X-ray Nanoprobe - Modes of Operation

Modes of Operation

Transmission. 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.

Diffraction. By measuring X-rays diffracted from the sample, one can obtain local structural information, such as crystallographic phase, strain, and texture, with an accuracy 100 times higher than with standard electron diffraction.

Fluorescence. Induced X-ray fluorescence reveals the spatial distribution of individual elements in a sample. Because an X-ray probe offers 1,000 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.

Spectroscopy. In spectroscopy mode, the primary X-ray beam’s energy is scanned across the absorption edge of an element, providing information on its chemical state (XANES) or its local environment (EXAFS), which allows the study of disordered samples.

Polarization. Both linearly and circularly polarized X-rays will be available. Contrast due to polarization is invaluable in distinguishing fluorescence and diffraction signals and imaging magnetic domain structure by using techniques such as linear and circular dichroism and magnetic diffraction.

Tomography. In X-ray tomography, one of these modes is combined with sample rotation to produce a series of two-dimensional projection images, to be used for reconstructing the sample’s internal three-dimensional structure. This will be particularly important for observing the morphology of complex nanostructures.

In summary, a hard X-ray nanoprobe provides advantages such as being noninvasive and quantitative, requiring minimal sample preparation, giving sub-optical spatial resolution, having the ability to penetrate inside a sample and study its internal structure, and having enhanced ability to study processes in situ. Another important distinction from charged-particle probes is that X-rays do not interact with applied electric or magnetic fields, which is an advantage for in-field studies. The design of the nanoprobe beamline aims to preserve these potential advantages.