Tension in the Initial Growth Stages of Sputter Deposited WSi$_{2}$ on Si in Multilayers

We concentrate on the initial stages of growth of sputtered amorphous multilayers with equal WSi$_{2}$ and Si layer thicknesses of 5.5 nm, and we report observations of tension in the first 1.1 nm of WSi$_{2}$ grown on Si layers. Measurements of wafer curvature were made \textit{in-situ} in the sputtering chamber. Stresses in the conjugate interface of Si on WSi$_{2}$ were observed to be significantly smaller. A clear asymmetry in the stress of these conjugate interfaces rules out an explanation based solely on lattice misfit. We find a value of 1.3 x 10$^{10}$ dynes/cm$^{2}$ for the biaxial film stress at the WSi$_{2}$ on Si interface grown at 2.3 mTorr of Ar pressure, a value comparable to values calculated for hybridization of Si(111) facets by various adatoms [1]. Our observations thereby support a model for chemically induced changes in packing density during sputtering of the interfaces. As an example of a particular application, WSi$_{2}$/Si multilayers consisting of many hundreds periods have been used to make lenses for nanofocusing of hard x-rays [2-3].\\[0pt] [1] D. Vanderbilt, PRL 59, 1456 (1987). [2] H.C. Kang et al. PRL 96, 127401 (2006); APL 92, 221114 (2008). [4] L. Zhou et al. PRB 82, 075408 (2010).