Chemical analysis by high-angle hollow cone illumination

The high-angle hollow cone illumination realized in a conventional transmis sion microscope is known to suppress coherent contrast mechanisms. It is sh own that under suitable experimental conditions, orientation and strain con trasts are sufficiently suppressed to obtain a Z-contrast image. Various fa ctors, influencing the image intensity, are determined by a quantitative im age analysis of pure metals. Based on these measurements an incoherent mult iscattering model is generalized to binary alloys in order to describe the chemical image contrast and to determine the local composition of the speci men from an intensity measurement. To test the concept, the early stages of interdiffusion between thin films of Cu and Au are investigated. The resul ts demonstrate that a useful chemical analysis is possible, even in the cas e of nanocrystalline specimens. Complete composition profiles are determine d on a length scale of 10 nm. The spatial and chemical resolution of the me thod are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.