Theoretical physicists at the Department of Energy’s SLAC National Accelerator Laboratory used computer simulations to show how special light pulses could create robust channels where electricity flows without resistance in an atomically thin semiconductor.
If this approach is confirmed by experiments, it could open the door to a new way of creating and controlling this desirable property in a wider range of materials than is possible today.
The result was published in Nature Communications.
Over the past decade, understanding how to create this exotic type of material – known as “topologically protected” because its surface states are impervious to minor distortions – has been a hot research topic in materials science. The best-known examples are topological insulators, which conduct electricity with no resistance in confined channels along their edges or surfaces, but not through their interiors.
Scientists at the U.S. Naval Research Laboratory (NRL), Materials Science and Technology Division, have demonstrated that the intensity and spectral composition of the photoluminescence emitted from a single monolayer of tungsten disulphide (WS2) can be spatially controlled by the polarization domains in an adjacent film of the ferroelectric material lead zirconium titanate (PZT).
These domains are written in the PZT using a conductive atomic force microscope, and the photoluminescence (PL) is measured in air at room temperature. Because the polarization domain wall width in a ferroelectric can be as low as 1-10 nm, this approach enables spatial modulation of PL intensity and the corresponding carrier populations with potential for nanoscale resolution.
Single monolayer transition metal dichalcogenides (TMDs) such as WS2 exhibit striking optical properties due to their direct band gap. The dielectric screening is very low due to their two dimensional (2D) character, and thus their properties are strongly affected by their immediate environment, and can be modified and controlled by variations in local charge density due to adsorbates or electrostatic gating. This has generated keen interest in a wide variety of electronic and optical device applications.
Fundamental research sheds light on new many-particle quantum physics in atomically thin semiconductors
A paper published in Nature Communications by Sufei Shi, assistant professor of chemical and biological engineering at Rensselaer, increases our understanding of how light interacts with atomically thin semiconductors and creates unique excitonic complex particles, multiple electrons, and holes strongly bound together. These particles possess a new quantum degree of freedom, called “valley spin.” The “valley spin” is similar to the spin of electrons, which has been extensively used in information storage such as hard drives and is also a promising candidate for quantum computing.
The paper, titled “Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2,” was published in the Sept. 13, 2018, edition of Nature Communications. Results of this research could lead to novel applications in electronic and optoelectronic devices, such as solar energy harvesting, new types of lasers, and quantum sensing.
Shi’s research focuses on low dimensional quantum materials and their quantum effects, with a particular interest in materials with strong light-matter interactions. These materials include graphene, transitional metal dichacogenides (TMDs), such as tungsten diselenide (WSe2), and topological insulators.
You turn on a switch and the light switches on because electricity ‘flows’. The usual perception is that this is like opening a faucet and the water starts to flow. But this analogy is misleading. The flow of water is determined by the theory of hydrodynamics, where the behavior of the fluid requires no knowledge of the movements of individual molecules.
However, electric currents in solids are formed by electrons. In metals, the electrons do not collide with each other, but they scatter with lattice defects. In conventional materials, the movement of electrons is therefore more akin to the motion of balls in a pinball machine.
Hydrodynamic electron flow can only be observed in high-purity quantum materials. An international team of members from the IBM Research Laboratory Zurich, the University of Hamburg and the Max Planck Institute for Chemical Physics of Solids has now found signatures of electron hydrodynamics in the semimetal tungsten diphosphide. The results were published in the journal Nature Communications. On closer inspection, it could be shown that the hydrodynamic behavior of the electrons is rooted in the strongly interacting quantum nature of the electron system.
Physicists have discovered a novel kind of nanotube that generates current in the presence of light. Devices such as optical sensors and infrared imaging chips are likely applications, which could be useful in fields such as automated transport and astronomy. In future, if the effect can be magnified and the technology scaled up, it could lead to high-efficiency solar power devices.
Working with an international team of physicists, University of Tokyo Professor Yoshihiro Iwasa was exploring possible functions of a special semiconductor nanotube when he had a lightbulb moment. He took this proverbial lightbulb (which was in reality a laser) and shone it on the nanotube to discover something enlightening. Certain wavelengths and intensities of light induced a current in the sample—this is called the photovoltaic effect. There are several photovoltaic materials, but the nature and behavior of this nanotube is cause for excitement.
“Essentially our research material generates electricity like solar panels, but in a different way,” said Iwasa. “Together with Dr. Yijin Zhang from the Max Planck Institute for Solid State Research in Germany, we demonstrated for the first time nanomaterials could overcome an obstacle that will soon limit current solar technology. For now solar panels are as good as they can be, but our technology could improve upon that.”
So this is a Scanning Electron Microscope (SEM) photo I took today of one of my samples of tungsten (VI) oxide, this is the sample marketed as <20 micrometers (10^-6 m ) in diameter. As you can see there are some particles that at bigger than this which tells you that suppliers can’t be trusted with what they say…
But It also shows that the particles are not regular shapes which can effect the stability of the emulsions formed with them. This was what the powder looks like as it has been supplied, if I was to sonicate this the particles should be much smaller on average
I just thought it was a really nice picture and there you go
Unexpected Beauty by FEI Company Via Flickr: It’s a contamination of iron oxide involving the tungsten filament of an automotive light bulb. Courtesy of Mr. FRANCISCO RANGEL , MCT/INT Image Details Instrument used: Quanta SEM Magnification:3963xHorizontal Field Width: 75.3 μm Vacuum: 9.27e-7 mbar Voltage: 20 kV Spot:2.0Working Distance:10.8Detector: Mix: SE plus BSE.
You may be most familiar with the element lithium as an integral component of your smart phone’s battery, but the element also plays a role in the development of clean fusion energy. When used on tungsten surfaces in fusion devices, lithium can reduce periodic instabilities in plasma that can damage the reactor walls, scientists have found.
The results, demonstrated by scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and collaborators on China’s Experimental Advanced Superconducting Tokamak (EAST) found that lithium powder can eliminate instabilities known as edge-localized modes (ELMs) when used to coat a tungsten plasma-facing component called the “divertor” – the unit that exhausts waste heat and particles from plasma that fuels fusion reactions. If left alone, such instabilities can damage the divertor and cause fusion reactions to fizzle.
The results are good news for future devices that plan to use tungsten for their own divertors that are designed to work with lithium.
A team led by DESY scientists has designed, fabricated and successfully tested a novel X-ray lens that produces sharper and brighter images of the nano world. The lens employs an innovative concept to redirect X-rays over a wide range of angles, making a high convergence power. The larger the convergence the smaller the details a microscope can resolve, but as is well known it is difficult to bend X-rays by large enough angles. By fabricating a nano-structure that acts like an artificial crystal it was possible to mimic a high refracting power. Although the fabrication needed to be controlled at the atomic level — which is comparable to the wavelength of X-rays — the DESY scientists achieved this precision over an unprecedented area, making for a large working-distance lens and bright images. Together with the improved resolution these are key ingredients to make a super X-ray microscope. The team led by Dr. Saša Bajt from DESY presents the novel lens in the journal Scientific Reports (Nature Publishing Group).
“X-rays are used to study the nano world, as they are able to show much finer details than visible light and their penetrating power allows you to see inside objects,” explains Bajt. The size of the smallest details that can be resolved depends on the wavelength of the radiation used. X-rays have very short wavelengths of only about 1 to 0.01 nanometres (nm), compared to 400 to 800 nm for visible light. A nanometre is a millionth of a millimetre. The high penetration of X-rays is favoured for three-dimensional tomographic imaging of objects such as biological cells, computer chips, and the nanomaterials involved in energy conversion or storage. But this also means that the X-rays pass straight through conventional lenses without being bent or focussed. One possible method to focus X-rays is to merely graze them from the surface of a mirror to nudge them towards a new direction. But such X-ray mirrors are limited in their convergence power and must be mechanically polished to high precision, making them extremely expensive.
This piece is very special to me. This is a huge sample of Wolframite crystal with Milky Quartz, and chalcopyrite and Mica Crystal. This piece is from the Oregon Mine near Nederland, Colorado. This piece has made me want to go claim the old mine and try to find more of this fabulous tungsten mineral.
