20th November 2013
Engineers make world's smallest FM radio
A team at the University of Columbia has taken advantage of graphene's special properties – its mechanical strength and electrical conduction – to create a nano-mechanical system producing FM signals, in effect the world's smallest FM radio transmitter. The study is published in Nature Nanotechnology.
“This work is significant in that it demonstrates an application of graphene that cannot be achieved using conventional materials,” said Mechanical Engineering Professor James Hone, who led the study. “And it’s an important first step in advancing wireless signal processing and designing ultrathin, efficient cell phones. Our devices are much smaller than any other sources of radio signals, and can be put on the same chip that’s used for data processing.”
Graphene – a single atomic layer of carbon – is the strongest material known to man, and also has electrical properties superior to the silicon found in modern electronics. The combination of these properties makes graphene an ideal material for nano-electromechanical systems (NEMS), which are scaled-down versions of the micro-electromechanical systems (MEMS) used widely for sensing of vibration and acceleration. For example, Hone explains, MEMS sensors figure out how your smartphone or tablet is tilted to rotate the screen.
In this new study, Hone’s team took advantage of graphene’s mechanical ‘stretchability’ to tune the output frequency of their custom oscillator – producing a nano-mechanical version of a component known as a voltage controlled oscillator (VCO). With a VCO, explained Hone, it is easy to generate a frequency-modulated (FM) signal – exactly what is used for FM radio broadcasting. The team built a graphene NEMS whose frequency was 100 megahertz, which lies right in the middle of the FM radio band (87.7 to 108 MHz). They used low-frequency music signals (both pure tones and songs from an iPhone) to modulate the 100 MHz carrier signal from the graphene, and then retrieved the musical signals again using an ordinary FM radio receiver.
“This device is by far the smallest system that can create such FM signals,” says Hone.
While graphene NEMS will not be used to replace conventional radio transmitters, they have many applications in wireless signal processing. Electrical Engineering Professor Kenneth Shepard: “Due to the continuous shrinking of electrical circuits known as ‘Moore’s Law’, today’s cell phones have more computing power than systems that used to occupy entire rooms. However, some types of devices, particularly those involved in creating and processing radio-frequency signals, are much harder to miniaturise. These ‘off-chip’ components take up a lot of space and electrical power. In addition, most of these components cannot be easily tuned in frequency, requiring multiple copies to cover the range of frequencies used for wireless communication.”
Graphene NEMS can address both problems: they are very compact and easily integrated with other types of electronics, and their frequency can be tuned over a wide range, because of graphene’s tremendous mechanical strength.
“There is a long way to go toward actual applications in this area,” notes Hone, “but this work is an important first step. We are excited to have demonstrated successfully how this wonder material can be used to achieve a practical technological advancement – something particularly rewarding to us as engineers.”
Hone and Shepard are now working on improving the performance of the graphene oscillators to have lower noise. At the same time, they are also trying to demonstrate integration of graphene NEMS with silicon integrated circuits, making the oscillator design even more compact.
10th November 2013
Bulletproof nanotechnology suit goes on sale
Luxury bespoke tailoring house, Garrison Bespoke, has launched the first fashion-forward bulletproof suit with a live ammo field-testing event in Toronto, Canada.
Michael Nguyen, co-owner of Garrison Bespoke: "After receiving requests from high-profile clients who travel to dangerous places for work, we set out to develop a lightweight, fashion-forward bulletproof suit as a more discreet and stylish alternative to wearing a bulky vest underneath."
The Garrison Bespoke bulletproof suit is made with carbon nanotubes created using nanotechnology and originally developed to protect the US 19th Special Forces in Iraq. The patented material is thinner, more flexible and 50 percent lighter than Kevlar, which is traditionally used for bulletproof gear. The suit also protects against stabbing – the carbon nanotubes harden on impact to prevent a knife from penetrating.
The live ammo field-testing event was held in the Ajax Rod and Gun Club, Ontario. It demonstrated the suit's ability to shield against 9mm bullets. Nguyen claims the suit can block .45 bullets as well. Garrison Bespoke's latest collection – Town & Country – features a range of new clothing, all of which can be made bulletproof by request, with prices starting from $20,000.
30th October 2013
Super-thin membranes clear the way for chip-sized pumps
The ability to shrink laboratory-scale processes to automated chip-sized systems would revolutionise biotechnology and medicine. For example, inexpensive and highly portable devices that process blood samples to detect biological agents, such as anthrax, are needed by the U.S. military and for homeland security efforts.
A microfluidic bioreactor. Credit: Adam Fenster/University of Rochester.
One of the challenges of "lab-on-a-chip" technology is the need for miniaturised pumps to move solutions through micro-channels. Electroosmotic pumps (EOPs) — devices in which fluids appear to magically move through porous media in the presence of an electric field — are ideal, because they can be readily miniaturised. EOPs however, require bulky and external power sources, which defeats the concept of portability. But a super-thin silicon membrane developed at the University of Rochester could now make it possible to drastically shrink the power source, paving the way for new diagnostic devices the size of a credit card.
"Up until now, electroosmotic pumps have had to operate at a very high voltage, about 10 kilovolts," said James McGrath, associate professor of biomedical engineering. "Our device works in the range of one-quarter of a volt, which means it can be integrated into devices and powered with small batteries."
McGrath's research paper is published this week by the journal Proceedings of the National Academy of Sciences.
McGrath and his colleagues use porous nanocrystalline silicon (pnc-Si) membranes that are microscopically thin – it takes more than one thousand stacked on top of each other to equal the width of a human hair. And that's what allows for a low-voltage system.
A porous membrane needs to be placed between two electrodes in order to create what's known as electroosmotic flow, which occurs when an electric field interacts with ions on a charged surface, causing fluids to move through channels. Membranes previously used in EOPs have resulted in a significant voltage drop between the electrodes, forcing engineers to begin with bulky and high-voltage power sources. The thin pnc Si membranes allow the electrodes to be placed much closer to each other, creating a much stronger electric field with a much smaller drop in voltage. As a result, a smaller power source is needed.
"Until now, not everything associated with miniature pumps was miniaturised," said McGrath. "Our device opens the door for a tremendous number of applications."
Along with medical applications, it's been suggested that EOPs could be used to cool electronic devices. As electronic devices get smaller, components are packed more tightly, making it easier for the devices to overheat. With miniature power supplies, it may be possible to use EOPs to help cool laptops and other portable electronic devices.
McGrath said there's one other benefit to the silicon membranes. "Due to scalable fabrication methods, the nanocrystalline silicon membranes are inexpensive to make and can be easily integrated on silicon or silica-based microfluid chips."
9th October 2013
Major leap towards graphene for solar cells
Researchers in Germany have discovered that graphene retains its properties even when coated with silicon, paving the way for solar cells with much greater efficiency.
Graphene – a revolutionary new material discovered in 2004 – has extreme conductivity and is completely transparent, while being inexpensive and non-toxic. This makes it a perfect candidate material for layers in solar cells to conduct electricity without reducing the amount of incoming light; at least in theory. Whether or not this holds true in a real world setting is questionable as there is no such thing as "ideal" graphene – a free floating, flat honeycomb structure formed by a single layer of carbon atoms: interactions with adjacent layers can change its properties dramatically.
Now, researchers at Helmholtz-Zentrum Berlin (HZB) have shown that graphene retains its impressive properties when coated with a thin silicon film. These findings pave the way for entirely new possibilities to use in thin-film photovoltaics.
"We examined how graphene's conductive properties change if incorporated into a stack of layers similar to a silicon-based thin film solar cell, and were surprised to find that these properties actually change very little," Dr. Marc Gluba explains.
To this end, they grew graphene on a thin copper sheet, next transferred it to a glass substrate, and finally coated it with a thin film of silicon. They examined two different versions that are commonly used in conventional silicon thin-film technologies: one sample contained an amorphous silicon layer, in which the silicon atoms are in a disordered state similar to a hardened molten glass; the other sample contained poly-crystalline silicon to help them observe the effects of a standard crystallization process on graphene's properties.
The team obtained their measurements on one square centimetre samples. Even though the morphology of the top layer changed completely as a result of being heated to a temperature of several hundred degrees Celsius, the graphene was still detectable.
"That's something we didn't expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon," says Norbert Nickel. Their measurements of carrier mobility, using the Hall effect, showed that the mobility of charge carriers within the embedded graphene layer was roughly 30 times greater than that of conventional zinc oxide-based contact layers.
"Admittedly, it's been a real challenge connecting this thin contact layer – just one atom thick – to external contacts. We're still having to work on that," said Gluba.
"Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it," added Gluba.
HZB is the same company which last month achieved a solar cell with 44.7% efficiency, a new record. Third-generation solar cells with graphene could, in theory, reach efficiencies in the range of 60%.
20th September 2013
Densest array of carbon nanotubes grown to date
Researchers at Cambridge University have developed a new technique allowing carbon nanotube "forests" to be grown at five times the density of previous methods.
Scanning electron microscope images of CNT forests, low and high density.
Carbon nanotubes' outstanding mechanical, electrical and thermal properties make them an alluring material to electronics manufacturers. Until recently, however, scientists believed that growing the high density of tiny graphene cylinders needed for many microelectronics applications would be difficult.
Now a team from Cambridge University in England has devised a simple technique to increase the density of nanotube forests grown on conductive supports about five times over previous methods. The high density nanotubes might one day replace some metal electronic components, leading to faster devices.
"The high density aspect is often overlooked in many carbon nanotube growth processes, and is an unusual feature of our approach," says John Robertson, a professor in the electronic devices and materials group in the department of engineering at Cambridge. High-density forests are necessary for certain applications of carbon nanotubes, such as electronic interconnects and thermal interface materials.
Robertson and his colleagues grew carbon nanotubes on a conductive copper surface that was coated with co-catalysts cobalt and molybdenum. In a novel approach, they grew at lower temperature than is typical which is applicable in the semiconductor industry. When the interaction of metals was analysed by X-ray photoelectron spectroscopy, it revealed the creation of a more supportive substrate for the forests to root in. The subsequent nanotube growth exhibited the highest mass density reported so far.
"In microelectronics, this approach to growing high-density carbon nanotube forests on conductors can potentially replace and outperform the current copper-based interconnects in a future generation of devices," says Cambridge researcher Hisashi Sugime. In the future, more robust carbon nanotube forests may also help to improve thermal interface materials, battery electrodes, and supercapacitors.
The article, "Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports" appears in the journal Applied Physics Letters.
17th September 2013
Microrobots for cell and drug delivery in the human body
A team of researchers at the Chinese University of Hong Kong (CUHK) has developed a novel type of magnetic "micro-robot" capable of transporting cells and delivering drugs to specific locations inside the body. This new technology has the potential to revolutionise minimally invasive medical treatment such as targeted therapy and tissue regeneration.
The development of microrobots requires interdisciplinary knowledge including mechatronics, materials science, biology, computing and automation. These tiny devices have the potential to work in very small and confined spaces and thus have broad applications in many fields, but particularly in minimally invasive medical treatment.
Prof. Zhang Li, from CUHK's Department of Mechanical and Automation Engineering, collaborated with Daegu Gyeongbuk Institute of Science and Technology (DGIST) in Korea, and ETH Zurich. Together, they innovated a new microrobot capable of transporting the appropriate amount of cells and therapeutic drugs to specific areas of the body. The team used laser lithography to construct porous 3D scaffolds which were coated with a thin layer of magnetic material (nickel) and biocompatible material (titanium). This allowed remote manipulation of the devices using external magnetic fields to guide them, while causing no harm to living cells.
Prof. Zhang commented: "Our microrobots have enormous potential in on-demand, minimally invasive medical treatments. They allow accurate cell and drug delivery and reduce risk of complications arising from more invasive treatment methods. The low-strength magnetic fields are biologically harmless to living cells and tissues, and are therefore safe to use in the human body. This innovation is a great leap forward in the development of wirelessly-controlled medical microrobots."
One lab test involved cultivating human kidney cells in the microbot model, which grew and interacted with the model, Zhang said. This confirmed that the model could interoperate with the kidney cells, he said, adding that tests were currently conducted on rabbits and mice. This technology could lead to targeted treatment of various diseases such as cancer, cerebral infarction and retinal degeneration.
Professor Zhang is now leading the CUHK research team to improve the performance, intelligence and design of these micro-devices by paying close attention to their locomotion and dynamic properties in fluid. At present, they are just over 100 micrometres (µm) in length. However, as technology improves, they will become even smaller and more sophisticated. Experts believe that nano-scale robots may be possible by 2025 – able to repair individual cells and even work directly inside them. Further into the future, these machines could become a permanent part of our physiology.
The research results of this latest study will be featured as the cover story in a forthcoming issue of Advanced Materials.
11th September 2013
New NIH awards focus on nanopore technology for DNA sequencing
The National Institutes of Health (NIH) has awarded grants of $17 million to eight research teams, with a focus on nanopore technology aimed at more accurate and efficient DNA sequencing.
These grants are the latest awarded through the National Human Genome Research Institute (NHGRI)’s Advanced DNA Sequencing Technology program, which was launched in 2004. NHGRI is part of NIH.
“Nanopore technology shows great promise, but is still a new area of science. We have much to learn about how nanopores can work effectively as a DNA sequencing technology, which is why five of the program’s eight grants are exploring this approach,” said Jeffery A. Schloss, Ph.D., program director for NHGRI’s Advanced DNA Sequencing Technology program and director of the Division of Genome Sciences.
Nanopore-based DNA sequencing involves threading single DNA strands through tiny pores. The individual base pairs – chemical letters of DNA – are then read one at a time as they pass through the nanopore. The bases are identified by measuring the difference in their effect on current flowing through the pore. For perspective, a human hair is 100,000 nanometres in diameter; a strand of DNA is only 2 nanometres in diameter.
This technology offers many potential advantages over current sequencing methods, e.g. real-time sequencing of single DNA molecules at low cost and the ability for the same molecule to be reassessed over and over again. Current systems involve isolating DNA and chemically labelling and copying it. DNA has to be broken up, and small segments are sequenced many times. Only the first step of isolating DNA would be necessary with nanopore technology.
Innovation is crucial in these, as well as the other (non-nanopore) genome studies being funded. For example, one team eventually hopes to use light to sequence DNA on a smartphone chip for under $100.