X-Ray Microscopy Facilities
The Hard X-Ray Nanoprobe (HXN) facility provides scanning fluorescence, scanning diffraction, and full-field transmission and tomographic imaging capabilities with a spatial resolution of 30 nm over a spectral range of 6-12 keV.
Modes of Operation
Full-Field Transmission Imaging and Nanotomography
X-ray transmission imaging uses both the absorption and phase shift of the X-ray beam by the sample as contrast mechanisms. Absorption contrast is used to map the sample density. Elemental constituents can be located by using differential edge contrast in this mode. Phase contrast can be highly sensitive to edges and interfaces even when the X-ray absorption is weak. These contrast mechanisms are exploited to image samples rapidly in full-field transmission mode under various environmental conditions, or combined with nanotomography methods to study the three-dimensional structure of complex and amorphous nanomaterials with the HXN.
Scanning Fluorescence X-Ray Microscopy
In scanning X-ray fluorescence microscopy, the spatial distribution of the elements in a sample are mapped by scanning a nanofocused X-ray spot over it as the emitted fluorescence X-rays are measured by an energy-dispersive detector. Characteristic fluorescence X-rays emitted by the sample uniquely identify the elements present in it with 1000 times greater sensitivity than electron probes; the incident photon energy can also be tuned over absorption edges to analyze the sample's chemical state. Nanoscale elemental and chemical mapping with the HXN enables understanding material properties, such as trace contaminants, second-phase particles, defects, and interfacial segregation.
Scanning Nanodiffraction and Bragg Ptychography
Nanoscale structural information, such as crystallographic phase, strain, and texture, are obtained at the HXN by measuring the X-rays diffracted by a crystalline sample as a nanofocused X-ray spot is scanned over it. Bragg ptychography, a new imaging technique based on coherent diffraction and iterative phase retrieval, provides nanoscale structure and lattice strain information within crystalline samples at a resolution well beyond that of X-ray focusing optics. Scanning nanodiffraction and Bragg ptychography are in high demand at the HXN as tools for probing crystal ordering, defects, and phase transitions in nanomaterials.
In Situ/In Operando Experiments
The working distance between the X-ray focusing optics and the sample is typically 10-20 mm, enabling a variety of in situ and in operando experiments. A heating/cooling specimen stage supports variable temperature experiments with the HXN over a temperature range of 95-525K with a step-size of 0.01 K and a stability of 0.005 K. The absolute position drift is less than ~10 nm/h.