EXPERIMENTAL CHARACTERIZATION AND THEORETICAL SIMULATION OF DIAMOND-LIKE CARBON THIN FILMS

Abstract

Diamond-like carbon (DLC) films produced with radio-frequency plasma-enhanced chemical vapour deposition (PECVD) from two distinct hydrocarbon precursor gases were characterized to determine the effect of processing conditions on the structureproperty relationships exhibited by the films. The bias voltage was systematically varied and was shown to influence the hydrogen content, mechanical hardness, and chemical bonding. Films were produced with hydrogen contents between 25 to 30 at.%, graphite (sp2) to diamond (sp3) bonding near a 1 to 1 ratio, and indentation hardness reaching 24 GPa. Adhesion tests indicated that DLC was more strongly bonded to silicon than aluminum. Varying the bias voltage from 300 to 450 V was shown to decrease hydrogen content and increase the mechanical hardness, while the sp2 content remained unchanged. A mechanism was proposed to describe the structure evolution of the films with respect to the obtained results. The similarities in properties between films from distinct precursors suggested a similar dissociation of molecular species within the PECVD chamber. Separately, hydrogenated amorphous carbon (a-C:H) structures were prepared with molecular dynamics (MD) and translated to density functional theory (DFT) simulations for calculation of mechanical properties. The DFT results showed overlap with the experimental results and allowed for an estimation of the densities of the DLC films investigated between 2.0 and 2.6 g cm−3.