IMAGE: THE DISCOVERY OF MULTI-MESSENGER NANOPROBES ALLOWS SCIENTISTS TO SIMULTANEOUSLY PROBE MULTIPLE PROPERTIES OF QUANTUM MATERIALS AT NANOMETER-SCALE SPATIAL RESOLUTIONS. view more CREDIT: ELLA MARU STUDIO
Researchers at Columbia University and University of California, San Diego, have introduced a novel “multi-messenger” approach to quantum physics that signifies a technological leap in how scientists can explore quantum materials.
The findings appear in a recent article published in Nature Materials, led by A. S. McLeod, postdoctoral researcher, Columbia Nano Initiative, with co-authors Dmitri Basov and A. J. Millis at Columbia and R.A. Averitt at UC San Diego.
“We have brought a technique from the inter-galactic scale down to the realm of the ultra-small,” said Basov, Higgins Professor of Physics and Director of the Energy Frontier Research Center at Columbia. Equipped with multi-modal nanoscience tools we can now routinely go places no one thought would be possible as recently as five years ago.”
The work was inspired by “multi-messenger” astrophysics, which emerged during the last decade as a revolutionary technique for the study of distant phenomena like black hole mergers. Simultaneous measurements from instruments, including infrared, optical, X-ray and gravitational-wave telescopes can, taken together, deliver a physical picture greater than the sum of their individual parts.
The search is on for new materials that can supplement the current reliance on electronic semiconductors. Control over material properties using light can offer improved functionality, speed, flexibility and energy efficiency for next-generation computing platforms.
Experimental papers on quantum materials have typically reported results obtained by using only one type of spectroscopy. The researchers have shown the power of using a combination of measurement techniques to simultaneously examine electrical and optical properties.
The researchers performed their experiment by focusing laser light onto the sharp tip of a needle probe coated with magnetic material. When thin films of metal oxide are subject to a unique strain, ultra-fast light pulses can trigger the material to switch into an unexplored phase of nanometer-scale domains, and the change is reversible.
By scanning the probe over the surface of their thin film sample, the researchers were able to trigger the change locally and simultaneously manipulate and record the electrical, magnetic and optical properties of these light-triggered domains with nanometer-scale precision.
The study reveals how unanticipated properties can emerge in long-studied quantum materials at ultra-small scales when scientists tune them by strain.
“It is relatively common to study these nano-phase materials with scanning probes. But this is the first time an optical nano-probe has been combined with simultaneous magnetic nano-imaging, and all at the very low temperatures where quantum materials show their merits,” McLeod said. “Now, investigation of quantum materials by multi-modal nanoscience offers a means to close the loop on programs to engineer them.”
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The study, “Multi-messenger nanoprobes of hidden magnetism in a strained manganite,” was developed with support from Programmable Quantum Materials, an Energy Frontier Research Center funded by the United States Department of Energy (DOE), Office of Science and Basic Energy Sciences.
Pictured: Applying pressure to twisted bilayer graphene pushes the layer together, and transforms the material from a metal to a superconductor. Credit: Ella Maru Studio
A Columbia-led team has discovered a new method to manipulate the electrical conductivity of this game-changing material, the strongest known to man with applications ranging from nano-electronic devices to clean energy.
Graphene has been heralded as a wonder material. Not only is it the strongest, thinnest material ever discovered, its exceptional ability to conduct heat and electricity paves the way for innovation in areas ranging from electronics to energy to medicine.
Now, a Columbia University-led team has developed a new method to finely tune adjacent layers of graphene—lacy, honeycomb-like sheets of carbon atoms—to induce superconductivity. Their research provides new insights into the physics underlying this two-dimensional material’s intriguing characteristics.
The team’s paper is published in the Jan. 24 issue of Science.
“Our work demonstrates new ways to induce superconductivity in twisted bilayer graphene, in particular, achieved by applying pressure,” said Cory Dean, assistant professor of physics at Columbia and the study’s principal investigator. “It also provides critical first confirmation of last year’s MIT results—that bilayer graphene can exhibit electronic properties when twisted at an angle—and furthers our understanding of the system, which is extremely important for this new field of research.”
In March 2018 researchers at the Massachusetts Institute of Technology reported a groundbreaking discovery that two graphene layers can conduct electricity without resistance when the twist angle between them is 1.1 degrees,referred to as the “magic angle.”
But hitting that magic angle has proven difficult. “The layers must be twisted to within roughly a tenth of a degree around 1.1, which is experimentally challenging,” Dean said. “We found that very small errors in alignment could give entirely different results.”
So Dean and his colleagues, who include scientists from the National Institute for Materials Science and the University of California, Santa Barbara, set out to test whether magic-angle conditions could be achieved at bigger rotations.
“Rather than trying to precisely control the angle, we asked whether we could instead vary the spacing between the layers,” said Matthew Yankowitz, a postdoctoral research scientist in Columbia’s physics department and first author on the study. “In this way any twist angle could, in principle, be turned into a magic angle.”
They studied a sample with twist angle of 1.3 degrees—only slightly larger than the magic angle but still far enough away to preclude superconductivity.
Applying pressure transformed the material from a metal into either an insulator—in which electricity cannot flow—or a superconductor—where electrical current can pass without resistance—depending on the number of electrons in the material.
“Remarkably, by applying pressure of over 10,000 atmospheres we observe the emergence of the insulating and superconducting phases,” Dean said. Additionally, the superconductivity develops at the highest temperature observed in graphene so far, just over 3 degrees above absolute zero.”
To reach the high pressures needed to induce superconductivity the team worked closely with the National High Magnetic Field user facility, known as the Maglab, in Tallahassee, Florida.
“This effort was a huge technical challenge,” said Dean. “After fabricating one of most unique devices we’ve ever worked with, we then had to combine cryogenic temperatures, high magnetic fields, and high pressure—all while measuring electrical response. Putting this all together was a daunting task and our ability to make it work is really a tribute to the fantastic expertise at the Maglab.”
The researchers believe it may be possible to enhance the critical temperature of the superconductivity further at even higher pressures. The ultimate goal is to one day develop a superconductor which can perform under room temperature conditions, and although this may prove challenging in graphene, it could serve as a roadmap for achieving this goal in other materials.
Andrea Young, assistant professor of physics at UC Santa Barbara, a collaborator on the study, said the work clearly demonstrates that squeezing the layers has same effect as twisting them and offers an alternative paradigm for manipulating the electronic properties in graphene.
“Our findings significantly relax the constraints that make it challenging to study the system and gives us new knobs to control it,” Young said.
Dean and Young are now twisting and squeezing a variety of atomically-thin materials in the hopes of finding superconductivity emerging in other two-dimensional systems.
“Understanding ‘why’ any of this is happening is a formidable challenge but critical for eventually harnessing the power of this material—and our work starts unraveling the mystery,'” Dean said.
Etched pillars define the positions of quantum dots (red puddles) arranged in an hexagonal lattice. When the spacing between the quantum dots is sufficiently small, electrons can move between them. Credit: Diego Scarabelli/Columbia Engineering
Researchers at Columbia Engineering, experts at manipulating matter at the nanoscale, have made an important breakthrough in physics and materials science, recently reported in Nature Nanotechnology. Working with colleagues from Princeton and Purdue Universities and Istituto Italiano di Tecnologia, the team has engineered “artificial graphene” by recreating, for the first time, the electronic structure of graphene in a semiconductor device.
“This milestone defines a new state-of-the-art in condensed matter science and nanofabrication,” says Aron Pinczuk, professor of applied physics and physics at Columbia Engineering and senior author of the study. “While artificial graphene has been demonstrated in other systems such as optical, molecular, and photonic lattices, these platforms lack the versatility and potential offered by semiconductor processing technologies. Semiconductor artificial graphene devices could be platforms to explore new types of electronic switches, transistors with superior properties, and even, perhaps, new ways of storing information based on exotic quantum mechanical states.”
The discovery of graphene in the early 2000s generated tremendous excitement in the physics community not only because it was the first real-world realization of a true two-dimensional material but also because the unique atomic arrangement of the carbon atoms in graphene provided a platform for testing new quantum phenomena that are difficult to observe in conventional materials systems. With its unusual electronic properties—its electrons can travel great distances before they are scattered—graphene is an outstanding conductor. These properties also display other unique characteristics that make electrons behave as if they are relativistic particles that move close to the speed of light, conferring upon them exotic properties that “regular,” non-relativistic electrons do not have.
But graphene, a natural substance, comes in only one atomic arrangement: the positions of the atoms in the graphene lattice are fixed, and thus all experiments on graphene must adapt to those constraints. On the other hand, in artificial graphene the lattice can be engineered over a wide range of spacings and configurations, making it a holy grail of sorts for condensed matter researchers because it will have more versatile properties than the natural material.
“This is a rapidly expanding area of research, and we are uncovering new phenomena that couldn’t be accessed before,” says Shalom Wind, faculty member of the department of applied physics and applied mathematics and co-author of the study. “As we explore novel device concepts based on electrical control of artificial graphene, we can unlock the potential to expand frontiers in advanced optoelectronics and data processing.”
The green layer represents the 2-D sheet where the electrons can move. Nanolithography and etching form small pillars beneath which lie the quantum dots arranged in an hexagonal lattice. Scanning electron micrographs at the bottom show the …more
“This work is really a major advance in artificial graphene. Since the first theoretical prediction that system with graphene-like electronic properties may be artificially created and tuned with patterned 2D electron gas, no one had succeeded, until the Columbia work, in directly observing these characteristics in engineered semiconductor nanostructures,” says Steven G. Louie, professor of physics, University of California, Berkeley. “Previous work with molecules, atoms and photonic structures represent far less versatile and stable systems. The nanofabricated semiconductor structures open up tremendous opportunities for exploring exciting new science and practical applications.”
The researchers used the tools of conventional chip technology to develop the artificial graphene in a standard semiconductor material, gallium arsenide. They designed a layered structure so that the electrons could move only within a very narrow layer, effectively creating a 2D sheet. They used nanolithography and etching to pattern the gallium arsenide: the patterning created a hexagonal lattice of sites in which the electrons were confined in the lateral direction. By placing these sites, which could be thought of as “artificial atoms,” sufficiently close to one another (~ 50 nanometers apart), these artificial atoms could interact quantum mechanically, similar to the way atoms share their electrons in solids.
The team probed the electronic states of the artificial lattices by shining laser light on them and measuring the light that was scattered. The scattered light showed a loss of energy that corresponded to transitions in the electron energy from one state to another. When they mapped these transitions, the team found that they were approaching zero in a linear fashion around what is called the “Dirac point” where the electron density vanishes, a hallmark of graphene.
This artificial graphene has several advantages over natural graphene: for instance, researchers can design variations into the honeycomb lattice to modulate electronic behavior. And because the spacing between the quantum dots is much larger than the inter-atomic spacing in natural graphene, researchers can observe even more exotic quantum phenomena with the application of a magnetic field.
The discovery of new low-dimensional materials, such as graphene and other ultrathin, layered van der Waals films that exhibit exciting new physical phenomena that were previously inaccessible, laid the groundwork for this study. “What was really critical to our work was the impressive advancements in nanofabrication,” Pinczuk notes. “These offer us an ever-increasing toolbox for creating a myriad of high-quality patterns at nanoscale dimensions. This is an exciting time to be a physicist working in our field.”
More information: Sheng Wang et al, Observation of Dirac bands in artificial graphene in small-period nanopatterned GaAs quantum wells, Nature Nanotechnology (2017). DOI: 10.1038/s41565-017-0006-x
Graphite/PMMA/Li trilayer electrode before (left) and after (right) being soaked in battery electrolyte for 24 hours. Before soaking in electrolyte, the trilayer electrode is stable in air. After soaking, lithium reacts with graphite and …more
Yuan Yang, assistant professor of materials science and engineering at Columbia Engineering, has developed a new method to increase the energy density of lithium (Li-ion) batteries. He has built a trilayer structure that is stable even in ambient air, which makes the battery both longer lasting and cheaper to manufacture. The work, which may improve the energy density of lithium batteries by 10-30%, is published online today in Nano Letters.
“When lithium batteries are charged the first time, they lose anywhere from 5-20% energy in that first cycle,” says Yang. “Through our design, we’ve been able to gain back this loss, and we think our method has great potential to increase the operation time of batteries for portable electronics and electrical vehicles.”
During the first charge of a lithiumbattery after its production, a portion of liquid electrolyte is reduced to a solid phase and coated onto the negative electrode of the battery. This process, usually done before batteries are shipped from a factory, is irreversible and lowers the energy stored in the battery. The loss is approximately 10% for state-of-the-art negative electrodes, but can reach as high as 20-30% for next-generation negative electrodes with high capacity, such as silicon, because these materials have large volume expansion and high surface area. The large initial loss reduces achievable capacity in a full cell and thus compromises the gain in energy density and cycling life of these nanostructured electrodes.
The traditional approach to compensating for this loss has been to put certain lithium-rich materials in the electrode. However, most of these materials are not stable in ambient air. Manufacturing batteries in dry air, which has no moisture at all, is a much more expensive process than manufacturing in ambient air. Yang has developed a new trilayer electrode structure to fabricate lithiated battery anodes in ambient air. In these electrodes, he protected the lithium with a layer of the polymer PMMA to prevent lithium from reacting with air and moisture, and then coated the PMMA with such active materials as artificial graphite or silicon nanoparticles. The PMMA layer was then dissolved in the battery electrolyte, thus exposing the lithium to the electrode materials. “This way we were able to avoid any contact with air between unstable lithium and a lithiated electrode,” Yang explains, “so the trilayer-structured electrode can be operated in ambient air. This could be an attractive advance towards mass production of lithiated battery electrodes.”
Illustration showing the procedure to fabricate the trilayer electrode. PMMA is used to protect lithium and make the trilayer electrode stable in ambient air. PMMA is dissolved in battery electrolyte and graphite contacts with lithium to …more
Yang’s method lowered the loss capacity in state-of-the-art graphite electrodes from 8% to 0.3%, and in silicon electrodes, from 13% to -15%. The -15% figure indicates that there was more lithium than needed, and the “extra” lithium can be used to further enhance cycling life of batteries, as the excess can compensate for capacity loss in subsequent cycles. Because the energy density, or capacity, of lithium-ion batteries has been increasing 5-7% annually over the past 25 years, Yang’s results point to a possible solution to enhance the capacity of Li-ion batteries. His group is now trying to reduce the thickness of the polymer coating so that it will occupy a smaller volume in the lithium battery, and to scale up his technique.
“This three-layer electrode structure is indeed a smart design that enables processing of lithium-metal-containing electrodes under ambient conditions,” notes Hailiang Wang, assistant professor of chemistry at Yale University, who was not involved with the study. “The initial Coulombic efficiency of electrodes is a big concern for the Li-ion battery industry, and this effective and easy-to-use technique of compensating irreversible Li ion loss will attract interest.”
More information: Zeyuan Cao et al, An Ambient-air Stable Lithiated Anode for Rechargeable Li-ion Batteries with High Energy Density, Nano Letters (2016). DOI: 10.1021/acs.nanolett.6b03655
Illustration of refraction through a normal optical medium versus what it would look like for a medium capable of negative refraction. Credit: Cory Dean, Columbia University
A team led by Cory Dean, assistant professor of physics at Columbia University, Avik Ghosh, professor of electrical and computer engineering at the University of Virginia, and James Hone, Wang Fong-Jen Professor of Mechanical Engineering at Columbia Engineering, has directly observed—for the first time—negative refraction for electrons passing across a boundary between two regions in a conducting material. First predicted in 2007, this effect has been difficult to confirm experimentally. The researchers were able to observe the effect in graphene, demonstrating that electrons in the atomically thin material behave like light rays, which can be manipulated by such optical devices as lenses and prisms. The findings, which are published in the September 30 edition of Science, could lead to the development of new types of electron switches, based on the principles of optics rather than electronics.
“The ability to manipulate electrons in a conducting material like light rays opens up entirely new ways of thinking about electronics,” says Dean. “For example, the switches that make up computer chips operate by turning the entire device on or off, and this consumes significant power. Using lensing to steer an electron ‘beam’ between electrodes could be dramatically more efficient, solving one of the critical bottlenecks to achieving faster and more energy efficient electronics.”
Dean adds, “These findings could also enable new experimental probes. For example, electron lensing could enable on-chip versions of an electron microscope, with the ability to perform atomic scale imageing and diagnostics. Other components inspired by optics, such as beam splitters and interferometers, could additionally enable new studies of the quantum nature of electrons in the solid state.”
While graphene has been widely explored for supporting high electron speed, it is notoriously hard to turn off the electrons without hurting their mobility. Ghosh says, “The natural follow-up is to see if we can achieve a strong current turn-off in graphene with multiple angled junctions. If that works to our satisfaction, we’ll have on our hands a low-power, ultra-high-speed switching device for both analog (RF) and digital (CMOS) electronics, potentially mitigating many of the challenges we face with the high energy cost and thermal budget of present day electronics.”
Light changes direction – or refracts – when passing from one material to another, a process that allows us to use lenses and prisms to focus and steer light. A quantity known as the index of refraction determines the degree of bending at the boundary, and is positive for conventional materials such as glass. However, through clever engineering, it is also possible to create optical “metamaterials” with a negative index, in which the angle of refraction is also negative. “This can have unusual and dramatic consequences,” Hone notes. “Optical metamaterials are enabling exotic and important new technologies such as super lenses, which can focus beyond the diffraction limit, and optical cloaks, which make objects invisible by bending light around them.”
Electrons travelling through very pure conductors can travel in straight lines like light rays, enabling optics-like phenomena to emerge. In materials, the electron density plays a similar role to the index of refraction, and electrons refract when they pass from a region of one density to another. Moreover, current carriers in materials can either behave like they are negatively charged (electrons) or positively charged (holes), depending on whether they inhabit the conduction or the valence band. In fact, boundaries between hole-type and electron-type conductors, known as p-n junctions (“p” positive, “n” negative), form the building blocks of electrical devices such as diodes and transistors.
An illustration of a ballistic electron refracting across a PN junction in high purity graphene. Credit: Cory Dean, Columbia University
“Unlike in optical materials”, says Hone, “where creating a negative index metamaterial is a significant engineering challenge, negative electron refraction occurs naturally in solid state materials at any p-n junction.”
The development of two-dimensional conducting layers in high-purity semiconductors such as GaAs (Gallium arsenide) in the 1980s and 1990s allowed researchers to first demonstrate electron optics including the effects of both refraction and lensing. However, in these materials, electrons travel without scattering only at very low temperatures, limiting technological applications. Furthermore, the presence of an energy gap between the conduction and valence band scatters electrons at interfaces and prevents observation of negative refraction in semiconductor p-n junctions. In this study, the researchers’ use of graphene, a 2D material with unsurpassed performance at room temperature and no energy gap, overcame both of these limitations.
The possibility of negative refraction at graphene p-n junctions was first proposed in 2007 by theorists working at both the University of Lancaster and Columbia University. However, observation of this effect requires extremely clean devices, such that the electrons can travel ballistically, without scattering, over long distances. Over the past decade, a multidisciplinary team at Columbia – including Hone and Dean, along with Kenneth Shepard, Lau Family Professor of Electrical Engineering and professor of biomedical engineering, Abhay Pasupathy, associate professor of physics, and Philip Kim, professor of physic at the time (now at Harvard) – has worked to develop new techniques to construct extremely clean graphene devices. This effort culminated in the 2013 demonstration of ballistic transport over a length scale in excess of 20 microns. Since then, they have been attempting to develop a Veselago lens, which focuses electrons to a single point using negative refraction. But they were unable to observe such an effect and found their results puzzling.
In 2015, a group at Pohang University of Science and Technology in South Korea reported the first evidence focusing in a Veselago-type device. However, the response was weak, appearing in the signal derivative. The Columbia team decided that to fully understand why the effect was so elusive, they needed to isolate and map the flow of electrons across the junction. They utilized a well-developed technique called “magnetic focusing” to inject electrons onto the p-n junction. By measuring transmission between electrodes on opposite sides of the junction as a function of carrier density they could map the trajectory of electrons on both sides of the p-n junction as the incident angle was changed by tuning the magnetic field.
Crucial to the Columbia effort was the theoretical support provided by Ghosh’s group at the University of Virginia, who developed detailed simulation techniques to model the Columbia team’s measured response. This involved calculating the flow of electrons in graphene under the various electric and magnetic fields, accounting for multiple bounces at edges, and quantum mechanical tunneling at the junction. The theoretical analysis also shed light on why it has been so difficult to measure the predicted Veselago lensing in a robust way, and the group is developing new multi-junction device architectures based on this study. Together the experimental data and theoretical simulation gave the researchers a visual map of the refraction, and enabled them to be the first to quantitatively confirm the relationship between the incident and refracted angles (known as Snell’s Law in optics), as well as confirmation of the magnitude of the transmitted intensity as a function of angle (known as the Fresnel coefficients in optics).
“In many ways, this intensity of transmission is a more crucial parameter,” says Ghosh, “since it determines the probability thatelectrons actually make it past the barrier, rather than just their refracted angles. The transmission ultimately determines many of the performance metrics for devices based on these effects, such as the on-off ratio in a switch, for example.”
Researchers created a single-molecule diode, which has been sought after since the 1970s.
Scientists have designed a new way to create a single-molecule diode that performs 50 times better than past models.
These single-molecule diodes are the first that could be used for real-world applications in nanoscale devices, Columbia University School of Engineering and Applied Sciencereported. The idea of creating a single-molecule diode was first proposed in the 1970s by Arieh Aviram and Mark Ratner, who theorized that a molecule could act as a “rectifier” to conduct one-way currents.
molecular electronics ever since its inception with Aviram and Ratner’s 1974 seminal paper, represents the ultimate in functional miniaturization that can be achieved for an electronic device,” said Latha Venkataraman, associate professor of applied physics at Columbia Engineering.
Since the 1974 paper, scientists have determined single-molecules attached themselves to metal electrodes, and act as a number of circuit elements such as switches, resistors, and diodes. A diode works as an “electricity valve,” and requires an asymmetrical structure in order to create different environments for electricity flowing in each direction.
“While such asymmetric molecules do indeed display some diode-like properties, they are not effective,” said Brian Capozzi, a PhD student working with Venkataraman and lead author of the paper. “A well-designed diode should only allow current to flow in one direction-the ‘on’ direction-and it should allow a lot of current to flow in that direction. Asymmetric molecular designs have typically suffered from very low current flow in both ‘on’ and ‘off’ directions, and the ratio of current flow in the two has typically been low. Ideally, the ratio of ‘on’ current to ‘off’ current, the rectification ratio, should be very high.”
To remedy this, the researchers worked to develop asymmetry in the environment around the molecular junction. They accomplished this by surrounding the active molecule with an ionic solution and employed the use of gold metal electrodes that differed in size to contact the molecule. The method led to rectification ratios as high as 250, which is 50 times higher than earlier designs.
“It’s amazing to be able to design a molecular circuit, using concepts from chemistry and physics, and have it do something functional,” Venkataraman said. “The length scale is so small that quantum mechanical effects are absolutely a crucial aspect of the device. So it is truly a triumph to be able to create something that you will never be able to physically see and that behaves as intended.”
The findings were published in a recent edition of the journal Nature Nanotechnology.
According to the World Water Management Institute, over one-third of the human population is affected by water scarcity. If nothing is done to prevent it, an estimated 1.8 billion people will be living in countries or regions with absolute water scarcity by 2025. Thankfully, due to bio-mimicry and advancements in physics, water filtration and desalination technologies have been growing and improving.
Graphene is a material possessing a very unique structure and properties, giving it a wide range of implications and uses, such as improved water filtration. Graphene is a one-atom thick sheet of carbon atoms. It is nearly transparent, very light, an excellent conductor of both heat and electricity, hydrophobic, and extremely strong. It is so strong that James Hone, professor of mechanical engineering at Columbia University, claims, “It would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.”
But how can graphene be such a great water filter if it is also hydrophobic? Single-atom-wide holes (called capillaries or defects) are made in the graphene sheet by bombarding it with gallium ions. This allows water to be vigorously sucked through the holes in the material structure. Not everything can fit through these tiny holes and, like a sieve, whatever is too big will be filtered out.
University of Manchester researchers discovered that graphene is impermeable to all gases and vapors, except for water; even helium, the hardest gas to separate out, cannot pass through, along with any salts nine Angstroms or larger.
This process is most efficient when the water layer being filtered is only one atom thick (the same thickness as graphene), but filtration will still occur when the graphene is submerged in water. Due to graphene’s increased permeability – fifty times greater than that of conventional membranes – the filtration is ultrafast and has even been compared to the speed of an ordinary coffee filter. The University of Manchester team’s ultimate goal is to “make a filter device that allows a glass of drinkable water made from seawater after a few minutes of hand pumping.” A scientific advance like this would have game changing implications for water supply and policy around the world.
Due to its interesting properties, scientists have been trying to create and implement graphene more effectively since its discovery a few years ago. Columbia University engineering researchers have experimentally demonstrated for the first time that it is possible to electrically contact a two-dimensional material like graphene along its one-dimensional edge rather than contacting it from the top, which has been the conventional approach.
Through this approach, a new assembly technique has been developed that prevents contamination within layered materials (including layered graphene). Kenneth Shepard, Professor of Electrical Engineering at Columbia University, says that this “novel edge-contact geometry provides more efficient contact than the conventional geometry,” opening up possibilities in device applications and fundamental physics exploration.
So keep your eyes peeled; smart phones and other portable devices using graphene “could potentially be commercially available within the next 5-10 years.” Graphene could also be used for more efficient and economically viable biofuel creation or lithium ion batteries found in electrically powered vehicles.
Scientists are also actively fighting water scarcity by taking inspiration from the creatures that handle it best. The Namibian Beetle (Stenocara gracilipes) is native to the southwest coast of Africa, one of the driest deserts in the world. The Namib Desert is known for its high temperatures, strong winds, and negligible rainfall, although it does experience fogs that move in from the Atlantic Ocean early in the morning and late at night.
The Namibian Beetle capitalizes on this windborne dew and gains an average of about twelve percent of its body weight through a technique known as fog-basking. When fog-basking, the beetle points its back at the oncoming breeze carrying the tiny dewdrops and waits. The back of the beetle is hydrophobic, but spotted with small hydrophilic bumps. When the dew-carrying breeze blows by, tiny water droplets are attracted to the hydrophilic bumps and condense, accumulating on the beetle’s back.
When the drops grow to a substantial size, the weight of the droplets and the force of the wind exceed the hydrophilic forces and the drops fall down the hydrophobic back, finally sliding into the beetle’s mouth. Products like fog nets have been enlisted to help solve human water scarcity, but mimicking the beetle’s perfectly efficient biology can help scientists confront the water issue more effectively.
The challenge now is to create passive devices to collect water in desiccated environments for local consumption, particularly in poor countries. One example of a bio-mimicry product that seems to take inspiration from the Namibian Beetle is the Dew Bank Bottle. More bio-mimicry in the future, in many scientific fields, could help scientists discover more efficient, natural ways of solving some of our greatest issues.
Advances in physical understanding, its applications, and the study of our environment and bio-mimicry help us develop more effective ways to fight freshwater scarcity around the world. Graphene has proven to be an incredible material with a vast range of unique, useful properties, but taking a step outside the lab to examine how life naturally overcomes different problems can be just as informative. Hopefully, humble creatures like the Namibian Beetle will help usher in a day when the lack of clean drinking water is no longer an issue. In the words of Dr. Irina Grigorieva, “We are not there yet but this is no longer science fiction.”
Fog coming in from the Atlantic Ocean, near Sossusvlei, Namib desert. Credit: Moongateclimber
Illustration of refraction through a normal optical medium versus what it would look like for a medium capable of negative refraction. Credit: Cory Dean, Columbia University
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