A stretchable, wearable gas sensor for environmental sensing has been developed and tested by researchers at Penn State, Northeastern University and five universities in China.
The sensor combines a newly developed laser-induced graphene foam material with a unique form of molybdenum disulfide and reduced-graphene oxide nanocomposites. The researchers were interested in seeing how different morphologies, or shapes, of the gas-sensitive nanocomposites affect the sensitivity of the material to detecting nitrogen dioxide molecules at very low concentration. To change the morphology, they packed a container with very finely ground salt crystals.
Nitrogen dioxide is a noxious gas emitted by vehicles that can irritate the lungs at low concentrations and lead to disease and death at high concentrations.
When the researchers added molybdenum disulfide and reduced graphene oxide precursors to the canister, the nanocomposites formed structures in the small spaces between the salt crystals. They tried this with a variety of different salt sizes and tested the sensitivity on conventional interdigitated electrodes, as well as the newly developed laser-induced graphene platform. When the salt was removed by dissolving in water, the researchers determined that the smallest salt crystals enabled the most sensitive sensor.
“We have done the testing to 1 part per million and lower concentrations, which could be 10 times better than conventional design,” says Huanyu Larry Cheng, assistant professor of engineering science and mechanics and materials science and engineering. “This is a rather modest complexity compared to the best conventional technology which requires high-resolution lithography in a cleanroom.”
Ning Yi and Han Li, doctoral students at Penn State and co-authors on the paper in Materials Today Physics, added, “The paper investigated the sensing performance of the reduced graphene oxide/moly disulfide composite. More importantly, we find a way to enhance the sensitivity and signal-to-noise ratio of the gas sensor by controlling the morphology of the composite material and the configuration of the sensor-testing platform. We think the stretchable nitrogen dioxide gas sensor may find applications in real-time environmental monitoring or the healthcare industry.”
Other Penn State authors on the paper, titled “Stretchable, Ultrasensitive, and Low-Temperature NO2 Sensors Based on MoS2@rGO Nanocomposites,” are Li Yang, Jia Zhu, Xiaoqi Zheng and Zhendong Liu.
The discovery of graphene – a material made of a single layer of carbon atoms – 15 years ago was the first step in what has become an ongoing revolution. Using such two-dimensional layers of carbon or other compounds, materials can now be precisely engineered for particular properties in ways that had not previously been possible. Around two years ago, scientists at the Massachusetts Institute of Technology (MIT) added yet another twist – literally. They created a material made of two layers of graphene in which the top layer was slightly askew – twisted at a “magic angle” of a tad over one degree. A single layer of graphene generally behaves as a semimetal, but the magic twist turns the two graphene layers into a superconductor, in which electrons can carry electric current with no loss of energy. This superconductor somewhat resembles a completely different group of materials – so-called high-temperature superconductors – that have subject of intense research for decades but are still not fully understood.
Researchers at the Weizmann Institute of Science recently teamed up with the magic-angle group at MIT to uncover the physics of this interesting twist. Along the way, they identified a new kind of disorder – a discovery that could advance the emerging field of “twistronics.”
PhD student Aviram Uri and Dr. Sameer Grover, who led the research in the group of Prof. Eli Zeldov of the Weizmann’s Condensed Matter Physics Department, together with Yuan Cao and colleagues from the group of Prof. Pablo Jarillo-Herrero at MIT, measured the flow of electrons in magic-angle graphene using the scanning SQUID-on-tip microscope developed in Zeldov’s lab. An ultra-sensitive magnetometer with nanoscale resolution, the SQUID-on-tip is perfect for this purpose, explains Aviram. It visualizes, in great detail, what happens on the level of a single atomic, super-lattice period that is induced by the two rotated layers. The double layers of graphene-with-a-twist devices were prepared for the experiment at MIT and sent to Zeldov’s lab.
The first thing the researchers noted in their measurements was that the electrons followed “preferred” narrow paths through the material. These paths resembled quantum “edge states” that Zeldov and his team had identified in their previous experiments in graphene; but as opposed to those experiments, where the edge states were actually on the edges, here they were running right through the middle. How and why did these strange edge states form?
The solution to this puzzle, says Zeldov, is that these currents still flow along edges, but in this case the edges are the boundaries of patches within the material, each made up of different twist angles. The researchers found that even if one aims for a specific twist-angle when fabricating the device, there will be random strains and stresses so that the twist angle varies throughout -- creating a complex structure rather than a uniform one. By tracing the exact positions of the edge states, the researchers were in fact able to construct spatial maps of the local twist angle with unprecedented resolution and accuracy. These new maps revealed an intricate landscape consisting of valleys, peaks and saddle points, and a network of sharp jumps.
“Close to the magic angle, the electronic properties of the material depend strongly on the exact twist angle. That means that regions with different twist angles should really be thought of as different materials that are somehow attached together,” explains Aviram. This new perspective has far reaching implications. The researchers in Zeldov’s group showed that gradients in the twist angle lead to the formation of strong internal electric fields that do not behave as would be expected, given the metallic nature of the material. Moreover, these fields can be tuned and amplified significantly simply by changing the density of the electrons. Unlike the electric fields produced by the more familiar “charge disorder,” these electric fields reflect a fundamentally new type of disorder – “twist-angle disorder” – a phenomenon that affects the very properties of its electrons, causing them to alter their mass as they traverse the different regions of the material.
Qantum Hall edge states surprisingly appear in the bulk of magic angle graphene rather than along the edges of the device (black outline). Each edge state consists of a pair of red and blue colors indicating counterpropagating persistent currents. A scanning nanoSQUID-on-tip was used to directly image the currents through their magnetic field imprint.
The nature of this new kind of disorder gave the researchers some clues as to how edge states form in the interior of the sample. “You can think of the twisted material as a series of egg cartons with different periodicities placed side by side,” says Aviram. “The edge states run in the narrow areas that separate those ‘cartons’ – this is where intense in-plane electric fields exist, pointing from one egg carton to the next.”
Mason Graphite Inc. announces today the following Board and management changes, to become effective on September 1st, 2020.
As previously announced, Chair and interim CEO Paul R. Carmel is resigning, to become President and CEO of Sidex S.E.C. Sidex is an institutional investment fund sponsored by the government of Quebec and the Fonds de Solidarité FTQ and whose mission it is to invest in companies engaged in the mineral exploration in Quebec.
Gilles Gingras, who sits on the Board of Directors since 2018, has been appointed as Chair of the Board.
Leadership at the management level will be assumed by COO Jean L’Heureux until such time as a permanent CEO can be identified.
Peter Damouni has been appointed as Chair of the corporate governance, nomination and compensation committee; such committee is also composed of Gaston Morin and Gilles Gingras.
François Laurin will continue in his role as Chair of the Audit committee, alongside existing audit committee members Guy Chamard and Gilles Gingras.
Mr. Gilles Gingras, newly appointed Chair of the Board of Mason Graphite, commented: “On behalf of the Board of Directors, I would like to show my gratitude to Paul Carmel who has led the Corporation through challenging markets and has laid the foundation for a brighter future. We wish him all the best in his future endeavors.”
Mr. Paul R. Carmel also commented: “The Corporation has a strong board of directors, a strong management team and a very sound balance sheet and the future is indeed bright. I have very much enjoyed my experience with Mason and leave knowing the Corporation is healthy and in good hands.”
Assistant Professor Kevin Daniels (ECE/IREAP) and his colleagues, have developed an epitaxial graphene based biosensor that provides rapid detection of COVID-19.
The biosensor, created by Daniels, Dr. Soaram Kim of the Institute for Research in Electronics and Applied Physics (IREAP), Dr. Heeju Ryu of the Fred Hutchinson Cancer Research Center, Dr. Seo Hyun Kim of the University of Georgia, and Dr. Rachael Myers-Ward of the U.S. Naval Research Laboratory, tested COVID spike protein ranging from one attogram to one microgram, and can detect COVID spike protein in a few seconds, reuse sensors by simply rinsing in sodium chloride (NaCl), and attain results without sending it off to a lab, unlike the current real-time reverse transcription-polymerase chain reaction (RT-PCR) test. Although It is the fastest, most reliable and universally used method for diagnosis, RT-PCR requires a ribonucleic acid (RNA) preparation step, causing a decrease in accuracy as well as sensitivity. In addition, it takes over three hours to complete the current diagnosis for COVID-19.
The researchers use epitaxial graphene, a single to a few layers of carbon atoms with incredibly high surface area, high electronic conductivity and carrier mobility resulting in ultimate sensitivity for biological sensors. SARS-CoV-2 spike protein antibody & antigen allows high selectivity and an experimental environment that is not dangerous. Therefore the antibody/graphene heterostructure can synergistically improve sensitivity and provide ultra-fast detection.
“These graphene-based sensors are not only much faster than PCR and Rapid test for detecting COVID, but are orders of magnitude more sensitive with the possibility of detecting the virus sooner post-exposure," says Daniels. "The ability to rapidly detect the virus in individuals, even those who were exposed too recently to be detected by other means, is the goal.”
Quantum technologies promise to revolutionize information technology and communications by taking advantage of some peculiar aspects of quantum physics, such as quantum state superposition and entanglement. Research is moving forward in different directions with the goal of building optimal devices for quantum information processing, secure communication, and high-precision sensing.
Systems based on rare-earth ions, such as erbium, are very relevant to this quest, in particular because they typically have very long decoherence times, which means that quantum states persist longer than in other systems. Furthermore, erbium emits light at a wavelength of 1.5 micrometers, one of the main bands for optical communications systems. Hybrid systems containing nanoscale rare-earth components may prove highly versatile and useful to meet the needs of various (quantum) optoelectronic applications.
A team of researchers including Dr Klaas-Jan Tielrooij, leader of the Ultrafast Dynamics in Nanoscale Systems group at the ICN2, and scientists from the Institute of Photonic Sciences (ICFO) and the Institut de Recherche de Chimie Paris (IRCP) have combined a 10 nm thin film of an erbium-doped oxide crystal with monolayer graphene. This hybrid system exhibits extremely strong emitter-environment interactions due to the physical closeness of the emitters to graphene, and the strong dipole-dipole coupling to Dirac electrons.
Their study, recently published in Nature Communications, showed that a large fraction of excited erbium ions decays more than a thousand times faster than normal due to the presence of graphene. This implies that more than 99.9% of the energy flows from these excited emitters to graphene through near-field interactions – where the near-field is the region of the electromagnetic field closest to the object that emits the radiation; in this specific case, it means at a distance from the emitter much smaller than the wavelength of the emitted light. The energy that is transferred from excited emitters to graphene leads to either electron-hole pair generation or plasmon launching (see illustration) in graphene, depending on the Fermi energy of graphene.
Moreover, as reported in the paper, the authors were able to efficiently control the near-field interactions of this hybrid system and to modulate them dynamically by applying a small electrical voltage of just a few volts. This is possible because the gate voltage allows for tuning graphene’s Fermi energy over a large range. The emitter-environment interactions were controlled with high modulation frequencies — up to 300 kHz, which is three orders of magnitude higher than the emitter’s normal radiative decay rate.
This fast dynamic modulation can lead to interesting phenomena and applications, such as the emission of single photons with controlled waveform and quantum entanglement generation by collective plasmon emission. The development of hybrid systems enabling fast control over the near-field interactions, as this erbium-graphene platform, also provides an interesting tool to manipulate quantum states in nanoscale solid state devices by means of conventional electronics. Further studies on these structures will certainly open the way to wider applications in optoelectronic, plasmonic and quantum technologies.
Saint Jean Carbon is pleased to announce that it intends to complete a non-brokered private placement financing of up to 8,000,000 Units at a price of $0.025 per Unit for gross proceeds of up to $200,000.
Each Unit will consist of one (1) common share in the capital of the Company and one (1) common share purchase warrant (each a “Warrant”). Each Warrant will entitle the holder to acquire one (1) additional common share in the capital of the Company (each a “Warrant Share”) at an exercise price of $0.05 per Warrant Share for a period of 36 months from the date of issuance. All securities issued as part of the Offering will be subject to a four month and one (1) day hold period. The Company intends to use the proceeds of the Units to preserve the Company’s existing operations and for general corporate and administrative purposes.
Although the Company intends to use the proceeds of the Offering as described above, the actual allocation of net proceeds may vary from the uses set forth above, depending on future operations or unforeseen events or opportunities.
Closing of the Offering is subject to customary conditions and regulatory approvals including the approval of the TSX Venture Exchange . The proposed Offering and pricing of the Units is in reliance upon the Exchange’s bulletin dated April 8, 2020 titled “Temporary Relief of $0.05 Minimum Pricing Requirements”. The Company intends to close the Offering as soon as practicable.
Engineers at Australia’s Monash University have developed world-first technology that can help industry identify and export high quality graphene cheaper, faster and more accurately than current methods.
Published in international journal Advanced Science ("A High Throughput and Unbiased Machine Learning Approach for Classification of Graphene Dispersions"), researchers used the data set of an optical microscope to develop a machine-learning algorithm that can characterise graphene properties and quality, without bias, within 14 minutes.
This technology is a game changer for hundreds of graphene or graphene oxide manufacturers globally. It will help them boost the quality and reliability of their graphene supply in quick time.
Currently, manufacturers can only detect the quality and properties of graphene used in a product after it has been manufactured.
Through this algorithm, which has the potential to be rolled out globally with commercial support, graphene producers can be assured of quality product and remove the time-intensive and costly process of a series of characterisation techniques to identify graphene properties, such as the thickness and size of the atomic layers.
Professor Mainak Majumder from Monash University’s Department of Mechanical and Aerospace Engineering and the Australian Research Council’s Hub on Graphene Enabled Industry Transformation led this breakthrough study.
“Graphene possesses extraordinary capacity for electric and thermal conductivity. It is widely used in the production of membranes for water purification, energy storage and in smart technology, such as weight loading sensors on traffic bridges,” Professor Majumder said.
“At the same time, graphene is rather expensive when it comes to usage in bulk quantities. One gram of high quality graphene could cost as much as $1,000 AUD ($720 USD) a large percentage of it is due to the costly quality control process.
“Therefore, manufacturers need to be assured that they’re sourcing the highest quality graphene on the market. Our technology can detect the properties of graphene in under 14 minutes for a single dataset of 1936 x 1216 resolution. This will save manufacturers vital time and money, and establish a competitive advantage in a growing marketplace.”
Discovered in 2004, graphene is touted as a wonder material for its outstanding lightweight, thin and ultra-flexible properties. Graphene is produced through the exfoliation of graphite. Graphite, a crystalline form of carbon with atoms arranged hexagonally, comprises many layers of graphene.
However, the translation of this potential to real-life and usable products has been slow. One of the reasons is the lack of reliability and consistency of what is commercially often available as graphene.
The most widely used method of producing graphene and graphene oxide sheets is through liquid phase exfoliation (LPE). In this process, the single layer sheets are stripped from its 3D counterpart such as graphite, graphite oxide film or expanded graphite by shear-forces.
But, this can only be imaged using a dry sample (i.e. once the graphene has been coated on a glass slide). “Although there has been a strong emphasis on standardisation guidelines of graphene materials, there is virtually no way to monitor the fundamental unit process of exfoliation, product quality varies from laboratory to laboratory and from one manufacturer to other,” Dr Shaibani said.
“As a result, discrepancies are often observed in the reported property-performance characteristics, even though the material is claimed to be graphene.
“Our work could be of importance to industries that are interested in delivering high quality graphene to their customers with reliable functionality and properties. There are a number of ASX listed companies attempting to enter this billion-dollar market, and this technology could accelerate this interest.”
Researchers applied the algorithm to an assortment of 18 graphene samples – eight of which were acquired from commercial sources and the rest produced in a laboratory under controlled processing conditions.
Using a quantitative polarised optical microscope, researchers identified a technique for detecting, classifying and quantifying exfoliated graphene in its natural form of a dispersion.
To maximise the information generated from hundreds of images and large numbers of samples in a fast and efficient manner, researchers developed an unsupervised machine-learning algorithm to identify data clusters of similar nature, and then use image analysis to quantify the proportions of each cluster.
Mr Abedin said this method has the potential to be used for the classification and quantification of other two-dimensional materials.
“The capability of our approach to classify stacking at sub-nanometer to micrometer scale and measure the size, thickness, and concentration of exfoliation in generic dispersions of graphene/graphene oxide is exciting and holds exceptional promise for the development of energy and thermally advanced products,” Mr Abedin said.
Professor Dusan Losic, Director of Australian Research Council’s Hub on Graphene Enabled Industry Transformation, said: “These outstanding outcomes from our ARC Research Hub will make significant impact on the emerging multibillion dollar graphene industry giving graphene manufacturers and end-users new a simple quality control tool to define the quality of their produced graphene materials which is currently missing.”
This August, the Aachen Graphene & 2D Materials Center has gained new valuable expertise with the arrival of Dr. Lutz Waldecker as senior researcher in the Stampfer Group (2nd Institute of Physics A).
Waldecker is an expert on exciton physics and ultrafast dynamics in solids, in particular two-dimensional (2D) semiconductors. On his background, he has a Ph.D. at the Fritz Haber Institute of the Max Planck Society in Berlin, under the supervision of Ralph Ernstorfer, and a post-doc at Stanford University, in the group of Tony Heinz, where he worked on the optical and electronic properties of 2D semiconductors.
Among Waldecker’s recent results is the demonstration that dielectric screening causes a rigid shift of the single particle bands of 2D semiconductors, with little changes of the electronic dispersion . This observation suggests a new, noninvasive way of inducing nanoscale functionality in 2D semiconductors by acting on the substrate dielectrics – an approach that Waldecker is planning to explore as part of his research in Aachen.
Waldecker’s position is funded by a Feodor-Lynen return fellowship of the Alexander von Humboldt Foundation. “It is great to see that the Aachen Graphene & 2D Materials Center is getting increasingly competitive in attracting top-class researchers”, says Prof. Christoph Stampfer, “I’m looking very much forward to working together with Lutz!”
A team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has demonstrated for the first time the fabrication of folded bilayer-bilayer graphene (fBBLG)/hexagonal boron nitride (hBN) superlattices. This achievement could pave the way for expanded applications of superlattices, such as in a variety of quantum devices.
Graphene superlattices represent a novel class of quantum metamaterials that have promising prospects. They have been generating a lot of attention recently, ever since the discovery of superconductivity in twisted bilayer graphene (BLG). This was followed by studies related to twisted bilayer-bilayer graphene. Bernal-stacked BLG has a parabolic energy dispersion with a four-fold spin and valley degeneracy.
A superlattice is a periodic structure of layers of two or more materials. Typically, the width of layers is orders of magnitude larger than the lattice constant, and is limited by the growth of the structure. The WPI-MANA team's superlattices are made up of vertically stacked ultrathin/atomic-layer quasi 2D materials.
The WPI-MANA team's results point to the emergence of a unique electronic band structure in the fBBLG, which could provide a way for investigating correlated electron phenomena by performing energy-band engineering with superlattice structures.
The results of this study indicate the emergence of a unique electronic band structure in fBBLG, which could be modified by the moire superlattice potential. Although a systematic way to fold graphene is still lacking, it should be a fruitful topic of future research, leading to 2D paper-folding engineering like "origami." The team's results suggest a possible way to engineer 2D electronic systems by mechanical folding, similar to "tear and stack" for twisted heterostructures.
This work could lead the way to expanded applications of superlattices, including quantum devices such as Bloch oscillators, quantum cascade lasers and terahertz source generators.