Archive : 13 December 2017 год
A three year project undertaken at the US Sandia National Laboratories has determined the flow of lithium ions across battery interfaces is a major obstacle to efforts to improve solid-state lithium-ion battery performance.
“The underlying goal of the work is to make solid-state batteries more efficient and to improve the interfaces between different materials,” said Sandia physicist Farid El Gabaly. “In this project, all the materials are solid; we don’t have a liquid-solid interface like in traditional lithium-ion batteries.”
El Gabaly explained that, in any lithium battery, lithium must travel from one electrode to the other when it is charged and discharged. However, the mobility of lithium ions is not the same in all materials and interfaces between materials are a major obstacle.
According to El Gabaly, there are two important interfaces in solid state batteries – the cathode-electrolyte and electrolyte-anode junctions – and either could dictate the performance limits of a full battery.
Fellow researcher Forrest Gittleson noted: “When we identify one of these bottlenecks, we ask ‘can we modify it?’. Then we try to change the interface and make the chemical processes more stable over time.”
El Gabaly said Sandia is interested in the research mainly because solid-state batteries are low maintenance, reliable and safe. “Our focus wasn’t on large batteries, like in electric vehicles. It was more for small or integrated electronics.”
Sandia’s California laboratory has not conducted research into solid-state batteries, which meant the project had to work out how to prototype batteries and examine their interfaces. The research was conducted using materials that have been used in previous proof-of-concept solid-state batteries.
“Since these materials are not produced on a massive commercial scale, we needed to be able to fabricate full devices on-site,” El Gabaly explained. “We sought methods to improve the batteries by either inserting or changing the interfaces in various ways or exchanging materials.”
The next phase of the research is to improve the performance of the batteries and to assemble them alongside other Sandia technologies.
“We can now start combining our batteries with LEDs, sensors, small antennas or any number of integrated devices,” El Gabaly said. “Even though we are happy with our battery performance, we can always try to improve it.”
Researchers at Princeton University have constructed silicon hardware that can control quantum behaviour between two electrons with extremely high precision.
The team constructed a gate that controls interactions between the electrons in a way that allows them to act as the quantum bits of information, or qubits, necessary for quantum computing. The demonstration of this two-qubit gate is being seen as an early step in building a more complex quantum computing device from silicon.
"The creation of this high-fidelity two-qubit gate opens the door to larger scale experiments,” said Jason Petta, a professor of physics at Princeton University.
Silicon-based devices could prove less expensive and easier to manufacture than other technologies for achieving a quantum computer and although other quantum devices containing 50 or more qubits have been developed, they have required exotic materials such as superconductors or charged atoms held in place by lasers.
Quantum computers are expected to be able to factor extremely large numbers and could help researchers understand the physical properties of extremely small particles such as atoms and molecules, leading to advances in areas such as materials science and drug discovery.
Building a quantum computer requires the creation of qubits and their coupling to each other with high fidelity. Silicon-based quantum devices use a quantum property of electrons called "spin" to encode information. The spin can point either up or down in a manner analogous to the north and south poles of a magnet. In contrast, conventional computers work by manipulating the electron's negative charge.
Achieving a high-performance, spin-based quantum device has been hampered by the fragility of spin states, but by building the silicon quantum devices in Princeton's Quantum Device Nanofabrication Laboratory, the researchers were able to keep the spins coherent for relatively long periods of time.
The two-qubit gate was constructed by layering tiny aluminum wires onto a highly ordered silicon crystal. The wires deliver voltages that trap two single electrons, separated by an energy barrier, in a well-like structure called a double quantum dot.
By temporarily lowering the energy barrier, the researchers allow the electrons to share quantum information, creating the quantum state called entanglement. These entangled electrons are now ready for use as qubits, which are like conventional computer bits but while a conventional bit can represent a zero or a 1, each qubit can be simultaneously a zero and a 1, greatly expanding the number of possible permutations that can be compared instantaneously.
According to David Zajac, a graduate student in physics at Princeton and first-author on the study, "This is the first demonstration of entanglement between two electron spins in silicon, a material known for providing one of the cleanest environments for electron spin states."
The researchers demonstrated that they can use the first qubit to control the second qubit, signifying that the structure functioned as a controlled NOT (CNOT) gate, which is the quantum version of a commonly used computer circuit component. The behaviour of the first qubit is controlled by applying a magnetic field. The gate produces a result based on the state of the first qubit: If the first spin is pointed up, then the second qubit's spin will flip, but if the first spin is down, the second one will not flip.
"The gate is basically saying it is only going to do something to one particle if the other particle is in a certain configuration," Petta said. "What happens to one particle depends on the other particle."
The researchers showed that they can maintain the electron spins in their quantum states with a fidelity exceeding 99 percent and that the gate works reliably to flip the spin of the second qubit about 75 percent of the time.
The technology has the potential to scale to more qubits with even lower error rates, according to the researchers.
Looking to meet demand for low power components for a range of battery powered IoT applications, Redpine Signals has launched the RS14100, which it says is the lowest-power multiprotocol wireless MCU currently available.
The MCU, which features an ARM Cortex-M4F core running at up to 180MHz, offers a choice of dual-band 802.11abgn Wi-Fi, Bluetooth 5 and 802.15.4, which can be used for Thread or ZigBee connectivity.
Dhiraj Sogani, vp of marketing, said: “We’ve put a lot of effort into developing the system architecture; it’s not just about taking advantage of the power savings from the latest process node. These devices are fabbed on a 40nm line, but we’ve had to develop new techniques that reduced power consumption even further.”
According to Sogani, the RS14100 – which the company also calls WiSeMCU, short for wireless secure MCU – has a Wi-Fi standby associated power of less than 50µA. “This is three to four times less than the competition,” he contended. Meanwhile, data throughput is said to be greater than 90Mbit/s.
The RS14100 includes a Cortex-M4F core running at up to 180MHz acting as an applications processor. Sogani said this features a ‘gear shifting’ capability, allowing it to respond to processing needs. In its lowest power mode, the M4F draws 12µA/MHz. Also featured is a four threaded processor for networking and security tasks and a physically unclonable function.
A choice of SoC and module packages is available, including an integrated module measuring 4.6mm x 7.8mm.
Redpine has also launched the RS9116, available in hosted and embedded configurations. Similar to the RS14100, the device is supplied without the Cortex-M4F core.
A metamaterial developed by researchers at King’s College London uses quantum effects to turn electrons flowing through a circuit into ‘hot electrons’ and light in a highly controlled manner. According to the team, this has potential application in optoelectronics and sensing.
The nanomaterial takes advantage of electron tunnelling to produce streams of particles which can have important applications, when properly controlled.
Researcher Dr Pan Wang said: “This one tiny device offers several amazing applications: plasmon excitation, light generation and chemical reaction activation. And all this is achieved by a small, easy to produce material which only requires a small voltage to function.”
A voltage applied across the device causes electrons to flow from one material (eutectic gallium indium) to another (gold nanorods). These are separated by an air gap, which would usually stop the electron flow, but because the air gap is less than 1nm, the electrons can ‘tunnel’ through.
Most of the tunnelling electrons arrive at the gold nanorod tips in the form of ‘hot electrons’, but a small proportion excite plasmons in the metamaterial to emit light whose wavelength is directly related to the applied voltage.
According to the team, this conversion is usually inefficient, but the use of array gold nanorods provides 100billion tunnel junctions, improving electron-to-plasmon conversion and making the emitted light visible.
While there are applications in sensing, the researchers point to a benefit in small scale electronics. Since light is generated by applying a voltage along a 10nm thick nanorod, it can be used to transmit information optically between or within chips. The metamaterial allows optical signals to be produced within a much smaller device, holding the potential of faster electronics.
King’s College Professor Anatoly Zayats added: “When we began these studies, we expected to generate some weak light which we thought should be enough for various nanophotonic applications. But as sometimes happens in the research, the applications are much richer.”