Seeman-Bohlin X-ray diffractometer for thin films

A focusing Seeman-Bohlin diffractometer of 20 inches diameter has been designed and constructed with special emphasis on its suitability for the examination of polycrystalline thin films. The apparatus employs a pyrolytic graphite monochromator crystal to obtain a high-intensity beam, which is incident upon the specimen at a selected low angle of incidence, so as to increase the path length through the sample. Atmospheric scattering of the diffracted rays is reduced substantially by the use of a helium chamber. The attitude of the X-ray counter is controlled by a simple servomechanism, without the use of lever arms. The unit is operated by a data acquisition and control system, and executes a preset step-scan with data collection on punched cards or paper tape. The performance of the diffractometer is illustrated by a variety of measurements made on metallic films of 150 to 8000 Å in thickness. The results demonstrate the utility of the diffractometer for precise lattice parameter measurements, for the determination of internal strains and crystallite size, and as a tool for studying reactions in multicomponent or multilayer films.