First photograph of light as a particle and a wave

Quantum mechanics tells us that light can behave simultaneously as a particle or a wave. However, there has never been an experiment able to capture both natures of light at the same time; the closest we have come is seeing either wave or particle, but always at different times. Taking a radically different experimental approach, EPFL scientists have now been able to take the first ever snapshot of light behaving both as a wave and as a particle. The breakthrough work is published in Nature Communications.

When UV light hits a metal surface, it causes an emission of electrons. Albert Einstein explained this “photoelectric” effect by proposing that light – thought to only be a wave – is also a stream of particles. Even though a variety of experiments have successfully observed both the particle- and wave-like behaviors of light, they have never been able to observe both at the same time.

A new approach on a classic effect

A research team led by Fabrizio Carbone at EPFL has now carried out an experiment with a clever twist: using electrons to image light. The researchers have captured, for the first time ever, a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle.

The experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves traveling in opposite directions meet each other they form a new wave that looks like it is standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.

This is where the experiment’s trick comes in: The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using the ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualize the standing wave, which acts as a fingerprint of the wave-nature of light.

While this phenomenon shows the wave-like nature of light, it simultaneously demonstrated its particle aspect as well. As the electrons pass close to the standing wave of light, they “hit” the light’s particles, the photons. As mentioned above, this affects their speed, making them move faster or slower. This change in speed appears as an exchange of energy “packets” (quanta) between electrons and photons. The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle.

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Fabrizio Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. As Carbone explains: “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”



Nuclear battery developed


Long-lasting, water-based nuclear battery developed

Long-lasting, water-based nuclear battery developed

Researchers working at the University of Missouri (MU) claim to have produced a prototype of a nuclear-powered, water-based battery that is said to be both longer-lasting and more efficient than current battery technologies and may eventually be used as a dependable power supply in vehicles, spacecraft, and other applications where longevity, reliability, and efficiency are paramount.

“Betavoltaics, a battery technology that generates power from radiation, has been studied as an energy source since the 1950s,” said associate professor Jae W. Kwon, of the College of Engineering at MU. “Controlled nuclear technologies are not inherently dangerous. We already have many commercial uses of nuclear technologies in our lives including fire detectors in bedrooms and emergency exit signs in buildings.”

Utilizing the radioactive isotope strontium-90 to enhance the electrochemical energy produced in a water-based solution, the researchers have incorporated a nanostructured titanium dioxide electrode acting as a catalyst for water decomposition. That is, the catalyst assists the breakdown of water in conjunction with the applied radiation into assorted oxygen compounds.

As a result, when high-energy beta radiation passes through the platinum and the nanoporous titanium dioxide, electron-hole pairs are produced within the titanium dioxide, creating an electron flow and a resultant electric current.

“Water acts as a buffer and surface plasmons created in the device turned out to be very useful in increasing its efficiency,” Kwon said. “The ionic solution is not easily frozen at very low temperatures and could work in a wide variety of applications including car batteries and, if packaged properly, perhaps spacecraft.”

By no means the first-ever nuclear battery – the NanoTritium device from City Labs being one recent notable example – this is the first nuclear battery that has been produced to exploit the inherent advantages of radiolysis (water-splitting with radiation) to produce an electric current, at higher energy levels and lower temperatures than previously possible. And at much greater claimed efficiencies than other water-splitting energy production techniques.

This is because, unlike other forms of photocatalytic methods of water-splitting to produce energy, the high-energy beta radiation in the MU device produces free radicals in water such that the kinetic energy is recombined or trapped in water molecules so that the radiation can be converted into electricity – using the platinum/titanium dioxide electrode previously described – to achieve water splitting efficiently and at room temperature.

As a result, whilst solar cells use a similar mechanism for the transference of energy via hole-electron pairs, very few free radicals are produced because the photon energies are principally in the visible spectrum and subsequently at lower levels of energy.

Beta radiation produced by the strontium source, on the other hand, with its ability to enhance the chemical reactions involving free radicals at greater electron energy levels, is a much more efficient way to produce extremely long-lasting and reliable energy. So much so, that the water-based nuclear battery may well offer a viable alternative to the solar cell as a sustainable, low-pollution energy source.



3-D Nano printer World Record

3-D Printer With Nano-Precision:

3D Printer

3D Printer

Printing three-dimensional objects with incredibly fine details is now possible using “two-photon lithography.” With this technology, tiny structures on a nanometer scale can be fabricated. Researchers at the Vienna University of Technology (TU Vienna) have now made a major breakthrough in speeding up this printing technique: The high-precision-3D-printer at TU Vienna is orders of magnitude faster than similar devices. This opens up completely new areas of application, such as in medicine.  Setting a New World Record.  The 3D printer uses a liquid resin, which is hardened at precisely the correct spots by a focused laser beam. The focal point of the laser beam is guided through the resin by movable mirrors and leaves behind a hardened line of solid polymer, just a few hundred nanometers wide. This fine resolution enables the creation of intricately structured sculptures as tiny as a grain of sand. “Until now, this technique used to be quite slow,” says Professor Jürgen Stampfl from the Institute of Materials Science and Technology at the TU Vienna. “The printing speed used to be measured in millimeters per second — our device can do five meters in one second.” In two-photon lithography, this is a world record.  This amazing progress was made possible by combining several new ideas. “It was crucial to improve the steering mechanism of the mirrors,” says Jan Torgersen (TU Vienna). The mirrors are continuously in motion during the printing process. The acceleration and deceleration-periods have to be tuned very precisely to achieve high-resolution results at a record-breaking speed.  Photoactive Molecules Harden the Resin.  3D-printing is not all about mechanics — chemists had a crucial role to play in this project too. “The resin contains molecules, which are activated by the laser light. They induce a chain reaction in other components of the resin, so-called monomers, and turn them into a solid,” says Jan Torgersen. These initiator molecules are only activated if they absorb two photons of the laser beam at once — and this only happens in the very center of the laser beam, where the intensity is highest. In contrast to conventional 3D-printing techniques, solid material can be created anywhere within the liquid resin rather than on top of the previously created layer only. Therefore, the working surface does not have to be specially prepared before the next layer can be produced, which saves a lot of time. A team of chemists led by Professor Robert Liska (TU Vienna) developed the suitable ingredients for this special resin.  Researchers all over the world are working on 3D printers today — at universities as well as in industry. Because of the dramatically increased speed, much larger objects can now be created in a given period of time. This makes two-photon-lithography an interesting technique for industry.  At the TU Vienna, scientists are now developing bio-compatible resins for medical applications. They can be used to create scaffolds to which living cells can attach themselves facilitating the systematic creation of biological tissues. The 3d printer could also be used to create tailor made construction parts for biomedical technology or nanotechnology.