Hydrogen-contained nanoamorphous carbon films (a-C: H) were deposited on Si substrates by using microwave plasma chemical vapor deposition. A low turn-on field of 2.77 V/mu m was obtained. The current density of 0.28 mA/cm(2) was obtained at an electric field of 4.8 V/mu m. When the electric field was increased to 6.85 V/mu m, the current density was dramatically decreased to 0.067 mA/cm(2) and the bonding ratio sp(2)/Sp(3) of 1.25 was decreased to 0.53. It was suggested that some of the sp(2) phase changed to sp(3) due to arc discharging and that the sp(2) phase played an important role in field emission for a-C:H films. The measurements of field emission from local emission sites of a-C:H films were carried out by using scanning tunneling, microscopy. The results revealed that emission sites could be located either at the boundaries of amorphous particles or on the top of particle surface. The defected graphite model was suggested to describe the field-electron-emission characteristics of the film. (c) 2006 American Vacuum Society.