A High-Precision Kossel Camera for Research and Routine Analytical Use

Abstract

AbstractA transmission Kossel camera unit has been built for the Cambridge Mark II electron probe. It replaces the standard specimen stage assembly, and is useful also for regular electron probe microanalysis and projection microradiography.Its design extends the attainable precision of lattice parameter measurements to near-ultimate practical limits, while providing special features for research studies, and speed, flexibility, and convenience of operation for routine analytical use on a wide variety of specimens, particularly semiconductor materials.The most significant feature is a novel X-ray projection box structure which casts index-mark images on each pattern. From these images, the exact source distance and pattern-center positions are determined for each exposure. Precise crystal-piane spacings can be measured, therefore, from conic intersections anywhere on the exposed area of the plate. Since the conics need not be in any particular favorable location, it is not necessary to achieve an exact orientation of the sample. Precise lattice dimensions in several different crystallographic directions are obtainable from a single pattern exposure if their various sensitive conics appear anywhere on the pattern. The need for a reference measurement of “fixed” conics is eliminated, being replaced by a much more precise measurement of very sharp, high contrast, widely spaced index-mark images.Camera length is 12.5 cm and exposed pattern area is 9.4 cm square. Glass photo plates are used to eliminate errors due to film shrinkage and warp. A removable cassette holds ten 4″×5″ glass plates, interchangeableiunder vacuum. The X-ray shutter has ten positions for making exposure-time sequences. The specimen stage is thermostatted to ±0.01° C, controllable from room temperature up to 200° C, and;temperature is measured to +0.005° C. Stage movement range is 25mmx50mn, with coordinates shown on external digital dials. Interchangeable inserts provide for a wide range of specimen sizes and shapes. Electrical contacts to the specimen are available.An externally adjustable plate holds 24 different target foils or target-filter combinations for pseudo-Kossel patterns. An open position provides for true Kossel work and for scatteredelectron image viewing.