Example 2
Materials Characterization.
Laboratory powder X-ray diffraction data were collected in Bragg-Brentano geometry using a Bruker D8-Focus diffractometer (Cu Kα: λ, =1.5418 Å; 40 kV voltage 25 mA current). Powders were lightly ground and packed into an aluminum sample holder with a Si(111) surface with an average depth of 0.7 mm S. High-resolution synchrotron X-ray diffraction was collected on a sample packed into in a poly(4,4′-oxydiphenylenepyromellitimide) capillary in transmission geometry at 295 K at beamline 11-BM of the Advanced Photon Source (λ=0.4133410 Å). Rietveld refinement of the high-resolution data was performed using the EXPGUI interface of GSAS software suite.27 Details of the refinement and the resulting structure including bond distances and angles are found in Tables 1-3. Structures depicted in FIG. 1 were plotted using the VESTA software suite.28 Scanning electron microscopy (SEM) images were collected using a JEOL JSM-7500F FE-SEM equipped with an Oxford energy-dispersive X-ray spectrometer (EDS), which was used to collect EDS spectra depicted in FIGS. 2, 5, and 6. SEM images were collected at accelerating voltages between 3-5 kV; EDS spectra were collected at an accelerating voltage of 20 kV until a minimum of 450,000 counts was achieved. Prior to SEM characterization, samples were lightly ground in a mortar and pestle and affixed to an aluminum substrate with carbon tape and subsequently analyzed without any further manipulation. Transmission electron microscopy (TEM) images were collected using a JEOL JEM-2010 instrument at an accelerating voltage of 200 kV. Scanning transmission X-ray microscopy (STXM) measurements were collected at beamline 10-ID1 of the Canadian Light Source, a 2.9-GeV third-generation synchrotron facility. A 25-nm outermost-zone zone plate was used to obtain a diffraction-limited spatial resolution of, at all times, greater than 30 nm. A 500-line per mm plane grating monochromator was used to acquire the V L-edge and O K-edge spectral stacks. The incident photon flux (I0) count rate was adjusted to be <20 MHz and was further optimized to 17.5 MHz as read by the STXM detector by adjusting the exit slits of the incident beam. The V L- and O K-edge stacks covered an energy range from 508-560 eV with energy steps of 0.2 eV in regions with spectral features of interest and 1 eV in the continuum region beyond the specific elemental edges with a uniform dwell time of 1 ms for each section. Transmission spectra were converted to absorption spectra using a background spectrum from the STXM maps, selected so as not to include sample signal. All STXM data were analyzed and processed using aXis2000 software (unicorn.mcmaster.ca/aXis2000.html).
