Jem 1011

The morphology of the Co–B NWs was inspected using transmission electron microscopy (TEM; JEM-1011) with an accelerating voltage of 120 kV. Their crystal structure was measured using powder X-ray diffraction (XRD; Philips). Their chemical compositions and electronic states were studied using X-ray photoelectron spectroscopy (XPS; Thermo ESCALAB 250). The nitrogen-sorption isotherms of the Co–B NWs were characterized using the ASAP 2020 apparatus. H₂ temperature programmed desorption was tested by using an apparatus (H₂-TPD; AutoChem TP-5080) with a thermal conductivity detector.

The nanosheets were characterized by transmission electron microscopy (JEOL Jem-1011), X-ray diffraction (Philips X'Pert System with a Bragg-Brentano geometry and a Cu K-alpha X-ray with a wavelength of 0.154 nm) and AFM (Veeco Dimension 3100). For the optical measurements, the nanosheets were drop-casted from toluene on a quartz substrate. The quartz was functionalized via silanization in order to provide better adherence of the nanocrystals, as has been described previously26 (link). All optical measurements were performed without exposing the samples to air, by using air-tight sample holders that were loaded inside a nitrogen-filled glovebox. The absorption spectra of the samples were measured with a Perkin Elmer Lambda 900 photospectrometer, equipped with an integrating sphere. The sample was placed inside the integrating sphere, so that light scattered from the sample also enters the photodetector. Background absorption of the quartz substrate was subtracted. The relative uncertainty in the fraction of absorbed light is 2%, which was statistically determined via repeated measurements.