Microlithographic fabrication of structures

An optical device comprising:

• a substrate;
• and
• a diffraction pattern on the substrate, the diffraction pattern comprising a plurality of asymmetric structures extending from a common surface of the substrate, wherein each asymmetric structure of the plurality of asymmetric structures has a first side surface and a second side surface opposite the first side surface, wherein a profile of the first side surface is asymmetric with respect to a profile of the second side surface, wherein at least one asymmetric structure of the plurality of asymmetric structures has an asymmetric profile, and wherein the plurality of asymmetric structures are formed by a process comprising:
• applying a metal catalyst layer over a plurality of discrete structures under first conditions that cause the metal catalyst layer to asymmetrically cover the plurality of discrete structures such that at least a first portion of a first side of each structure of the plurality of discrete is free of the metal catalyst layer;
• after applying the metal catalyst layer, applying a masking material over the plurality of discrete structures under second conditions that cause the masking material to asymmetrically cover the plurality of discrete structures such that at least a second portion of a second side of each structure is free of the masking material, wherein the masking material comprises one of SiO2, Al2O3, or ZrO2;
• etching a first area of the plurality of discrete structures that is not covered by the masking material;
• stripping the masking material from the plurality of discrete structures;
• and
• wet etching a second area of the plurality of discrete structures with metal assisted chemical etching to yield the asymmetric structures,
• wherein:
• the first side surface of the at least one asymmetric structure extends linearly from the common surface to a top portion of the asymmetric structure,
• the second side surface of the at least one asymmetric structure comprises at least a first portion and a second portion, wherein:
• the first portion of the second side surface is angled with respect to the common surface at a first angle, wherein the first angle is a non-zero angle, and
• the second portion of the second side surface is angled with respect to the common surface at a second angle different from the first angle, wherein the second angle is a non-zero angle,
• the first portion extends linearly from the second portion of the side surface to the top portion of the asymmetric structure, and
• a plane extending along the first side surface and a plane extending along the first portion of the second side surface intersect above the top portion of the asymmetric structure.