Chiang Mai Journal of Science

Acetylene/argon plasma was used to deposit hydrogenated amorphous carbon (a-C:H) films using showerhead plasma CVD. The upper electrode was designed like a showerhead to spray gasses onto the grounded electrode and is connected to 10 kHz RF power. The a-C:H films were fabricated with a deposition time of one hour and a substrate temperature of 280 ฐC for different acetylene concentrations of 3, 4, and 5 %. The result from SEM image shows the thickness of the films increases from 742 nm to 1456 nm. The optical properties of the samples were measured by UV-Vis spectroscopy. It gives the average optical transmittance in the visible light range (400-800 nm) is around 64%, 63%, and 61%. The optical gap energy of the a-C:H films was determined using the Tauc plot method which gives the value around 1.8-2.0 eV. The structural bonding of the prepared films was investigated by x-ray photoelectron spectroscopy and visible Raman spectroscopy with laser wavelengths of 473 nm. All the prepared samples of a-C:H indicated an overall sp3 content around 18-24%. The Raman spectra were fitted with two Gaussians corresponding to D and G peaks. The peak positions at 1367 cm-1 and 1594 cm-1 were the D and G peaks of the amorphous carbon, which mixes the sp2 and sp3 structures.