Formation of images and surface relief gratings in photosensitive polymers containing SCN groups

Full Paper: Poly(4-vinylbenzyl thiocyanate) (PVBT) and a copolymer of styrene and 4-vinylbenzyl thiocyanate (PST-ca-VBT) were assessed as dual-tone imaging systems. These polymers change their refractive index under deep UV irradiation as a result of the photoisomerization of SCN to NCS groups. Subsequent modification of the illuminated zones with gaseous amines gave thiourea groups via an addition reaction. The post-exposure modification of the films with gaseous amines produced large increases of the film thickness (formation of negative images). This effect was utilized to produce surface relief gratings. Using contact lithography with lambda = 193 and 248 nm, gratings with periods Lambda = 300 and Lambda = 600 nm were obtained. Under selected experimental conditions, a nucleophilic substitution (S-N) of the SCN units in the unirradiated zones by amines was achieved (formation of positive images). Gratings of these types are of general interest for the setup of organic lasers based upon the principle of distributed feedback (DFB) as well as for holographic recordings.