New Applications of Graphene

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Information about New Applications of Graphene

Published on November 8, 2016

Author: ruchicakumar


1. Ruchica Kumar Novocus Legal LLP 11/8/2016 New Applications of Graphene

2. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE INTRODUCTION Purpose of this document is to provide readers with a glimpse of new applications of well- known nanomaterial – Graphene. These applications have been reported within date range 3 November 2016 and 8 November 2016. We have compiled this document from reported facts and our sources are also given herein. USE OF GRAPHENE TEMPLATES TO MAKE NEW METAL-OXIDE NANOSTRUCTURES METAL-OXIDE FILMS WITH WRINKLES AND CRUMPLES TRANSFERRED FROM GRAPHENE TEMPLATES HAVE IMPROVED PROPERTIES AS CATALYSTS AND ELECTRODES (Researchers from Brown University have developed a method of using graphene templates to make metal-oxide films with intricate surface textures. A study shows that those textures can enhance the performance of the films as battery electrodes and as photo catalysts. Credit: Hurt lab / Wong lab / Brown University)1 Researchers from Brown University have found a new method for making ultrathin metal- oxide sheets containing intricate wrinkle and crumple patterns2. In a study published in the journal ACS Nano, the researchers show that the textured metal-oxide films have better performance when used as photo catalysts and as battery electrodes. 1 2

3. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE The new findings build on previous work done by the same research group in which they developed a method for introducing finely tuned wrinkle and crumple textures into sheets of the nanomaterial graphene oxide. The study showed that the process enhanced some of graphene’s properties. The textures made the graphene better able to repel water, which would be useful in making water-resistant coatings, and enhanced graphene’s ability to conduct electricity. The researchers thought that similar structures might enhance the properties of other materials — specifically metal oxides — but there’s a problem. To introduce wrinkle and crumple structures in graphene, the team compressed the sheets multiple times in multiple orientations. That process won’t work for metal oxides. “Metal oxides are too stiff,” said Po-Yen Chen, a Hibbitt Postdoctoral Researcher in Brown’s School of Engineering who led the work. “If you try to compress them, they crack.” So, Chen, working with the labs of Robert Hurt and Ian Y. Wong, both engineering professors at Brown, developed a method of using the crumpled graphene sheets as templates for making crumpled metal-oxide films. “We showed that we can transfer those surface features from the graphene onto the metal oxides,” Chen said. The team started by making stacks of crumpled graphene sheets using the method they had developed previously. They deposited the graphene on a polymer substrate that shrinks when heated. As the substrate shrinks, it compresses the graphene sitting on top, creating wrinkle or crumple structures. The substrate is then removed, leaving free-standing sheets of crumpled graphene behind. The compression process can be done multiple times, creating ever more complex structures. The process also allows control of what types of textures are formed. Clamping shrink film on opposite sides and shrinking it in only one direction creates periodic wrinkles. Shrinking in all directions creates crumples. These shrinks can be performed multiple times in multiple configurations to create a wide variety of textures. To transfer those patterns onto metal oxides, Chen placed the stacks of wrinkled graphene sheets in a water-based solution containing positively charged metal ions. The negatively

4. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE charged graphene pulled those ions into the spaces between the sheets. The particles bonded together within the interlayer space, creating thin sheets of metal that followed the wrinkle patterns of the graphene. The graphene was then oxidized away, leaving the wrinkled metal- oxide sheets. Chen showed that the process works with a variety of metal oxides — zinc, aluminium, manganese and copper oxides. Once they had made the materials, the researchers then tested them to see if, as was the case with graphene, the textured surfaces enhanced the metal oxides’ properties. They showed that wrinkled manganese oxide, when used as a battery electrode, had charge- carrying capacity that was four times higher than a planar sheet. That’s probably because the wrinkle ridges give electrons a defined path to follow, enabling the material to carry more of them at a time, the researchers say. The team also tested the ability of crumpled zinc oxide to perform a photocatalytic reaction — reducing a dye dissolved in water under ultraviolet light. The experiment showed the crumpled zinc oxide film to be four times more reactive than a planar film. That’s probably because the crumpled films have higher surface area, which give the material more reactive sites, Chen said. In addition to improving the properties of the metals, Chen points out that the process also represents a way of making thin films out of materials that don’t normally lend themselves to ultrathin configurations. “Using graphene confinement, we can guide the assembly and synthesis of materials in two dimensions,” he said. “Based on what we learned from making the metal-oxide films, we can start to think about using this method to make new 2D materials that are otherwise unstable in bulk solution. But with our confinement method, we think it’s possible.” In addition to Chen, Hurt and Wong, other authors on the paper were Muchun Liu, Thomas Valentin, Zhongying Wang, Ruben Spitz Steinberg and Jaskiranjeet Sodhi. The work was supported by the Hibbitt Engineering Postdoctoral Fellowship and seed funding from Brown University.

5. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE GRAPHENE BALLOONS SHOW THEIR COLORS RESEARCHERS FROM THE GRAPHENE FLAGSHIP HAVE FOUND A NEW POTENTIAL APPLICATION FOR GRAPHENE: MECHANICAL PIXELS. By applying a pressure difference across graphene membranes, the perceived color of the graphene can be shifted continuously from red to blue. This effect could be exploited for use as colored pixels in e-readers and other low-powered screens. The research was a collaborative effort from researchers at TU Delft, Netherlands, and Graphenea, Spain, and the study has recently been published in the journal Nano Letters3. (Artist's impression of graphene balloons showing colors. Under large deformations, Newton rings appear. Credit: Delft University of Technology) In graphene balloon devices, a double layer of graphene two atoms thick is deposited on top of circular indents cut into silicon. The graphene membranes enclose air inside the cavities, and the position of the membranes can be changed by applying a pressure difference 3

6. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE between the inside and the outside. When the membranes are closer to the silicon they appear blue; when the membranes are pushed away they appear red. The color change effect arises from interference between light waves reflected from the bottom of the cavity and the membrane on top. These reflected waves interfere constructively or destructively depending on the position of the membrane – either adding up or cancelling out different parts of the spectrum of white light. This interference enhances or reduces certain colors in the reflected light. Dr. Samer Houri, a researcher at TU Delft, led the exiting work. "At the beginning, we did not pay attention to the colors of the membranes because graphene is 'colorless' when isolated. However, we observed Newton rings and noticed their color changing over time," he said. When the membranes are extremely deformed, their color is no longer homogeneous, but instead circular rings appear. These rings are called Newton rings in honor of Sir Isaac Newton, who studied them in 1717. Santiago Cartamil-Bueno is a Ph.D. student at TU Delft, who carried out the experimental work and was first to observe the change in color. "Not only does this provide the colorimetry technique for characterizing suspended graphene, which is useful for companies developing graphene mechanical sensors, but it also provides a means to implement display technology based on interferometry modulation," says Cartamil-Bueno. Interferometry modulation, or IMOD, is employed in displays that have low-power consumption requirements, such as smart watches and e-books, and is increasing in importance for Internet of Things devices. Currently, such displays are composed of mechanical pixels made of silicon materials. "By instead using graphene, with its extraordinary mechanical properties," Cartamil-Bueno says, "a GIMOD (Graphene IMOD) could drastically improve the device performance –power consumption, pixel response time, failure rates, etc.– while enabling electrical integration and even flexible devices." The researchers are now working to control the color of the membranes with electricity, and hope to have a screen prototype for the Mobile World Conference 2017 in Barcelona.

7. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE ON-CHIP OBSERVATION OF THZ GRAPHENE PLASMONS Researchers developed a technique for imaging THz photocurrents with nanoscale resolution, and applied it to visualize strongly compressed THz waves (plasmons) in a graphene photodetector. The extremely short wavelengths and highly concentrated fields of these plasmons open new venues for the development of miniaturized optoelectronic THz devices4. (THz plasmons of extremely short wavelength propagate along the graphene sheet of a THz detector, as visualized with photocurrent images obtained by scanning probe microscopy.) Radiation in the terahertz (THz) frequency range is attracting large interest because of its manifold application potential for non-destructive imaging, next-generation wireless communication or sensing. But still, the generating, detecting and controlling of THz radiation faces numerous technological challenges. Particularly, the relatively long wavelengths (from 30 to 300 μm) of THz radiation require solutions for nanoscale integration of THz devices or for nanoscale sensing and imaging applications. In recent years, graphene plasmonics has become a highly promising platform for shrinking THz waves. It is based on the interaction of light with collective electron oscillations in graphene, giving rise to electromagnetic waves that are called plasmons. The graphene 4

8. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE plasmons propagate with strongly reduced wavelength and can concentrate THz fields to subwavelength-scale dimensions, while the plasmons themselves can be controlled electrically. Now, researchers at CIC nanoGUNE (San Sebastian, Spain) in collaboration with ICFO (Barcelona, Spain), IIT (Genova, Italy) - members of the EU Graphene Flagship - Columbia University (New York, USA), Radboud University (Nijmegen, Netherlands), NIM (Tsukuba, Japan) and Neaspec (Martinsried, Germany) could visualize strongly compressed and confined THz plasmons in a room-temperature THz detector based on graphene. To see the plasmons, they recorded a nanoscale map of the photocurrent that the detector produced while a sharp metal tip was scanned across it. The tip had the function to focus the THz illumination to a spot size of about 50 nm, which is about 2000 times smaller than the illumination wavelength. This new imaging technique, named THz photocurrent nanoscopy, provides unprecedented possibilities for characterizing optoelectronic properties at THz frequencies. The team recorded photocurrent images of the graphene detector, while it was illuminated with THz radiation of around 100 μm wavelength. The images showed photocurrent oscillations revealing that THz plasmons with a more than 50 times reduced wavelength were propagating in the device while producing a photocurrent. “In the beginning we were quite surprised about the extremely short plasmon wavelength, as THz graphene plasmons are typically much less compressed”, says former nanoGUNE researcher Pablo Alonso, now at the University of Oviedo, and first author of the work. “We managed to solve the puzzle by theoretical studies, which showed that the plasmons couple with the metal gate below the graphene”, he continues. “This coupling leads to an additional compression of the plasmons and an extreme field confinement, which could open the door towards various detector and sensor applications”, adds Rainer Hillenbrand, Ikerbasque Research Professor and Nanooptics Group Leader at nanoGUNE who led the research. The plasmons also show a linear dispersion – that means that their energy is proportional to their momentum - which could be beneficial for information and communication technologies. The team also analysed the lifetime of the THz plasmons, which showed that the damping of THz plasmons is determined by the impurities in the graphene.

9. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE THz photocurrent nanoscopy relies on the strong photothermoelectric effect in graphene, which transforms heat generated by THz fields, including that of THz plasmons, into a current. In the future, the strong thermoelectric effect could be also applied for on-chip THz plasmon detection in graphene plasmonic circuits. The technique for THz photocurrent nanoimaging could find further application potential beyond plasmon imaging, for example, for studying the local THz optoelectronic properties of other 2D materials, classical 2D electron gases or semiconductor nanostructures. ADDING HYDROGEN TO GRAPHENE Adding hydrogen to graphene could improve its future applicability in the semiconductor industry, when silicon leaves off. Researchers have recently gained further insight into this chemical reaction. These findings extend the knowledge of the fundamental chemistry of graphene and bring scientists perhaps closer to realizing new graphene-based materials5. (Hydrogenation (in red) of bilayer graphene via Birch-type reaction begins from the edges. The images show a graphene flake before (a), two minutes (b), and eight minutes (c), after exposure to a solution of lithium and liquid ammonia (Birch-type reaction). Graphene gets gradually hydrogenated starting from the edges. Credit: Zhang X et al, JACS, Copyright 2016 American Chemical Society6 ) 5 6

10. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE Adding hydrogen to graphene could improve its future applicability in the semiconductor industry, when silicon leaves off. Researchers at the Center for Multidimensional Carbon Materials (CMCM), within the Institute for Basic Science (IBS) have recently gained further insight into this chemical reaction. Published in Journal of the American Chemical Society, these findings extend the knowledge of the fundamental chemistry of graphene and bring scientists perhaps closer to realizing new graphene-based materials. Understanding how graphene can chemically react with a variety of chemicals will increase its utility. Indeed, graphene has superior conductivity properties, but it cannot be directly used as an alternative to silicon in semiconductor electronics because it does not have a bandgap, that is, its electrons can move without climbing any energy barrier. Hydrogenation of graphene opens a bandgap in graphene, so that it might serve as a semiconductor component in new devices. While other reports describe the hydrogenation of bulk materials, this study focuses on hydrogenation of single and few-layers thick graphene. IBS scientists used a reaction based on lithium dissolved in ammonia, called the "Birch-type reaction," to introduce hydrogen onto graphene through the formation of C-H bonds. The research team discovered that hydrogenation proceeds rapidly over the entire surface of single-layer graphene, while it proceeds slowly and from the edges in few-layer graphene. They also showed that defects or edges are actually necessary for the reaction to occur under the conditions used, because pristine graphene with the edges covered in gold does not undergo hydrogenation. Using bilayer and trilayer graphene, IBS scientists also discovered that the reagents can pass between the layers, and hydrogenate each layer equally well. Finally, the scientists found that the hydrogenation significantly changed the optical and electric properties of the graphene. "A primary goal of our Center is to undertake fundamental studies about reactions involving carbon materials. By building a deep understanding of the chemistry of single-layer graphene and a few layer graphene, I am confident that many new applications of chemically functionalized graphenes could be possible, in electronics, photonics, optoelectronics, sensors, composites, and other areas," notes Rodney Ruoff, corresponding author of this

11. RUCHICA KUMAR 11/8/16 NEW APPLICATIONS OF GRAPHENE paper, CMCM director, and UNIST Distinguished Professor at the Ulsan National Institute of Science and Technology (UNIST).

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