Entropic Confinement of Colloidal Spheres in Corners on Silicon Substrates

We have investigated depletion effects among dispersed, submicron, polystyrene spheres of two different sizes near a faceted silicon substrate. The larger spheres were confined to the corners where two silicon facets intersected (as where a wall meets a floor). The entropic confinement potential increased by 1.2kBT when the small-sphere volume fraction was increased by 14% to 0.37. Large-sphere crystallites nucleated along the corner and grew out along the flat surfaces before crystals nucleated on the flat surface or in the bulk. The results demonstrate a novel way to sort particles or to organize them along geometric features in a substrate for microfabrication.