Amorphous nitrogenated carbon films with nitrogen atomic concentration betw
een 12% and 29% were deposited using a filtered cathodic vacuum are and a K
aufman-type ion source. The surface topography of the samples has been inve
stigated by scanning tunneling microscopy in ultrahigh vacuum, showing that
the roughness of the film surface decreases with nitrogen concentration. S
canning tunneling spectroscopy is employed to understand the role of nitrog
en in the change of the surface microstructure and electronic structure nea
r the Fermi level. The tunneling current (I)-bias voltage (V) curve is flat
at low bias regions indicating a finite gap for the sample with low (12%)
nitrogen concentration. An increase of tunneling current and its nonlineari
ty along with the decrease of energy gap occurs in the samples with increas
e of N concentration. The observed surface density of states [(dI/dV)/(I/V)
] has been fitted as a square-root function of bias voltage. An improvement
of the quality of these fits in the films with the increase of nitrogen co
ncentration suggests that a depletion of defect density of states near the
Fermi level (E-F) takes place. These analyses could be attributed to the mo
dification of the structure of amorphous carbon by a large concentration of
nitrogen. (C) 2001 American Institute of Physics.