Dia. Rel. Mater. 8 (6), 1067-1072 (1999). [PDF]

A Method to Determine Elastic Properties of Diamond-like Carbon Films

Sung-Jin Cho, Kwang-Ryeol Lee, Kwang Yong Eun, Jeung-hyun Jeong and Dongil Kwon

The elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF) glow discharge at a deposition pressure of 1.33 Pa. Because of high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1-v), where E is the elastic modulus and v is Poisson's ratio of the DLC film. The biaxial elastic modulus with the plane-strain modulus, E/(1-v²), measured by nanoindentation, we could further determine the elastic modulus and Poisson's ratio, indepently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson's ratio due to the pile up of errors in the measurements of the elastic properties and the residual stress.