THE EFFECT OF SPECIMEN TILT ON THE MEASUREMENT OF FILM THICKNESS AND COMPOSITION BY BACKSCATTERED ELECTRON IMAGE-CONTRAST

The charge thickness of a film measures the number of nuclear charges per square metre of the film and is simply related to its mass thickne ss. It is possible to determine the charge thickness and composition o f a thin film of a binary alloy on a substrate of a different material by comparing the contrast k(E) of backscattered electron images from the film and from a bulk reference specimen, where E is the energy of the electron beam. The method has been previously applied to specimens which were perpendicular to the electron beam. It is shown that the m ethod also applies to specimens tilted by up to 40-degrees provided th at a correction factor of sec theta is applied, where theta is the ang le of tilt of the specimen, i.e. the angle between the normal to the s pecimen face and the direction of the electron beam. The correction ha s been tested for films in the mass thickness range (1.0-4) X 10(-3) k g m-2.