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UV-resistant elastic for N95 masks receives NSF RAPID grant

Posted By Graphene Council, Wednesday, May 20, 2020
Northwestern University’s Mark Hersam has received funding to develop a new elastic material that could enable N95 medical face masks to be disinfected and reused dozens of times.

Last week, the project received a $200,000 rapid response research (RAPID) grant from the National Science Foundation, which has called for immediate proposals that have potential to address the spread of the novel coronavirus (COVID-19).

“The ongoing COVID-19 pandemic has led to a shortage of critical medical equipment, including N95 medical masks. To conserve resources, medical workers have been reusing masks,” said Hersam, a Walter P. Murphy Professor of Materials Science and Engineering in Northwestern’s McCormick School of Engineering. “The problem is that sterilization using ultraviolet light breaks down the elastic in the nose foam and head straps, preventing the masks from fitting properly.”

To disinfect equipment, including N95 masks, medical professionals use ultraviolet germicidal irradiation (UVGI). While the widely used technique is highly effective in killing or inactivating pathogens, such as viruses and bacteria, UVGI also rapidly ages plastics and rubber.

The outcomes of this research not only address the current COVID-19 crisis, but are applicable for general medical use, including in future pandemics.” Mark Hersam, materials scientist.

Hersam’s team is developing a new type of elastic composite based on hydrated graphene oxide (hGO), a material that shows resistance to ultraviolet radiation and has proven intrinsic antimicrobial properties. By incorporating this material into N95 masks, the elastic components could better withstand UVGI and continue to maintain a snug fit even after being reused dozens of time.

A world-renowned graphene expert, Hersam will lead proof-of-concept experiments in his laboratory throughout the summer. He believes that better materials for medical equipment will be important well into the future.

“The outcomes of this research not only address the current COVID-19 crisis,” he said, “but are applicable for general medical use, including in future pandemics.”

The project, “Hydrated graphene oxide elastomeric composites for sterilizable and reusable N95 masks,” is funded by NSF award number 2029058.

Tags:  Graphene  Healthcare  Mark Hersam  Medical  Northwestern University 

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'Atomic dance' reveals new insights into performance of 2D materials

Posted By Graphene Council, Monday, February 17, 2020
A team of Northwestern University materials science researchers have developed a new method to view the dynamic motion of atoms in atomically thin 2D materials. The imaging technique, which reveals the underlying cause behind the performance failure of a widely used 2D material, could help researchers develop more stable and reliable materials for future wearables and flexible electronic devices.

These 2D materials - such as graphene and borophene - are a class of single-layer, crystalline materials with widespread potential as semiconductors in advanced ultra-thin, flexible electronics. Yet due to their thin nature, the materials are highly sensitive to external environments, and have struggled to demonstrate long-term stability and reliability when utilized in electronic devices.

"Atomically thin 2D materials offer the potential to dramatically scale down electronic devices, making them an attractive option to power future wearable and flexible electronics," said Vinayak Dravid, Abraham Harris Professor of Materials Science and Engineering at the McCormick School of Engineering.

The study, titled "Direct Visualization of Electric Field induced Structural Dynamics in Monolayer Transition Metal Dichalcogenides," was published on February 11 in the journal ACS Nano. Dravid is the corresponding author on the paper. Chris Wolverton, the Jerome B. Cohen Professor of Materials Science and Engineering, also contributed to the research.

"Unfortunately, electronic devices now operate as a kind of 'black box.' Although device metrics can be measured, the motion of single atoms within the materials responsible for these properties is unknown, which greatly limits efforts to improve performance," added Dravid, who serves as director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center. The research allows a way to move past that limitation with a new understanding of the structural dynamics at play within 2D materials receiving electrical voltage.

Building upon a previous study in which the researchers used a nanoscale imaging technique to observe failure in 2D materials caused by heat, the team used a high-resolution, atomic-scale imaging method called electron microscopy to observe the movement of atoms in molybdenum disulfide (MoS2), a well-studied material originally used as a dry lubricant in greases and friction materials that has recently gained interest for its electronic and optical properties. When the researchers applied an electric current to the material, they observed its highly mobile sulfur atoms move continuously to vacant areas in the crystalline material, a phenomenon they dubbed, "atomic dance."

That movement, in turn, caused the MoS2's grain boundaries -- a natural defect created in the space where two crystallites within the material meet-- to separate, forming narrow channels for the current to travel through.

"As these grain boundaries separate, you are left with only a couple narrow channels, causing the density of the electrical current through these channels to increase," said Akshay Murthy, a PhD student in Dravid's group and the lead author on the study. "This leads to higher power densities and higher temperatures in those regions, which ultimately leads to failure in the material."

"It's powerful to be able to see exactly what's happening on this scale," Murthy continued. "Using traditional techniques, we could apply an electric field to a sample and see changes in the material, but we couldn't see what was causing those changes. If you don't know the cause, it's difficult to eliminate failure mechanisms or prevent the behavior going forward."

With this new way to study 2D materials at the atomic level, the team believes researchers could use this imaging approach to synthesize materials that are less susceptible to failure in electronic devices. In memory devices, for example, researchers could observe how regions where information is stored evolve as electric current is applied and adapt how those materials are designed for better performance.

The technique could also help improve a host of other technologies, from transistors in bioelectronics to light emitting diodes (LEDs) in consumer electronics to photovoltaic cells that comprise solar panels.

"We believe the methodology we have developed to monitor how 2D materials behave under these conditions will help researchers overcome ongoing challenges related to device stability," Murthy said. "This advance brings us one step closer to moving these technologies from the lab to the marketplace."

Tags:  2D materials  Akshay Murthy  Chris Wolverton  Electronics  Graphene  Northwestern University  Vinayak Dravid 

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Creating 2D heterostructures for future electronics

Posted By Graphene Council, Thursday, November 7, 2019
Updated: Thursday, November 7, 2019
While many nanomaterials exhibit promising electronic properties, scientists and engineers are still working to best integrate these materials together to eventually create semiconductors and circuits with them.

Northwestern Engineering researchers have created two-dimensional (2D) heterostructures from two of these materials, graphene and borophene, taking an important step toward creating intergrated circuits from these nanomaterials.

"If you were to crack open an integrated circuit inside a smartphone, you'd see many different materials integrated together," said Mark Hersam, Walter P. Murphy Professor of Materials Science and Engineering, who led the research. "However, we've reached the limits of many of those traditional materials. By integrating nanomaterials like borophene and graphene together, we are opening up new possibilities in nanoelectronics."

Supported by the Office for Naval Research and the National Science Foundation, the results were published October 11 in the journal Science Advances. In addition to Hersam, applied physics PhD student Xiaolong Liu co-authored this work.

Creating a new kind of heterostructure

Any integrated circuit contains many materials that perform different functions, like conducting electricity or keeping components electrically isolated. But while transistors within circuits have become smaller and smaller -- thanks to advances in materials and manufacturing -- they are close to reaching the limit of how small they can get.

Ultrathin 2D materials like graphene have the potential to bypass that problem, but integrating 2D materials together is difficult. These materials are only one atom thick, so if the two materials' atoms do not line up perfectly, the integration is unlikely to be successful. Unfortunately, most 2D materials do not match up at the atomic scale, presenting challenges for 2D integrated circuits.

Borophene, the 2D version of boron that Hersam and coworkers first synthesized in 2015, is polymorphic, meaning it can take on many different structures and adapt itself to its environment. That makes it an ideal candidate to combine with other 2D materials, like graphene.

To test whether it was possible to integrate the two materials into a single heterostructure, Hersam's lab grew both graphene and borophene on the same substrate. They grew the graphene first, since it grows at a higher temperature, then deposited boron on the same substrate and let it grow in regions where there was no graphene. This process resulted in lateral interfaces where, because of borophene's accommodating nature, the two materials stitched together at the atomic scale.

Measuring electronic transitions

The lab characterized the 2D heterostructure using a scanning tunneling microscope and found that the electronic transition across the interface was exceptionally abrupt -- which means it could be ideal for creating tiny electronic devices.

"These results suggest that we can create ultrahigh density devices down the road," Hersam said. Ultimately, Hersam hopes to achieve increasingly complex 2D structures that lead to novel electronic devices and circuits. He and his team are working on creating additional heterostructures with borophene, combining it with an increasing number of the hundreds of known 2D materials.

"In the last 20 years, new materials have enabled miniaturization and correspondingly improved performance in transistor technology," he said. "Two-dimensional materials have the potential to make the next leap."

Tags:  2D materials  Graphene  Mark Hersam  nanoelectronics  nanomaterials  Northwestern University  Xiaolong Liu 

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Coating for metals rapidly heals over scratches and scrapes to prevent corrosion

Posted By Graphene Council, Wednesday, February 6, 2019
Updated: Wednesday, February 6, 2019
It’s hard to believe that a tiny crack could take down a gigantic metal structure. But sometimes bridges collapse, pipelines rupture and fuselages detach from airplanes due to hard-to-detect corrosion in tiny cracks, scratches and dents.

A Northwestern University team has developed a new coating strategy for metal that self-heals within seconds when scratched, scraped or cracked. The novel material could prevent these tiny defects from turning into localized corrosion, which can cause major structures to fail.

“Localized corrosion is extremely dangerous,” said Jiaxing Huang, who led the research. “It is hard to prevent, hard to predict and hard to detect, but it can lead to catastrophic failure.” 

When damaged by scratches and cracks, Huang’s patent-pending system readily flows and reconnects to rapidly heal right before the eyes. The researchers demonstrated that the material can heal repeatedly — even after scratching the exact same spot nearly 200 times in a row.

The study was published today (Jan. 28) in Research, the first Science Partner Journal recently launched by the American Association for the Advancement of Science (AAAS) in collaboration with the China Association for Science and Technology (CAST). Huang is a professor of materials science and engineering in Northwestern’s McCormick School of Engineering.

While a few self-healing coatings already exist, those systems typically work for nanometer- to micron-sized damages. To develop a coating that can heal larger scratches in the millimeter-scale, Huang and his team looked to fluid. 

“When a boat cuts through water, the water goes right back together,” Huang said. “The ‘cut’ quickly heals because water flows readily. We were inspired to realize that fluids, such as oils, are the ultimate self-healing system.”

But common oils flows too readily, Huang noted. So he and his team needed to develop a system with contradicting properties: fluidic enough to flow automatically but not so fluidic that it drips off the metal’s surface. 

The team met the challenge by creating a network of lightweight particles — in this case graphene capsules — to thicken the oil. The network fixes the oil coating, keeping it from dripping. But when the network is damaged by a crack or scratch, it releases the oil to flow readily and reconnect. Huang said the material can be made with any hollow, lightweight particle — not just graphene.

“The particles essentially immobilize the oil film,” Huang said. “So it stays in place.”

The coating not only sticks, but it sticks well — even underwater and in harsh chemical environments, such as acid baths. Huang imagines that it could be painted onto bridges and boats that are naturally submerged underwater as well as metal structures near leaked or spilled highly corrosive fluids. The coating can also withstand strong turbulence and stick to sharp corners without budging. When brushed onto a surface from underwater, the coating goes on evenly without trapping tiny bubbles of air or moisture that often lead to pin holes and corrosion. 

“Self-healing microcapsule-thickened oil barrier coatings” was supported by the Office of Naval Research (ONR N000141612838). Graduate student Alane Lim and Chenlong Cui, a former member of Huang’s research group, served as the paper’s co-first authors.

Tags:  Graphene  Jiaxing Huang  Northwestern University 

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