Direct observation of Pt-terminating carbyne on graphene

Theoretical studies predict that carbynes (single-atomic linear carbon chains) have unique properties that rival those of graphene and carbon nanotubes. However, experimental studies on carbynes are rare due to the lack of reliable and effective means of production. Here, we report a direct observation of carbyne formation and dynamics by in situ transmission electron microscopy. Using Pt atoms on graphene, we succeeded in forming and observing carbynes reproducibly. Free carbon adatoms on graphene were trapped by Pt atoms, which served as nucleation sites for carbyne formation. Each end of the carbyne chain was eventually terminated by a Pt atom, and the Pt-terminating carbyne chains exhibited a variety of straight, curved, and ringed shapes

Large negative uniaxial magnetic anisotropy in highly distorted Co-ferrite thin films

The strain induced magnetic anisotropy (MA) of epitaxial Co-ferrite (CFO) thin films grown on MgAl2O4(001) (MAO) by reactive sputtering was studied. These films underwent large tetragonal compressive strain due to the lattice mismatch between the substrates and films, resulting in tetragonalities of up to −0.04. Scanning transmission electron microscopy observation combined with fast Fourier transform analysis revealed that the lattice distortion monotonically relaxed with the increasing film thickness. Unlike the CFO(001) films on MgO(001) substrates, a magnetically enhanced layer exists at the interface between CFO and MAO. A large negative uniaxial MA energy of −5.9 MJ/m3 was confirmed for the thinnest film of 12.9 nm at 300 K by magneto-torque measurements. The induced uniaxial anisotropy decreased with the increasing film thickness owing to misfit relaxation. The magneto-elastic (ME) constant, which was determined by a fitting line for films with different thicknesses and therefore different tetragonalities, was 0.15±0.01 GJ/m3. This result is consistent with the value of 0.14 GJ/m3 for the bulk and suggests that the framework of the phenomenological ME theory for CFO is valid for a wide range of tetragonalities, at least up to −0.04. Our results also indicate that the misfit engineering of CFO thin films has great potential in inducing enhanced uniaxial MA

Graphene-oxide-semiconductor planar-type electron emission device

Graphene was used as the topmost electrode for a metal-oxide-semiconductor planar-type electron emission device. With several various layers, graphene as a gate electrode on the thin oxide layer was directly deposited by gallium vapor-assisted chemical vapor deposition. The maximum efficiency of the electron emission, defined as the ratio of anode current to cathode current, showed no dependency on electrode thickness in the range from 1.8 nm to 7.0 nm, indicating that electron scattering on the inside of the grapheneelectrode is practically suppressed. In addition, a high emission current density of 1–100 mA/cm2 was obtained while maintaining a relatively high electron emission efficiency of 0.1%–1.0%. The graphene-oxide-semiconductor planar-type electron emission device has great potential to achieve both high electron emission efficiency and high electron emissioncurrent density in practical applications

Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to 50–100 °C. Our results represent a significant progress in reducing graphene synthesis temperature and understanding its mechanism

Oxidation and reduction behavior of Ni and NiO layers sputter deposited onto yttrium-stabilized zirconia single crystals

Thin single-crystal yttrium-stabilized zirconia (YSZ) substrate was prepared by indentation fracture and mechanical polishing. The specimen was analyzed in detail by transmission electron microscopy (TEM). The (110) edge surface was faceted, in contrast to the smooth (001) edge surface, and the facet surfaces were identified as (111)-type planes. Good cross-sectional TEM specimens comprised of crystalline Ni and NiO layers deposited on YSZ edge surface could be prepared by sputtering of a Ni support grid using Ar(+) ion milling and subsequent re-deposiotion on the smooth (001) fracture surface of the YSZ specimen. The epitaxial growth of a pure Ni layer on the YSZ edge planes occurred during ion milling in vacuum. However, subsequent ion milling of the specimen after exposure in air for several minutes resulted in the formation of a NiO layer on top of the first Ni layer. Reduction of the NiO layer was confirmed by electron energy-loss spectroscopy after annealing at 973 K in a vacuum of 1.2 x 10(-5)Pa. This Ni layer was re-oxidized upon annealing in air at 1073 K for 1 h. The deposition behavior of the Ni and NiO layers was discussed on the basis of the surface oxidation of Ni layer. (C) 2011 Elsevier B.V. All rights reserved.11Nsciescopu

Initial transient structure and chemistry of intergranular glassy films in ferric-oxide doped strontium titanate ceramics

Intergranular glassy films (IGFs) often play a key role in the formation of microstructure and the resultant properties in titanate-based materials. In this article, a systematic study of IGF structure and chemistry is reported in Fe2O3-doped SrTiO3 ceramics sintered under different temperatures and dwelling times. IGFs exhibit a large variation in their thicknesses, although majority of them are still formed by the lower energy {100}, {110}, and {111} planes from one side, which is also true for those grain boundaries (GBs) without IGF and reveals no particular effect of crystallography on IGF width. Furthermore, two trends of IGF chemical composition were found coexisting in each sample, one rich in Ti and the other in Sr, and both containing Fe segregants. The change of sintering temperature did not show significant effect on the distributions for both trends. However, increase of the dwelling time is effective to turn some Sr-rich IGFs to Ti-rich IGF, indicating that the former is in a transient state and the equilibrium IGF has most likely a TiO2-based composition.11Nsciescopu