A LASER-ACOUSTIC METHOD FOR TESTING AND CLASSIFYING HARD SURFACE-LAYERS

The laser-acoustic method is accepted to be an interesting method of t esting thin films. It is based on measuring the dispersion of surface acoustic waves which are generated by short laser pulses. A reliable t est equipment was developed that allows a user-friendly operation. The method is non-destructive, the test takes little time and special sam ple preparation is not required. It is mainly applied to measure the Y oung's modulus of thin films with thickness down to less than 50 nm. R ecent studies showed these results to correlate with important microst ructural and mechanical properties of hard and superhard films. The la ser-acoustic technique was improved to test multilayer films consistin g of two components. The approach of an effective medium of transversa l symmetry is used to describe the elastic behavior of multilayer film s. It enables the elastic anisotropy of the multilayer film to be eval uated. Applications are presented, performed at multilayers of diamond -like carbon and aluminum deposited by laser-arc on steel and silicon. The films consisted of four and twenty single layers, respectively. T he Young's modulus of the diamond-like carbon in thr multilayer was de termined with the laser-acoustic technique. The results reveal the rep roducibility of the deposition technique and demonstrate the potential of the laser-acoustic technique to test multilayer films. The laser-a coustic method is shown to be sensitive to machining layers. The effec t of grinding and polishing steel surfaces was studied. Studies were p erformed to compare the results of the laser-acoustic technique with t hose of membrane deflection and micro-indentation. TiN, CrN and TiCN f ilms (thickness: 0.8-2.3 mu m) were tested with laser-acoustics and mi cro-indentation, polysilicon films (thickness: 0.46 mu m) with laser-a coustics and the membrane deflection technique. (C) 1998 Elsevier Scie nce S.A. All rights reserved.