|(Nanowerk News) Researchers at the Technische Universitaet Muenchen (TUM) are showing the way toward low-cost, industrial-scale manufacturing of a new family of electronic devices. A leading example is a gas sensor that could be integrated into food packaging to gauge freshness, or into compact wireless air-quality monitors. New types of solar cells and flexible transistors are also in the works, as well as pressure and temperature sensors that could be built into electronic skin for robotic or bionic applications. All can be made with carbon nanotubes, sprayed like ink onto flexible plastic sheets or other substrates.|
|Carbon nanotube-based gas sensors created at TUM offer a unique combination of characteristics that can’t be matched by any of the alternative technologies. They rapidly detect and continuously respond to extremely small changes in the concentrations of gases including ammonia, carbon dioxide, and nitrogen oxide. They operate at room temperature and consume very little power. Furthermore, as the TUM researchers report in their latest papers, such devices can be fabricated on flexible backing materials through large-area, low-cost processes.|
|Flexible, high-performance gas sensors (left) were made by spraying a solution of carbon nanotubes (right) onto a plastic backing.|
|Thus it becomes realistic to envision plastic food wrap that incorporates flexible, disposable gas sensors, providing a more meaningful indicator of food freshness than the sell-by date. Measuring carbon dioxide, for example, can help predict the shelf life of meat. “Smart packaging” – assuming consumers find it acceptable and the devices’ non-toxic nature can be demonstrated – could enhance food safety and might also vastly reduce the amount of food that is wasted. Used in a different setting, the same sort of gas sensor could make it less expensive and more practical to monitor indoor air quality in real time.|
|Not so easy – but “really simple”|
|Postdoctoral researcher Alaa Abdellah and colleagues at the TUM Institute for Nanoelectronics have demonstrated that high-performance gas sensors can be, in effect, sprayed onto flexible plastic substrates. With that, they may have opened the way to commercial viability for carbon nanotube-based sensors and their applications. “This really is simple, once you know how to do it,” says Prof. Paolo Lugli, director of the institute.|
|The most basic building block for this technology is a single cylindrical molecule, a rolled-up sheet of carbon atoms that are linked in a honeycomb pattern. This so-called carbon nanotube could be likened to an unimaginably long garden hose: a hollow tube just a nanometer or so in diameter but perhaps millions of times as long as it is wide. Individual carbon nanotubes exhibit amazing and useful properties, but in this case the researchers are more interested in what can be done with them en masse.|
|Laid down in thin films, randomly oriented carbon nanotubes form conductive networks that can serve as electrodes; patterned and layered films can function as sensors or transistors. “In fact,” Prof. Lugli explains, “the electrical resistivity of such films can be modulated by either an applied voltage (to provide a transistor action) or by the adsorption of gas molecules, which in turn is a signature of the gas concentration for sensor applications.”|
|And as a basis for gas sensors in particular, carbon nanotubes combine advantages (and avoid shortcomings) of more established materials, such as polymer-based organic electronics and solid-state metal-oxide semiconductors. What has been lacking until now is a reliable, reproducible, low-cost fabrication method.|
|Spray deposition, supplemented if necessary by transfer printing, meets that need. An aqueous solution of carbon nanotubes looks like a bottle of black ink and can be handled in similar ways. Thus devices can be sprayed – from a computer-controlled robotic nozzle – onto virtually any kind of substrate, including large-area sheets of flexible plastic. There is no need for expensive clean-room facilities.|
|“To us it was important to develop an easily scalable technology platform for manufacturing large-area printed and flexible electronics based on organic semiconductors and nanomaterials,” Dr. Abdellah says. “To that end, spray deposition forms the core of our processing technology.”|
|Remaining technical challenges arise largely from application-specific requirements, such as the need for gas sensors to be selective as well as sensitive.|
|Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing. Ahmed Abdelhalim, Alaa Abdellah, Giuseppe Scarpa, Paolo Lugli. Carbon, Vol. 61, September 2013, 72-79.|
|Flexible carbon nanotube-based gas sensors fabricated by large-scale spray deposition. Alaa Abdellah, Zubair Ahmad, Philipp Köhler, Florin Loghin, Alexander Weise, Giuseppe Scarpa, Paolo Lugli. IEEE Sensors Journal, Vol. 13 Issue 10, October 2013, 4014-4021.|
|Scalable spray deposition process for high performance carbon nanotube gas sensors. Alaa Abdellah, Ahmed Abdelhalim, Markus Horn, Giuseppe Scarpa, and Paolo Lugli. IEEE Transactions on Nanotechnology 12, 174-181, 2013.|
|Source: Technische Universität München|
The sixth element, carbon, has given us an amazing abundance of extraordinary materials. Once there was simply carbon, graphite and diamond. But in recent years chemists have added buckyballs, nanotubes and any number of exotic shapes created out of graphene, the molecular equivalent of chickenwire.
So it’s hard to believe that carbon has any more surprises up its sleeve. And yet today, Mingjie Liu and pals at Rice University in Houston calculate the properties of another form of carbon that is stronger, stiffer and more exotic than anything chemists have seen before.
The new material is called carbyne. It is a chain of carbon atoms that are linked either by alternate triple and single bonds or by consecutive double bonds.
Carbyne is something of a mystery. Astronomers believe they have detected its signature in interstellar space but chemists have been bickering for decades over whether they had ever created this stuff on Earth. A couple of years ago, however, they synthesised carbyne chains up to 44 atoms long in solution.
The thinking until now has been that carbyne must be extremely unstable. In fact some chemists have calculates that two strands of carbyne coming into contact would react explosively.
Nevertheless, nanotechnologists have been fascinated with potential of this material because it ought to be both strong and stiff and therefore useful. But exactly how strong and how stiff, no one has been quite sure.
This is where Liu and co step in. These guys have calculated from first principles the bulk properties of carbyne and the results make for interesting reading.
For a start, they say that carbyne is about twice as stiff as the stiffest known materials today. Carbon nanotubes and grapheme, for example, have a stiffness of 4.5 x 10^8 N.m/kg but carbyne tops them with a stiffness of around 10^9 N.m/kg.
Just as impressive is the new material’s strength. Liu and co calculate that it takes around 10 nanoNewtons to break a single strand of carbyne. “This force translates into a specific strength of 6.0–7.5×10^7 N∙m/kg, again significantly outperforming every known material including graphene (4.7–5.5×10^7 N∙m/ kg), carbon nanotubes (4.3–5.0×10^7 N∙m/ kg), and diamond (2.5–6.5×10”7 N∙m/kg4),” they say.
Carbyne has other interesting properties too. Its flexibility is somewhere between that of a typical polymer and double-stranded DNA. And when twisted, it can either rotate freely or become torsionally stiff depending on the chemical group attached to its end.
Perhaps most interesting is the Rice team’s calculation of carbyne’s stability. They agree that two chains in contact can react but there is an activation barrier that prevents this happening readily. “This barrier suggests the viability of carbyne in condensed phase at room temperature on the order of days,” they conclude.
All this should whet the appetite of nanotechnologists hoping to design ever more exotic nanomachines, such as nanoelectronic and spintronic devices. Given the advances being made in manufacturing this stuff, we may not have long to wait before somebody begins exploiting the extraordinary mechanical properties of carbyne chains for real.
(Nanowerk News) Linde Electronics, the global electronics business of The Linde Group, launched a revolutionary new carbon nanotube ink to drive innovation in the development of next generation displays, sensors and other electronic devices. Linde’s carbon nanotube inks can be used to manufacture completely new technologies, such as a smartphone with a screen that rolls up like a window shade and a see-through GPS device embedded in the windshield of a car.
Carbon nanotubes are an allotrope of carbon like graphite and diamond, and they have unique physical and electronic properties. These include a higher thermal conductivity than diamond; greater mechanical strength than steel (orders of magnitude by weight); and a larger electrical conductivity than copper. It is due to these properties that carbon nanotubes will enable electronic device manufacturers develop more innovative electronic devices.
To help device manufacturers and the research and development community to explore the full potential of carbon nanotube based technologies, Linde is making its nanotube inks available to developers. These nanotube inks contain individual carbon nanotubes and are produced without damaging or shortening the nanotubes and therefore preserve the unique nanotube properties.
This landmark development drastically improves the performance of transparent conductive thin films made from the inks and opens the door for the development of nanotube applications in not only consumer electronics, but also the healthcare sector and sensor manufacturing.
“While we’ve seen a lot of excitement around nanotubes in the past ten years, we’ve not yet seen a commercially viable nanotube solution in the market because of challenges in the processing of this great material,” said Dr Sian Fogden, Market and Technology Development Manager for Linde Electronics’ nanomaterials unit. “Our nanotube technology and our unique nanotube inks overcome these challenges, paving the way for completely new types of high-functionality electronic devices.”
Linde, which develops and supplies specialist materials and gases for the world’s leading electronic manufacturers, is in the final development stages with its single wall carbon nanotube technology. Alongside the launch of the nanotube ink into the development community, the company will also provide its nanotube ink at large scale directly to electronic device manufacturers.
About The Linde Group
The Linde Group is a world-leading gases and engineering company with around 62,000 employees in more than 100 countries worldwide. In the 2012 financial year, Linde generated revenue of EUR 15.280 bn. The strategy of the Group is geared towards long-term profitable growth and focuses on the expansion of its international business with forward-looking products and services. Linde acts responsibly towards its shareholders, business partners, employees, society and the environment — in every one of its business areas, regions and locations across the globe. The company is committed to technologies and products that unite the goals of customer value and sustainable development.
For more information, see The Linde Group online at http://www.linde.com