The Application of a Model Function Describing Beam Broadening to Elemental Analysis of Rapidly Varying Concentration Gradients

Abstract

As microanalysis by X-ray spectrometry in STEM is increasingly applied in materials science, a particular set of problems is being identified in which beam spreading in the sample and the associated concept of the X-ray spatial resolution are crucial to the interpretation of experimental data. These problems include the investigation of solute segregation to, or depletion near, grain boundaries, the determination of composition profiles across dendrite cell walls, especially in rapidly solidified material, composition determination in phase separated systems where the separation takes place on a fine scale, as for example in spinodal decomposition, and many other problems involving small precipitates or interfaces between phases. We intend to discuss beam spreading separately at this meeting. We propose the use of a model, parameterized function to describe beam spreading for application to the problems mentioned above. With this description, an analytic expression for the X-ray emission from a region of known or modeled composition variation can be obtained, being proportional to the convolution of the two functions describing the electron intensity distribution and the concentration variatioa For many simple cases this expression can be simply solved, either analytically or with the aid of a small computer or programmable calculator.