Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption. ne structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp(2) structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp(3)-rich region remained at the topmost DLC surface. The formation of an sp(3)-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface. (C) 2010 Elsevier B.V. All rights reserved.