Posted By Graphene Council,
Wednesday, September 23, 2020
The Center for Nanoscale Science, a National Science Foundation Materials Science and Engineering Center (MRSEC), has again successfully renewed its NSF support in the highly competitive MRSEC program. The new iteration of the center encompasses two of NSF's Big Ideas -- "Quantum Leap" and "Harnessing the Data Revolution."
More than 20 Penn State faculty are involved in the MRSEC's two new interdisciplinary research groups (IRGs). IRG1, 2D Polar Metals and Heterostructures, is led by Joshua Robinson, professor of materials science and engineering and Jun Zhu, professor of physics. It pioneers new methods of encasing two-dimensional metals in graphene to achieve exceptional optical properties and intriguing potential for quantum devices and biosensing. Before the IRG's pioneering work, only gold among metals was known to resist oxidation in the air. Penn State researchers are now extending that critical property across wide swathes of the periodic table.
IRG2, Crystalline Oxides with High Entropy, is led by Jon-Paul Maria, professor of materials science and engineering and Ismaila Dabo, associate professor of materials science and engineering. It seeks to write a new chapter in the crystal chemistry rulebook by creating materials that take advantage of the enormous number of ways that different kinds of atoms can be arranged onto a common crystal lattice. This innovative technique enables Penn State researchers to put atoms into environments that they normally do not assume, with potential applications across a wide domain, from new energy materials to new quantum devices, guided by a close interplay of theory, computation, data and experiment.
"These two intriguing research directions define new materials platforms- whole classes of new materials - that are being pioneered here at Penn State," says Vin Crespi, the director of the Center for Nanoscale Science.
The MRSEC also provides career development opportunities for dozens of graduate students with a focus during this renewal on sustainability in research practice and outcomes. A recently launched educational website, "Mission: Materials Science," will expand its content and reach out to youth audiences through a new partnership with the local Discovery Space museum. Outreach through participation in summer science camps, STEM programs for students who are blind or visually impaired, and partnerships with universities that serve underrepresented students will remain core to the Center's mission.
Program Director for Education and Outreach Kristin Dreyer said, "The best and most effective messengers for communicating important science concepts to youth and public audiences and inspiring the next generation of materials scientists are current researchers themselves. My colleague, Tiffany Mathews, and I get to help make those opportunities happen and provide the necessary support for our members to do it successfully."
The Center for Nanoscale Science is among eight MRSECs successfully renewing their funding along with three new centers, and has been funded continuously since 2000.
According to NSF, "The U.S. economy and its competitiveness depend on innovation, an essential part of which is fueled by technological breakthroughs in basic research. Our comfort, work, and well-being depend on the development of new materials for anything ranging from smart electronics to implantable medical devices."
Posted By Graphene Council,
Friday, August 28, 2020
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.
Researchers found a way to strengthen carbon fibers, which are widely used in the airline industry but are typically very expensive. Adding graphene boosts the strength and stiffness of the material, and paved the way for making a cost-effective material that could one day strengthen cars. Shown is a computer simulation of adding graphene to the process of growing carbon fibers. This project is a collaboration between Penn State, the University of Virginia, Oak Ridge National Laboratory, Solvay and Oshkosh.
Posted By Graphene Council,
Wednesday, May 6, 2020
A new supercapacitor based on manganese oxide could combine the storage capacity of batteries with the high power and fast charging of other supercapacitors, according to researchers at Penn State and two universities in China.
“Manganese oxide is definitely a promising material,” said Huanyu "Larry" Cheng, assistant professor of engineering science and mechanics and faculty member in the Materials Research Institute, Penn State. “By combining with cobalt manganese oxide, it forms a heterostructure in which we are able to tune the interfacial properties.”
The group started with simulations to see how manganese oxide’s properties change when coupled with other materials. When they coupled it to a semiconductor, they found it made a conductive interface with a low resistance to electron and ion transport. This will be important because otherwise the material would be slow to charge.
“Exploring manganese oxide with cobalt manganese oxide as a positive electrode and a form of graphene oxide as a negative electrode yields an asymmetric supercapacitor with high energy density, remarkable power density and excellent cycling stability,” according to Cheng Zhang, who was a visiting scholar in Cheng’s group and is the lead author on a paper published recently in Electrochimica Acta.
The group has compared their supercapacitor to others and theirs has much higher energy density and power. They believe that by scaling up the lateral dimensions and thickness, their material has the potential to be used in electric vehicles. So far, they have not tried to scale it up. Instead, their next step will be to tune the interface where the semiconducting and conducting layers meet for even better performance. They want to add the supercapacitor to already developed flexible, wearable electronics and sensors as an energy supply for those devices or directly as self-powered sensors.
Cheng Zhang is now an assistant professor at Minjiang University, China. The second Chinese university is Guizhou Education University. The paper is “Efficient Coupling of Semiconductors into Metallic MnO2@CoMn2O4 Heterostructured Electrode with Boosted Charge Transfer for High-performance Supercapacitors.”
Posted By Graphene Council, The Graphene Council,
Tuesday, January 28, 2020
Two-dimensional materials are atomically thin, the most well-known being graphene, a single-atom-thick layer of carbon atoms. "People have struggled to make these 2D materials without defects," said Mauricio Terrones, Verne M. Willaman Professor of Physics, Penn State. "That's the ultimate goal. We want to have a 2D material on a four-inch wafer with at least an acceptable number of defects, but you want to evaluate it in a quick way."
The researchers' -- who represent Penn State, Northeastern University, Rice University and Universidade Federal de Minas Gerais in Brazil -- solution is to use laser light combined with second harmonic generation, a phenomenon in which the frequency of the light shone on the material reflects at double the original frequency. They add dark field imaging, a technique in which extraneous light is filtered out so that defects shine through. According to the researchers, this is the first instance in which dark field imaging was used, and it provides three times the brightness of the standard bright field imaging method, making it possible to see types of defects previously invisible.
"The localization and identification of defects with the commonly used bright field second harmonic generation is limited because of interference effects between different grains of 2D materials," said Leandro Mallard, a senior author on a recent paper in Nano Letters and a professor at Universidade Federal de Minas Gerais. "In this work we have shown that by the use of dark field SHG we remove the interference effects and reveal the grain boundaries and edges of semiconducting 2D materials. Such a novel technique has good spatial resolution and can image large area samples that could be used to monitor the quality of the material produced in industrial scales."
Vincent H. Crespi, Distinguished Professor of Physics, Materials Science and Engineering, and Chemistry, Penn State, added, "Crystals are made of atoms, and so the defects within crystals -- where atoms are misplaced -- are also of atomic size.
"Usually, powerful, expensive and slow experimental probes that do microscopy using beams of electrons are needed to discern such fine details in a material," said Crespi. "Here, we use a fast and accessible optical method that pulls out just the signal that originates from the defect itself to rapidly and reliably find out how 2D materials are stitched together out of grains oriented in different ways."
Another coauthor compared the technique to finding a particular zero on a page full of zeroes. "In the dark field, all the zeroes are made invisible so that only the defective zero stands out," said Yuanxi Wang, assistant research professor at Penn State's Materials Research Institute.
The semiconductor industry wants to have the ability to check for defects on the production line, but 2D materials will likely be used in sensors before they are used in electronics, according to Terrones. Because 2D materials are flexible and can be incorporated into very small spaces, they are good candidates for multiple sensors in a smartwatch or smartphone and the myriad of other places where small, flexible sensors are required.
"The next step would be an improvement of the experimental setup to map zero dimension defects -- atomic vacancies for instance -- and also extend it to other 2D materials that host different electronic and structural properties," said lead author Bruno Carvalho, a former visiting scholar in Terrones' group.
Just as in other uses of graphene for sensors, in this application graphene’s property of being only one-thick and highly conductive makes it extremely sensitive to detecting biological signals. The way the actual device exploits that property is that when DNA or RNA molecules bind to the graphene surface, they dramatically change the materials conductivity.
This is not the first time that this basic design has been used as a biological sensor. However, in this case instead of using a single-stranded DNA that can only bind to the target DNA molecule, they developed what they have dubbed a “DNA hairpin” in which its curled structure opens up when the target molecule binds to it.
When it opens, another DNA molecule that has been added to the system kicks the target molecule out, making it possible to bind with many different sites on the graphene.