Thermal stability of germanium-carbon coatings prepared by a RF plasma enhanced chemical vapor deposition method

In this work, germanium-carbon coatings were deposited on ZnS substrates by RF plasma enhanced chemical vapor deposition (RF-PECVD) using GeH4 and CH4 as precursors. Thermal stability of coatings were investigated by annealing treatment of samples at different temperatures (200 degrees C, 300 degrees C, 400 degrees C and 500 degrees C for 3 min , an air atmosphere). Then, the samples were characterized by fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM), methods. With annealing samples at 200 degrees C and 300 degrees C, the optical transmittance was increased by 3% in the wavelength region between 3 and 15 mu m. There was no remarkable change in transmittance with annealing samples at 400 degrees C, except for a slight increase in transmittance at the wavelength region between 8 and 9 mu m and a slight decrease at the wavelength region between 11 and 12 mu m. However, as annealing temperature (T-a) was further increased to 500 degrees C, the coating was partly peeled off from the ZnS substrate, leading to a sharp decrease in the transmittance of coatings in the wavelength range of 8-12 mu m. Annealed coatings at the temperatures of 200, 300 and 400 degrees C exhibited a structure free of pores. However, as T-a was further increased to 500 degrees C, the coatings were disintegrated.