) and low-energy electron diffraction (LEED). It was found that at room temperature the CuPc molecules are only weakly bound to the InSb surface and the adjacent molecules and consequently they are relatively mobile at submonolayer coverage. STM images show that at the initial stages of growth molecules are assembled in ordered molecular chains parallel to the surface reconstruction rows, i.e. along the [110] crystallographic direction. Furthermore, adsorption of the molecules at step edges is observed. At coverages below 1 ML molecules diffuse at the surface and form two-dimensional islands, which leads to an additional characteristic (n × 3) LEED pattern indicating one-dimensional ordering within the molecular chains. High-resolution STM imaging at negative sample bias reveals a unique structure of the molecular contrast which may be related to the highest occupied molecular orbital (HOMO) of the individual CuPc molecules. For CuPc monolayer coverage submolecular resolution is also obtained for nc-AFM imaging. Finally, examples of single molecule manipulation by the STM tip are given.


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