Near total reflection x-ray photoelectron spectroscopy: quantifying chemistry at solid/liquid and solid/solid interfaces

Abstract

Near total reflection regime has been widely used in x-ray science, specifically in grazing incidence small angle x-ray scattering and in hard x-ray photoelectron spectroscopy (XPS). In this work, we introduce some practical aspects of using near total reflection (NTR) in ambient pressure XPS and apply this technique to study chemical concentration gradients in a substrate/photoresist system. Experimental data are accompanied by x-ray optical and photoemission simulations to quantitatively probe the photoresist and the interface with the depth accuracy of ∼1 nm. Together, our calculations and experiments confirm that NTR XPS is a suitable method to extract information from buried interfaces with highest depth-resolution, which can help address open research questions regarding our understanding of concentration profiles, electrical gradients, and charge transfer phenomena at such interfaces. The presented methodology is especially attractive for solid/liquid interface studies, since it provides all the strengths of a Bragg-reflection standing-wave spectroscopy without the need of an artificial multilayer mirror serving as a standing wave generator, thus dramatically simplifying the sample synthesis.

Deeper mechanistic insights into epitaxial nickelate electrocatalysts for the oxygen evolution reaction

“… 63 In this example, they demonstrated the oxidation and hydroxylation of an 8 nm thick Ni film while maintaining sub-nanometer depth resolution using the increasingly popular dip-and-pull geometry, which was introduced in the seminal paper by Axnanda, Crumlin et al 64 The same depth resolution can be now achieved using near total reflection geometry, which is especially attractive because it provides all the strengths of a standard SW-XPS without the need of an artificial multilayer mirror, making the technique more broadly applicable. 65 …”

“…63 In this example, they demonstrated the oxidation and hydroxylation of an 8 nm thick Ni film while maintaining sub-nanometer depth resolution using the increasingly popular dip-and-pull geometry, which was introduced in the seminal paper by Axnanda, Crumlin et al 64 The same depth resolution can be now achieved using near total reflection geometry, which is especially attractive because it provides all the strengths of a standard SW-XPS without the need of an artificial multilayer mirror, making the technique more broadly applicable. 65 For atomic-level spatial resolution, environmental transmission electron microscopy (ETEM) is a key development as it enables the direct imaging of surface processes on the atomic scale under exposure to ambient gases. When operated in H 2 O conditions, a thin water layer condensates on the perovskite surface, as pioneered in the group of Jooss.…”

Operando X-ray characterization of interfacial charge transfer and structural rearrangements

“…This methodology makes use of X-ray optical effects in the near total reflection (NTR), where the penetration depth of X-rays, and therefore the locus of photoelectron generation, can be tuned via Xray energy and incidence angle, resulting in a depth-resolution of ~1 nm. 139 4 Surface X-ray diffraction -Crystal Truncation Rod…”

In situ/operando investigation of catalytic and electrocatalytic interfaces

“…Jiang et al developed a model system for an all-solid-state Na 2 O 2 battery and performed operando analysis of the formation and decomposition of Na 2 O 2 in Na-O 2 batteries using both optical Raman spectroscopy and APXPS [23]. Finally, Martins et al presented a new methodology of using APXPS under a near total reflection regime for probing buried interfaces with extreme depth resolution, which can be highly valuable for solid/liquid interface study [24].…”