The origin of surface stress experienced by a micro-cantilever beam

We study the origin, cause and factors influencing surface stress, experienced by a micro-cantilever beam. The adsorption based biosensor experiences surface stress caused by surface reconstruction, substrate mediated interaction, charge density redistribution and inter-molecular repulsive forces. The surface stress developed, is calculated by applying the Stoney Equation. The COMSOL Multiphysics software was used in analyzing and studying the dynamics of the micro-cantilever beam. The deflection of the beam should not exceed half the thickness value, to maintain accuracy of Stoney Equation and avoid non-linearity. It was observed that surface stress was influenced by coverage of the adsorbate relative to substrate, molecular mass of adsorbate and the pair interaction energy. The paper also demonstrates the use of Langmuir adsorption isotherm to study the adsorption kinetics and immobilization affects on surface stress. We have found that the surface free energy technique of measuring surface stress is best suited due its non dependence on material properties.