Investigation of C₆₀ epitaxial growth mechanism on GaAs substrates

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 C ₆₀ 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.