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Graphene is a zero-gap semiconductor with low work function and high leakage current which limit its applications. Doping of nitrogen is one of the ways to tailor the properties of graphene. However, there remain some defects, such as the low nitrogen content and poor controllability. In order to enhance the content of nitrogen and control the bonding characters to embed nitrogen atoms inside the carbon lattice, solid-state sources (melamine) and gas-state sources (methane) were used to prepare nitrogen doped graphene (NG) films. The preparation time, the dosage of melamine and temperature were set as tunable parameters. The morphology of NG, the content of nitrogen (mass fraction of nitrogen atoms) and the bonding characters for the embedding of N atoms were studied. The results indicated that the preparation process of NG films was involved with nucleation, growth and aggregation. Proper temperature (990 °C) was conductive for the improvement of the content of nitrogen. Pyrrolic N was produced at high temperature (＞1 000 °C), while graphitic N was on the opposite. With increasing the dosage of melamine, the content of nitrogen was increased and then decreased with the maximum value of 6.98%. The content of Pyridinic N will be elevated with increasing the amount of melamine. Compared with graphene, NG films were capable of detecting the Raman signals from Rhodamine B molecules even at the concentration as low as 10−5 mol/L. [ABSTRACT FROM AUTHOR]