Category Archives: Group-related news

Rice finds path to nanodiamond from graphene

Posted on by

A spot of pressure enables chemical conversion to hardened 2D material

Marrying two layers of graphene is an easy route to the blissful formation of nanoscale diamond, but sometimes thicker is better.

While it may only take a bit of heat to turn a treated bilayer of the ultrathin material into a cubic lattice of diamane, a bit of pressure in just the right place can convert few-layer graphene as well.

The otherwise chemically driven process is theoretically possible according to scientists at Rice University, who published their most recent thoughts on making high-quality diamane — the 2D form of diamond — in the journal Small (featured on the inside Front Cover).

The research led by materials theorist Boris Yakobson and his colleagues at Rice’s Brown School of Engineering suggests a pinpoint of pressure on few-layer graphene, the atom-thin form of carbon known for its astonishing strength, can nucleate a surface chemical reaction with hydrogen or fluorine.

– See more at Rice News

Sunny Gupta wins Best Oral Presentation Award

Posted on by

Sunny Gupta, a fourth-year graduate student in Yakobson’s Group, has received a “Best Oral Presentation” Award at the 6th Annual SCI Summer Research Colloquium.

The nine judges who have listened in to all the talks were very impressed by the overall level of the presentations. They have recognized the outstanding quality of Sunny’s talk, and have assigned you one of the four SCI Bronze Oral Presentation Awards.

Sunny’s presentation covered his recent work on heterobilayers of 2D materials as a platform for excitonic superfluidity. After screening hundreds of 2D materials, a number of candidates were identified where spontaneous excitonic condensation mediated by purely electronic interaction should occur, and hetero-pairs Sb2Te2Se/BiTeCl, Hf2N2I2/Zr2N2Cl2, and LiAlTe2/BiTeI emerge promising. The predicted materials can be used to access different parts of electron-hole phase diagram, including BEC-BCS crossover, enabling tantalizing applications in superfluid transport, Josephson-like tunneling, and dissipationless charge counterflow.

– 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

“I do,” just in time: Newlywed grad students rush to return to Rice from India

Posted on by

Between an international pandemic and a dissertation defense from home, it’s a honeymoon they’ll never forget

Nitant is a Rice graduate student working in the lab of Boris Yakobson, while Lehigh University grad student Megha is preparing to defend her dissertation.

Their honeymoon was unique. Now, as the newlyweds adhere to social distancing guidelines put in place to combat the coronavirus pandemic, Nitant Gupta and Megha Sharma Gupta are spending plenty of quality time together at their new apartment in Houston.

“I am sure that Megha and I will cherish this for a long time,” Nitant said.

On March 11, the couple were married in Megha’s hometown of Udaipur, a joyous and well-attended occasion in one of India’s most beautiful cities. They were scheduled to return to the U.S. later in the month.

But with coronavirus spreading across the globe, the two graduate students quickly realized if they didn’t leave soon they might not be able to get back to Rice, where Nitant is pursuing his Ph.D. in material science.

– 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

A small step for atoms, a giant leap for microelectronics

Posted on by

Nature paper reports making and moving large-scale hexagonal boron nitride

Step by step, scientists are figuring out new ways to extend Moore’s Law. The latest reveals a path toward integrated circuits with two-dimensional transistors.

A Rice University scientist and his collaborators in Taiwan and China reported in Nature today that they have successfully grown atom-thick sheets of hexagonal boron nitride (hBN) as two-inch diameter crystals across a wafer.

Surprisingly, they achieved the long-sought goal of making perfectly ordered crystals of hBN, a wide band gap semiconductor, by taking advantage of disorder among the meandering steps on a copper substrate. The random steps keep the hBN in line.

Brown School of Engineering materials theorist Boris Yakobson is co-lead scientist on the study with Lain-Jong (Lance) Li of the Taiwan Semiconductor Manufacturing Co. (TSMC) and his team. Yakobson and Chih-Piao Chuu of TSMC performed theoretical analysis and first principles calculations to unravel the mechanisms of what their co-authors saw in experiments.

– See more at Rice News

Stretched to the Limit and Sparkling on Curved Surfaces

Posted on by

Department of Energy’s Office of Science (BES) highlights our work with ORNL

Image courtesy of Oak Ridge National Laboratory

… Scientists use chemical vapor deposition to deposit WS2 films on substrates that have first been lithographically patterned with three-dimensional features such as trenches and tori (donut shapes).

The team has developed a model that explains that the accelerated crystal growth caused by the strain is because of an increase in the number of sites at which new particles are deposited during film growth (nucleation). When the height of the donut or trench is too high (above 40 nm), the strain becomes too high, and the films crack to release the strain.

– See more at energy.gov

Related:

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

Prof. Yakobson on the list of Highly Cited Researchers 2019

Posted on by

Boris I. Yakobson, the Karl F. Hasselmann Chair of Engineering, Professor of Materials Science & NanoEngineering and of Chemistry, has been named a Highly Cited Researcher for 2019 in the Materials Science award category.

Highly Cited Researchers are among those who have demonstrated significant and broad influence reflected in their publication of multiple papers, highly cited by their peers over the course of the last decade.

These highly cited papers rank in the top 1% by citations for a chosen field or fields and year in Web of Science. Of the world’s population of scientists and social scientists, the Web of Science Group’s Highly Cited Researchers are one in 1,000.

The Highly Cited Researchers 2019 list from the Web of Science Group contributes to the identification of that small fraction of the researcher population that contributes disproportionately to extending the frontiers of knowledge and gaining for society innovations that make the world healthier, richer, more sustainable, and more secure.

Making light work of computing

Posted on by

The Rice Engineering Magazine features our work on 2D materials for single photon emission

The Fall 2019 issue of the Rice Engineering Magazine [1] features our recent work on 2D materials for single photon emission (SPE).

Single photon emission by a solid-state source requires presence of a distinct two-level quantum system, usually provided by point defects. In a recent Nano Lett., we note that a number of qualities offered by novel, two-dimensional materials, their all-surface openness and optical transparence, tighter quantum confinement, and reduced charge screening—are advantageous for achieving an ideal SPE. On the basis of first-principles calculations and point-group symmetry analysis, we have proposed a strategy  to design paramagnetic defect complex with reduced symmetry, meeting all the requirements for SPE: its electronic states are well isolated from the host material bands, belong to a majority spin eigenstate, and can be controllably excited by polarized light. The defect complex is thermodynamically stable and appears feasible for experimental realization to serve as an SPE-source, essential for quantum computing, with ReMoVS in MoS2 as one of the most practical candidates.

[1] M. Williams, “Making light work of computing”, Rice Eng. Mag. (Fall 2019), 34-35 (2019)

– 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

Microscopic ‘donuts’ a treat for quantum tech

Posted on by

Rice, Oak Ridge scientists study potential of synthetic strain engineering in 2D materials

Dedicating dollars to “donuts,” scientists at Rice University are helping a national laboratory bring about a revolution in electronics and, perhaps, quantum computing.

By patterning nanoscale donuts into a two-dimensional crystal, researchers at Oak Ridge National Laboratory and their colleagues, including theoretical scientists at Rice’s Brown School of Engineering, have achieved a new level of control over its electrical and optical properties.

As researchers eye nanoscale materials for applications like quantum information processing, a method to tailor them from the bottom up will make them more practical.

The research team, which includes Rice materials theorist Boris Yakobson and graduate students Nitant Gupta and Henry Yu, published its results in Science Advances.

– See more at Rice News

Sunny Gupta awarded the Nettie S. Autrey Fellowship

Posted on by

Sunny Gupta, a third-year graduate student in Yakobson’s Group, has been awarded the Nettie S. Autrey Fellowship for 2019–2020. This award is given to one Rice graduate student in either the School of Natural Sciences or the School of Engineering who has demonstrated outstanding achievement and promise, and pays a stipend over the coming academic year.

Sunny’s research focuses on designing novel two-dimensional quantum materials for next-generation electronics. Using first-principles quantum theory methods and high-performance computing, he is tackling some of the challenging problems related to fundamental physics and materials realization for optoelectronics, spintronics, and quantum computing. All three areas constitute a current topic of intense research leading to next-generation electronics and are highly required to go beyond Moore’s law and to make faster, secure, and more power efficient computing devices.

Jincheng Lei wins Franz and Frances Brotzen Fellowship Award

Posted on by

Jincheng Lei, a fourth-year graduate student in Yakobson’s Group, has received the 2019 Franz and Frances Brotzen Fellowship Award from the MSNE Department. To honor Franz R. Brotzen, the Stanley C. Moore Professor Emeritus of Materials Science and a former dean of engineering, this fellowship was established by David Lee Davidson and his wife, Patricia, and to support an endowed fellowship for graduate students researching in the area of materials science.

Jincheng’s research focuses on the growth of 2D materials with specific focus on the reaction mechanisms during their growth. He uses DFT calculations and ab initio molecular dynamics simulations to provide detailed insights into the atomistic growth mechanism of MoS2 monolayer. He also works on predicting novel properties and exploring potential applications of nanomaterials.