Cheap as LED chips

Light-emitting diodes almost ubiquitously provide the illumination in electronics and potentially will provide energy-efficient brightness in our homes. However, the LED material of choice, gallium nitride, and its method of processing and manufacture into working devices is relatively expensive. Now, US engineers have developed a novel semiconducting material based on zinc oxide that could be used in a new type of LED that is just as effective but could reduce costs for a wide range of applications.

According to Deli Wang and colleagues at the University of California San Diego, an LED requires a positive and a negative semiconducting material. While n-type negative-charge carrying nanowires of inexpensive zinc oxide have been easy to make, the researchers have now synthesized nanoscale cylindrical wires of the material that can transport positive charges. These so-called p-type ZnO nanowires complete the circuit for making a new type of inexpensive LED.

Deli Wang

Deli Wang

To make the p-type ZnO nanowires, the engineers doped ZnO crystals with phosphorus using a simple chemical vapour deposition technique that is less expensive than the metal organic chemical vapour deposition (MOCVD) technique often used to synthesize the building blocks of gallium nitride LEDs. Adding phosphorus atoms to the ZnO crystal structure leads to p-type semiconducting materials through the formation of a defect complex that increases the number of positive-charge carrying holes relative to the number of free electrons in the material.

Zinc oxide is a very good light emitter, explains Wang, Electrically driven zinc oxide single nanowire lasers could serve as high efficiency nanoscale light sources for optical data storage, imaging, and biological and chemical sensing. He adds that Zinc oxide nanostructures are incredibly well studied because they are so easy to make. Now that we have p-type zinc oxide nanowires, the opportunities for LEDs and beyond are limitless.

LEDs

LEDs

Wang and his colleagues at Peking University report their synthesis this month in the journal Nano Letters. A provisional patent application for p-type ZnO nanowires has been filed and Wang’s lab is currently working on a variety of nanoscale applications for their nanowires. Transistors that use the semiconducting properties of zinc oxide are also on the horizon, Wang believes. p-type doping in nanowires would make complementary ZnO nanowire transistors possible, he explains.

Further reading

Nano Lett. 2007, in press;
http://dx.doi.org/10.1021/nl062410c

Deli Wang homepage
http://circuit.ucsd.edu/~dwang/

Suggested searches

light emitting diodes
semiconductors
nanotechnology

The rough and smooth of fraud prevention

UK scientists believe the microscopic imperfections found on non-reflective surfaced could be the key to a unique identification fingerprint for almost any object from paper documents and passports to credit cards and product packaging. They have developed a system to scan a surface with a laser and generate a unique identity code that can be stored in a secure database and used to confirm the authenticity of an object by comparing a live surface scan with the stored ID. The technique is almost impossible to fool so could become an inexpensive method of combating fraud suggest researchers from Imperial College London and Durham University.

Russell Cowburn, Professor of Nanotechnology at Imperial, and colleagues explain how they have exploited the inherent random roughness of non-reflective materials to generate a unique code for almost any object with a non-reflective surface including passports, ID and credit cards and pharmaceutical packaging. The approach could quickly displace more costly security tags, such as diffraction gratings (credit card holograms) or security inks.

Russell Cowburn

Russell Cowburn

The researchers used the optical phenomenon of laser speckle to examine the fine surface features of various materials. A focused laser essentially scans the surface and the intensity of reflections is recorded to produce a digital signature for the surface, which can be stored in a secure database. The researchers tested the scanning technique successfully on matt-finish plastic cards, identity cards and coated paperboard packaging and were able to uniquely identify each object from its surface signature. The objects were still uniquely identifiable even after the team subjected them to rough handling, immersion in water, scorching, scrubbing with an abrasive cleaning pad, and scribbled on them with black marker pen.

Many scientists would have known that there were differences, Cowburn told us. What was not known was that it was possible to probe these differences in a simple, portable way and that the differences would be so robust against degradation, he adds, Without this, the differences in the surface aren’t useful in security.

Scanning electron micrograph of the surface of normal office paper. The complex pattern of fibres revealed forms the basis of a fingerprint for paper documents. (Picture by Del Atkinson, Durham University)

Scanning electron micrograph of the surface of normal office paper. The complex pattern of fibres revealed forms the basis of a fingerprint for paper documents. (Picture by Del Atkinson, Durham University)

The beauty of this system is that there is no need to modify the item being protected in any way with tags, chips or inks – it’s as if documents and packaging have their own unique DNA, explains Cowburn. This, he adds, makes protection covert, low-cost, simple to integrate into the manufacturing process and immune to attacks against the security feature itself.

Schematic showing how the technology could be used. A focused laser is scanned over the surface of the item to be identified. The sensor records an imprint in the reflected laser light of the underlying naturally occurring irregularities on the surface (paper fibres in this case, shown in the pull-out) and converts this into a serial code. (c) Ingenia Technology Ltd. Not to be reproduced without permission.

Schematic showing how the technology could be used. A focused laser is scanned over the surface of the item to be identified. The sensor records an imprint in the reflected laser light of the underlying naturally occurring irregularities on the surface (paper fibres in this case, shown in the pull-out) and converts this into a serial code. (c) Ingenia Technology Ltd. Not to be reproduced without permission.

The researchers, who have spun-off Ingenia Technology to commercialise the idea add that their technology could prove invaluable not only in fighting fraud and theft but in preventing illicit use of breeder documents, such as birth certificates, in identity theft. Our findings open the way to a new and much simpler approach to authentication and tracking, says Cowburn. The system is so secure that not even the inventors would be able to crack it since there is no known manufacturing process for copying surface imperfections at the necessary level of precision.

Atomic force micrograph of the surface of a plastic ID card. Although there are no fibres, there are still slight undulations to the surface. These form the fingerprint for plastic items. (Picture by Gang Xiong, Durham University)

Atomic force micrograph of the surface of a plastic ID card. Although there are no fibres, there are still slight undulations to the surface. These form the fingerprint for plastic items. (Picture by Gang Xiong, Durham University)

Further reading

Nature, 2005, 436, 475
http://dx.doi.org/10.1038/436475a

Russell Cowburn
http://www3.imperial.ac.uk/people/r.cowburn

Ingenia Technology
http://www.ingeniatechnology.com/

Suggested searches

lasers

Quark, strangeness, and charm

Quarks are strange and equally charming, but all attempts to observe them in isolation would be in vain. Now, particle physicists are embarking on a new attempt to solve the mysteries of quarks with the completion of the three most powerful supercomputers ever applied to this problem. One of these is housed at the University of Edinburgh and will be used by the UK Quantum Chromodynamics (UKQCD) group of scientists from seven British universities.

UKQCD is a collaboration of particle physicists from the Universities of Edinburgh, Southampton, Swansea, Liverpool, Glasgow, Oxford and Cambridge and was formed in 1989 to simulate and study the behaviour of matter at the sub-atomic levels in the colourful field of quantum chromodynamics. It has since its founding, exploited a series of novel architecture computers for QCD simulations, becoming an internationally leading team. With the completion of the Edinburgh computer, the UKQCD scientists can probe the properties of quarks ever more closely.

Chris Sachrajda

Chris Sachrajda

Quarks are the fundamental particles that make up 99.9% of ordinary matter acting as the building blocks of hadrons, of which the best known are protons and neutrons. Quarks have proved impossible to separate, preferring to exist in colour-neutral groups of two or three. For quarks, colour is a property akin to electrical charge, rather than anything to do with the colours we see with our eyes. This indivisibility means that we know little about the basic properties of quarks. For instance, what are their precise masses? Why are there six different types? And, why are they so strongly bound together?

It is the strong nuclear force that binds quarks, a term that belies its weakness at the incredibly short distances between quarks themselves. But, try to separate any two (or three) quarks and this force begins to live up to its name. As such, much that particle physicists know about quarks is down to pure simulation.

Richard Kenway

Richard Kenway

The UKQCD computer is the first of three similar machines and has been operating since January 2005. The second computer was inaugurated in May 2005 at the RIKEN Brookhaven Research Center in Brookhaven National Laboratory in the USA. The third is part of the US Department of Energy Program in High Energy and Nuclear Physics, and is also installed at Brookhaven where it is currently undergoing testing.

UKQCD team member Chris Sachrajda of the University of Southampton explains the relevance of the machine. The QCDOC [QCD-on-a-chip] machine at Edinburgh, combined with new theoretical techniques which we have been developing, provides us with the opportunity to study the Strong Force to unprecedented precision, he says. This will enable us to extract detailed information about the fundamental constituents of nature, by combining our calculations with experimental data from the major accelerator laboratories. Southampton’s QCDgrid node will help the researchers there run simulations and exploit the emerging data.

The computers are built with processing chips specifically designed for the purpose, known as QCD-on-a-chip, or QCDOC for short. A little slower than the microprocessor in your laptop, the QCDOC chip was designed to consume a tenth of the electrical power, so that tens of thousands of them could be put into a single machine. The computers were designed and built jointly by the University of Edinburgh, Columbia University (USA), the RIKEN Brookhaven Research Center (USA) and IBM.

Each QCDOC machine operates at a speed of 10 Teraflops, or 10 trillion (i.e. million million) floating point operations per second. By comparison, a regular desktop computer operates at a few Gigaflops (a thousand million floating point operations per second), whilst IBM’s BlueGene, a close relative of QCDOC and the fastest computer in the world, operates at over 100 Teraflops.

We are certainly very excited by our new machine and the opportunities it affords, Edinburgh’s Chris Maynard told Spotlight. Richard Kenway, who led UK participation in the QCDOC Project, echoed the sentiment. After five years building this machine, it’s exhilarating to be able to compute in days things which take everybody else months, he says. Now we are about to run QCDOC for months to do the most realistic QCD simulation yet. It’s like standing on the shore of a new continent after a long voyage, we’ve chosen our path of exploration, but we don’t know what we’re going to find.

Further reading

http://phys.columbia.edu/~cqft/qcdoc/qcdoc.htm
Chris Sachrajda

http://www.phys.soton.ac.uk/staff/index.php?staff=cts
Richard Kenway

http://www.nesc.ac.uk/nesc/staff/rdkenway.html
RIKEN BNL Research Center

http://www.bnl.gov/riken/
Theorists get to grips with the strong force (PDF article)

http://www.physics.gla.ac.uk/lattice_EU_network/physics_world.pdf

Suggested searches

quarks
quantum chromodynamics
particle physics