Vapor-Deposited Polyimide for Freestanding Multilayer X-ray Filters

Freestanding metallized polyimide films have become a standard for soft x-ray filters. The strength and thermal stability of polyimide has been used to advantage in producing increasingly larger and thinner filters. To continue this trend and to improve the durability and throughput of filters for current instruments, it is proposed to develop a new generation of freestanding thin film filter designs by incorporating multilayer techniques. Multilayer films consist of hundreds or thousands of alternating layers, and can be considerably stronger than the component materials. To use this technique for building optical filter foils, the polyimide fabrication process must be changed from a solution-cast method to vapor deposition. Vapor depositing polyimide could have several advantages in x-ray filter fabrication. It would permit the ultrathin layering required for multilayer film construction and would reduce film contamination resulting from vacuum cycling. The use of vapor deposition to produce freestanding polyimide/metal multilayer films may result in even stronger and thinner soft x-ray filters, which would allow larger and higher-performance instruments to be realized.