Facile method to align crystalline needles composed of organic semiconducting materials using a balance between centrifugal and capillary forces

Methods to align one-dimensional microstructures composed of organic materials have attracted much attention because of their potential applications to devices such as field-effect transistors. Although dip coating is one of the methods (using self-assembly) used for the purpose, its disadvantage is that a larger amount of the material dissolves in the solution than what actually gets deposited on substrate. In this study, we developed a novel method that requires a small amount of precursor solution. By placing a polydimethylsiloxane block on a glass substrate and rotating the substrate using a spin coater, a small amount of the precursor solution was confined in a narrow region along the foot of the block. When we used an organic semiconducting material, 9,10-dibromoanthracene, as a solute, aligned and roughly oriented crystalline needles were precipitated. The thicknesses and lengths of the crystalline needles were controlled by the composition of the solvent and the rotation speed.