Raman scattering and photoluminescence of nitrogenated amorphous carbon films.

The structural and optical properties of nitrogenated amorphous carbon films, grown by rf-magnetron sputtering on silicon substrates, were studied by Raman and photoluminescence (PL) spectroscopy as a function of the nitrogen concentration and the substrate bias voltage V[sub b]. For films deposited with V[sub b]=10 V, the photoluminescence emission was most intense at nitrogen concentrations in the carrier gas of 25% (75% Ar), while the intensity ratio I(D)/I(G) of the Raman bands of disordered graphite (D band) and graphite (G band) partially substituted by nitrogen exhibited a minimum simultaneously observed with a minimum of G-band frequency and a maximum of G-band width. Changes in spectral characteristics of Raman scattering at a concentration of 25% (≅30 at %) are indicative of an increase of sp³-bonded fraction and disorder. PL-enhancement coincides, in this case, with structural changes and is probably correlated to the substitution of nitrogen in the tetrahedraly bonded amorphous matrix. In the case of films deposited in a pure nitrogen atmosphere, N[sub 2] = 100%, no significant PL-intensity changes appeared to exist between films deposited at low positive (10 V) and highly negative (-200 V) substrate bias. After several months of sample storage in air, samples grown at negative V[sub b] were found to preserve their structural and optical properties, while films grown at positive bias (V[sub b]=10) and nitrogen concentrations in the carrier gas above 70% (≅40 at %) delaminated. [ABSTRACT FROM AUTHOR]