A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from the mechanical constr aints 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 the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measurin g the amplitude with a known bridge length, we could determine the strain o f the film which occurred by stress relaxation. Combined with independent s tress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1 - nu), where E is the ela stic modulus and nu is Poisson's ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane -strain modulus, E/(1-nu(2)), measured by nano-indentation, we could furthe r determine the elastic modulus and Poisson's ratio, independently. The ela stic modulus, E, ranged from 16 to 133 GPa in this range of the negative bi as voltage. However, large errors were incorporated in the calculation of P oisson's ratio due to the pile up of errors in the measurements of the elas tic properties and the residual compressive stress. (C) 1999 Elsevier Scien ce S.A. All rights reserved.