Supermagnetron plasma was used to deposit amorphous hydrogenated carbon (a-C:H) and hydrogenated carbon nitride (a-CNx:H) films for field-emission devices using i-C4H10/(H-2 or N-2). It was also used to improve the field-emission characteristics by surface etching using N-2/H-2 plasma. The best emission threshold electric field (E-TH) was 13 and 12 V/mu m for devices using as-deposited a-C:H and as-deposited a-CNx:H films, respectively, while they were remarkably improved to 11 and 8 V/mu m by surface etching using N-2/H-2 (120/40 sccm) gas, though surface roughness was slightly increased by the surface etching. The hardness of as-deposited films was higher than 22 GPa. (c) 2007 Elsevier B.V. All rights reserved.