Measuring the interface stress: Silver/nickel interfaces
- PDF / 461,639 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 66 Downloads / 174 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Measuring the interface stress: Silver/nickel interfaces D. Josell and J.E. Bonevich National Institute of Standards and Technology, Gaithersburg, Maryland, 20899
I. Shao and R.C. Cammarata The Johns Hopkins University, Baltimore, Maryland (Received 11 May 1999; accepted 12 August 1999)
Interface stress is a surface thermodynamics quantity associated with the reversible work of elastically straining an internal solid interface. In a multilayered thin film, the combined effect of the interface stress of each interface results in an in-plane biaxial volume stress acting within the layers of the film that is inversely proportional to the bilayer thickness. We calculated the interface stress of an interface between {111} textured Ag and Ni on the basis of direct measurements of the dependence of the in-plane elastic strains on the bilayer thickness. The strains were obtained using transmission x-ray diffraction. Unlike previous studies of this type, we used freestanding films so that there was no need to correct for intrinsic stresses resulting from forces applied by the substrate that can lead to large uncertainties of the calculated interface stress value. Based on the lattice parameters of the bulk, pure elements, an interface stress of −2.02 ± 0.26 N/m was calculated using the x-ray diffraction results from films with bilayer thicknesses greater than 5 nm. This value is somewhat smaller than previous measurements obtained from as-deposited films supported by substrates. For smaller bilayer thicknesses the apparent interface stress becomes smaller in magnitude, possibly due to a loss of layering in the specimens.
I. INTRODUCTION
It is axiomatic that as layers in a solid with a laminate microstructure become thinner, interfaces become more important. For the materials scientist concerned with the thermodynamics of interfaces, one of the important quantities is the interface free energy. For simplicity, this quantity is frequently described as the cost of breaking bonds within bulk specimens of the two adjacent materials minus the energy of rejoining some, or all, of those bonds to create the interface. In fact, this described quantity is the interface excess energy (or simply interface energy); it is only when terms for the excess volume and entropy of the interface have been appropriately included that one truly is describing the interface free energy. The structure of the materials near the interface can differ from that in the bulk, specifically interatomic and interplanar spacings. In particular, interface energy, volume, and entropy can be affected. The driving force for such changes is always reduction of the free energy associated with the material as a whole, i.e. both the interface as well as all material constrained to deform with it. The free energy change of the interface arising from this change of in-plane lattice parameter is quantified by the interface stress.1–3 4358
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 11, Nov 1999 Downloaded:
Data Loading...
