Direct Imaging of Single Au Atoms Within GaAs Nanowires

Incorporation of catalyst atoms during the growth process of semiconductor nanowires reduces the electron mean free path and degrades their electronic properties. Aberration-corrected scanning transmission electron microscopy (STEM) is now capable of directly imaging single Au atoms within the dense matrix of a GaAs crystal, by slightly tilting the GaAs lattice planes with respect to the incident electron beam. Au doping values in the order of 10^17–18 cm³ were measured, making ballistic transport through the nanowires practically inaccessible

Silver, Gold, Palladium, and Platinum N‑heterocyclic Carbene Complexes Containing a Selenoether-Functionalized Imidazol-2-ylidene Moiety

The selenoether-functionalized imidazolium salt <i>N</i>-[(phenylseleno)­methylene)]-<i>N</i>′-methylimidazolium chloride (LH⁺Cl^–) was transformed into the metal–carbene complexes [AgCl­(L)], [AuCl­(L)], [PdCl₂(L)], and [PtCl₂(L)] by the reaction with Ag₂O and an additional transmetalation reaction of [AgCl­(L)] with [(THT)­AuCl], [(COD)­PdCl₂], and [(COD)­PtCl₂], respectively (THT = tetrahydrothiophene, COD = cyclooctadiene). The compound [AuI₂Cl­(L)] was prepared by oxidation of [AuCl­(L)] with elemental iodine. The microwave-assisted decomposition of [PdCl₂(L)] in the ionic liquid 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([BMIm]­NTf₂) or in propylene carbonate led to the formation of Pd₁₇Se₁₅ nanoparticles of 51 ± 17 or 26 ± 7 nm diameter, respectively. The decomposition of the platinum complex resulted in either small Pt clusters around 1 nm size from the ionic liquid suspension or Pt nanoparticles of 3 ± 1 nm diameter in propylene carbonate. High-resolution X-ray photoelectron spectroscopy (HR-XPS) and ¹³C cross-polarization magic-angle spinning (CP MAS) NMR indicated that the surface of Pt clusters and crystalline Pt nanoparticles is formed by an amorphous Pt­(II)/Se shell and by carbene ligand residues

Understanding Structural Incorporation of Oxygen Vacancies in Perovskite Cobaltite Films and Potential Consequences for Electrocatalysis

Owing to their excellent mixed-ionic and electronic conductivity, fast oxygen kinetics, and cost efficiency, layered oxygen-deficient perovskite oxides hold great potential as highly efficient cathodes for solid oxide fuel cells and anodes for water oxidation. Under working conditions, cation ordering is believed to substantially enhance oxygen diffusion while maintaining structural stability owing to the formation of double perovskite (DP), thus attracting extensive research attention. In contrast, the incorporation of oxygen vacancies and the associated vacancy ordering have rarely been studied at the atomic scale, despite their decisive roles in regulating the electronic and spin structures as well as in differentiating the crystal structure from DP. Here, atomic-resolution transmission electron microscopy is used to directly image oxygen vacancies and measure their concentration in (Pr,Ba)CoO3‑δ films grown on SrTiO3 substrates. We find that accompanied by the presence of oxygen vacancy ordering at Co–O planes, the A–O (A = Pr/Ba) planes also exhibit a breathing-like lattice modulation. Specifically, as confirmed by first-principle calculations, the AO–AO interplanar spacings are found to be linearly correlated with the vacancy concentration in the enclosing Co–O planes. On this basis, potential consequences of oxygen occupancy for the catalytic properties of structurally pure PBCO phases are discussed. Through establishing a simple correlation of oxygen concentration with the easily achievable lattice measurement, our results pave a way for better understanding the structure–performance relationship of oxygen-deficient complex cobaltites used for electrocatalysis

Tungsten Bronze Barium Neodymium Titanate (Ba_{6–3<i>n</i>}Nd_8+2<i>n</i>Ti₁₈O₅₄): An Intrinsic Nanostructured Material and Its Defect Distribution

We investigated the structure of the tungsten bronze barium neodymium titanates Ba_{6–3<i>n</i>}Nd_8+2<i>n</i>Ti₁₈O₅₄, which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba_{6–3<i>n</i>}Nd_8+2<i>n</i>Ti₁₈O₅₄ (<i>n</i> = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the <i>b</i> lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba_{6–3<i>n</i>}Nd_8+2<i>n</i>Ti₁₈O₅₄ “perovskite” superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity