A Theoretical Model Of Adsorption On Multiscale Silicon Cantilever Beams

Nanoelectromechanical system (NEMS) is a branch of nanotechnology. Attributed to the characteristics of nanotechnology, NEMS comes with high quality factor, extremely high fundamental resonance frequency, extremely low power dissipation and extremely small size and quality. Therefore, these attributes collectively make the nanocantilever suitable for immense potential applications. Crystalline silicon is considered to be the most important material for MEMS technology, and since silicon has excellent mechanical and thermal properties, the silicon nanocantilever has attracted the significant attention. When adsorption is confined to the cantilever, small molecule adsorption will directly cause the cantilever mechanical bending. When the cantilever is scaled down to nano level, the classical mechanical theory is inapplicable to this model, therefore, it is significant to establish a simple and accurate model to analyze the property of the nanocantilever. In this dissertation, based on a semi-continuum method, a theoretical model of the nanocantilever is established using the energy theory. The main work and innovations of this dissertation are described as following:(1) A theoretical model of the nanocantilever is developed when the adsorbed molecule is H2O. It is the first time to describe the effect of native oxide on the property of the nanocantilever. The model provides a simple and useful theoretical basis to analyze the property of the nanocantilever, based on a semi-continuum method, using the energy theory. The molecular dynamics simulation is used to verify the theoretical model.(2) A theoretical model of the nanocantilever is established when the adsorbed molecule is different. It is the first time to describe the effect of the adsorbed molecule on the property of the nanocantilever. A theoretical model of the nanocantilever is established when the adsorbed molecule is CH4, and then a theoretical model of the nanocantilever is established when the adsorbed molecule is different.(3) A theoretical model of the nanocantilever is established when the adsorption layer is different. It is the first time to describe the effect of the adsorption layer on the property of the nanocantilever. A theoretical model of the nanocantilever is established when the adsorption layer is Au, and then a theoretical model of the nanocantilever is established when the adsorption layer is different.(4) A theoretical model of the nanocantilever is established when the adsorbed molecule is different and the adsorption layer is different. The model is used to analyze the effect of the Si layer thickness and SiC>2 layer thickness on the property of the nanocantilever.All models presented here can obtain many physical parameters of the nanocantilever, such as the beam curvature, the displacement of the free end and the surface stress. They are in good agreement with molecular dynamics simulation results. The theoretical model of the nanocantilever may be valuable for the design and optimization of Si-based NEMS.