Tag Archives: Rice University

Deriving graphene-like films from salt

This research comes from Russia (mostly). A July 29, 2016 news item on ScienceDaily describes a graphene-like structure derived from salt,

Researchers from Moscow Institute of Physics and Technology (MIPT), Skolkovo Institute of Science and Technology (Skoltech), the Technological Institute for Superhard and Novel Carbon Materials (TISNCM), the National University of Science and Technology MISiS (Russia), and Rice University (USA) used computer simulations to find how thin a slab of salt has to be in order for it to break up into graphene-like layers. Based on the computer simulation, they derived the equation for the number of layers in a crystal that will produce ultrathin films with applications in nanoelectronics. …

Caption: Transition from a cubic arrangement into several hexagonal layers. Credit: authors of the study

Caption: Transition from a cubic arrangement into several hexagonal layers. Credit: authors of the study

A July 29, 2016 Moscow Institute of Physics and Technology press release on EurekAlert, which originated the news item,  provides more technical detail,

From 3D to 2D

Unique monoatomic thickness of graphene makes it an attractive and useful material. Its crystal lattice resembles a honeycombs, as the bonds between the constituent atoms form regular hexagons. Graphene is a single layer of a three-dimensional graphite crystal and its properties (as well as properties of any 2D crystal) are radically different from its 3D counterpart. Since the discovery of graphene, a large amount of research has been directed at new two-dimensional materials with intriguing properties. Ultrathin films have unusual properties that might be useful for applications such as nano- and microelectronics.

Previous theoretical studies suggested that films with a cubic structure and ionic bonding could spontaneously convert to a layered hexagonal graphitic structure in what is known as graphitisation. For some substances, this conversion has been experimentally observed. It was predicted that rock salt NaCl can be one of the compounds with graphitisation tendencies. Graphitisation of cubic compounds could produce new and promising structures for applications in nanoelectronics. However, no theory has been developed that would account for this process in the case of an arbitrary cubic compound and make predictions about its conversion into graphene-like salt layers.

For graphitisation to occur, the crystal layers need to be reduced along the main diagonal of the cubic structure. This will result in one crystal surface being made of sodium ions Na? and the other of chloride ions Cl?. It is important to note that positive and negative ions (i.e. Na? and Cl?)–and not neutral atoms–occupy the lattice points of the structure. This generates charges of opposite signs on the two surfaces. As long as the surfaces are remote from each other, all charges cancel out, and the salt slab shows a preference for a cubic structure. However, if the film is made sufficiently thin, this gives rise to a large dipole moment due to the opposite charges of the two crystal surfaces. The structure seeks to get rid of the dipole moment, which increases the energy of the system. To make the surfaces charge-neutral, the crystal undergoes a rearrangement of atoms.

Experiment vs model

To study how graphitisation tendencies vary depending on the compound, the researchers examined 16 binary compounds with the general formula AB, where A stands for one of the four alkali metals lithium Li, sodium Na, potassium K, and rubidium Rb. These are highly reactive elements found in Group 1 of the periodic table. The B in the formula stands for any of the four halogens fluorine F, chlorine Cl, bromine Br, and iodine I. These elements are in Group 17 of the periodic table and readily react with alkali metals.

All compounds in this study come in a number of different structures, also known as crystal lattices or phases. If atmospheric pressure is increased to 300,000 times its normal value, an another phase (B2) of NaCl (represented by the yellow portion of the diagram) becomes more stable, effecting a change in the crystal lattice. To test their choice of methods and parameters, the researchers simulated two crystal lattices and calculated the pressure that corresponds to the phase transition between them. Their predictions agree with experimental data.

Just how thin should it be?

The compounds within the scope of this study can all have a hexagonal, “graphitic”, G phase (the red in the diagram) that is unstable in 3D bulk but becomes the most stable structure for ultrathin (2D or quasi-2D) films. The researchers identified the relationship between the surface energy of a film and the number of layers in it for both cubic and hexagonal structures. They graphed this relationship by plotting two lines with different slopes for each of the compounds studied. Each pair of lines associated with one compound has a common point that corresponds to the critical slab thickness that makes conversion from a cubic to a hexagonal structure energetically favourable. For example, the critical number of layers was found to be close to 11 for all sodium salts and between 19 and 27 for lithium salts.

Based on this data, the researchers established a relationship between the critical number of layers and two parameters that determine the strength of the ionic bonds in various compounds. The first parameter indicates the size of an ion of a given metal–its ionic radius. The second parameter is called electronegativity and is a measure of the ? atom’s ability to attract the electrons of element B. Higher electronegativity means more powerful attraction of electrons by the atom, a more pronounced ionic nature of the bond, a larger surface dipole, and a lower critical slab thickness.

And there’s more

Pavel Sorokin, Dr. habil., [sic] is head of the Laboratory of New Materials Simulation at TISNCM. He explains the importance of the study, ‘This work has already attracted our colleagues from Israel and Japan. If they confirm our findings experimentally, this phenomenon [of graphitisation] will provide a viable route to the synthesis of ultrathin films with potential applications in nanoelectronics.’

The scientists intend to broaden the scope of their studies by examining other compounds. They believe that ultrathin films of different composition might also undergo spontaneous graphitisation, yielding new layered structures with properties that are even more intriguing.

Here’s a link to and a citation for the paper,

Ionic Graphitization of Ultrathin Films of Ionic Compounds by A. G. Kvashnin, E. Y. Pashkin, B. I. Yakobson, and P. B. Sorokin. J. Phys. Chem. Lett., 2016, 7 (14), pp 2659–2663 DOI: 10.1021/acs.jpclett.6b01214 Publication Date (Web): June 23, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

A de-icer and a preventative for airplane wings from Rice University

I last mentioned this graphene-based work (from James Tour at Rice University in Texas, US) on de-icing not just airplane wings but also windshields, skyscrapers and more in a Sept. 17, 2014 posting. The latest study indicates the technology could be used as a preventative according to a May 23, 2016 news item on phys.org,

Rice University scientists have advanced their graphene-based de-icer to serve a dual purpose. The new material still melts ice from wings and wires when conditions get too cold. But if the air is above 7 degrees Fahrenheit, ice won’t form at all.

A May 23, 2016 Rice University news release (also on EurekAlert), which originated the news item, goes on to describe the work in more detail,

The Rice lab of chemist James Tour gave its de-icer superhydrophobic (water-repelling) capabilities that passively prevent water from freezing above 7 degrees. The tough film that forms when the de-icer is sprayed on a surface is made of atom-thin graphene nanoribbons that are conductive, so the material can also be heated with electricity to melt ice and snow in colder conditions.

The material can be spray-coated, making it suitable for large applications like aircraft, power lines, radar domes and ships, according to the researchers. …

“We’ve learned to make an ice-resistant material for milder conditions in which heating isn’t even necessary, but having the option is useful,” Tour said. “What we now have is a very thin, robust coating that can keep large areas free of ice and snow in a wide range of conditions.”

Tour, lead authors Tuo Wang, a Rice graduate student, and Yonghao Zheng, a Rice postdoctoral researcher, and their colleagues tested the film on glass and plastic.

Materials are superhydrophobic if they have a water-contact angle larger than 150 degrees. The term refers to the angle at which the surface of the water meets the surface of the material. The greater the beading, the higher the angle. An angle of 0 degrees is basically a puddle, while a maximum angle of 180 degrees defines a sphere just touching the surface.

The Rice films use graphene nanoribbons modified with a fluorine compound to enhance their hydrophobicity. They found that nanoribbons modified with longer perfluorinated chains resulted in films with a higher contact angle, suggesting that the films are tunable for particular conditions, Tour said.

Warming test surfaces to room temperature and cooling again had no effect on the film’s properties, he said.

The researchers discovered that below 7 degrees, water would condense within the structure’s pores, causing the surface to lose both its superhydrophobic and ice-phobic properties. At that point, applying at least 12 volts of electricity warmed them enough to retain its repellant properties.

Applying 40 volts to the film brought it to room temperature, even if the ambient temperature was 25 degrees below zero. Ice allowed to form at that temperature melted after 90 seconds of resistive heating.

The researchers found that while effective, the de-icing mode did not remove water completely, as some remained trapped in the pores between linked nanoribbon bundles. Adding a lubricant with a low melting point (minus 61 degrees F) to the film made the surface slippery, sped de-icing and saved energy.

Here’s a link to and a citation for the paper,

Passive Anti-icing and Active Deicing Films by Tuo Wang, Yonghao Zheng, Abdul-Rahman O. Raji, Yilun Li, William K.A. Sikkema, and James M. Tour. ACS Appl. Mater. Interfaces, Just Accepted Manuscript DOI: 10.1021/acsami.6b03060 Publication Date (Web): May 18, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Teslaphoresis; self-assembling materials from a distance

Getting carbon nanotubes to self-assemble from a distance is possible according to an April 14, 2016 news item on ScienceDaily,

Scientists at Rice University have discovered that the strong force field emitted by a Tesla coil causes carbon nanotubes to self-assemble into long wires, a phenomenon they call “Teslaphoresis.”

An April 14, 2016 Rice University (US) news release, (also on EurekAlert) which originated the news item, expands on the theme,

Cherukuri [Rice chemist Paul Cherukuri] sees this research as setting a clear path toward scalable assembly of nanotubes from the bottom up.

The system works by remotely oscillating positive and negative charges in each nanotube, causing them to chain together into long wires. Cherukuri’s specially designed Tesla coil even generates a tractor beam-like effect as nanotube wires are pulled toward the coil over long distances.

This force-field effect on matter had never been observed on such a large scale, Cherukuri said, and the phenomenon was unknown to Nikola Tesla, who invented the coil in 1891 with the intention of delivering wireless electrical energy.

“Electric fields have been used to move small objects, but only over ultrashort distances,” Cherukuri said. “With Teslaphoresis, we have the ability to massively scale up force fields to move matter remotely.”

The researchers discovered that the phenomenon simultaneously assembles and powers circuits that harvest energy from the field. In one experiment, nanotubes assembled themselves into wires, formed a circuit connecting two LEDs and then absorbed energy from the Tesla coil’s field to light them.

Cherukuri realized a redesigned Tesla coil could create a powerful force field at distances far greater than anyone imagined. His team observed alignment and movement of the nanotubes several feet away from the coil. “It is such a stunning thing to watch these nanotubes come alive and stitch themselves into wires on the other side of the room,” he said.

Nanotubes were a natural first test material, given their heritage at Rice, where the HiPco production process was invented. But the researchers envision many other nanomaterials can be assembled as well.

Lindsey Bornhoeft, the paper’s lead author and a biomedical engineering graduate student at Texas A&M University, said the directed force field from the bench-top coil at Rice is restricted to just a few feet. To examine the effects on matter at greater distances would require larger systems that are under development. Cherukuri suggested patterned surfaces and multiple Tesla coil systems could create more complex self-assembling circuits from nanoscale-sized particles.

Cherukuri and his wife, Tonya, also a Rice alum and a co-author of the paper, noted that their son Adam made some remarkable observations while watching videos of the experiment. “I was surprised that he noticed patterns in nanotube movements that I didn’t see,” Cherukuri said. “I couldn’t make him an author on the paper, but both he and his little brother John are acknowledged for helpful discussions.”

Cherukuri knows the value of youthful observation — and imagination — since he started designing Tesla coils as a teen. “I would have never thought, as a 14-year-old kid building coils, that it was going to be useful someday,” he said.

Cherukuri and his team self-funded the work, which he said made it more meaningful for the group. “This was one of the most exciting projects I’ve ever done, made even more so because it was an all-volunteer group of passionate scientists and students. But because Rice has this wonderful culture of unconventional wisdom, we were able to make an amazing discovery that pushes the frontiers of nanoscience.”

The teammates look forward to seeing where their research leads. “These nanotube wires grow and act like nerves, and controlled assembly of nanomaterials from the bottom up may be used as a template for applications in regenerative medicine,” Bornhoeft said.

“There are so many applications where one could utilize strong force fields to control the behavior of matter in both biological and artificial systems,” Cherukuri said. “And even more exciting is how much fundamental physics and chemistry we are discovering as we move along. This really is just the first act in an amazing story.”

Rice University has produced a video featuring the research and the researchers,

Here’s a link to and a citation for the paper,

Teslaphoresis of Carbon Nanotubes by Lindsey R. Bornhoeft, Aida C. Castillo, Preston R. Smalley, Carter Kittrell, Dustin K. James, Bruce E. Brinson, Thomas R. Rybolt, Bruce R. Johnson, Tonya K. Cherukuri†, and Paul Cherukuri. ACS Nano, Article ASAP DOI: 10.1021/acsnano.6b02313 Publication Date (Web): April 13, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

The Tesla coil was created by Nikola Tesla, a renowned Serbian-American scientist and engineer.

2-D boron as a superconductor

A March 31, 2016 news item on ScienceDaily highlights some research into 2D (two-dimensional) boron at Rice University (Texas, US),

Rice University scientists have determined that two-dimensional boron is a natural low-temperature superconductor. In fact, it may be the only 2-D material with such potential.

Rice theoretical physicist Boris Yakobson and his co-workers published their calculations that show atomically flat boron is metallic and will transmit electrons with no resistance. …

The hitch, as with most superconducting materials, is that it loses its resistivity only when very cold, in this case between 10 and 20 kelvins (roughly, minus-430 degrees Fahrenheit). But for making very small superconducting circuits, it might be the only game in town.

A March 30, 2016 Rice University news release (also on EurekAlert but dated March 31, 2016), which originated the news item, expands on the theme,

The basic phenomenon of superconductivity has been known for more than 100 years, said Evgeni Penev, a research scientist in the Yakobson group, but had not been tested for its presence in atomically flat boron.

“It’s well-known that the material is pretty light because the atomic mass is small,” Penev said. “If it’s metallic too, these are two major prerequisites for superconductivity. That means at low temperatures, electrons can pair up in a kind of dance in the crystal.”

“Lower dimensionality is also helpful,” Yakobson said. “It may be the only, or one of very few, two-dimensional metals. So there are three factors that gave the initial motivation for us to pursue the research. Then we just got more and more excited as we got into it.”

Electrons with opposite momenta and spins effectively become Cooper pairs; they attract each other at low temperatures with the help of lattice vibrations, the so-called “phonons,” and give the material its superconducting properties, Penev said. “Superconductivity becomes a manifestation of the macroscopic wave function that describes the whole sample. It’s an amazing phenomenon,” he said.

It wasn’t entirely by chance that the first theoretical paper establishing conductivity in a 2-D material appeared at roughly the same time the first samples of the material were made by laboratories in the United States and China. In fact, an earlier paper by the Yakobson group had offered a road map for doing so.

That 2-D boron has now been produced is a good thing, according to Yakobson and lead authors Penev and Alex Kutana, a postdoctoral researcher at Rice. “We’ve been working to characterize boron for years, from cage clusters to nanotubes to planer sheets, but the fact that these papers appeared so close together means these labs can now test our theories,” Yakobson said.

“In principle, this work could have been done three years ago as well,” he said. “So why didn’t we? Because the material remained hypothetical; okay, theoretically possible, but we didn’t have a good reason to carry it too far.

“But then last fall it became clear from professional meetings and interactions that it can be made. Now those papers are published. When you think it’s coming for real, the next level of exploration becomes more justifiable,” Yakobson said.

Boron atoms can make more than one pattern when coming together as a 2-D material, another characteristic predicted by Yakobson and his team that has now come to fruition. These patterns, known as polymorphs, may allow researchers to tune the material’s conductivity “just by picking a selective arrangement of the hexagonal holes,” Penev said.

He also noted boron’s qualities were hinted at when researchers discovered more than a decade ago that magnesium diborite is a high-temperature electron-phonon superconductor. “People realized a long time ago the superconductivity is due to the boron layer,” Penev said. “The magnesium acts to dope the material by spilling some electrons into the boron layer. In this case, we don’t need them because the 2-D boron is already metallic.”

Penev suggested that isolating 2-D boron between layers of inert hexagonal boron nitride (aka “white graphene”) might help stabilize its superconducting nature.

Without the availability of a block of time on several large government supercomputers, the study would have taken a lot longer, Yakobson said. “Alex did the heavy lifting on the computational work,” he said. “To turn it from a lunchtime discussion into a real quantitative research result took a very big effort.”

The paper is the first by Yakobson’s group on the topic of superconductivity, though Penev is a published author on the subject. “I started working on superconductivity in 1993, but it was always kind of a hobby, and I hadn’t done anything on the topic in 10 years,” Penev said. “So this paper brings it full circle.”

Here’s a link to and a citation for the paper,

Can Two-Dimensional Boron Superconduct? by Evgeni S. Penev, Alex Kutana, and Boris I. Yakobson. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.6b00070 Publication Date (Web): March 22, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Dexter Johnson has published an April 5, 2016 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) about this latest Rice University work on 2D boron that includes comments from his email interview with Penev.

What robots and humans?

I have two robot news bits for this posting. The first probes the unease currently being expressed (pop culture movies, Stephen Hawking, the Cambridge Centre for Existential Risk, etc.) about robots and their increasing intelligence and increased use in all types of labour formerly and currently performed by humans. The second item is about a research project where ‘artificial agents’ (robots) are being taught human values with stories.

Human labour obsolete?

‘When machines can do any job, what will humans do?’ is the question being asked in a presentation by Rice University computer scientist, Moshe Vardi, for the American Association for the Advancement of Science (AAAS) annual meeting held in Washington, D.C. from Feb. 11 – 15, 2016.

Here’s more about Dr. Vardi’s provocative question from a Feb. 14, 2016 Rice University news release (also on EurekAlert),

Rice University computer scientist Moshe Vardi expects that within 30 years, machines will be capable of doing almost any job that a human can. In anticipation, he is asking his colleagues to consider the societal implications. Can the global economy adapt to greater than 50 percent unemployment? Will those out of work be content to live a life of leisure?

“We are approaching a time when machines will be able to outperform humans at almost any task,” Vardi said. “I believe that society needs to confront this question before it is upon us: If machines are capable of doing almost any work humans can do, what will humans do?”

Vardi addressed this issue Sunday [Feb. 14, 2016] in a presentation titled “Smart Robots and Their Impact on Society” at one of the world’s largest and most prestigious scientific meetings — the annual meeting of the American Association for the Advancement of Science in Washington, D.C.

“The question I want to put forward is, Does the technology we are developing ultimately benefit mankind?” Vardi said. He asked the question after presenting a body of evidence suggesting that the pace of advancement in the field of artificial intelligence (AI) is increasing, even as existing robotic and AI technologies are eliminating a growing number of middle-class jobs and thereby driving up income inequality.

Vardi, a member of both the National Academy of Engineering and the National Academy of Science, is a Distinguished Service Professor and the Karen Ostrum George Professor of Computational Engineering at Rice, where he also directs Rice’s Ken Kennedy Institute for Information Technology. Since 2008 he has served as the editor-in-chief of Communications of the ACM, the flagship publication of the Association for Computing Machinery (ACM), one of the world’s largest computational professional societies.

Vardi said some people believe that future advances in automation will ultimately benefit humans, just as automation has benefited society since the dawn of the industrial age.

“A typical answer is that if machines will do all our work, we will be free to pursue leisure activities,” Vardi said. But even if the world economic system could be restructured to enable billions of people to live lives of leisure, Vardi questioned whether it would benefit humanity.

“I do not find this a promising future, as I do not find the prospect of leisure-only life appealing. I believe that work is essential to human well-being,” he said.

“Humanity is about to face perhaps its greatest challenge ever, which is finding meaning in life after the end of ‘In the sweat of thy face shalt thou eat bread,’” Vardi said. “We need to rise to the occasion and meet this challenge” before human labor becomes obsolete, he said.

In addition to dual membership in the National Academies, Vardi is a Guggenheim fellow and a member of the American Academy of Arts and Sciences, the European Academy of Sciences and the Academia Europa. He is a fellow of the ACM, the American Association for Artificial Intelligence and the Institute for Electrical and Electronics Engineers (IEEE). His numerous honors include the Southeastern Universities Research Association’s 2013 Distinguished Scientist Award, the 2011 IEEE Computer Society Harry H. Goode Award, the 2008 ACM Presidential Award, the 2008 Blaise Pascal Medal for Computer Science by the European Academy of Sciences and the 2000 Goedel Prize for outstanding papers in the area of theoretical computer science.

Vardi joined Rice’s faculty in 1993. His research centers upon the application of logic to computer science, database systems, complexity theory, multi-agent systems and specification and verification of hardware and software. He is the author or co-author of more than 500 technical articles and of two books, “Reasoning About Knowledge” and “Finite Model Theory and Its Applications.”

In a Feb. 5, 2015 post, I rounded up a number of articles about our robot future. It provides a still useful overview of the thinking on the topic.

Teaching human values with stories

A Feb. 12, 2016 Georgia (US) Institute of Technology (Georgia Tech) news release (also on EurekAlert) describes the research,

The rapid pace of artificial intelligence (AI) has raised fears about whether robots could act unethically or soon choose to harm humans. Some are calling for bans on robotics research; others are calling for more research to understand how AI might be constrained. But how can robots learn ethical behavior if there is no “user manual” for being human?

Researchers Mark Riedl and Brent Harrison from the School of Interactive Computing at the Georgia Institute of Technology believe the answer lies in “Quixote” — to be unveiled at the AAAI [Association for the Advancement of Artificial Intelligence]-16 Conference in Phoenix, Ariz. (Feb. 12 – 17, 2016). Quixote teaches “value alignment” to robots by training them to read stories, learn acceptable sequences of events and understand successful ways to behave in human societies.

“The collected stories of different cultures teach children how to behave in socially acceptable ways with examples of proper and improper behavior in fables, novels and other literature,” says Riedl, associate professor and director of the Entertainment Intelligence Lab. “We believe story comprehension in robots can eliminate psychotic-appearing behavior and reinforce choices that won’t harm humans and still achieve the intended purpose.”

Quixote is a technique for aligning an AI’s goals with human values by placing rewards on socially appropriate behavior. It builds upon Riedl’s prior research — the Scheherazade system — which demonstrated how artificial intelligence can gather a correct sequence of actions by crowdsourcing story plots from the Internet.

Scheherazade learns what is a normal or “correct” plot graph. It then passes that data structure along to Quixote, which converts it into a “reward signal” that reinforces certain behaviors and punishes other behaviors during trial-and-error learning. In essence, Quixote learns that it will be rewarded whenever it acts like the protagonist in a story instead of randomly or like the antagonist.

For example, if a robot is tasked with picking up a prescription for a human as quickly as possible, the robot could a) rob the pharmacy, take the medicine, and run; b) interact politely with the pharmacists, or c) wait in line. Without value alignment and positive reinforcement, the robot would learn that robbing is the fastest and cheapest way to accomplish its task. With value alignment from Quixote, the robot would be rewarded for waiting patiently in line and paying for the prescription.

Riedl and Harrison demonstrate in their research how a value-aligned reward signal can be produced to uncover all possible steps in a given scenario, map them into a plot trajectory tree, which is then used by the robotic agent to make “plot choices” (akin to what humans might remember as a Choose-Your-Own-Adventure novel) and receive rewards or punishments based on its choice.

The Quixote technique is best for robots that have a limited purpose but need to interact with humans to achieve it, and it is a primitive first step toward general moral reasoning in AI, Riedl says.

“We believe that AI has to be enculturated to adopt the values of a particular society, and in doing so, it will strive to avoid unacceptable behavior,” he adds. “Giving robots the ability to read and understand our stories may be the most expedient means in the absence of a human user manual.”

So there you have it, some food for thought.

Graphene-boron nitride material research from Rice University (US) and Polytechnique Montréal (Canada)

A Jan. 13, 2016 Rice University news release (also on EurekAlert) highlights computational research on hybrid material (graphene-boron nitride),

Developing novel materials from the atoms up goes faster when some of the trial and error is eliminated. A new Rice University and Montreal Polytechnic study aims to do that for graphene and boron nitride hybrids.

Rice materials scientist Rouzbeh Shahsavari and Farzaneh Shayeganfar, a postdoctoral researcher at Montreal Polytechnic (also known as École Polytechnique de Montréal or Polytechnique de Montréal), designed computer simulations that combine graphene, the atom-thick form of carbon, with either carbon or boron nitride nanotubes.

Their hope is that such hybrids can leverage the best aspects of their constituent materials. Defining the properties of various combinations would simplify development for manufacturers who want to use these exotic materials in next-generation electronics. The researchers found not only electronic but also magnetic properties that could be useful.

Shahsavari’s lab studies materials to see how they can be made more efficient, functional and environmentally friendly. They include macroscale materials like cement and ceramics as well as nanoscale hybrids with unique properties.

“Whether it’s on the macro- or microscale, if we can know specifically what a hybrid will do before anyone goes to the trouble of fabricating it, we can save cost and time and perhaps enable new properties not possible with any of the constituents,” Shahsavari said.

His lab’s computer models simulate how the intrinsic energies of atoms influence each other as they bond into molecules. For the new work, the researchers modeled hybrid structures of graphene and carbon nanotubes and of graphene and boron nitride nanotubes.

“We wanted to investigate and compare the electronic and potentially magnetic properties of different junction configurations, including their stability, electronic band gaps and charge transfer,” he said. “Then we designed three different nanostructures with different junction geometry.”

Two were hybrids with graphene layers seamlessly joined to carbon nanotubes. The other was similar but, for the first time, they modeled a hybrid with boron nitride nanotubes. How the sheets and tubes merged determined the hybrid’s properties. They also built versions with nanotubes sandwiched between graphene layers.

Graphene is a perfect conductor when its atoms align as hexagonal rings, but the material becomes strained when it deforms to accommodate nanotubes in hybrids. The atoms balance their energies at these junctions by forming five-, seven- or eight-member rings. These all induce changes in the way electricity flows across the junctions, turning the hybrid material into a valuable semiconductor.

The researchers’ calculations allowed them to map out a number of effects. For example, it turned out the junctions of the hybrid system create pseudomagnetic fields.

“The pseudomagnetic field due to strain was reported earlier for graphene, but not these hybrid boron nitride and carbon nanostructures where strain is inherent to the system,” Shahsavari said. He noted the effect may be useful in spintronic and nano-transistor applications.

“The pseudomagnetic field causes charge carriers in the hybrid to circulate as if under the influence of an applied external magnetic field,” he said. “Thus, in view of the exceptional flexibility, strength and thermal conductivity of hybrid carbon and boron nitride systems, we propose the pseudomagnetic field may be a viable way to control the electronic structure of new materials.”

All the effects serve as a road map for nanoengineering applications, Shahsavari said.

“We’re laying the foundations for a range of tunable hybrid architectures, especially for boron nitride, which is as promising as graphene but much less explored,” he said. “Scientists have been studying all-carbon structures for years, but the development of boron nitride and other two-dimensional materials and their various combinations with each other gives us a rich set of possibilities for the design of materials with never-seen-before properties.”

Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering.

###

Rice supported the research, and computational resources were provided by Calcul Quebec and Compute Canada.

Here’s a link to and a citation for the paper,

Electronic and pseudomagnetic properties of hybrid carbon/boron-nitride nanomaterials via ab-initio calculations and elasticity theory by Farzaneh Shayeganfar and Rouzbeh Shahsavari. Carbon Volume 99, April 2016, Pages 523–532 doi:10.1016/j.carbon.2015.12.050

This paper is behind a paywall.

Here’s an image illustrating the hybrid material,

Caption: The calculated properties of a three-dimensional hybrid of graphene and boron nitride nanotubes would have pseudomagnetic properties, according to researchers at Rice University and Montreal Polytechnic. Credit: Shahsavari Lab/Rice University

Caption: The calculated properties of a three-dimensional hybrid of graphene and boron nitride nanotubes would have pseudomagnetic properties, according to researchers at Rice University and Montreal Polytechnic. Credit: Shahsavari Lab/Rice University

International NanoCar race: 1st ever to be held in Autumn 2016

They have a very intriguing set of rules for the 1st ever International NanoCar Race to be held in Toulouse, France in October 2016. From the Centre d’Élaboration de Matériaux et d’Études Structurales (CEMES) Molecule-car Race International page (Note: A link has been removed),

1) General regulations

The molecule-car of a registered team has at its disposal a runway prepared on a small portion of the (111) face of the same crystalline gold surface. The surface is maintained at a very low temperature that is 5 Kelvin = – 268°C (LT) in ultra-high vacuum that is 10-8 Pa or 10-10 mbar 10-10 Torr (UHV) for at least the duration of the competition. The race itself last no more than 2 days and 2 nights including the construction time needed to build up atom by atom the same identical runway for each competitor. The construction and the imaging of a given runway are obtained by a low temperature scanning tunneling microscope (LT-UHV-STM) and certified by independent Track Commissioners before the starting of the race itself.

On this gold surface and per competitor, one runway is constructed atom by atom using a few surface gold metal ad-atoms. A molecule-car has to circulate around those ad-atoms, from the starting to the arrival lines, each line being delimited by 2 gold ad-atoms. The spacing between two metal ad-atoms along a runway is less than 4 nm. A minimum of 5 gold ad-atoms line has to be constructed per team and per runway.

The organizers have included an example of a runway,

A preliminary runway constructed by C. Manzano and We Hyo Soe (A*Star, IMRE) in Singapore, with the 2 starting gold ad-atoms, the 5 gold ad-atoms for the track and the 2 gold ad-atoms had been already constructed atom by atom.

A preliminary runway constructed by C. Manzano and We Hyo Soe (A*Star, IMRE) in Singapore, with the 2 starting gold ad-atoms, the 5 gold ad-atoms for the track and the 2 gold ad-atoms had been already constructed atom by atom.

A November 25, 2015 [France] Centre National de la Recherche Scientifique (CNRS) press release notes that five teams presented prototypes at the Futurapolis 2015 event preparatory to the upcoming Autumn 2016 race,

The French southwestern town of Toulouse is preparing for the first-ever international race of molecule-cars: five teams will present their car prototype during the Futurapolis event on November 27, 2015. These cars, which only measure a few nanometers in length and are propelled by an electric current, are scheduled to compete on a gold atom surface next year. Participants will be able to synthesize and test their molecule-car until October 2016 prior to taking part in the NanoCar Race organized at the CNRS Centre d’élaboration des matériaux et d’études structurales (CEMES) by Christian Joachim, senior researcher at the CNRS and Gwénaël Rapenne, professor at Université Toulouse III-Paul Sabatier, with the support of the CNRS.

There is a video describing the upcoming 2016 race (English, spoken and in subtitles),


NanoCar Race, the first-ever race of molecule-cars by CNRS-en

A Dec. 14, 2015 Rice University news release provides more detail about the event and Rice’s participation,

Rice University will send an entry to the first international NanoCar Race, which will be held next October at Pico-Lab CEMES-CNRS in Toulouse, France.

Nobody will see this miniature grand prix, at least not directly. But cars from five teams, including a collaborative effort by the Rice lab of chemist James Tour and scientists at the University of Graz, Austria, will be viewable through sophisticated microscopes developed for the event.

Time trials will determine which nanocar is the fastest, though there may be head-to-head races with up to four cars on the track at once, according to organizers.

A nanocar is a single-molecule vehicle of 100 or so atoms that incorporates a chassis, axles and freely rotating wheels. Each of the entries will be propelled across a custom-built gold surface by an electric current supplied by the tip of a scanning electron microscope. The track will be cold at 5 kelvins (minus 450 degrees Fahrenheit) and in a vacuum.

Rice’s entry will be a new model and the latest in a line that began when Tour and his team built the world’s first nanocar more than 10 years ago.

“It’s challenging because, first of all, we have to design a car that can be manipulated on that specific surface,” Tour said. “Then we have to figure out the driving techniques that are appropriate for that car. But we’ll be ready.”

Victor Garcia, a graduate student at Rice, is building what Tour called his group’s Model 1, which will be driven by members of Professor Leonhard Grill’s group at Graz. The labs are collaborating to optimize the design.

The races are being organized by the Center for Materials Elaboration and Structural Studies (CEMES) of the French National Center for Scientific Research (CNRS).

The race was first proposed in a 2013 ACS Nano paper by Christian Joachim, a senior researcher at CNRS, and Gwénaël Rapenne, a professor at Paul Sabatier University.

Joining Rice are teams from Ohio University; Dresden University of Technology; the National Institute for Materials Science, Tsukuba, Japan; and Paul Sabatier [Université Toulouse III-Paul Sabatier].

I believe there’s still time to register an entry (from the Molecule-car Race International page; Note: Links have been removed),

To register for the first edition of the molecule-car Grand Prix in Toulouse, a team has to deliver to the organizers well before March 2016:

  • The detail of its institution (Academic, public, private)
  • The design of its molecule-vehicle including the delivery of the xyz file coordinates of the atomic structure of its molecule-car
  • The propulsion mode, preferably by tunneling inelastic effects
  • The evaporation conditions of the molecule-vehicles
  • If possible a first UHV-STM image of the molecule-vehicle
  • The name and nationality of the LT-UHV-STM driver

Those information are used by the organizers for selecting the teams and for organizing training sessions for the accepted teams in a way to optimize their molecule-car design and to learn the driving conditions on the LT-Nanoprobe instrument in Toulouse. Then, the organizers will deliver an official invitation letter for a given team to have the right to experiment on the Toulouse LT-Nanoprobe instrument with their own drivers. A detail training calendar will be determined starting September 2015.

The NanoCar Race website’s homepage notes that it will be possible to view the race in some fashion,

The NanoCar Race is a race where molecular machines compete on a nano-sized track. A NanoCar is a single molecule-car that has wheels and a chassis… and is propelled by a small electric shock.

The race will be invisible to the naked eye: a unique microscope based in Toulouse, France, will make it possible to watch the competition.

The NanoCar race is mostly a fantastic human and scientific adventure that will be broadcast worldwide. [emphasis mine]

Good luck to all the competitors.

Russians offer nanotechnology report at Paris Climate talks

Sadly I cannot find the report presented by the Russians  at the Paris Climate Talks (also known as World Climate Change Conference 2015 [COP21]) but did find this reference to it in a Dec. 7, 2015 article in the New York Times,

One of the surprises of the Paris climate talks was the sudden interest by Russia in appearing as a player in the efforts to reel in greenhouse gases.

The second part occurred on Monday, when an event was added to the schedule of news briefings: “Russia Proposes a New Approach to Climate Change.”

And so Russia did, putting forth a plan — and a report — that in the end seemed largely geared toward promoting a government-funded business, run by a prominent politician.

The Russian Times (rt.com) published a Nov. 30, 2015 article detailing President Vladimir Putin’s address to the conference attendees,

“We have gone beyond the target fixed by the Kyoto Protocol for the period from 1991 to 2012. Russia not only prevented the growth of greenhouse gas emission, by also significantly reduced it,” Putin said.

“Nearly 40 billion tons of carbon dioxide equivalent weren’t released into the atmosphere. As a comparison, the total emissions of all countries in 2012 reached 46 billion tons.”

Russia is planning to keep progressing by bringing breakthrough technologies into practice, “including nanotechnology,” Putin continued saying the country is also open to exchange and share the findings.

Apart from that, Putin has also promised Russia will reduce its polluting emissions by 70 percent by 2030 as compared to base level in 1990.

A Dec. 8, 2015 article by Jasper Nikki De La Cruz for The Science Times provides more detail about the Russian report/proposal (Note: A link has been removed),

Russia proposes a “New Approach” when it comes to dealing with climate change. The proposal focuses on efforts to reduce emissions involving five materials: steel, cement, aluminum, plastic and paper. The proposal is not on the reduction of the production of these materials but rather making these materials lighter, stronger and more efficient. With this approach, nanotechnology is put into the spotlight as the primary technology in making this proposal possible in real-world applications.

Rusnano is a company that is dedicated to nanotechnology. They received $10B of funding from the Russian government. They are pegged to be the frontrunner in research and application of nanotechnology in the production of the mentioned materials.

“Carbon nanotubes have been shown to toughen aluminum, make plastics conductive, extend the life of lithium-ion batteries,” Anatoly B. Chubais, Rusnano founder, said. “So all that is true. Tangentially, that can then lower CO2 emissions, I suppose.”

James Tour, a scientist at Rice University, commented for the New York Times Dec. 7, 2015 article on this suggestion that greater use of carbon nanotubes could reduce emissions,

A report laying out the materials thesis rested heavily on contentions about the use of carbon nanotubes. For a moment that puzzled James M. Tour, a professor of chemistry and materials science at Rice University and an expert on nanomaterials, who was asked about the proposal.

“Carbon nanotubes have been shown to toughen aluminum, make plastics conductive, extend the life of lithium-ion batteries,” he said in an email. “So all that is true. Tangentially, that can then lower CO2 emissions, I suppose.”

But, he added, “All of the above was well known long before Rusnano came around.”

Reporters, too, were confused. When one asked whether the announcement was “a distraction from real action,” Mr. Chubais said the proposal was a means to the same end.

I don’t find the Russian proposal all that outlandish although the emphasis on carbon nanotubes seems a bit outsized (pun intended). In any event, there’s certainly a role for emerging technologies to play in the attempts to change our lifestyles and ameliorate climate change.

‘Stained glass nanotechnology’ for color displays

From a Dec. 4, 2015 news item on ScienceDaily,

A new method for building “drawbridges” between metal nanoparticles may allow electronics makers to build full-color displays using light-scattering nanoparticles that are similar to the gold materials that medieval artisans used to create red stained-glass.

“Wouldn’t it be interesting if we could create stained-glass windows that changed colors at the flip of a switch?” said Christy Landes, associate professor of chemistry at Rice and the lead researcher on a new study about the drawbridge method that appears this week in the open-access journal Science Advances.

The research by Landes and other experts at Rice University’s Smalley-Curl Institute could allow engineers to use standard electrical switching techniques to construct color displays from pairs of nanoparticles that scatter different colors of light.

For centuries, stained-glass makers have tapped the light-scattering properties of tiny gold nanoparticles to produce glass with rich red tones. Similar types of materials could increasingly find use in modern electronics as manufacturers work to make smaller, faster and more energy-efficient components that operate at optical frequencies.

A Dec. 4, 2015 Rice University news release (also on EurekAlert), which originated the news item, describes the research in more detail,

Though metal nanoparticles scatter bright light, researchers have found it difficult to coax them to produce dramatically different colors, Landes said.

Rice’s new drawbridge method for color switching incorporates metal nanoparticles that absorb light energy and convert it into plasmons, waves of electrons that flow like a fluid across a particle’s surface. Each plasmon scatters and absorbs a characteristic frequency of light, and even minor changes in the wave-like sloshing of a plasmon shift that frequency. The greater the change in plasmonic frequency, the greater the difference between the colors observed.

“Engineers hoping to make a display from optically active nanoparticles need to be able to switch the color,” Landes said. “That type of switching has proven very difficult to achieve with nanoparticles. People have achieved moderate success using various plasmon-coupling schemes in particle assemblies. What we’ve shown though is variation of the coupling mechanism itself, which can be used to produce huge color changes both rapidly and reversibly.”

To demonstrate the method, Landes and study lead author Chad Byers, a graduate student in her lab, anchored pairs of gold nanoparticles to a glass surface covered with indium tin oxide (ITO), the same conductor that’s used in many smartphone screens. By sealing the particles in a chamber filled with a saltwater electrolyte and a silver electrode, Byers and Landes were able form a device with a complete circuit. They then showed they could apply a small voltage to the ITO to electroplate silver onto the surface of the gold particles. In that process, the particles were first coated with a thin layer of silver chloride. By later applying a negative voltage, the researchers caused a conductive silver “drawbridge” to form. Reversing the voltage caused the bridge to withdraw.

“The great thing about these chemical bridges is that we can create and eliminate them simply by applying or reversing a voltage,” Landes said. “This is the first method yet demonstrated to produce dramatic, reversible color changes for devices built from light-activated nanoparticles.”

This research has its roots in previous work (from the news release),

Byers said his research into the plasmonic behavior of gold dimers began about two years ago.

“We were pursuing the idea that we could make significant changes in optical properties of individual particles simply by altering charge density,” he said. “Theory predicts that colors can be changed just by adding or removing electrons, and we wanted to see if we could do that reversibly, simply by turning a voltage on or off.”

The experiments worked. The color shift was observed and reversible, but the change in the color was minute.

“It wasn’t going to get anybody excited about any sort of switchable display applications,” Landes said.

But she and Byers also noticed that their results differed from the theoretical predictions.

Landes said that was because the predictions were based upon using an inert electrode made of a metal like palladium that isn’t subject to oxidation. But silver is not inert. It reacts easily with oxygen in air or water to form a coat of unsightly silver oxide. This oxidizing layer can also form from silver chloride, and Landes said that is what was occurring when the silver counter electrode was used in Byers’ first experiments.

The scientists decided to embrace imperfection (from the news release),

“It was an imperfection that was throwing off our results, but rather than run away from it, we decided to use it to our advantage,” Landes said.

Rice plasmonics pioneer and study co-author Naomi Halas, director of the Smalley-Curl Institute, said the new research shows how plasmonic components could be used to produce electronically switchable color-displays.

“Gold nanoparticles are particularly attractive for display purposes,” said Halas, Rice’s Stanley C. Moore Professor of Electrical and Computer Engineering and professor of chemistry, bioengineering, physics and astronomy, and materials science and nanoengineering. “Depending upon their shape, they can produce a variety of specific colors. They are also extremely stable, and even though gold is expensive, very little is needed to produce an extremely bright color.”

In designing, testing and analyzing the follow-up experiments on dimers, Landes and Byers engaged with a brain trust of Rice plasmonics experts that included Halas, physicist and engineer Peter Nordlander, chemist Stephan Link, materials scientist Emilie Ringe and their students, as well as Paul Mulvaney of the University of Melbourne in Australia.

Together, the team confirmed the composition and spacing of the dimers and showed how metal drawbridges could be used to induce large color shifts based on voltage inputs.

Nordlander and Hui Zhang, the two theorists in the group, examined the device’s “plasmonic coupling,” the interacting dance that plasmons engage in when they are in close contact. For instance, plasmonic dimers are known to act as light-activated capacitors, and prior research has shown that connecting dimers with nanowire bridges brings about a new state of resonance known as a “charge-transfer plasmon,” which has its own distinct optical signature.

“The electrochemical bridging of the interparticle gap enables a fully reversible transition between two plasmonic coupling regimes, one capacitive and the other conductive,” Nordlander said. “The shift between these regimes is evident from the dynamic evolution of the charge transfer plasmon.”

Halas said the method provides plasmonic researchers with a valuable tool for precisely controlling the gaps between dimers and other multiparticle plasmonic configurations.

“In an applied sense, gap control is important for the development of active plasmonic devices like switches and modulators, but it is also an important tool for basic scientists who are conducting curiosity-driven research in the emerging field of quantum plasmonics.”

I’m glad the news release writer included the background work leading to this new research and to hint at the level of collaboration needed to achieve the scientists’ new understanding of color switching.

Here’s a link to and a citation for the paper,

From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties by Chad P. Byers, Hui Zhang, Dayne F. Swearer, Mustafa Yorulmaz, Benjamin S. Hoener, Da Huang, Anneli Hoggard, Wei-Shun Chang, Paul Mulvaney, Emilie Ringe, Naomi J. Halas, Peter Nordlander, Stephan Link, and Christy F. Landes. Science Advances  04 Dec 2015: Vol. 1, no. 11, e1500988 DOI: 10.1126/sciadv.1500988

In case you missed it in the news release, this is an open access paper.

A 244-atom submarine powered by light

James Tour lab researchers at Rice University announce in a Nov. 16, 2015 news item on Nanowerk,

Though they’re not quite ready for boarding a lá “Fantastic Voyage,” nanoscale submarines created at Rice University are proving themselves seaworthy.

Each of the single-molecule, 244-atom submersibles built in the Rice lab of chemist James Tour has a motor powered by ultraviolet light. With each full revolution, the motor’s tail-like propeller moves the sub forward 18 nanometers.
And with the motors running at more than a million RPM, that translates into speed. Though the sub’s top speed amounts to less than 1 inch per second, Tour said that’s a breakneck pace on the molecular scale.

“These are the fastest-moving molecules ever seen in solution,” he said.

Expressed in a different way, the researchers reported this month in the American Chemical Society journal Nano Letters that their light-driven nanosubmersibles show an “enhancement in diffusion” of 26 percent. That means the subs diffuse, or spread out, much faster than they already do due to Brownian motion, the random way particles spread in a solution.

While they can’t be steered yet, the study proves molecular motors are powerful enough to drive the sub-10-nanometer subs through solutions of moving molecules of about the same size.

“This is akin to a person walking across a basketball court with 1,000 people throwing basketballs at him,” Tour said.

A Nov. 16, 2015 Rice University news release (also on EurekAlert), which originated the news item, provides context and details about the research,

Tour’s group has extensive experience with molecular machines. A decade ago, his lab introduced the world to nanocars, single-molecule cars with four wheels, axles and independent suspensions that could be “driven” across a surface.

Tour said many scientists have created microscopic machines with motors over the years, but most have either used or generated toxic chemicals. He said a motor that was conceived in the last decade by a group in the Netherlands proved suitable for Rice’s submersibles, which were produced in a 20-step chemical synthesis.

“These motors are well-known and used for different things,” said lead author and Rice graduate student Victor García-López. “But we were the first ones to propose they can be used to propel nanocars and now submersibles.”

The motors, which operate more like a bacteria’s flagellum than a propeller, complete each revolution in four steps. When excited by light, the double bond that holds the rotor to the body becomes a single bond, allowing it to rotate a quarter step. As the motor seeks to return to a lower energy state, it jumps adjacent atoms for another quarter turn. The process repeats as long as the light is on.

For comparison tests, the lab also made submersibles with no motors, slow motors and motors that paddle back and forth. All versions of the submersibles have pontoons that fluoresce red when excited by a laser, according to the researchers. (Yellow, sadly, was not an option.)

“One of the challenges was arming the motors with the appropriate fluorophores for tracking without altering the fast rotation,” García-López said.

Once built, the team turned to Gufeng Wang at North Carolina State University to measure how well the nanosubs moved.

“We had used scanning tunneling microscopy and fluorescence microscopy to watch our cars drive, but that wouldn’t work for the submersibles,” Tour said. “They would drift out of focus pretty quickly.”

The North Carolina team sandwiched a drop of diluted acetonitrile liquid containing a few nanosubs between two slides and used a custom confocal fluorescence microscope to hit it from opposite sides with both ultraviolet light (for the motor) and a red laser (for the pontoons).

The microscope’s laser defined a column of light in the solution within which tracking occurred, García-López said. “That way, the NC State team could guarantee it was analyzing only one molecule at a time,” he said.

Rice’s researchers hope future nanosubs will be able to carry cargoes for medical and other purposes. “There’s a path forward,” García-López said. “This is the first step, and we’ve proven the concept. Now we need to explore opportunities and potential applications.”

Here’s a link to and a citation for the paper,

Unimolecular Submersible Nanomachines. Synthesis, Actuation, and Monitoring by Víctor García-López, Pinn-Tsong Chiang, Fang Chen, Gedeng Ruan, Angel A. Martí, Anatoly B. Kolomeisky, Gufeng Wang, and James M. Tour. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.5b03764 Publication Date (Web): November 5, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

There is an illustration of the 244-atom submersible,

Rice University scientists have created light-driven, single-molecule submersibles that contain just 244 atoms. Illustration by Loïc Samuel

Rice University scientists have created light-driven, single-molecule submersibles that contain just 244 atoms. Illustration by Loïc Samuel