Molecular mechanics modelling and simulation of the adsorption-induced surface stress in micro-nano-cantilever sensors

Micro-nano-cantilevers have the exclusive potential to be an extremely sensitive sensor for chemical and biological detections. The mechanism of the sensor is that the adsorption-induced surface stresses cause the cantilever to bend, which can be measured by electronic or optical methods. In this paper, molecular mechanics method and theoretical energy minimization method are developed to study this bending behaviour. Molecular mechanics simulations were carried out on a homoepitaxy copper nano-cantilever to investigate the dependence of adsorption-induced surface stress on adatom concentration. Non-even pattern of development of adsorption-induced surface stress as adatom concentration increases was observed in the present atomistic simulations. To study the bending of micro-cantilever induced by adsorption, e. g. mercury adsorption on gold-coated cantilevers, the total energy consisting of atomic interaction energy of elastic bending energy is minimized. The Lennard-Jones model is employed to represent the interaction between mercury and gold atoms. Based on Dareinga's model, we developed a model with more atoms and considered the periodic boundary conditions. Calculated deflections with the proposed new model agree better with measured deflection data. This discussion can contribute to our knowledge base about mechanisms of surface stress and micro-nano-cantilever bio-sensor.