Category: Physics

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.

You can read the full story in the January issue of Intute Spotlight.

I am currently writing about the latest research from Mark Kuzyk – famed discoverer of the Kuzyk effect also known as the Kuzyk quantum gap. He and his colleagues have discovered a whole new class of compounds that could eventually revolutionize optical information processing (more on that in the January issue of Intute Spotlight). Anyway, he told me that getting a stronger and stronger optical, so-called non-linear response, from the materials he and his colleagues are devising will “require deliberate and painstaking molecular design and synthesis.”

But, there are also some even more serious obstacles than acumen in synthetic chemistry. He explained that molecules that have a large nonlinear-optical susceptibility, i.e. are perfect for the job in hand are often rather unstable too. Now, obviously that’s something that you have to avoid if you’re going to incorporate a molecule into a device (ask Richard Friend who has spent the last decade and a half working with his chemist colleagues to make their plastic LEDs not only bright and useful but as long-lived as possible).

All compounds are created with an intrinsic stability but some are created more unstable than others. Kuyzk told me that he had once suggested to a chemist colleague when he was at Bell Labs in the 1980s that he should try and make a specific molecule the structure of which should have produced a large optical response. “He laughed when he saw the structure,” Kuyzk said, “claiming that it would be much more explosive than TNT.” Now, I wouldn’t have liked to have been the project student charged with synthesising that nonlinear optical compound without some understanding of the stability, or otherwise, of conjugated organic bonding systems.

On a related matter, photo-stability (as opposed to thermal stability), Kuzyk also revealed to me that several years ago, a student in his group, Brent Howell, serendipitously stumbled upon a dye-doped polymer system that not only acted as a laser but recovered from photo-degradation if the system was left in the dark for a couple of days.

Furthermore, the material could be hardened to photodegradation by cycling through degradation and recovery. “We have proposed a model of the mechanisms, and are still doing experiments to test our hypothesis,” Kuyzk adds. A paper that shows recovery in two-photon absorbing materials appears in Optics Letters.

Over at the American Institute of Physics my colleague Phillip Schewe and his team have been putting together their pick of the physics discoveries for 2006.

Their number one choice had to be the new ultra precise measurement (0.76 parts per trillion uncertainty) by Gerald Gabrielse and his colleagues at Harvard University of the electron’s magnetic moment closely followed by the refinement by the same team of the fine structure constant that reveals that the electromagnetic force allowing atoms to hold on to their electrons is lower than previously thought.

Other top physics discoveries included new evidence that dark energy, the hypothetical mechanism for the accelerating expansion of the universe, was present even in the early universe; elemental discoveries of 118 and 116.

Next on the list are

• The world’s sharpest object
• The best direct test of Einstein’s (in)famous E=mc² formula
• The first direct measurement of turbulence in space
• A new measurement of the cosmic microwave background radiation
• The first study of matter-antimatter chemistry
• Advances in “two-dimensional light”, plasmonics
• Advances in “two-dimensional carbon”, graphene
• Gravityy wave model
• 2006 Nobel prize in Physics for George Smoot and John Mather

More details on the PNU site here.

The classic fish-eye lens gives photographers the visual equivalent of surround sound, capturing an all-encompassing view. But, while the results are dramatic the subject is considerably distorted to fit within the bounds of the circular image formed. This renders such lens ineffective as an all-seeing-eye in a security setting or for providing robots with better navigation.

South Korean researchers have now designed and built an inexpensive optical lens that collects light from a large area and produces an almost distortion-free wide-angle image with the more familiar rectangular shape.

The complete story is available in the latest edition of the Intute Spotlight column.

NIST physicists have taken a step towards making entanglement, the quantum phenomenon Einstein referred to as “spooky action at a distance” – into a practical tool.

The team demonstrated a method for refining entangled atom pairs (a process called purification) so they might be used in quantum computers, communications systems with potentially “unbreakable” data encryption, and highly accurate atomic clocks.

The research reported in today’s issue of Nature marks the first time atoms have been both entangled and subsequently purified. This had only been done before with entangled photons. The new experiment entangles two pairs of atoms but measures only one pair.

According to NASA, Einstein never liked entanglement as it seemed to run counter to the central tenet of his theory of relativity that nothing, not even information, could travel faster than the speed of light. Because it is possible to prepare two particles in a single quantum state so that when one is particle is observed, the other will be observed simultaneously to be in the complimentary state and vice versa. As a result, measurements performed on one system seem to be instantaneously influencing other systems with which it is entangled.

However, although two entangled systems appear to interact even though they are separated no useful “information” can be transmitted in this way, which means causality is not compromised and Einstein’s theory remains intact.

Researchers at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia, Russia’s Joint Institute for Nuclear Research and the Lawrence Livermore National Laboratory in California, have announced new indirect evidence of element 118 in the journal Phys Rev C.

Previously, the LBNL retracted its 1999 claims of having found element 118 because of reproducability issues. (They couldn’t make it again, in other words). It turned out that one of the team had been fabricating lab-book entries.

However, experiments conducted at the JINR U400 cyclotron between February and June 2005, produced atomic decay chains that establish the existence of element 118. In these decay chains, previously observed element 116 is produced via the alpha decay of element 118. The details will be published in the October 2006 edition of the journal, Physical Review C and we’ll have a more complete report later.

New Scientist and others are already casting doubts on whether North Korea really did detonate a nuclear device underground on Monday. The magazine points to discrepancies in the reporting of the size of the explosion as hinting that NK may have simply detonated a massive cache of conventional explosive in the hope of simulating the effects of a nuclear device.

The magazine says that the Korea Earthquake Research Centre in South Korea reported a 3.58-magnitude tremor from North Korea’s North Hamgyong province, which is equivalent to a 800 tonnes of TNT, but the Russian defence minister says the explosion was closer to 5000-15000 tonnes. By contrast, the Hiroshima bomb was estimated at 15 kilotonnes.

Scientists are frantically analysing the seismographic evidence and assessing whether or not this could have been a large conventional explosion, a failed nuclear detonation, or the claimed success that North Korea’s smiling TV correspondent claimed.