Category Archives: Group-related news

Nicholas Tjahjono wins the Outstanding Teaching Assistant Award

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Nicholas Tjahjono, a fourth-year doctoral student in our group and a NASA Space Technology Graduate Research Opportunities Fellow has been awarded the Outstanding Teaching Assistant Award of the Rice’s MSNE Department.

Tjahjono’s research aims to aid in NASA’s Artemis mission to the moon and beyond. His objective is to develop mechanically robust and self-healing materials capable of operating under, and protecting astronauts from, extreme space environments such as extreme heat and cold, bombardment from micrometeoroids and orbital debris, and galactic cosmic radiation.

Bending 2D nanomaterial could ‘switch on’ future technologies

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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

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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

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Bumps could smooth quantum investigations

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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

Don’t underestimate undulating graphene

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Rice theorists show unique electronics made possible by wavy patterns that channel electrons

A theory by Rice researchers suggests growing graphene on a surface that undulates like an egg crate would stress it enough to create a minute electromagnetic field. The phenomenon could be useful for creating 2D electron optics or valleytronics devices. Illustration by Henry Yu

Lay some graphene down on a wavy surface, and you’ll get a guide to one possible future of two-dimensional electronics.

Rice University scientists put forth the idea that growing a tom-thick graphene on a gently textured surface creates peaks and valleys in the sheets that turn them into “pseudo-electromagnetic” devices.

The channels create their own minute but detectable magnetic fields. According to a study by materials theorist Boris Yakobson, alumnus Henry Yu and research scientist Alex Kutana at Rice’s George R. Brown School of Engineering, these could facilitate nanoscale optical devices like converging lenses or collimators.

Their study appears in the American Chemical Society’s Nano Letters.

– See more at Rice News

Rusting iron can be its own worst enemy

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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

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Nanotube fibers stand strong – but for how long?

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Rice scientists calculate how carbon nanotubes and their fibers experience fatigue

Up here in the macro world, we all feel fatigue now and then. It’s the same for bundles of carbon nanotubes, no matter how perfect their individual components are.

A Rice University study calculates how strains and stresses affect both “perfect” nanotubes and those assembled into fibers and found that while fibers under cyclic loads can fail over time, the tubes themselves may remain perfect. How long the tubes or their fibers sustain their mechanical environment can determine their practicality for applications.

That made the study, which appears in Science Advances, important to Rice materials theorist Boris Yakobson,graduate student Nitant Gupta and assistant research professor Evgeni Penev of Rice’s George R. Brown School of Engineering. They quantified the effects of cyclic stress on nanotubes using state-of-the-art simulation techniques like a kinetic Monte Carlo method. They hope to give researchers and industry a way to predict how long nanotube fibers or other assemblies can be expected to last under given conditions.

– See more at Rice News

Nickel’s need for speed makes unusual nanoribbons

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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

Bilayer borophene is a first

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Rice theories, Northwestern experiments combine to produce exotic material

If one layer of borophene is good, will two be better? Scientists at Rice University and Northwestern University hope so, because they’ve now made the elusive material.

Borophene is a one-atom-thick material made of boron atoms, which mostly fall together in neat triangles when grown in a furnace on a proper substrate. Its high strength and excellent conductivity make it a good candidate for use in quantum electronics, energy storage and sensors.

Unlike graphene, which can be exfoliated from bulk graphite, borophene can only be synthesized. And until now, it was only possible to make it in a single layer.

But the theory group at Rice led by Boris Yakobson and experimentalists at Northwestern led by Mark Hersam have given borophene a second deck. Their success at making bilayer borophene is detailed in Nature Materials.

“This is a significant step up, because it should enhance the coveted properties of 2D borophene as well as bring about new ones,” said Yakobson, a materials physicist at Rice’s Brown School of Engineering whose lab designed and performed simulations to guide the experiments.

– See more at Rice News

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Carbon nanotube research in its 30th year

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Our work featured in ACS Nano virtual issue celebrating CNT research

Since its inception in August 2007, ACS Nano has published over 1000 papers on carbon nanotubes (CNTs). To celebrate the 30th year of CNT research, the journal Editors have collected ~60 papers on CNTs published in ACS Nano, forming a virtual issue. The papers are listed by topic and reflect current trends in the field: preparation, macroassemblies and composites, electronics, energy and sustainability, bioapplications and bioeffects, and optics.

Our recent work on Janus segregation at the CNT–catalyst Interface appears in the Synthesis section of the virtual issue, and Macroassemblies & Composites features our recent comprehensive analysis of the universal strength scaling in CNT bundles with frictional load transfer.

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Rice lab peers inside 2D crystal synthesis

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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

2D coplanar heterojunctions on the cover of J. Phys. Chem. Lett.

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Our work on dimensionality-reduced Fermi level pinning in coplanar 2D heterojunctions is featured in the May issue of J. Phys. Chem. Lett. 

Electronic transport through a metal | semiconductor (M|S) heterojunction is largely determined by its Schottky barrier.  In light of the general interest in building 2D electronics, in a just-published work in J. Phys. Chem. Lett. we discover the relevant material parameters which dictate the behavior and strength of Fermi level pinning in 2D M|S contacts, using a multiscale model combining first-principles, continuum electrostatics, and transport calculations.

The cover is a graphical representation of the Fermi level pinning in 2D coplanar M|S  contacts which is greatly reduced due to weak electric screening in low dimensions. The interface states, while unable to alter the band alignment as in 3D, create a thin “spire” barrier to the transport electrons. Hence, the pinning strength in 2D contacts is now controlled by a new parameter: the interface width. These findings should guide the methods of contact engineering for future 2D electronic devices.

Nicholas Tjahjono awarded NASA space tech research fellowship

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Rice PhD student aims to aid in NASA’s Artemis mission to the moon and beyond

Nicholas Tjahjono, a first-year doctoral student in Yakobson Research Group,  has been awarded the NASA Space Technology Graduate Research Opportunities Fellowship.

His research proposal, “Virtual Prototyping of Multifunctional Boron-Nitrogen Nanostructures and their Composites for Extreme Space Environments,” aims to aid in NASA’s Artemis mission to the moon and beyond.

The goal of Artemis is to land two astronauts on the moon by 2024 and explore the feasibility of establishing sustainable colonies, in preparation for sending the first astronauts to Mars by 2030. Tjahjono’s objective is to develop materials capable of operating under, and protecting astronauts from, extreme space environments such as extreme heat and cold, variable gravity, abrasive lunar dust, galactic cosmic radiation and solar particle events.

Nicholas earned his B.S. in the joint major of bioengineering and materials science and engineering, and his B.A. in music, from the University of California at Berkeley in 2018. Before coming to Rice, he worked as a research assistant in the Lawrence Berkeley National Laboratory’s Molecular Foundry in Berkeley, Calif.

A little friction goes a long way toward stronger nanotube fibers

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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

2D compound shows unique versatility

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Multifunctional nanomaterial proposed by Rice could enhance solar energy, quantum computing

An atypical two-dimensional sandwich has the tasty part on the outside for scientists and engineers developing multifunctional nanodevices.

An atom-thin layer of semiconductor antimony paired with ferroelectric indium selenide would display unique properties depending on the side and polarization by an external electric field.

The field could be used to stabilize indium selenide’s polarization, a long-sought property that tends to be wrecked by internal fields in materials like perovskites but would be highly useful for solar energy applications.

Calculations by Rice materials theorist Boris Yakobson, lead author and researcher Jun-Jie Zhang and graduate student Dongyang Zhu shows switching the material’s polarization with an external electric field makes it either a simple insulator with a band gap suitable for visible light absorption or a topological insulator, a material that only conducts electrons along its surface.

Turning the field inward would make the material good for solar panels. Turning it outward could make it useful as a spintronic device for quantum computing.

The lab’s study appears in the American Chemical Society journal Nano Letters.

– See more at Rice News