9625903 Seidman The tomographic atom probe (TAP) is a fundamental extension of the atom-probe field-ion microscope (APFIM or simply atom probe), which provides atomic-resolution depth profiling capability in one dimension. While the TAP yields three- dimensional (3D) chemical profiles in direct lattice space at a lateral spatial resolution of 0.2-0-5 nm, and a depth resolution equal to the interplanar spacing along the direction being probed (<0.2-0.3 nm). The TAP's principal features are: subnanometric 3D images with quantitative compositional information on an atomic scale, multi-impact position sensitive detector (PSD) with 100 anodes that allows for the detection of up to 8ions per field- evaporation pulse, an average detection rate of 1 ion pulse -1 and a pulse frequency of 100 Hz, a million individual atoms can be collected and analyzed in three hours employing a modern work station, high mass resolution (m/m = 200) with atomic scale images in direct lattice space. There is no other instrument with the above unique experimental capabilities of the TAP. This award provides support for the acquisition of a multi- impact PSD, associated data acquisition electronics, a work station, and an advanced visualization program for creating 3D images from the collected data. This TAP will be part of a facility that is named "The Chicago-Area Consortium for Atomic-Scale Chemistry"; in addition to Northwestern University, the University of Illinois' Materials Research Laboratory and Argonne National Laboratory's Materials Science Division are involved. %%% The proposed research centers around problems that require a knowledge of interfacial chemistry on an atomic scale, and chemical information associated with 0.5-2 nm size nuclei that form in the decomposition of alloys of technological importance. ***
