This illustration shows lithium atoms (red) adhered to a graphene lattice that will produce electricity when bent, squeezed or twisted. Conversely, the graphene will deform when an electric field is applied, opening new possibilities in nanotechnology. Illustration: Mitchell Ong, Stanford School of Engineering

Bulk piezoelectric materials are already used for atomically precise nanopositioning to position the tips of scanning probe microscopes. Would there be any advantages to engineered control of piezoelectrical properties in a two-dimensional material? Currently piezoelectric properties of materials cannot be engineered—it is a property only available in certain 3D crystals. Now calculations have demonstrated that graphene can be made piezoelectric by adsorbing atoms on one surface. A hat tip to Physorg.com for reprinting this Stanford University news release written by Andrew Myers “Straintronics: Engineers create piezoelectric graphene“:

Graphene is a wonder material. It is a one-hundred-times-better conductor of electricity than silicon. It is stronger than diamond. And, at just one atom thick, it is so thin as to be essentially a two-dimensional material. Such promising physics have made graphene the most studied substance of the last decade, particularly in nanotechnology. In 2010, the researchers who first isolated it shared the Nobel Prize.

Yet, while graphene is many things, it is not piezoelectric. Piezoelectricity is the property of some materials to produce electric charge when bent, squeezed or twisted. Perhaps more importantly, piezoelectricity is reversible. When an electric field is applied, piezoelectric materials change shape, yielding a remarkable level of engineering control.

Piezoelectrics have found application in countless devices from watches, radios and ultrasound to the push-button starters on propane grills, but these uses all require relatively large, three-dimensional quantities of piezoelectric materials.

Now, in a paper published in the journal ACS Nano [abstract], two materials engineers at Stanford have described how they have engineered piezoelectrics into graphene, extending for the first time such fine physical control to the nanoscale.

“The physical deformations we can create are directly proportional to the electrical field applied. This represents a fundamentally new way to control electronics at the nanoscale,” said Evan Reed, head of the Materials Computation and Theory Group at Stanford and senior author of the study.

This phenomenon brings new dimension to the concept of ‘straintronics,’ he said, because of the way the electrical field strains—or deforms—the lattice of carbon, causing it to change shape in predictable ways.

“Piezoelectric graphene could provide an unparalleled degree of electrical, optical or mechanical control for applications ranging from touchscreens to nanoscale transistors,” said Mitchell Ong, a post-doctoral scholar in Reed’s lab and first author of the paper.

Using a sophisticated modeling application running on high-performance supercomputers, the engineers simulated the deposition of atoms on one side of a graphene lattice — a process known as doping — and measured the piezoelectric effect.

They modeled graphene doped with lithium, hydrogen, potassium and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine on either side of the lattice. Doping just one side of the graphene, or doping both sides with different atoms, is key to the process as it breaks graphene’s perfect physical symmetry, which otherwise cancels the piezoelectric effect.

The results surprised both engineers.

“We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials,” said Reed. “It was pretty significant.”

The researchers were further able to fine tune the effect by pattern doping the graphene—selectively placing atoms in specific sections and not others.

“We call it designer piezoelectricity because it allows us to strategically control where, when and how much the graphene is deformed by an applied electrical field with promising implications for engineering,” said Ong.

While the results in creating piezoelectric graphene are encouraging, the researchers believe that their technique might further be used to engineer piezoelectricity in nanotubes and other nanomaterials with applications ranging from electronics, photonics, and energy harvesting to chemical sensing and high-frequency acoustics.

“We’re already looking at new piezoelectric devices based on other 2D and low-dimensional materials, hoping they might open new and dramatic possibilities in nanotechnology,” said Reed.

Could piezoelectric graphene be used with, for example, DNA origami scaffolding to position molecular tools to execute programmed actions? To hear the researchers discussing their work and plans, including possible application to nanomechanical systems, an ACS Nano podcast is available.
—James Lewis, PhD

285-micron racecar (credit: Vienna University of Technology)

For those interested in atomically precise manufacturing, 3D-printing is an interesting microscale technology for making centimeter-scale objects. We commented on this technology a few months ago with the introduction of two competing technologies for printing complex digitally-designed plastic consumer items. Foresight Senior Associate Charles Vollum sends word of the extension of 3D-printing to nanoscale (approximately 100 nm) resolution. In addition, the new procedure is much faster and enables true 3D fabrication, without requiring layer-by-layer fabrication. A hat tip to KurzweilAI for describing this Vienna University of Technology news release “3D-printer with nano-precision“:

Printing three dimensional objects with incredibly fine details is now possible using “two-photon lithography”. With this technology, tiny structures on a nanometer scale can be fabricated. Researchers at the Vienna University of Technology (TU Vienna) have now made a major breakthrough in speeding up this printing technique: The high-precision-3D-printer at TU Vienna is orders of magnitude faster than similar devices (see video). This opens up completely new areas of application, such as in medicine.

The video shows the 3d-printing process in real time. Due to the very fast guiding of the laser beam, 100 layers, consisting of approximately 200 single lines each, are produced in four minutes.

Setting a New World Record

The 3D printer uses a liquid resin, which is hardened at precisely the correct spots by a focused laser beam. The focal point of the laser beam is guided through the resin by movable mirrors and leaves behind a polymerized line of solid polymer, just a few hundred nanometers wide. This high resolution enables the creation of intricately structured sculptures as tiny as a grain of sand. “Until now, this technique used to be quite slow”, says Professor Jürgen Stampfl from the Institute of Materials Science and Technology at the TU Vienna. “The printing speed used to be measured in millimeters per second – our device can do five meters in one second.” In two-photon lithography, this is a world record. …

Photoactive Molecules Harden the Resin

3D-printing is not all about mechanics – chemists had a crucial role to play in this project too. “The resin contains molecules, which are activated by the laser light. They induce a chain reaction in other components of the resin, so-called monomers, and turn them into a solid”, says Jan Torgersen. These initiator molecules are only activated if they absorb two photons of the laser beam at once – and this only happens in the very center of the laser beam, where the intensity is highest. In contrast to conventional 3D-printing techniques, solid material can be created anywhere within the liquid resin rather than on top of the previously created layer only. Therefore, the working surface does not have to be specially prepared before the next layer can be produced (see Video), which saves a lot of time. A team of chemists led by Professor Robert Liska (TU Vienna) developed the suitable initiators for this special resin. …

Because of the dramatically increased speed, much larger objects can now be created in a given period of time. This makes two-photon-lithography an interesting technique for industry. At the TU Vienna, scientists are now developing bio-compatible resins for medical applications. They can be used to create scaffolds to which living cells can attach themselves facilitating the systematic creation of biological tissues. The 3d printer could also be used to create tailor made construction parts for biomedical technology or nanotechnology.

We are still three orders of magnitude away from atomic precision and limited in the choice of materials to one polymer; however, the more useful 3D printing technology becomes, the more interest to extend it toward general purpose atomically precise manufacturing.
—James Lewis, PhD

Integrating a complex, single-crystal material with “giant” piezoelectric properties onto silicon, University of Wisconsin-Madison engineers and physicists can fabricate low-voltage, near-nanoscale electromechanical devices that could lead to improvements in high-resolution 3-D imaging, signal processing, communications, energy harvesting, sensing, and actuators for nanopositioning devices, among others.

Led by Chang-Beom Eom, a UW-Madison professor of materials science and engineering and physics, the multi-institutional team published its results in the November 18 issue of the journal Science [abstract]. …

Eom studies the advanced piezoelectric material lead magnesium niobate-lead titanate, or PMN-PT. Such materials exhibit a “giant” piezoelectric response that can deliver much greater mechanical displacement with the same amount of electric field as traditional piezoelectric materials. They also can act as both actuators and sensors. For example, they use electricity to deliver an ultrasound wave that penetrates deeply into the body and returns data capable of displaying a high-quality 3-D image.

Currently, a major limitation of these advanced materials is that to incorporate them into very small-scale devices, researchers start with a bulk material and grind, cut and polish it to the size they desire. It’s an imprecise, error-prone process that’s intrinsically ill-suited for nanoelectromechanical systems (NEMS) or microelectromechanical systems (MEMS).

Until now, the complexity of PMN-PT has thwarted researchers’ efforts to develop simple, reproducable microscale fabrication techniques.

Applying microscale fabrication techniques such as those used in computer electronics, Eom’s team has overcome that barrier. He and his colleagues worked from the ground up to integrate PMN-PT seamlessly onto silicon. Because of potential chemical reactions among the components, they layered materials and carefully planned the locations of individual atoms.

“You have to lay down the right element first,” says Eom.

Onto a silicon “platform,” his team adds a very thin layer of strontium titanate, which acts as a template and mimics the structure of silicon. Next comes a layer of strontium ruthenate, an electrode Eom developed some years ago, and finally, the single-crystal piezoelectric material PMN-PT.

The researchers have characterized the material’s piezoelectric response, which correlates with theoretical predictions.

“The properties of the single crystal we integrated on silicon are as good as the bulk single crystal,” says Eom.

His team calls devices fabricated from this giant piezoelectric material “hyper-active MEMS” for their potential to offer researchers a high level of active control. Using the material, his team also developed a process for fabricating piezoelectric MEMS.

We will have to watch to see if the use of this material in fabricating piezoelectric MEMS leads to improvements in the use of scanning probes for atomically precise manufacturing.

The possibility of a doctor using tiny robots in your body to diagnose and treat medical conditions is one step closer to becoming reality today, with the development of artificial muscles small and strong enough to push the tiny Nanobots along.

Although Nanorobots (Nanobots) have received much attention for the potential medical use in the body, such as cancer fighting, drug delivery and parasite removal, one major hurdle in their development has been the issue of how to propel them along in the bloodstream.

An international collaborative team led by Dr Javad Foroughi and Prof Geoff Spinks at UOW’s Intelligent Polymer Research Institute, part of the ARC Centre of Excellence for Electromaterials Science (ACES), have developed a new twisting artificial muscle that could be used for propelling nanobots. The muscles use very tough and highly flexible yarns of carbon nanotubes (nanoscale cylinders of carbon), which are twist-spun into the required form. When voltage is applied, the yarns rotate up to 600 revolutions per minute, then rotate in reverse when the voltage is changed.

Due to their complexity, conventional motors are very difficult to miniaturise, making them unsuitable for use in nanorobotics. The twisting artificial muscles, on the other hand, are simple and inexpensive to construct either in very long, or in millimetre lengths. …

Further details are available on EurekAlert from the University of Texas at Dallas “Carbon nanotube muscles generate giant twist for novel motors“:

Twist per muscle length is over a thousand times higher than for previous artificial muscles and the muscle diameter is ten times smaller than a human hair

New artificial muscles that twist like the trunk of an elephant, but provide a thousand times higher rotation per length, were announced on Oct. 13 for a publication in Science magazine by a team of researchers from The University of Texas at Dallas, The University of Wollongong in Australia, The University of British Columbia in Canada, and Hanyang University in Korea.

These muscles, based on carbon nanotubes yarns, accelerate a 2000 times heavier paddle up to 590 revolutions per minute in 1.2 seconds, and then reverse this rotation when the applied voltage is changed. The demonstrated rotation of 250 per millimeter of muscle length is over a thousand times that of previous artificial muscles, which are based on ferroelectrics, shape memory alloys, or conducting organic polymers. The output power per yarn weight is comparable to that for large electric motors, and the weight-normalized performance of these conventional electric motors severely degrades when they are downsized to millimeter scale. …

The combination of mechanical simplicity, giant torsional rotations, high rotation rates, and micron-size yarn diameters are attractive for applications, such as microfluidic pumps, valve drives, and mixers. In a fluidic mixer demonstrated by the researchers, a 15 micron diameter yarn rotated a 200 times larger radius and 80 times heavier paddle in flowing liquids at up to one rotation per second. …

A EurekAlert release from the University of British Columbia adds:

… Using yarns of carbon nanotubes that are enormously strong, tough and highly flexible, the researchers developed artificial muscles that can rotate 250 degrees per millimetre of muscle length. This is more than a thousand times that of available artificial muscles composed of shape memory alloys, conducting organic polymers or ferroelectrics, a class of materials that can hold both positive and negative electric charges, even in the absence of voltage.

“What’s amazing is that these barely visible yarns composed of fibres 10,000 times thinner than a human hair can move and rapidly rotate objects two thousand times their own weight,” says UBC Assoc. Prof. John Madden, Dept. of Electrical and Computer Engineering.

Madden says, “While not large enough to drive an arm or power a car, this new generation of artificial muscles – which are simple and inexpensive to make – could be used to make tiny valves, positioners, pumps, stirrers and flagella for use in drug discovery, precision assembly and perhaps even to propel tiny objects inside the bloodstream.”

Central to the team’s success are nanotubes that are spun into helical yarns, which means that they have left and right handed versions, which allows the yearn to be controlled by applying an electrochemical charge, and to twist and untwist.…

At the forefront of nanotechnology, researchers design miniature machines to do big jobs, from treating diseases to harnessing sunlight for energy. But as they push the limits of this technology, devices are becoming so small and sensitive that the behavior of individual atoms starts to get in the way. Now Caltech researchers have, for the first time, measured and characterized these atomic fluctuations—which cause statistical noise—in a nanoscale device.

Physicist Michael Roukes and his colleagues specialize in building devices called nanoelectromechanical systems—NEMS for short—which have a myriad of applications. For example, by detecting the presence of proteins that are markers of disease, the devices can serve as cheap and portable diagnostic tools—useful for keeping people healthy in poor and rural parts of the world. Similar gadgets can measure toxic gases in an enclosed room, providing a warning for the inhabitants.

Two years ago, Roukes’s group created the world’s first nanomechanical mass spectrometer, enabling the researchers to measure the mass of a single biological molecule. The device, a resonator that resembles a tiny bridge, consists of a thin strip of material 2 microns long and 100 nanometers wide that vibrates at a resonant frequency of several hundred megahertz. When an atom is placed on the bridge, the frequency shifts in proportion to the atom’s mass.

But with increasingly sensitive devices, the random motions of the atoms come into play, generating statistical noise. “It’s like fog or smoke that obscures what you’re trying to measure,” says Roukes, who’s a professor of physics, applied physics, and bioengineering. In order to distinguish signal from noise, researchers have to understand what’s causing the ruckus.

So Roukes—along with former graduate student and staff scientist Philip X. L. Feng, former graduate student Ya-Tang (Jack) Yang, and former postdoc Carlo Callegari—set out to measure this noise in a NEMS resonator. They described their results in the April issue of the journal Nano Letters [abstract]. …

The full text of the research article is available as a PDF at Michael Roukes’s web site. The Roukes group is part of

…the Alliance for Nanosystems VLSI, a close and enthusiastic collaboration with scientists and engineers at CEA/LETI-MINATEC in Grenoble, France. Together we have already demonstrated the first examples of very-large-scale integration (VLSI) of nanoelectromechanical systems. Our current work is focused on highly-multiplexed bio/chemical detection systems, producible en masse to enable both new commercializable applications and fundamental explorations at the frontiers of the life sciences.

A team of physicists from the University of Illinois have employed nanofabrication methods to observe a rare state of matter known as a ‘half-quantum vortex’. The research, led by Mr. Rafi Budakian, may prove vital in advancing the science of quantum computing. To make this observation, the researchers attached a ring of strontium ruthenium oxide (SRO) about one micron across to the tip of a micrometer-scale silicon cantilever. This ring is then subjected to magnetic fields which change the ring’s fluxoid states and allow detection of changes in current. This circulating current produces a magnetic moment and, by observing the change in frequency of the cantilever, the magnetic moment can be determined by researchers.

The reasoning behind the importance of this discovery in terms of quantum computing is explained by Professor Anothony J. Legget, the John D. and Catherine T. MacArthur Professor and Center for Advanced Study Professor of Physics. One of the major hurdles in quantum computing is the problem of decoherence, which is the decay of information stored in a quantum computer due to fluctuations from the environment. According to Mr. Legget, SRO may be a suitable physical material for use of storing information in quantum computing. “A rather radical solution to the decoherence problem is to encode the quantum information nonlocally; that is, in the global topological properties of the states in question. Only a very restricted class of physical systems is appropriate for such topological quantum computing, and SRO may be one of them, provided that certain conditions are fulfilled in it. One very important such condition is precisely the existence of half-quantum vortices, as suggested by the Budakian experiment.”

Source: A to Z Nano
http://www.azonano.com/news.asp?newsID=21231

Dr. Long Que, assistant professor of electrical engineering at Louisiana Tech University, has reported success in designing and fabricating a device that allows microscale electronic devices to harvest their own wasted energy.

… this technology uses a cantilever made out of piezoelectric material — material capable of converting distortions to itself into electrical energy — and is coated with a carbon nanotube film on one side. When the film absorbs light and/or thermal energy, it causes the cantilever to bend back and forth repeatedly, which causes the piezoelectric material to generate power as long as the light and/or heat source is active. …

“The greatest significance of this work is that it offers us a new option to continuously harvest both solar and thermal energy on a single chip, given the self-reciprocating characteristics of the device upon exposure to light and/or thermal radiation,” said Que. “This characteristic might enable us to make perpetual micro/nano devices and micro/nanosystems, and could significantly impact the wireless sensory network.”

…Que believes that, in the future, the device could be used to power a number of different nano and microsystems such as implanted biomedical devices or remotely located sensors and communication nodes.

Enabling microsensors and microcomputers to harvest power from their environments should advance the advent of global networks of sensing and surveillance devices. Those interested in the looming conflict between those using sensors to collect data and those whose data is being collected should take a look at Foresight Institute’s “Open Source Sensing Initiative“.

Journal Reference (courtesy of ScienceDaily):
Venu Kotipalli, Zhongcheng Gong, Pushparaj Pathak, Tianhua Zhang, Yuan He, Shashi Yadav, Long Que. Light and thermal energy cell based on carbon nanotube films. Applied Physics Letters, 2010; 97 (12): 124102; 10.1063/1.3491843

The snowman is 10 µm across, 1/5th the width of a human hair.
The snowman was made from two tin beads used to calibrate electron microscope astigmatism. The eyes and smile were milled using a focused ion beam, and the nose, which is under 1 µm wide, is ion beam deposited platinum.
A nanomanipulation system was used to assemble the parts ‘by hand’ and platinum deposition was used to weld all elements together.

It’s likely that better mechanical components, and the cognitive-radio techniques they enable, will usher in the next wave of mobile telephony by giving our cellphones access to much more spectrum. These phones will operate in multiple bands, provide greater data throughput, and minimize if not eliminate the need for wireless providers to drop our calls because traffic exceeds capacity. Consumers will love the result, even if they don’t know anything about the high-tech mechanics that may soon make it possible.
How can mechanical devices outperform electronic ones? One reason is that they generally consume no battery power. Another has to do with the quality factor of the resonating components, a quantity that physicists and engineers denote with the letter Q. The higher the Q, the more selective the resonator will be in responding only to a narrow range of frequencies.
Like any good radio receiver, the one in a cellphone requires resonators with Qs greater than 1000. Resonant electrical circuits, typically built with capacitors and inductors, have great difficulty achieving values that high. Indeed, the inductors in conventional integrated circuits are dismal, generally yielding circuits with Qs of less than 10. Vibrating mechanical resonators, on the other hand, can easily provide values in the required range.