Rice, Oak Ridge National Laboratory technique grows pristine foot-long graphene

Original image by Andy Sproles/Oak Ridge National Laboratory, U.S. Dept. of Energy.

Is there a way to make big sheets of pristine graphene or other two-dimensional materials? The answer is blowing in the wind.

That’s the heart of a discovery by scientists at Rice University, New Mexico State University and the Department of Energy’s Oak Ridge National Laboratory (ORNL) who grew single-atom-thick graphene monocrystals to unprecedented sizes.

The technique developed by ONRL researcher and lead author Ivan Vlassiouk, New Mexico scientist Sergei Smirnov and Rice materials theorist and co-author Boris Yakobson in principle produces pristine graphene of unlimited size and makes it suitable for roll-to-roll production. Their process deposits a narrow band of hydrocarbon precursor onto a moving substrate, with a buffer gas blowing the carbon atoms toward the growing front. Once the atoms grab ahold of the substrate and crystallize into a seed of graphene, the buffer wind prompts them to cohere into a single growing sheet.

The researchers reported in Nature Materials their success in growing atom-thin sheets of graphene a foot long and a few inches wide, limited only by the width of the equipment. The single crystal of two-dimensional carbon grows at an inch per hour in a custom-built chemical vapor deposition (CVD) furnace.

The work is featured also on the popular YouTube Science channel SciShow:

– See more at Rice News

Rice scientists create flat composite with tunable optical bandgap

Rice University scientists have discovered a two-dimensional alloy with an optical bandgap that can be tuned by the temperature used to grow it.

The Rice lab of materials scientist Pulickel Ajayan grew the four-component alloy of transition metals molybdenum and tungsten with chalcogens sulfur and selenium in a chemical vapor deposition furnace. They found changes in temperature made subtle changes in the way atoms assembled and also altered the properties that determine how they absorb and emit light.

Their experiments were built upon work by the lab of Rice theoretical physicist Boris Yakobson, which created scores of models to predict how various combinations of the four elements should work.

The process should be of interest to engineers looking to make smaller, more-efficient devices. Because the bandgap falls in the optical range of the electromagnetic spectrum, the researchers said solar cells and light-emitting diodes might be the first beneficiaries.

The paper appears as a cover story in the current issue of Advanced Materials.

– See more at Rice News

Rice, Oak Ridge scientists show growing atom-thin sheets on cones allows control of defects

“Hands of Henry” (Nitant Gupta, c. 2017; WS₂ on conical canvas)

Rice University researchers have learned to manipulate two-dimensional materials to design in defects that enhance the materials’ properties.

The Rice lab of theoretical physicist Boris Yakobson and colleagues at Oak Ridge National Laboratory are combining theory and experimentation to prove it’s possible to give 2-D materials specific defects, especially atomic-scale seams called grain boundaries. These boundaries may be used to enhance the materials’ electronic, magnetic, mechanical, catalytic and optical properties.

The key is introducing curvature to the landscape that constrains the way defects propagate. The researchers call this “tilt grain boundary topology,” and they achieve it by growing their materials onto a topographically curved substrate — in this case, a cone. The angle of the cone dictates if, what kind and where the boundaries appear.

The research is the subject of a paper in the American Chemical Society journal ACS Nano.

– See more at Rice News

Rice, Lawrence Livermore scientists replace expensive platinum for efficient hydrogen production

Scientists at Rice University and the Lawrence Livermore National Laboratory have predicted and created new two-dimensional electrocatalysts to extract hydrogen from water with high performance and low cost.

In the process, they also created a simple model to screen materials for catalytic activity.

Several catalysts were modeled by Rice theoretical physicist Boris Yakobson and lead author Yuanyue Liu, a former graduate student in his lab, and made and tested by Rice materials scientists led by Pulickel Ajayan and Jun Lou. They found the new dichalcogenide catalysts matched the efficiency of platinum — the most common hydrogen evolution reaction (HER) catalyst in water-splitting cells — and can be made at a fraction of the cost.

The study is a cover story in the September issue of Nature Energy.

– See more at Rice News

Department of Energy’s Office of Science (BES) highlights our work on 2D boron

… Can boron, which is adjacent to carbon on the Periodic Table, also form a 2-D material and, if so, what are its properties? Researchers at Rice University used theory and simulation techniques to identify possible 2-D boron structures. Their findings showed that, based upon the metal substrate used during the fabrication process, the structure of monolayer boron changed drastically. Using this information, researchers from Argonne National Laboratory, Northwestern University, and their collaborators from other institutions utilized the Department of Energy’s Center for Nanoscale Material, a user facility, to attempt the synthesis of borophene on a silver substrate.

– See more at science.energy.gov

The December 14 issue of Advanced Materials features our work on carbon fibers on its back cover.

The study presents the “D-loops”, a new type of structural defect in carbon fibers, which may have highly detrimental effect on their mechanical properties and can define a new fundamental upper limit to their strength. These defects form exclusively during polyacrylonitrile (PAN) carbonization, act as stress concentrators in the graphitic basal plane, and cannot be removed by local annealing.

Related:

• Rice News: Study explains strength gap between graphene, carbon fiber
• Futurity.org: Bad ‘zipper’ explains trouble with carbon fibers
•  E. S. Penev, V. I. Artyukhov, B. I. Yakobson, “Basic structural units in carbon fibers: Atomistic models and tensile behavior”, Carbon 85, 72–78 (2015)

Luqing Wang, a 4th-year graduate student in Yakobson Group, has received the 2016 Shell Graduate Fellowship awarded by the Ken Kennedy Institute for Information Technology.

The Ken Kennedy Institute is dedicated to the advancement of research in the fields of computing, data science and information technology, and the award recipients were selected on the basis of their research proposals which contribute to computing and data issues the oil and gas industry currently faces.

While a majority of the program’s fellowship awards are funded by energy industry players, including BP, ExxonMobil, Schlumberger and Shell, support is also provided from the Ken Kennedy Cray Graduate Fellowship, the Andrew Ladd Memorial Excellence Fund in Computer Science Fellowship and funding from the annual Rice Oil and Gas High Performance Computing Conference (OG-HPC).

– See more at Rice News

Henry Yu, a 4th year graduate student in the Applied Physics/MSNE program, has won 2nd place in the 2016 NSCI Image Contest held by the Wiess School of Natural Sciences, Rice University. The image shows a graphite screw dislocation structure as a nano solenoid, which can hold magnetic field orders of magnitude greater than that of planet Earth. It was produced from an actual atomic geometry, using VMD, our own Edgecount tool, MeshLab, Python scripting, and the mighty Gimp.

To learn more about the science behind the image, see:
– Rice News: Graphene nano-coils are natural electromagnets
– F. Xu, H. Yu, A. Sadrzadeh, and B. I. Yakobson, “Riemann Surfaces of Carbon as Graphene Nanosolenoids“, Nano Lett. 16, 34–39 (2016)

Rice researchers simulate defects in popular fiber, suggest ways to improve it 

The D-shaped loop, due to the misfusion of PAN-based nanoribbons, seen as a puckered-rug illustration by graduate student Nitant Gupta.

Carbon fiber, a pillar of strength in materials manufacturing for decades, isn’t as good as it could be, but there are ways to improve it, according to Rice University scientists.

They found the polymer chains that make up a common carbon fiber are prone to misalign during manufacture, a defect the researchers compared with a faulty zipper that weakens the product.

The Rice lab of theoretical physicist Boris Yakobson set out to analyze these overlooked defects and suggest how they might be curtailed. The lab’s work appears this month in Advanced Materials.

– See more at Rice News