A process for forming trenches in a target material includes forming a masking layer onto the target material, where the masking layer comprises a material having high selectivity to a plasma etch gas adapted for etching the target material. A pattern is formed in the masking layer to expose portions of the target material and the sample is placed on an angle mount at a pre-determined angle relative to a cathode of a reactive ion etcher so that the target material is within a plasma dark space of the plasma etch gas. Ballistic ions within the plasma dark space form a trench structure within the target material. The process may further include repeating the steps of positioning the sample and etching the exposed portions of the target material with the substrate at a different angle to define a triangular structure.