Borophene on silver grows freely into an atomic ‘skin’

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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

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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

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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

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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

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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.

Prof. Yakobson receives Outstanding Faculty Research Award, the top honor for faculty

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School of Engineering celebrates faculty and staff

The 2019 Outstanding Faculty Research Award is awarded to a faculty member who most contributed to highly impactful publications or publicly available software, based on research conducted at Rice and published/developed during the period January 1, 2014, to December 31, 2018.

Prof. Yakobson has 4 patents and has published ~350 journal papers with more than 32,000 citations and an h-index of 86. Among the 20 Rice faculty profiles on Google Scholar with highest total number of citations, he is one of the top-three with the highest citations growth, ~600/yr, for the period 2013–2017. Yakobson’s Research Group maintains a vivid research group website that has been visited over this period by ~25,000 users from ~110 countries, collecting ~100,000 pageviews.

This Award also culminates a period of exciting breakthroughs in the pursuit of novel low-dimensional nanomaterials, resulting from Yakobson’s more recent work (2013–2015) in the field of materials discovery.

2D borophene gets a closer look

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Rice, Northwestern find new ways to image, characterize unique material

Graphene can come from graphite. But borophene? There’s no such thing as borite.

Unlike its carbon cousin, two-dimensional borophene can’t be reduced from a larger natural form. Bulk boron is usually only found in combination with other elements, and is certainly not layered, so borophene has to be made from the atoms up. Even then, the borophene you get may not be what you need.

For that reason, researchers at Rice and Northwestern universities have developed a method to view 2D borophene crystals, which can have many lattice configurations — called polymorphs — that in turn determine their characteristics.

Knowing how to achieve specific polymorphs could help manufacturers incorporate borophene with desirable electronic, thermal, optical and other physical properties into products.

Boris Yakobson, a materials physicist at Rice’s Brown School of Engineering, and materials scientist Mark Hersam of Northwestern led a team that not only discovered how to see the nanoscale structures of borophene lattices but also built theoretical models that helped characterize the crystalline forms.

Their results are published in Nature Communications.

– See more at Rice News

Gold soaks up boron, spits out borophene

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Rice, Argonne, Northwestern scientists show unique mechanism makes valuable 2D material

In the heat of a furnace, boron atoms happily dive into a bath of gold. And when things get cool, they resurface as coveted borophene.

The discovery by scientists from Rice University, Argonne National Laboratory and Northwestern University is a step toward practical applications like wearable or transparent electronics, plasmonic sensors or energy storage for the two-dimensional material with excellent conductivity.

Teams led by Boris Yakobson at Rice, Nathan Guisinger at Argonne and Mark Hersam at Northwestern both formed the theory for and then demonstrated their novel method to grow borophene – the atom-thick form of boron – on a gold surface.

They found that with sufficient heat in a high vacuum, boron atoms streamed into the furnace sink into the gold itself. Upon cooling, the boron atoms reappear and form islands of borophene on the surface.

This is distinct from most other 2D materials made by feeding gases into a furnace. In standard chemical vapor deposition, the atoms settle onto a substrate and connect with each other. They typically don’t disappear into the substrate.

The discovery was described in a paper in the American Chemical Society journal ACS Nano.

– See more at Rice News

Step right up for bigger 2D sheets

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Rice theory shows how monocrystals of hexagonal boron nitride come together

Very small steps make a big difference to researchers who want to create large wafers of two-dimensional material.

Atom-sized steps in a substrate provide the means for 2D crystals growing in a chemical vapor furnace to come together in perfect rank. Scientists have recently observed this phenomenon, and now a Rice University group has an idea why it works.

Rice materials theorist Boris Yakobson and researcher Ksenia Bets led the construction of simulations that show atom-sized steps on a growth surface, or substrate, have the remarkable ability to keep monolayer crystal islands in alignment as they grow.

If the conditions are right, the islands join into a larger crystal without the grain boundaries so characteristic of 2D materials like graphene grown via chemical vapor deposition (CVD). That preserves their electronic perfection and characteristics, which differ depending on the material.

The Rice theory appears in the American Chemical Society journal Nano Letters.

– See more at Rice News

Imperfections make photons perfect for quantum computing

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Rice scientists show how atom-flat materials could produce polarized photons on demand

If you can make a single photon, tell it how to spin and tell it where to go, you have a basic element for next-generation computers that work with light instead of wires.

That appears to be possible with atom-thick materials, as demonstrated by several labs. Now, Rice University scientists have developed an understanding of the mechanism by which two-dimensional materials can be manipulated to produce the desired photons.

The Rice lab of materials theorist Boris Yakobson reported this month that by adding pre-arranged imperfections to atom-thick materials like molybdenum disulfide, they become perfectly capable of emitting single photons in either left or right polarization on demand.

The discovery through first-principles simulations is detailed in the American Chemical Society journal Nano Letters.

– See more at Rice News

Rice U. study sheds light on – and through – 2D materials

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High-performance computing helps to survey optical qualities of atom-thick materials for optoelectronics

Two-dimensional materials have been a hot research topic since graphene, a flat lattice of carbon atoms, was identified in 2001. Since then, scientists have raced to develop, either in theory or in the lab, novel 2D materials with a range of optical, electronic and physical properties.

Until now, they have lacked a comprehensive guide to the optical properties those materials offer as ultrathin reflectors, transmitters or absorbers.

The Rice lab of materials theorist Boris Yakobson took up the challenge. Yakobson and his co-authors, graduate student and lead author Sunny Gupta, postdoctoral researcher Sharmila Shirodkar and research scientist Alex Kutana, used state-of-the-art theoretical methods to compute the maximum optical properties of 55 2D materials.

Their work, which appears this month in the American Chemical Society journal ACS Nano, details the monolayers’ transmittance, absorbance and reflectance, properties they collectively dubbed TAR. At the nanoscale, light can interact with materials in unique ways, prompting electron-photon interactions or triggering plasmons that absorb light at one frequency and emit it in another.

– See more at Rice News

Two-faced edge makes nanotubes obey

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Rice theorists find mechanism behind nearly pure nanotubes from the unusual catalyst

Growing a batch of carbon nanotubes that are all the same may not be as simple as researchers had hoped, according to Rice University scientists.

Rice materials theorist Boris Yakobson and his team bucked a theory that when growing nanotubes in a furnace, a catalyst with a specific atomic arrangement and symmetry would reliably make carbon nanotubes of like chirality, the angle of its carbon-atom lattice.

Instead, they found the catalyst in question starts nanotubes with a variety of chiral angles but redirects almost all of them toward a fast-growing variant known as (12,6). The cause appears to be a Janus-like interface that is composed of armchair and zigzag segments – and ultimately changes how nanotubes grow.

The Rice theoretical study detailed in the American Chemical Society journal Nano Letters could be a step toward catalysts that produce homogeneous batches of nanotubes, Yakobson said.

– See more at Rice News

In borophene, boundaries are no barrier

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Rice, Northwestern researchers make and test atom-thick boron’s unique domainsA scanning electron microscope image (top) shows two periodic assemblies of borophene, a synthetic, two-dimensional array of boron atoms, that join at a line defect. Computational models in the middle and bottom images correspond to the regions, with 1-to-6 borophene in red and 1-to-5 in blue. Researchers at Rice and Northwestern universities determined that phases of borophene line up in such a way that the material's conductive, metallic nature is maintained. (Credit: Graphics by Luqing Wang/Rice University)

The research led by Rice materials theorist Boris Yakobson and Northwestern materials scientist Mark Hersam appears in Nature Materials.

Borophene differs from graphene and other 2D materials in an important way: It doesn’t appear in nature. When graphene was discovered, it was famously yanked from a piece of graphite with Scotch tape. But semiconducting bulk boron doesn’t have layers, so all borophene is synthetic. Also unlike graphene, in which atoms connect to form chicken wire-like hexagons, borophene forms as linked triangles. Periodically, atoms go missing from the grid and leave hexagonal vacancies. The labs investigated forms of borophene with “hollow hexagon” concentrations of one per every five triangles and one per every six in the lattice.

Yakobson and Hersam also co-authored a recent Nature Nanotechnology perspective about “the lightest 2D metal.”In that piece, the authors suggested borophene may be ideal for flexible and transparent electronic interconnects, electrodes and displays. It could also be suitable for superconducting quantum interference devices and, when stacked, for hydrogen storage and battery applications.

– See more at Rice News

Nitant Gupta wins Franz and Frances Brotzen Fellowship Award

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Nitant Gupta, a third-year graduate student in Yakobson’s Group, has received the 2018 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.

Nitant’s research focuses on the growth of 2D nanomaterials with special interest in grain boundary morphology, crystal shape evolution and also effects of substrate topography. He uses computational methods like molecular dynamics, phase-field simulations and interface tracking, to explore the fundamental aspects governing these phenomena. He also works on the nanomechanics of carbon-based materials such as graphene and carbon fibers.

Sharmila Shirodkar wins the 2018 Outstanding Postdoctoral Research Award

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Sharmila Shirodkar, a postdoctoral research associate in  Yakobson’s Group, is the recipients of the 2018 Outstanding Postdoctoral Research Award of Rice University’s George R. Brown School of Engineering.

Sharmila’s research focuses on the electronic and plasmonic properties of 2D materials using first-principles calculations. Her recent work involved exploring plasmonic response of recently discovered 2D sheets of boron, and determining the stability of these sheets with doping via atypical simulation technique.  She also works on the optical properties of 2D materials, and tinkers on finding new combinations of nano-catalysts for enhanced hydrogen evolution reactions.

Sharmila finished her Ph.D. from the Theoretical Sciences Unit in JNCASR, Bangalore, India in 2014. She was a postdoc at the John A. Paulson’s School of Engineering and Applied Sciences, at Harvard University from 2015 to 2016 before joining Prof. Yakobson’s group in the Material Science and NanoEngineering department at Rice University in 2016.