Evaluation of Thin Film Coating Adhesion with an Opto-Acoustic Technique

An opto-acoustic technique to evaluate the adhesion strength at the interface of nano-scale thin film systems has been demonstrated. The specimens have been integrated into a Michelson interferometer as the end mirrors, and driven from the rear with an acoustic transducer at moderate frequencies. The resultant film surface displacement has been detected as a fringe shift of the interference intensity pattern behind the beam splitter with a digital imaging device at a normal frame rate. Comparison has been made between strongly and weakly adhered film specimens. The difference in the adhesion strength has been successfully visualized as the difference in the fringe contrast. Fourier analysis on the fringe pattern has quantified the fringe contrast.