Pattern wise imaging

In the 1960s, there was already a forerunner of photochemically induced phase transition in LC (20). When mixtures of cholesteryl iodide and cholesteryl bromide with cholesteryl nonanoate were exposed to UV irradiation, the helical pitch of cholesteric LC changes as a result of photodecomposition of the halides. The reflected color shifts gradually to red with progression of photodecomposition. Pattern-wise imaging was demonstrated but the image was blurred within 15 min. since LC of small molecules is a viscous fluid. 

The basic steps of the lithographic process are shown schematically in Figure 1. The example shown corresponds to photolithography in which the photosensitive resist or photoresist is applied as a thin film to the substrate (Si02 on Si) and subsequently exposed in an image-wise fashion through a mask. The mask contains clear and opaque features that define the circuit pattern. The areas in the photoresist that are exposed to light are made either... 

Our approach is validated by comparison of the treatment time when the sample is treated continuously and step-wise for snapshot imaging. Since in both cases the complete orientation of the stripe pattern along the electric field vector is achieved within 6-7 h, we concluded that the quasi in situ treatment has no significant effect on the mechanism of the microdomain alignment and ordering. 

In industrial practice, these methods (and others) are used to create image-wise patterns of photopolymers using either direct (often laser-based) writing, or using imposition masks to delineate light and dark regions (Fig. 20.1). 

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