Amorphous hydrogenated carbon nitride (a-CNx:H) films were prepared on Si and glass (SiO2) substrates using i-C4H10/N-2 supermagnetron plasma chemical vapor deposition. By controlling the rf power ratio (i.e., keeping the upper electrode rf power [UPRF] at 800 W but the lower electrode rf power [LORF] was varied in 0-100 W), wide or narrow optical bandgap a-CNx:H films were realized. At LORF > 25 W, the deposited a-CNx:H layers became hard and opaque. Optical bandgap of the films was below 0.8 eV, electrical resistivity was low, and hardness was above 20 GPa. At LORF < 20 W, however, deposited a-CNx:H layers became soft and transparent. Optical bandgap of the films was above 1.9 eV, electrical resistivity was high, and hardness was about 7 GPa. Nitrogen atom concentrations of all of the films were 12.5-13.4 mass% at LORF of 10-100 W (c) 2007 Elsevier B.V. All rights reserved.