Origin of the Substitution Mechanism for the Binding of Organic Ligands on the Surface of CsPbBr3 Perovskite Nanocubes.

Optoelectronic properties of CsPbBr3 perovskite nanocubes (NCs) depend strongly on the interaction of the organic passivating molecules with the inorganic crystal. To understand this interaction, we employed a combination of synchrotron-based X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) spectroscopy, and first-principles density functional theory (DFT)-based calculations. Variable energy XPS elucidated the internal structure of the inorganic part in a layer-by-layer fashion, whereas NMR characterized the organic ligands. Our experimental results confirm that oleylammonium ions act as capping ligands by substituting Cs+ ions from the surface of CsPbBr3 NCs. DFT calculations shows that the substitution mechanism does not require much energy for surface reconstruction and, in contrast, stabilizes the nanocrystal by the formation of three hydrogen bonds between the -NH3+ moiety of oleylammonium and surrounding Br- on the surface of NCs. This substitution mechanism and its origin are in stark contrast to the usual adsorption of organic ligands on the surface of typical NCs.

Hydrogenation of Ferrimagnetic Graphene on a Co Surface: Significant Enhancement of Spin Moments by C-H Functionality.

Using ab initio density functional theory, we present a novel way of simultaneously enhancing the induced magnetic moment and opening up the band gap of a graphene sheet supported on ferromagnetic transition metal surface. Specifically, we have demonstrated that by simply hydrogenating graphene supported on ferromagnetic Co surface at saturation coverage, (i) there is a six-fold increase in the magnitude of the induced magnetic moment compared with the pristine graphene on the Co surface and (ii) for both the spin-up and the spin-down channels there is a band gap opening at the K-point of the Brillouin zone.