Wafer curvature and cantilever bending techniques have been used by the electrochemical community to examine stress development during electrochemical processing. Surface stress changes as low as 10−3 N/m can typically be resolved from cantilever electrodes immersed in solution and under potential control. Such resolution makes this measurement useful for examining virtually all aspects of electrochemistry; i.e., electrocapillarity, adsorption processes, underpotential deposition, electrodeposition, etc. Often these processes occur either simultaneously or in rapid succession and we are often limited to measuring the influence of the dominant process in the time-scale of the experiment. In the case of electrocapillarity (charge-induced stress), the figure of merit is the stress-charge coefficient (ς) which captures the fundamental surface mechanics associated with charging the electrode surface. It has been well documented in the literature that ς is influenced by the anion in solution and its concentration.1,2 However, a steady state measurement cannot separate the contributions of anion adsorption from that of simple capacitive charging.
Similar to electrochemical impedance spectroscopy (EIS) where electrochemical processes with different characteristic time constants can be separated, dynamic stress analysis (DSA) allows us to study the dynamics of any particular stress-generating process and link the stress to specific electrochemical and surface phenomena. We have demonstrated the technique by examining the electrocapillarity of both Pt and Au in HClO4 electrolyte.3,4 ς can be obtained from the following equation,
ς = jωYsZe
where Ze is the electrochemical impedance, Ys is the stress admittance (with units of N/(V-m), ω is the angular frequency, and j =√-1. In order to include adsorbate-induced contributions to the surface stress, one considers an equivalent circuit that adequately describes both the double layer and adsorption contributions to the electrochemical impedance. One can then obtain unique stress-charge coefficients that capture both electrocapillarity and anion adsorption as a function of potential. This will be demonstrated using (111)-textured Au cantilever electrodes in both sulfate and perchlorate electrolyte.
References
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R.N. Viswanath, D. Kramer, and J. Weissmüller, Langmuir, 21, 4604 (2005).
M. C. Lafouresse, U. Bertocci, C. R. Beauchamp, and G. R. Stafford, J. Electrochem. Soc. 159, H816 (2012).
M. C. Lafouresse, U. Bertocci, and G. R. Stafford, J. Electrochem. Soc. 160, H636 (2013).
Stress Analysis of Rotary Vibration of Rigid Friction Pile and Stress General Solution of Central Symmetry Plane Elastic Problem