Transverse Shear Microscopy (TSM), with its sensitivity to grain orientation, was studied to show that it is a powerful approach to probe the microstructure of ultra-thin crystalline organic films. Monolayers of pentacene and other organic semiconductors were grown by thermal evaporation of the corresponding source material onto insulating substrates under vacuum pressure of δ6×10-7 Torr and deposition rates of δ0.0i Ȧs-1. The probes used for AFM measurements were silicon nitride V-shaped cantilevers with integrated contact mode tips fabricated by Veeco Metrology, USA. Pentacene monolayers were grown on SiO2 at different substrate temperatures at a constant deposition rate of δ0.0i Ȧs -1, to determine the kinetics of grain growth. This nucleation energy can be used in conjunction with conventional diffusion-limited growth models to estimate the activation energy of diffusion.