2D-RIXS: Resonant inelastic x-ray scattering microscopy with high energy and spatial resolutions

TL;DR

This work addresses the challenge of obtaining spatially resolved resonant inelastic x-ray scattering (RIXS) in the soft x-ray regime. It introduces 2D-RIXS microscopy by integrating a Wolter-type imaging mirror with a high-performance varied-line-spacing (VLS) grating spectrometer to achieve micrometer-scale spatial resolution alongside ultrahigh energy resolution (∼$17.3$ meV at the Ni L3 edge). Validation with a patterned Ni logo and exfoliated NiPS3 nanosheets demonstrates 2D-RIXS’s ability to map energy-loss features across microscale regions, with vertical resolution ∼1.0 μm and horizontal resolution ∼0.8 μm, and to discriminate thickness-dependent excitations in inhomogeneous samples. This position-sensitive spectroscopic capability provides a practical, efficient tool for probing elementary excitations in quantum materials and vdW devices, enabling targeted investigations of micro- to nanoscale phenomena.

Abstract

A two-dimensional resonant inelastic x-ray scattering (2D-RIXS) microscopy system has been developed at the beamline BL02U of NanoTerasu. The instrument combines a Wolter type-I mirror for spatial imaging with a varied-line-spacing grating spectrometer, simultaneously achieving micrometer-scale spatial resolution and ultrahigh energy resolution in the soft x-ray regime. Test chart measurements confirm a vertical spatial resolution of 1.0 um near the field-of-view center, and the horizontal resolution determined by the incident beam footprint is 0.8 um. RIXS imaging capabilities have been demonstrated by the measurements of a patterned NanoTerasu logo and exfoliated NiPS${}_3$ nanoflakes, highlighting its efficiency in locating specific microscale regions within inhomogeneous samples. These results establish 2D-RIXS microscopy as a position-sensitive probe of elementary excitations in quantum materials and functional devices.

Figures (4)

• Figure 1: Optical layout of the 2D-RIXS spectrometer. Dashed lines with bidirectional arrows indicate motor axes used for spectrometer alignment.
• Figure 2: (a) Scatter plot of detected photons around the sharp edge of the test chart made of Co thin film, as a function of photon energy and vertical position $\tilde{Z}$ around $\tilde{Z}=-0.014mm$. Right panel shows the corresponding line profile. (b) Line profiles measured at different $Z$ positions. The solid lines are the fitted curves by an error function. $\tilde{Z}_\textrm{edge}$ indicates the center of the fitted error function and the line shape is plotted as a function of deviation from $\tilde{Z}_\textrm{edge}$, $\Delta \tilde{Z} = \tilde{Z}-\tilde{Z}_\textrm{edge}$. $\tilde{Z}_\textrm{edge}$ was changed by moving the test pattern. (b) The estimated resolution as a function of $\tilde{Z}$ position. The solid line shows the resolution determined by ray-tracing simulation (offset from the ideal Wolter mirror position $\delta=0$), while the dashed line shows the resolution considering the finite alignment error ($\delta=0.06mm$).
• Figure 3: (a) RIXS image of the patterned NanoTerasu logo collected at the Ni $L_3$ edge. The dashed line indicates horizontal position ($X=80µm$) where the scatter plot (b) was obtained. Inset: Design of the Ni pattern fabricated on the substrate. (b) Scatter plot of detected x-ray photons at $X=80µm$ as a function of photon energy and vertical position $\tilde{Z}$. The RIXS colormap in (a) was constructed by integrating the photon counts within the gray-shaded loss-energy window.
• Figure 4: (a) Optical microscope image of exfoliated NiPS3 nanoflakes. The dashed square indicates the region investigated by the RIXS imaging. (b) Example scatter plot showing detected x-ray photons versus photon energy (horizontal axis) and vertical position $\tilde{Z}$ (vertical axis) at a single horizontal position $X$. Blue- and red-shaded areas indicate the energy integration windows used to generate the maps in (c) and (d), respectively. (c, d) Colormap of RIXS intensity of the NiPS3 nanoflakes acquired at the Ni $L_3$ edge, obtained by integrating photon counts within the (c) inelastic and (d) elastic regions, respectively.