The Complementarity of NEXAFS Microscopy and Soft X-Ray Resonant Scattering
Harald Ade
Department of Physics, North Carolina State University
NEXAFS microscopy and resonant scattering are complementary soft x-ray techniques that offer high intrinsic contrast to image materials in real space or characterize the structure function in reciprocal space, respectively. Furthermore, the high contrast is strongly photon energy dependent and correlated to the chemical moieties present in the sample, thus allowing compositionally sensitive characterization. The carbon, nitrogen and oxygen NEXAFS is particularly sensitive to composition, and NEXAFS microscopy and resonant scattering are thus excellent tools to characterize organic soft condensed matter and organic/inorganic hybrid materials.
Presently, NEXAFS microscopy is limited in spatial resolution to about 35 nm due to limitations in zone plate optics. The increased brightness of an ERL offers a number of new pathways forward: i) it would allow different zone plate manufacturing trade-offs, pushing the spatial resolution below 10 nm at the cost of efficiency, or ii) data acquisition times could be shortened to allow time-resolved imaging. However, since X-rays are ionizing, radiation damage will be a limiting factor for some applications. As the spatial resolution Δr is improved an increase in dose of at least (Δr)-2 is required. This limitation is an issue even for novel developments such as coherent imaging techniques with absorption contrast, and can only partially avoided by using phase contrast. Reducing data acquisition times for dynamic studies poses serious technical challenges. We will explore and delineate the possibilities and limitations.
In contrast to real space imaging, resonant scattering can provide ensemble average morphological information with the advantage of spreading the radiation dose over a much larger total sample volume. Resonant scattering methods might thus have intrinsic advantages over real space methods to exploit the increased brightness of an ER and should be particularly important as a complement to conventional x-ray scattering to provide dynamic information from a wide range of multicomponent nano-assemblies/systems. An extension of soft x-ray resonant methods to resonant soft x-ray photon correlation spectroscopy might be a particular interesting development that will be enabled by the proposed ERL.
