COMING TO A WINDOW NEAR YOU

Self-cleaning glass does not clean a surface instantaneously – it operates continuously as the window is exposed to natural sunlight and rainfall. The coating cannot be applied to existing windows because it is deposited during the manufacture of the glass itself. However, once Pilkington Activ™ has been installed, after a short 'running in' period, which allows the coating to absorb enough ultraviolet radiation to start working properly, the durable coating will last for the lifetime of the glass.

Pilkington Activ™ is the latest in a line of innovations from Pilkington, including fire-resistant glass (Pilkington Pyrostop), and Hotscreen-glass embedded with tungsten wires, finer than a human hair, that can defrost an icy windscreen at the touch of a burton. In July 2001, the research scientist who headed the team that pioneered the development of Pilkington Activ™, Dr Kevin Sanderson, won the prestigious Worshipful Company of Glass Sellers’ “Award of Excellence”. In agreement, homeowners everywhere are certain to be celebrating as the new glass appears in window products across Europe (Figure 3) and the window-cleaning chore becomes a thing of the past.

Figure 3. Typical sealed unit of Pilkington Activ™ product for a window.

 

BOX 1 Glass manufacture — the float glass process

The float glass process is the principal method of producing flat glass throughout the world. The silica and other added chemicals (the 'batch') are melted at white heat (~ 1600°C) to a highly viscous consistency, and held in a controlled atmosphere long enough for the surface to become flat and parallel. The red-hot glass flows onto a mirror-like lake of molten metal and spreads into a thin ribbon. The ribbon is cooled as it flows down the molten metal (the 'float bath') and gradually solidifies into place (at about 600°C). This is now 'float glass'.

Coatings that change the properties of the glass can be applied to the cooling ribbon of glass. On-line chemical vapour deposition (CVD) is the most significant advance in the float glass process since it was invented. CVD occurs following the reaction of gases in a chamber, the products of which deposit on and adhere to the glass substrate.

 

 

CARBON NANOTUBES AND GENERAL ELECTRO-OP

TO-MECHANIC PROPERTIES

Since the chance discovery (or re-discovcry) of Iijima in 1991, carbon nanotubes have been investigated extensively. The results to date show that they arc truly remarkable materials. As has been known experimentally² and theoretically³, carbon nanotubes can be semiconducting with a bandgap anywhere between 20mcV to 2cV. They can be metallic, but capable of sustaining current density hundreds of times greater than a metal. They are many times stronger than steel but much lighter. They are thermally more conductive than all crystals and metals'¹. And, they may be superconducting. electrostrictive⁶, ...etc. A list of merits already long and still growing. A " one size fits all" magic material! No wonder, many think, and some stated, that carbon nanotubc is the greatest development in electronic materials.

All these wonderful properties come about not by coincidence. They are rooted in the fact that in this system the electronic degree freedom is strongly coupled to the mechanic degree of freedom, more so than in any other semiconductor or metal. As such, they offer an ideal platform for extending electronics and therefore information technology into the vast and relatively untapped areas of information acquisition and execution. It is in this broad context, nanotubes stand out as a likely most enabling new materials.

One of the areas in which new break through technologies might be enabled by nanotubes is sensors - electrical, mechanic, optical and magnetic etc. either distributed over large areas or highly localized to sizes smaller than ever possible before.

In the context of Sensing and Photonics for Space Environments - the theme of this SPIE Conference, a few additional real or potential attributes of the nanotubc technology are perhaps particularly worth citing:

• Radiation hardness -arising from the strong covalent bonding

• Defect localization - arising from the nanotubc to nanombe spatial and electrical separations

• Normal incidence detection in the ordered array setting - arising from the cylindrical symmetry and the nanometric diameter

• Reduced sensitivity to temperature - arising from the quasi 1 -D phonon density of states therefore greatly suppressed phonon coupling to the surrounding, and from the related high thermal conductivity

Although the details of the underlying physics of the remarkable clcctxo-mechanic-optic properties of nanotubes arc sufficiently complex and not fully understood, an intuitive understanding of why carbon nanotube, be it single-walled and or multi-walled, can be reached via first principle considerations.

Carbon is interesting and unique in that it can form either the semi-metallic graphite or the very hard and nearly insulating diamond. In grahite, the carbon bonds arc in the same plane, so called SP2 bonds, whereas in diamond the bonds arc in the three-dimensional space, referred to as SP3 bonding. Carbon nanotube is a third form of Carbon lattice structure. Intuitively, it can be viewed as graphitic sheets rolled up into single-walled or multi-walled tubes in which the originally planar SP2 bond vectors arc bent along with the graphite plane, thus projecting a component to the third dimension and picking up some of the characteristics and hence the properties of the SP3 bonds. It is therefore not surprising to find that carbon nanotubes exhibit mechanical and electronic properties in between graphite and diamond. The smaller the diameter, the more the SP2 bonds arc bent, and the more SP3 like characteristics they pick up, hence the wider the nanorube band gap.

We presented a more detailed and quantitative analysis earlier, which arrives at an inverse dependence of the bandgap on the local bending curvature (i.e., diameter and helicity). In the case of multi-walled nanotubes, the system is likely to favor a distribution of the helicity of each wall over a wide range to minimize the overall energy. As a result, the multi-walled nanotubes lack a well defined helicity. However, this should be viewed as more of an assertion than experimentally verified fact, the measured bandgaps of multi-welled nanotubes do confirm that the bandgap of multi-walled nanotubes follows a simple linear relation to the inverse of the diameter, with little indication of the presence of a helicity dependence.

Underlying this intuitive model of nanotube's general properties is the observation that carbon nanorube is a unique physical system in which the mechanic and electronic degrees of freedom are tightly coupled. To minimize its total energy, the system can respond to a change in electronic properties with one in mechanical properties, and vice L versa, giving rise to giant electro-mechanical effects. Further discussion along this line, however interesting, is beyond the scope of this review as it is unlikely to be relevant beyond the bandgap-diameter dependence to IR applications.

 

 

ABSTRACT WRITING

However, we always provide, or we should provide, an additional mechanism for telling people whether to go ahead, and that is the abstract. Now, an abstract, as you know, is something that's about anywhere, between, say fifty and two or three hundred words long, a description of the work, really to supplement the title in telling people whether this is something that they ought to be pursuing further. One mistake that people often make is they don't give the results. They'll tell what was done - an experiment was carried out to measure this, that and the other, and to test some theory - but they'll never mention whether in fact the theory was true or not. So always make sure that your abstract does include the results that you've actually achieved. Don't give afterthoughts. The nature of things is such that abstracts are usually written right at the end of the paper, and often people who've written the paper and then a couple of days later they think of something they should have said but didn't, will stick it in the abstract. Now that's not appropriate, rewrite the paper but the abstract should correspond to the paper and not be a further extension of it.

Abstracts are frequently published by themselves in Abstracting journals, so that a person who doesn't have the paper before him may read the abstract. Hence, you can't use undefined symbols like this Greek thing - I don't know, zeta, I don't even know what it is. But often you'll see somebody stick in " a zeta value of 3.8 was obtained". Well, if you don't define what this zeta is - I'm assuming it is a zeta by the way - this doesn't help the reader at all who doesn't have the paper before him. And similarly, often people use some very pompous terms which I'm sure are perfectly well defined in the paper but if you don't have the paper it doesn't help. " A compound beneficent quotient of 3.7 was established in category A". Well, you know, if this isn't the stan­dard term and if the reader doesn't know it, it doesn't help. And the final comment I might make is that often abstracts are read by very simple people - laymen, controllers, lawyers, directors - so try and keep the technical level of the abstract just a notch below that of the paper. I don't mean to say that, you know, make it such that a seven-year-old can read it. But don't make it as fiercely technical as you know how. I don't think that's appropriate in an abstract.

Well, these are the shorting mechanisms - by these means we reduce the readers down to the number who ought to be reading the paper. It does no good to have a man read your paper who shouldn't be reading it. It just makes him angry and it retards the progress of science. So try and don't use it as a come on so much but make it a device to deter people who've no interest in what follows. However, those who ought to be reading it then are going to be with us and we're going to have to take them further.

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