Imaging ion microscopy

Abstract

Ion induced sputtering of materials can be used to generate images which contain morphological and chemical information. This method of image generation has several key advantages over other techniques. All elements can be detected and imaged. Discrimination among the various isotopes of the elements is possible with sufficiently high mass resolution. Analytical sensitivity is high for many elements, especially those of biological importance such as Na, K, Mg, Ca. The extension of these principles to imaging of molecular ion species is straightforward. Since the sputtering of the sample surface causes erosion, the distribution of elements as a function of depth can be investigated. Depth profiling, in conjunction with imaging is a powerful technique for solving problems of multielement microcharacterization of materials. This technique, which the authors have dubbed Image Depth Profiling, (IDP) also forms the basis for three dimensional reconstruction of elemental distributions within microvolumes of materials.In imaging ion microscopy, the image is acquired in a manner reminiscent of light microscopy. The analogy is depicted in figure 1. An energy homogeneous beam of primary ions irradiates the sample surface and sputtered secondary ions are focused directly on a microchannel ion to electron conversion plate. The primary ions are analogous to the illuminating photons of light microscopy and the secondary ions are analogous to the transmitted or reflected photons.