Frustrated Etching during H/Si(111) Methoxylation Produces Fissured Fluorinated Surfaces, Whereas Direct Fluorination Preserves the Atomically Flat Morphology

Abstract

Two solution-based strategies for the preparation of partially fluorinated Si(111) surfaces from H/Si(111) were investigated using a combination of scanning tunneling microscopy, X-ray photoemission spectroscopy, infrared spectroscopy, and kinetic Monte Carlo simulations. Direct fluorination of H/Si(111) with HF (aq) produced atomically flat surfaces with 11% fluorination. A two-step reaction that first methoxylated the surface by reaction in methanol and then converted the methoxy termination to F termination by reaction in HF (aq) produced atomically rough, fissured surfaces with 24% fluorination. The atomic-scale roughness was induced by the methoxylation reaction. Methanol was shown to react with H/Si(111) surfaces through two parallel mechanisms: an etching reaction and a methoxylation reaction. The methoxylation reaction locally inhibited or “frustrated” the etching reaction, leading to the development of a characteristic fissured morphology. The H and F atoms on the fluorinated surface were imaged with atomic resolution, and no evidence of the previously proposed nanopatterning mechanism was observed.