Titan chemistem

A JEOL 6500F SEM was used to investigate the morphology. A JEOL 2010 HRTEM was used to observe the morphologies and lattice fringes of the samples. The atomic-resolution TEM and STEM structural characterizations of IFONFs were carried out with a probe-corrected Titan G2 60–300 (FEI, USA) and Titan ChemiSTEM (FEI, USA) at acceleration voltages of 300 kV and 200 kV, respectively. The crystal structure was evaluated using XRD analysis. XPS was conducted on a PHI Quantera SXM scanning X-ray microscope. An Al anode at 25 W was used as an X-ray source with a pass-energy of 26.00 eV, 45 take-off angle, and a 100-μm beam size.

The sample was transferred onto a TEM grid following a previous report with minor modifications48 . The MoSe₂ ribbons together with a few layers of graphite (∼1–2 nm in thickness) were first exfoliated from the substrate. Then, the samples were transferred onto the TEM grid after removing the glue used in the cleavage. Due to the finite thickness and relatively light mass of the carbon atoms, the electron scattering from the residual graphite layers is much weaker than those from the MoSe₂ layer, making the substrate invisible. The TEM images were recorded with a probe-corrected Titan ChemiSTEM (FEI, USA), which was operated at an acceleration voltage of 200 kV. The probe current was set at 47 pA with a convergent angle of 22 mrad for illumination. The inner collection angle was adjusted to be 44 mrad to enhance the contrast of Se atoms. The experimental TEM images shown in the main text were processed with improved Wiener-Filtering to increase the signal-to-noise ratio for better display.

Material crystal phases of the β-FeOOH and the hematite were confirmed using X-ray diffraction and Raman. The X-ray diffraction studies were carried out in the range of scanning angle 20–70° using an X-ray diffractometer with Cu Kα radiation of wavelength 0.154060 nm (D8 Discover). A field emission scanning electron microscope (SEM Zeiss Supra 50 VP) was used to observe the surface morphology and estimate the surface texture. XPS was performed with a polychromatic MgKα (hν = 1253.6 eV) and a mono-chromatized AlKα (hν = 1486.6 eV) source in a modified Vacuum Generators ESCALAB 220 (p < 10⁻⁹ mbar)^{41 (link)}. The energy scale was calibrated as described in this literature^{42 (link)}. STEM studies were performed using an FEI Titan ChemiSTEM operated at 200 kV equipped with a Cs-probe corrector and a HAADF detector. This technique offers Z-contrast conditions, i.e., the image intensity is roughly proportional to Z^1.6–Z^1.9,where Z is the atomic number of the present element^{43 (link),44 (link)}. “Z-contrast” conditions were achieved using a probe semi-angle of 25 mrad and an inner collection angle of the detector of 70 mrad. Compositional maps were obtained with EDX using four large-solid-angle symmetrical Si drift detectors.