Adhesion Measurement of Thin Films

TLDR

Adhesion measurement of thin films is largely limited to metallic coatings, with few studies on polymeric films, and most techniques provide relative rather than absolute strength values, highlighting challenges in quantifying adhesion and its dependence on processing and aging. This review surveys quantitative and qualitative adhesion measurement methods for thin films, outlines the unmet requirements of an ideal test, and discusses the applicability of techniques developed for thicker coatings. The authors categorize adhesion determination methods into nucleation, mechanical, and miscellaneous techniques, with mechanical methods further divided by force application mode, and emphasize applicability to sub‑micron films while considering methods successful on thicker coatings.

Abstract

A critical and comprehensive review of the various methods for the measurement of adhesion of thin films is presented. Emphasis has been placed on the techniques used for thin films (<1 μ m) but consideration has also been extended to methods which have proved successful in case of relatively thicker coatings and are potentially applicable in the study of thin films. Most of the methods catalogued in this review have been harnessed in measuring the adhesion of thin evaporated or sputtered metallic films on an assortment of substrates; the literature references to the study of thin polymeric films are extremely meager. The methods of determination of adhesion are discussed under three headings: Nucleation Methods, Mechanical Methods and Miscellaneous Techniques. Furthermore, the mechanical methods are categorized depending upon the mode of application of the force to disrupt the interface. Although the emphasis is on the quantitative methods of measuring adhesion, but for completeness qualitative as well as the methods which are still in a state of infancy have been included. Requirements for the ideal adhesion test are outlined and, apparently, there does not exist any test which fulfils all the virtues. Many of the techniques may not provide absolute quantitative values of adhesion strength but these can profitably be used to follow relative changes in adhesion strength due to process variables, ageing weathering, etc. The principle, merits, potentialities, and limitations of each technique are outlined, and the difficulties associated with measuring adhesion strengths and their relationship to “basic adhesion” are discussed.