  The effect of surface stress on the stiffness of cantilever beams remains an
outstanding problem in the physical sciences. While numerous experimental
studies report significant stiffness change due to surface stress, theoretical
predictions are unable to rigorously and quantitatively reconcile these
observations. In this Letter, we present the first controlled measurements of
stress-induced change in cantilever stiffness with commensurate theoretical
quantification. Simultaneous measurements are also performed on equivalent
clamped-clamped beams. All experimental results are quantitatively and
accurately predicted using elasticity theory. We also present conclusive
experimental evidence for invalidity of the longstanding and unphysical axial
force model, which has been widely applied to interpret measurements using
cantilever beams. Our findings will be of value in the development of micro-
and nanoscale resonant mechanical sensors.
