(Invited) In Situ Stress and Nanogravimetric Measurements during Underpotential Deposition
Equation (1) quantifies the change in surface stress associated with epitaxial overlayer growth1,
ΔF = Δfo + Δfpzc + Δh + Σcohtf (1)
where Δfo is the intrinsic surface stress difference between the overlayer and the substrate, Δfpzc is an electrocapillary term that reflects the change in capacitance and potential of zero charge (pzc) associated with changing the surface from the substrate metal to the overlayer metal, Δh is the interface stress, and ΔΣcohtf is the product of the coherency stress and the film thickness. For sub-monolayers, Eqn. (1) may also contain an additional term that captures the contribution of the compressive strain due to island size effects2. Although the misfit term in Eqn. (1) is often assumed to dictate the overall change in surface stress, this is not always the case. The upd of Al and Cu onto Au are clear examples where the stress change is compressive even though the lattice misfit is positive. In some cases, pseudomorphic film growth of several monolayers allows the coherency term to be distinguished from the interfacial terms, which are independent of film thickness. Measurements of this type have been made for the electrodeposition of Pd onto (111)-textured Au3, and have resulted in estimates of Δh for the Pd-Au interface to be about -1.2 N/m. This is similar in both sign and magnitude to values reported for Ag-Cu4.
This talk will examine the surface stress changes associated with underpotential deposition, paying particular attention to the interfacial contributions, in addition to that associated with lattice misfit.
1. T. Trimble, L. Tang, N. Vasiljevic, N. Dimitrov, M. van Schilfgaarde, C. Friesen, C.V. Thompson, S.C. Seel, J.A. Floro, K. Sieradzki, Phys. Rev. Let. 95, 166106 (2005).
2. S.-E. Bae, D. Gokcen, P. Liu, P. Mohammadi, S. R. Brankovic, Electrocatal. 3, 203 (2012).
3. G. R. Stafford, and U. Bertocci, J. Phys. Chem. C, 113 (1), 261 (2009).
4. A. L. Shull and F. Spaepen, J. Appl. Phys. 80, 6243 (1996).