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Category: particle physics – Page 656

Breakthrough in the search for graphene-based electronics

For 15 years, scientists have tried to exploit the “miracle material” graphene to produce nanoscale electronics. On paper, graphene should be great for just that: it is ultra-thin—only one atom thick and therefore two-dimensional, it is excellent for conducting electrical current, and holds great promise for future forms of electronics that are faster and more energy efficient. In addition, graphene consists of carbon atoms – of which we have an unlimited supply.

In theory, graphene can be altered to perform many different tasks within e.g. electronics, photonics or sensors simply by cutting tiny patterns in it, as this fundamentally alters its . One “simple” task, which has turned out to be surprisingly difficult, is to induce a band gap—which is crucial for making transistors and optoelectronic devices. However, since graphene is only an atom thick all of the atoms are important and even tiny irregularities in the pattern can destroy its properties.

“Graphene is a fantastic material, which I think will play a crucial role in making new nanoscale electronics. The problem is that it is extremely difficult to engineer the electrical properties,” says Peter Bøggild, professor atDTU Physics.

Artificial intelligence alone won’t solve the complexity of Earth sciences

One way to crack this problem, according to the authors of a Perspective in this issue, is through a hybrid approach. The latest techniques in deep learning should be accompanied by a hand-in-glove pursuit of conventional physical modelling to help to overcome otherwise intractable problems such as simulating the particle-formation processes that govern cloud convection. The hybrid approach makes the most of well-understood physical principles such as fluid dynamics, incorporating deep learning where physical processes cannot yet be adequately resolved.

Studies of complex climate and ocean systems could gain from a hybrid between artificial intelligence and physical modelling.

Exotic spiraling electrons discovered

Rutgers and other physicists have discovered an exotic form of electrons that spin like planets and could lead to advances in lighting, solar cells, lasers and electronic displays.

It’s called a “chiral surface ,” and it consists of particles and anti-particles bound together and swirling around each other on the surface of solids, according to a study in the Proceedings of the National Academy of Sciences.

Chiral refers to entities, like your right and left hands, that match but are asymmetrical and can’t be superimposed on their mirror image.

How Do Particles Escape Black Holes? Supercomputers May Have the Answer

The gravitational pull of a black hole is so strong that nothing, not even light, can escape once it gets too close. However, there is one way to escape a black hole — but only if you’re a subatomic particle.

As black holes gobble up the matter in their surroundings, they also spit out powerful jets of hot plasma containing electrons and positrons, the antimatter equivalent of electrons. Just before those lucky incoming particles reach the event horizon, or the point of no return, they begin to accelerate. Moving at close to the speed of light, these particles ricochet off the event horizon and get hurled outward along the black hole’s axis of rotation.

Known as relativistic jets, these enormous and powerful streams of particles emit light that we can see with telescopes. Although astronomers have observed the jets for decades, no one knows exactly how the escaping particles get all that energy. In a new study, researchers with Lawrence Berkeley National Laboratory (LBNL) in California shed new light on the process. [The Strangest Black Holes in the Universe].

Turning Light into Matter May Soon Be Possible

Circa 2014

Scientists may soon create matter entirely from light, using technology that is already available to complete a quest 80 years in the making.

The experiment would re-create events that were critical in the first 100 seconds of the universe and that are also expected to happen in gamma-ray bursts, the most powerful explosions in the cosmos and one of the greatest unsolved mysteries in physics, researchers added.

As Einstein’s famous equation E=mc proved, mass can get converted into energy and vice versa. For instance, when an electron meets its antimatter counterpart, a positron, they annihilate each other, releasing photons, the particles making up light.

Engineered metasurfaces reflect waves in unusual directions

In our daily lives, we can find many examples of manipulation of reflected waves such as mirrors to see our reflections or reflective surfaces for sound that improve auditorium acoustics. When a wave impinges on a reflective surface with a certain angle of incidence and the energy is sent back, the angle of reflection is equal to the angle of incidence. This classical reflection law is valid for any homogenous surface. Researchers at Aalto University have developed new metasurfaces for the arbitrary manipulation of reflected waves, essentially breaking the law to engineer the reflection of a surface at will.

Metasurfaces are artificial structures, composed of periodic arranged of meta-atoms at subwavelength scale. Meta-atoms are made of traditional materials but, if they are placed in a periodic manner, the surface can show many unusual effects that cannot be realized by the materials in nature. In their article published 15 February 2019 in Science Advances, the researchers use power-flow conformal metasurfaces to engineer the direction of reflected waves.

‘Existing solutions for controlling reflection of waves have low efficiency or difficult implementation,’ says Ana Díaz-Rubio, postdoctoral researcher at Aalto University. ‘We solved both of those problems. Not only did we figure out a way to design high efficient metasurfaces, we can also adapt the design for different functionalities. These metasurfaces are a versatile platform for arbitrary control of reflection.’

China made an artificial star that’s 6 times as hot as the sun, and it could be the future of energy

Imagine if we could replace fossil fuels with our very own stars. And no, we’re not talking about solar power: We’re talking nuclear fusion. And recent research is helping us get there. Meet the Experimental Advanced Superconducting Tokamak, or EAST.

EAST is a fusion reactor based in Hefei, China. And it can now reach temperatures more than six times as hot as the sun. Let’s take a look at what’s happening inside. Fusion occurs when two lightweight atoms combine into a single, larger one, releasing energy in the process. It sounds simple enough, but it’s not easy to pull off. Because those two atoms share a positive charge. And just like two opposing magnets, those positive atoms repel each other.

Stars, like our sun, have a great way of overcoming this repulsion … their massive size, which creates a tremendous amount of pressure in their cores … So the atoms are forced closer together making them more likely to collide. There’s just one problem: We don’t have the technology to recreate that kind of pressure on Earth.

Safer-by-Design Fluorescent Nanocrystals: Metal Halide Perovskites vs Semiconductor Quantum Dots

Despite the young age of the research field, substantial progress has been made in the study of metal halide perovskite nanocrystals (HPNCs). Just as their thin-film counterparts are used for light absorption in solar cells, they are on the way to revolutionizing research on novel chromophores for light emission applications. Exciting physics arising from their peculiar structural, electronic, and excitonic properties are being discovered with breathtaking speed. Many things we have learned from the study of conventional semiconductor quantum dots (CSQDs) of II–VI (e.g., CdSe), IV–VI (e.g., PbS), and III–V (e.g., InP) compounds have to be thought over, as HPNCs behave differently. This Feature Article compares both families of nanocrystals and then focuses on approaches for substituting toxic heavy metals without sacrificing the unique optical properties as well as on surface coating strategies for enhancing the long-term stability.

In the early 1980s the quest for novel photocatalysts, fueled by the oil crisis in the preceding decade, led to the discovery of semiconductor quantum dots. Pioneering works by Efros, Brus, and Henglein showed both experimentally and theoretically that the reduction of size of semiconductor particles (e.g., CdS) down to the nanometer range induces a significant change in their band gap energy.(1−3) The underlying quantum confinement effect, occurring when the nanocrystal size is (significantly) smaller than twice the exciton Bohr radius of the semiconductor material (Table 1), leads to an increase, scaling with 1/r, of the band gap energy. It also gives rise to the appearance of discrete energy levels at the place of continuous valence and conduction energy bands. In the same period Ekimov as well as Itoh and co-workers observed quantum confinement in small CuCl crystallites embedded in a glass or a NaCl matrix.

The atomic dynamics of rare everlasting electric fields

By ricocheting neutrons off the atoms of yttrium manganite (YMnO3) heated to 3,000 degrees Fahrenheit, researchers have discovered the atomic mechanisms that give the unusual material its rare electromagnetic properties. The discovery could help scientists develop new materials with similar properties for novel computing devices and micro-actuators.

The experiment was conducted as a collaboration between Duke University and Oak Ridge National Laboratory (ORNL) and appeared online in Nature Communications on January 2, 2018.

Ferromagnetism is the scientific term for the phenomenon responsible for permanent magnets like iron. Such exist because their molecular structure consists of tiny magnetic patches that all point in the same direction. Each patch, or domain, is said to have a , with a north and a south pole, which, added together, produce the magnetic fields so often seen at work on refrigerator doors.

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