Structural and optical properties of diamond like carbon films using direct current plasma enhanced chemical vapor deposition

Abstract

The amorphous diamond like carbon (a - DLC) thin films were deposited in 3 hours on glass substrates at the vacuum pressure, 8.0 x 10-2 Torr ; deposition pressure, 4.0 x 10-1 Torr and deposition temperatures, 300 – 500 °C by using direct current plasma enhanced chemical vapour deposition (DC - PECVD) system with the precursor gas, 1 % of methane, 39 % of hydrogen and 60 % of argon. The (a - DLC) films which have completely been deposited were post annealed for 3 hours in the tube furnace at 500 – 700 °C with nitrogen ambient to obtain the nitrogen doped amorphous diamond like carbon (a:N - DLC) films. The characterizations were studied by using X-Ray Diffractometer, Energy and Dispersive Analysis of X-Ray, Fourier Transform Infrared Spectrometer, UV / VIS / NIR Spectrophotometer and Photoluminescence Spectrometer. The annealed films are verified as amorphous structure as discovered by X-Ray Diffractometer. It was revealed that carbon, nitrogen, oxygen and silicon are emitting the x-ray energy spectra at 0.28 keV, 0.39 keV, 0.5 keV and 1.74 keV, respectively. The infrared absorptions have shown at 880 cm-1 as C-H bending bonds, 1100 and 1220 cm-1 as C-N stretching bonds, 1300 cm-1 as C-C stretching bonds, 1600 cm-1 as C=N stretching bonds and 2200 cm-1 as C=N stretching bonds for the films annealed from 500 °C to 700 °C. Stretching bond has been observed when annealed at 500 °C and C=N stretching bond has formed when annealed at 700 °C. Moreover the transmittance of (a:N - DLC) films was increasing from 24.9 % to 70.7 % when annealing temperature increased from 500 °C to 700 °C; transition changed from allowed indirect transition, r = 2 to forbidden direct transition, r = 3/2; the optical band gap decreases from 1.60 - 0.85 eV at 500 - 650 °C, but increases to 1.62 eV at 700°C. With the fixed excitation wavelength at 245 nm within the measurement range of 200 – 800 nm, the emission wavelengths were obtained at 290 nm and 393 nm which correspond to n - n* transition and violet emission transition, 4P01/2 4P½, respectively.