Category Archives: Nano-Tech
Carbon nanotubes could help make computers faster and more efficient—if they can be incorporated into complex circuits.
Carbon complexity: This wafer is patterned with a complex carbon nanotube circuit that serves as a sensor interface.
Researchers at Stanford University have built one of the most complex circuits from carbon nanotubes yet. They showed off a simple hand-shaking robot with a sensor-interface circuit last week at the International Solid-State Circuits Conference in San Francisco.
As the silicon transistors inside today’s computers reach their physical limits, the semiconductor industry is eyeing alternatives, and one of the most promising is carbon nanotubes. Tiny transistors made from these nanomaterials are faster and more energy efficient than silicon ones, and computer models predict that carbon nanotube processors could be an order of magnitude less power hungry. But it’s proved difficult to turn individual transistors into complex working circuits (see “How to Build a Nano-Computer ”).
The demonstration carbon nanotube circuit converts an analog signal from a capacitor—the same type of sensor found in many touch screens—into a digital signal that’s comprehensible by a microprocessor. The Stanford researchers rigged a wooden mannequin hand with the capacitive switch in its palm. When someone graspsed the hand, turning on the switch, the nanotube circuit sent its signal to the computer, which activated a motor on the robot hand, moving it up and down to shake the person’s hand.
Other researchers have demonstrated simple nanotube circuits before, but this is the most complex made so far, and it also demonstrates that nanotube transistors can be made at high yields, says Subhasish Mitra , an associate professor of electrical engineering and computer science, who led the work with Philip Wong , a professor of electrical engineering at Stanford.
The nanotube circuit is still relatively slow—its transistors are large and far apart compared to the latest silicon circuits. But the work is an important experimental demonstration of the potential of carbon nanotube computing technology.
“This shows that carbon nanotube transistors can be integrated into logic circuits that perform at low voltage,” says Aaron Franklin , who is developing nanotube electronics at the IBM Watson Research Center. This feat has been demonstrated by Franklin’s group at the single-transistor level, and been shown to be theoretically possible by others, but seeing it in a complex circuit is important, says Franklin.
Working with carbon nanotubes presents many challenges—as many as 30 percent of them are metallic, rather than semiconducting, with the potential to burn out a circuit. Nanotubes also tend to grow in a spaghetti-like tangle, which can cause circuits to switch unpredictably. The approach taken by the Stanford group is to work with their imperfections, coming up with error-tolerant circuit design techniques that allow them to build circuits that work even when the starting materials are flawed. “We want to build up the circuit complexity, then go back to improving the building methods, then make more complex circuits,” says Wong.
“This is no different from the early days in silicon,” says Ashraf Alam , professor of electrical and computer engineering at Purdue University. Compared to the electronics in today’s silicon-based smartphones and supercomputers, the first silicon transistors were poor quality, as were the first integrated circuits. But silicon got through its growing pains, and the semiconductor industry perfected building ever-denser arrays of integrated circuits made up of ever-smaller transistors.
“Variation and imperfection are going to be the air we breathe in semiconductor technology,” says Wong, not just for those working with new materials, but for conventional silicon technology, too. Today’s state-of-the-art chips use 22-nanometer transistors—billions on each chip—and there is very little variation in their performance; the semiconductor industry has mastered making these tiny devices at tremendous scales, and with very high yields.
The drive to continually miniaturize transistors while maintaining scrupulous quality control has enabled technologies ranging from smartphones and supercomputers. But unavoidable flaws, at the level of single atoms, will soon lead to variation in performance that will have to be accounted for in circuit design. “Error-tolerant design has to be part of the way forward, because we will never get the materials completely perfect,” says Wong.
In a recent article published along with cover art engineers showed how simple shape and charge modifications of a nanoparticle can cause tremendous changes in the chemical interactions between the nanoparticle and a cell membrane. (Credit: Image courtesy of Syracuse University)
Jan. 23, 2013 — Researchers at Syracuse University’s Department of Biomedical and Chemical Engineering at L.C. Smith College of Engineering and Computer Science are studying the toxicity of commonly used nanoparticles, particles up to one million times smaller than a millimeter that could potentially penetrate and damage cell membranes.
In a recent article published along with cover art in the journal Langmuir, researchers Shikha Nangia, assistant professor of biomedical and chemical engineering (BMCE), and Radhakrishna Sureshkumar, Department Chair of BMCE and professor of physics, showed how simple shape and charge modifications of a nanoparticle can cause tremendous changes in the chemical interactions between the nanoparticle and a cell membrane.
Nanomaterials, which are currently being used as drug carriers, also pose a legitimate concern, since no universal standards exist to educate and fully protect those who handle these materials. Nanoparticles are comparable to chemicals in their potential threat because they could easily penetrate the skin or be inhaled.
“Nanotechnology has immense potential that is starting to be being realized; a comprehensive understanding of toxicity of nanoparticles will help develop better safe handling procedures in nanomanufacturing and nano-biotechnology” says Sureshkumar and Nangia, In addition, the toxicity levels of various nanoparticles can be used to our advantage in targeting cancer cells and absorbing radiation during cancer therapy. Nanotoxicity is becoming a major concern as the use of nanoparticles in imaging, therapeutics, diagnostics, catalysis, sensing and energy harvesting continues to grow dramatically.
This research project has taken place over the past year utilizing a state of the art 448 core parallel computer nicknamed “Prophet” housed in Syracuse University’s Green Data Center. The research was funded by the National Science Foundation.
Langmuir is a notable, interdisciplinary journal of American Chemical Society publishing articles in: colloids, interfaces, biological interfaces, nano-materials, electrochemistry and devices and applications.
Posted January 23, 2013 – 03:33 by Kate Taylor
Super-small particles of silicon react with water to produce hydrogen almost instantaneously, University at Buffalo researchers have discovered.
It means that soldiers or campers, for example, need only take a small hygrogen fuel cell and a bag of the powder to power electronics and other devices on the move.
“It was previously unknown that we could generate hydrogen this rapidly from silicon, one of Earth’s most abundant elements,” says research assistant professor Folarin Erogbogbo.
“Safe storage of hydrogen has been a difficult problem, even though hydrogen is an excellent candidate for alternative energy, and one of the practical applications of our work would be supplying hydrogen for fuel cell power. It could be military vehicles or other portable applications that are near water.”
Spherical silicon particles about 10 nanometers in diameter combine with water and react to form silicic acid – which is non-toxic – and hydrogen, a potential source of energy for fuel cells.
The reaction doesn’t require any light, heat or electricity – and also creates hydrogen about 150 times faster than similar reactions using silicon particles 100 nanometers wide, and 1,000 times faster than bulk silicon.
The reason’s down to to geometry. As they react, the larger particles form nonspherical structures whose surfaces react with water less readily and less uniformly than the surfaces of the smaller, spherical particles.
Though it does take significant energy and resources to produce the powder, the particles could help power portable devices in situations where water is available and portability is more important than low cost.
“Perhaps instead of taking a gasoline or diesel generator and fuel tanks or large battery packs with me to the campsite (civilian or military) where water is available, I take a hydrogen fuel cell (much smaller and lighter than the generator) and some plastic cartridges of silicon nanopowder mixed with an activator,” says Professor Mark Swihart.
“Then I can power my satellite radio and telephone, GPS, laptop, lighting, etc. If I time things right, I might even be able to use excess heat generated from the reaction to warm up some water and make tea.”
Sequencing DNA base pairs — the individual molecules that make up DNA — is key for medical researchers working toward personalized medicine. Being able to isolate, study and sequence these DNA molecules would allow scientists to tailor diagnostic testing, therapies and treatments based on each patient’s individual genetic makeup.
But being able to isolate individual molecules like DNA base pairs, which are just two nanometers across — or about 1/50,000th the diameter of a human hair — is incredibly expensive and difficult to control. In addition, devising a way to trap DNA molecules in their natural aqueous environment further complicates things. Scientists have spent the past decade struggling to isolate and trap individual DNA molecules in an aqueous solution by trying to thread it through a tiny hole the size of DNA, called a “nanopore,” which is exceedingly difficult to make and control.
Now a team led by Yale University researchers has proven that isolating individual charged particles, like DNA molecules, is indeed possible using a method called “Paul trapping,” which uses oscillating electric fields to confine the particles to a space only nanometers in size. (The technique is named for Wolfgang Paul, who won the Nobel Prize for the discovery.) Until now, scientists have only been able to use Paul traps for particles in a vacuum, but the Yale team was able to confine a charged test particle — in this case, a polystyrene bead — to an accuracy of just 10 nanometers in aqueous solutions between quadruple microelectrodes that supplied the electric field.
Their device can be contained on a single chip and is simple and inexpensive to manufacture. “The idea would be that doctors could take a tiny drop of blood from patients and be able to run diagnostic tests on it right there in their office, instead of sending it away to a lab where testing can take days and is expensive,” said Weihua Guan, a Yale engineering graduate student who led the project.
Story Continues -> Particle Trap Paves Way for Personalized Medicine
“Seeing something invisible with your own eyes is an exciting experience,” say Joachim Fischer and Tolga Ergin. For about one year, both physicists and members of the team of Professor Martin Wegener at KIT’s Center for Functional Nanostructures (CFN) have worked on refining the structure of the Karlsruhe invisibility cloak to such an extent that it is also effective in the visible spectral range.
In invisibility cloaks, light waves are guided by the material such that they leave the invisibility cloak again as if they had never been in contact with the object to be disguised. Consequently, the object is invisible to the observer. The exotic optical properties of the camouflaging material are calculated using complex mathematical tools.
These properties result from a special structuring of the material. It has to be smaller than the wavelength of the light that is to be deflected. For example, the relatively large radio or radar waves require a material “that can be produced using nail scissors,” says Wegener. At wavelengths visible to the human eye, materials have to be structured in the nanometer range.
The minute invisibility cloak produced by Fischer and Ergin is smaller than the diameter of a human hair. It makes the curvature of a metal mirror appear flat, as a result of which an object hidden underneath becomes invisible. The metamaterial placed on top of this curvature looks like a stack of wood, but consists of plastic and air. These “logs” have precisely defined thicknesses in the range of 100 nm. Light waves that are normally deflected by the curvature are influenced and guided by these logs such that the reflected light corresponds to that of a flat mirror.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Karlsruhe Institute of Technology.
- J. Fischer, T. Ergin, M. Wegener. Three-dimensional polarization-independent visible-frequency carpet invisibility cloak. Optics Letters, 2011; (in press)
A new kind of lens reaches an unprecedentedly sharp focus by giving up on being perfect. The lens is the first ever to help take visual light images of structures smaller than 100 nanometers (four one-millionths of inch), which could make it useful for nanotechnology and probing the insides of cells.
Ordinary lenses, like those used in magnifying glasses, have curved surfaces that bend light to a single point. A small object sitting at that point appears larger and sharply focused, helping myopic readers discern fine print and old-school detectives search for fingerprints. But conventional lenses need to be almost perfect to work. Scratches and roughness destroy the clear image.
“Every deviation from the perfect surface results in a deteriorated focus,” said Elbert van Putten, a graduate student at the University of Twente in the Netherlands. “And in practice you’ll always see surface defects.”
The smallest object on which physicists have managed to focus a single conventional lens is 200 nanometers across, just larger than the smallest known bacteria (although more complicated microscopy systems have reached down to 50 nanometers). But a lot of structures that physicists and chemists are interested in, like subcellular structures, nanoelectric circuits and photonic structures, are less than half that size.
Story Continues -> New NanoLens
A “forest” of molecules holds the promise of turning waste heat into electricity. UA physicists discovered that because of quantum effects, electron waves traveling along the backbone of each molecule interfere with each other, leading to the buildup of a voltage between the hot and cold electrodes (the golden structures on the bottom and top). (Credit: Justin Bergfield, University of Arizona)
What do a car engine, a power plant, a factory and a solar panel have in common? They all generate heat — a lot of which is wasted.
University of Arizona physicists have discovered a new way of harvesting waste heat and turning it into electrical power.
Using a theoretical model of a so-called molecular thermoelectric device, the technology holds great promise for making cars, power plants, factories and solar panels more efficient, to name a few possible applications. In addition, more efficient thermoelectric materials would make ozone-depleting chlorofluorocarbons, or CFCs, obsolete.
The research group led by Charles Stafford, associate professor of physics, published its findings in the September issue of the scientific journal, ACS Nano.
“Thermoelectricity makes it possible to cleanly convert heat directly into electrical energy in a device with no moving parts,” said lead author Justin Bergfield, a doctoral candidate in the UA College of Optical Sciences.
“Our colleagues in the field tell us they are pretty confident that the devices we have designed on the computer can be built with the characteristics that we see in our simulations.”
“We anticipate the thermoelectric voltage using our design to be about 100 times larger than what others have achieved in the lab,” Stafford added.
Catching the energy lost through waste heat has been on the wish list of engineers for a long time but, so far, a concept for replacing existing devices that is both more efficient and economically competitive has been lacking.
Article Continues -> http://www.sciencedaily.com/releases/2010/09/100930154610.htm
Scientists can now peer into the inner workings of catalyst nanoparticles 3,000 times smaller than a human hair within nanoseconds.
The findings point the way toward future work that could greatly improve catalyst efficiency in a variety of processes that are crucial to the world’s energy security, such as petroleum catalysis and catalyst-based nanomaterial growth for next-generation rechargeable batteries. The work was performed in a collaborative effort by Lawrence Livermore National Laboratory and the University of California at Davis.
Using a new imaging technique on Lawrence Livermore’s Dynamic Transmission Electron Microscope (DTEM), researchers have achieved unprecedented spatial and temporal resolution in single-shot images of nanoparticulate catalysts.
The DTEM uses a laser-driven photocathode to produce short pulses of electrons capable of recording electron micrographs with 15-nanosecond (one billionth of a second) exposure time. The recent addition of an annular dark field (ADF) aperture to the instrument has greatly improved its ability to time-resolve images of nanoparticles as small as 30 nanometers in diameter.
“Nanoparticles in this size range are of crucial importance to a wide variety of catalytic process of keen interest to energy and nanotechnology researchers,” said UC Davis’ Dan Masiel, formerly of LLNL and lead author of a paper appearing in the journal, ChemPhysChem. “Time-resolved imaging of such materials will allow for unprecedented insight into the dynamics of their behavior.”
Previously, particles smaller than 50 nanometers could not be resolved in the 15-nanosecond exposure because of the limited signal and low contrast without ADF aperature. But by using DTEM’s ADF, almost every 50-nanometer particle and many 30-nanometer ones became clearly visible because of the fast time resolution and high contrast.
“The stark difference between these two images clearly demonstrates the efficacy of annual dark field imaging when imaging samples with feature sizes near the resolution limit of DTEM,” Masiel said.
The new technique makes it easier to discern significant features when compared to bright field pulsed imaging. It allows for vastly improved contrast for smaller particles, widening the range of catalyst systems that can be studied using DTEM.
DTEM can record images with six orders of magnitude higher temporal resolution than conventional TEM and can provide important insights into processes such as phase transformations, chemical reactions and nanowire and nanotube growth.
Co-authors include LLNL’s Bryan Reed, Thomas LaGrange, Geoffrey Campbell, Ting Guo and Nigel Browning. The work was funded by the Department of Energy’s Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
The article appears in the May 27 online edition of ChemPhys Chem.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Livermore National Laboratory.
- Daniel J. Masiel, Bryan W. Reed, Thomas B. LaGrange, Geoffrey H. Campbell, Ting Guo, Nigel D. Browning. Time-Resolved Annular Dark Field Imaging of Catalyst Nanoparticles. ChemPhysChem, 2010; DOI: 10.1002/cphc.201000274