Effects of positively and negatively pulsed voltages on the microstructure of DLC films prepared by bipolar-type plasma based ion implantation

Diamond like carbon (DLC) films were prepared by the bipolar-type plasma based ion implantation, and the microstructure was examined as a function of positively and negatively pulsed voltages (Vp and Vn) by transmission electron microscopy (TEM) and Raman spectroscopy. Densities of the films were obtained from Rutherford backscattering spectrometry, elastic recoil detection analysis and surface profilemeter measurements. It was found that the density of the film was approximately 2.0 g/cm3 and slightly decreased with increasing Vp and Vn. TEM observation revealed that DLC films were amorphous structure and small size disordered graphite structure appeared as Vp increased. With increasing Vn, however, turbostratic structure was clearly developed. Raman spectra were fitted by 4 peaks (D1: 1190 cm−1, D2: 1380 cm−1, G1: around 1550 cm−1 and G2: 1590 cm−1). The G1 peak shifted to higher wave numbers and the intensity of G2 peak was increased with increasing Vp. In addition, the intensity ratio of D (D1+D2) to G (G1+G2) peaks was also increased. These results suggested that graphite structure was formed as Vp increased. With increasing Vn, on the other hand, the G1 peak did not shift so much and the intensity of G2 peak was decreased. This corresponds to the development of the turbostratic form (t-DLC). The influence of electron and ion bombardment induced by Vp and Vn on the microstructure was discussed.