Physicists at the University of Washington have conducted the most precise and controlled measurements yet of the interaction between the atoms and molecules that comprise air and the type of carbon surface used in battery electrodes and air filters — key information for improving those technologies. A team led by David Cobden, UW professor of physics, used a carbon nanotube — a seamless, hollow graphite structure a million times thinner than a drinking straw — acting as a transistor to study what happens when gas atoms come into contact with the nanotube’s surface. Their findings were published in May in the journal ("Surface electron perturbations and the collective behaviour of atoms adsorbed on a cylinder"). 
An illustration of atoms sticking to a carbon nanotube, affecting the electrons in its surface. (Image: David Cobden and students) Cobden said he and co-authors found that when an atom or molecule sticks to the nanotube a tiny fraction of the charge of one electron is transferred to its surface, resulting in a measurable change in electrical resistance. “This aspect of atoms interacting with surfaces has never been detected unambiguously before,” Cobden said. “When many atoms are stuck to the miniscule tube at the same time, the measurements reveal their collective dances, including big fluctuations that occur on warming analogous to the boiling of water.” Lithium batteries involve lithium atoms sticking and transferring charges to carbon electrodes, and in activated charcoal filters, molecules stick to the carbon surface to be removed, Cobden explained. “Various forms of carbon, including nanotubes, are considered for hydrogen or other fuel storage because they have a huge internal surface area for the fuel molecules to stick to. However, these technological situations are extremely complex and difficult to do precise, clear-cut measurements on.” This work, he said, resulted in the most precise and controlled measurements of these interactions ever made, “and will allow scientists to learn new things about the interplay of atoms and molecules with a carbon surface,” important for improving technologies including batteries, electrodes and air filters.
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An illustration of atoms sticking to a carbon nanotube, affecting the electrons in its surface. (Image: David Cobden and students) Cobden said he and co-authors found that when an atom or molecule sticks to the nanotube a tiny fraction of the charge of one electron is transferred to its surface, resulting in a measurable change in electrical resistance. “This aspect of atoms interacting with surfaces has never been detected unambiguously before,” Cobden said. “When many atoms are stuck to the miniscule tube at the same time, the measurements reveal their collective dances, including big fluctuations that occur on warming analogous to the boiling of water.” Lithium batteries involve lithium atoms sticking and transferring charges to carbon electrodes, and in activated charcoal filters, molecules stick to the carbon surface to be removed, Cobden explained. “Various forms of carbon, including nanotubes, are considered for hydrogen or other fuel storage because they have a huge internal surface area for the fuel molecules to stick to. However, these technological situations are extremely complex and difficult to do precise, clear-cut measurements on.” This work, he said, resulted in the most precise and controlled measurements of these interactions ever made, “and will allow scientists to learn new things about the interplay of atoms and molecules with a carbon surface,” important for improving technologies including batteries, electrodes and air filters.
Infrared light enters this silicon structure from the left. The cut-out patterns, determined by an algorithm, route two different frequencies of this light into the pathways on the right. This is a greatly magnified image of a working device that is about the size of a speck of dust. (Image: Alexander Piggott) Proven technology In essence, the Stanford engineers want to miniaturize the proven technology of the Internet, which moves data by beaming photons of light through fiber optic threads. "Optical transport uses far less energy than sending electrons through wires," Piggott said. "For chip-scale links, light can carry more than 20 times as much data." Theoretically, this is doable because silicon is transparent to infrared light - the way glass is transparent to visible light. So wires could be replaced by optical interconnects: silicon structures designed to carry infrared light. But so far, engineers have had to design optical interconnects one at a time. Given that thousands of such linkages are needed for each electronic system, optical data transport has remained impractical. Now the Stanford engineers believe they've broken that bottleneck by inventing what they call an inverse design algorithm. It works as the name suggests: the engineers specify what they want the optical circuit to do, and the software provides the details of how to fabricate a silicon structure to perform the task. "We used the algorithm to design a working optical circuit and made several copies in our lab," Vuckovic said. In addition to Piggott, the research team included former graduate student Jesse Lu (now at Google,) graduate student Jan Petykiewicz and postdoctoral scholars Thomas Babinec and Konstantinos Lagoudakis. As they reported in Nature Photonics, the devices functioned flawlessly despite tiny imperfections. "Our manufacturing processes are not nearly as precise as those at commercial fabrication plants," Piggott said. "The fact that we could build devices this robust on our equipment tells us that this technology will be easy to mass-produce at state-of-the-art facilities." The researchers envision many other potential applications for their inverse design algorithm, including high bandwidth optical communications, compact microscopy systems and ultra-secure quantum communications. Light and silicon The Stanford work relies on the well-known fact that infrared light will pass through silicon the way sunlight shines through glass. And just as a prism bends visible light to reveal the rainbow, different silicon structures can bend infrared light in useful ways. The Stanford algorithm designs silicon structures so slender that more than 20 of them could sit side-by-side inside the diameter of a human hair. These silicon interconnects can direct a specific frequency of infrared light to a specific location to replace a wire. By loading data onto these frequencies, the Stanford algorithm can create switches or conduits or whatever else is required for the task. The inverse design algorithm is what makes optical interconnects practical by describing how to create what amount to silicon prisms to bend infrared light. Once the algorithm has calculated the proper shape for the task, engineers can use standard industrial processes to transfer that pattern onto a slice of silicon. "Our structures look like Swiss cheese but they work better than anything we've seen before," Vuckovic said. She and Piggott have made several different types of optical interconnects and they see no limits on what their inverse design algorithm can do. In their Nature photonics paper, the Stanford authors note that the automation of large-scale circuit design enabled engineers to create today's sophisticated electronics. By automating the process of designing optical interconnects, they feel that they have set the stage for the next generation of even faster and far more energy-efficient computers that use light rather than electricity for internal data transport.
Chemists at the University of Waterloo have discovered the key reaction that takes place in sodium-air batteries that could pave the way for development of the so-called holy grail of electrochemical energy storage. The key lies in Nazar's group discovery of the so-called proton phase transfer catalyst. By isolating its role in the battery's discharge and recharge reactions, Nazar and colleagues were not only able to boost the battery's capacity, they achieved a near-perfect recharge of the cell. When the researchers eliminated the catalyst from the system, they found the battery no longer worked. Unlike the traditional solid-state battery design, a metal-oxygen battery uses a gas cathode that takes oxygen and combines it with a metal such as sodium or lithium to form a metal oxide, storing electrons in the process. Applying an electric current reverses the reaction and reverts the metal to its original form. (Image: University of Waterloo) "Our new understanding brings together a lot of different, disconnected bits of a puzzle that have allowed us to assemble the full picture," says Nazar, a Chemistry professor in the Faculty of Science. "These findings will change the way we think about non-aqueous metal-oxygen batteries." Sodium-oxygen batteries are considered by many to be a particularly promising metal-oxygen battery combination. Although less energy dense than lithium-oxygen cells, they can be recharged with more than 93 per cent efficiency and are cheap enough for large-scale electrical grid storage. The key lies in Nazar's group discovery of the so-called proton phase transfer catalyst. By isolating its role in the battery's discharge and recharge reactions, Nazar and colleagues were not only able to boost the battery's capacity, they achieved a near-perfect recharge of the cell. When the researchers eliminated the catalyst from the system, they found the battery no longer worked. Unlike the traditional solid-state battery design, a metal-oxygen battery uses a gas cathode that takes oxygen and combines it with a metal such as sodium or lithium to form a metal oxide, storing electrons in the process. Applying an electric current reverses the reaction and reverts the metal to its original form. In the case of the sodium-oxygen cell, the proton phase catalyst transfers the newly formed sodium superoxide (NaO