Microscratch analysis of the work of adhesion for Pt thin films on NiO
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D. L. Kohlstedt Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455
W.W. Gerberich Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (Received 10 June 1991; accepted 14 January 1992)
The adhesion of as-sputtered Pt thin films to NiO single crystals has been characterized by a continuous microscratch technique. In these experiments, a conical indenter was driven into a 1.2 /zm thick Pt film at a rate of 15 nm/s, and across the sample surface at a rate of 0.5 fim/s, until a load drop was observed indicating that the film had delaminated. Using the width of the scratch track at the point at which the film delaminated from the substrate, the critical load required for delamination, and the area of the delaminated region, a model has been developed to determine the work of adhesion of the Pt/NiO system. This model uses an elastic contact mechanics approach to relate the stresses acting in a scratch experiment to the strain energy released during film delamination. Using this model, the work of adhesion and hence the interfacial fracture toughness have been determined to be 0.023-0.06 J/m 2 and 0.07-0.11 MPai/rn, respectively. These values are in reasonable agreement with those determined by other methods for metal-ceramic systems.
I. INTRODUCTION Metal-ceramic adhesion has found special significance in issues of technological importance to composites, electronic packaging, multi-layer substrates, and capacitors.^ 3 In order to engineer the mechanical behavior of a metal-ceramic couple, a basic understanding of the adhesive bond strength at the interface is important.4 Although techniques for fabricating thin film materials have advanced rapidly over the past ten years, the development of an understanding of the mechanical properties of interfaces, such as interfacial shear strength and fracture toughness, lags far behind. Methods for measuring adhesion strength are generally lacking, especially for very thin films. The characterization of the adhesion strength by scratch testing is commonly used in the hard coatings industry for films several microns thick.5"10 However, because thin films only a fraction of a micron thick are required by the electronic packaging and magnetic recording industries, new specifications are imposed on scratch test apparatuses, particularly relating to the range and resolution of the applied load and radius and quality of the indenter tip. Hence, a new generation of micro-mechanical testing apparatuses has been developed to characterize the adhesion of very thin films.11"15 1126 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 5, May 1992 Downloaded: 31 Mar 2015
In this paper, the adhesion strength of metal-ceramic interfaces is characterized and a model to determine the work of adhesion and the interfacial fracture toughness is presented. Using a high resolution microindenter, which can be used for both micro/nanoindentation and microscratch testing,11"15 scratch tests were per
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