Volume 1, Issue 2 (March 1973)
Quantitative Adhesion Tests of Vacuum Deposited Thin Films
An apparatus for performing quantitative adhesion tests of vacuum deposited thin films on a routine basis was developed by modification of a microhardness tester. The instrument employs a sapphire stylus which is drawn across the film surface until a critical load is established in one pass. This critical load is defined as the weight, in grams, at which the stylus completely removes the film in the contacted area. A number of critical loads for various metallic and dielectric coatings have been established and are being used to control the reliability of optical coatings. In addition, tests were conducted to determine the highest critical load, that is, the best adhesion possible for a given combination of materials and substrates. Typical values ranged from 25 to 100 g, the upper limit being determined by the cohesive strength of the substrate and the hardness and wear resistance of the stylus. The scribe method appears to be a substantial improvement on the “Scotch Tape” technique in that it yields quantitative adhesion data; and, thus, can be used to evaluate optimum deposition parameters, detect coatings of questionable quality, and give an early indication of coating deterioration.