Gas-phase production of multifunctional composite nanoparticles by photoinduced chemical vapor deposition

As these results indicate, photo-CVD coating is a robust process that allows for the creation of core-shell nanoparticles. In the present work we demonstrated that photo-CVD can effectively coat Fe2O3 particles with silica for purposes of biological applications. TDMA results combined with TEM images indicate that all particles are effectively coated and that particle coating thicknesses can be tuned to desired thickness depending on the application. In addition, the ability to vary coating properties and to coat high concentrations of particles makes this technique of interest for industrial production where uniform properties are needed for large quantities of particles [2]. Copyright © 2010 by ASME.

A metal-polymer composite with unusual properties

Electrically conductive composites that contain conductive filler dispersed in an insulating polymer matrix are usually prepared by the vigorous mixing of the components. This affects the structure of the filler particles and thereby the properties of the composite. It is shown that by careful mixing nano-scale features on the surface of the filler particles can be retained. The fillers used possess sharp surface protrusions similar to the tips used in scanning tunnelling microscopy. The electric field strength at these tips is very large and results in field assisted (Fowler-Nordheim) tunnelling. In addition the polymer matrix intimately coats the filler particles and the particles do not come into direct physical contact. This prevents the formation of chains of filler particles in close contact as the filler content increases. In consequence the composite has an extremely high resistance even at filler loadings above the expected percolation threshold. The retention of filler particle morphology and the presence of an insulating polymer layer between them endow the composite with a number of unusual properties. These are presented here together with appropriate physical models. © 2005 IOP Publishing Ltd.

Metal-polymer composite sensors for volatile organic compounds: Part 1. Flow-through chemi-resistors

A new type of chemi-resistor based on a novel metal-polymer composite is described. The composite contains nickel particles with sharp nano-scale surface features, which are intimately coated by the polymer matrix so that they do not come into direct physical contact. No conductive chains of filler particles are formed even at loadings above the percolation threshold and the composite is intrinsically insulating. However, when subjected to compression the composite becomes conductive, with sample resistance falling from ≥ 1012 Ω to < 0.01 Ω. The composite can be formed into insulating granules, which display similar properties to the bulk form. A bed of granules compressed between permeable frits provides a porous structure with a start resistance set by the degree of compression while the granules are free to swell when exposed to volatile organic compounds (VOCs). The granular bed presents a large surface area for the adsorption of VOCs from the gas stream flowing through it. The response of this system to a variety of vapours has been studied for two different sizes of the granular bed and for different matrix polymers. Large responses, ΔR/R0 ≥ 10^7, are observed when saturated vapours are passed through the chemi-resistor. Rapid response allows real time sensing of VOCs and the initial state is recovered in a few seconds by purging with an inert gas stream. The variation in response as a function of VOC concentration is determined.

Performance of thin film carbon materials and carbon nanotubes as cold cathodes

The field emissions from three different types of carbon films are studied using a Kiethly voltage-current source-measure unit under computer control. The three types of carbon films are : 1) a-C:H:N deposited using an inductively coupled rf PECVD process, where the N content in the films can be as high as 30 at %; 2) cathodic arc deposited tetrahedral amorphous carbon with embedded regions of carbon nanotube and anion structures and 3) unoriented carbon nanotube films on a porous substrate. The films are formed by filtering a solution of nanotubes dispersed in alcohol through the pores and drying.

Plasma enhancement of current from carbon cathodes for field emission displays

This paper examines the possibility of using a background gas medium to enhance the current available from low threshold carbon cathodes. The field emission current is used to initiate a plasma in the gas medium, and thereby achieve a current multiplication effect. Results on the variation of anode current as a function of electric field and gas pressure are presented. These are compared with model calculations to verify the principles of operation. The influence of ion bombardment on the long term performance thin film carbon cathodes is examined for He and Ar multiplication plasmas. A measure of the influence of current multiplication on display quality is presented by examining light output from two standard low voltage phosphors. Also studied are the influence of doping the carbon with N to lower the threshold voltage for emission as well as the consequent impact on anode current from the plasma.