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Manufactured Nanoparticles Could Pose a Hazard to Crops, But Are They a Risk?

Once again, here come the headlines, across both the trade and mainstream press, warning us that manufactured nanoparticles are a danger to our health and environment. This time it's that nanoparticles stunt soybean crop growth.

The warnings are based on research at the University of California Santa Barbara's Bren School for Environmental Science & Management. The language of the research, however, falls somewhat short of making such unconditional claims.

Instead the research, which was published the Proceedings of the National Academy of Sciences (PNAS),  claims to demonstrate “what could arise over the long term” if plants were grown in soil that had been contaminated with manufactured nanomaterials (MNMs), zinc oxide and cerium oxide.

Even the research that inspired the UC Santa Barbara team to put metal oxides in farming soil only suggested that MNMs “could” alter food crop quality and yield. Of course, if the researchers were to take ordinary household bleach from under the kitchen sink and pour it onto farming soil, they would surely conclude that it "could" alter the quality of the crop.

The real issue—and indeed as with any issue related to chemicals and Environmental, Health and Safety (EHS) concerns—is what is the real risk of these nanoparticles finding themselves in soil concentrations equal to those that were used in the experiments. The relevant formula is Hazard x Exposure = Risk. If we say that MNMs are a hazard, but have no figures on the level of exposure, how are we supposed to determine risk?

In other words, what concentrations of metal oxides did the researchers use in the soil? The answer is not explicit in either the news stories covering the research, nor the abstract that we have access to in the PNAS journal reference. While the researchers do say in at least one of the articles covering the research that “"MNMs…have a high affinity for activated sludge bacteria, and thus concentrate in biosolids," it’s still not clear in what kind of concentrations these nanoparticles exist in the environment, or what that might mean in terms of risk.

In one of the stories covering the research, Patricia Holden, one of the scientists in the research and a professor at the Bren School, has this to say about the risk of these nanoparticles getting into our plant soil: "There could be hotspots, places where you have accumulation, including near manufacturing sites where the materials are being made, or if there are spills."

Could we say then that if you grow your soybeans far from manufacturing sites and far from where there may likely be spills—which is largely the case now, as I understand—that we would mitigate the risk? 

Another troubling aspect of this research is that it has as its "ultimate goal" to help find more environmentally compatible substitutes, according to Holden. Shouldn't the research be to determine if nanoparticles pose a real risk? Instead, that seems to be a given, despite the limited, at best, evidence being provided to prove it.

And what are we substituting in this case? Zinc oxide nanoparticles are found in sunscreens and cosmetics and cerium oxide is used in catalytic converters to reduce carbon monoxide from automobiles. Where is the research to determine how much of these materials are produced, followed by measurements of how much of them are found in random water and soil samples? From there we could determine the key variable of exposure: how much of these nanoparticles in our environment pose a risk. That seems to be an essential line of research if our goal is protecting our environment from substances that are otherwise pretty useful. I am not so sure that setting out to replace them as your ultimate goal really satisfies that aim.

Graphene Is Losing Favor as the Two-Dimensional Material of the Future

 

About 18 months ago, research at Ecole Polytechnique Federale de Lausanne’s (EPFL) Laboratory of Nanoscale Electronics and Structures in Switzerland was beginning to suggest that molybdenum disulfide (MoS2)—which occurs as the mineral molybdenite—may serve as preferable choice over graphene in a post-silicon world. 

Since that time, research has been hotly pursuing the use of this abundant mineral for electronic applications since not only does it possess some of graphene’s attractive qualities, but it brings them to the table with a band gap, unlike graphene. So attractive has this material become that even the discoverers of graphene are now focusing much of their research into using MoS2

Now researchers at MIT, who have struggled to get graphene to do anything in electronics except for some radio-frequency applications, have turned to MoS2 and have quickly managed to get the one-atom-thick material to serve as the basis for a variety of electronic components

The research, which was published this month in the journal Nano Letters ("Integrated Circuits Based on Bilayer MoS2 Transistors"),  produced an inverter, a NAND (Negated AND) gate, a memory device and a ring oscillator using large sheets of the MoS2.

The MIT researchers believe that this list of electronic components is only the beginning of what is possible with the material. One of the researchers, Tomás Palacios, Associate Professor in the Department of Electrical Engineering and Computer Science, believes that the material could find early applications in large-screen displays in which a separate transistor would control each pixel of the display.

Palacios further notes in the MIT press release that the MoS2 when used in combination with other 2-D materials could make light-emitting devices that could be made to make an entire wall glow, making for a warmer and less glaring light that comes from single light bulbs.

This work certainly seems to promise a far greater range of applications for the material than the EPFL research initially indicated. At that time, the Swiss researchers believed the material would probably see use as a complement to graphene in applications that required thin and transparent semiconductors. It seems now the material has much greater promise.

New Form of Carbon Dents Diamonds and More

Nanomaterial science has sometimes resulted in redefining the known forms of carbon. When carbon nanotubes were first discovered over twenty years ago the long-held paradigm of there being just three forms of carbon (diamond, graphite, and amorphous carbon) had to be reassessed. 

Now an international team of researchers working at Argonne National Laboratory's Advanced Photon Source is reporting that they have developed another new form of carbon that is so strong it can dent a diamond.

"We created a new type of carbon material, one that is comparable to diamond in its inability to be compressed," says scientist Lin Wang in an Argonne press release. "Once created under extreme pressures, this material can exist at normal conditions, meaning it could be used for a wide array of practical applications."

The research, which was published in the journal Science ("Long-Range Ordered Carbon Clusters: A Crystalline Material with Amorphous Building Blocks"), combined two forms of carbon—one with an organized structure and another without one—to create a hybrid material that until now had only been theorized about.

The researchers started with carbon-60 “buckyballs”—for which the riddle of their formation was just recently solved--and crushed them with flattened diamond tips. After being crushed, the buckyballs form themselves into a new, harder form of carbon.

The key to the process  is that the crushing had to be done just right with the right amount of pressure. If not done to the correct pressure, the new material would return to its original, less durable buckyball form.

The research also points to this being just the tip of the iceberg in creating new forms of carbon.

Lin Wang further notes in the press release: “The thing that stands out for me from this work is that carbon-60 can crystallize with various solvents, and those solvates would have different periodicities, which enables us to synthesize a series of similar carbon materials with different packing symmetry and carbon cluster size by compressing different types of carbon molecules."

Although it was not discussed in the press release, I couldn’t help but wonder if this new form of carbon will be of interest to the Robert Freitas and Ralph Merkle sect of the molecular nanotechnology community.  Maybe these new carbon materials can serve as the basic building blocks for automated exponential manufacturing where diamonds have not been able to impress even Eric Drexler himself

Entropy Outweighs Gravity in Forming Nanoparticles into Structures

 

Researchers at the University of Michigan have used newly developed computer simulations to demonstrate how one can exploit both the geometry of nanoparticles and the thermodynamic property of entropy to get nanoparticles to organize themselves into structures. 

Physicist and chemical engineering professor Sharon Glotzer and her collaborators in the research, Michael Engel and Pablo Damasceno, recognized—along with others—that nanoparticles with certain geometries have a greater tendency to organize themselves into structures when they were crowded together. From this observation they wondered if nanoparticles with other geometries would do the same.

"We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers," Glotzer says in the university press release covering the research. "With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends."

The research, which was published in the journal Science (“Predictive Self-Assembly of Polyhedra into Complex Structures”), seems to have revealed some confusion about what entropy is. Even the University of Michigan press release seemed somewhat nonplussed about how a tendency towards “disorder” could create “order.”

It might be better to think of entropy as a tendency toward equilibrium rather than disorder.  This might help better describe how entropy aids the nanoparticles in self-assembling into structures.

To clarify this, Glotzer urges a remake of entropy’s image in the press release. In her explanation, entropy is a measure of possibilities. To describe how this measure of possibilities influences the nanoparticles, Glotzer says to imagine the nanoparticles as a bag of dice being emptied into a jar where there is no gravity. Based on entropy, the dice would find themselves dispersed throughout the jar. However, when you put enough dice into the jar—and they run out of space—they begin to align themselves.

According to the University of Michigan team's simulations, this metaphorical description holds true as well for the nanoparticles. The nanoparticles are so small that the forces of gravity have less of an impact on them than does this property of entropy.

"It's all about options. In this case, ordered arrangements produce the most possibilities, the most options. It's counterintuitive, to be sure," Glotzer says in the release.

What the simulation demonstrated was that by knowing the geometry of the nanoparticles, you can predict the kind of structure they will form.

One of the unresolved mysteries from the simulation the researchers observed is that around 30 percent of the nanoparticles never form into a more complex structure. Why this is the case, they are not sure.

"These may still want to form crystals but got stuck. What's neat is that for any particle that gets stuck, we had other, awfully similar shapes forming crystals," Glotzer said.

IBM Researchers Confirm Decade-Old Theory of Locking Electron Spin Rotation

 

IBM is again taking the lead in spintronics research. Researchers at IBM Zurich and scientists at ETH Zurich for the first time have shown that electrons can be programmed to spin in unison in a semiconductor in what is called a persistent spin helix.

Importantly, the research, which was published in the journal Nature Physics, demonstrated that synchronizing the electrons in this way extends the spin lifetime by 30 times to 1.1 nanoseconds—the same time it takes for an existing 1GHz processor to cycle. It is expected that this level of control over the spin of electrons could result in more energy efficient electronic devices.

In 2003, a theory was proposed that it was possible to lock the spin rotation of electrons. The IBM and ETH Zurich researchers have not only been able to confirm this theory but also demonstrated that electron spins move tens of micrometers in a semiconductor with their orientations synchronously rotating along a path—not unlike a couple dancing a waltz.

In explaining the electron spin with the waltz metaphor, Dr. Gian Salis of the Physics of Nanoscale Systems research group at IBM Zurich said: “If all couples start with the women facing north, after a while the rotating pairs are oriented in different directions. We can now lock the rotation speed of the dancers to the direction they move. This results in a perfect choreography where all the women in a certain area face the same direction. This control and ability to manipulate and observe the spin is an important step in the development of spin-based transistors that are electrically programmable.”

The researchers were able to achieve this feat by first setting up the ability to monitor the spins of the electrons using a time-resolved scanning microscope technique. The researchers were then able to induce the synchronous spin motion by carefully engineering the spin-orbit interaction—a mechanism that couples the spin with the motion of the electron.

While this research promises to bring a greater level of control to spintronics, this research is far from finding its way into our electronic devices any time soon. For example, the experiments performed by the IBM scientists were performed at 40 Kelvin (-233 C, -387 F)—a temperature not suitable for your tablet computer.

Nanotechnology Comes to TedTalks, with Mixed Results

 

For all the TEDTalks that there have been, few have adequately addressed the topic of nanotechnology, with the possible exception of Bill Joy’s ironic path from nanotechnology doomsayer to cheerleader

That is why when I saw that venture capitalist and Nanoholdings CEO Justin Hall-Tipping had been given a forum to discuss nanotechnology for the illustrious TedTalks last year, I had to give a listen (see video below).

Hall-Tipping did not disappoint. As you will see in the video, he provides all the “gee-whiz” nanotech applications one could hope for and throws in some emotion to pull at our heartstrings.

Hall-Tipping highlights three technologies in the video that, as he explains, “exhibit exquisite control over the electron” and could change our current energy paradigm—which, according to his calculations, is doomed to ultimate failure. Two of the technologies come from research originated at the University of Florida; the third comes from the University of Texas at Dallas.

Hall-Tipping says that one of the technologies developed at the University of Florida will result in a world that doesn’t need artificial light to illuminate our nights. In this case, I believe he is referring to the work of Prof. Franky So, developer of lightweight night-vision technologies.  That’s great, but if Hall-Tipping really expects that nearly ubiquitous night-vision capabilities are going to spell the end for artificial light, I think he may have overstated his point.

The other University of Florida technology that Hall-Tipping highlights uses carbon nanotubes embedded in transparent polymer films to absorb the sun’s energy and release it indoors during the winter. And as Hall-Tipping describes it, the same film will “flip it back” in the summer, preventing solar energy from heating living spaces when you want to keep things cool. This application seems to be built around the work of John Reynolds and Andrew Rinzler. I suppose this work could be adapted to collect solar power and reflect away sunlight, but I would like to see some figures on energy conversion efficiency before I start disconnecting myself from the grid.

In the final technology, from the University of Texas at Dallas, nanomaterials (of the carbon nanotube variety, we assume ) enable a device that, according to Hall-Tipping, can “park an electron on the outside, hold it until it's needed, and then to release it and pass it off.” The machine that accomplishes this electron parking, dubbed eBox, has apparently been around since 2009. A prototype has been running for over a year—without, it seems, any effort to commercialize it.

Later in the video, Hall-Tipping makes the cogent point that water shortages are already becoming acute around the world and that energy-intensive desalination is a problematic solution based our current energy paradigm. But removing the grid, or depending on solar power to change the dynamics, seems to be missing the point of a lot of nanotech research related to desalination. I suppose Hall-Tipping’s company is not backing those horses. 

Finally, Hall-Tipping makes his concerns about water shortages personal when he reveals a photograph that he has carried with him for the last 18 years; in it, a young girl in the Sudan is dying of thirst. A truly heart-wrenching image, and as Hall-Tipping says, one that should never happen. But maybe that girl would have been better served by rather simple nanotech-based solutions for providing clean drinking water instead of reinventing the electrical grid.

Mysteries of Electron-Electron Interaction in Graphene Revealed

 

It seems there’s a new development in graphene research daily. One day the ‘wonder material’ is made into a semiconductor, and the next it becomes an insulator

Despite all the research that is ongoing with graphene, no one has been quite sure what role electron-electron interaction played in giving graphene its unique properties, including its high electron mobility.

Now Michael Crommie, a physicist who holds joint appointments with Lawrence Berkeley National Laboratory’s (LBL) Materials Sciences Division and University of California Berkeley’s Physics Department, has peered into these interactions with scanning tunneling microscopy (STM) and solved the mystery

Crommie is among the researchers who as been pushing the boundaries of graphene’s capabilities since he discovered that graphene could be stretched, and in so doing, introduced the concept of ‘straintronics’ for graphene. One of the offshoots of that research has been the idea of using graphene for piezoelectric applications

In this latest research, which was published in the journal Nature Physics (“Mapping Dirac quasiparticles near a single Coulomb impurity on graphene”), Crommie and his colleagues looked at and recorded how electrons and holes react to a charged impurity (a single Coulomb potential) that had been located on a gated graphene device.

The researchers were already aware that the electrons traveled through graphene at relativistic speeds comparable to the speed of light. It is for this reason that physicists have referred to them as “Dirac quasiparticles,” which travel at the speed of light if they are massless excitations, but cannot reach that speed if the have mass. 

“In graphene, electrons behave as massless Dirac fermions,” Crommie says in the LBL press release . “As such, the response of these electrons to a Coulomb potential is predicted to differ significantly from how non-relativistic electrons behave in traditional atomic and impurity systems. However, until now, many key theoretical predictions for this ultra-relativistic system had not been tested.”

Crommie and his team took theoretical predictions of how Dirac quasiparticles would respond to a charged impurity in graphene and compared those with their physical measurements. They were able to take the physical measurements by using an STM tip to combine cobalt monomers into cobalt trimers that served as the charged impurities. Then, with the same STM, the team measured the response of the Dirac quasiparticles to the Coulomb potential created by the trimers.

“Theorists have predicted that compared with other materials, electrons in graphene are pulled into a positively-charged impurity either too weakly, the subcritical regime; or too strongly, the supercritical regime,” Crommie further noted in the LBL press release. “In our study, we verified the predictions for the subcritical regime and found the value for the dielectric to be small enough to indicate that electron–electron interactions contribute significantly to graphene properties. This information is fundamental to our understanding of how electrons move through graphene.”

By measuring how Dirac fermions react when they are near a charged impurity in the grapehen (a Coulomb potential), the researchers have been able to determine graphene's dielectric constant and in this way they have confirmed that electron-electron interaction is a factor in how electrons behave inside graphene.

Prospect of Ubiquitous Flexible Displays Just Got a Lot More Realistic

 

The ability to manufacture flexible lithium-ion (Li-ion) batteries is not new, as evidenced by some of the commercial efforts over the last couple of years to bring this technology to market. 

However, the quest to achieve flexibility for these Li-ion batteries has typically meant using materials that sacrifice performance to the degree that they have little hope of powering consumer gadgets, like a flexible display.

Keon Jae Lee, a professor in the Department of Materials Science and Engineering, Flexible and Nano-bio-energy Device Lab, at Korea Advanced Institute of Science and Technology (KAIST), and his colleagues have developed a new manufacturing technique that should allow for inorganic materials to be used that will produce better battery performance. (A demonstration video of the flexible Li-ion can be seen below.) 

You may remember back in May that Lee developed a method for producing nanogenerators more cheaply and easily than ever before.  It seems Lee has done the same with flexible Li-ion batteries.

The current research, which was published in the journal Nano Letters (“Bendable Inorganic Thin-Film Battery for Fully Flexible Electronic Systems”), demonstrated the use of high-density inorganic thin films employing a newly developed universal transfer approach. The process results in what the researchers describe as the “highest performance ever achieved for flexible LIBs [Li-ion batteries].”

The so-called “universal transfer approach” involves physical delamination of the battery’s mica substrate using sticky tapes. One of the key steps of the process comes right before the delamination when lithium cobalt oxide (LiCoO2) is exposed to high-temperature annealing to create the crystallinity of material that results in the high-performance solid-state LIB.

"We would like to emphasize that solid state thin-film battery has been developed for quite a long time and commercialized for various applications," says Lee in Nanowerk. "Our achievement is not the development of a thin-film battery but focused on the development of a flexible thin-film battery using a transfer protocol for the ultra-thin battery film itself – with less than 10µm thickness."

What is perhaps most intriguing about the manufacturing process is that it manages to create an “all-in-one” product in which both the LED display and energy source are produced all together in one flexible device.

Lee further notes in the Nanowerk article: "Our novel transfer approach can be expanded to various high-performance flexible applications, such as thin-film nanogenerators, thin-film transistors, and thermoelectric devices. As far as we know, this is the first prototype of a fully functional all-flexible electronic system.”

Researchers Unravel Twenty-Five-Year-Old Riddle of Buckyball Formation

When Richard Smalley, Robert Curl, James Heath, Sean O'Brien, and Harold Kroto prepared the first buckminsterfullerene (C60) (or buckyball), they kicked off the next 25 years of nanomaterial science.

What’s interesting about the buckyball—considering all the carbon nanoscience that has followed it—is that nobody quite understood the mechanism by which buckyballs formed—until now. Researchers at Florida State University and the National Science Foundation claim to have solved the quarter-century old mystery of how these buckyballs take shape

The research, which was published in the journal Nature Communications (“Closed network growth of fullerenes”), discovered that “fullerenes self-assemble through a closed network growth mechanism.” They are able to pull this off by incorporation of atomic carbon and diatomic carbon.

Making this discovery required some ingenious approaches and a bit of serendipity since fullerene formation happens in an instant. “We started with a paste of pre-existing fullerene molecules mixed with carbon and helium, shot it with a laser, and instead of destroying the fullerenes we were surprised to find they’d actually grown," the university press release quotes the researchers as saying.

The researchers further determined that fullerenes did not grow by splitting open but instead managed their growth trick by absorbing and incorporating carbon from the surrounding gas. They knew this because the fullerene cages contained heavy metal atoms in their centers. “If the cages grew by splitting open, we would have lost the metal atoms, but they always stayed locked inside,” Paul Dunk, a doctoral student in chemistry and biochemistry at Florida State and lead author of the work noted in a press release.

The clearest applications for solving this riddle will be in better understanding fullerene formation in extraterrestrial environments where C60 crystals have been observed orbiting stars, leading to the speculation that fullerenes are more abundant than originally thought.

Harry Kroto, a Nobel Prize winner for the discovery of C60 and co-author of the current study, and now a professor at Florida State further noted in the release: “The results of our study will surely be extremely valuable in deciphering fullerene formation in extraterrestrial environments.” 

Colloidal Quantum Dot Solar Cells Break Conversion Efficiency Record

Over the years, this blog has reported on the work of Edward H. Sargent, and his research team at the University of Toronto, in employing colloidal quantum dots (CQD) for photovoltaics (PVs).

Last year, Sargent’s work, which had been backed by funding from the King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia, managed to develop a CQD multijunction PV that had a “graded recombination layer” that served as an interface between the visible and infrared junction, passing electrons between the two layers.

While being able to harvest both visible and invisible light with PVs was impressive, the PVs had comparatively low conversion efficiencies of 4.2 percent, which was significantly lower than the 5 percent levels that were the state of the art at the time for CQD multijunction PVs. Even with Sargent’s team reaching 6 percent with their CQD multijunction PVs later in the year,  it seemed there was still room for improvement, especially if you consider theoretical levels for CQDs of 42 percent.

Now Sargent and his team—along with both financial and research support from his Saudi backers at KAUST—have pushed the conversion efficiencies of these devices up to what they claim is a record-breaking 7 percent efficiency. 

The research, which was published in the journal Nature Nanotechnology in a paper titled “Hybrid passivated colloidal quantum dot solids” (available without a subscription),  looked at the problem of the high number of electron traps in the surfaces of CQD films. They determined that a hybrid passivation scheme could dramatically improve the combination of surface passivation and film density and thereby reduce the trap densities.

The "hybrid passivation scheme” consisted of introducing chlorine atoms to the quantum dots immediately after synthesizing them. This made it possible to coat areas on CQD films that had been unreachable before.

“Previously, quantum dot solar cells have been limited by the large internal surface areas of the nanoparticles in the film, which made extracting electricity difficult,” said lead co-author Susanna Thon, in a University of Toronto press release. “Our breakthrough was to use a combination of organic and inorganic chemistry to completely cover all of the exposed surfaces.” Thon is a post-doctoral fellow at the university.

The researchers believe that this latest 37-percent improvement in conversion efficiency for the CQD PVs represents a sign of things to come.

As Sargent further notes in the press release: “This work shows that the abundant materials interfaces inside colloidal quantum dots can be mastered in a robust manner, proving that low cost and steadily-improving efficiencies can be combined."

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
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Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
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