AFM OBSERVATION OF SELF-ASSEMBLED MONOLAYER FILMS ON GAAS(110)

We have confirmed that a self-assembled monolayer (SAM) film of octade canethiol (ODT), CH3(CH2)(17)SH, can be formed on a cleaved GaAs (110) surface, by using an atomic force microscope (AFM) and X-ray photoele ctron spectroscopy (XPS). Circular depressions were observed on the su rface after film formation. The area of the circular depressions incre ased with immersion time, indicating that the solution oxidized the in terface between ODT molecules and the GaAs surface, resulting in remov al of ODT molecules. The oxidation was considerably faster in pure eth anol solution than that in ODT solution, demonstrating that the SAM fi lm protects the GaAs surface from-oxidation. High-resolution lateral f orce microscope (LFM) images revealed a periodic structure that had tw o types of lines: periodic lines 0.57 nm apart and lines rotated 55 de grees with respect to them. A structural model of the SAM successfully explained both the features in high-resolution LFM images and the dep ression depth observed in AFM images.