credit: Goldberger et al.

Soon after graphene sheets were being produced on a laboratory scale routinely, researchers began producing the hydrogenated version graphane (with a hydrogen atom on each carbon). This step is one of many approaches aimed at harnessing graphene’s powerful conductivity and is also being explored for hydrogen storage and other potential applications (more info in this 2009 ScienceDaily article From Graphene to Graphane…). Despite the divergence from planarity which naturally accompanies the shift from sp² to sp³ hybridization, graphane is considered a 2D material.

Brought to our attention by Christine Peterson, a new addition to the family of 2D honeycomb-lattice materials has arrived: germanane. Structurally analogous to graphane, germanane comprises hydrogenated, hexagonally arranged germanium atoms in single (or few) layer sheets. Like silicane and silicene (see companion post Silicene: silicon’s answer to graphene), germanane should have a band gap, possibly allowing it to be implemented sooner than graphene.

While bulk germanium was semi-successfully used to make the first transistors, its low resistivity at higher temperatures and high production costs limited its practical use, and silicon soon became the semiconductor of choice. But going nanoscale may be a game changer, if the right combination of performance, cost, and ease of manufacture can be found.

For most 2D materials, getting stable sheets is the first hurdle. In an important step toward production of germanane sheets, a research team led by Joshua Goldberger at Ohio State University has devised a method for chemical synthesis of germanane crystals, which can be exfoliated down to single layer sheets. The work is published in ACS Nano (abstract) and is described in a Gizmag article:

“…we’ve been searching for unique forms of silicon and germanium with advantageous properties, to get the benefits of a new material but with less cost and using existing technology.”

The resulting material has been shown to conduct electrons ten times faster than silicon (and five times faster than conventional germanium), meaning that it could carry a proportionately higher load if used in microchips. It’s also more chemically stable than silicon, not oxidizing in the presence of air or water, plus it’s much better at absorbing and emitting light – this means that it could prove particularly useful in solar cells.

Ordinarily, germanium takes the form of multilayered crystals. The single-atom-thick layers are bonded to one another, and each one is quite unstable on its own. The OSU researchers created their own germanium crystals, in which calcium atoms were inserted between the layers. That calcium was then dissolved using water, leaving empty chemical bonds in its absence. Those bonds were subsequently plugged with hydrogen, resulting in much more stable layers that could be peeled from the crystal while remaining intact.

A down side of germanium-based technologies may still be cost – germanium is far less abundant than silicon and carbon. From a Productive Nanosystems point of view, graphene technology may prevail in the long run due not only to performance metrics but to the abundance of carbon as well. For nearer-term, intermediate technologies, many hats remain in the ring. Although Group 14 elements are highlighted here, serious research into a broad range of 2D (especially honeycomb structured) materials has been around for a while and is growing fast.
-Posted by Stephanie C

The book  has shipped, and Drexler’s tour schedule now includes a few stops on the coasts of the U.S:

New York: May 6th

Los Angeles: May 8th & 9th

Seattle: May 9th

Find exact times and locations on Drexler’s website, and find more information about the book from publisher Public Affairs and/or from your favorite book store.

If you’ve been imagining an updated version of Nanosystems, you’re in for a surprise. The book invites us to take a remarkable journey through the personal and educational experiences that led Drexler to contemplate the global future and to develop the foundations and concepts of atomically precise manufacturing, through a surprisingly accessible tour of the nanoscale world, and through a deeply thoughtful discussion of not only crucial realities of revolutionary new technology, but of crucial uncertainties as well.

-Posted by Stephanie C

Credit: Le Lay et al.

On the list of potential post-silicon materials for electronics and chips is none other than silicon. More specifically, silicene — 2D sheets of hexagonally arranged silicon atoms, structurally analogous to graphene and experimentally characterized by physicist Guy Le Lay of Aix-Marseille University in France (2012 abstract here).

While graphene possesses exceptional performance qualities, it can’t be directly swapped in to existing silicon-based industry and technology. As described last year in the ExtremeTech article Silicene discovered: Single-layer silicon that could beat graphene to market:

Unlike silicon (or germanium)*, graphene doesn’t have a bandgap, which makes it very hard to actually build a switching device — such as a transistor — out of it. Researchers have had some luck in introducing a bandgap, but graphene is still a long way away from being used in current silicon processes.

Silicene … should be compatible with silicon-based electronics and the huge, existing semiconductor fabrication processes.

*Speaking of germanium, if you’re wondering whether it’s getting a piece of the action the answer is yes. See the companion post Germanane: germanium’s answer to graphane.

So, while the prospects of graphene-based devices are still tremendous, other materials that might allow more near-term integration into existing systems remain attractive.

But the honeycomb lattice may be silicene’s only resemblance to graphene. In the recent Nature news article Sticky Problem Snares Wonder Material, silicene is described as a “super sticky” material that “crinkles into bumps and ridges.” Before silicene’s theoretical properties can be experimentally tested, stable sheets of silicene need to be fabricated. A number of labs are working on it (find graphics and references in this pdf of a talk by Prof. Le Lay), and silicene is being included in more research programs under the graphene/honeycomb lattice umbrella.

What fascinates me most is the notion that a material on the nanoscale could replace its own bulk-scale counterpart for advanced, future applications – a great example of the wonder of the nanoscale. We may need to revise the term “post-silicon” to “post-bulk-silicon”.
-Posted by Stephanie C

Foresight's Director of Education Miguel F. Aznar

Last year we announced a talk that Miguel F. Aznar, Foresight’s Director of Education, would be givng a talk on critical thinking about nanotechnology. The talk “Critical Thinking about Nanotechnology” is now available on the web; however, only in Spanish. Here for comparison with the output from translate.Google.com, are the first two paragraphs from the English draft that Mr. Aznar forwarded:

Most people do not know what nanotechnology is, but they make choices that are influenced by nanotechnology. As individuals and as groups we make choices in education, career/employment, politics, health, energy, and environment that are influenced by nanotechnology because it is changing the tools that we use in an increasing number of fields. What does the general public need to know about nanotechnology in order to make informed, rational choices?

Nanotechnology presents several challenges. First, it crosses disciplines, so understanding a given example of it could require familiarity with, for example, physics and microbiology. Few experts span such diverse fields. Second, it requires experts. Designing a nanoscale enclosure to carry chemicals into a cell’s mitochondria requires expert understanding of chemistry and cell biology. Third, the field—or fields—of nanotechnology are expanding all the time. So a full understanding becomes ever less possible with global, around-the-clock experimentation and publication.

Aznar presents an approach to developing critical thinking and contextual understanding of the issues surrounding nanotechnology that has been tested for more than a decade in classes of children aged 10-17. The approach is framed around nine questions, each of which is then considered in some detail:

1. What is nanotechnology?
2. Why do we use nanotechnology?
3. Where does nanotechnology come from?
4. How does nanotechnology work?
5. How does nanotechnology change?
6. How does nanotechnology change us?
7. How do we change nanotechnology?
8. What are nanotechnology’s costs and benefits?
9. How do we evaluate nanotechnology?

The framework presented has the virtues of being simple enough for the general public to use and flexible enough to accommodate changing nanotechnology as current nanoscale science and technology evolves toward the atomically precise manufacturing that will eventually revolutionize civilization.
—James Lewis, PhD

Nickel nanocrystals mechanically coupled to a piezoelectric substrate allowed a magnetic field to be controlled by an electric field. Credit: Carman et al., UCLA

Even though the sound of it is something quite atrocious, superparamagnetism may become a familiar term in the context of nanoscale electronics and devices.

Loosely speaking, superparamagnetism is a size-based phenomenon in which materials that are ferromagnetic on the macroscale — meaning predisposed toward strong magnetization at room temperature, such as iron and nickel — display zero net magnetization at nanoparticle sizes. This phenomenon occurs because, at nanoparticle sizes, the energy required to disturb alignment of the material’s magnetic moment(s) decreases enough that ambient thermal energy is sufficient, and net magnetization gets zeroed out. The temperature required for thermal disruption of magnetization in bulk nickel is over 300 °C, but drops to about room temperature below 50-nm particle size (and continues to drop rapidly with decreasing particle size).

If you’re like me, your beanie is already spinning, but what does this have to do with nanoscale devices?

Much of technology as we know it utilizes natural electromagnetism: when a current runs through a wire, a weak magnetic field is produced. To maximize the magnetic field strength, a typical macroscale electromagnet is made by coiling a conducting wire around a ferromagnetic (usually iron) core. Controlling the electrical current through the wire then allows a very strong magnetic field to be turned on and off and tuned in magnitude.

The problem is, this configuration doesn’t work well at very small sizes primarily due to resistive loss (energy lost as heat). Further, bringing ferromagnetic core materials down to nanoparticle sizes means dealing with superparamagnetic behavior, a significant divergence from the macroscale.

Thus, the push for device miniaturization includes research into new approaches for electrically controlling magnetization on small (especially nano) size scales, at room temperature.

In a recent breakthrough out of UCLA, a research team led by Gregory Carman and Sarah Tolbert succeeded at controlling magnetization of 16-nm superparamagnetic nickel nanocrystals using a clever design in which the nanocrystals were mechanically coupled to a piezoelectric substrate. Electric-field-induced strain on the piezo produced an axis of maximum strain, which in turn created a magnetic easy axis in the Ni nanocrystals (i.e. an axis of preferred alignment of their magnetic moments). This resulted in an increase in the temperature required for (superparamagnetic) thermal disruption of magnetization (from room temperature) to 67 °C. Additionally, the magnetization state sustained after the electric field was removed, and could be controlled via subsequent electric-field induced manipulation of the piezo. In other words, the researchers were able to turn net magnetization on and off, as well as manipulate its magnitude (analogous to, yet markedly distinct from, conventional macroscale electromagnets).

As described at Phys.org:

In a discovery that could lead to big changes in storing digital information and powering motors in small hand-held devices, researchers at UCLA have developed a method for switching tiny magnetic fields on and off with an electric field—a sharp departure from the traditional approach of running a current through a wire.

The researchers, affiliated with the university’s National Science Foundation–funded TANMS (Translational Applications of Nanoscale Multiferroic Systems), developed a composite that can control magneto-electric activity at a scale of about 10 nanometers…

The team used a composite of nickel nanocrystals coupled with a single crystal of piezoelectric material—which can generate power when a small amount of force is applied to it—to control the north–south orientation of the particles as well as their tendency to spin around, which are essential aspects of activating or deactivating a magnetic field.
…

In the Nano Letters abstract, the authors state, “We believe this is the first example of a system where an electric field can be used to switch on and off a permanent magnetic moment.” In the full length paper, the authors describe the potential application of this breakthrough to magnetic memory.

The magnetic properties of nanoparticles are also of key significance in other areas of nanoscale research, including imaging and drug delivery. Expect to see plenty more examples of exploitation and/or circumventing of superparamagnetism and other uniquely size-based phenomena in the decades ahead.
-Posted by Stephanie C

'Scanning tunnelling microscopy (STM) images of the quantum states of an artificial atomic defect structure in silicon. This structure was fabricated by using the STM to individually remove five hydrogen atoms from a hydrogen-terminated silicon (001) surface. The absence of the hydrogen atoms creates “dangling bond” states that interact to form extended, artificial molecular orbitals. Only the imaging bias voltage has been changed in the three images shown (from left to right, -1.4, +1.4, and +1.8 Volts).' (credit: London Centre for Nanotechnology)

We have previously speculated here whether the continued improvement of technology to place single atoms on silicon with atomic precision for the purpose of developing practical quantum computers would also lead to more general methods of atomically precise or molecular manufacturing. That speculation remains open, but we note that the field of atomically precise quantum engineering continues to advance. A hat tip to ScienceDaily for reprinting this University College London news release “Building quantum states with individual silicon atoms“:

By introducing individual silicon atom ‘defects’ using a scanning tunnelling microscope, scientists at the London Centre for Nanotechnology have coupled single atoms to form quantum states.

Published today in Nature Communications [open access paper: Quantum engineering at the silicon surface using dangling bonds], the study demonstrates the viability of engineering atomic-scale quantum states on the surface of silicon – an important step toward the fabrication of devices at the single-atom limit.

Advances in atomic physics now allow single ions to be brought together to form quantum coherent states. However, to build coupled atomic systems in large numbers, as required for applications such as quantum computing, it is highly desirable to develop the ability to construct coupled atomic systems in the solid state.

Semiconductors, such as silicon, routinely display atomic defects that have clear analogies with trapped ions. However, introducing such defects deterministically to observe the coupling between extended systems of individual defects has so far remained elusive.

Now, LCN scientists have shown that quantum states can be engineered on silicon by creating interacting single-atom defects. Each individual defect consisted of a silicon atom with a broken, or “dangling”, bond. During this study, these single-atom defects were created in pairs and extended chains, with each defect separated by just under one nanometer.

Importantly, when coupled together, these individual atomic defects produce extended quantum states resembling artificial molecular orbitals. Just as for a molecule, each structure exhibited multiple quantum states with distinct energy levels.

The visibility of these states to the scanning tunneling microscope could be tuned through the variation of two independent parameters – the voltage applied to the imaging probe and its height above the surface.

The study was led by Dr Steven Schofield, who said: “We have created precise arrays of atomic defects on a silicon surface and demonstrated that they couple to form unique and interesting quantum states.”

He added: “The next step is to replicate these results in other material systems, for example using substitutional phosphorus atoms in silicon, which holds particular interest for quantum computer fabrication.”

Ongoing research at the LCN is exploring even more complex arrangements of these defects, including the incorporation of impurity atoms within the defect structures, which is expected to alter the symmetry of the defects (similar to the role of the nitrogen atom in the nitrogen-vacancy center defect in diamond).

Will this demonstrated ability of ‘quantum engineering’ dangling silicon atom bonds lead to applications to more general atomically precise manufacturing or productive nanosystems?
—James Lewis, PhD

Credit: Zhengyi Zhao, University of Kentucky

One of nature’s many types of molecular motors combines protein and RNA subunits to force viral (in this case, bacteriophage) DNA into a protein capsid. The understanding of the molecular mechanism by which this motor works has been advanced by the discovery that it revolves the DNA around a central channel, as the Earth revolves around the sun, rather than by rotating, as the Earth does about it axis. A hat tip to ScienceDaily for pointing to this research. From a University of Kentucky news release “Guo lab discovers new class of revolution biomotor and solves mystery in viral DNA packaging:”

Scientists at the University of Kentucky have cracked a 35-year-old mystery about the workings of natural “biomotors.” These molecular machines are serving as models for development of synthetic nanomotors that will someday pump therapeutic DNA, RNA or drugs into individual diseased cells.

The report, revealing the innermost mechanisms of these motors in a bacteria-killing virus and a “new way to move DNA through cells,” is being published online today in the journal ACS Nano.

The article, “Mechanism of One-Way Traffic of Hexameric Phi29 DNA Packaging Motor with Four Electropositive Relaying Layers Facilitating Anti-Parallel Revolution,” can be downloaded with free, open access from http://pubs.acs.org/doi/abs/10.1021/nn4002775.

Peixuan Guo, director of the UK Nanobiotechnology Center, and his colleagues explain that two motors have been found in nature: A linear motor and a rotating motor. Now they report discovery of a third type, a revolving molecular motor.

Guo points out that nanomotors will open the door to practical machines and other nanotechnology devices so small that 100,000 would fit across the width of a human hair. One major natural prototype for those development efforts has been the motor that packages DNA into the shell of bacteriophage phi29, a virus that infects and kills bacteria.

Guo’s own research team wants to embed a synthetic version of that motor into nanomedical devices that are injected into the body, travel to diseased cells and pump in medication. A major barrier in doing so has been uncertainty and controversy about exactly how the phi29 motor moves. Scientists thought that it worked by rotating or spinning in the same motion as the Earth turning once every 24 hours upon its own axis.

In their ACS Nano paper, Guo — with his team, Zhengyi Zhao, Emil Khisamutdinov, and Chad Schwartz — challenge that idea. Indeed, they discovered that the phi29 motor moves DNA without any rotational motion. The motor moves DNA with a revolving in the same motion as the Earth revolving around the sun in one orbit ever 365 days. The “revolution without rotation” model could resolve a big conundrum troubling the past 35 years of painstaking investigation of the mechanism of these viral DNA packaging motors, the report states.

Near-term application of artificial molecular motors based on this work are not difficult to imagine, such as in drug delivery or gene delivery for nanomedicine. Could motors like these be useful for more complicated molecular machine systems, such as running pulleys using DNA cables to transport components in primitive molecular manufacturing systems?
—James Lewis, PhD

…
In what fields would APM cause the most pronounced economic disruption and the collapse of global supply chains to more local chains?

The digital revolution had far-reaching effects on information industries. APM-based production promises to have similarly far-reaching effects, but transposed into the world of physical products. In thinking about implications for international trade and economic organization, three aspects should be kept in mind: a shift from scarce to common raw materials, a shift from long supply chains to more direct paths from raw materials to finished products, and a shift toward flexible, localized manufacturing based on production systems with capabilities that are comparable on-demand printing. This is enough to at least suggest the scope of the changes to expect from a mature form of APM-based production — which again is a clear prospect but emphatically not around the corner.
…

-Posted by Stephanie C

Credit: Biodesign Institute

Of all of the paths toward molecular manufacturing, structural DNA nanotechnology seems to provide the most frequent and photogenic advances. By re-engineering the Holliday junction, the basic cross-over structure adapted to build complex structures from DNA, Prof. Hao Yan and his colleagues has been able to construct a variety of new wire frame and mesh structures. A hat tip to ScienceDaily for reprinting this Arizona State University news release “ASU scientists develop innovative twists to DNA nanotechnology“:

In a new discovery that represents a major step in solving a critical design challenge, Arizona State University Professor Hao Yan has led a research team to produce a wide variety of 2-D and 3-D structures that push the boundaries of the burgeoning field of DNA nanotechnology.

The field of DNA nanotechnology utilizes nature’s design rules and the chemical properties of DNA to self-assemble into an increasingly complex menagerie of molecules for biomedical and electronic applications. Some of the Yan lab’s accomplishments include building Trojan horse-like structures to improve drug delivery to cancerous cells, electrically conductive gold nanowires, single molecule sensors and programmable molecular robots.

With their bio-inspired architectural works, the group continues to explore the geometrical and physical limits of building at the molecular level.

“People in this field are very interested in making wire frame or mesh structures,” said Yan. “We needed to come up with new design principles that allow us to build with more complexity in three dimensions.”

In their latest twist to the technology, Yan’s team made new 2-D and 3-D objects that look like wire-frame art of spheres as well as molecular tweezers, scissors, a screw, hand fan, and even a spider web.

The Yan lab, which includes ASU Biodesign Institute colleagues Dongran Han, Suchetan Pal, Shuoxing Jiang, Jeanette Nangreave and assistant professor Yan Liu, published their results in the March 22 issue of Science [abstract].

The twist in their ‘bottom up,’ molecular Lego design strategy focuses on a DNA structure called a Holliday junction.

In nature, this cross-shaped, double-stacked DNA structure is like the 4-way traffic stop of genetics – where 2 separate DNA helices temporality meet to exchange genetic information. The Holliday junction is the crossroads responsible for the diversity of life on Earth, and ensures that children are given a unique shuffling of traits from a mother and father’s DNA.

In nature, the Holliday junction twists the double-stacked strands of DNA at an angle of about 60-degrees, which is perfect for swapping genes but sometimes frustrating for DNA nanotechnology scientists, because it limits the design rules of their structures.

“In principal, you can use the scaffold to connect multiple layers horizontally,” [which many research teams have utilized since the development of DNA origami by Cal Tech's Paul Rothemund in 2006]. However, when you go in the vertical direction, the polarity of DNA prevents you from making multiple layers,” said Yan. “What we needed to do is rotate the angle and force it to connect.”

Making the new structures that Yan envisioned required re-engineering the Holliday junction by flipping and rotating around the junction point about half a clock face, or 150 degrees. Such a feat has not been considered in existing designs.

“The initial idea was the hardest part,” said Yan. “Your mind doesn’t always see the possibilities so you forget about it. We had to break the conceptual barrier that this could happen.”

In the new study, by varying the length of the DNA between each Holliday junction, they could force the geometry at the Holliday junctions into an unconventional rearrangement, making the junctions more flexible to build for the first time in the vertical dimension. Yan calls the backyard barbeque grill-shaped structure a DNA Gridiron.

“We were amazed that it worked!” said Yan. “Once we saw that it actually worked, it was relatively easy to implement new designs. Now it seems easy in hindsight. If your mindset is limited by the conventional rules, it’s really hard to take the next step. Once you take that step, it becomes so obvious.”

The DNA Gridiron designs are programmed into a viral DNA, where a spaghetti-shaped single strand of DNA is spit out and folded together with the help of small ‘staple’ strands of DNA that help mold the final DNA structure. In a test tube, the mixture is heated, then rapidly cooled, and everything self-assembles and molds into the final shape once cooled. Next, using sophisticated AFM and TEM imaging technology, they are able to examine the shapes and sizes of the final products and determine that they had formed correctly.

This approach has allowed them to build multilayered, 3-D structures and curved objects for new applications.

“Most of our research team is now devoted toward finding new applications for this basic toolkit we are making,” said Yan. “There is still a long way to go and a lot of new ideas to explore. We just need to keep talking to biologists, physicists and engineers to understand and meet their needs.”

The video (computer simulation) of the sphere made from DNA, included in the news release, represents an impressive new capability. One thing I like about structural DNA nanotechnology is that every time I think they have just about exhausted the bag of tricks that DNA provides, someone proves me wrong. I look forward to seeing what else they come up with.
—James Lewis, PhD

Graphic representation of a 3-D atomic resolution screw dislocation in a platinum nanoparticle. Credit: Chien-Chun Chen and I-Sheng Chou, UCLA

Researchers from UCLA’s California NanoSystems Institute and Northwestern University have combined multiple imaging techniques to produce high quality 3D images of platinum nanoparticles, allowing advanced visualization of atomic-scale structural defects (an important advancement over X-ray crystallography).

The original 2012 work, published in Nature and posted by Jim Lewis here, used electron tomography to study 10-nm gold particles and was described at Phys.org:

…
“This is the first experiment where we can directly see local structures in three dimensions at atomic-scale resolution — that’s never been done before,” said Jianwei (John) Miao, a professor of physics and astronomy and a researcher with the California NanoSystems Institute (CNSI) at UCLA.
…
X-ray crystallography is a powerful technique for revealing the structure of perfect crystals, which are materials with an unbroken honeycomb of perfectly spaced atoms lined up as neatly as books on a shelf. Yet most structures existing in nature are non-crystalline, with structures far less ordered than their crystalline counterparts — picture a rock concert mosh pit rather than soldiers on parade.
…
Miao and his colleagues used a scanning transmission electron microscope to sweep a narrow beam of high-energy electrons over a tiny gold particle only 10 nanometers in diameter (almost 1,000 times smaller than a red blood cell). The nanoparticle contained tens of thousands of individual gold atoms, each about a million times smaller than the width of a human hair. These atoms interact with the electrons passing through the sample, casting shadows that hold information about the nanoparticle’s interior structure onto a detector below the microscope.

Miao’s team discovered that by taking measurements at 69 different angles, they could combine the data gleaned from each individual shadow into a 3-D reconstruction of the interior of the nanoparticle. Using this method, which is known as electron tomography, Miao’s team was able to directly see individual atoms and how they were positioned inside the specific gold nanoparticle.
…

The new study, using multiple imaging techniques, will be published in an upcoming issue of Nature, and includes a video showing three-dimensional volume renderings (available for viewing at Phys.org:

The authors describe being able to see how the atoms of a platinum nanoparticle—only 10 namometers in diameter—are arranged in three dimensions. They also identify how the atoms are arranged around defects in the platinum nanoparticle.
…
This novel method is a combination of three techniques: scanning transmission electron microscopy, equally sloped tomography (EST) and three-dimensional Fourier filtering. Compared to conventional CT, the combined method produces much higher quality 3-D images and allows the direct visualization of atoms inside the platinum nanoparticle in three dimensions.
…
“This is the first instance where the three-dimensional structure of dislocations in nanoparticles has been directly revealed at atomic resolution,” Ajayan said. “The elegant work demonstrates the power of electron tomography and leads to possibilities of directly correlating the structure of nanoparticles to properties, all in full 3-D view.” Defects can influence many properties of materials, and a technique for visualizing these structures at atomic resolution could lead to new insights beneficial to researchers in a wide range of fields.

-Posted by Stephanie C