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Description
Hyun-Joon Shin1 Jaeyoon Baik1 Namdong Kim1

1, Pohang Accelerator Laboratory, Pohang, , Korea (the Republic of)

Two soft-x-ray spectromicroscopes, scanning photoelectron microscope (SPEM) and scanning transmission x-ray microscope (STXM), are operational at the Pohang Light Source, enabling us to investigate element-, chemical state-, valence state-, crystal structure-, electronic structure-specific local distribution within a sample with a space resolution down to hundreds of nm in SPEM and tens of nm in STXM. As a nano-focused x-ray photoelectron spectroscopy (200 – 1,000 nm x-ray size at the sample), SPEM is operating at 400 – 1,000 eV photon energy and is surface sensitive (less than ~2nm probing depth). SPEM has been practically applied to investigate local chemical states and electronic structure of graphene layers, functionalized graphene layers, single layer of CVD synthesized MoS2, h-BN encapsulated WSe2, and laser-illumination-induced phase-changed MoTe2. As an absorption spectroscopy, STXM normally operates in transmission mode and probes crystal structure, chemical state, and valence state through the sample. The sample thickness is ~hundreds of nm at the photon energy of strong absorption or several micrometers to even thicker at non-absorbing photon energy. Usable photon energy of the STXM ranges from ~200 eV to ~1600 eV. The space resolution is ~30 nm by using a 25 nm outermost zone-wide zone plate in the photon energy range from ~250 eV to ~850 eV, with worse space resolution at higher photon energy. The data acquisition time for one image is typically ~1 min. and thus in-situ or operando investigation is feasible, such as to investigate charging and discharging details of the lithium ion battery materials. Applications to nano-bio materials, energy storage materials, catalyst materials are becoming very active. Recently, we have added a soft x-ray fluorescence measurement setup in order to probe thicker samples’ elemental distribution as well as chemical state information, at a space resolution of ~50 nm. Also, we have implemented Ptychography setup in order to improve the space resolution down to less than 10 nm.

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