The Northwestern University Center for Atom Probe Tomography (NUCAPT) operates a CAMECA LEAP 4000X Si atom-probe tomograph (APT) to produce an atom-by-atom three-dimensional (3D) image of a sample, with sub-nanometer spatial resolution and a typically 150 x 150 x 500 nm3 analyzed volume, by simultaneous high resolution imaging and single-atom time of flight mass spectrometry. APT thus is particularly suited to study nano- or nanostructured materials: composition, size, and morphology of second-phase particles or precipitates, 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 buried interfaces. Specimen preparation of almost any material is now possible employing a dual-beam focused-ion beam (FIB) microscope, which also allows targeted sample preparation of a specific feature for APT analysis, such as a grain boundary or an individual transistor in a semiconductor device. In a correlative study, the very same sample can also be first characterized by transmission electron microscopy (TEM). To compare these atomic-scale experimental results with atomistic simulations on the same size scale, we use the VASP code for ab-initio atomistic calculations and Monte-Carlo simulations for understanding formation and evolution of specific microstructures. Thermocalc and MEDEA software packages are available for thermodynamic calculations and materials simulations. Specimen tips can also be prepared by electropolishing (metals). Ion beam sputter deposition creates thin film structures that aid with APT specimen preparation. A small arc melter is available for synthesizing alloys and compounds.