Category Archives: Press releases

Wrinkles in atomically thin materials unlock ultraefficient electronics

Posted on by
Reply

Representation of electron spins in a bent 2D material exhibiting the persistent spin helix structure. (Image courtesy of Sunny Gupta)

Wrinkles can be an asset — especially for next-generation electronics. Rice University scientists have discovered that tiny creases in two-dimensional materials can control electrons’ spin with record precision, opening the path to ultracompact, energy-efficient electronic devices.

If most devices today use the charge of electrons flowing through silicon to process and encode information, future computing may instead harness spin — a quantum property of electrons that takes on either an “up” or “down” value. Computing with spin could overcome the limitations of current silicon-based technology, reducing the energy footprint of devices and data centers at a moment when computing-driven energy use is soaring globally.

However, spintronics has to contend with a major challenge: Information encoded in spin is quick to decay and can be lost when the electrons in a material scatter and collide with atoms.

In a new study published in the journal Matter, Rice materials scientists have reported that bending atomically thin layers of materials like molybdenum ditelluride, MoTe2, gives rise to a unique spin texture called persistent spin helix, or PSH, which can preserve spin state even in scattering collisions.

– See more at Rice News

‘Hopelessly attached’: Scientists discover new 2D material that sticks the landing

Posted on by
Reply

Discovery confirms decade-old prediction and sheds light on underexplored class of 2D materials

Atomic-resolution scanning tunneling microscopy image (left) overlapped with the copper boride (Cu8B14) structural model.

More than ten years ago, researchers at Rice University led by materials scientist Boris Yakobson predicted that boron atoms would cling too tightly to copper to form borophene, a flexible, metallic two-dimensional material with potential across electronics, energy and catalysis. Now, new research shows the prediction holds up, but in an unexpected way.

Unlike systems such as graphene on copper, where atoms may diffuse into the substrate without forming a distinct alloy, the boron atoms in this case formed a defined 2D copper boride  — a new compound with a distinct atomic structure. The finding, published in Science Advances by researchers from Rice and Northwestern University, sets the stage for further exploration of a relatively untapped class of 2D materials.

– See more at Rice News

Bending 2D nanomaterial could ‘switch on’ future technologies

Posted on by

Rice University scientists find new workable feature of a class of 2D materials

Rice University materials scientist Boris Yakobson and collaborators uncovered a property of ferroelectric 2D materials that could be exploited as a feature in future devices.

Because they bend in response to an electrical stimulus, single-layer ferroelectric materials can be controlled to act as a nanoscale switch or even a motor, according to the study published in ACS Nano.

Polarization drives the larger atoms to one side of the 2D-material layer and the smaller atoms to the other side. This asymmetrical distribution of the atoms or ions causes the material surface to bend in ferroelectric state.

The study looked at 2D indium phosphide (InP) as a representative of the class of ferroelectrics for which it predicts this property.

“This new property or flexing behavior has to be tested in a laboratory for specific substances,” Yakobson said. “Its most likely use will be as a type of switch. This behavior is very fast, very sensitive, which means that with a very tiny local signal you can maybe switch on a turbine or electrical engine, or control adaptive-optics telescopes’ mirrors. That’s basically the essence of these actuators.”

–  See more at Rice News

A crystal shape conundrum is finally solved

Posted on by

Rice theorists’ method can predict shapes of crystals that lack symmetry

A crystal’s shape is determined by its inherent chemistry, a characteristic that ultimately determines its final form from the most basic of details. But sometimes the lack of symmetry in a crystal makes the surface energies of its facets unknowable, confounding any theoretical prediction of its shape.

Theorists at Rice University say they’ve found a way around this conundrum by assigning arbitrary latent energies to its surfaces or, in the case of two-dimensional materials, its edges.

Yes, it seems like cheating, but in the same way a magician finds a select card in a deck by narrowing the possibilities, a little algebraic sleight-of-hand goes a long way to solve the problem of predicting a crystal’s shape.

The method described in Nature Computational Science shows using what they call auxiliary edge energies can bring predictions back in line with the Wulff construction, a geometrical recipe in use for more than a century to determine how crystals arrive at their final equilibrium shapes.

–  See more at Rice News

Related

Bumps could smooth quantum investigations

Posted on by

Rice University models show unique properties of 2D materials stressed by A new theory by Rice University researchers suggests that 2D materials like hexagonal boron nitride, at top, could be placed atop a contoured surface, center, and thus be manipulated to form 1D bands that take on electronic or magnetic properties. Courtesy of the Yakobson Research Groupcontoured substrates

Atoms do weird things when forced out of their comfort zones. Rice University engineers have thought up a new way to give them a nudge.

Materials theorist Boris Yakobson and his team at Rice’s George R. Brown School of Engineering have a theory that changing the contour of a layer of 2D material, thus changing the relationships between its atoms, might be simpler to do than previously thought.

While others twist 2D bilayers — two layers stacked together — of graphene and the like to change their topology, the Rice researchers suggest through computational models that growing or stamping single-layer 2D materials on a carefully designed undulating surface would achieve “an unprecedented level of control” over their magnetic and electronic properties.

They say the discovery opens a path to explore many-body effects, the interactions between multiple microscopic particles, including quantum systems.

The paper by Yakobson and two alumni, co-lead author Sunny Gupta and Henry Yu, of his lab appears in Nature Communications.

– See more at Rice News

Rusting iron can be its own worst enemy

Posted on by

Rice team’s simulations show iron catalyzes corrosion in ‘inert’ carbon dioxide

 Iron that rusts in water theoretically shouldn’t corrode in contact with an “inert” supercritical fluid of carbon dioxide. But it does.

Materials theorist Boris Yakobson and his colleagues at Rice’s George R. Brown School of Engineering found through atom-level simulations that iron itself plays a role in its own corrosion when exposed to supercritical CO2 (sCO2) and trace amounts of water by promoting the formation of reactive species in the fluid that come back to attack it.

In their research, published in the Cell Press journal Matter, they conclude that thin hydrophobic layers of 2D materials like graphene or hexagonal boron nitride could be employed as a barrier between iron atoms and the reactive elements of sCO2.

“Eliminating corrosion is a constant challenge, and it’s on a lot of people’s minds right now as the government prepares to invest heavily in infrastructure,” said Yakobson, the Karl F. Hasselmann Professor of Materials Science and NanoEngineering and a professor of chemistry. “Iron is a pillar of infrastructure from ancient times, but only now are we able to get an atomistic understanding of how it corrodes.”

– See more at Rice News

Related:

Nickel’s need for speed makes unusual nanoribbons

Posted on by

Rice lab studies mechanism behind bilayer molybdenum disulfide ribbons

It’s now possible to quickly make ultrathin nanoribbons of molybdenum disulfide, with a speedy nickel nanoparticle leading the way.Materials theorist Boris Yakobson and his team at Rice University’s George R. Brown School of Engineering collaborated with the Honda Research Institute and others to make tightly controlled bilayer nanoribbons of the material commonly known as MoS2, a step forward with potential applications in quantum computing.

Honda, with scientists at Rice, Columbia University and Oak Ridge National Laboratory, found that nanoparticles of nickel exposed to molybdenum oxide and sodium bromide powders and sulfur gas in a chemical vapor deposition furnace wrangle the resulting nanoribbons into shape, constraining their width to several micrometers. At the same time, the nickel catalyzes a thinner second layer of less than 30 nanometers, roughly equivalent to the width of the nanoparticle itself.

The study appears in Science Advances.

– See more at Rice News

Rice lab peers inside 2D crystal synthesis

Posted on by

Simulations could help molecular engineers enhance creation of semiconducting nanomaterials

Scientific studies describing the most basic processes often have the greatest impact in the long run. A new work by Rice University engineers could be one such, and it’s a gas, gas, gas for nanomaterials.

Rice materials theorist Boris Yakobson, graduate student Jincheng Lei and alumnus Yu Xie of Rice’s Brown School of Engineering have unveiled how a popular 2D material, molybdenum disulfide (MoS2), flashes into existence during chemical vapor deposition (CVD).

Knowing how the process works will give scientists and engineers a way to optimize the bulk manufacture of MoS2 and other valuable materials classed as transition metal dichalcogenides (TMDs), semiconducting crystals that are good bets to find a home in next-generation electronics.

Their study in the American Chemical Society journal ACS Nano focuses on MoS2‘s “pre-history”, specifically what happens in a CVD furnace once all the solid ingredients are in place. CVD, often associated with graphene and carbon nanotubes, has been exploited to make a variety of 2D materials by providing solid precursors and catalysts that sublimate into gas and react. The chemistry dictates which molecules fall out of the gas and settle on a substrate, like copper or silicone, and assemble into a 2D crystal.

– See more at Rice News

A little friction goes a long way toward stronger nanotube fibers

Posted on by

Rice model may lead to better materials for aerospace, automotive, medical applications

Carbon nanotube fibers are not nearly as strong as the nanotubes they contain, but Rice University researchers are working to close the gap.

A computational model by materials theorist Boris Yakobson and his team at Rice’s Brown School of Engineering establishes a universal scaling relationship between nanotube length and friction between them in a bundle, parameters that can be used to fine-tune fiber properties for strength.

The model is a tool for scientists and engineers who develop conductive fibers for aerospace, automotive, medical and textile applications like smart clothing. Carbon nanotube fibers have been considered as a possible basis for a space elevator, a project Yakobson has studied.

The research is detailed in the American Chemical Society journal ACS Nano.

– See more at Rice News

Excitons form superfluid in certain 2D combos

Posted on by

Rice researchers find ‘paradox’ in ground-state bilayers

Mixing and matching computational models of 2D materials led scientists at Rice University to the realization that excitons — quasiparticles that exist when electrons and holes briefly bind — can be manipulated in new and useful ways.

The researchers identified a small set of 2D compounds with similar atomic lattice dimensions that, when placed together, would allow excitons to form spontaneously. Generally, excitons happen when energy from light or electricity boosts electrons and holes into a higher state.

But in a few of the combinations predicted by Rice materials theorist Boris Yakobson and his team, excitons were observed stabilizing at the materials’ ground state. According to their determination, these excitons at their lowest energy state could condense into a superfluid-like phase. The discovery shows promise for electronic, spintronic and quantum computing applications.

The open-access study by Yakobson, graduate student Sunny Gupta and research scientist Alex Kutana, all of Rice’s Brown School of Engineering, appears in Nature Communications.

– See more at Rice News

Double-walled nanotubes have electro-optical advantages

Posted on by

Rice University calculations show they could be highly useful for solar panels

One nanotube could be great for electronics applications, but there’s new evidence that two could be tops.

Rice University engineers already knew that size matters when using single-walled carbon nanotubes for their electrical properties. But until now, nobody had studied how electrons act when confronted with the Russian doll-like structure of multiwalled tubes.

The Rice lab of materials theorist Boris Yakobson has now calculated the impact of curvature of semiconducting double-wall carbon nanotubes on their flexoelectric voltage, a measure of electrical imbalance between the nanotube’s inner and outer walls.

This affects how suitable nested nanotube pairs may be for nanoelectronics applications, especially photovoltaics.

The theoretical research by Yakobson’s Brown School of Engineering group appears in the American Chemical Society journal Nano Letters.

– See more at Rice News

Rice lab turns trash into valuable graphene in a flash

Posted on by

‘Green’ process promises pristine graphene in bulk using waste food, plastic and other materials

A new process introduced by the Rice University lab of chemist James Tour can turn bulk quantities of just about any carbon source into valuable graphene flakes. The process is quick and cheap; Tour said the “flash graphene” technique can convert a ton of coal, food waste or plastic into graphene for a fraction of the cost used by other bulk graphene-producing methods.

As reported in Nature, flash graphene is made in 10 milliseconds by heating carbon-containing materials to 3,000 Kelvin (about 5,000 degrees Fahrenheit). The source material can be nearly anything with carbon content. Food waste, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates, Tour said. “With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb,” he said.

Atom-level simulations by Rice researcher and co-author Ksenia Bets confirmed that temperature is key to the material’s rapid formation.“It is amazing how state-of-the-art computer simulations, notoriously slow for observing such kinetics, reveal the details of high temperature-modulated atomic movements and transformation,” Bets said.

– See more at Rice News

Borophene on silver grows freely into an atomic ‘skin’

Posted on by

Rice scientists lead effort to improve manufacture of valuable 2D material

Borophene has a nearly perfect partner in a form of silver that could help the trendy two-dimensional material grow to unheard-of lengths.

A well-ordered lattice of silver atoms makes it possible to speed the growth of pristine borophene, the atom-thick allotrope of boron that so far can only form via synthesis by molecular-beam epitaxy (MBE).

By using a silver substrate and through careful manipulation of temperature and deposition rate, scientists have discovered they can grow elongated hexagon-shaped flakes of borophene. They suggested the use of a proper metal substrate could facilitate the growth of ultrathin, narrow borophene ribbons.

New work published in Science Advances by researchers at Rice and Northwestern universities, Nanjing University of Aeronautics and Astronautics and Argonne National Laboratory will help streamline the manufacture of the conductive material, which shows potential for use in wearable and transparent electronics, plasmonic sensors and energy storage.

– See more at Rice News

Oddball edge wins nanotube faceoff

Posted on by

Rice theory shows peculiar ‘Janus’ interface a common mechanism in carbon nanotube growth

When is a circle less stable than a jagged loop? Apparently when you’re talking about carbon nanotubes.

Rice University theoretical researchers have discovered that nanotubes with segregated sections of “zigzag” and “armchair” facets growing from a solid catalyst are far more energetically stable than a circular arrangement would be.

Under the right circumstances, they reported, the interface between a growing nanotube and its catalyst can reach its lowest-known energy state via the two-faced “Janus” configuration, with a half-circle of zigzags opposite six armchairs.

The terms refer to the shape of the nanotube’s edge: A zigzag nanotube’s end looks like a saw tooth, while an armchair is like a row of seats with armrests. They are the basic edge configurations of the two-dimensional honeycomb of carbon atoms known as graphene (as well as other 2D materials) and determine many of the materials’ properties, especially electrical conductivity.

The Brown School of Engineering team of materials theorist Boris Yakobson, researcher and lead author Ksenia Bets and assistant research professor Evgeni Penev reported their results in the American Chemical Society journal ACS Nano.

– See more at Rice News

Borophene shines alone as 2-D plasmonic material

Posted on by

Rice University scientists calculate flat boron capable of visible plasmon emissions

Illustration by Sharmila Shirodkar.

An atom-thick film of boron could be the first pure two-dimensional material able to emit visible and near-infrared light by activating its plasmons, according to Rice University scientists. That would make the material known as borophene a candidate for plasmonic and photonic devices like biomolecule sensors, waveguides, nanoscale light harvesters and nanoantennas. Plasmons are collective excitations of electrons that flow across the surface of metals when triggered by an input of energy, like laser light. Significantly, delivering light to a plasmonic material in one color (determined by the light’s frequency) can prompt the emission of light in another color.

Models by Rice theoretical physicist Boris Yakobson and his colleagues predict that borophene would be the first known 2-D material to do so naturally, without modification. The lab’s simulations are detailed in a paper by Yakobson with lead authors Yuefei Huang, a graduate student, and Sharmila Shirodkar, a postdoctoral researcher, in the Journal of the American Chemical Society.

– See more at Rice News