Phi 5000 versaprobe 2 xps system

PXRD patterns were recorded on an X'Pert Philips diffractometer with monochromatic Cu_Kα radiation (λ=1.540598 Å) and a fast Si-PIN multi-strip detector. As-synthesized NiSe₂ and Ni_xFe_1−xSe₂ were used directly for PXRD measurements. Morphology and microstructure was examined by a Phillips (FEI) XLF-30 FEG SEM and a FEI Tecnai Osiris TEM equipped with high-brightness field emission gun (XFEG). Energy-dispersive X-ray spectroscopy (EDX) mapping images were taken under a scanning TEM modal. Samples for TEM were prepared by drop-drying the samples from their diluted ethanol suspensions onto carbon-coated copper grids. XPS measurements were performed on a PHI5000 VersaProbe II XPS system by Physical Electronics (PHI) with a detection limit of one atomic per cent. Monochromatic X-rays were generated by an Al Kα source (14,867 eV). The diameter of the analysed area is 10 μm. N₂ adsorption–desorption measurements were conducted on Micromeritics 3Flex adsorption analyser at 77K. Before the measurements, the samples were degassed at 100 °C under vacuum for 1 h. Pore size distributions were calculated by the Barrett-Joyner-Halenda (BJH) method from the desorption branches of the isotherms.

The X-ray photoelectron spectroscopy (XPS) measurements were carried out with the PHI 5000 VersaProbe II XPS system (Physical Electronics) with a monochromatic Al-Ka source (15 kV, 50 W) and a photon energy of 1486.7 eV. All the spectra were measured in a vacuum of 1.1 × 10⁻⁷ Pa and at a room temperature of 20 °C. Dual beam charge compensation was used for all measurements. The spectra were evaluated with MultiPak software, version 9 (Ulvac—PHI, Inc., Chanhassen, MN, USA).