X-Ray Microscopy

Group Leader: Ian McNulty

The Center for Nanoscale Materials' Hard X-Ray Nanoprobe at sector 26 of the Advanced Photon Source is a next-generation hard X-ray microscopy and X-ray imaging beamline with the highest spatial resolution. For general user experiments, the system provides fixed-energy X-ray fluorescence, X-ray diffraction, Bragg coherent diffraction, and transmission imaging with hard X-rays at a spatial resolution of 30-50 nm. The instrument is key to the specific research areas of the CNM, and is also of general utility to the broader nanoscience community in studying nanomaterials and nanostructures, particularly for embedded structures.

The combination of diffraction, fluorescence, and transmission contrast in a single instrument provides unique characterization capabilities for nanoscience. The instrument has demonstrated a spatial resolution of better than 30 nm in X-ray transmission and 40 nm in scanning probe mode. Advanced X-ray optics are expected to improve the spatial resolution further. The nanoprobe currently operates in the energy range between 8 and 12 keV. The working distance between the focusing optics and the sample is typically in the range of 10-20 mm. A heating/cooling specimen stage offers variable temperature hard X-ray microscopy over a temperature range of 95-525K at a step of 0.01 K and a stability of 0.005 K.

Available Modes of Operation

Transmission and Tomography

In this mode, either attenuation or phase shift of the X-ray beam by the sample can be measured. Absorption contrast can be used to map the sample's density. Particular elemental constituents can be located using measurements on each side of an absorption edge to give an element-specific difference image with moderate sensitivity. Phase-contrast imaging can be sensitive to internal structure even when absorption is low and can be enhanced by tuning the X-ray energy. X-ray tomography collects in transmission mode, is used to study the internal three-dimensional structure, and is particularly important for observing the morphology of complex nanostructures.

Diffraction

By measuring X-rays diffracted from the sample, one can obtain local structural information, such as crystallographic phase, strain, and texture, with accuracy 100 times higher than with standard electron diffraction. Coherent diffraction methods in Bragg geometry provide information on subregions of the sample inside the focal spot.

Fluorescence

Induced X-ray fluorescence reveals the spatial distribution of individual elements in a sample. Because an X-ray probe offers 1000 times higher sensitivity than electron probes, the fluorescence technique is a powerful tool for quantitative trace element analysis, important for understanding material properties such as second-phase particles, defects, and interfacial segregation.

Research Activities

• Hard X-ray nanoprobe
• Highest-resolution optics for hard X-rays
• Time-resolved stroboscopic measurements
• Full-field imaging
• Fixed-energy scanning probe fluorescence, diffraction, and transmission phase contrast imaging