Developments toward a high speed, high mass resolution three-dimensional atom probe.

摘要

This work forms the underlying support for technological improvements and advances designed to increase the applicability of atom probe microscopy (APFIM).; In order to investigate the feasibility of using a beam of high energy electrons for pulsed field evaporation in AP, modeling of both the incoming electron trajectories and their resultant heating effects on the specimen has been done. Paraboloidal electric field distributions were used to calculate electron trajectories. Both modeling and experimental results indicate that electrons can be directed to a sample in the high fields typical of APFIM. The axial spatial shift of the specimen backscattered electron image with tip voltage compared favorably with the model results. Although the FIM image cannot be viewed during electron irradiation, single atoms have been observed on a W (011) pole both before and after brief electron irradiation and this suggests that no electron-beam-stimulated field desorption is taking place. Attempts to use higher electron currents, lower beam energies and to verify the position of the beam on the sample are ongoing.; A new type of AP, the "local-electrode atom probe" (LEAP) is currently under construction. It employs an electrode with a 1-10 {dollar}mu{dollar}m aperture to enhance and localize an electric field into a small region near the apex of a single "microtip" formed on a planar sample. By post-acceleration after the local electrode, high mass resolution may also be achievable. Microtip specimens have been prepared for LEAP analysis by the method of ion beam mask etching. Novel methods of fabricating non-local electrode atom probe samples with specific desired orientations are also proposed.; By combining three different techniques, a method of specimen preparation of BiSrCaCuO high temperature superconductor (HTS) material has been developed which requires less sophisticated equipment and meticulous specimen handling than previous methods. Samples can be routinely fabricated which have apex radii of curvature {dollar}le{dollar}50 nm. The characteristic "striped" image contrast of HTS materials, which is believed to arise from Cu-O planes, is shown to be present. Thus, it is likely that defects and compositional changes are not being introduced by the addition of the one or more preparation methods.