Investigating the hydrothermal growth of zinc oxide nanostructures through seed layer control

Controlling the growth of ZnO nanostructures for photovoltaic applications will ensure greater device efficiency and parameter control. This paper reports on methods to engineer the morphology and tailor the nanostructure growth direction through the hydrothermal synthesis method. Effective control is achieved through the use of a sputtered zinc layer together with modifications of the growth solution. These nanostructures have been developed with a view to incorporation into excitonic solar cells, and methods to improve surface stability using a fully aqueous synthesis method will be discussed. © by Oldenbourg Wissenschaftsverlag, München.

Wet-spinning of amyloid protein nanofibers into multifunctional high-performance biofibers.

Amyloid nanofibers derived from hen egg white lysozyme were processed into macroscopic fibers in a wet-spinning process based on interfacial polyion complexation using a polyanionic polysaccharide as cross-linker. As a result of their amyloid nanostructure, the hierarchically self-assembled protein fibers have a stiffness of up to 14 GPa and a tensile strength of up to 326 MPa. Fine-tuning of the polyelectrolytic interactions via pH allows to trigger the release of small molecules, as demonstrated with riboflavin-5'-phophate. The amyloid fibrils, highly oriented within the gellan gum matrix, were mineralized with calcium phosphate, mimicking the fibrolamellar structure of bone. The formed mineral crystals are highly oriented along the nanofibers, thus resulting in a 9-fold increase in fiber stiffness.

Numerical simulation of the growth of ZnO nanostructures in a tube furnace by physical vapour deposition

Zinc oxide is a versatile II-VI naturally n-type semiconductor that exhibits piezoelectric properties. By controlling the growth kinetics during a simple carbothermal reduction process a wide range of 1D nanostructures such as nanowires, nanobelts, and nanotetrapods have been synthesized. The driving force: for the nanostructure growth is the Zn vapour supersaturation and supply rate which, if known, can be used to predict and explain the type of crystal structure that results. A model which attempts to determine the Zn vapour concentration as a function of position in the growth furnace is described. A numerical simulation package, COMSOL, was used to simultaneously model the effects of fluid flow, diffusion and heat transfer in a tube furnace made specifically for ZnO nanostructure growth. Parameters such as the temperature, pressure, and flow rate are used as inputs to the model to show the effect that each one has on the Zn concentration profile. An experimental parametric study of ZnO nanostructure growth was also conducted and compared to the model predictions for the Zn concentration in the tube. © 2008 Materials Research Society.

Fiber laser processing of amorphous rare earth NeFeB magnetic materials

Since the exchange coupling theory was proposed by Kneller and Hawig in 1991 there has been a significant effort within the magnetic materials community to enhance the performance of rare earth magnets by utilising nano-composite meta-materials. Inclusions of magnetically soft iron smaller than approximately 10 nm in diameter are exchange coupled to a surrounding magnetically hard Nd2Fe14B matrix and provide an enhanced saturisation magnetisation without reducing coercivity. For such a fine nanostructure to be produced, close control over the thermal history of the material is needed. A processing route which provides this is laser annealing from an amorphous alloy precursor. In the current work, relationships between laser parameters, thermal histories of laser processed amorphous stoichiometric NdFeB ribbons and the magnetic properties of the resulting nanocrystalline products have been determined with a view to applying the process to thick film nanocomposite magnet production.

Design of carbon nanotube fiber microelectrode for glucose biosensing

BACKGROUND: Carbon nanotube (CNT) fiber directly spun from an aerogel has a unique, well-aligned nanostructure (nano-pore and nano-brush), and thus provides high electro-catalytic activity and strong interaction with glucose oxidase enzyme. It shows great potential as a microelectrode for electrochemical biosensors. RESULTS: Cyclic voltammogram results indicate that post-synthesis treatments have great influence on the electrocatalytic activity of CNT fibers. Raman spectroscopy and electrical conductivity tests suggest that fibers annealed at 250 °C remove most of the impurities without damaging the graphite-like structure. This leads to a nano-porous morphology on the surface and the highest conductivity value (1.1 × 10 5 S m -1). Two CNT fiber microelectrode designs were applied to enhance their electron transfer behaviour, and it was found that a design using a 30 nm gold coating is able to linearly cover human physiological glucose level between 2 and 30 mmol L -1. The design also leads to a low detection limit of 25 μmol L -1. CONCLUSIONS: The high performance of CNT fibers not only offers exceptional mechanical and electrical properties, but also provides a large surface area and electron transfer pathway. They consequently make excellent bioactive microelectrodes for glucose biosensing, especially for potential use in implantable devices. © 2011 Society of Chemical Industry.

Cylindrical Fresnel lenses based on carbon nanotube forests

The forests of carbon nanotubes have been termed as the darkest man-made materials. Such materials exhibit near-perfect optical absorption (reflectance∼0.045%) due to low reflectance and nanoscale surface roughness. We have demonstrated the utilization of these perfectly absorbing forests to produce binary amplitude cylindrical Fresnel lenses. The opaque Fresnel zones are defined by the dark nanotube forests and these lenses display efficient focusing performance at optical wavelengths. Lensing performance was analyzed both computationally and experimentally with good agreement. Such nanostructure based lenses have many potential applications in devices like photovoltaic solar cells. © 2012 American Institute of Physics.

Synthesis of zinc oxide nanostructures by microheaters in the ambient environment

A catalyst-free synthesis of ZnO nanostructures using platinum microheaters under ambient environmental conditions has been developed. Different types of ZnO nanostructures are synthesized from the oxidization of Zn thin film by local heating. The characterization of two shapes of Pt microheaters is investigated and the relationship between the applied power for heat generation and ZnO nanostructure synthesis is investigated by local heating experiments under ambient conditions. Based on the developed heating approach, synthesis area, location, and morphologies of ZnO nanostructures can be controlled through the deposited thickness of Zn layer and applied heating voltages. Furthermore, a connected multiple-structure (Zn-ZnO-Zn) layer is synthesized using combinative multimicroheaters. © 2002-2012 IEEE.

Advanced carbon nanotubes and carbon nanotube fibers for biosensing applications

Since the discovery of Carbon Nanotubes (CNTs) by Iijima in 1991[1, 2], there has been an explosion of research into the physical and chemical properties of this novel material. CNT based biosensors can play an important role in amperometric, immunosensor and nucleic-acid sensing devices, e.g. for detection of life threatening biological agents in time of war or in terrorist attacks, saving life and money for the NHS. CNTs offer unique advantages in several areas, like high surfacevolume ratio, high electrical conductivity, chemical stability and strong mechanical strength, and CNT based sensors generally have higher sensitivities and lower detection limit than conventional ones. In this review, recent advances in biosensors utilising carbon nanotubes and carbon nanotube fibres will be discussed. The synthesis methods, nanostructure approaches and current developments in biosensors using CNTs will be introduced in the first part. In the second part, the synthesis methods and up-to-date progress in CNT fibre biosensors will be reviewed. Finally, we briefly outline some exciting applications for CNT and CNT fibres which are being targeted. By harnessing the continual advancements in micro and nano- technology, the functionality and capability of CNT-based biosensors will be enhanced, thus expanding and enriching the possible applications that can be delivered by these devices. © 2012 Bentham Science Publishers. All rights reserved.

Field emission characteristics of contact printed graphene fins.

Carbon nanostructures have been much sought after for cold-cathode field emission applications. Herein a printing technique is reported to controllably nanostructure chemical vapor deposited graphene into vertically standing fins. The method allows for the creation of regular arrays of bilayer graphene fins, with sharp ridges that, when printed onto gold electrodes, afford a new type of field emission electron source geometry. The approach affords tunable morphologies and excellent long term and cyclic stabilities.

Evaluation of the functionality of biodegradable polymeric platforms for drug delivery systems

We present the development of a drug-loaded triple-layer platform consisting of thin film biodegradable polymers, in a properly designed form for the desired gradual degradation. Poly(dl-lactide-co-glycolide) (PLGA (65:35), PLGA (75:25)) and polycaprolactone (PCL) were grown by spin coating technique, to synthesize the platforms with the order PCL/PLGA (75:25)/PLGA (65:35) that determine their degradation rates. The outer PLGA (65:35) layer was loaded with dipyridamole, an antiplatelet drug. Spectroscopic ellipsometry (SE) in the Vis-far UV range was used to determine the nanostructure, as well as the content of the incorporated drug in the as-grown platforms. In situ and real-time SE measurements were carried out using a liquid cell for the dynamic evaluation of the fibrinogen and albumin protein adsorption processes. Atomic force microscopy studies justified the SE results concerning the nanopores formation in the polymeric platforms, and the dominant adsorption mechanisms of the proteins, which were defined by the drug incorporation in the platforms. © 2013 Elsevier B.V. All rights reserved.