1. A method of forming a predetermined pattern on a substrate which comprises (a) forming a thin (g-Ge.sub.x Se.sub.1-x) film on a solid substrate by vacuum vapor deposition wherein the angle of deposition is an angle between 5.degree. to about 85.degree. with respect to the normal, (b) masking a portion of said film with an ion beam penetration retarding masking material, (c) exposing the unmasked portion of the film to an ion beam at a voltage adapted to and with an ion dose sufficient to provide a substantial differential dissolution rate between the masked and unmasked portion of the film when developed with a solvent for said film, and (d) developing said film by removing the exposed portion of that film to uncover the corresponding portion of the substrate while the portion of said film which was masked during the exposure remains adhered to the substrate.