Near-edge X-ray absorption spectroscopy (NEXAFS) is an essential analytical tool in material science. Combining NEXAFS with scanning transmission X-ray microscopy (STXM) adds spatial resolution and the possibility to study individual nanostructures. Here, we describe a full-field transmission X-ray microscope (TXM) that generates high resolution, large-area NEXAFS data with a collection rate two orders of magnitude faster than is possible with STXM. The TXM optical design combines a spectral resolution of E/DE5 13104 with a spatial resolution of 25 nm in a field of view of 15–20 mm and a data acquisition time of ∼1 s. As an example, we present image stacks and polarization-dependent NEXAFS spectra from individual anisotropic sodium and protonated titanate nanoribbons. Our NEXAFS-TXM technique has the advantage that one image stack visualizes a large number of nanostructures and therefore already contains statistical information. This new high-resolution NEXAFS-TXM technique opens the way to advanced nanoscale science studies.
COBISS.SI-ID: 25317671
Co2+-doped sodium titanate nanoribbons (NaTiNRs) were grown under hydrothermal conditions from Co2+-doped TiO2. The obtained nanoribbons with lengths up to several microns were identified to be of trititanate structure ((Na,H)2Ti3O7). Transmission electron microscopy disclosed nanoparticles, not exceeding 15-20 nm in length, as well as hexagonal nanoflakes located on the surface of the nanoribbons. Nanoflakes are most likely originating from Co(OH)2 (beta phase) side product according to X-ray diffraction investigation. High angle annular dark filed scanning transmission electron microscopy combined with electron energy loss spectroscopy showed that amount of cobalt in the surface nanoparticles is much higher than in the nanoribbons. X-ray photoelectron spectroscopy (XPS) revealed that cobalt atomic concentration in the sample is 1.5 wt. % of which a low is in the oxidation state Co3+. Detailed electron paramagnetic resonance characterization of this sample proved that Co2+ ions occupy octahedral sites with rhombic distortion in a high-spin S = 3/2 state. Temperature dependent susceptibility measurement reveals prevailing paramagnetic behavior from which a mass ratio 1.3 wt % of Co2+ was obtained and is in agreement with elemental analysis results and value extracted from XPS measurements. A weak antiferromagnetic transition at 12 K is associated with -Co(OH)2 nanoflakes.
COBISS.SI-ID: 25878055