Ballasted & electrically steerable carbon nanotube field emitters

Here we present our on-going efforts toward the development of stable ballasted carbon nanotube-based field emitters employing hydrothermally synthesized zinc oxide nanowires and thin film silicon-on-insulator substrates. The semiconducting channel in each controllably limits the emission current thereby preventing detrimental burn-out of individual emitters that occurs due to unavoidable statistical variability in emitter characteristics, particularly in their length. Fabrication details and emitter characterization are discussed in addition to their field emission performance. The development of a beam steerable triode electron emitter formed from hexagonal carbon nanotube arrays with central focusing nanotube electrodes, is also described. Numerical ab-initio simulations are presented to account for the empirical emission characteristics. Our engineered ballasted emitters have shown some of the lowest reported lifetime variations (< 0.7%) with on-times of < 1 ms, making them ideally-suited for next-generation displays, environmental lighting and portable x-rays sources. © 2012 SPIE.

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.

Tantalum-oxide catalysed chemical vapour deposition of single- and multi-walled carbon nanotubes

Tantalum-oxide thin films are shown to catalyse single- and multi-walled carbon nanotube growth by chemical vapour deposition. A low film thickness, the nature of the support material (best results with SiO2) and an atmospheric process gas pressure are of key importance for successful nanotube nucleation. Strong material interactions, such as silicide formation, inhibit nanotube growth. In situ X-ray photoelectron spectroscopy indicates that no catalyst reduction to Ta-metal or Ta-carbide occurs during our nanotube growth conditions and that the catalytically active phase is the Ta-oxide phase. Such a reduction-free oxide catalyst can be technologically advantageous. © 2013 The Royal Society of Chemistry.

SOI CMOS integrated zinc oxide nanowire for toluene detection

The paper reports on the in-situ growth of zinc oxide nanowires (ZnONWs) on a complementary metal oxide semiconductor (CMOS) substrate, and their performance as a sensing element for ppm (parts per million) levels of toluene vapour in 3000 ppm humid air. Zinc oxide NWs were grown using a low temperature (only 90°C) hydrothermal method. The ZnONWs were first characterised both electrically and through scanning electron microscopy. Then the response of the on-chip ZnONWs to different concentrations of toluene (400-2600ppm) was observed in air at 300°C. Finally, their gas sensitivity was determined and found to lie between 0.1% and 0.3% per ppm. © 2013 IEEE.

Characterization and fabrication of zinc oxide nanowire devices

In this paper, we demonstrate an approach for the local synthesis of ZnO nanowires (ZnO NWs) and the potential for such structures to be incorporated into device applications. Three network ZnO NW devices are fabricated on a chip by using a bottom-up synthesis approach. Microheaters (defined by standard semiconductor processing) are used to synthesize the ZnO NWs under a zinc nitrate (Zn(NO3)2·6H2O) and hexamethylenetetramine (HMTA, (CH2)6·N4) solution. By controlling synthesis parameters, varying densities of networked ZnO NWs are locally synthesized on the chip. The fabricated networked ZnO NW devices are then characterized using UV excitation and cyclic voltammetry (CV) experiments to measure their photoresponse and electrochemical properties. The experimental results show that the techniques and material systems presented here have the potential to address interesting device applications using fabrication methods that are fully compatible with standard semiconductor processing. © 2013 IEEE.

Electrical transport and percolation in magnetoresistive manganite / insulating oxide composites: case of La0.7Ca0.3MnO3 / Mn3O4

We report the results of electrical resistivity measurements carried out on well-sintered La0.7Ca0.3MnO3 / Mn3O4 composite samples with almost constant composition of the magnetoresistive manganite phase (La0.7Ca0.3MnO3). A percolation threshold (fc) occurs when the La0.7Ca0.3MnO3 volume fraction is ~ 0.19. The dependence of the electrical resistivity as a function of La0.7Ca0.3MnO3 volume fraction (fLCMO) can be described by percolation-like phenomenological equations. Fitting the conducting regime (fLCMO > fc) by the percolation power law returns a critical exponent t value of 2.0 +/- 0.2 at room temperature and 2.6 +/-0.2 at 5 K. The increase of t is ascribed to the influence of the grain boundaries on the electrical conduction process at low temperature.

Spray drying: An alternative synthesis method for polycationic oxide compounds

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi1.68Ca2Co1.69O 8, La0.95A0.05CoO3 (A=Ca, Sr, Ba)] or magnetoresistance [La0.70A0.30MnO3 (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties. © 2010 Elsevier Ltd All rights reserved.

Analysis of amorphous indium-gallium-zinc-oxide thin-film transistor contact metal using Pilling-Bedworth theory and a variable capacitance diode model

It is widely reported that threshold voltage and on-state current of amorphous indium-gallium-zinc-oxide bottom-gate thin-film transistors are strongly influenced by the choice of source/drain contact metal. Electrical characterisation of thin-film transistors indicates that the electrical properties depend on the type and thickness of the metal(s) used. Electron transport mechanisms and possibilities for control of the defect state density are discussed. Pilling-Bedworth theory for metal oxidation explains the interaction between contact metal and amorphous indium-gallium-zinc-oxide, which leads to significant trap formation. Charge trapping within these states leads to variable capacitance diode-like behavior and is shown to explain the thin-film transistor operation. © 2013 AIP Publishing LLC.