“…The peak about 1598 cm À1 is assigned to G band, and it is related to sp 2 -bonded carbon residing at grain boundaries. It is worthy that the presence of N can increase sp 2 banding at the grain boundaries and a low temperature can lead to high density of defects incorporated in the films [3,4,16,22,23], thus, the Raman peaks of such samples are broadened as a band.…”