Researchers experimenting with the properties of Graphene have discovered that when the single-atom-thick sheet is exposed to extreme low temperatures and high magnetic field it has the ability to filter electrons according to their spin direction.
At room temperature and with no magnetic field the flake of graphene functions as a normal conductor with electrons flowing throughout the sheet. With the application of a magnetic field perpendicular to the sheet the electrons migrate out to the sheet edges while the rest of the sheet has the properties of an insulator. Current flow around the edges is either clockwise or anticlockwise depending on the orientation of the field (known as the quantum Hall effect).
When the MIT researchers switched a second magnetic field in the same plane as the Graphene sheet they found that electrons move around the edge in either clockwise or counterclockwise direction depending on the electron’s direction of spin. [via]
Graphene could be good for Quantum Computing - [Link]
The Stanford University theoretical physicist Shoucheng Zhang and colleagues have suggested that a new material called Stanene, composed of a one-atom-thick sheet of tin, could act much like a room temperature superconductor.
Stanene is a type of topological insulator where the body of the material is an insulator but the surface and edges are electrically conductive. As electrons move around in the surfaces and edges of topological insulators, their spin axis aligns with their direction of flow. This effect (known as the quantum spin Hall state) means that electrons can’t easily reverse direction. In normal conductors when they hit an impurity they scatter and dissipate energy.
Although Stanene and superconductors can both exhibit zero resistance, Zhang emphasized that Stanene is not a superconductor. While the edges of Stanene act as a zero resistance path for electrons, they still encounter contact resistance at their junctions with normal conductors. In superconductors however, electrons travel in pairs, a phenomenon that eliminates contact resistance so that normal conductors effectively act like superconductors when in contact with a superconductor. [via]
Zero Resistance but not Superconducting? - [Link]
A team of Columbia Engineering researchers, led by Mechanical Engineering Professor James Hone and Electrical Engineering Professor Kenneth Shepard, exploring the properties of graphene have demonstrated a new electro-mechanical resonant component.
The resonator’s structure consists of a 2-4 micrometer long strip of graphene suspended over a metal gate electrode. The strip of graphene has a natural resonance governed by its physical dimension and is used in the demonstration as the frequency determining element in an RF feedback oscillator circuit. Applying a voltage to the gate electrode stresses and deflects the graphene strip changing its resonant frequency. The team applied baseband audio and tones to the gate electrode to produce a 100 MHz FM signal.[via]
Tiny FM Transmitter uses Voltage Controlled Graphene Resonator - [Link]
Graphene is by definition flat and planar, but researchers at Michigan Tech have discovered a manner of fabricating 3-D graphene–a honeycomb structure that can replace the expensive precious metals in solar cells and potentially other energy applications such as batteries and even superconductors. [via]
3D Graphene for Cheaper Solar Cells - [Link]
Larry Desjardin writes:
I had the fortune to visit CERN (European Council for Nuclear Research) earlier this month. Located on the Franco-Swiss border, CERN is home to the most powerful particle accelerator mankind has ever built, the Large Hadron Collider, otherwise known as the LHC. Here, bunches of approximately 100 billion protons each are accelerated in opposing directions around a 27-kilometer ring to collide at needle-point accuracy.
Fellow blogger, Ransom Stephens, published an excellent 8-part series last year about the LHC and the Higgs Boson discovery, which you can read here. I highly recommend it. I will relate my own first-hand experience in today’s post, and the impressive engineering required to create the experiments. Though I lived near Geneva for nearly four years, this was the first time I ever visited the facility.
Journey to the center of the universe - [Link]
A team of researchers at Brown University (USA) has concluded that graphene, a material touted to replace silicon in future semiconductor devices, disrupts functions of living cells. If the results of the study are confirmed by others, graphene could end up in the same hazardous material category as carbon nanotubes.
Graphene has many unique properties, but from a toxicology perspective the most important is that it is often made as a dry powder with the potential for inhalation exposure. Graphene fragments that make up the powder have sharp, pointy edges that can penetrate cell walls and allow the rest of the fragment to be drawn into the cell.
The researchers started with toxicity studies of graphene, which showed that it did in fact disrupt cell functions. To discover why, atomically detailed computer simulations of the graphene material interacting with a living cell were created. The simulations indicated the same results as the toxicity experiments. After the simulations follow-up studies were performed on human lung, skin, and immune cells in Petri dishes, and they confirmed that graphene fragments as large as 10 microns can pierce and be swallowed up by living cells. [via]
Graphene a Possible Health Hazard? - [Link]
A team at the University of Illinois has unveiled a battery design which offers 10 times the energy density and 1000 times faster recharge time compared to current cell technology according to a paper in the Journal Nature Communications.
The battery uses a LiMnO2 cathode and NiSn anode but the real innovation is in the novel electrode design. The electrodes are fabricated using a lattice of tiny polystyrene spheres which are coated with metal. The spheres are then dissolved to leave a 3D-metal scaffold onto which a nickel-tin alloy is added to form the anode, and the mineral manganese oxyhydroxide forms the cathode. In the last stage the glass surface is immersed into a liquid heated to 300˚C (572˚F). The resulting structure massively increases the electrode surface area and reduces the clearance between the electrodes. [via]
New Battery Technology Charges 1000 Times Faster - [Link]
The Massachusetts Institute of Technology (MIT) has discovered that pure crystalline carbon–graphene–sandwiched between two ferroelectric layers results in devices with built-in memory that operate in the terahertz range, potentially opening the door to next-generation applications: [via]
Terahertz Graphene Ferroelectrics Debut at MIT – [Link]
Inspired by trees scientists at the University of Maryland have developed a nanobattery that uses tin-coated wood fibers to store liquid electrolytes. Replacing the lithium found in many rechargeable batteries by sodium makes the battery environmentally benign. Sodium doesn’t store energy as efficiently as lithium, so you won’t see this battery in your cell phone – instead, its low cost and common materials would make it ideal to store huge amounts of energy at once, such as solar energy at a power plant.
Existing batteries are often created on stiff bases, which are too brittle to withstand the swelling and shrinking that happens as electrons are stored in and used up from the battery. The researchers found that wood fibers are supple enough to let their sodium-ion battery with an initial capacity of 339 mAh/g last more than 400 charging cycles. This puts it among the longest lasting nanobatteries. [via]
Rechargeable Wooden Battery - [Link]
New Si50x CMEMS® Oscillators Leap Ahead of Quartz-Based Timing Devices with Superior Frequency Stability, Reliability and Programmability
Silicon Labs has developed a new low-drift, single-die MEMS oscillator fabricated using a CMOS process. By porting low-temperature MEMS technology to the SMIC foundry, they managed to build a SiGe structure on top of the passivation layer of a CMOS logic chip using an existing CMOS production line. The drift problems of dual-die devices are eliminated by selecting specific materials to counteract thermal drift. The programmable oscillators operate at up to 100 MHz with frequency stability down to 20 ppm. Higher speed devices are planned, according to a Silicon Labs’ source.
CMOS MEMS (CMEMS) technology allows data sheet performance for frequency stability to be guaranteed for ten years, including solder shift, load pulling, supply voltage variation, operating temperature range, vibration and shock. This is ten times longer than typically offered by comparable crystal and MEMS oscillators. The oscillators tightly couple the MEMS resonator with CMOS temperature sensing and compensation circuitry, ensuring a highly stable frequency output despite thermal transients and over the full industrial temperature range. [via]
New MEMS Oscillators Boast Long-term Stability - [Link]