Pore structure, barrier layer topography and matrix alumina structure of porous anodic alumina film

Different anodic voltages and methods were adopted to produce porous anodic alumina films (PAAF) in an aqueous solution of oxalic acid. Carbon tube growth by chemical vapor deposition (CVD) in the films was used to copy the internal pore structure and was recorded by transmission electron microscopy (TEM) photos. Atomic force microscope (AFM) was employed to obtain the topography of the barrier layer of the corresponding films. When the anodic voltage was 40 V and the two-step method adopted, the barrier layer of the film had domains with highly ordered hexagonal cell distribution, and the corresponding pores were straight. When the anodic voltage increased to 60 V, the barrier layer showed random cell distribution with an obvious difference in cell size and form, and the corresponding pores exhibited multi-branch features. When the anodic voltage increased further to 110 V, the barrier layer also showed a random cell distribution. Additionally, smaller protrusions connected to bigger cells were found, which can be correlated to the formation of branches with smaller diameters. Most of the branches of carbon tubes grown in the film anodized at 110 V have a saw-tooth like feature. X-Ray diffraction analysis shows that all the anodic films are amorphous, regardless of the anodic voltage. However, unoxidized aluminum particles in the film anodized at 110 V was observed by TEM

FePt nanodot arrays with perpendicular easy axis, large coercivity, and extremely high density

Ordered FePt nanodot arrays with extremely high density have been developed by physical vapor deposition using porous alumina templates as evaporation masks. Nanodot diameter of 18 nm and periodicity of 25 nm have been achieved, resulting in an areal density exceeding 1 x1012 dots/in2. Rapid thermal annealing converts the disordered fcc to L10 phase, resulting in (001)-oriented FePt nanodot arrays with perpendicular anisotropy and large coercivity, without the need of epitaxy. High anisotropy and coercivity, perpendicular easy axis orientation and extremely high density are desirable features for future magnetic data storage media applications

CaCu3Ti4O12: Low-Temperature Synthesis by Pyrolysis of an Organic Solution

The giant-dielectric-constant material CaCu3Ti4O12 (CCTO) has been synthesized by pyrolyzing an organic solution containing stoichiometric amounts of the metal cations, which is done at lower temperature and shorter reaction time than the conventional solid-state reaction. A stable solution was prepared by dissolving calcium nitrate, copper(II) nitrate, and titanium(IV) isopropoxide in 2-methoxyethanol. This solution was pyrolyzed and heat-treated to achieve single-phase CCTO. The phases, microstructures, and dielectric properties of intermediate and final samples were characterized by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy

Genome sequence and evolution of Betula platyphylla

Betula L. (birch) is a pioneer hardwood tree species with ecological, economic, and evolutionary importance in the Northern Hemisphere. We sequenced the Betula platyphylla genome and assembled the sequences into 14 chromosomes. The Betula genome lacks evidence of recent whole-genome duplication and has the same paleoploidy level as Vitis vinifera and Prunus mume. Phylogenetic analysis of lignin pathway genes coupled with tissue-specific expression patterns provided clues for understanding the formation of higher ratios of syringyl to guaiacyl lignin observed in Betula species. Our transcriptome analysis of leaf tissues under a time-series cold stress experiment revealed the presence of the MEKK1–MKK2–MPK4 cascade and six additional mitogen-activated protein kinases that can be linked to a gene regulatory network involving many transcription factors and cold tolerance genes. Our genomic and transcriptome analyses provide insight into the structures, features, and evolution of the B. platyphylla genome. The chromosome-level genome and gene resources of B. platyphylla obtained in this study will facilitate the identification of important and essential genes governing important traits of trees and genetic improvement of B. platyphylla

Magnetic nanotubes produced by hydrogen reduction

FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometry. Loading the templates with an Fe chloride and Pt chloride mixture, followed by hydrogen reduction at 560 °C, leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. An Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The versatility of the method indicates that materials with a wide range of parameters can be produced

Nanotube magnetism

FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction analysis, and magnetic measurements. Loading the templates with a Fe chloride and Pt chloride mixture followed by hydrogen reduction at 560 °C leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. Using a Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The length of the nanotubes is about 50 mm and their diameters range from about 150 to 220 nm, depending on the thickness of the template film and the pore diameter distribution. Reflecting the different magnetocrystalline anisotropies of the compounds, the coercivities range from 0.61 kOe for Fe3O4 to 20.9 kOe for FePt. The hysteresis is explained in terms of a tubular random-anisotropy model, which yields a diameter and anisotropy dependent transition from a curling-type mode (Fe3O4) to a localized mode (FePt)

Growth and magnetism of FePt:C composites in nanoscale channels

Nanochannels of porous alumina films were used as nanoreactors for the reaction of hydrogen gas with a mixture of Fe nitrate and Pt chloride. This results in the formation of of FePt clusters within the nanochannels. Both the sizes of the clusters and the coercivity the cluster assembly increase with the increase of annealing temperature. In order to reduce excessive agglomeration at high temperature, carbon was introduced by chemical vapor deposition and FePt:C composites in nanoscale channels were created. When FePt clusters were synthesized with carbon and heat treated at high temperatures, cluster sizes were much smaller than those without carbon, suggesting that the introduced carbon serves effectively to block the agglomeration of clusters. The coercivity of the FePt:C composite containing the smaller clusters is as high as 29.0 kOe

Rapidly annealed exchange-coupled Sm-Co/Co multilayers

In exchange-coupled two-phase permanent magnets, the length scale of soft phase is limited to about twice of the domain-wall width of the hard phase. To optimize the energy product, it is important to realize this length experimentally. In this work, we investigate the Sm–Co/Co hard/soft multilayers with varying thickness of soft phase layers. On rapidly annealing, the multilayered hard-soft structure forms. Transmission electron microscopy micrography confirms that the multilayer structure is retained after the annealing. Single-phase-like hysteresis loops are obtained for samples with Co layers up to 13 nm thick. This behavior indicates that the soft phase is well exchange coupled to the neighboring SmCoz hard phase. An optimal energy product of 16.6 MGOe has been obtained. Longer annealing time results in more diffusion at the interface and yields two-phase-like hysteresis behavior. Direct current demagnetization measurement shows exchange-spring behavior of the samples annealed for longer time. Micromagnetic simulations with varying interface exchange coupling have been performed to compare with the experimental results

Assembly of high-anisotropy L1\u3csub\u3e0\u3c/sub\u3e FePt nanocomposite films

In this paper we report results on the synthesis and magnetic properties of L10 FePt nanocomposite films. Three fabrication methods have been developed to produce high-anisotropy FePt films: non-epitaxial growth of (0 0 1)-oriented FePt:X (X=Ag, C) composite films that might be used for perpendicular media; monodispersed FePt(CFx) core–shell nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; and template-mediated self-assembled FePt clusters prepared with chemical synthesis by a hydrogen reduction technique, which has a high potential for controlling both cluster size and orientation. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. Analytical and numerical simulations have been done for these films, providing better understanding of the magnetization reversal mechanisms. The films show promise for development as magnetic recording media at extremely high areal densities