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<?xml version="1.0" encoding="UTF-8"?> Ultrafast synthesis of high-quality graphene films combined with roll-to-roll processes ushers in a new era in graphene production Image: Peking University/Nature Nanotechnology The adaptation of chemical vapor deposition (CVD) production of graphene so that it’s compatible with roll-to-roll processing is transforming graphene manufacturing. That effort is being led by companies like Graphene Frontiers, based in Philadelphia. However, the production of single-crystal graphene on copper foils in a CVD process remains a fairly time consuming procedure. Fabrication of centimeter-size single crystals of graphene still takes as much as a day. Now researchers at Hong Kong Polytechnic University and Peking University have developed a technique that accelerates the process so that the growth happens at 60 micrometers per second—far faster than the typical 0.4 µm per second. The key to this 150-fold speed increase was adding a little oxygen directly to the copper foils. In the research, which is described in the journal Nature Nanotechnology , the China-based researchers placed an oxide substrate 15 micrometers below the copper foil. The result: a continuous supply of oxygen that lowers the energy barrier to the decomposition of the carbon feedstock, thereby increasing the graphene growth rate. The expectations were that the oxide substrate would release the oxygen at the high temperatures inside the CVD surface (over 800 degrees Celsius). The researchers confirmed this through the use of electron spectroscopy. While the measurements indicated that oxygen was indeed being released, the amount was still fairly minimal. Nevertheless, this minuscule amount of oxygen proved sufficient for their purposes because the very small space between the oxide substrate and the copper foil created a trapping effect that multiplied the effect of the oxygen. In their experiments, the researchers were able to successfully produce single-crystal graphene materials as large as 0.3 millimeter in just five seconds. That, according to the researchers, is more than two orders of magnitude faster than other methods in which graphene is grown on copper foils. The researchers believe that this ultrafast synthesis of graphene makes possible a new era of scalable production of high-quality, single-crystal graphene films by combining this process with roll-to-roll methods. Counterintuitively, speeding up the process of producing single-crystal graphene films may not automatically lead to wider adoption of graphene in various devices. Just a few years ago, graphene production was stuck at around a 25-percent utilization rate, and there is no reason to believe that demand has increased enough to have dramatically changed those figures. (Graphene producers will tell you that if demand for CVD-produced graphene suddenly spiked, volume could be doubled nearly overnight.) Nonetheless, speed in manufacturing is always an attractive option for any product. It just might not offer a change to the graphene landscape as much as a few “killer apps” might.
MIT NewsMartin Schmidt named Ray and Maria Stata ProfessorMIT NewsIn addition to research, Schmidt has taught courses in micro/nanofabrication and MEMS, as well as core undergraduate subjects in EECS. His teaching has been recognized with the Ruth and Joel Spira Teaching Award and the Eta Kappa Nu Teaching ...
Engineers at the University of California San Diego have developed a flexible wearable sensor that can accurately measure a person's blood alcohol level from sweat and transmit the data wirelessly to...
IBM Lab-on-a-Chip Breakthrough Aims to Help Physicians Detect Cancer and Diseases at the Nanoscale: IBM scientists will collaborate with the Icahn School of Medicine at Mt. Sinai to test on prostate cancer
IBM (NYSE: IBM) scientists have developed a new lab-on-a-chip technology that can, for the first time, separate biological particles at the nanoscale and could enable physicians to detect diseases suc...
<?xml version="1.0" encoding="UTF-8"?> By applying a voltage to graphene sandwiching a piece of paper, researchers have created a new display technology Images: Bilkent University Graphene has been building quite a reputation for itself in flexible displays. Among the ways graphene has been used in this field is as an alternative to the relatively scarce indium tin oxide (ITO), a transparent conductor that controls display pixels. Graphene has also been used in a display’s pixel electronics, or backplane, where a solution-processed graphene is used as an electrode. Now researchers at Bilkent University in Ankara, Turkey, have demonstrated that an ordinary sheet of paper that is sandwiched between two films of multilayer graphene can act as a rudimentary flexible electronic display. In an interview with Nature Photonics , the corresponding author, Coskun Kocabas, says that this system could serve as a framework for turning ordinary printing paper into an optoelectronic display. Kocabas explained: We would like to fabricate a display device that can reconfigure the displayed information electronically on a sheet of printing paper. Several technologies based on electrophoretic motion of particles, thermochromic dyes and electrowetting of liquids have been developed to realize electronic paper, or e-paper, which has great potential for consumer electronics. Contrasting with the primary aim of e-paper, these technologies, however, are not compatible with conventional cellulose-based printing papers. The researchers described their device in the journal ACS Photonics. It operates by applying a bias voltage to the graphene to trigger an intercalation of ions so that the optical absorption of the graphene layers is altered. That turns them from transparent to dark and back again. (Intercalation is the reversible inclusion of a molecule or ions between two other molecules in multilayered structures or compounds.) In the experiments, the display’s transition to transparent takes a bit of time— about 4 seconds; reverting to its darker form takes under half a second. While this may be suitable for signs that don’t need to change their images that often, the lapse is still too long for display applications that require quick refresh times. The multilayer graphene was produced through chemical vapor deposition in which the graphene is grown on a metal surface inside a furnace. After it’s removed from the furnace, the metal is etched away, leaving a thin film of graphene on the surface of the water in which the etching occurs. Then the paper is simply submersed into the liquid, which transfers the thin film of graphene onto the paper. While the initial experiments showed that there were some issues with oxidation of the doped graphene layers, the researchers believe that this hiccup can be overcome with the addition of a simple polymer coating. In future research, Kocabas and his colleagues are planning to make a fully functional sheet of e-paper with pixels and an integrated driving circuit. They would like to see the process they have developed adapted into a roll-to-roll-compatible manufacturing process.
Research ArticlesBeril Ozcelik, Celaletdin Ergun Journal of Materials Research,FirstView Article(s), 15 pagesAbstract