Fig. 2: Materials evolution and characterization of Co@Si SACs (Co concentration: 1.4 wt%).
From: Epitaxially grown silicon-based single-atom catalyst for visible-light-driven syngas production
a XRD results of the sol–gel precursor and products after thermal annealing. b, c High-resolution XPS results of silicon 2p and cobalt 2p regions. Spectra of (b) to which we have curve-fit are shown for the Si 2p3/2 emissions. Silicon 2p1/2 components are omitted for clarity. “Sat.” refers to the satellite peak of the cobalt 2p signal. d HAADF-STEM images of Co@Si NCs extracted from the SAC solid and functionalized by octene. Co atoms are highlighted by yellow circles (scale bar: 5 nm). e A high-resolution HAADF-STEM image of a Co@Si NC (scale bar, 1 nm) and f, a fast Fourier transform (FFT) pattern from the area denoted by a red square in (e) (scale bar: 5 1/nm). g Electron energy loss spectrum (EELS) result reveals the presence of cobalt (L3, 779 eV) from a selected area of a HAADF-STEM image of Co@Si NCs as inset (scale bar, 20 nm). h Schematic illustration of the CoSi2-assisted Co@Si SAC formation mechanism. The process is initiated by CoSi2 nanodomains formation by doping Co(II) in a silicon-rich network homogeneously (Step i) and annealing at low temperature (T1 = 500 °C) (Step ii); the thermally-induced CoSi2 decomposition occurred at high temperature (T2 = 700 °C) during the silicon crystallization enables the crystal re-arrangement (Step iii); the diffusion of Co and Si atoms during extended annealing (T2 = 700 °C) enables single Co dispersion in the lattice of c-Si, yielding Co@Si SAC (Step iv).
