The 2016 Nobel Prize in Chemistry has been awarded to three individuals for designing and developing molecular machines. Jean-Pierre Sauvage of France’s University of Strasbourg, J. Fraser Stoddart of Northwestern University in the US and Bernard L. Feringa from the University of Groningen in the the Netherlands will share a sum of US$928,000.
The machines – including motors, pumps and switches – are all on the scale of molecules. It is hoped that such inventions could find use in a range of material and medical applications.
In the 1980s and 90s, Sauvage and Stoddart became the first to efficiently make interlocked molecules, which consist of either interlocked molecular rings (catenanes) or rings of atoms threaded onto an molecular rod (rotaxanes). Critically, both scientists saw the opportunity that such molecules could act as molecular-scale machines, if they could control, for example, the rotation of the rings of a catenane or the shuttling of a ring up and down the rod of a rotaxane. Both went on to achieve this by applying an appropriate stimulus, for example an electrical current or light, which made the interlocked components move relative to one another.
Rotaxane crystal structure. M stone at English Wikipedia, CC BY-SA
Feringa’s work on molecular machines has focused on developing a family of non-interlocked molecular motors. In these machines, the molecule contains a twisted bond, around which rotation may be modulated by application of an external stimulus as for catenanes and rotaxanes.
Exciting future
All three chemists, along with others, have been looking to develop ever more sophisticated and useful examples of molecular machines. A whole range of molecules have been prepared that are chemical versions of real-world machines, including switches, pumps, motors and even cars and elevators. Notably, Sauvage and Stoddart have also developed molecular machines that can reversibly contract like muscles. These typically respond by exposure to different metal ions (charged atoms) or variation in acidity.
Bagels were used by the Nobel committee to explain both the physics and chemistry prize this year. TT news agency/EPA
The motions in certain molecular machines are accompanied by changes in colour of the molecule, and so they can act as sensors for the stimulus that causes the molecular motion – signalling whenever that specific substance is present. Scientists are also looking to incorporate molecular machines into smart materials so that the motion they can induce in a single molecular machine may then affect the macroscopic material properties. For instance, a sheet of plastic could be made to expand and shrink upon exposure to light or water.
Sauvage, Stoddart and Feringa’s molecular machines are, of course, man-made. Yet there are many examples of amazing functional molecular machines in our own bodies, such as the “motor protein” kinesin and the enzyme ATP synthase, which are essential for a range of biological functions. A truly exciting possibility for the future is the use of lab-produced molecular machines as treatments for diseases that arise from the failure of our own molecular machinery. Molecular machines could also act as delivery agents for drugs, releasing them by undergoing molecular motion when they comes across a stimulus to be found at the appropriate point in the body.
The award of this Nobel Prize reflects the outstanding work that all three scientists and their research teams have contributed to this area of chemical science research, and acts as an inspiration for all those working in the fields of supramolecular chemistry and nanotechnology.
For the first time in the field of solid-state chemistry scientists at NYU Abu Dhabi have developed a smart crystal that can heal itself after breakage without any chemical or biological intervention. The crystal relies on its own molecular structure and physical contact to heal — similar to cuts on skin.
Self-healing polymers has been researched by chemists extensively for more than a decade and until now has only been observed in softer materials like rubber and plastic.
Credit: NYU Abu Dhabi
Pale yellow crystals the size of a baby’s fingernail — and about 0.5 mm thick — were grown in a lab by Dr. Patrick Commins, postdoctoral associate researcher at NYU Abu Dhabi and lead author of the research paper recently published in leading peer-reviewed scientific journal Angwandte Chemie International Edition. The two-year study was conducted on dipyrazolethiuram disulfide crystals.
Commin said his research was inspired by the relationship between sulphur atoms in soft polymers, which tend to flow toward neighbouring sulphur atoms and bond with them easily resulting in self-repair. He decided to test the same bond in crystals.
“What happens when we break the crystal is that we have all these sulphurs moving around and when we press them together they reform their bonds and they heal,” Commins explained.
Commins said the crystal was broken using a machine built specifically to hold tiny objects and that has the capability to break the object cleanly. The two halves of the broken crystal were mechanically brought into contact with each other at room temperature. 24 hours later the crystal was whole again healed. The only defect was a superficial mark left behind by the crack in the middle. The percentage of healing was 6.7 percent and was calculated by comparing the amount of force required to break the crystal before and after the healing process.
Credit: NYU Abu Dhabi
“This is actually a small breakthrough because it kind of shows a concept that was not considered possible before,” said Dr. Pance Naumov, NYU Abu Dhabi associate professor of chemistry and study co-author. “It is the first time we’ve observed that rigid entities like crystals can self-repair. This was not expected. It’s certainly a shift in our understanding of crystals.”
“Crystals found in nature are made from minerals, like calcium and silicates but this crystal is different,” Commins added. “The crystal has been made specifically to have many close sulfur-sulfur bonds and they grow in rather small sizes.”
Commins believes this research is just the beginning.
“We think other crystals can do it (self-heal) but no one has actually explored it. We’ve only investigated one aspect of this field. We are expanding upon the subject and are trying to find other self-healing crystals,” he said.
Dr. Hideyuki Hara, research scientist at Bruker in Japan, is also a co-author on the paper.
Despite decades of research, scientists haven’t been able to fully understand how batteries work at the smallest of scales.
In a paper published in the journal Science, researchers describe a way to peer as never before into the electrochemical reaction that fuels the most common rechargeable cell in use today: the lithium-ion battery.
By visualizing the fundamental building blocks of batteries—small particles typically measuring less than 1/100th of a human hair in size—the team from Stanford University has illuminated a process that is far more complex than once thought. Both the method they developed to observe the battery in real time and their improved understanding of the electrochemistry could have far-reaching implications for battery design, management, and beyond.
“It gives us fundamental insights into how batteries work,” says Jongwoo Lim, a co-lead author of the paper and postdoctoral researcher at the Department of Energy’s SLAC National Accelerator Laboratory. “Previously, most studies investigated the average behavior of the whole battery. Now, we can see and understand how individual battery particles charge and discharge.”
Make batteries last longer
At the heart of every lithium-ion battery is a simple chemical reaction in which positively charged lithium ions nestle in the lattice-like structure of a crystal electrode as the battery is discharging, receiving negatively charged electrons in the process. In reversing the reaction by removing electrons, the ions are freed and the battery is charged.
These basic processes—known as lithiation (discharge) and delithiation (charge)—are hampered by an electrochemical Achilles heel. Rarely do the ions insert uniformly across the surface of the particles.
Greatly magnified nanoscale particles are shown here charging (red to green) and discharging (green to red). The animation shows regions of faster and slower charge. (Credit: SLAC National Accelerator Laboratory)
Instead, certain areas take on more ions, and others fewer. These inconsistencies eventually lead to mechanical stress as areas of the crystal lattice become overburdened with ions and develop tiny fractures, sapping battery performance and shortening battery life.
“Lithiation and delithiation should be homogenous and uniform,” says Yiyang Li, a doctoral candidate and co-lead author of the paper. “In reality, however, they’re very non-uniform. In our better understanding of the process, this paper lays out a path toward suppressing the phenomenon.”
For researchers hoping to improve batteries, counteracting these detrimental forces could lead to batteries that charge faster and more fully, lasting much longer than today’s models.
This study visualizes the charge/discharge reaction in real-time—something scientists refer to as operando—at fine detail and scale. The team utilized brilliant X-rays and cutting-edge microscopes at Lawrence Berkeley National Laboratory’s Advanced Light Source.
“The phenomenon revealed by this technique, I thought would never be visualized in my lifetime. It’s quite game-changing in the battery field,” says Martin Bazant, a professor of chemical engineering and of mathematics at MIT who led the theoretical aspect of the study.
A transparent battery
The researchers fashioned a transparent battery using the same active materials as ones found in smartphones and electric vehicles. It was designed and fabricated in collaboration with Hummingbird Scientific. It consists of two very thin, transparent silicon nitride “windows.”
The battery electrode, made of a single layer of lithium iron phosphate nanoparticles, sits on the membrane inside the gap between the two windows. A salty fluid, known as an electrolyte, flows in the gap to deliver the lithium ions to the nanoparticles.
Artist’s rendition shows lithium-ion battery particles under the illumination of a finely focused X-ray beam. (Credit: Courtesy Chueh Lab)
“This was a very, very small battery, holding ten billion times less charge than a smartphone battery,” says William Chueh, an assistant professor of materials science and engineering at Stanford and a faculty scientist at SLAC, who led the team. “But it allows us a clear view of what’s happening at the nanoscale.”
The researchers discovered that the charging process (delithiation) is significantly less uniform than discharge (lithiation). Intriguingly, the researchers also found that faster charging improves uniformity, which could lead to new and better battery designs and power management strategies.
“The improved uniformity lowers the damaging mechanical stress on the electrodes and improves battery cyclability,” Chueh says. “Beyond batteries, this work could have far-reaching impact on many other electrochemical materials.”
He points to catalysts, memory devices, and so-called smart glass, which transitions from translucent to transparent when electrically charged.
“What we’ve learned here is not just how to make a better battery, but offers us a profound new window on the science of electrochemical reactions at the nanoscale,” Bazant says.
The US Department of Energy, Office of Basic Energy Sciences, and the Ford-Stanford Alliance funded the work. Bazant was a visiting professor at Stanford and was supported by the Global Climate and Energy Project. The team’s work was published in the journal Science.
With each terrorist attack on another airport, train station or other public space, the urgency to find new ways to detect bombs before they’re detonated ratchets up.
Chemical detection of explosives is a cornerstone of aviation security. Typically called “trace detection,” this approach can find minuscule amounts of residue left behind after someone handles an explosive. A form of this technology called ion mobility spectroscopy is what Transportation Security Administration officers are using when they swab and test your laptop, hands or other items at the airport. In a few seconds, a sample is vaporized, and the resulting chemical ions are separated by molecular size and shape, triggering an alarm if an explosive compound is detected.
Contact sampling can be an effective approach, but the terrorist must be screened before reaching an intended target. Jason Reed/Reuters
But this method is labor-intensive and slow for large volumes of stuff, and its effectiveness can depend on the sampling skill of the officer. It relies on contact sampling, which requires security personnel to have access to surfaces where residue may have been left. That’s not useful if a bomber has no intention of going through a security line and having his personal effects searched.
Bomb-sniffing canines are security partners at airports. Rebecca Cook/Reuters
Some security teams rely on dogs, which can be trained to sniff out explosives using their exquisite sense of smell. But the logistics and training involved with the routine deployment of canines can be arduous, and there are cultural barriers to using dogs to directly screen people.
What researchers have wanted to develop for a long time is a new chemical detection technology that could “sniff” for explosives vapor, much like a canine does. Many efforts over the years fell short as not being sensitive enough. My research team has been working on this problem for nearly two decades – and we’re making good headway.
More and more sensitive
The one big hurdle to engineering some kind of technology to rival a dog’s nose is the extremely low vapor pressures of most explosives. What we call the “equilibrium vapor pressure” of a material is basically a measure of how much of it is in the air, available for detection, under perfect conditions at a specific temperature.
Commonly used by military forces around the world, nitro-organic explosives such as TNT, RDX and PETN have equilibrium vapor pressures in the parts per trillion range. To reliably sniff out related vapors in operational environments, like a busy check-in area of an airport, the detection capability would need to be well below that – down into the parts per quadrillion range for many explosives.
These levels have been beyond the capability of trace detection instrumentation. Achieving a 325 parts per quadrillion level of detection is analogous to finding one specific tree on the entire planet Earth.
But recent research has pushed the detection envelope into that part-per-quadrillion range. In 2008, an international team used an advanced ionization technique, called secondary electrospray ionization mass spectrometry, to get better than part per trillion level detection of TNT and PETN.
In 2012, our research team at Pacific Northwest National Laboratory (PNNL) achieved direct, real-time detection of RDX vapors at levels below 25 parts per quadrillion using atmospheric flow tube mass spectrometry (AFT-MS).
Schematic diagram of the elegant simplicity of the AFT-MS device. PNNL, CC BY
Sensitivity for a mass spectrometer is related to how many of the target molecules can be ionized and transferred into the mass spectrometer for detection. The more complete that process is, the better sensitivity will be. Our AFT-MS scheme is different because it uses time to maximize the benefits of the collisions of the explosive vapor molecules with air ions created from the ion source. It is the extent of reaction between the created ions and the explosives molecules that defines the sensitivity. Using AFT-MS, we’ve now expanded the capability to be able to detect a suite of explosives at single-digit part per quadrillion level.
Next step: putting it into practice
So we’ve moved the state of the art of chemical-based explosives detection into a realm where contact sampling is no longer necessary and instruments can “sniff” for explosives in a manner similar to canines.
PNNL research scientist Robert Ewing presenting a trace vapor sample to the detector. PNNL, CC BY
Instruments that have the vapor detection capability of canines and can also operate continuously open up exciting new security screening possibilities. Trace detection wouldn’t need to rely on direct access to suspicious items for sampling. Engineers could create a noninvasive walk-through explosive detection device, similar to a metal detector.
The real innovation is in the direct detection of the vapor plume, enabled by the extreme sensitivity. There is no longer a need to collect explosive particles for vaporization – as is the case in past trace detection technologies that use loud air jets to dislodge particles from people. Instead, the greater sensitivity means the air could simply be constantly sampled for explosives molecules as people pass through.
This approach would certainly make airport checkpoints less onerous, improving throughput and the passenger experience. These types of devices could also be set up at entrances to airport terminals and other public facilities. It would be a major security leap to be able to detect explosives that are entering a building, not only when passing through a checkpoint.
Making two measurements – vapor detection via mass spectrometer and visual image via currently deployed body scanner – in the same time and space. PNNL , CC BY
A deployed vapor detection capability would also increase safety by adding a second independent form of information to what scanners have available. Currently, most screening techniques, such as x-ray and millimeter wave imaging, are based on spotting anomalies – a TSA operator notices a strange shape in the image. A vapor detection technology would add to their toolkit the ability to identify specific chemicals.
It allows for a two-pronged approach to finding explosives: spotting them on an image and sniffing them out in the vapor plume emitted by a checked bag or a person. It’s like recognizing a person you know but haven’t seen in a long time; both seeing a recent picture and hearing their voice may be necessary to identify them, rather than just one of those pieces of information on its own.
Inspired by the tremendous detection capabilities of dogs, we’ve made remarkable advances toward developing technology that can follow in their footsteps. Deploying vapor analysis for explosives can both enhance security levels and provide a less intrusive screening environment. Continuing research aims to hone the technology and lower its costs so it can be deployed at an airport near you.
The strong force field emitted by a Tesla coil causes carbon nanotubes to self-assemble into long wires, a phenomenon scientists are calling “Teslaphoresis.”
Chemist Paul Cherukuri of Rice University, who led the team that made the discovery, thinks the research sets a clear path toward scalable assembly of nanotubes from the bottom up.
The system works by remotely oscillating positive and negative charges in each nanotube, causing them to chain together into long wires. Cherukuri’s specially designed Tesla coil even generates a tractor beam-like effect as nanotube wires are pulled toward the coil over long distances.
This force-field effect on matter had never been observed on such a large scale, says Cherukuri, and the phenomenon was unknown to Nikola Tesla, who invented the coil in 1891 with the intention of delivering wireless electrical energy.
“Electric fields have been used to move small objects, but only over ultrashort distances,” adds Cherukuri. “With Teslaphoresis, we have the ability to massively scale up force fields to move matter remotely.”
The researchers discovered that the phenomenon simultaneously assembles and powers circuits that harvest energy from the field. In one experiment, nanotubes assembled themselves into wires, formed a circuit connecting two LEDs, and then absorbed energy from the Tesla coil’s field to light them.
Cherukuri realized a redesigned Tesla coil could create a powerful force field at distances far greater than anyone imagined. His team observed alignment and movement of the nanotubes several feet away from the coil. “It is such a stunning thing to watch these nanotubes come alive and stitch themselves into wires on the other side of the room,” he says.
Nanotube wires self-assemble under the influence of a directed electric field from the Tesla coil. (Credit: Jeff Fitlow/Rice University)
Nanotubes were a natural first test material, given their heritage at Rice, where the HiPco production process was invented. But the researchers envision many other nanomaterials can be assembled as well.
Lindsey Bornhoeft, the lead author of the paper in ACS Nano and a biomedical engineering graduate student at Texas A&M University, says the directed force field from the bench-top coil at Rice is restricted to just a few feet. To examine the effects on matter at greater distances would require larger systems that are under development. Cherukuri suggests patterned surfaces and multiple Tesla coil systems could create more complex self-assembling circuits from nanoscale-sized particles.
Cherukuri and his wife, Tonya, a coauthor of the paper, say their son Adam made some remarkable observations while watching videos of the experiment.
“I was surprised that he noticed patterns in nanotube movements that I didn’t see,” Cherukuri says. “I couldn’t make him an author on the paper, but both he and his little brother John are acknowledged for helpful discussions.”
Cherukuri and his team look forward to seeing where their research leads. “These nanotube wires grow and act like nerves, and controlled assembly of nanomaterials from the bottom up may be used as a template for applications in regenerative medicine,” Bornhoeft says.
“There are so many applications where one could utilize strong force fields to control the behavior of matter in both biological and artificial systems,” Cherukuri says. “And even more exciting is how much fundamental physics and chemistry we are discovering as we move along. This really is just the first act in an amazing story.”
It seems pretty obvious that researchers at the University of Michigan would be interested in finding a solution for keeping ice from sticking to various surfaces. For example, on your car windshield, ice is a nuisance. But on an airplane, wind turbine, oil rig, or power line, it can be downright dangerous. And removing it with current methods—usually chemical melting agents or labor-intensive scrapers and hammers—is difficult and expensive work.
But a new durable and inexpensive ice-repellent coating could change that. Thin, clear, and slightly rubbery to the touch, the spray-on formula could make ice slide off equipment, airplanes, and car windshields with only the force of gravity or a gentle breeze.
Researchers say the discovery could have major implications in industries like energy, shipping, and transportation, where ice is a constant problem in cold climates.
The coating could also lead to big energy savings in freezers, which today rely on complex and energy-hungry defrosting systems to stay frost-free. An ice-repelling coating could do the same job with zero energy consumption, making household and industrial freezers up to 20 percent more efficient.
DIAL DOWN ADHESION STRENGTH
Made of a blend of common synthetic rubbers, the formula marks a departure from earlier approaches that relied on making surfaces either very water-repellent or very slippery.
“Researchers had been trying for years to dial down ice adhesion strength with chemistry, making more and more water-repellent surfaces,” says Kevin Golovin, a doctoral student in materials science and engineering at the University of Michigan. “We’ve discovered a new knob to turn, using physics to change the mechanics of how ice breaks free from a surface.”
Led by Anish Tuteja, associate professor of materials science and engineering, researchers initially experimented with water-repelling surfaces as well, but found that they weren’t effective at shedding ice. But during those experiments, they noticed something unexpected: rubbery coatings worked best for repelling ice, even when they weren’t water-repellent. Eventually, they discovered that the ability to shed water wasn’t important at all. The rubbery coatings repelled ice because of a different phenomenon, called “interfacial cavitation.”
Two rigid surfaces—say, ice and your car windshield—can stick tightly together, requiring a great deal of force to break the bond between them. But because of interfacial cavitation, a solid material stuck to a rubbery surface behaves differently. Even a small amount of force can deform the rubbery surface, breaking the solid free.
“Nobody had explored the idea that rubberiness can reduce ice adhesion,” Tuteja says. “Ice is frozen water, so people assumed that ice-repelling surfaces had to also repel water. That was very limiting.”
The new approach makes it possible to dramatically improve durability compared to previous icephobic coatings, which relied on fragile materials that lost their ice-shedding abilities after just a few freeze-thaw cycles. The new coatings stood up to a variety of lab tests including peel tests, salt spray corrosion, high temperatures, mechanical abrasion, and hundreds of freeze-thaw cycles.
The team has also found that by slightly altering the smoothness and rubberiness of the coating, they can fine-tune its degree of ice repellency and durability. Softer surfaces tend to be more ice-repellent but less durable, while the opposite is true for harder coatings. That flexibility will allow scientists to create coatings for a huge variety of applications.
“An airplane coating, for example, would need to be extremely durable, but it could be less ice-repellent because of high winds and vibration that would help push ice off,” Golovin says.
EASY TO FINE-TUNE
“A freezer coating, on the other hand, could be less durable, but would need to shed ice with just the force of gravity and slight vibrations. The great thing about our approach is that it’s easy to fine-tune it for any given application.”
The team has already designed hundreds of ice-repelling formulas. Some are rough to the touch, some smooth; some shed water while others don’t.
“I think the first commercial application will be in linings for commercial frozen food packaging, where sticking is often a problem. We’ll probably see that within the next year,” Tuteja says. “Using this technology in places like cars and airplanes will be very complex because of the stringent durability and safety requirements, but we’re working on it.”
The University of Michigan MTRAC program, the Office of Naval Research, the Air Force Office of Scientific Research, and the National Science Foundation funded the work. The paper is published in the journal Science Advances.
Our modern world is based on semiconductors. In addition to your computer, cellphones and digital cameras, semiconductors are a critical component of a growing number of devices. Think of the high-efficiency LED lights you are putting in your house, along with everything with a lit display or control circuit: cars, refrigerators, ovens, coffee makers and more. You would be hard-pressed to find a modern device that uses electricity that does not have semiconductor circuits in it.
While most people have heard of silicon and Silicon Valley, they do not realize that this is just one example of a whole class of materials.
But the workhorse silicon – used in all manner of computers and electronic gadgets – has its technical limits, particularly as engineers look to use electronic devices for producing or processing light. The search for new semiconductors is on. Where will these materials innovations come from?
What’s a semiconductor?
Probing a newly fabricated device. Corey Shemelya and Tom Vandervelde, Tufts University, CC BY-ND
As the name suggests, semiconductors are materials that conduct electricity at some temperatures but not others – unlike most metals, which are conductive at any temperature, and insulators like glass, plastic and stone, which usually don’t conduct electricity.
However, this is not their most important trait. When constructed properly, these materials can modify the electricity moving through them, including limiting the directions it flows and amplifying a signal.
The combination of these properties is the basis of diodes and transistors which make up all our modern gadgets. These circuit elements perform a multitude of tasks, including converting the electricity from your wall socket to something usable by the devices, and processing information in the form of zeros and ones.
Light can also be absorbed into semiconductors and turned into electrical current and voltage. The process works in reverse as well, allowing for the emission of light. Using this property, we make lasers, LED lights, digital cameras and many other devices.
The rise of silicon
While this all seems very modern, the original discoveries of semiconductors date back to the 1830s. By the 1880s, Alexander Graham Bell experimented with using selenium to transmit sound over a beam of light. Selenium was also used to make some of the first solar cells in the 1880s.
A key limitation was the inability to purify the elements being used. Tiny impurities – as small as one in a trillion, or 0.0000000001 percent – could fundamentally change the way a semiconductor behaved. As technology evolved to make purer materials, better semiconductors followed.
A semiconductor chip fabricated in a Tufts University lab. Corey Shemelya and Tom Vandervelde, Tufts University, CC BY-ND
The first semiconducting transistor was made of germanium in 1948, but silicon quickly rose to become the dominant semiconductor material. Silicon is mechanically strong, relatively easy to purify, and has reasonable electrical properties.
It is also incredibly abundant: 28.2 percent of the Earth’s crust is silicon. That makes it literally dirt cheap. This almost-perfect semiconductor worked well for making diodes and transistors and still is the basis of almost every computer chip out there. There was one problem: silicon is very inefficient at converting light into an electrical signal, or turning electricity back into light.
When the primary use of semiconductors was in computer processors connected by metal wires, this wasn’t much of a problem. But, as we moved toward using semiconductors in solar panels, camera sensors and other light-related applications, this weakness of silicon became a real obstacle to progress.
Finding new semiconductors
A section of the periodic table of the elements. Armtuk, Alessio Rolleri, Gringer, CC BY-SA
The search for new semiconductors begins on the periodic table of the elements, a portion of which is in the figure at right.
In the column labeled IV, each element forms bonds by sharing four of its electrons with four neighbors. The strongest of these “group IV” elements bonds is for carbon (C), forming diamonds. Diamonds are good insulators (and transparent) because carbon holds on to these electrons so tightly. Generally, a diamond would burn before you could force an electrical current through it.
The elements at the bottom of the column, tin (Sn) and lead (Pb), are much more metallic. Like most metals, they hold their bonding electrons so loosely that when a small amount of energy is applied the electrons are free to break their bonds and flow through the material.
Silicon (Si) and germanium (Ge) are in between and accordingly are semiconductors. Due to a quirk in the way both of them are structured, however, they are inefficient at exchanging electricity with light.
To find materials that work well with light, we have to step to either side of the group IV column. Combining elements from the “group III” and “group V” columns results in materials with semiconducting properties. These “III-V” materials, such as gallium arsenide (GaAs), are used to make lasers, LED lights, photodetectors (as found in cameras) and many other devices. They do what silicon does not do well.
A solar cell being tested under the illumination of an artificial sun, in one of our solar simulators. Corey Shemelya and Tom Vandervelde, Tufts University, CC BY-ND
But why is silicon used for solar panels if it is so bad at converting the light into electricity? Cost. Silicon could be refined from a shovel full of dirt scooped up from anywhere on the Earth’s surface; the III-V compounds’ constituent elements are far rarer.
A standard silicon solar panel converts the sunlight with an efficiency of 10 to 15%. A III-V panel can be three times as efficient, but often costs more than three times as much. The III-V materials are also more brittle than silicon, making them hard to work with in wide panels.
Ghosts in the machine: A scanning electron microscopy image of a damaged gallium-antimonide semiconductor sample. Corey Shemelya and Tom Vandervelde, Tufts University, CC BY-ND
However, the III-V materials’ increased electron speeds enable construction of much faster transistors, with speeds hundreds of times faster than the ones you find in your computers. They may pave the way for wires inside computers to be replaced with beams of light, significantly improving the speed of data flow.
In addition to III-V materials, there are also II-VI materials in use. These materials include some of the sulfides and oxides researched in the 1800s. Combinations of zinc, cadmium, and mercury with tellurium have been used to create infrared cameras as well as solar cells from companies such as First Solar. These materials are notoriously brittle and very challenging to fabricate.
The future of semiconductors
How might new semiconductor materials be used?
A photonic crystal consisting of a periodic metal structure on a semiconductor. Corey Shemelya and Tom Vandervelde, Tufts University, CC BY-ND
High power III-V (gallium-nitride) semiconductor electronics will be the backbone of our electrical grid system, converting power for high voltage transmission and back again. New III-V materials (antimonides and bismuthides) are leading the way for infrared sensing for medical, military, other civilian uses, as well new telecommunication possibilities. Earth-abundant element combinations are being explored to make new semiconductors for high-efficiency, but inexpensive, solar cells.
And what of the old standby, silicon? Its inability to harness light efficiently does not mean that it is destined for the dust bin of history. Researchers are giving new life to silicon, creating “silicon photonics” to better handle light, rather than just shuttling electrons.
One method is the inclusion of small amounts of another group IV element, tin, into silicon or germanium. That changes their properties, allowing them to absorb and emit light more efficiently.
The act of including that tin turns out to be difficult, like many other challenges in material science. But as I tell my students all the time, “if it were easy, then it would not be research.”
Flint’s recent water crisis is a stinging reminder that the infrastructure we often take for granted has many vulnerabilities.
The crisis also underscores the complexity of providing communities with safe, high-quality potable water.
Water utilities interested in using a new river water source, as the city of Flint was last year, would normally hire engineering firms to conduct detailed studies of the raw water quality and pilot studies to evaluate various water treatment process options before choosing a treatment approach.
As a researcher on water disinfection and professor of civil and environmental engineering, I know that a planning period of at least two to three years to get to a ribbon-cutting for such a facility is normal. The design of these systems is iterative by its nature and requires input from multiple stakeholders at various points in the design process.
Why is the design of a new surface water treatment facility so complex?
That’s right, in one of those unusual twists of science, chemical engineers have discovered a way to use pollen – that stuff that makes many people sneeze – to make batteries. Specifically, what they’ve found is that pollen from bees and cattails could potentially be a renewable material for making anodes in lithium-ion batteries.
Batteries have two electrodes, called an anode and a cathode. The anodes in most of today’s lithium-ion batteries are made of graphite. Lithium ions are contained in a liquid called an electrolyte, and these ions are stored in the anode during recharging.
“Both are abundantly available,” says Vilas Pol, an associate professor in the School of Chemical Engineering and the School of Materials Engineering at Purdue University. “The bottom line here is we want to learn something from nature that could be useful in creating better batteries with renewable feedstock.”
Whereas bee pollen is a mixture of different pollen types collected by honeybees, the cattail pollens all have the same shape.
“I started looking into pollens when my mom told me she had developed pollen allergy symptoms about two years ago,” says doctoral student Jialiang Tang. “I was fascinated by the beauty and diversity of pollen microstructures. But the idea of using them as battery anodes did not really kick in until I started working on battery research and learned more about carbonization of biomass.”
Read on to learn how they processed the pollen in order to make them into anodes an how well that worked.
A new water filter can remove toxic heavy metal ions and radioactive substances in just one pass.
The filter membrane is a hybrid of two low-cost materials: whey protein fibers and activated charcoal. The simple technology overcomes several disadvantages of existing methods, which are typically expensive and can only remove a specific element or have a very small filter capacity.
“The project is one of the most important things I might have ever done,” says Raffaele Mezzenga, a professor of food and soft materials at ETH Zurich. He and colleague Sreenath Bolisetty describe the technology in the journal Nature Nanotechnology.
At the heart of the filtration system is a new type of hybrid membrane made up of activated charcoal and tough, rigid whey protein fibers. The two components are inexpensive and simple to produce.
The whey proteins are denatured, which causes them to stretch, and ultimately come together in the form of amyloid fibrils. Together with activated carbon, these fibers are applied to a suitable substrate material, such as a cellulose filter paper. The carbon content is 98 percent, with a mere 2 percent made up by the protein.
The filter can even be used for recovering gold, read on to learn how.
Nicholas Evans, Lecturer in Chemistry, Lancaster University
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