Investigation of C60 Epitaxial Growth Mechanism on GaAs Substrates

Abstract

Intensity oscillations of reflection high-energy electron diffraction are observed during epitaxial growth of a C60 layer on GaAs (111)B, (111)A, and (001) substrates. The frequencies of the oscillations coincide well with the growth rates of C60 layers, suggesting that C60 layers grow by repeating nucleation and step-flow growth mode, as is the case with GaAs and other semiconductor materials. Anomalous oscillations are observed in the initial stage of C60 layer growth on a GaAs (111)B surface with (2×2) structure. These oscillations indicate that the growth of the first C60 layer is completed at the point of approximately 0.5 monolayer coverage by C60 molecules. This phenomenon is explained by a model in which C60 adsorption sites are limited by As trimers adsorbed on the GaAs (111)B surface. A similar relationship between C60 adsorption and surface reconstruction is observed on (001) GaAs substrates, i.e., the first C60 layer on the (2×4) surface is terminated at approximately 0.5 monolayer coverage, while full coverage is needed of the c(4×4) surface. These observed results are strongly supported by the reported results of scanning tunnel microscopy.