Hydrogenated amorphous carbon (a-C:H) films were fabricated using mixed acetylene and argon plasmas with various flow rate ratios of acetylene to argon. The flow rate ratios (F-C2H2 to F-Ar) have a large impact on the structure of the films. Enhanced film hardness and reduced sp(2) content were achieved at larger flow ratios attributable to the high ion flux and efficient etching by hydrogen. However, an excessively high flow rate leads to hydrogen loss from the structure, large stress during deposition, and potential deterioration in the film structure. The appropriate deposition rate is determined based on the scratch behavior of the film. (C) 2007 Elsevier B.V. All rights reserved.