The properties of a-C:H films deposited by plasma decomposition of C2H2

Abstract

Diamondlike a‐C:H films have been deposited by plasma decomposition of C₂ H₂. 50 samples were prepared with a systematic variation of the deposition parameters: the substrate bias voltage was between −100 and −1400 V and the C₂ H₂ gas pressure was between 4×10⁻⁴ and 2.6×10⁻¹ mbar. The following properties of the films were measured: the density by Rutherford backscattering, the total concentration of hydrogen by elastic recoil detection, the bonding ratio sp³ /sp² by infrared spectroscopy, the internal stress by the bending beam method, and the hardness with a Knoop microhardness tester. It has been shown that the hardness and other mechanical properties cannot be correlated to the average carbon coordination number m_c. This is because m_c is calculated under the assumption of a homogenous single‐phase model, which does not seem to be justified. It is demonstrated that the mechanical properties can be explained by the application of a void model.