One of ordinary skill in the art will appreciate that substantially planar boundary surfaces 27 and 127 may be formed by immersing (e.g., dipping, spraying, or otherwise initiating contact between) a first selected region of the polycrystalline diamond layer 20 and a liquid (e.g., an acid or other solvent for the catalyst) and subsequently immersing (e.g., dipping, spraying, or otherwise initiatin