An energy conservation approach to adsorbate-induced surface stress and the extraction ofbinding energy using nanomechanics

Abstract

Surface stress induced by molecular adsorption in three different binding processes has beenstudied experimentally using a microcantilever sensor. A comprehensive free-energyanalysis based on an energy conservation approach is proposed to explain the experimentalobservations. We show that when guest molecules bind to atoms/molecules on amicrocantilever surface, the released binding energy is retained in the host surface, leadingto a metastable state where the excess energy on the surface is manifested as an increase insurface stress leading to the bending of the microcantilever. The released bindingenergy appears to be almost exclusively channeled to the surface energy, andenergy distribution to other channels, including heat, appears to be inactive forthis micromechanical system. When this excess surface energy is released, themicrocantilever relaxes back to the original state, and the relaxation time dependson the particular binding process involved. Such vapor phase experiments wereconducted for three binding processes: physisorption, hydrogen bonding, andchemisorption. Binding energies for these three processes were also estimated.