Grain Orientation Mapping of Polycrystalline Organic Semiconductor Films by Transverse Shear Microscopy


Vivek Kalihari,1 E. B. Tadmor,2 Greg Haugstad3 and C. Daniel Frisbie1

1Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, 2Department of Aerospace Engineering and Mechanics, University of Minnesota 107 Akerman Hall, 110 Union St SE, and 3Characterization Facility, Institute of Technology, University of Minnesota, 100 Union Street SE, Minneapolis, Minnesota 55455

Abstract

The development of new microscopy methods to enhance understanding of the micro- or atomistic structure of materials is a recurring challenge for materials scientists. We demonstrate that a variant of lateral force microscopy (LFM), which we term transverse shear microscopy (TSM), produces striking images of grain shape, size, and crystallographic orientation in smooth, coalesced layers of polycrystalline organic materials. The most interesting aspect of TSM is its sensitivity to grain orientation, and TSM-generated Grain Orientation Maps allow convenient analysis of overall grain alignment and the distribution of high and low angle grain boundaries. The origin of transverse shear is related to the elastic anisotropy of individual crystallites, indicating that TSM contrast can be observed on any suitably smooth solid exhibiting a tensorial elastic modulus in the image plane. Thus, TSM represents a powerful method for visualizing microstructure in smooth, anisotropic crystalline films.