Issue no. 21, 2010
Published: Jun 25, 2010 |
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 Hot electrons could double solar cell efficiency |
| Memories made of light |
| Sub-atomic particle signals simulated as sound |
| 'Dark pulse laser' could improve telecoms |
| Researchers develops green process for producing fuel additive |
| Electron 'invisible ink' promises purer nanocrystals |
| Zap of UV light may have triggered life |
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| Hot electrons could double solar cell efficiency |
The most efficient silicon solar cells turn 25% of the incoming light
into electricity, but even with further improvements these cells will
reach a theoretical limit at 31%, because incoming light creates large
numbers of extremely energetic electrons. These 'hot' electrons lose
their energy in less than a picosecond - too rapidly to be harnessed.
Previous research suggested that nanoscale chunks of semiconducting
material could help slow the rate at which hot electrons lose energy as
heat. That's because the energy levels within quantum dots are widely
spaced, making it difficult for electrons to jump between them. The
energy levels are more closely packed in larger chunks of semiconductor
such as the silicon wafers often used in solar cells, so jumping levels
and losing energy as heat is easier.
Now, researchers at the University of Texas in Austin have shown that
those longer-lived hot electrons can pass from quantum dots to a
semiconducting wafer before the electrons give up their energy as heat -
a step towards a solar cell that can harness hot electrons for their
energy, boosting the theoretical maximum efficiency to 66%. The
researchers coated a wafer of semiconducting titanium dioxide with
quantum dots of lead selenide and shone light on it. A change in the
optical properties of the wafer showed that electrons had entered it
from the quantum dots. But the materials were engineered such that the
electrons could enter the substrate only when hot. |
| New Scientist / Science
Jun 24, 2010 |
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| Memories made of light |
Researchers have coaxed laboratory crystals to capture and release
information carried within a light pulse at the highest efficiency yet.
Light is the ideal carrier of information, because it is so fast. Until
now, researchers have tried to fashion 'quantum memories' for light
primarily by sending lasers into a vapour made of atoms. The atoms
preserve information in the light that can then be read out again. But
quantum memories based on atomic vapours are inefficient. The best such
system reported to date has an efficiency of 17%. A system needs at
least 50% recall to be useful in quantum applications.
The new work by researchers at the Australian National University in
Canberra instead uses a solid crystal, in which the atoms are rigidly
packed together instead of bouncing around diffusely as they would in a
vapour. That control helps to achieve a memory efficiency of 69%.
As the light pulse enters the crystal, it begins to slow down, its front
reaching one end of the crystal and stopping as the rest of the light
squeezes itself in. The crystal is mostly transparent but can absorb one
particular colour very strongly. The researchers switch on an electric
field gradient, which changes the strongest absorption colour in
different parts of the crystal, so that one end of it absorbs strongly
at the blue end of the spectrum and the other end toward the red.
Quantum information from the light is stored in the oscillations of the
crystal's atoms. Reversing the electric field causes the atoms to
re-emit light containing the same information as the original pulse. |
| ScienceNews / Nature
Jun 23, 2010 |
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| Sub-atomic particle signals simulated as sound |
Scientists have simulated the sounds set to be made by sub-atomic
particles such as the Higgs boson when they are produced at the Large
Hadron Collider (LHC). Their aim is to develop a means for physicists at
CERN to 'listen to the data' and pick out the Higgs particle if and when
they finally detect it.
The researchers modelled data from the giant Atlas experiment at the
LHC, converting data expected from collisions at the LHC into sounds.
Atlas is one of the experiments at the LHC. An instrument inside Atlas
called the calorimeter is used for measuring energy and is made up of
seven concentric layers. Each layer is represented by a note and their
pitch is different depending on the amount of energy that is deposited
in that layer. The process of converting scientific data into sounds is
called sonification.
The researchers have so far generated a number of simulations based on
predictions of what might happen during collisions inside the LHC. The
team is only now feeding in real results from real experiments. The aim
is to give physicists at the LHC another way to analyse their data. The
sonification team believes that ears are better suited than eyes to pick
out the subtle changes that might indicate the detection of a new
particle. |
| BBC News
Jun 22, 2010 |
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| 'Dark pulse laser' could improve telecoms |
A new type of laser that emits 'dark' pulses could provide better
signals for telecommunications, according to physicists at the National
Institute of Standards and Technology (NIST) in the US who have created
the device. The dark pulses, which consist of intensity dips in an
otherwise continuous beam of laser light, are effectively the opposite
of the bright bursts in a normal pulsed laser.
Dark lasers are not entirely new. For some 20 years, physicists have
been able to create so-called dark soliton lasers. Solitons are light
pulses that propagate without spreading, and are often used in fibre
optics. Their dark counterparts are simply gaps in a continuous beam
that do not spread either. But dark solitons are difficult to create
and, when they are created, it is done outside the laser using a
combination of tricky pulse-shaping techniques. The new dark pulse
laser, on the other hand, forms the dark pulses inside the laser itself.
The researchers suggest that the dark pulse laser could find
applications in telecommunications, because the dark pulses are less
prone to disperse than regular, bright pulses. |
| PhysicsWorld / Optics Express
Jun 16, 2010 |
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| Researchers develops green process for producing fuel additive |
A new green, bio-based method for producing a much-used fuel additive
and industrial chemical that is currently made from petroleum products
has been developed by researchers at Iowa State University. They
invented a process for manufacturing isobutene or isobutylene by
identifying a new, natural enzyme that produces the fuel organically.
The enzyme makes it possible to convert the glucose found naturally in
plants to make isobutene. The enzyme is found naturally in about half of
all organisms in the world. Isobutene is a gas used to produce chemicals
and also in the manufacturing of fuel additives, adhesives, plastics and
synthetic rubber. It can be chemically converted to isooctane, which is
a fuel that could be used to replace gasoline additive methyl tert-butyl
ether (MBTE), which can be environmentally harmful.
Isooctane is used in gasoline to stop engine knocking and other
problems. Currently, isooctane is produced from petroleum products. By
using his naturally occurring, biological process to produce isobutene,
the researchers believes there will be environmental and cost benefits
to the biofuels industry. |
| PhysOrg / Iowa State University
Jun 23, 2010 |
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| Electron 'invisible ink' promises purer nanocrystals |
By its very nature, nanotechnology is too small to see with the naked
eye. Even so, chemists at the University of Erlangen-Nuremberg in
Germany have found a way to make it even less perceptible by creating a
nanoscopic form of 'invisible ink'. The technique offers a way of
growing nanocrystals of a much higher purity than achieved to date.
The researchers used an electron beam to remove oxygen ions from a
silicon oxide wafer, leaving nanoscopic dents in the surface. The
process leaves virtually no visible trace. The dents facilitate chemical
reactions, though, so a hidden message written onto the wafer with the
electron beam can later be revealed by flowing iron pentacarbonyl gas
across the surface.
The gas reacts at the indentations to form carbon monoxide while leaving
solid - and reflective - iron nanocrystals fixed to the surface. The
process leaves virtually no visible trace, but the hidden message can
later be revealed. |
| New Scientist / Angewandte Chemie International
Jun 23, 2010 |
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| Zap of UV light may have triggered life |
A blast of ultraviolet light may have helped create an important
molecular building block for life, say scientists from Georgia Tech in
Atlanta and the University of Roma 'La Sapienza'.
The researchers focused on the molecule formamide, the simplest
structure containing the required four building blocks of life - carbon,
hydrogen, oxygen and nitrogen. Previous studies have already shown how
heating formamide in a mineral stew creates most of the ingredients for
ribonucleic acid, commonly known as RNA. RNA is thought to have served
as an early operating system for life, later joined by the more robust
deoxyribonucleic acid, or DNA, genetic coder.
Missing from the formamide brew, however, has been guanine, one of RNA's
four critical ingredients (the others are adenine, cytosine and uracil.)
One lightning rod for guanine's creation, scientists discovered, is
ultraviolet light. Today, Earth's atmosphere blocks most UV rays from
the sun, but in its early years the planet lacked ozone and other
shielding chemicals in its skies. The research demonstrates a scenario
for creating RNA that would not require lots of heat or standing pools
of liquid water. The finding could also mean conditions for life
elsewhere in the solar system may not be as stringent.
Scientists are now working to mimic the day-night cycles of solar
ultraviolet radiation and adding different minerals to see how that
changes the resulting RNA brew. |
| ABC / ChemBioChem
Jun 16, 2010 |
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