Operando Pattern-Enhanced Resonant Scattering for Sub-Nm Interfacial “Spectromicroscopy”­ of Energy Materials

Abstract

The advent of highly precise nanofaborication tools has enabled the development of the next generation of mesoscale energy materials, but it requires concomitant progress in the characterization techniques used to address the new challenges and questions inherent to their interfacial behavior at this scale. We present a powerful, yet simple, patterning approach for interface characterization that takes advantage of the physical processes intrinsic to small angle resonant X-ray scattering in order to 1) decouple the bulk from the interface scattering signal, 2) enhance the strength of said signal, and 3) collect site-specific absorption spectra. In addition to the reconstructing the thickness and shape of the interfacial layer, changes in scattering contrast as a function of energy may be tracked in order to produce a full site-specific x-ray absorption spectrum that can identify small, yet vital, fluctuations in local chemistry. In addition, unlike nm-resolution microscopic techniques, the highly sensitive spatio-chemical information obtained via scattering processes doesn't require a highly focused beam whose flux is more likely to inadvertently affect the chemical reactions at the interface, thus making it more amenable to in-situ/operando characterization. In this presentation, we demonstrate the ability to selectively probe the interfacial regions of inorganic materials used throughout the fields of energy conversion and storage with nm-scale precision. we leverage a newly-developed in-situ cell for gas/liquid flow and electrical biasing that is compatible with many "soft" and "tender" X-ray beamlines and use it conduct an operando study of Ni/Ni(OH)2 core/shell system undergoing cycling under aqueous conditions. We find that the pattern-enhanced RSoXS approach enables the monitoring of the interfacial region's local morphology as it is electrochemically charged and discharged with millisecond time resolution and sub-nm precision, thus shedding quantifiable insights into the kinetics of the OH- intercalation process. In addition, the Ni L-edge XAS from the metal bulk region that is directly decoupled from that from the hydroxide surface is consistent with previously reported spectra. We will also reveal preliminary results showing how this technique may be applicable to study a variety of interfaces, even if the junction of interest is buried under another solid, liquid, or gas material. Finally, we describe the practical considerations of this characterization technique as it is extended to other material systems, patterning designs, sources, etc.