graphene carbon spaserThe first ever spaser to be made completely of carbon has been modelled by researchers from Monash University. The technology could lead to mobile phones becoming so small, efficient, and flexible they could be printed on clothing.

A spaser (an acronym for Surface Plasmon Amplification by Stimulated Emission of Radiation) is essentially a nanoscale laser or nanolaser. It emits a beam of light through the vibration of free electrons, instead of the space-consuming electromagnetic wave emission process of a traditional laser.

“Other spasers designed to date are made of gold or silver nanoparticles and semiconductor quantum dots while our device would be comprised of a graphene resonator and a carbon nanotube gain element,” said lead researcher Chanaka Rupasinghe. “The use of carbon means our spaser would be more robust and flexible, would operate at high temperatures, and be eco-friendly. Because of these properties, there is the possibility that in the future an extremely thin mobile phone could be printed on clothing.”

Graphene and Carbon Nanotubes

Spaser-based devices are able be used as a substitute for current transistor-based devices like microprocessors, memory, and displays in order to surmount current miniaturisation and bandwidth limitations.

The researchers opted to develop their spaser using graphene and carbon nanotubes. These materials are more than a hundred times stronger than steel and can conduct heat and electricity much better than copper. They can also withstand higher temperatures.

The research demonstrated for the first time that graphene and carbon nanotubes can interact and transfer energy to each other through light. These optical interactions are very fast and energy-efficient, and so are suitable for applications such as computer chips.

“Graphene and carbon nanotubes can be used in applications where you need strong, lightweight, conducting, and thermally stable materials due to their outstanding mechanical, electrical and optical properties. They have been tested as nanoscale antennas, electric conductors and waveguides,” Chanaka said.

Spasers generate high-intensity electric fields, concentrated into a nanoscale space. The fields are much stronger than those generated by illuminating metal nanoparticles by a laser in applications such as cancer therapy.

“Scientists have already found ways to guide nanoparticles close to cancer cells. We can move graphene and carbon nanotubes following those techniques and use the high concentrate fields generated through the spasing phenomena to destroy individual cancer cells without harming the healthy cells in the body,” Chanaka said.

Reference:

Spaser Made of Graphene and Carbon Nanotubes.
Chanaka Rupasinghe, Ivan D. Rukhlenko, and Malin Premaratne.
ACS Nano 2014 8 (3), 2431-2438. DOI: 10.1021/nn406015d

Linac Coherent Light SourceScientists at Brookhaven National Laboratory have uncovered a key factor behind the emergence of superconductivity, the ability to conduct electricity with 100 percent efficiency.

Precisely timed pairs of laser pulses at the SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS) triggered superconductivity in the copper-oxide material under investigation. Researchers took x-ray snapshots of its atomic and electronic structure as superconductivity emerged.

The scientists found that so-called charge stripes of increased electrical charge vanished as superconductivity appeared. The results help rule out the theory that shifts in the material’s atomic lattice hinder the onset of superconductivity.

Light Induced Superconductivity

The new understanding may help scientists develop new techniques to eliminate charge stripes and open the door to room-temperature superconductivity, frequently looked upon as the holy grail of condensed matter physics. The demonstrated ability to rapidly switch between the insulating and superconducting states could also prove useful in advanced electronics and computation.

“The very short timescales and the need for high spatial resolution made this experiment extraordinarily challenging,” said co-author Michael Först. “Now, using femtosecond x-ray pulses, we found a way to capture the quadrillionths-of-a-second dynamics of the charges and the crystal lattice. We’ve broken new ground in understanding light-induced superconductivity.”

The material used in this study was a layered compound made of barium, lanthanum, copper, and oxygen. Each copper oxide layer contained the critical charge stripes.

Strings in a pile of Tennis Racquets

charge stripes LCLS“Imagine these stripes as ripples frozen in the sand,” said John Hill, coauthor on the study. “Each layer has all the ripples going in one direction, but in t
he neighboring layers they run crosswise. From above, this looks like strings in a pile of tennis racquets. We believe that this pattern prevents each layer from talking to the next, thus frustrating superconductivity.”

Mid-infrared laser pulses were used by the scientists used “melt” those frozen ripples, exciting the material and push it into the superconducting phase. Such pulses had previously been shown to induce superconductivity in a related compound at a frigid 10 Kelvin (minus 442 degrees Fahrenheit).

“The charge stripes disappeared immediately,” Hill said. “But specific distortions in the crystal lattice, which had been thought to stabilize these stripes, lingered much longer. This shows that only the charge stripes inhibit superconductivity.”

Catching Charge Stripes in the Act

SLAC’s LCLS x-ray laser works like a camera with a shutter speed faster than 100 femtoseconds, or quadrillionths of a second, and gives atomic-scale image resolution. LCLS uses a section of SLAC’s 2-mile-long linear accelerator to generate the electrons that give off x-ray light.

“This represents a very important result in the field of superconductivity using LCLS,” said Linac Coherent Light Source staff scientist Josh Turner. “It demonstrates how we can unravel different types of complex mechanisms in superconductivity that have, up until now, been inseparable.To make this measurement, we had to push the limits of our current capabilities. We had to measure a very weak, barely detectable signal with state-of-the-art detectors, and we had to tune the number of x-rays in each laser pulse to see the signal from the stripes without destroying the sample.”

For measuring the changes in high spatial resolution, the team used a technique called resonant soft x-ray diffraction. The LCLS x-rays strike and scatter off the crystal into the detector, carrying time-stamped signatures of the material’s charge and lattice structure that the physicists then used to reconstruct the rise and fall of superconducting conditions.

Superior Superconductor Materials

The x-ray scattering measurements showed that the lattice distortion persists for more than 10 picoseconds (trillionths of a second), long after the charge stripes melted and superconductivity appeared, which happened in less than 400 femtoseconds. Slight as it may sound, those extra trillionths of a second make a huge difference.

“The findings suggest that the relatively weak and long-lasting lattice shifts do not play an essential role in the presence of superconductivity,” Hill said. “We can now narrow our focus on the stripes to further pin down the underlying mechanism and potentially engineer superior materials.”

Reference:

Melting of Charge Stripes in Vibrationally Driven La1.875Ba0.125CuO4: Assessing the Respective Roles of Electronic and Lattice Order in Frustrated Superconductors
M. Först, R. I. Tobey, H. Bromberger, S. B. Wilkins, V. Khanna, A. D. Caviglia, Y.-D. Chuang, W. S. Lee, W. F. Schlotter, J. J. Turner, M. P. Minitti, O. Krupin, Z. J. Xu, J. S. Wen, G. D. Gu, S. S. Dhesi, A. Cavalleri, and J. P. Hill
Phys. Rev. Lett. 112, 157002 – Published 16 April 2014

Chromebook “Easy Unlock” would use Android Smartphone instead of Password

by James Anderson April 18, 2014

A new option in development for the Chrome OS could in future Chrome versions let users unlock their Chromebooks automatically just by their phone being in close proximity. Spotted by Android Police, this feature, called “Easy Unlock”, is by default disabled, but people running Chrome OS on the dev channel can enable it with chrome://flags/#enable-easy-unlock. […]

Read the full article →

Hubble Galaxy Cluster Image Looks halfway to the Universe’s Edge

by James Anderson April 18, 2014

A 14-hour exposure image cluster taken by the Hubble Space Telescope shows objects around a billion times fainter than can be seen with the naked eye. The image of a galaxy cluster gives astronomers an amazing cross-section of the Universe, showing objects at various distances and stages in cosmic history. The galaxies in this image […]

Read the full article →

Graphene Nano-Membrane 1000 times more breathable than Goretex

by James Anderson April 18, 2014

A stable, porous membrane thinner than a nanometre has been produced by researchers at ETH Zurich. That is 100,000 times thinner than a human hair. The new membrane opens the door to a new generation of waterproof clothing, and also to ultra-rapid filtration. Made of two layers of graphene, a two-dimensional film made of carbon […]

Read the full article →

Hunting Dark Energy with Very Slow Neutrons

by Wesley Roberts April 17, 2014

Gravity resonance spectroscopy is so sensitive that it can now be used to search for Dark Matter and Dark Energy. This low energy, table top alternative to massive particle accelerators takes validity of Newtonian gravity down by five orders of magnitude. It also narrows the potential properties of the forces and particles that may exist […]

Read the full article →