Advanced Materials Research Laboratory

Nanomagnetic domains of chromium deposited on vertically-aligned carbon nanotubes

Andrew C. Wright et al. — Wed, 08 Aug 2012 02:06:11 PDT

The drive to create ever smaller magnetic memory devices has led to the development of new nanomagnetic domains on surfaces. This paper reports the development of nano-chromium magnetic domains obtained using electrodeposition on vertically aligned carbon nanofibers arrays. Attempts to achieve this using conventional aqueous solutions were unsuccessful even after thin nickel underlayers were applied. The use of a novel electrolyte, a deep eutectic solvent, made from choline chloride: chromium (III) chloride enabled highly conformal overcoatings of chromium on individual bare carbon nanotubes to be obtained. Very high aspect ratio metal microstructures could be obtained by this novel technology. Magnetic imaging of the coated nanoarrays showed there to be clear magnetic character to the coating when the thin coatings were applied but this disappeared when the deposits were thicker and more contiguous.

Magnetophoretic assembly and printing of nanowires

Andrew C. Wright et al. — Thu, 12 Apr 2012 07:36:15 PDT

Nanowires are a well-established class of materials covering both metals and semiconductors. Although the synthesis of nanowires has been highly developed, their manipulation into specific device structures has lagged behind. Here we report a simple room temperature method for creating directly patterned structures out of nickel nanowires of submicron diameters as previously formed by electrotemplating. Specially shaped magnetic pole-pieces are used to form patterns of these ferromagnetic rods on thin flexible plastic foils, which were then fixed permanently into place either by electrodepositing an additional thin nickel coating or by a UV-curable polymer solution. It is shown that it is possible with oriented and patterned magnetic fields to create both vertically and, by using additional surface tension forces upon drying, horizontally aligned arrays of nickel rods. The authors show that linewidths down to 50 μm can easily be realized with this technique and also show that direct printing of these magnetophoretically assembled structures onto adhesive or rubber substrates is also possible. The simplicity and low-cost inherent in this lithography-free method suggests that it is suitable as a general manufacturing method for nanowire assembly. As an example, a simple field emission display device is demonstrated.

A novel synthetic route to metal-polymer nanocomposites by in situ suspension and bulk polymerizations

Jixin Yang et al. — Wed, 13 Oct 2010 06:26:42 PDT

A novel strategy to synthesize hybrid metal–polymer nanocomposites has been achieved based on in situ free radical suspension and bulk polymerization techniques. An organometallic precursor complex is dissolved in a liquid monomer phase prior to polymerization, where upon the precursor molecules are immobilized inside the polymer matrix during its formation. In a separate step, metal nanoparticles are then formed by H₂-assisted reduction of the precursor in the polymer product in supercritical carbon dioxide (scCO₂). The synthesized nanocomposites were characterized by GPC, TGA, SEM and TEM. It is shown that the metal nanoparticles are uniformly distributed inside the polymer matrix and the inclusion of the metal precursor has no significant influence on the polymerization process. The current work represents a simple and universal way to prepare a variety of metal–polymer nanocomposite functional materials.

Loss measurements of microstructured optical fibres with metal-nanoparticle inclusions

Arian Amezcula-Correa et al. — Wed, 13 Oct 2010 06:13:46 PDT

Optical losses of measured optical fibres (MOFs) with silver nanoparticle inclusions are measured when visible light is guided in the core. The high pressure chemical deposition technique used to deposit the metal offers good control of the particle sizes allowing for varying transmission properties. The low losses demonstrate the potential for the silver impregnated MOFs to be integrated with conventional optical fibre devices.

Continuous flow supercritical chemical fluid deposition of optoelectronic quality CdS

Jixin Yang et al. — Tue, 24 Aug 2010 04:53:04 PDT

Supercritical chemical fluid deposition (SCFD) has been shown to have remarkable advantages for deposition inside nanostructured templates however so far the technique has mostly been used to deposit metals. In this paper we present the SCFD of optoelectronic grade CdS. The quality of this material is demonstrated by a range of techniques including reflectivity (A) and photoluminescence spectroscopy (B and C). At 4 K the bandedge luminescence has a full-width-at-half-maximum linewidth of 30 meV comparable with that of single crystal CdS.

Experimental and Theoretical Investigation into the Formation and Reactivity of M(Cp)(CO)₂(CO₂) (M = Mn or Re) in Liquid and Supercritical CO₂ and the Effect of Different CO₂ Coordination Modes on Reaction Rates with CO, H₂, and N₂

Jixin Yang et al. — Wed, 21 Jul 2010 06:16:44 PDT

Nanosecond time-resolved infrared spectroscopy (TRIR) has been used to study the coordination of CO₂ to the metal centers by UV photolysis of M(Cp)(CO)₃ (M = Mn or Re) in liquid or supercritical CO₂ (scCO₂) solution, which led to the formation of the CO₂ complexes M(Cp)(CO)₂(CO₂). Differences between the positions of the ν(C−O) IR bands of the CO ligands in Mn(Cp)(CO)₂(CO₂) and Re(Cp)(CO)₂(CO₂) suggest that the CO₂ ligand has different coordination modes to the metal centers in these complexes. The kinetic data and the IR spectra of the CO₂, Xe, and heptane complexes provided evidence that the CO₂ coordination mode is η¹-O end-on bound in Mn(Cp)(CO)₂(CO₂), and η²-C,O side-on bound in Re(Cp)(CO)₂(CO₂). These different coordination modes lead to dramatic differences in reactivity with CO, H₂, and N₂, with the Re complexes being significantly less reactive. To provide more evidence for the nature of the CO₂ binding modes, a series of DFT calculations were performed at the B3LYP/SDD-6-311G** level. The calculations supported the experimentally proposed CO₂ coordination modes. A significant charge transfer from Re to CO₂ occurs, resulting in partial oxidation of Re.

Supercritical chemical fluid deposition of high quality compound semiconductors

Mohammad Afzaal et al. — Wed, 21 Jul 2010 06:00:13 PDT

The main advantage of deposition from supercritical fluids over conventional CVD is the ability to fill high aspect ratio templates. Deposition of metals, indirect semiconductors and insulators into templates with dimensions down to 3 nm has been demonstrated by others, with no apparent pore blocking. In this paper we present a demonstration that it is also possible to deposit high quality, luminescent compound semiconductor films from supercritical CO2 or CO2/hexane mixtures. Depositions of CdS and III-V materials such as InP have been achieved through careful optimisation of precursor chemistry, reactor geometry and deposition conditions, supported by detailed measurements of the semiconductor film properties

Deposition in Supercritical Fluids: From Silver to Semiconductors

Jixin Yang et al. — Wed, 21 Jul 2010 05:42:37 PDT

There is great interest in developing new routes to novel functional materials, particularly for heterogeneous nanocomposites of metals or semiconductors with polymeric hosts. Supercritical fluids have become important media for the synthesis of such nanocomposites largely because of their unique properties, but also through their perceived environmental benefits over conventional routes. In this feature article, we focus on the deposition of silver and semiconductor nanoparticles into polymer substrates by use of supercritical fluids. These processes develop nanocomposites with distinct characteristics for optical and biomedical applications. The preparation and characterisation of silver and semiconductor nanoparticles is described and a brief discussion is also extended to some other novel deposition systems in supercritical fluids.

Two-Component Dendritic Gels: Easily Tunable Materials

A R. Hirst et al. — Wed, 03 Mar 2010 09:09:02 PST

This paper reports the tunability of a two-component gel system based on dendritic l-lysine with a focal point carboxylic acid group and aliphatic diamines. The microscopic structure and macroscopic properties of the gel can be modulated by changing the concentration of the components, altering their molecular structures, or tuning their relative molar ratio. In the latter case, there is a complete change in the morphology of the gel that has a direct impact on its macroscopic properties, specifically its gel-sol transition temperature.

The influence of the substrate on the growth of carbon nanotubes from nickel clusters—an investigation using STM, FE-SEM, TEM and Raman spectroscopy

Andrew C. Wright et al. — Wed, 03 Mar 2010 09:08:59 PST

Chemical Vapour Deposition (CVD) is now a well-established route to the growth of carbon nanotubes (CNT). Generally, a transition metal such as nickel dispersed as clusters on a nonreactive substrate acts as a catalyst for growth from carbon-bearing gases such as acetylene. While the diameter of the tubes is closely linked to the size of the metal clusters, the nature of the substrate itself influences the size and size distribution of the clusters themselves. Using Scanning Tunnelling Microscopy (STM) to study the clusters and high resolution Field Emission Scanning Electron Microscopy (FE-SEM) to study the resultant nanotubes, we show that nickel clusters created on TiN-coated SiC substrates have a much smaller size distribution than MoSi2-coated SiC substrates. This is reflected in the nanotube diameter after CVD growth. Raman spectroscopy and Transmission Electron Microscopy has also been used to provide further data on the nature of the nanotubes and clusters grown on these substrates.

On the origin of compositional fluctuations in ZnSe1-xSx alloys grown by metal-organic vapour-phase epitaxy

Andrew C. Wright et al. — Wed, 03 Mar 2010 08:32:54 PST

Periodic vertical modulations of the sulphur concentration have been observed in epitaxial layers of ZnSe1-xSx grown by metal-organic vapour-phase epitaxy. High-spatial-resolution microanalysis has shown that the sulphur variation is of the order of 1 at.% with a period of about 44 ± 0.1 nm. A detailed analysis of the possible causes of this modulation is presented which shows that periodic temperature fluctuations of the substrate are the most likely source.

A structural evaluation of ZnS-based electroluminescent phosphors and devices: a comparison with performance

Andrew C. Wright et al. — Wed, 03 Mar 2010 08:18:09 PST

A number of ZnS phosphor powders, both commercial and experimental, have been characterized by transmission electron microscopy (TEM). The microstructure of the phosphors has been compared with the light output (intensity and spectra) obtained when incorporated into an ac-driven electroluminescent test lamp. No evidence has been found in any samples examined by TEM of Cu2S precipitates. It was also found that the brightest emission is obtained when the phosphor particles have a very heavily multiply twinned structure together with a rough profile, and least output when they show the cubic phase. Examination of the electroluminescence output of individual phosphor grains indicates that emission is mostly from material close to the surface and suggests that field emission occurs from the surface which is aided by a marked surface roughness. Finally, the microstructure of a commercial ac powder phosphor sheet device was examined and also found to contain ZnS in the same heavily twinned form.

Medical Applications of Solid State Ionics

Roger Linford et al. — Thu, 22 Oct 2009 06:14:20 PDT

Solid State Ionic materials and devices are being used in medicine in many ways. A brief initial introduction to the materials, the devices and the pertinent electrophysiological and clinical aspects is presented. To exemplify the breadth of SSI material and device applications, an overview is given of three main areas: Biomedical applications of solid state power sources; Biofuel cells; and Iontophoretic and related devices used for controlled transdermal drug delivery and monitoring of physiological parameters

Polymer electrolytes based on modified natural rubber

Roger Linford et al. — Tue, 13 Oct 2009 04:07:43 PDT

Modified natural rubber polymer hosts having low transition glass temperatures have been investigated for use in polymer electrolytes. Two types of modified natural rubber, namely 25% epoxidised natural rubber (ENR-25) and 50% epoxidised natural rubber (ENR-50) were employed in conjunction with poly(ethylene oxide), PEO. Results are reported for ionic conductivity and thermal properties for both unplasticized and plasticized polymer electrolyte systems with lithium triflate. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizers. Unplasticized modified natural rubber-based systems exhibit ionic conductivities in the range 10−6 to 10−5 S cm−1 at ambient temperatures. Incorporating 100% of EC/PC by weight fraction of polymer (ENR/PEO) to the systems yielded mechanically stable films and ionic conductivities in the range of 10−4 S cm−1 at ambient temperature.

Biomedical Applications of Batteries

Roger Linford et al. — Tue, 13 Oct 2009 04:07:40 PDT

An overview is presented of the many ways in which batteries and battery materials are used in medicine and in biomedical studies. These include the use of batteries as power sources for motorised wheelchairs, surgical tools, cardiac pacemakers and defibrillators, dynamic prostheses, sensors and monitors for physiological parameters, neurostimulators, devices for pain relief, and iontophoretic, electroporative and related devices for drug administration. The various types of battery and fuel cell used for this wide range of applications will be considered, together with the potential harmful side effects, including accidental ingestion of batteries and the explosive nature of some of the early cardiac pacemaker battery systems.