SUMMARY

Modeling Micro- and NanoElectroMechanical Systems (MEMS and NEMS) has created the need for new modeling techniques that can deal efficiently with geometric complexity and scale dependent effects. Multiscale modeling couples continuum solvers with detailed microscale models to provide accurate and efficient models of complete systems. This thesis presents the development of multiscale modeling techniques for non-equilibrium microscale gas phase phenomena, especially thermally driven microflows. The three necessary components for multiscale modeling are efficient and accurate microscale and continuum models and a coupling scheme. Much of the research of this thesis focuses on developing an efficient low-noise DSMC based technique for non-equilibrium problems. The resulting Octant Information Preserving DSMC (OIP-DSMSC) method is able to predict microscopic flow fields induced by non-equilibrium systems which previous IP-DSMC methods fail to capture, including phenomena such as thermal transpiration. In addition the OIP-DSMC provides a useful tool for exploring rarefied gas transport phenomena which may lead to a greater physical understanding of these phenomena and new concepts for their utilization in practical engineering systems. Multiscale modeling will be demonstrated utilizing the OIP-DSMC for the microscale model and a 2D BEM solver for the continuum model coupled with a modified Alternating Schwarz coupling. Thermal Sensing Atomic Force Microscopy (TSAFM) provides an interesting application for the modeling techniques developed in this thesis. TSAFM relies on gas phase heat transfer between heated cantilever probes and the scanned surface to determine the scan height, and thus the surface topography. Data interpretation requires accurate models of the heat transfer phenomena. This thesis presents results demonstrating the effect of subcontinuum heat transfer on TSAFM operation and explores the mechanical effects of the Knudsen Force on the heated cantilevers.