Tag Archives: borospherene

New boron nanostructure—carbon, watch out!

Carbon nanotubes, buckminsterfullerenes (also known as, buckyballs), and/or graphene are names for different carbon nanoscale structures and, as far as I’m aware,carbon is the only element that merits some distinct names at the nanoscale. By comparison, gold can be gold nanorods, gold nanostars, gold nanoparticles, and so on. In short, nanostructures made of gold (and most other elements) are always prefaced with the word ‘gold’ followed by a word with ‘nano’ in it.

Scientists naming a new boron nanoscale structure seem to have adopted both strategies for a hybrid name. Here’s more from a June 25, 2020 news item on phys.org,

The discovery of carbon nanostructures like two-dimensional graphene and soccer ball-shaped buckyballs helped to launch a nanotechnology revolution. In recent years, researchers from Brown University [located in Rhode Island, US] and elsewhere have shown that boron, carbon’s neighbor on the periodic table, can make interesting nanostructures too, including two-dimensional borophene and a buckyball-like hollow cage structure called borospherene.

Caption: The family of boron-based nanostructures has a new member: metallo-borospherenes, hollow cages made from 18 boron atoms and three atoms of lanthanide elements. Credit: Wang Lab / Brown University

A June 25, 2020 Brown University news release (also on EurekAlert), wbich originated the news item, describes these new structures in detail,

Now, researchers from Brown and Tsinghua University have added another boron nanostructure to the list. In a paper published in Nature Communications, they show that clusters of 18 boron atoms and three atoms of lanthanide elements form a bizarre cage-like structure unlike anything they’ve ever seen.

“This is just not a type of structure you expect to see in chemistry,” said Lai-Sheng Wang, a professor of chemistry at Brown and the study’s senior author. “When we wrote the paper we really struggled to describe it. It’s basically a spherical trihedron. Normally you can’t have a closed three-dimensional structure with only three sides, but since it’s spherical, it works.”

The researchers are hopeful that the nanostructure may shed light on the bulk structure and chemical bonding behavior of boron lanthanides, an important class of materials widely used in electronics and other applications. The nanostructure by itself may have interesting properties as well, the researchers say.

“Lanthanide elements are important magnetic materials, each with very different magnetic moments,” Wang said. “We think any of the lanthanides will make this structure, so they could have very interesting magnetic properties.”

Wang and his students created the lanthanide-boron clusters by focusing a powerful laser onto a solid target made of a mixture of boron and a lanthanide element. The clusters are formed upon cooling of the vaporized atoms. Then they used a technique called photoelectron spectroscopy to study the electronic properties of the clusters. The technique involves zapping clusters of atoms with another high-powered laser. Each zap knocks an electron out of the cluster. By measuring the kinetic energies of those freed electrons, researchers can create a spectrum of binding energies for the electrons that bond the cluster together.

“When we see a simple, beautiful spectrum, we know there’s a beautiful structure behind it,” Wang said.

To figure out what that structure looks like, Wang compared the photoelectron spectra with theoretical calculations done by Professor Jun Li and his students from Tsinghua. Once they find a theoretical structure with a binding spectrum that matches the experiment, they know they’ve found the right structure.

“This structure was something we never would have predicted,” Wang said. “That’s the value of combining theoretical calculation with experimental data.”

Wang and his colleagues have dubbed the new structures metallo-borospherenes, and they’re hopeful that further research will reveal their properties.

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

Spherical trihedral metallo-borospherenes by Teng-Teng Chen, Wan-Lu Li, Wei-Jia Chen, Xiao-Hu Yu, Xin-Ran Dong, Jun Li & Lai-Sheng Wang. Nature Communications volume 11, Article number: 2766 (2020) DOI: https://doi.org/10.1038/s41467-020-16532-x Published: 02 June 2020

This paper is open access.

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.