Bent crystal Laue analyser combined with total reflection fluorescence X-ray absorption fine structure (BCLA + TRF-XAFS) and its application to surface studies

Abstract

A bent crystal Laue analyser (BCLA) is an X-ray energy analyser used for fluorescence X-ray absorption fine-structure (XAFS) spectroscopy to separate the fluorescence X-ray emission line of a target atom from the elastic scattering X-rays and other fluorescence emission lines. Here, the feasibility of the BCLA for total reflection fluorescence XAFS (TRF-XAFS), which has a long X-ray footprint on the substrate surface owing to grazing incidence, was tested. The focal line of the BCLA was adjusted on the X-ray footprint and the XAFS signal for one monolayer of Pt deposited on a 60 nm Au film with high sensitivity was obtained. Although range-extended XAFS was expected by the rejection of Au fluorescence arising from the Au substrate, a small glitch was found in the Au L 3 edge because of the sudden change of the complex refraction index of the Au substrate at the Au edge. This abnormal spectrum feature can be removed by reflectivity correction using Au foil absorption data. BCLA combined with TRF-XAFS spectroscopy (BCLA + TRF-XAFS) is a new technique for the in situ surface analysis of highly dispersed systems even in the presence of a liquid overlayer.

Abnormal Metal Bond Distances in PtAu Alloy Nanoparticles: In Situ Back-Illumination XAFS Investigations of the Structure of PtAu Nanoparticles on a Flat HOPG Substrate Prepared by Arc Plasma Deposition

“…The L 3 edge is superior to the K-edge because of the availability of stronger X-ray sources emitted from the undulator and the high energy resolution; however, the Pt and Au L 3 edges overlap because of their close proximity. In our previous work, , we demonstrated that the BCLA can completely separate the Au L α and Pt L α fluorescence X-rays, enabling an analysis of the Pt XAFS in the k -range beyond 10 Å –1 . Note that the Au effect was not observed because the amount of Au was so small that its incident X-ray absorption and the inelastic scattering of Au fluorescence X-ray were negligible.…”

“…(4) The interference of the L 3 edges of Pt and Au can be eliminated by separating the Au and Pt fluorescence Xrays. 46 In the high-energy-resolution fluorescence detection (HERFD)-empowered back-illuminated X-ray absorption near-edge structure (HERFD + BI-XANES) method, another type of crystal monochromator is adopted to reduce the lifetime broadening effect and obtain high-energy-resolution XANES spectra that provide more precise information about the electronic state. HERFD + BI-XANES spectra can be obtained by replacing the BCLA with a Johann-type crystal analyzer.…”

“…The BCLA + BI-XAFS technique offers four main advantages in the analysis of PtAu nanoparticles: The electrolyte thickness has no limitation because fluorescence X-rays are detected from the backside of the substrate window, minimizing the effects of absorption and elastic scattering by the electrolyte. In situ measurements can be carried out under electrochemical conditions to characterize the structure of PtAu nanoparticles under controlled electrochemical conditions. The HOPG surface is atomically flat, which enables characterization via surface science techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The interference of the L 3 edges of Pt and Au can be eliminated by separating the Au and Pt fluorescence X-rays …”

“…The interference of the L 3 edges of Pt and Au can be eliminated by separating the Au and Pt fluorescence X-rays …”

High Energy Resolution Fluorescence Detection of the Pt L3,2-Edge Whitelines of Pt-Based Bimetallic Systems: Implications for the Pt 5d5/2,3/2 Density of States

“…Herein, we report the high energy resolution fluorescence detection (HERFD) , of the Pt L 3 - and L 2 -edge XANES of a series of Pt-M (M = Ni, Cu) bimetallic samples by carefully selecting Pt L α fluorescence X-rays (L α1 = 9442.3 eV) with a spherically bent crystal analyzer (SBCA) in a Rowland Circle, − and we used it to record the HERFD–XANES. It should be noted that HERFD–XANES can also be obtained using similar analyzers such as the bent crystal Laue analyzer (BCLA, smaller size, lower energy resolution) − and cylindrically bent crystal analyzer (von Hamos-type, higher efficiency at the expense of sensitivity). − …”