We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 x 10(11) wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.

/pdf/ultrahigh-density-nanowire-arrays-grown-in-self-assembled-1mgxshd8uu.pdf

Ultrahigh-Density Nanowire Arrays Grown in Self-Assembled Diblock Copolymer Templates

https://www.pnas.org/content/pnas/90/5/1635.full.pdf

Supramolecular chemistry.

In the present review we try to give a comprehensive and most up to date view to the field, with an emphasis on the currently most investigated anodic TiO2 nanotube arrays. We will first give an overview of different synthesis approaches to produce TiO2 nanotubes and TiO2 nanotube arrays, and then deal with physical and chemical properties of TiO2 nanotubes and techniques to modify them. Finally, we will provide an overview of the most explored and prospective applications of nanotubular TiO2.

One-dimensional titanium dioxide nanomaterials: nanotubes.

Transmission electron microscopy analysis of self-ordered porous alumina obtained by electrochemical anodization shows that self-ordering requires a porosity of 10%, independent of the specific anodization conditions. This corresponds to a volume expansion of alumina to aluminum of about 1.2. We propose that self-ordering of porous alumina with any interpore distance is possible if the applied potential, which mainly determines the interpore distance, and the pH value of the electrolyte, which mainly defines the pore radius, match the 10% porosity rule.

Self-ordering Regimes of Porous Alumina: The 10% Porosity Rule

Ordered magnetic nanostructures: fabrication and properties

The magnetic behavior of 100 nm period arrays of Ni nanowires embedded in a highly ordered alumina pore matrix were characterized by magnetometry and magnetic force microscopy. Reducing the diameter of the nanowires from 55 to 30 nm while keeping the interwire distance constant leads to increasing coercive fields from 600 to 1200 Oe and to increasing remanence from 30% to 100%. The domain structure of the arrays exhibits in the demagnetized state a labyrith-like pattern. These results show that stray field interactions of single domain nanowires are entirely dependent on the nanowire diameter.

/pdf/hexagonally-ordered-100-nm-period-nickel-nanowire-arrays-54tsanlm35.pdf

Hexagonally ordered 100 nm period nickel nanowire arrays

Single-crystalline ${\mathrm{Co}}_{2}\mathrm{MnSi}$ Heusler alloy films have been grown on GaAs(001) substrates by pulsed laser deposition (PLD) The best crystallographic quality of the ${\mathrm{Co}}_{2}\mathrm{MnSi}$ films has been achieved after deposition at 450 K The films exhibit in-plane uniaxial magnetic anisotropy with the easy axis of magnetization along the [1-10] direction superimposed with a fourfold anisotropy with the easy axis along ⟨110⟩ Spin-resolved photoemission measurements of the single-crystalline ${\mathrm{Co}}_{2}\mathrm{MnSi}$ films reveal a spin-resolved density of states that is in qualitative agreement with recent band structure calculations The spin polarization of photoelectrons close to the Fermi level is found to be at most 12%, in contrast to the predicted half-metallic behavior We suggest that these discrepancies may be attributed to a partial chemical disorder in the ${\mathrm{Co}}_{2}\mathrm{MnSi}$ lattice

Magnetic properties and spin polarization of Co 2 MnSi Heusler alloy thin films epitaxially grown on GaAs(001)

Single-crystal epitaxial MgO thin films were grown directly onto high-quality Fe single crystal and Fe whisker substrates and covered with Fe/Au layers. Reflection high-energy electron diffraction and low-energy electron diffraction patterns and scanning tunneling microscopy images showed that the growth of MgO proceeded pseudomorphically in a nearly layer-by-layer mode up to six monolayers. A misfit dislocation network is formed for MgO layers thicker than six monolayers. The thin MgO films were characterized electrically by scanning tunneling spectroscopy. The tunneling barrier in MgO was found to depend on the MgO layer thickness, starting from 2.5 eV at two monolayer thickness to the expected full barrier of MgO of 3.6 eV at six monolayers. A small fraction of the scanned area showed randomly placed spikes in the tunneling conductance. Tunneling I-V curves at the defects showed a lower tunneling barrier than that in the majority of the MgO film. The total tunneling current integrated over areas of 1003100 nm 2 , however, was not dominated by spikes of higher conductance. These local defects in the MgO barrier were neither related to atomic steps on the Fe substrates nor to individual misfit dislocations. Magnetic anisotropies and exchange coupling in Fe/ MgO~001! and Fe/MgO/Fe~001! structures were studied using ferromagnetic resonance and Brillouin light scattering.

/pdf/growth-structure-electronic-and-magnetic-properties-of-mgo-vcszus05hl.pdf

Growth, structure, electronic, and magnetic properties of MgO/Fe(001) bilayers and Fe/MgO/Fe(001) trilayers

http://www-old.mpi-halle.mpg.de/mpi/publi/pdf/3885_02.pdf

High density hexagonal nickel nanowire array

Starting from the conventional self-organized arrays of flat Co dots on Au(111), we extended the growth vertically to fabricate Co pillars. The principle is to deposit sequentially a fraction $x$ of an atomic layer (AL) of Co and $1\ensuremath{-}x$ AL of Au. At each step, the deposited Co atoms aggregate on top of the previous dots, increasing their height by 1 AL. Pillars with a 2:1 vertical aspect ratio were achieved. Because of the large number of atoms per pillar, the superparamagnetic blocking temperature is 300 K in the pillars, whereas it is only 20 K in conventional flat dots with the same lateral density.

J. Barthel

Papers

Hexagonally ordered 100 nm period nickel nanowire arrays

Magnetic properties and spin polarization of Co 2 MnSi Heusler alloy thin films epitaxially grown on GaAs(001)

Growth, structure, electronic, and magnetic properties of MgO/Fe(001) bilayers and Fe/MgO/Fe(001) trilayers

High density hexagonal nickel nanowire array

Self-Organized Growth of Nanosized Vertical Magnetic Co Pillars on Au(111)