New type of Al-based decagonal quasicrystal in Al\u3csub\u3e60\u3c/sub\u3eCr\u3csub\u3e20\u3c/sub\u3eFe\u3csub\u3e10\u3c/sub\u3eSi\u3csub\u3e10\u3c/sub\u3e alloy

A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the other Al-based DQCs. The neighboring D clusters are connected by sharing one edge rather than covering, suggesting the tiling model is better than the covering model for structural description

About the step-flow mechanism at the origin of graphene crystallisation at the surface of catalysts

The nucleation and growth of multiwall carbon nanotubes (MWCNTs) at the surface of crystalline iron-based catalysts are studied by in situ annealing and high-resolution transmission electron microscopy. Graphene planes, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene layers. More interestingly, as the catalyst particles have curved or poly-faceted surfaces, those catalyst atomic layers correspond to no definite atomic plane. The step height may thus vary along a given step flow process. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering this mechanism opens up the way to tailor the structure of MWCNTs, e.g. with highly parallel carbon walls

Nanodomains in Fe[sup +3]-doped lead zirconate titanate ceramics at the morphotropic phase boundary do not correlate with high properties

Configuration of domain walls in undoped and Fe+3-doped lead zirconate titanate (PZT) ceramics at the morphotropic phase boundary has been investigated by the transmission electron microscopy. The distance between domain walls in undoped PZT is on the order of hundreds of nanometers and is drastically reduced to tens of nanometers by acceptor doping. The properties of doped and undoped samples are compared and discussed in terms of domain size, phase mixture, and presence of dopants. It is suggested that the small domain size cannot be a dominant effect in the enhancement of the properties in morphotropic PZT

Atomic Layer Deposition-Based Synthesis of Photoactive TiO2 Nanoparticle Chains by Using Carbon Nanotubes as Sacrificial Templates

Highly ordered and self supported anatase TiO2 nanoparticle chains were fabricated by calcining conformally TiO2 coated multi-walled carbon nanotubes (MWCNTs). During annealing, the thin tubular TiO2 coating that was deposited onto the MWCNTs by atomic layer deposition (ALD) was transformed into chains of TiO2 nanoparticles (~12 nm diameter) with an ultrahigh surface area (137 cm2 per cm2 of substrate), while at the same time the carbon from the MWCNTs was removed. Photocatalytic tests on the degradation of acetaldehyde proved that these forests of TiO2 nanoparticle chains are highly photo active under UV light because of their well crystallized anatase phase

Growth mechanisms of carbon nanotrees with branched carbon nanofibers synthesized by plasma-enhanced chemical vapour deposition

International audienceY- and comb-type carbon nanotrees formed from branched carbon nanofibres grown by plasma-enhanced chemical vapour deposition were studied by transmission electron microscopy. Different growth mechanisms are proposed for the two types of nanotrees based on the observed and reconstituted dynamic transformations of the catalyst particles during synthesis. However, the splitting of the larger catalyst particles is required for both kinds of nanotrees, whatever the involved growth mechanism. The carbon nanotrees are well crystallized and connections of the branches are continuous, which may be interesting for future applications in nanoelectronic devices and also composite materials

Structure determination of the zeolite IM-5 using electron crystallography

The structure of the complex zeolite IM-5 (Cmcm, a = 14.33(4) Å, b = 56.9(2) Å, c = 20.32(7) Å) was determined by combining selected area electron diffraction (SAED), 3D reconstruction of high resolution transmission electron microscopy (HRTEM) images from different zone axes and distance least squares (DLS) refinement. The unit cell parameters were determined from SAED. The space group was determined from extinctions in the SAED patterns and projection symmetries of HRTEM images. Using the structure factor amplitudes and phases of 144 independent reflections obtained from HRTEM images along the [100], [010] and [001] directions, a 3D electrostatic potential map was calculated by inverse Fourier transformation. From this 3D potential map, all 24 unique Si positions could be determined. Oxygen atoms were added between each Si-Si pair and further refined together with the Si positions by distance-least-squares. The final structure model deviates on average 0.16 Å for Si and 0.31 Å for O from the structure refined using X-ray powder diffraction data. This method is general and offers a new possibility for determining the structures of zeolites and other materials with complex structure

Laser-induced periodic annular surface structures on fused silica surface

International audienceWe report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse

Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films

International audienceThe synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film

New type of Al-based decagonal quasicrystal in Al\u3csub\u3e60\u3c/sub\u3eCr\u3csub\u3e20\u3c/sub\u3eFe\u3csub\u3e10\u3c/sub\u3eSi\u3csub\u3e10\u3c/sub\u3e alloy

A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the other Al-based DQCs. The neighboring D clusters are connected by sharing one edge rather than covering, suggesting the tiling model is better than the covering model for structural description