Enhanced columnar structure in CsI layer by substrate patterning

Columnar structure in evaporated can be controlled by patterning substrates as well as varying evaporation conditions. Mesh-patterned substrates with various dimensions were created by spin-coating polyimide on glass or amorphous silicon substrates and defining patterns with a standard photolithography technique. CsI(Tl) layers 200-1000 mu m were evaporated. Scintillation properties of these evaporated layers, such as light yield and speed, were equivalent to those of the source materials. The spatial resolution of X-ray detectors consisting of these layers and a linear array of Si photodiodes was evaluated by exposing them to a 25- mu m narrow beam of X-rays. The results obtained with 200- mu m-thick CsI layers coupled to a linear photodiode array with 20-dots/mm resolution showed that the spatial resolution of CsI(Tl) evaporated on patterned substrates was about 75 mu m full width at half maximum (FWHM) whereas that of CsI(T) on flat substrates was about 220 mu m FWHM. Micrographs taken by scanning electron microscopy revealed that these layers retained the well-defined columnar structure originating from substrate patterns.<>