Optical transmittance of antireflective diamond-like coatings on ZnS substrates

Diamond-like carbon films were prepared from C2H2 and Ar by r.f. plasma chemical vapor deposition, The hydrogen content and ratio of sp(3) to sp(2) bonds in the deposited films were investigated as a function of negative d.c. bias voltage. The deposited films were characterized by spectroscopic ellipsometry and IR spectrophotometry. The results show that the ratio of sp(3) to sp(2) bonds and the hydrogen content of the deposited films increase with increasing bias voltage V-B. The percentage of sp(1) carbon sites decreases with V-B and disappears when V-B reaches 700 V. The optimum condition for depositing antireflective diamond-like carbon coatings onto the II-VI compound zinc sulfide was achieved by optimizing the deposition process. The peak IR transmission of the zinc sulfide substrate coated with DLC films on both sides reached 95.8% at a wavelength of 2.5 mu M, and the reproducibility of the results is excellent. The change in IR transmittance of the DLC coated zinc sulfide substrate after annealing in atmosphere for 2 h at temperatures up to 300 degrees C shows that the film is thermally stable.