Center for Atom Probe Tomography (NUCAPT)

Cook Hall, 1086
Tel: (847) 491-7826

Facility Director: David M. Seidman, MSE
Facility Manager: Dieter Isheim, MSE

Vist the NUCAPT website here.

More information:
Subnanoscale analysis of metallic materials (PDF download)
Subnanoscale analysis of semiconducting materials (PDF download)
Subnanoscale analysis of biomaterials (PDF download)

Atom-probe tomography (APT) is a microanalytical instrument producing an atom-by-atom three-dimensional reconstruction of a sample, with sub-nanometer resolution with a typical analyzed volume of about 150 x 150 x 500 nm3. APT is particularly suitable to investigate nano-structured materials. Typical micro- and nanostructural features studied are: composition and morphology of second-phase precipitates or small clusters of solute atoms, compositional variation in modulated structures, multi-layer thin-film structures, dopant profiles of semiconductor structures (transistors), and analysis of the chemistry and topology of internal interfaces. Specimen preparation of almost any material is now possible employing a dual-beam focused-ion beam (FIB) microscope, which allows targeted sample preparation of a specific feature, such as a grain boundary or an individual transistor in a semiconductor device.

EQUIPMENT:

1. LEAP 4000XSI manufactured by Imago Scientific Instruments, Madison, Wisconsin: This instrument, a local electrode atom-probe (LEAP) tomograph, has an ultrafast detector capable of collecting up to 360 million ions per hour. Ions are evaporated from a sample’s surface either by voltage or ultraviolet (UV) laser pulses, which allows for the analysis of a broad spectrum of materials: metals, semiconductors, ceramics, biominerals, organic and biological samples, albeit with different degrees of success. A computer reconstructs a three-dimensional image of a sample with both the chemical identities and positions of individual atoms, with a depth resolution equal to the interplanar spacing, which can be as small as 0.1 nm: the lateral resolution in an atomic plane is between 0.3 to 0.5 nm. The microelectrode in the LEAP tomograph allows the analysis of microtips, prepared by FIB (ion-milling and/or the lift-out technique to target specific features), or wire microtips prepared by conventional electropolishing. Additionally, digital field-ion microscopy can be performed with this instrument..

2. A specimen preparation laboratory for preparing needle-shaped specimens for atom-probe tomography. Our lab features a high-speed precision saw to cut specimen blanks, an electropolishing station with a high-resolution stereo-microscope, and a commercial Simplex Electropointer automated electropolisher.

3. An Ion-beam sputter system (IBS/e) manufactured by South Bay Technologies. This system is utilized for depositing high-quality thin films for: (1) generating multi-layer structures; and (2) to assist with LEAP-tip preparation by FIB milling where the thin-film deposit marks and protects a sample’s surface when milling with gallium ions. The ion-beam sputter system does not use magnetron-based sputter guns and therefore is suitable for the deposition of magnetic materials, such as iron, nickel, and cobalt.

4. Arc Melter: Arc-melting is a fast and clean way of producing alloys of electrically conductive materials. The raw materials are placed on a water-cooled hearth in a vacuum chamber. After evacuation, the chamber is re-filled with Argon to be employed as an inert working gas. An electric arc is produced with a pointed electrode which heats the raw materials above their melting point, fusing them into an alloy droplet. The facility operates a MAM-1 arc melter manufactured by Edmund Bühler GmbH, Germany. The arc melter can process about 10-15 grams of material in one melting charge. A specially designed hearth allows for suction casting into a 3 mm diameter mold.

5. NUCAPT computing facility comprising

5.1 An 8 TB data server
5.2 Five individual high-end PC workstations for running IVAS for LEAP-data reconstruction and analysis
5.3 One workstation for Thermocalc, DICTra and MedeA simulations
5.4 Microway AMD Quad-core Opteron cluster with 31 nodes and 62 quad-core processors, with a total of 248 CPUs, 372 GB shared-memory and high-quality fiber- optical DDR InfiniBand Network for large-scale parallel calculations. This cluster is currently optimized for performing VASP DFT calculations and lattice kinetic Monte Carlo simulations.

The Materials Research Science and Engineering Center (MRSEC) is supported by the National Science Foundation under NSF Award Number DMR-1121262. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation.
© 2012 Northwestern University