Structural Properties of Self-Organized Organo-Silicon Macromolecular Films Investigated by Scanning Tunneling Microscopy and X-ray Diffraction

Abstract

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been applied to investigate thin films of a model silicon-containing macromolecule, silicon phthalocyanine dichloride (SiPcCl 2 ), deposited from solution on to the H-passivated Si(111) surface. In a high coverage film, clusters of about 5.5 nm × 4.5 nm in size are observed. These clusters are believed to partially stack on each other, suggesting a tilted growth mechanism of the layers on the surface. In a low coverage film, well-ordered monolayers are found, with a close structural similarity to the bulk crystal structure of SiPcCl 2 . In this work, the bulk crystal structure of SiPcCl 2 was determined directly from powder X-ray diffraction data using the Monte Carlo method. The results of STM manipulation and the observation of well-ordered SiPcCl 2 layers on the Si(111) surface indicate a weaker interaction between the SiPcCl 2 molecules and the substrate than between the SiPcCl 2 molecules. STS measurements show rectifying behavior which is attributed to the H-passivated silicon surface.