For the first time, researchers have created a nanocomposite of ceramics and a two-dimensional material, opening the door for new designs of nanocomposites with such applications as solid-state batteries, thermoelectrics, varistors, catalysts, chemical sensors and much more.
Sintering uses high heat to compact powder materials into a solid form. Widely used in industry, ceramic powders are typically compacted at temperatures of 1472 degrees Fahrenheit or higher. Many low-dimensional materials cannot survive at those temperatures.
But a sintering process developed by a team of researchers at Penn State, called the cold sintering process (CSP), can sinter ceramics at much lower temperatures, less than 572 degrees F, saving energy and enabling a new form of material with high commercial potential.
“We have industry people who are already very interested in this work,” said Jing Guo, a post-doctoral scholar working in the group of Clive Randall, professor of materials science and engineering, Penn State. “They are interested in developing some new material applications with this system and, in general, using CSP to sinter nanocomposites.” Guo is first coauthor on the paper appearing online in Advanced Materials.
The remarkable properties of 2-D materials—made up of a single layer of atoms—have made them among the most intensely studied materials of our time. They have the potential to usher in a new generation of improved electronics, batteries and sensory devices, among other applications.
One obstacle to realizing applications of these materials is the cost and time needed for experimental studies. However, computer simulations are helping researchers overcome this challenge in order to accurately characterize material structures and functions at an accelerated pace.
At the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers have simulated the growth of silicene, a 2-D material with attractive electronic properties. Their work, published in Nanoscale, delivers new and useful insights on the material’s properties and behavior and offers a predictive model for other researchers studying 2-D materials.
Going forward, this model can accelerate researchers’ understanding of 2-D materials, and bring us closer to realizing their applications within a wide range of industries.
by Yury Gogotsi, Asia Sarycheva, and Babak Anasori
Spraying an antenna onto a flat surface. Drexel University Nanomaterials Lab, CC BY-ND
Hear the word “antenna” and you might think about rabbit ears on the top of an old TV or the wire that picks up radio signals for a car. But an antenna can be much smaller – even invisible. No matter its shape or size, an antenna is crucial for communication, transmitting and receiving radio signals between devices. As portable electronics become increasingly common, antennas must, too.
Wearable monitors, flexible smart clothes, industrial sensors and medical sensors will be much more effective if their antennas are lightweight and flexible – and possibly even transparent. We and our collaborators have developed a type of material that offers many more options for connecting antennas to devices – including spray-painting them on walls or clothes.
Kirigami is the Japanese art of paper cutting. Likely derived from the Chinese art of jiǎnzhǐ, it emerged around the 7th century in Japan, where it was used to decorate temples. Still in practice today, the kirigami artist uses one piece of paper to cut decorative designs, like birds and fish or the more intricate and popular snowflake.
But, this ancient art, which relies on exacting cuts to determine or replicate patterns, is finding more modern and practical applications in electronics. Specifically, in the manufacture of 2D stretchable materials that can play host to wearable electronics, like electronic skins for health monitoring.
The process combines the art of kirigami with an artificial intelligence technique called autonomous reinforcement learning. And to better synchronize the old with the new, researchers from the University of Southern California use the computing power available to them at the U.S. Department of Energy’s (DOE) Argonne National Laboratory.
Fundamental research sheds light on new many-particle quantum physics in atomically thin semiconductors
A paper published in Nature Communications by Sufei Shi, assistant professor of chemical and biological engineering at Rensselaer, increases our understanding of how light interacts with atomically thin semiconductors and creates unique excitonic complex particles, multiple electrons, and holes strongly bound together. These particles possess a new quantum degree of freedom, called “valley spin.” The “valley spin” is similar to the spin of electrons, which has been extensively used in information storage such as hard drives and is also a promising candidate for quantum computing.
The paper, titled “Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2,” was published in the Sept. 13, 2018, edition of Nature Communications. Results of this research could lead to novel applications in electronic and optoelectronic devices, such as solar energy harvesting, new types of lasers, and quantum sensing.
Shi’s research focuses on low dimensional quantum materials and their quantum effects, with a particular interest in materials with strong light-matter interactions. These materials include graphene, transitional metal dichacogenides (TMDs), such as tungsten diselenide (WSe2), and topological insulators.
A novel technique that nudges single atoms to switch places within an atomically thin material could bring scientists another step closer to realizing theoretical physicist Richard Feynman’s vision of building tiny machines from the atom up.
A significant push to develop materials that harness the quantum nature of atoms is driving the need for methods to build atomically precise electronics and sensors. Fabricating nanoscale devices atom by atom requires delicacy and precision, which has been demonstrated by a microscopy team at the Department of Energy’s Oak Ridge National Laboratory.
They used a scanning transmission electron microscope, or STEM, at the lab’s Center for Nanophase Materials Sciences to introduce silicon atoms into a single-atom-thick sheet of graphene. As the electron beam scans across the material, its energy slightly disrupts the graphene’s molecular structure and creates room for a nearby silicon atom to swap places with a carbon atom.
“We observed an electron beam-assisted chemical reaction induced at a single atom and chemical bond level, and each step has been captured by the microscope, which is rare,” said ORNL’s Ondrej Dyck, co-author of a study published in the journal Small that details the STEM demonstration.
With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists at the University of California, Berkeley, and Lawrence Berkeley National Laboratory (Berkeley Lab) have created new inorganic crystals made of stacks of atomically thin sheets that unexpectedly spiral like a nanoscale card deck.
Their surprising structures, reported in a new study appearing online Wednesday, June 20, in the journal Nature, may yield unique optical, electronic and thermal properties, including superconductivity, the researchers say.
These helical crystals are made of stacked layers of germanium sulfide, a semiconductor material that, like graphene, readily forms sheets that are only a few atoms or even a single atom thick. Such “nanosheets” are usually referred to as “2-D materials.”
“No one expected 2-D materials to grow in such a way. It’s like a surprise gift,” said Jie Yao, an assistant professor of materials science and engineering at UC Berkeley. “We believe that it may bring great opportunities for materials research.”
I finally got to try my hand at sample preparation these past 2 weeks. Materials can exhibit striking electronic and mechanical properties when stripped to few layers / monolayer. Graphene (single layer graphite) is one popular example, first to be discovered among the family of 2D materials in 2004. But the search for conducting 2D materials has now extended beyond graphene.
I tried to exfoliate a single layer of molybdenum disulfide (MoS2), one type of transition metal dichalcogenides (TMD), under the guidance of my lab colleague. The properties of these TMD in the form of 2D sheets have application in more efficient electronics, semiconductors, solar cells, and touch screen display panels, just to name a few.
Exfoliation in this context is actually applying the material of interest onto a scotch tape, then folding and opening the tape several times until the flakes on it are as thin as possible. Judging with my naked eyes, this usually just means for the flakes to not appear as shiny (for metal compounds) anymore. Then, I will have to transfer the flakes on the Scotch tape to a tiny piece of transparent gel (PDMS gel). The procedure is pretty simple, but the flakes produced are not guaranteed to be thin enough. Through my many trials, I find random thickness of flakes distributed all over the gel under optical microscope. And among them, we need to locate the thinnest of all that could potentially be a monolayer.
Below is the flake that I suspect to be a single layer of MoS2 at different magnification level. Can you find it in the last picture?
Here is the relative size of the PDMS gel on which all these flakes lie.
This also happened when I managed to transfer plenty of flakes onto the PDMS gel, while most of the time I do not get enough to choose from when observed under the microscope. After identifying this flake, I had to transfer it onto another substrate (such as a silicon nitride grid), before I can put it into an electron microscope that offer higher resolution through electrons scattering method. The transfer patience takes some patience, as pressing or lifting the gel too quickly may break the hard-found flake. So it is just a lot of going back and forth between the sample preparation table and microscope to get one nice specimen. But it is important to get through this process for us to get to the characterization part, which is where all the fun stuff about science comes in!
In a paper to be published in a forthcoming issue of Nano, a team of researchers from Henan University have investigated the flame retardant performance of epoxy resin using a boron nitride nanosheet decorated with cobalt ferrite nanoparticles.
Polymers are widely used in our daily lives due to good physical and chemical stability, corrosion resistance and other superior properties. However, most polymers, due to their organic nature, are inherently flammable which is a potential threat to the safety of human life and property. In order to avoid or reduce the flammability of polymers, it is a good strategy to add flame retardants to the polymers.
Among them, two-dimensional (2-D) layered inorganic nanomateirals (nanosheets), represented by graphene oxide,molybdenum disulfide, and boron nitride nanosheets (BNNS), exhibit excellent flame retardant performance due to their good physical barrier effects. However, the flame retardance is not enough in the use of such 2-D inorganic flame retardants alone, and in particular, the ability to suppress toxic gases and smoke is weak.
Investigating the remarkable excitonic effects in two-dimensional (2-D) semiconductors and controlling their exciton binding energies can unlock the full potential of 2-D materials for future applications in photonicandoptoelectronic devices. In a recent study, Zhizhan Qiu and colleagues at the interdisciplinary departments of chemistry, engineering, advanced 2-D materials, physics and materials science in Singapore, Japan and the U.S. demonstrated large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide(ReSe2) on a back-gated graphene device. They used scanning tunneling spectroscopy (STS) and differential reflectance spectroscopy to measure the quasiparticle (QP) electronic and optical bandgap (Eopt) of single-layer ReSe2 to yield a large exciton binding energy of 520 meV.
The scientists achieved continuous tuning of the electronic bandgap and exciton binding energy of monolayer ReSe2by hundreds of milli-electron volts via electrostatic gating. Qiu et al. credited the phenomenon to tunable Coulomb interactions arising from the gate-controlled free carriers in graphene. The new findings are now published on Science Advances and will open a new avenue to control bandgap renormalization and exciton binding energies in 2-D semiconductors for a variety of technical applications.
Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea), and colleagues have reported a novel phenomenon, called Valley Acoustoelectric Effect, which takes place in 2D materials, similar to graphene. This research is published in Physical Review Letters and brings new insights to the study of valleytronics.
[…]
In acoustoelectronics, surface acoustic waves (SAWs) are employed to generate electric currents. In this study, the team of theoretical physicists modelled the propagation of SAWs in emerging 2D materials, such as single-layer molybdenum disulfide (MoS2). SAWs drag MoS2 electrons (and holes), creating an electric current with conventional and unconventional components. The latter consists of two contributions: a warping-based current and a Hall current. The first is direction-dependent, is related to the so-called valleys - electrons’ local energy minima - and resembles one of the mechanisms that explains photovoltaic effects of 2D materials exposed to light. The second is due to a specific effect (Berry phase) that affects the velocity of these electrons travelling as a group and resulting in intriguing phenomena, such as anomalous and quantum Hall effects.
In every modern microcircuit hidden inside a laptop or smartphone, you can see transistors—small semiconductor devices that control the flow of electric current, i.e. the flow of electrons. If we replace electrons with photons (elementary particles of light), then scientists will have the prospect of creating new computing systems that can process massive information flows at a speed close to the speed of light. At present, it is photons that are considered the best for transmitting information in quantum computers. These are still hypothetical computers that live according to the laws of the quantum world and are able to solve some problems more efficiently than the most powerful supercomputers.
Although there are no fundamental limits for creating quantum computers, scientists still have not chosen what material platform will be the most convenient and effective for implementing the idea of a quantum computer. Superconducting circuits, cold atoms, ions, defects in diamond and other systems now compete for being one chosen for the future quantum computer. It has become possible to put forward the semiconductor platform and two-dimensional crystals, specifically, thanks to scientists from: the University of Würzburg (Germany); the University of Southampton (United Kingdom); the University of Grenoble Alpes (France); the University of Arizona (USA); the Westlake university (China), the Ioffe Physical Technical Institute of the Russian Academy of Sciences; and St Petersburg University.
A two-dimensional (2D) nanomaterial-based flexible memory device is a critical element in the next-generation wearable market because it plays a crucial role in data storage, processing, and communication. An ultra-thin memory device materialized with a 2D nanomaterial of several nanometers (nm) can significantly increase the memory density, leading to the development of a flexible resistance-variable memory with the implementation of a 2D nanomaterial. However, memories using conventional 2D nanomaterials have limitations owing to the weak carrier trapping characteristics of the nanomaterials.
At the Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST, President Yoon, Seok-Jin), a research team led by Dr. Dong-Ick Son announced the development of a transparent and flexible memory device based on a heterogeneous low-dimensional ultra-thin nanostructure. To this end, monolayered zero-dimensional (0D) quantum dots were formed and sandwiched between two insulating 2D hexagonal boron nitride (h-BN) ultra-thin nanomaterialstructures.
The research team materialized a device that could become a next-generation memory candidate by introducing 0D quantum dots with excellent quantum limiting properties into the active layer, controlling carriers in 2D nanomaterial. Based on this, 0D quantum dots were shaped in a vertically stacked composite structure that was sandwiched between 2D hexagonal h-BN nanomaterials to produce a transparent and flexible device. Therefore, the developed device maintains above 80% transparency and memory function even when bent.
Through their study of two-dimensional iron selenide (FeSe) films, a research team has unlocked some intriguing clues about superconductivity.
Superconductors—materials that can transport electrons with no resistance—are a quantum phenomenon with numerous applications. They have fascinated physicists and engineers since their discovery more than 100 years ago, but the mechanisms of modern superconductors are still not fully understood and remain one of the most active areas of research in quantum materials.
Since it was discovered in 2012, FeSe in its three-atoms-thick monolayer form has received much attention from researchers for its unusual superconductive properties. In bulk form, it becomes a superconductor at 8 Kelvin, or -265 Celsius. As a monolayer, though, it starts superconducting at about 70 Kelvin, or 203 degrees below zero—still very chilly, but moving in the right direction. In a collaboration with the University of British Columbia, Yale researchers shed some light on behavior of electrons in this system, which could prove to be key to understanding superconductivity itself. The results are published in Nature Communications.
Salvador Barazza-Lopez, associate professor of physics at the University of Arkansas, is part of a team that published a review article on the properties of strained graphene and other strained two-dimensional atomic materials in the prestigious Reports of Progress in Physics, a review-style journal published by the Institute of Physics in the United Kingdom that has a large impact factor of 14.3.
Materials that are atomically thin can be thought as membranes. Membranes bend to adapt to other materials, and change their properties when pulled from two opposite edges. Electronic and optical properties of atomically-thin membranes are modified as a result of bending and stretching, and the 62-page published article provides a detailed descriptions of these effects.
“This comprehensive project was led by Gerardo G. Naumis at the Institute of Physics National University of Mexico, and it took about one year to be completed.” Barraza-Lopez said. “Besides giving me the opportunity to summarized work performed at Arkansas over the last six years, the two weeks spent working at the Institute were memorable.” Continued access to the Trestles supercomputer at the Arkansas High Performance Computing Center was crucial for completing many of these studies.
Materials scientists discover powerful effect that could benefit robotics, aviation, medicine and other fields
Imagine repeatedly lifting 165 times your weight without breaking a sweat – a feat normally reserved for heroes like Spider-Man.
New Brunswick engineers have discovered a simple, economical way to make a nano-sized device that can match the friendly neighborhood Avenger, on a much smaller scale. Their creation weighs 1.6 milligrams (about as much as five poppy seeds) and can lift 265 milligrams (the weight of about 825 poppy seeds) hundreds of times in a row.
Its strength comes from a process of inserting and removing ions between very thin sheets of molybdenum disulfide (MoS2), an inorganic crystalline mineral compound. It’s a new type of actuator – devices that work like muscles and convert electrical energy to mechanical energy.
The Rutgers discovery – elegantly called an “inverted-series-connected (ISC) biomorph actuation device” – is described in a study published online today in the journal Nature.
“We found that by applying a small amount of voltage, the device can lift something that’s far heavier than itself,” said Manish Chhowalla, professor and associate chair of the Department of Materials Science and Engineering in the School of Engineering. “This is an important finding in the field of electrochemical actuators. The simple restacking of atomically thin sheets of metallic MoS2 leads to actuators that can withstand stresses and strains comparable to or greater than other actuator materials.”
A group of scientists from Russia, the USA and China, led by Artyom Oganov from the Moscow Institute of Physics and Technology (MIPT), using computer generated simulation have predicted the existence of a new two-dimensional carbon material, a “patchwork” analogue of graphene called phagraphene. The results of their investigation were recently published in the journal Nano Letters.
“Unlike graphene, a hexagonal honeycomb structure with atoms of carbon at its junctions, phagraphene consists of penta-, hexa- and heptagonal carbon rings. Its name comes from a contraction of Penta-Hexa-heptA-graphene,” says Oganov, head of the MIPT Laboratory of Computer Design.
Two-dimensional materials, composed of a one-atom-thick layer, have attracted great attention from scientists in the last few decades. The first of these materials, graphene, was discovered in 2004 by two MIPT graduates, Andre Geim and Konstantin Novoselov. In 2010 Geim and Novoselov were awarded the Nobel Prize in physics for that achievement.
Due to its two-dimensional structure, graphene has absolutely unique properties. Most materials can transmit electric current when unbound electrons have an energy that corresponds to the conduction band of the material. When there is a gap between the range of possible electron energies, the valence band, and the range of conductivity (the so-called forbidden zone), the material acts as an insulator. When the valence band and conduction band overlap, it acts a conductor, and electrons can move under the influence of electric field.
New calculations from theoretical physicists at Rice University show it may be possible to guide the formation of 2-D boron by tailoring boron-metal interactions.
Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.
Calculation of the atom-by-atom energies involved in creating a sheet of boron revealed that the metal substrate – the surface upon which two-dimensional materials are grown in a chemical vapor deposition (CVD) furnace – would make all the difference.
Theoretical physicist Boris Yakobson and his Rice colleagues found in previous work that CVD is probably the best way to make highly conductive 2-D boron and that gold or silver might be the best substrates.
But their new calculations show it may be possible to guide the formation of 2-D boron by tailoring boron-metal interactions. They discovered that copper, a common substrate in graphene growth, might be best to obtain flat boron, while other metals would guide the resulting material in their unique ways.
Chemists are working to synthesize the next generation of super materials for high-performance electronics, solar cells, photodetectors and quantum computers. While they have made progress with compound materials, they have not yet succeeded in developing unaltered or “freestanding” materials for such devices, according to a review published in the journal Science and Technology of Advanced Materials.
Graphene is a carbon material derived from graphite, the same type of material found in pencils, but it is arranged in a one-atom-thin honeycomb lattice. Discovered in 2004, graphene’s two-dimensional arrangement gives it “extraordinary” properties, including extreme strength and “marvelously high” electron conductivity.
However, the tight lattice lacks a semiconducting bandgap, which is essential for electronic devices. Therefore, scientists have been hunting for alternative materials that have bandgaps, but still have a graphene-like structure.
Much focus has been placed on graphene quantum dots, which are small segments of graphene, about 10 to 100 nm carbon hexagons across and less than 30 atomic sheets thick. To make the dots behave more like 2-D graphene, research teams have added other molecules to change the structure and function of the material.
Researchers at the Nanoscience Center at the University of Jyväskylä, Finland, have made a new opening in nanomaterial research. Opening’s essence resides in the exclusive use of metallic elements in flat, atomically thin nanostructures.
The best known flat nanomaterial is graphene. Graphene is stable because the non-metallic element carbon prefers covalent, directional bonds that effectively cause structural planarity. Metallic bonds are less directional, whereby metals often coalesce into compact clusters. However, recent experiments suggest that, by using pores in other nanostructures, even metals can be stabilized into atomically thin planes.
Inspired by these experimental indications, researchers at the Nanoscience Center, University of Jyväskylä, used computer simulations to predict systematically the properties of atomically thin structures made exclusively from metallic elements.
“We made a new opening in material research, which was basic research, but highly rewarding as such,” says postdoctoral researcher Janne Nevalaita. “One could say that we hit on an untouched estate, bulldozed it and created a foundation. Now others can build solid scientific structures based on that foundation,” he continues.
