Tag Archives: Rice University

Gently measuring electrical signals in small animals with nano-SPEARs

This work comes from Rice University (Texas, US) according to an April 17, 2017 news item on Nanowerk,

Microscopic probes developed at Rice University have simplified the process of measuring electrical activity in individual cells of small living animals. The technique allows a single animal like a worm to be tested again and again and could revolutionize data-gathering for disease characterization and drug interactions.

The Rice lab of electrical and computer engineer Jacob Robinson has invented “nanoscale suspended electrode arrays” — aka nano-SPEARs — to give researchers access to electrophysiological signals from the cells of small animals without injuring them. Nano-SPEARs replace glass pipette electrodes that must be aligned by hand each time they are used.”

An April 17, 2017 Rice University news release (also on EurekAltert), which originated the news item, details the work,

“One of the experimental bottlenecks in studying synaptic behavior and degenerative diseases that affect the synapse is performing electrical measurements at those synapses,” Robinson said. “We set out to study large groups of animals under lots of different conditions to screen drugs or test different genetic factors that relate to errors in signaling at those synapses.”

Robinson’s early work at Rice focused on high-quality, high-throughput electrical characterization of individual cells. The new platform adapts the concept to probe the surface cells of nematodes, worms that make up 80 percent of all animals on Earth.

Most of what is known about muscle activity and synaptic transmission in the worms comes from the few studies that successfully used manually aligned glass pipettes to measure electrical activity from individual cells, Robinson said. However, this patch clamp technique requires time-consuming and invasive surgery that could negatively affect the data that is gathered from small research animals.

The platform developed by Robinson’s team works something like a toll booth for traveling worms. As each animal passes through a narrow channel, it is temporarily immobilized and pressed against one or several nano-SPEARS that penetrate its body-wall muscle and record electrical activity from nearby cells. That animal is then released, the next is captured and measured, and so on. Robinson said the device proved much faster to use than traditional electrophysiological cell measurement techniques.

The nano-SPEARs are created using standard thin-film deposition procedures and electron-beam or photolithography and can be made from less than 200 nanometers to more than 5 microns thick, depending on the size of animal to be tested. Because the nano-SPEARs can be fabricated on either silicon or glass, the technique easily combines with fluorescence microscopy, Robinson said.

The animals suitable for probing with a nano-SPEAR can be as large as several millimeters, like hydra, cousins of the jellyfish and the subject of an upcoming study. But nematodes known as Caenorhabditis elegans were practical for several reasons: First, Robinson said, they’re small enough to be compatible with microfluidic devices and nanowire electrodes. Second, there were a lot of them down the hall at the lab of Rice colleague Weiwei Zhong, who studies nematodes as transparent, easily manipulated models for signaling pathways that are common to all animals.

“I used to shy away from measuring electrophysiology because the conventional method of patch clamping is so technically challenging,” said Zhong, an assistant professor of biochemistry and cell biology and co-author of the paper. “Only a few graduate students or postdocs can do it. With Jacob’s device, even an undergraduate student can measure electrophysiology.”

“This meshes nicely with the high-throughput phenotyping she does,” Robinson said. “She can now correlate locomotive phenotypes with activity at the muscle cells. We believe that will be useful to study degenerative diseases centered around neuromuscular junctions.”

In fact, the labs have begun doing so. “We are now using this setup to profile worms with neurodegenerative disease models such as Parkinson’s and screen for drugs that reduce the symptoms,” Zhong said. “This would not be possible using the conventional method.”

Initial tests on C. elegans models for amyotrophic lateral sclerosis and Parkinson’s disease revealed for the first time clear differences in electrophysiological responses between the two, the researchers reported.

Testing the efficacy of drugs will be helped by the new ability to study small animals for long periods. “What we can do, for the first time, is look at electrical activity over a long period of time and discover interesting patterns of behavior,” Robinson said.

Some worms were studied for up to an hour, and others were tested on multiple days, said lead author Daniel Gonzales, a Rice graduate student in Robinson’s lab who took charge of herding nematodes through the microfluidic devices.

“It was in some way easier than working with isolated cells because the worms are larger and fairly sturdy,” Gonzales said. “With cells, if there’s too much pressure, they die. If they hit a wall, they die. But worms are really sturdy, so it was just a matter of getting them up against the electrodes and keeping them there.”

The team constructed microfluidic arrays with multiple channels that allowed testing of many nematodes at once. In comparison with patch-clamping techniques that limit labs to studying about one animal per hour, Robinson said his team measured as many as 16 nematodes per hour.

“Because this is a silicon-based technology, making arrays and producing recording chambers in high numbers becomes a real possibility,” he said.

A scanning electron micrograph shows a nano-SPEAR suspended midway between layers of silicon (grey) and photoresist material (pink) that form a recording chamber for immobilized nematodes. The high-throughput technology developed at Rice University can be adapted for other small animals and could enhance data-gathering for disease characterization and drug interactions. Courtesy of the Robinson Lab

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

Scalable electrophysiology in intact small animals with nanoscale suspended electrode arrays by Daniel L. Gonzales, Krishna N. Badhiwala, Daniel G. Vercosa, Benjamin W. Avants, Zheng Liu, Weiwei Zhong, & Jacob T. Robinson. Nature Nanotechnology (2017) doi:10.1038/nnano.2017.55 Published online 17 April 2017

This paper is behind a paywall.

Recycle electronic waste by crushing it into nanodust

Given the issues with e-waste this work seems quite exciting. From a March 21, 2017 Rice University news release (also on EurekAlert), Note: Links have been removed,

Researchers at Rice University and the Indian Institute of Science have an idea to simplify electronic waste recycling: Crush it into nanodust.

Specifically, they want to make the particles so small that separating different components is relatively simple compared with processes used to recycle electronic junk now.

Chandra Sekhar Tiwary, a postdoctoral researcher at Rice and a researcher at the Indian Institute of Science in Bangalore, uses a low-temperature cryo-mill to pulverize electronic waste – primarily the chips, other electronic components and polymers that make up printed circuit boards (PCBs) — into particles so small that they do not contaminate each other.

Then they can be sorted and reused, he said.

Circuit boards from electronics, like computer mice, can be crushed into nanodust by a cryo-mill, according to researchers at Rice and the Indian Institute of Science. The dust can then be easily separated into its component elements for recycling.

Circuit boards from electronics, like computer mice, can be crushed into nanodust by a cryo-mill, according to researchers at Rice and the Indian Institute of Science. The dust can then be easily separated into its component elements for recycling. Courtesy of the Ajayan Research Group

The process is the subject of a Materials Today paper by Tiwary, Rice materials scientist Pulickel Ajayan and Indian Institute professors Kamanio Chattopadhyay and D.P. Mahapatra. 

The researchers intend it to replace current processes that involve dumping outdated electronics into landfills, or burning or treating them with chemicals to recover valuable metals and alloys. None are particularly friendly to the environment, Tiwary said.

“In every case, the cycle is one way, and burning or using chemicals takes a lot of energy while still leaving waste,” he said. “We propose a system that breaks all of the components – metals, oxides and polymers – into homogenous powders and makes them easy to reuse.”

The researchers estimate that so-called e-waste will grow by 33 percent over the next four years, and by 2030 will weigh more than a billion tons. Nearly 80 to 85 percent of often-toxic e-waste ends up in an incinerator or a landfill, Tiwary said, and is the fastest-growing waste stream in the United States, according to the Environmental Protection Agency.

The answer may be scaled-up versions of a cryo-mill designed by the Indian team that, rather than heating them, keeps materials at ultra-low temperatures during crushing.

Cold materials are more brittle and easier to pulverize, Tiwary said. “We take advantage of the physics. When you heat things, they are more likely to combine: You can put metals into polymer, oxides into polymers. That’s what high-temperature processing is for, and it makes mixing really easy.

A transparent piece of epoxy, left, compared to epoxy with e-waste reinforcement at right. A cryo-milling process developed at Rice University and the Indian Institute of Science simplifies the process of separating and recycling electronic waste.

A transparent piece of epoxy, left, compared to epoxy with e-waste reinforcement at right. A cryo-milling process developed at Rice University and the Indian Institute of Science simplifies the process of separating and recycling electronic waste. Courtesy of the Ajayan Research Group

“But in low temperatures, they don’t like to mix. The materials’ basic properties – their elastic modulus, thermal conductivity and coefficient of thermal expansion – all change. They allow everything to separate really well,” he said.

The test subjects in this case were computer mice – or at least their PCB innards. The cryo-mill contained argon gas and a single tool-grade steel ball. A steady stream of liquid nitrogen kept the container at 154 kelvins (minus 182 degrees Fahrenheit).

When shaken, the ball smashes the polymer first, then the metals and then the oxides just long enough to separate the materials into a powder, with particles between 20 and 100 nanometers wide. That can take up to three hours, after which the particles are bathed in water to separate them.

“Then they can be reused,” he said. “Nothing is wasted.”

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

Electronic waste recycling via cryo-milling and nanoparticle beneficiation by C.S. Tiwary, S. Kishore, R. Vasireddi, D.R. Mahapatra, P.M. Ajayan, K. Chattopadhyay. Materials Today         http://dx.doi.org/10.1016/j.mattod.2017.01.015 Available online 20 March 2017

This paper is behind a paywall.

Nanocar Race winners: The US-Austrian team

Sadly, I didn’t stumble across the news about the US-Austrian team sooner but it was not published until a May 8, 2017 news item on Nanowerk,

Rice University chemist James Tour and his international team have won the first Nanocar Race.

The Rice and University of Graz team finished first in the inaugural Nanocar Race in Toulouse, France, April 28, completing a 150-nanometer course — roughly a thousandth of the width of a human hair — in about 1½ hours. (The race was declared over after 30 hours.)

Interestingly the Rice University news release announcing the win was issued prior to the ‘winning’ Swiss team’s and it explains why the Swiss team was declared a co-winner despite the additional hours (6.5 hours as compared to 1.5 hours [see my May 9, 2017 posting: Nanocar Race winners! where the Swiss appear to claiming they raced 38 hours]) before completing the race. From an April 28, 2017 Rice University news release,

The team led by Tour and Graz physicist Leonhard Grill deployed a two-wheeled, single-molecule vehicle with adamantane tires on its home track in Graz, Austria, achieving an average speed of 95 nanometers per hour. Tour said the speed ranged from more than 300 to less than 1 nanometer per hour, depending upon the location along the course.

The Swiss Nano Dragster team finished next, five hours later. But organizers at the French National Center for Scientific Research declared them a co-winner of first place as they were tops among teams that raced on a gold track.

Because the scanning tunneling microscope track in Toulouse could only accommodate four cars, two of the six competing international teams — Ohio University and Rice-Graz — ran their vehicles on their home tracks (Ohio on gold) and operated them remotely from the Toulouse headquarters.

The Dipolar Racer designed at Rice.

The Dipolar Racer designed at Rice.

Five cars were driven across gold surfaces in a vacuum near absolute zero by electrons from the tips of microscopes in Toulouse and Ohio, but the Rice-Graz team got permission to use a silver track at Graz. “Gold was the surface of choice, so we tested it there, but it turns out it’s too fast,” Grill said. “It’s so fast, we can’t even image it.”

The team got permission from organizers in advance of the race to use the slower silver surface, but with an additional handicap. “We had to go 150 nanometers around two pylons instead of 100 nanometers since our car was so much faster,” Tour said.

Tour said the race directors used the Paris-Rouen auto race in 1894, considered by some to be the world’s first auto race, as precedent for their decision April 29. “I am told there will be two first prizes regardless of the time difference and handicap,” he said.

The Rice-Graz car, called the Dipolar Racer, was designed by Tour and former Rice graduate student Victor Garcia-Lopez and raced by the Graz team, which included postdoctoral researcher and pilot Grant Simpson and undergraduate and co-pilot Philipp Petermeier.

The silver track under the microscope. Two Rice nanocars are in the blue circle at top. The lower car was the first to run the race, finishing in an hour-and-a-half. The top car was put through the course later, finishing in 2 hours.

The silver track under the microscope. Two Rice nanocars are in the blue circle at top. The lower car was the first to run the race, finishing in a 1½ hours. The top car was put through the course later, finishing in 2 hours. Click on the image for a larger version.

The purpose of the competition, according to organizers, was to push the science of how single molecules can be manipulated as they interact with surfaces.

“We chose our fastest wheels and our strongest dipole so that it could be pulled by the electric field more efficiently,” said Tour, whose lab has been designing nanocars since 1998. ‘We gave it two (side-by-side) wheels to minimize interaction with the surface and to lower the molecular weight.

“We built in every possible design parameter that we could to optimize speed,” he said.

While details of the Dipolar Racer remained a closely held secret until race time, Tour and Grill said they will be revealed in a forthcoming paper.

“This is the beginning of our ability to demonstrate nanoscale manipulation with control around obstacles and speed and will pave the way for much faster paces and eventually for carrying cargo and doing bottom-up assembly.

“It’s a great day for nanotechnology,” Tour said. “And a great day for Rice University and the University of Graz.”

Clearly all the winners were very excited. Still, there’s a little shade being thrown (one of the scientists is just a tiny bit miffed) as you can see in James Tour’s quote given after noting the US-Austrian racer was too fast for the gold surface so the team used the slower silver surface and were given another handicap. As per the Rice University news release: ““I am told [emphasis mine] there will be two first prizes regardless of the time difference and handicap,” he said.” Of course, the Swiss team’s news release didn’t mention the US-Austrian team’s speedier finish nor did it name (Dipolar Racer) the US-Austrian racer. As I noted before, scientists are people too.

Multicolor, electrochromic glass

Electrochromic (changes color to block light and heat) glass could prove to be a significant market by 2020 according to a March 8, 2017 news item on phys.org,

Rice University’s latest nanophotonics research could expand the color palette for companies in the fast-growing market for glass windows that change color at the flick of an electric switch.

In a new paper in the American Chemical Society journal ACS Nano, researchers from the laboratory of Rice plasmonics pioneer Naomi Halas report using a readily available, inexpensive hydrocarbon molecule called perylene to create glass that can turn two different colors at low voltages.

“When we put charges on the molecules or remove charges from them, they go from clear to a vivid color,” said Halas, director of the Laboratory for Nanophotonics (LANP), lead scientist on the new study and the director of Rice’s Smalley-Curl Institute. “We sandwiched these molecules between glass, and we’re able to make something that looks like a window, but the window changes to different types of color depending on how we apply a very low voltage.”

Adam Lauchner, an applied physics graduate student at Rice and co-lead author of the study, said LANP’s color-changing glass has polarity-dependent colors, which means that a positive voltage produces one color and a negative voltage produces a different color.

“That’s pretty novel,” Lauchner said. “Most color-changing glass has just one color, and the multicolor varieties we’re aware of require significant voltage.”

Glass that changes color with an applied voltage is known as “electrochromic,” and there’s a growing demand for the light- and heat-blocking properties of such glass. The projected annual market for electrochromic glass in 2020 has been estimated at more $2.5 billion.

A March 8, 2017 Rice University news release (also on EurekAlert), which originated the news item, provides more detail about the research,

Lauchner said the glass project took almost two years to complete, and he credited co-lead author Grant Stec, a Rice undergraduate researcher, with designing the perylene-containing nonwater-based conductive gel that’s sandwiched between glass layers.

“Perylene is part of a family of molecules known as polycyclic aromatic hydrocarbons,” Stec said. “They’re a fairly common byproduct of the petrochemical industry, and for the most part they are low-value byproducts, which means they’re inexpensive.”

Grant Stec and Adam Lauchner

Grant Stec and Adam Lauchner of Rice University’s Laboratory for Nanophotonics have used an inexpensive hydrocarbon molecule called perylene to create a low-voltage, multicolor, electrochromic glass. (Photo by Jeff Fitlow/Rice University)

There are dozens of polycyclic aromatic hydrocarbons (PAHs), but each contains rings of carbon atoms that are decorated with hydrogen atoms. In many PAHs, carbon rings have six sides, just like the rings in graphene, the much-celebrated subject of the 2010 Nobel Prize in physics.

“This is a really cool application of what started as fundamental science in plasmonics,” Lauchner said.

A plasmon is [a] wave of energy, a rhythmic sloshing in the sea of electrons that constantly flow across the surface of conductive nanoparticles. Depending upon the frequency of a plasmon’s sloshing, it can interact with and harvest the energy from passing light. In dozens of studies over the past two decades, Halas, Rice physicist Peter Nordlander and colleagues have explored both the basic physics of plasmons and potential applications as diverse as cancer treatment, solar-energy collection, electronic displays and optical computing.

The quintessential plasmonic nanoparticle is metallic, often made of gold or silver, and precisely shaped. For example, gold nanoshells, which Halas invented at Rice in the 1990s, consist of a nonconducting core that’s covered by a thin shell of gold.

Grant Stec, Naomi Halas and Adam Lauchner

Student researchers Grant Stec (left) and Adam Lauchner (right) with Rice plasmonics pioneer Naomi Halas, director of Rice University’s Laboratory for Nanophotonics. (Photo by Jeff Fitlow/Rice University)

“Our group studies many kinds of metallic nanoparticles, but graphene is also conductive, and we’ve explored its plasmonic properties for several years,” Halas said.

She noted that large sheets of atomically thin graphene have been found to support plasmons, but they emit infrared light that’s invisible to the human eye.

“Studies have shown that if you make graphene smaller and smaller, as you go down to nanoribbons, nanodots and these little things called nanoislands, you can actually get graphene’s plasmon closer and closer to the edge of the visible regime,” Lauchner said.

In 2013, then-Rice physicist Alejandro Manjavacas, a postdoctoral researcher in Nordlander’s lab, showed that the smallest versions of graphene — PAHs with just a few carbon rings — should produce visible plasmons. Moreover, Manjavacas calculated the exact colors that would be emitted by different types of PAHs.

“One of the most interesting things was that unlike plasmons in metals, the plasmons in these PAH molecules were very sensitive to charge, which suggested that a very small electrical charge would produce dramatic colors,” Halas said.

Electrochromic glass that glass that turns from clear to black

Rice University researchers demonstrated a new type of glass that turns from clear to black when a low voltage is applied. The glass uses a combination of molecules that block almost all visible light when they each gain a single electron. (Photo by Jeff Fitlow/Rice University)

Lauchner said the project really took off after Stec joined the research team in 2015 and created a perylene formulation that could be sandwiched between sheets of conductive glass.

In their experiments, the researchers found that applying just 4 volts was enough to turn the clear window greenish-yellow and applying negative 3.5 volts turned it blue. It took several minutes for the windows to fully change color, but Halas said the transition time could easily be improved with additional engineering.

Stec said the team’s other window, which turns from clear to black, was produced later in the project.

“Dr. Halas learned that one of the major hurdles in the electrochromic device industry was making a window that could be clear in one state and completely black in another,” Stec said. “We set out to do that and found a combination of PAHs that captured no visible light at zero volts and almost all visible light at low voltage.”

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

Multicolor Electrochromic Devices Based on Molecular Plasmonics by Grant J. Stec, Adam Lauchner, Yao Cui, Peter Nordlander, and Naomi J. Halas. ACS Nano, Article ASAP DOI: 10.1021/acsnano.7b00364 Publication Date (Web): February 22, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Nano-chimneys to cut down heat

Heat is always a problem with electronics—even nanoelectronics. Scientists at Rice University (US) believe they may have a solution for nanoelectronics heat problems, according to a Jan. 4, 2017 news item on ScienceDaily,

A few nanoscale adjustments may be all that is required to make graphene-nanotube junctions excel at transferring heat, according to Rice University scientists.

The Rice lab of theoretical physicist Boris Yakobson found that putting a cone-like “chimney” between the graphene and [carbon] nanotube all but eliminates a barrier that blocks heat from escaping.

Caption: Simulations by Rice University scientists show that placing cones between graphene and carbon nanotubes could enhance heat dissipation from nano-electronics. The nano-chimneys become better at conducting heat-carrying phonons by spreading out the number of heptagons required by the graphene-to-nanotube transition. Credit: Alex Kutana/Rice University

A Jan. 4, 2016 Rice University news release (also on EurekAlert), which originated the news item, describes the research in more detail,

Heat is transferred through phonons, quasiparticle waves that also transmit sound. The Rice theory offers a strategy to channel damaging heat away from next-generation nano-electronics.

Both graphene and carbon nanotubes consist of six-atom rings, which create a chicken-wire appearance, and both excel at the rapid transfer of electricity and phonons.

But when a nanotube grows from graphene, atoms facilitate the turn by forming heptagonal (seven-member) rings instead. Scientists have determined that forests of nanotubes grown from graphene are excellent for storing hydrogen for energy applications, but in electronics, the heptagons scatter phonons and hinder the escape of heat through the pillars.

The Rice researchers discovered through computer simulations that removing atoms here and there from the two-dimensional graphene base would force a cone to form between the graphene and the nanotube. The geometric properties (aka topology) of the graphene-to-cone and cone-to-nanotube transitions require the same total number of heptagons, but they are more sparsely spaced and leave a clear path of hexagons available for heat to race up the chimney.

“Our interest in advancing new applications for low-dimensional carbon — fullerenes, nanotubes and graphene — is broad,” Yakobson said. “One way is to use them as building blocks to fill three-dimensional spaces with different designs, creating anisotropic, nonuniform scaffolds with properties that none of the current bulk materials have. In this case, we studied a combination of nanotubes and graphene, connected by cones, motivated by seeing such shapes obtained in our colleagues’ experimental labs.”

The researchers tested phonon conduction through simulations of free-standing nanotubes, pillared graphene and nano-chimneys with a cone radius of either 20 or 40 angstroms. The pillared graphene was 20 percent less conductive than plain nanotubes. The 20-angstrom nano-chimneys were just as conductive as plain nanotubes, while 40-angstrom cones were 20 percent better than the nanotubes.

“The tunability of such structures is virtually limitless, stemming from the vast combinatorial possibilities of arranging the elementary modules,” said Alex Kutana, a Rice research scientist and co-author of the study. “The actual challenge is to find the most useful structures given a vast number of possibilities and then make them in the lab reliably.

“In the present case, the fine-tuning parameters could be cone shapes and radii, nanotube spacing, lengths and diameters. Interestingly, the nano-chimneys also act like thermal diodes, with heat flowing faster in one direction than the other,” he said.

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

Nanochimneys: Topology and Thermal Conductance of 3D Nanotube–Graphene Cone Junctions by Ziang Zhang, Alex Kutana, Ajit Roy, and Boris I. Yakobson. J. Phys. Chem. C, Article ASAP DOI: 10.1021/acs.jpcc.6b11350 Publication Date (Web): December 21, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Kinetic properties of cement at the nanoscale

There was a Vancouver-born architect, Arthur Erickson, who adored concrete as a building material. In fact, he gained an international reputation for his ‘concrete’ work. I have never been a fan, especially after attending Simon Fraser University (one of Erickson’s early triumphs) in Vancouver (Canada) and experiencing the joy of deteriorating concrete structures.

This somewhat related news concerns cement, (from a Dec.7, 2016 news item on ScienceDaily,

Bringing order to disorder is key to making stronger and greener cement, the paste that binds concrete.

Scientists at Rice University have decoded the kinetic properties of cement and developed a way to “program” the microscopic, semicrystalline particles within. The process turns particles from disordered clumps into regimented cubes, spheres and other forms that combine to make the material less porous and more durable.

A Dec. 7, 2016 Rice University news release, which originated the news item, explains further (Note: Links have been removed),

The technique may lead to stronger structures that require less concrete – and less is better, said Rice materials scientist and lead author Rouzbeh Shahsavari. Worldwide production of more than 3 billion tons of concrete a year now emits as much as 10 percent of the carbon dioxide, a greenhouse gas, released to the atmosphere.

Through extensive experiments, Shahsavari and his colleagues decoded the nanoscale reactions — or “morphogenesis” — of the crystallization within calcium-silicate hydrate (C-S-H) cement that holds concrete together.

For the first time, they synthesized C-S-H particles in a variety of shapes, including cubes, rectangular prisms, dendrites, core-shells and rhombohedra and mapped them into a unified morphology diagram for manufacturers and builders who wish to engineer concrete from the bottom up.

“We call it programmable cement,” he said. “The great advance of this work is that it’s the first step in controlling the kinetics of cement to get desired shapes. We show how one can control the morphology and size of the basic building blocks of C-S-H so that they can self-assemble into microstructures with far greater packing density compared with conventional amorphous C-S-H microstructures.”

He said the idea is akin to the self-assembly of metallic crystals and polymers. “It’s a hot area, and researchers are taking advantage of it,” Shahsavari said. “But when it comes to cement and concrete, it is extremely difficult to control their bottom-up assembly. Our work provides the first recipe for such advanced synthesis.

“The seed particles form first, automatically, in our reactions, and then they dominate the process as the rest of the material forms around them,” he said. “That’s the beauty of it. It’s in situ, seed-mediated growth and does not require external addition of seed particles, as commonly done in the industry to promote crystallization and growth.”

Previous techniques to create ordered crystals in C-S-H required high temperatures or pressures, prolonged reaction times and the use of organic precursors, but none were efficient or environmentally benign, Shahsavari said.

The Rice lab created well-shaped cubes and rectangles by adding small amounts of positive or negative ionic surfactants and calcium silicate to C-S-H and exposing the mix to carbon dioxide and ultrasonic sound. The crystal seeds took shape around surfactant micelles within 25 minutes. Decreasing the calcium silicate yielded more spherical particles and smaller cubes, while increasing it formed clumped spheres and interlocking cubes.

Once the calcite “seeds” form, they trigger the molecules around them to self-assemble into cubes, spheres and other shapes that are orders of magnitude larger. These can pack more tightly together in concrete than amorphous particles, Shahsavari said. Carefully modulating the precursor concentration, temperature and duration of the reaction varies the yield, size and morphology of the final particles.

The discovery is an important step in concrete research, he said. It builds upon his work as part of the Massachusetts Institute of Technology team that decoded cement’s molecular “DNA” in 2009. “There is currently no control over C-S-H shape,” Shahsavari said. “The concrete used today is an amorphous colloid with significant porosity that entails reduced strength and durability.”

Concrete is one focus of Shahsavari’s Rice lab, which has studied both its macroscale manufacture and intrinsic nanoscale properties. Because concrete is the world’s most common construction material and a significant source of atmospheric carbon dioxide, he is convinced of the importance of developing “greener” concrete.

The new technique has several environmental benefits, Shahsavari said. “One is that you need less of it (the concrete) because it is stronger. This stems from better packing of the cubic particles, which leads to stronger microstructures. The other is that it will be more durable. Less porosity makes it harder for unwanted chemicals to find a path through the concrete, so it does a better job of protecting steel reinforcement inside.”

The research required the team to develop a method to test microscopic concrete particles for strength. The researchers used a diamond-tipped nanoindenter to crush single cement particles with a flat edge.

They programmed the indenter to move from one nanoparticle to the next and crush it and gathered mechanical data on hundreds of particles of various shapes in one run. “Other research groups have tested bulk cement and concrete, but no group had ever probed the mechanics of single C-S-H particles and the effect of shape on mechanics of individual particles,” Shahsavari said.

He said strategies developed during the project could have implications for other applications, including bone tissue engineering, drug delivery and refractory materials, and could impact such other complex systems as ceramics and colloids.

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

Morphogenesis of Cement Hydrate by Sakineh E Moghaddam, vahid hejazi, Sung Hoon Hwang, Sreeprasad Srinavasan, Joseph B. Miller, Benhang Shi, Shuo Zhao, Irene Rusakova, Aali R. Alizadeh, Kenton Whitmire and Rouzbeh Shahsavari. J. Mater. Chem. A, 2016, DOI: 10.1039/C6TA09389B First published online 30 Nov 2016

I believe this paper is behind a paywall.

The brittleness of molybdenum diselenide

With the finding that molybdenum diselenide is not as strong as previously believed, industry may want to reconsider 2D materials before incorporating them in new products according to a Rice University (Texas, US) scientist. From a Nov. 14, 2016 news item on Nanowerk,

Scientists at Rice University have discovered that an atom-thick material being eyed for flexible electronics and next-generation optical devices is more brittle than they expected.

The Rice team led by materials scientist Jun Lou tested the tensile strength of two-dimensional, semiconducting molybdenum diselenide and discovered that flaws as small as one missing atom can initiate catastrophic cracking under strain.

The finding may cause industry to look more carefully at the properties of 2-D materials before incorporating them in new technologies, he said.

 

A Nov. 14, 2016 Rice University news release (also on EurekAlert), which originated the news item, provides more insight into the research,

“It turns out not all 2-D crystals are equal,” said Lou, a Rice professor of materials science and nanoengineering. “Graphene is a lot more robust compared with some of the others we’re dealing with right now, like this molybdenum diselenide. We think it has something to do with defects inherent to these materials.”

The defects could be as small as a single atom that leaves a vacancy in the crystalline structure, he said. “It’s very hard to detect them,” he said. “Even if a cluster of vacancies makes a bigger hole, it’s difficult to find using any technique. It might be possible to see them with a transmission electron microscope, but that would be so labor-intensive that it wouldn’t be useful.”

Molybdenum diselenide is a dichalcogenide, a two-dimensional semiconducting material that appears as a graphene-like hexagonal array from above but is actually a sandwich of metallic atoms between two layers of chalcogen atoms, in this case, selenium. Molybdenum diselenide is being considered for use as transistors and in next-generation solar cells, photodetectors and catalysts as well as electronic and optical devices.

Lou and colleagues measured the material’s elastic modulus, the amount of stretching a material can handle and still return to its initial state, at 177.2 (plus or minus 9.3) gigapascals. Graphene is more than five times as elastic. They attributed the large variation to pre-existing flaws of between 3.6 and 77.5 nanometers.

Its fracture strength, the amount of stretching a material can handle before breaking, was measured at 4.8 (plus or minus 2.9) gigapascals. Graphene is nearly 25 times stronger.

Part of the project led by Rice postdoctoral researcher Yingchao Yang required moving molybdenum diselenide from a growth chamber in a chemical vapor deposition furnace to a microscope without introducing more defects. Yang solved the problem using a dry transfer process in place of a standard acid washing that would have ruined the samples.

To test samples, Yang placed rectangles of molybdenum diselenide onto a sensitive electron microscope platform invented by the Lou group. Natural van der Waals forces held the samples in place on springy cantilever arms that measured the applied stress.

Lou said the group attempted to measure the material’s fracture toughness, an indicator of how likely cracks are to propagate, as they had in an earlier study on graphene. But they found that pre-cutting cracks into molybdenum diselenide resulted in it shattering before stress could be applied, he said.

“The important message of this work is the brittle nature of these materials,” Lou said. “A lot of people are thinking about using 2-D crystals because they’re inherently thin. They’re thinking about flexible electronics because they are semiconductors and their theoretical elastic strength should be very high. According to our calculations, they can be stretched up to 10 percent.

“But in reality, because of the inherent defects, you rarely can achieve that much strength. The samples we have tested so far broke at 2 to 3 percent (of the theoretical maximum) at most,” Lou said. “That should still be fine for most flexible applications, but unless they find a way to quench the defects, it will be very hard to achieve the theoretical limits.”

 

When seen from above, the atoms in two-dimensional molybdenum diselenide resemble a hexagonal grid, like graphene. But in reality, the darker molybdenum atoms are sandwiched between top and bottom layers of selenide atoms. Rice University researchers tested the material for its tensile strength. Courtesy of the Lou Group

When seen from above, the atoms in two-dimensional molybdenum diselenide resemble a hexagonal grid, like graphene. But in reality, the darker molybdenum atoms are sandwiched between top and bottom layers of selenide atoms. Rice University researchers tested the material for its tensile strength. Courtesy of the Lou Group

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

 

Brittle Fracture of 2D MoSe2 by Yingchao Yang, Xing Li, Minru Wen, Emily Hacopian, Weibing Chen, Yongji Gong, Jing Zhang, Bo Li, Wu Zhou, Pulickel M. Ajayan, Qing Chen, Ting Zhu, and Jun Lou. Advanced Materials DOI: 10.1002/adma.201604201 Version of Record online: 3 NOV 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

A new graphene-based contrast agent for magnetic resonance imaging (MRI)

After teaching a continuing studies course on bioelectronics for Simon Fraser University (Vancouver, Canada), I’ve developed a mild interest in magnetic resonance imaging and contrast agents which this Nov. 11, 2016 news item on phys.org satisfies,

Graphene, the atomically thin sheets of carbon that materials scientists are hoping to use for everything from nanoelectronics and aircraft de-icers to batteries and bone implants, may also find use as contrast agents for magnetic resonance imaging (MRI), according to new research from Rice University.

“They have a lot of advantages compared with conventionally available contrast agents,” Rice researcher Sruthi Radhakrishnan said of the graphene-based quantum dots she has studied for the past two years. “Virtually all of the widely used contrast agents contain toxic metals, but our material has no metal. It’s just carbon, hydrogen, oxygen and fluorine, and in all of our tests so far it has shown no signs of toxicity.”

The initial findings for Rice’s nanoparticles—disks of graphene that are decorated with fluorine atoms and simply organic molecules that make them magnetic—are described in a new paper in the journal Particle and Particle Systems characterization.

A Nov. 10, 2016 Rice University (Texas, US) news release, which originated the news item, describes the work in more detail,

Pulickel Ajayan, the Rice materials scientist who is directing the work, said the fluorinated graphene oxide quantum dots could be particularly useful as MRI contrast agents because they could be targeted to specific kinds of tissues.

“There are tried-and-true methods for attaching biomarkers to carbon nanoparticles, so one could easily envision using these quantum dots to develop tissue-specific contrast agents,” Ajayan said. “For example, this method could be used to selectively target specific types of cancer or brain lesions caused by Alzheimer’s disease. That kind of specificity isn’t available with today’s contrast agents.”

MRI scanners make images of the body’s internal structures using strong magnetic fields and radio waves. As diagnostic tests, MRIs often provide greater detail than X-rays without the harmful radiation, and as a result, MRI usage has risen sharply over the past decade. More than 30 million MRIs are performed annually in the U.S.

Radhakrishnan said her work began in 2014 after Ajayan’s research team found that adding fluorine to either graphite or graphene caused the materials to show up well on MRI scans.

All materials are influenced by magnetic fields, including animal tissues. In MRI scanners, a powerful magnetic field causes individual atoms throughout the body to become magnetically aligned. A pulse of radio energy is used to disrupt this alignment, and the machine measures how long it takes for the atoms in different parts of the body to become realigned. Based on these measures, the scanner can build up a detailed image of the body’s internal structures.

MRI contrast agents shorten the amount of time it takes for tissues to realign and significantly improve the resolution of MRI scans. Almost all commercially available contrast agents are made from toxic metals like gadolinium, iron or manganese.

“We worked with a team from MD Anderson Cancer Center to assess the cytocompatibility of fluorinated graphene oxide quantum dots,” Radhakrishnan said. “We used a test that measures the metabolic activity of cell cultures and detects toxicity as a drop in metabolic activity. We incubated quantum dots in kidney cell cultures for up to three days and found no significant cell death in the cultures, even at the highest concentrations.”

The fluorinated graphene oxide quantum dots Radhakrishnan studies can be made in less than a day, but she spent two years perfecting the recipe for them. She begins with micron-sized sheets of graphene that have been fluorinated and oxidized. When these are added to a solvent and stirred for several hours, they break into smaller pieces. Making the material smaller is not difficult, but the process for making small particles with the appropriate magnetic properties is exacting. Radhakrishnan said there was no “eureka moment” in which she suddenly achieved the right results by stumbling on the best formula. Rather, the project was marked by incremental improvements through dozens of minor alterations.

“It required a lot of optimization,” she said. “The recipe matters a lot.”

Radhakrishnan said she plans to continue studying the material and hopes to eventually have a hand in proving that it is safe and effective for clinical MRI tests.

“I would like to see it applied commercially in clinical ways because it has a lot of advantages compared with conventionally available agents,” she said.

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

Metal-Free Dual Modal Contrast Agents Based on Fluorographene Quantum Dots by Sruthi Radhakrishnan, Atanu Samanta, Parambath M. Sudeep, Kiersten L. Maldonado, Sendurai A. Mani, Ghanashyam Acharya, Chandra Sekhar Tiwary, Abhishek K. Singh, and Pulickel M. Ajayan. Particle & Particle Systems Characterization DOI: 10.1002/ppsc.201600221 Version of Record online: 21 OCT 2016

This paper is behind a paywall.

Boron nitride-graphene hybrid nanostructures could lead to next generation ‘green’ cars

An Oct. 24, 2016 phys.org news item describes research which may lead to improved fuel storage in ‘green’ cars,

Layers of graphene separated by nanotube pillars of boron nitride may be a suitable material to store hydrogen fuel in cars, according to Rice University scientists.

The Department of Energy has set benchmarks for storage materials that would make hydrogen a practical fuel for light-duty vehicles. The Rice lab of materials scientist Rouzbeh Shahsavari determined in a new computational study that pillared boron nitride and graphene could be a candidate.

An Oct. 24, 2016 Rice University news release (also on EurekAlert), which originated the news item, provides more detail (Note: Links have been removed),

Shahsavari’s lab had already determined through computer models how tough and resilient pillared graphene structures would be, and later worked boron nitride nanotubes into the mix to model a unique three-dimensional architecture. (Samples of boron nitride nanotubes seamlessly bonded to graphene have been made.)

Just as pillars in a building make space between floors for people, pillars in boron nitride graphene make space for hydrogen atoms. The challenge is to make them enter and stay in sufficient numbers and exit upon demand.

In their latest molecular dynamics simulations, the researchers found that either pillared graphene or pillared boron nitride graphene would offer abundant surface area (about 2,547 square meters per gram) with good recyclable properties under ambient conditions. Their models showed adding oxygen or lithium to the materials would make them even better at binding hydrogen.

They focused the simulations on four variants: pillared structures of boron nitride or pillared boron nitride graphene doped with either oxygen or lithium. At room temperature and in ambient pressure, oxygen-doped boron nitride graphene proved the best, holding 11.6 percent of its weight in hydrogen (its gravimetric capacity) and about 60 grams per liter (its volumetric capacity); it easily beat competing technologies like porous boron nitride, metal oxide frameworks and carbon nanotubes.

At a chilly -321 degrees Fahrenheit, the material held 14.77 percent of its weight in hydrogen.

The Department of Energy’s current target for economic storage media is the ability to store more than 5.5 percent of its weight and 40 grams per liter in hydrogen under moderate conditions. The ultimate targets are 7.5 weight percent and 70 grams per liter.

Shahsavari said hydrogen atoms adsorbed to the undoped pillared boron nitride graphene, thanks to  weak van der Waals forces. When the material was doped with oxygen, the atoms bonded strongly with the hybrid and created a better surface for incoming hydrogen, which Shahsavari said would likely be delivered under pressure and would exit when pressure is released.

“Adding oxygen to the substrate gives us good bonding because of the nature of the charges and their interactions,” he said. “Oxygen and hydrogen are known to have good chemical affinity.”

He said the polarized nature of the boron nitride where it bonds with the graphene and the electron mobility of the graphene itself make the material highly tunable for applications.

“What we’re looking for is the sweet spot,” Shahsavari said, describing the ideal conditions as a balance between the material’s surface area and weight, as well as the operating temperatures and pressures. “This is only practical through computational modeling, because we can test a lot of variations very quickly. It would take experimentalists months to do what takes us only days.”

He said the structures should be robust enough to easily surpass the Department of Energy requirement that a hydrogen fuel tank be able to withstand 1,500 charge-discharge cycles.

Shayeganfar [Farzaneh Shayeganfar], a former visiting scholar at Rice, is an instructor at Shahid Rajaee Teacher Training University in Tehran, Iran.

 

Caption: Simulations by Rice University scientists show that pillared graphene boron nitride may be a suitable storage medium for hydrogen-powered vehicles. Above, the pink (boron) and blue (nitrogen) pillars serve as spacers for carbon graphene sheets (gray). The researchers showed the material worked best when doped with oxygen atoms (red), which enhanced its ability to adsorb and desorb hydrogen (white). Credit: Lei Tao/Rice University

Caption: Simulations by Rice University scientists show that pillared graphene boron nitride may be a suitable storage medium for hydrogen-powered vehicles. Above, the pink (boron) and blue (nitrogen) pillars serve as spacers for carbon graphene sheets (gray). The researchers showed the material worked best when doped with oxygen atoms (red), which enhanced its ability to adsorb and desorb hydrogen (white). Credit: Lei Tao/Rice University

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

Oxygen and Lithium Doped Hybrid Boron-Nitride/Carbon Networks for Hydrogen Storage by Farzaneh Shayeganfar and Rouzbeh Shahsavari. Langmuir,  DOI: 10.1021/acs.langmuir.6b02997 Publication Date (Web): October 23, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

I last featured research by Shayeganfar and  Shahsavari on graphene and boron nitride in a Jan. 14, 2016 posting.

Nanorods as multistate switches

This research goes beyond the binary (0 or 1) and to an analog state that resembles quantum states. Fascinating, yes? An Oct. 10, 2016 news item on phys.org tells more,

Rice University scientists have discovered how to subtly change the interior structure of semi-hollow nanorods in a way that alters how they interact with light, and because the changes are reversible, the method could form the basis of a nanoscale switch with enormous potential.

“It’s not 0-1, it’s 1-2-3-4-5-6-7-8-9-10,” said Rice materials scientist Emilie Ringe, lead scientist on the project, which is detailed in the American Chemical Society journal Nano Letters. “You can differentiate between multiple plasmonic states in a single particle. That gives you a kind of analog version of quantum states, but on a larger, more accessible scale.”

Ringe and colleagues used an electron beam to move silver from one location to another inside gold-and-silver nanoparticles, something like a nanoscale Etch A Sketch. The result is a reconfigurable optical switch that may form the basis for a new type of multiple-state computer memory, sensor or catalyst.

An Oct. 10, 2016 Rice University news release, which originated the news item, describes the work in additional detail,

At about 200 nanometers long, 500 of the metal rods placed end-to-end would span the width of a human hair. However, they are large in comparison with modern integrated circuits. Their multistate capabilities make them more like reprogrammable bar codes than simple memory bits, she said.

“No one has been able to reversibly change the shape of a single particle with the level of control we have, so we’re really excited about this,” Ringe said.

Altering a nanoparticle’s internal structure also alters its external plasmonic response. Plasmons are the electrical ripples that propagate across the surface of metallic materials when excited by light, and their oscillations can be easily read with a spectrometer — or even the human eye — as they interact with visible light.

The Rice researchers found they could reconfigure nanoparticle cores with pinpoint precision. That means memories made of nanorods need not be merely on-off, Ringe said, because a particle can be programmed to emit many distinct plasmonic patterns.

The discovery came about when Ringe and her team, which manages Rice’s advanced electron microscopy lab, were asked by her colleague and co-author Denis Boudreau, a professor at Laval University in Quebec, to characterize hollow nanorods made primarily of gold but containing silver.

“Most nanoshells are leaky,” Ringe said. “They have pinholes. But we realized these nanorods were defect-free and contained pockets of water that were trapped inside when the particles were synthesized. We thought: We have something here.”

Ringe and the study’s lead author, Rice research scientist Sadegh Yazdi, quickly realized how they might manipulate the water. “Obviously, it’s difficult to do chemistry there, because you can’t put molecules into a sealed nanoshell. But we could put electrons in,” she said.

Focusing a subnanometer electron beam on the interior cavity split the water and inserted solvated electrons – free electrons that can exist in a solution. “The electrons reacted directly with silver ions in the water, drawing them to the beam to form silver,” Ringe said. The now-silver-poor liquid moved away from the beam, and its silver ions were replenished by a reaction of water-splitting byproducts with the solid silver in other parts of the rod.

“We actually were moving silver in the solution, reconfiguring it,” she said. “Because it’s a closed system, we weren’t losing anything and we weren’t gaining anything. We were just moving it around, and could do so as many times as we wished.”

The researchers were then able to map the plasmon-induced near-field properties without disturbing the internal structure — and that’s when they realized the implications of their discovery.

“We made different shapes inside the nanorods, and because we specialize in plasmonics, we mapped the plasmons and it turned out to have a very nice effect,” Ringe said. “We basically saw different electric-field distributions at different energies for different shapes.” Numerical results provided by collaborators Nicolas Large of the University of Texas at San Antonio and George Schatz of Northwestern University helped explain the origin of the modes and how the presence of a water-filled pocket created a multitude of plasmons, she said.

The next challenge is to test nanoshells of other shapes and sizes, and to see if there are other ways to activate their switching potentials. Ringe suspects electron beams may remain the best and perhaps only way to catalyze reactions inside particles, and she is hopeful.

“Using an electron beam is actually not as technologically irrelevant as you might think,” she said. “Electron beams are very easy to generate. And yes, things need to be in vacuum, but other than that, people have generated electron beams for nearly 100 years. I’m sure 40 years ago people were saying, ‘You’re going to put a laser in a disk reader? That’s crazy!’ But they managed to do it.

“I don’t think it’s unfeasible to miniaturize electron-beam technology. Humans are good at moving electrons and electricity around. We figured that out a long time ago,” Ringe said.

The research should trigger the imaginations of scientists working to create nanoscale machines and processes, she said.

“This is a reconfigurable unit that you can access with light,” she said. “Reading something with light is much faster than reading with electrons, so I think this is going to get attention from people who think about dynamic systems and people who think about how to go beyond current nanotechnology. This really opens up a new field.”

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

Reversible Shape and Plasmon Tuning in Hollow AgAu Nanorods by Sadegh Yazdi, Josée R. Daniel, Nicolas Large, George C. Schatz, Denis Boudreau, and Emilie Ringe. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.6b02946 Publication Date (Web): October 5, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

The researchers have made this video available for the public,