The instrument to be purchased is a tomographic atom probe, which provides a three-dimensional image of a reconstructed lattice with atomic resolution where the chemical identity of each atom ! is identified. The specific instrument involved is a local-electrode atom-probe (LEAP) microscope manufactured by Imago Scientific Instruments of Madison, Wisconsin. The cost of this instrument is to be shared between the National Science Foundation's Major Research Instrumentation (MRI) program and the Office of Naval Research's DURIP program. Specifically, the NSF is to provide $500,000 toward the purchase of this instrument with $214,000 in cost matching funds provided by Northwestern University. The Office of Naval Research is to provide $590,000 with an additional $295,000 in cost matching funds from Northwestern University for a grand total o f $1,599,000 for the instrument and ancillary equipment. This instrument is to be the show case instrument of the Northwestern University Center for Atom-Probe Tomography (NUCAPT), which is directed by Professor David N. Seidman, Materials Science and Engineering Department. It will be used both for research purposes, as described in the proposal, for a wide range of materials , and also for the education of postdoctoral students, Ph.D. students, and undergraduate students, REU students, in this new characterization technique
The local-electrode atom-probe (LEAP) microscope provides a spatial resolution in depth of 0.1 nm and a lateral resolution of 0.2 to 0.5 nm; the latter depends on the particular crystallographic plane, {hkl}, being analyzed. It provides a wide angle view of the surface of a specimen, upwards of 60o to 70o, and is capable of examining a given specimen on a routine basis to a depth of 2 micrometers. The specimen can be pulsed at a frequency of 250,000 Hz to obtain collection rates exceeding 55 million atoms per hour. Thus, data sets of 100 million atoms are readily obtained from a single specimen. The LEAP microscope is an ultrahigh vacuum instrument that operates at an ambient pressure below 10(-10) torr! . A specimen exchange systems perm its six to twelve specimens to be stored under ultrahigh vacuum conditions, which permits the rapid exchange of specimens during the course of a day. The LEAP microscope is computer controlled and the data collected can be analyzed on-line, to a certain level of detail, to evaluate the progress of a run. In addition, software has been and is being developed to further process the collected data to obtain the maximum amount of physical information.
