Ordered Arrays of Size-Selected Oxide Nanoparticles

A bottom-up approach to produce a long-range ordered superlattice of monodisperse and isomorphic metal-oxide nanoparticles (NP) supported onto an oxide substrate is demonstrated. The synthetic strategy consists of self-assembling metallic NP on an ultrathin nanopatterned aluminum oxide template followed by a morphology-conserving oxidation process, and is exemplified in the case of Ni, but is generally applicable to a wide range of metallic systems. Both fully oxidized and core-shell metal-metal-oxide particles are synthesized, up to 3-4 nm in diameter, and characterized via spectroscopic and theoretical tools. This opens up a new avenue for probing unit and ensemble effects on the properties of oxide materials in the nanoscale regime

Growth of Ceria Nano-Islands on a Stepped Au(788) Surface

The growth morphology and structure of ceria nano-islands on a stepped Au(788) surface has been investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Within the concept of physical vapor deposition, different kinetic routes have been employed to design ceria-Au inverse model catalysts with different ceria nanoparticle shapes and arrangements. A two-dimensional superlattice of ceria nano-islands with a relatively narrow size distribution (5 ± 2 nm2) has been generated on the Au(788) surface by the postoxidation method. This reflects the periodic anisotropy of the template surface and has been ascribed to the pinning of ceria clusters and thus nucleation on the fcc domains of the herringbone reconstruction on the Au terraces. In contrast, the reactive evaporation method yields ceria islands elongated in [01-1] direction, i.e., parallel to the step edges, with high aspect ratios (~6). Diffusion along the Au step edges of ceria clusters and their limited step crossing in conjunction with a growth front perpendicular to the step edges is tentatively proposed to control the ceria growth under reactive evaporation conditions. Both deposition recipes generate two-dimensional islands of CeO2(111)-type O–Ce–O single and double trilayer structures for submonolayer coverages

Ordered Au Nanoparticle Array on Au(111) through Coverage Control of Precursor Metal−Organic Chains

Metal–organic overlayer structures formed by 1,4-phenylene-diisocyanide (PDI) and Au adatoms on Au(111) in UHV, their stability in air, and the tip-induced Au nanoparticle formation on PDI–Au(111) surfaces in air were investigated using scanning tunneling microscopy (STM) and vibrational spectroscopy. This study reveals that the distribution of Au nanoparticles created during tip-induced release of Au atoms from molecule-Au adatom complexes shows strong dependence on the PDI coverage. Ordered Au nanoparticle arrays form in the medium-coverage regime, while more disordered distributions are observed at low and saturation coverages. The different distributions of Au nanoparticles are a direct consequence of the coverage-dependent assembly of (PDI–Au)n chains, their different stability in air, and a templating effect of the Au(111) surface, which is most pronounced for medium coverage, where phases of densely packed (PDI–Au)n chains and disordered PDI–Au assemblies are confined, respectively, to the fcc and hcp regions of the (22 × √3) surface reconstruction of Au(111). The Au nanoparticles nucleate preferentially in the disordered or defective regions of the PDI–Au precursor overlayer, and their formation requires ambient air and high negative tip-bias, suggesting an electrochemical initiation of Au release from the molecule–Au adatom complexes.Fil: Ghalgaoui, Ahmed. University Of Graz. Institute Of Physics; AustriaFil: Doudin, Nassar. University Of Graz. Institute Of Physics; AustriaFil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Fritz-Haber-Institut der Max-Planck-Gesellschaft; AlemaniaFil: Surnev, Svetlozar. University Of Graz. Institute Of Physics; AustriaFil: Sterrer, Martin. University Of Graz. Institute Of Physics; Austri

Ultrathin WO3 Bilayer on Ag(100): A model for the structure of 2D WO3 nanosheets

Two-dimensional (2D) WO3 nanosheets exhibit a range of novel properties and functionalities that render them attractive for advanced nanotechnologies. However, at the ultimate 2D limit of single-layer thickness, the structural properties of WO3 are unclear. Here, we fabricated, using molecular beam epitaxy techniques, a crystalline 2D WO3 overlayer on a Ag(100) surface and unveiled its geometric, electronic, and vibrational structure via a combination of state-of-the-art experimental (microscopic and spectroscopic) and computational techniques. The 2D WO3 phase forms a bilayer with a staggered arrangement of WO6 octahedra, linked together by corner-A nd edge-sharing, which is significantly different from the cubic and monoclinic WO3 bulk structures, but resembles a bilayer of the α-MoO3 layered bulk lattice. Such a 2D WO3 bilayer on Ag(100) is a robust nonpolar structure, which is incommensurate in various rotational orientations, weakly coupled to the metal substrate, and, according to the density functional theory calculations, should survive as a stable freestanding layer, that is, as a nanosheet.Fil: Negreiros Ribeiro, Fábio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Obermüller, Thomas. University of Graz; AustriaFil: Blatnik, Matthias. University of Graz; AustriaFil: Mohammadi, Malihe. University of Graz; AustriaFil: Fortunelli, Alessandro. Consiglio Nazionale delle Ricerche; ItaliaFil: Netzer, Falko. University of Graz; AustriaFil: Surnev, Svetlozar. University of Graz; Austri