In this letter we demonstrate a low temperature (≈ 345 • C) growth method for Cu deficient CuCrO 2 performed by spray pyrolysis using metal-organic precursors and a simple air blast nozzle. Smooth films were grown on glass substrates with a highest conductivity of 12 S/cm. The most conductive samples retain transparencies above 55% resulting in a figure of merit as high as 350 µS, which is the best performing p-type transparent conducting material grown by solution methods to date. Remarkably despite the nano-crystallinity of the films, properties comparable with crystalline CuCrO 2 are observed. No postannealing of the films is required in contrast to previous reports on crystalline material. The low processing temperature of this method means the material can be deposited on flexible substrates. As this is a solution based technique it is more attractive to industry as physical vapour deposition methods are slow and costly in comparison.p-type transparent conducting materials (TCMs) are sought after for optoelectronic devices. Currently commercially available n-type TCMs, such as indium tin oxide (ITO), possess conductivities as high as 1000 S/cm with transparencies greater than 80%. 1 Potential applications that require p-type materials with similar properties include transparent p-n junctions, which would allow for fully-transparent displays. 2 Alternatively, they can be used to minimize shunting as hole injection/extraction layers in light-emitting diodes/solar cells. 3,4 The main interest in this field originated from the potential of the delafossites with the A 1+ B 3+ O 2 lattice structure first highlighted in 1997 when CuAlO 2 was reported to exhibit ptype conductivity while maintaining high transparency. 5 Since then the field has extended to other materials such as oxychalcogenides, spinels and α-Cr 2 O 3 . 6-9 One of the delafossites, CuCrO 2 , has shown promise as a p-type TCM due to reports of high conductivity when doped with Mg. 10 However this is typically only achieved by physical vapour deposition (PVD) which is a relatively slow and costly technique in comparison to other depostion methods. CuCrO 2 has also been grown by chemical vapour deposition (CVD) using the metal-organic Acetylacetonate (acac) precursors Cr(acac) 3 and Cu(acac) 2 at 550 • C, resulting in polycrystalline films with conductivity of 0.86 S/cm (figure of merit (FOM) ≈ 45 µS). 11 Spray pyrolysis (SP) is an inexpensive technique that is suited to depositing films over a large area. Mg-doped films of CuCrO 2 have been synthesized by SP using the same acac precursors with the Mg(acac) 2 precursor for doping. Only after postannealing at 700 • C did they achieve conductivities of 0.6-1 S/cm. 12,13 CuCrO 2 :Zn grown by solgel processing show conductivities of around 0.47 S/cm after two postannealing steps. 14 The high temperature required by these methods is a major drawback for using a) Electronic mail: lefarrel@tcd.ie the material in practical devices. In this letter SP was used to grow thin (50-100 nm) Cu deficient CuCrO 2 film...

Planar nanowire (NW) arrays of Co grown on oxidized step-bunched Si(111) templates exhibit room temperature ferromagnetic behaviour for wire widths down to 25 nm. Temperature and thickness dependent magnetization studies on these polycrystalline NW arrays show that the magnetic anisotropy of the NW array is dominated by shape anisotropy, which keeps the magnetization in-plane with easy axis parallel to the wires. This shape related uniaxial anisotropy is preserved even at low temperatures (10 K). Thickness dependent studies reveal that the magnetization reversal is governed by the curling mode reversal for thick wires whereas thinner wires exhibit a more complex behaviour which is related to thermal effects and size distribution of the crystal grains that constitute the NWs.

No abstract

We describe the magnetic properties of nanoscale Fe shells grown on GaAs nanowires (NWs) by molecular beam epitaxy. The ferromagnetic character of these tubular Fe shells has been confirmed by dc magnetization measurements, and is further studied by ferromagnetic resonance (FMR), small-angle neutron scattering (SANS), and off-axis electron holography (EH).

GaAs nanowires were grown on (111)B GaAs substrates using the vapour-liquid-solid (VLS) mechanism. The Au/Pt nanodots used to catalyse wire growth were defined lithographically and had varying diameter and separation. An in-depth statistical analysis of the resulting nanowires, which had a cone-like shape, was carried out.This revealed that there were two categories of nanowire present, with differing height and tapering angle.The bimodal nature of wire shape was found to depend critically on the diameter of the Au-Ga droplet atop the nanowire. Transmission Electron Microscopy (TEM) analysis also revealed that the density of stacking faults in the wires varied considerably between the two categories of wire. It is believed that the cause of the distinction in terms of shape and crystal structure is related to the contact angle between the droplet and the solid-liquid interface. The dependency of droplet diameter on contact angle is likely related to line-tension, which is a correction to Young's equation for the contact angle of a droplet upon a surface. The fact that contact angle may influence resulting wire structure and shape has important implications for the planning of growth conditions and the preparation of wires for use in proposed devices. a) Electronic mail: odowdbj@tcd.ie

We report on the effect of cap layer material on the magnetic properties and aging of the Fe-NW (nanowire) arrays grown on oxidized vicinal Si (111) templates using atomic terrace low angle shadowing technique. We find that the Fe-NW arrays capped with metallic (Ag) layers do not show any sign of degradation with aging, whereas NW arrays capped with insulating dielectric (MgO) layers show degradation of the saturation magnetization and an out-of-plane unidirectional anisotropy. We find that this out-of-plane unidirectional anisotropy competes with the shape anisotropy which is still the dominant anisotropy. The origin of this additional anisotropy is explained on the basis of oxidation of Fe due to the presence of MgO that leads to the formation of an oxide interlayer. This oxide interlayer forms at the expense of NW materials, leading to reduction in the thickness of some of the Fe-NWs within the array, and orients their magnetic moments out-of-plane. The reduction in NW thickness and the presence of Fe-O interlayer facilitates stabilization of this anisotropy. Our model is supported by x-ray absorption spectroscopy studies performed as a function of aging, which suggests that the oxide interlayer thickness increases with aging. V

Template-based synthesis and magnetic properties of Mn-Zn ferrite nanotube and nanowire arrays

Epitaxial magnesium ferrite thin films have been grown by molecular beam epitaxy (MBE) on MgO(100). Growth conditions such as substrate temperature and growth rates were optimized. By using different characterization techniques, structural, electrical and optical properties of the films were studied as a function of Mg content. In particular, we highlight the importance of the growth rate on the actual Mg/Fe ratio in the film.