Tag Archives: boron

Boron nitride nanotubes

Most of the talk about nanotubes is focused on carbon nanotubes but there are other kinds as a May 21, 2018 Rice University news release (also received via email and on EurekAlert and in a May 21, 2018 news item on ScienceDaily), notes,

Boron nitride nanotubes are primed to become effective building blocks for next-generation composite and polymer materials based on a new discovery at Rice University – and a previous one.

Scientists at known-for-nano Rice have found a way to enhance a unique class of nanotubes using a chemical process pioneered at the university. The Rice lab of chemist Angel Martí took advantage of the Billups-Birch reaction process to enhance boron nitride nanotubes.

The work is described in the American Chemical Society journal ACS Applied Nano Materials.

Boron nitride nanotubes, like their carbon cousins, are rolled sheets of hexagonal arrays. Unlike carbon nanotubes, they’re electrically insulating hybrids made of alternating boron and nitrogen atoms.

Insulating nanotubes that can be functionalized will be a valuable building block for nanoengineering projects, Martí said. “Carbon nanotubes have outstanding properties, but you can only get them in semiconducting or metallic conducting types,” he said. “Boron nitride nanotubes are complementary materials that can fill that gap.”

Until now, these nanotubes have steadfastly resisted functionalization, the “decorating” of structures with chemical additives that allows them to be customized for applications. The very properties that give boron nitride nanotubes strength and stability, especially at high temperatures, also make them hard to modify for their use in the production of advanced materials.

But the Billups-Birch reaction developed by Rice Professor Emeritus of Chemistry Edward Billups, which frees electrons to bind with other atoms, allowed Martí and lead author Carlos de los Reyes to give the electrically inert boron nitride nanotubes a negative charge.

That, in turn, opened them up to functionalization with other small molecules, including aliphatic carbon chains.

“Functionalizing the nanotubes modifies or tunes their properties,” Martí said. “When they’re pristine they are dispersible in water, but once we attach these alkyl chains, they are extremely hydrophobic (water-avoiding). Then, if you put them in very hydrophobic solvents like those with long-chain hydrocarbons, they are more dispersible than their pristine form.

“This allows us to tune the properties of the nanotubes and will make it easier to take the next step toward composites,” he said. “For that, the materials need to be compatible.”

After he discovered the phenomenon, de los Reyes spent months trying to reproduce it reliably. “There was a period where I had to do a reaction every day to achieve reproducibility,” he said. But that turned out to be an advantage, as the process only required about a day from start to finish. “That’s the advantage over other processes to functionalize carbon nanotubes. There are some that are very effective, but they may take a few days.”

The process begins with adding pure ammonia gas to the nanotubes and cooling it to -70 degrees Celsius (-94 degrees Fahrenheit). “When it combines with sodium, lithium or potassium — we use lithium — it creates a sea of electrons,” Martí said. “When the lithium dissolves in the ammonia, it expels the electrons.”

The freed electrons quickly bind with the nanotubes and provide hooks for other molecules. De los Reyes enhanced Billups-Birch when he found that adding the alkyl chains slowly, rather than all at once, improved their ability to bind.

The researchers also discovered the process is reversible. Unlike carbon nanotubes that burn away, boron nitride nanotubes can stand the heat. Placing functionalized boron nitride tubes into a furnace at 600 degrees Celsius (1,112 degrees Fahrenheit) stripped them of the added molecules and returned them to their nearly pristine state.

“We call it defunctionalization,” Martí said. “You can functionalize them for an application and then remove the chemical groups to regain the pristine material. That’s something else the material brings that is a little different.”

The researchers have provided this pretty illustration of boron nitride nanotube,

Caption: Rice University researchers have discovered a way to ‘decorate’ electrically insulating boron nitride nanotubes with functional groups, making them more suitable for use with polymers and composite materials. Credit: Martí Research Group/Rice University

Here’s a link to and a citation for the paper,

Chemical Decoration of Boron Nitride Nanotubes Using the Billups-Birch Reaction: Toward Enhanced Thermostable Reinforced Polymer and Ceramic Nanocomposites by Carlos A. de los Reyes, Kendahl L. Walz Mitra, Ashleigh D. Smith, Sadegh Yazdi, Axel Loredo, Frank J. Frankovsky, Emilie Ringe, Matteo Pasquali, and Angel A. Martí. ACS Appl. Nano Mater., Article ASAP DOI: 10.1021/acsanm.8b00633 Publication Date (Web): May 16, 2018

Copyright © 2018 American Chemical Society

This paper is behind a paywall.

Graphene flakes bring spintronics a step closer?

Italian researchers are hoping that graphene flakes will be instrumental in the development of spintronics according to a March 14, 2018 news item on phys.org,

Graphene nanoflakes are promising for possible applications in the field of nanoelectronics, and the subject of a study recently published in Nano Letters. These hexagonal nanostructures exhibit quantum effects for modulating current flow. Thanks to their intrinsic magnetic properties, they could also represent a significant step forward in the field of spintronics. The study, conducted via computer analysis and simulations, was led by Massimo Capone.

A March 14, 2018 Scuola Internazionale Superiore di Studi Avanzati (SISSA) press release (also on EurekAlert), which originated the news item, expands on the theme,

“We have been able to observe two key phenomena by analysing the properties of graphene nanoflakes. Both are of great interest for possible future applications” explain Angelo Valli and Massimo Capone, authors of the study together with Adriano Amaricci and Valentina Brosco. The first phenomenon deals with the so-called interference between electrons and is a quantum phenomenon: «In nanoflakes, the electrons interfere with each other in a “destructive” manner if we measure the current in a certain configuration. This means that there is no transmission of current. This is a typically quantum phenomenon, which only occurs at very reduced sizes. By studying the graphene flakes we have understood that it is possible to bring this phenomenon to larger systems, therefore into the nano world and on a scale in which it is observable and can be exploited for possible uses in nanoelectronics». The two researchers explain that in what are called “Quantum interference transistors” destructive interference would be the “OFF” status. For the “ON” status, they say it is sufficient to remove the conditions for interference, thereby enabling the current to flow.

Magnetism and spintronics

But there’s more. In the study, the researchers demonstrated that the nanoflakes present new magnetic properties which are absent, for example, in an entire sheet of graphene: «The magnetism emerges spontaneously at their edges, without any external intervention. This enables the creation of a spin current». The union between the phenomena of quantum interference and of magnetism would allow to obtain almost complete spin polarization, with a huge potential in the field of spintronics, explain the researchers. These properties could be used, for example, in the memorising and processing information technologies, interpreting the spin as binary code. The electron spin, being quantised and having only two possible configurations (which we could call “up” and “down”), is very well suited for this kind of implementation.

Next step: the experimental test

To improve the efficiency of the possible device and the percentage of current polarization the researchers have also developed a protocol that envisages the interaction of the graphene flakes with a surface made of nitrogen and boron. «The results obtained are really interesting. This evidence now awaits the experimental test, to confirm what we have theoretically predicted» concludes Massimo Capone, head of the research and recently awarded the title of Outstanding Referee by the American Physical Society journal; in this way, each year, the journal indicates the male and female scientists who have distinguished themselves for their expertise in collaborating with the journal.

Here’s a link to and a citation for the paper,

Quantum Interference Assisted Spin Filtering in Graphene Nanoflakes by Angelo Valli, Adriano Amaricci, Valentina Brosco, and Massimo Capone. Nano Lett., 2018, 18 (3), pp 2158–2164 DOI: 10.1021/acs.nanolett.8b00453 Publication Date (Web): February 23, 2018

Copyright © 2018 American Chemical Society

This paper is behind a paywall.

Fireworks for fuel?

Scientists are attempting to harness the power in fireworks for use as fuel according to a Jan. 18, 2017 news item on Nanowerk,

The world relies heavily on gasoline and other hydrocarbons to power its cars and trucks. In search of an alternative fuel type, some researchers are turning to the stuff of fireworks and explosives: metal powders. And now one team is reporting a method to produce a metal nanopowder fuel with high energy content that is stable in air and doesn’t go boom until ignited.

A Jan. 18, 2017 American Chemical Society (ACS) news release, which originated the news item, expands on the theme,

Hydrocarbon fuels are liquid at room temperature, are simple to store, and their energy can be used easily in cars and trucks. Metal powders, which can contain large amounts of energy, have long been used as a fuel in explosives, propellants and pyrotechnics. It might seem counterintuitive to develop them as a fuel for vehicles, but some researchers have proposed to do just that. A major challenge is that high-energy metal nanopowder fuels tend to be unstable and ignite on contact with air. Albert Epshteyn and colleagues wanted to find a way to harness and control them, producing a fuel with both high energy content and good air stability.

The researchers developed a method using an ultrasound-mediated chemical process to combine the metals titanium, aluminum and boron with a sprinkle of hydrogen in a mixed-metal nanopowder fuel. The resulting material was both more stable and had a higher energy content than the standard nano-aluminum fuels. With an energy density of at least 89 kilojoules/milliliter, which is significantly superior to hydrocarbons’ 33 kilojoules/milliliter, this new titanium-aluminum-boron nanopowder packs a big punch in a small package.

Here’s a link to and a citation for the paper,

Optimization of a High Energy Ti-Al-B Nanopowder Fuel by Albert Epshteyn, Michael Raymond Weismiller, Zachary John Huba, Emily L. Maling, and Adam S. Chaimowitz. Energy Fuels, DOI: 10.1021/acs.energyfuels.6b02321 Publication Date (Web): December 30, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Diamond-based electronics?

A May 24, 2016 news item on ScienceDaily describes the latest research on using diamonds as semiconductors,

Along with being a “girl’s best friend,” diamonds also have remarkable properties that could make them ideal semiconductors. This is welcome news for electronics; semiconductors are needed to meet the rising demand for more efficient electronics that deliver and convert power.

The thirst for electronics is unlikely to cease and almost every appliance or device requires a suite of electronics that transfer, convert and control power. Now, researchers have taken an important step toward that technology with a new way to dope single crystals of diamonds, a crucial process for building electronic devices.

A May 24, 2016 American Institute of Physics (AIP) news release (also on EurekAlert), which originated the news item, provides more detail,

For power electronics, diamonds could serve as the perfect material. They are thermally conductive, which means diamond-based devices would dissipate heat quickly and easily, foregoing the need for bulky and expensive methods for cooling. Diamond can also handle high voltages and power. Electrical currents also flow through diamonds quickly, meaning the material would make for energy efficient devices.

But among the biggest challenges to making diamond-based devices is doping, a process in which other elements are integrated into the semiconductor to change its properties. Because of diamond’s rigid crystalline structure, doping is difficult.

Currently, you can dope diamond by coating the crystal with boron and heating it to 1450 degrees Celsius. But it’s difficult to remove the boron coating at the end. This method only works on diamonds consisting of multiple crystals stuck together. Because such polydiamonds have irregularities between the crystals, single-crystals would be superior semiconductors.

You can dope single crystals by injecting boron atoms while growing the crystals artificially. The problem is the process requires powerful microwaves that can degrade the quality of the crystal.

Now, Ma [Zhengqiang (Jack) Ma, an electrical and computer engineering professor at the University of Wisconsin-Madison] and his colleagues have found a way to dope single-crystal diamonds with boron at relatively low temperatures and without any degradation. The researchers discovered if you bond a single-crystal diamond with a piece of silicon doped with boron, and heat it to 800 degrees Celsius, which is low compared to the conventional techniques, the boron atoms will migrate from the silicon to the diamond. It turns out that the boron-doped silicon has defects such as vacancies, where an atom is missing in the lattice structure. Carbon atoms from the diamond will fill those vacancies, leaving empty spots for boron atoms.

This technique also allows for selective doping, which means more control when making devices. You can choose where to dope a single-crystal diamond simply by bonding the silicon to that spot.

The new method only works for P-type doping, where the semiconductor is doped with an element that provides positive charge carriers (in this case, the absence of electrons, called holes).

“We feel like we found a very easy, inexpensive, and effective way to do it,” Ma said. The researchers are already working on a simple device using P-type single-crystal diamond semiconductors.

But to make electronic devices like transistors, you need N-type doping that gives the semiconductor negative charge carriers (electrons). And other barriers remain. Diamond is expensive and single crystals are very small.

Still, Ma says, achieving P-type doping is an important step, and might inspire others to find solutions for the remaining challenges. Eventually, he said, single-crystal diamond could be useful everywhere — perfect, for instance, for delivering power through the grid.

Here’s an image the researchers have released,

Optical image of a diode array on a natural single crystalline diamond plate. (The image looks blurred due to light scattering by the array of small pads on top of the diamond plate.) Inset shows the deposited anode metal on top of heavy doped Si nanomembrane that is bonded to natural single crystalline diamond. CREDIT: Jung-Hun Seo

Optical image of a diode array on a natural single crystalline diamond plate. (The image looks blurred due to light scattering by the array of small pads on top of the diamond plate.) Inset shows the deposited anode metal on top of heavy doped Si nanomembrane that is bonded to natural single crystalline diamond. CREDIT: Jung-Hun Seo Courtesy: American Institute of Physics

Here’s a link to and a citation for the paper,

Thermal diffusion boron doping of single-crystal natural diamond by Jung-Hun Seo, Henry Wu, Solomon Mikael, Hongyi Mi, James P. Blanchard, Giri Venkataramanan, Weidong Zhou, Shaoqin Gong, Dane Morgan, and Zhenqiang Ma. J. Appl. Phys. 119, 205703 (2016); http://dx.doi.org/10.1063/1.4949327

This paper appears to be open access.

2-D boron as a superconductor

A March 31, 2016 news item on ScienceDaily highlights some research into 2D (two-dimensional) boron at Rice University (Texas, US),

Rice University scientists have determined that two-dimensional boron is a natural low-temperature superconductor. In fact, it may be the only 2-D material with such potential.

Rice theoretical physicist Boris Yakobson and his co-workers published their calculations that show atomically flat boron is metallic and will transmit electrons with no resistance. …

The hitch, as with most superconducting materials, is that it loses its resistivity only when very cold, in this case between 10 and 20 kelvins (roughly, minus-430 degrees Fahrenheit). But for making very small superconducting circuits, it might be the only game in town.

A March 30, 2016 Rice University news release (also on EurekAlert but dated March 31, 2016), which originated the news item, expands on the theme,

The basic phenomenon of superconductivity has been known for more than 100 years, said Evgeni Penev, a research scientist in the Yakobson group, but had not been tested for its presence in atomically flat boron.

“It’s well-known that the material is pretty light because the atomic mass is small,” Penev said. “If it’s metallic too, these are two major prerequisites for superconductivity. That means at low temperatures, electrons can pair up in a kind of dance in the crystal.”

“Lower dimensionality is also helpful,” Yakobson said. “It may be the only, or one of very few, two-dimensional metals. So there are three factors that gave the initial motivation for us to pursue the research. Then we just got more and more excited as we got into it.”

Electrons with opposite momenta and spins effectively become Cooper pairs; they attract each other at low temperatures with the help of lattice vibrations, the so-called “phonons,” and give the material its superconducting properties, Penev said. “Superconductivity becomes a manifestation of the macroscopic wave function that describes the whole sample. It’s an amazing phenomenon,” he said.

It wasn’t entirely by chance that the first theoretical paper establishing conductivity in a 2-D material appeared at roughly the same time the first samples of the material were made by laboratories in the United States and China. In fact, an earlier paper by the Yakobson group had offered a road map for doing so.

That 2-D boron has now been produced is a good thing, according to Yakobson and lead authors Penev and Alex Kutana, a postdoctoral researcher at Rice. “We’ve been working to characterize boron for years, from cage clusters to nanotubes to planer sheets, but the fact that these papers appeared so close together means these labs can now test our theories,” Yakobson said.

“In principle, this work could have been done three years ago as well,” he said. “So why didn’t we? Because the material remained hypothetical; okay, theoretically possible, but we didn’t have a good reason to carry it too far.

“But then last fall it became clear from professional meetings and interactions that it can be made. Now those papers are published. When you think it’s coming for real, the next level of exploration becomes more justifiable,” Yakobson said.

Boron atoms can make more than one pattern when coming together as a 2-D material, another characteristic predicted by Yakobson and his team that has now come to fruition. These patterns, known as polymorphs, may allow researchers to tune the material’s conductivity “just by picking a selective arrangement of the hexagonal holes,” Penev said.

He also noted boron’s qualities were hinted at when researchers discovered more than a decade ago that magnesium diborite is a high-temperature electron-phonon superconductor. “People realized a long time ago the superconductivity is due to the boron layer,” Penev said. “The magnesium acts to dope the material by spilling some electrons into the boron layer. In this case, we don’t need them because the 2-D boron is already metallic.”

Penev suggested that isolating 2-D boron between layers of inert hexagonal boron nitride (aka “white graphene”) might help stabilize its superconducting nature.

Without the availability of a block of time on several large government supercomputers, the study would have taken a lot longer, Yakobson said. “Alex did the heavy lifting on the computational work,” he said. “To turn it from a lunchtime discussion into a real quantitative research result took a very big effort.”

The paper is the first by Yakobson’s group on the topic of superconductivity, though Penev is a published author on the subject. “I started working on superconductivity in 1993, but it was always kind of a hobby, and I hadn’t done anything on the topic in 10 years,” Penev said. “So this paper brings it full circle.”

Here’s a link to and a citation for the paper,

Can Two-Dimensional Boron Superconduct? by Evgeni S. Penev, Alex Kutana, and Boris I. Yakobson. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.6b00070 Publication Date (Web): March 22, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Dexter Johnson has published an April 5, 2016 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) about this latest Rice University work on 2D boron that includes comments from his email interview with Penev.

Boron as a ‘buckyball’ or borospherene

First there was the borophene (like graphene but using boron rather than carbon) announcement from Brown University in my Jan. 28, 214 posting and now US (Brown University again) and Chinese researchers have developed a boron ‘buckyball’. Coincidentally, this announcement comes just after the 2014 World Cup final (July 13, 2014). Representations of buckyballs always resemble soccer balls. (Note: Germany won.)

From a July 14, 2014 news item on Azonano,

The discovery 30 years ago of soccer-ball-shaped carbon molecules called buckyballs helped to spur an explosion of nanotechnology research. Now, there appears to be a new ball on the pitch.

Researchers from Brown University, Shanxi University and Tsinghua University in China have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball. It’s the first experimental evidence that a boron cage structure—previously only a matter of speculation—does indeed exist.

“This is the first time that a boron cage has been observed experimentally,” said Lai-Sheng Wang, a professor of chemistry at Brown who led the team that made the discovery. “As a chemist, finding new molecules and structures is always exciting. The fact that boron has the capacity to form this kind of structure is very interesting.”

The researchers have provided an illustration of their borospherene,

The carbon buckyball has a boron cousin. A cluster for 40 boron atoms forms a hollow cage-like molecule. Courtesy Brown University

The carbon buckyball has a boron cousin. A cluster for 40 boron atoms forms a hollow cage-like molecule. Courtesy Brown University

A July 9, 2104 Brown University news release (also on EurekAlert), which originated the news item, describes the borosphene’s predecessor, the carbon buckyball, and provides more details about this new molecule,

Carbon buckyballs are made of 60 carbon atoms arranged in pentagons and hexagons to form a sphere — like a soccer ball. Their discovery in 1985 was soon followed by discoveries of other hollow carbon structures including carbon nanotubes. Another famous carbon nanomaterial — a one-atom-thick sheet called graphene — followed shortly after.

After buckyballs, scientists wondered if other elements might form these odd hollow structures. One candidate was boron, carbon’s neighbor on the periodic table. But because boron has one less electron than carbon, it can’t form the same 60-atom structure found in the buckyball. The missing electrons would cause the cluster to collapse on itself. If a boron cage existed, it would have to have a different number of atoms.

Wang and his research group have been studying boron chemistry for years. In a paper published earlier this year, Wang and his colleagues showed that clusters of 36 boron atoms form one-atom-thick disks, which might be stitched together to form an analog to graphene, dubbed borophene. Wang’s preliminary work suggested that there was also something special about boron clusters with 40 atoms. They seemed to be abnormally stable compared to other boron clusters.

Figuring out what that 40-atom cluster actually looks like required a combination of experimental work and modeling using high-powered supercomputers.

On the computer, Wang’s colleagues modeled over 10,000 possible arrangements of 40 boron atoms bonded to each other. The computer simulations estimate not only the shapes of the structures, but also estimate the electron binding energy for each structure — a measure of how tightly a molecule holds its electrons. The spectrum of binding energies serves as a unique fingerprint of each potential structure.

The next step is to test the actual binding energies of boron clusters in the lab to see if they match any of the theoretical structures generated by the computer. To do that, Wang and his colleagues used a technique called photoelectron spectroscopy.

Chunks of bulk boron are zapped with a laser to create vapor of boron atoms. A jet of helium then freezes the vapor into tiny clusters of atoms. The clusters of 40 atoms were isolated by weight then zapped with a second laser, which knocks an electron out of the cluster. The ejected electron flies down a long tube Wang calls his “electron racetrack.” The speed at which the electrons fly down the racetrack is used to determine the cluster’s electron binding energy spectrum — its structural fingerprint.

The experiments showed that 40-atom-clusters form two structures with distinct binding spectra. Those spectra turned out to be a dead-on match with the spectra for two structures generated by the computer models. One was a semi-flat molecule and the other was the buckyball-like spherical cage.

“The experimental sighting of a binding spectrum that matched our models was of paramount importance,” Wang said. “The experiment gives us these very specific signatures, and those signatures fit our models.”

The borospherene molecule isn’t quite as spherical as its carbon cousin. Rather than a series of five- and six-membered rings formed by carbon, borospherene consists of 48 triangles, four seven-sided rings and two six-membered rings. Several atoms stick out a bit from the others, making the surface of borospherene somewhat less smooth than a buckyball.

As for possible uses for borospherene, it’s a little too early to tell, Wang says. One possibility, he points out, could be hydrogen storage. Because of the electron deficiency of boron, borospherene would likely bond well with hydrogen. So tiny boron cages could serve as safe houses for hydrogen molecules.

But for now, Wang is enjoying the discovery.

“For us, just to be the first to have observed this, that’s a pretty big deal,” Wang said. “Of course if it turns out to be useful that would be great, but we don’t know yet. Hopefully this initial finding will stimulate further interest in boron clusters and new ideas to synthesize them in bulk quantities.”

The theoretical modeling was done with a group led by Prof. Si-Dian Li from Shanxi University and a group led by Prof. Jun Li from Tsinghua University. The work was supported by the U.S. National Science Foundation (CHE-1263745) and the National Natural Science Foundation of China.

Here’s a link to and a citation for the paper,

Observation of an all-boron fullerene by Hua-Jin Zhai, Ya-Fan Zhao, Wei-Li Li, Qiang Chen, Hui Bai, Han-Shi Hu, Zachary A. Piazza, Wen-Juan Tian, Hai-Gang Lu, Yan-Bo Wu, Yue-Wen Mu, Guang-Feng Wei, Zhi-Pan Liu, Jun Li, Si-Dian Li, & Lai-Sheng Wang. Nature Chemistry (2014) doi:10.1038/nchem.1999 Published online 13 July 2014

This paper is behind a paywall.

Borophene at Brown University (US)

It’s still theory at this point but researchers at Brown University (Rhode Island, US) have produced experimental proof that a single layer of boron atoms in a lattice reminiscent of  but not identical to a graphene layer is possible. A Jan. 28, 2014 news item on Azonano describes the research,

Researchers from Brown University have shown experimentally that a boron-based competitor to graphene is a very real possibility.

Graphene has been heralded as a wonder material. Made of a single layer of carbon atoms in a honeycomb arrangement, graphene is stronger pound-for-pound than steel and conducts electricity better than copper. Since the discovery of graphene, scientists have wondered if boron, carbon’s neighbor on the periodic table, could also be arranged in single-atom sheets. Theoretical work suggested it was possible, but the atoms would need to be in a very particular arrangement.

Boron has one fewer electron than carbon and as a result can’t form the honeycomb lattice that makes up graphene. For boron to form a single-atom layer, theorists suggested that the atoms must be arranged in a triangular lattice with hexagonal vacancies — holes — in the lattice.

“That was the prediction,” said Lai-Sheng Wang, professor of chemistry at Brown, “but nobody had made anything to show that’s the case.”

Wang and his research group, which has studied boron chemistry for many years, have now produced the first experimental evidence that such a structure is possible. In a paper published on January 20 in Nature Communications, Wang and his team showed that a cluster made of 36 boron atoms (B36) forms a symmetrical, one-atom thick disc with a perfect hexagonal hole in the middle.

Here’s an image that illustrates ‘borophene’,

Caption: This shows a 36-atom cluster of boron, left, arranged as a flat disc with a hexagonal hole in the middle, fits the theoretical requirements for making a one-atom-thick boron sheet, right, a theoretical nanomaterial dubbed "borophene." Credit: Wang Lab / Brown University

Caption: This shows a 36-atom cluster of boron, left, arranged as a flat disc with a hexagonal hole in the middle, fits the theoretical requirements for making a one-atom-thick boron sheet, right, a theoretical nanomaterial dubbed “borophene.”
Credit: Wang Lab / Brown University

The Jan. 27, 2014 Brown University news release (also on EurekAlert), which originated the news item, provides details about how the research was conducted,

The work required a combination of laboratory experiments and computational modeling. In the lab, Wang and his student, Wei-Li Li, probe the properties of boron clusters using a technique called photoelectron spectroscopy. They start by zapping chunks of bulk boron with a laser to create vapor of boron atoms. A jet of helium then freezes the vapor into tiny clusters of atoms. Those clusters are then zapped with a second laser, which knocks an electron out of the cluster and sends it flying down a long tube that Wang calls his “electron racetrack.” The speed at which the electron flies down the racetrack is used to determine the cluster’s electron binding energy spectrum — a readout of how tightly the cluster holds its electrons. That spectrum serves as fingerprint of the cluster’s structure.

Wang’s experiments showed that the B36 cluster was something special. It had an extremely low electron binding energy compared to other boron clusters. The shape of the cluster’s binding spectrum also suggested that it was a symmetrical structure.

To find out exactly what that structure might look like, Wang turned to Zachary Piazza, one of his graduate students specializing in computational chemistry. Piazza began modeling potential structures for B36 on a supercomputer, investigating more than 3,000 possible arrangements of those 36 atoms. Among the arrangements that would be stable was the planar disc with the hexagonal hole.

“As soon as I saw that hexagonal hole,” Wang said, “I told Zach, ‘We have to investigate that.'”

To ensure that they have truly found the most stable arrangement of the 36 boron atoms, they enlisted the help of Jun Li, who is a professor of chemistry at Tsinghua University in Beijing and a former senior research scientist at Pacific Northwest National Laboratory (PNNL) in Richland, Wash. Li, a longtime collaborator of Wang’s, has developed a new method of finding stable structures of clusters, which would be suitable for the job at hand. Piazza spent the summer of 2013 at PNNL working with Li and his students on the B36 project. They used the supercomputer at PNNL to examine more possible arrangements of the 36 boron atoms and compute their electron binding spectra. They found that the planar disc with a hexagonal hole matched very closely with the spectrum measured in the lab experiments, indicating that the structure Piazza found initially on the computer was indeed the structure of B36.

That structure also fits the theoretical requirements for making borophene, which is an extremely interesting prospect, Wang said. The boron-boron bond is very strong, nearly as strong as the carbon-carbon bond. So borophene should be very strong. Its electrical properties may be even more interesting. Borophene is predicted to be fully metallic, whereas graphene is a semi-metal. That means borophene might end up being a better conductor than graphene.

“That is,” Wang cautions, “if anyone can make it.”

Here’s a link to and a citation for the research paper,

Planar hexagonal B36 as a potential basis for extended single-atom layer boron sheets by Zachary A. Piazza, Han-Shi Hu, Wei-Li Li, Ya-Fan Zhao, Jun Li, & Lai-Sheng Wang. Nature Communications 5, Article number: 3113 doi:10.1038/ncomms4113 Published 20 January 2014

This paper is behind a paywall.