#borophene

From fullerenes to 2D structures: A unified design principle for boron nanostructures

Boron, a chemical element next to carbon in the periodic table, is known for its unique ability to form complex bond networks. Unlike carbon, which typically bonds with two or three neighboring atoms, boron can share electrons among several atoms. This leads to a wide variety of nanostructures. These include boron fullerenes, which are hollow, cage-like molecules, and borophenes, ultra-thin metallic sheets of boron atoms arranged in triangular and hexagonal patterns. Dr. Nevill Gonzalez Szwacki has developed a model explaining the variety of boron nanostructures. The analysis, published in the journal 2D Materials, combines more than a dozen known boron nanostructures, including the experimentally observed B₄₀ and B₈₀ fullerenes.

Stronger and more flexible than graphene, a single-atom layer of boron could revolutionize sensors, batteries, and catalytic chemistry.

Not so long ago, graphene was the great new wonder material. A super-strong, atom-thick sheet of carbon “chicken wire,” it can form tubes, balls, and other curious shapes.

And because it conducts electricity, materials scientists raised the prospect of a new…

Credit: Mark C Hersam

What is it?

A two-dimensional, atomically thin phase of boron.

Who is involved?

A team led by Mark C Hersam, Walter P Murphy Professor of Materials Science and Engineering in Northwestern University’s McCormick School of Engineering.

How is it novel?

Hersam’s team were attempting to integrate borophene, which is synthesised on a sliver sheet, with perylene-3,4,9,10-tetracarboxylic dianhydride, a self-assembling, organic material. When the organic material was placed on top of the borophene it diffused off and onto the silver sheet, on which the borophene sits. An interface was formed between the borophene and the self-assembled organic material.

How can it be used?

The team expects borophene could be used as an interconnect or electrode in 2D nanoelectronic circuits, and potentially a transparent conductor for flexible electronics because of its flexibility and high mechanical strength. The borophene must first be moved off the silver sheet and onto a chemically inactive substrate.

More than ten years ago, researchers at Rice University led by materials scientist Boris Yakobson predicted that boron atoms would cling too tightly to copper to form borophene, a flexible, metallic two-dimensional material with potential across electronics, energy and catalysis. Now, new research shows that prediction holds up, but not in the way anyone expected. Unlike systems such as graphene on copper, where atoms may diffuse into the substrate without forming a distinct alloy, the boron atoms in this case formed a defined 2D copper boride -- a new compoundwith a distinct atomic structure. The finding, published in Science Advances by researchers from Rice and Northwestern University, sets the stage for further exploration of a relatively untapped class of 2D materials.

Exploring how to develop better rechargeable aluminum batteries

A team from China published new work on rechargeable aluminum batteries in Energy Material Advances.

"Rechargeable aluminum batteries (RABs) have great potential as powerful candidates for large-scale energy storage devices," said the corresponding author Chuan Wu, professor at School of Materials Science and Engineering in Beijing Institute of Technology. "The high theoretical capacity, abundant reserves and high security will help RABs achieve application and commercialization."

Professor Wu explained that due to the multi-electron reaction of Al (three-electron-transfer in theory), the direct adoption of Al anode could lead to highly competitive gravimetric and volumetric capacities (2980 mAh g−1 and 8046 mAh cm−3 based on Al) as well as suitable redox potential (−1.66 V versus standard hydrogen for Al3+/Al). However, stemming from the basic properties of a small radius (54 pm) and high charge (+3), Al3+ ions exhibit extremely slow migration activity and strong electrostatic force to damage the crystal structure if migrated.

Disorder in surface materials key to better hydrogen storage

Lawrence Livermore National Laboratory (LLNL) scientists have found that atomic disorder in certain boron-based hydrogen storage systems can potentially improve the rate of hydrogen uptake.

Metal boride surfaces and their single-layer variants—known as borophenes—are generally thought to feature a regular arrangement of atoms at low to moderate temperatures. The LLNL team proved that in many cases, these atoms actually disorder dynamically: A surprising phenomenon in contrast to conventional understanding of how most solid-state surfaces behave. The surface disorder means each atomic site has different local properties. According to the team's research, some of these sites can make dissociation of hydrogen molecules easier, which in turn is expected to accelerate activation of the material during hydrogen storage.

The findings have implications for other applications, too. In addition to hydrogen storage, metal borides and borophenes can be used for superconductivity, electrocatalysis, optoelectronics and as coatings for thermal and corrosion resistance. In several of these applications, the specific boron surface atom arrangements play an outsized role in determining the overall performance.

Inorganic borophene liquid crystals may provide a superior new material for optoelectronic devices

Liquid crystals derived from borophene have risen in popularity, owing to their applicability in optoelectronic and photonic devices. However, their development requires a very narrow temperature range, which hinders their large-scale application. Now, Tokyo Tech researchers investigated a liquid-state borophene oxide, discovering that it exhibited high thermal stability and optical switching behavior even at low voltages. These findings highlight the strong potential of borophene oxide-derived liquid crystals for use in widespread applications.

Two-dimensional (2D) atomic layered materials, such as the carbon-based graphene and the boron-based borophene, are highly sought after for their applications in a variety of optoelectronic devices, owing to their desirable electronic properties. The monolayer structure of borophene with a network of boron bonds endows it with high flexibility, which can be beneficial for the generation of a liquid state at low temperatures. Thus, it is not surprising that liquid crystals derived from 2D networked structures are in high demand. However, the poor stability of borophene, in particular, makes it difficult for it to undergo a phase transition to the liquid state.

Engineers create double layer of borophene for first time

For the first time, Northwestern University engineers have created a double layer of atomically flat borophene, a feat that defies the natural tendency of boron to form non-planar clusters beyond the single-atomic-layer limit.

Although known for its promising electronic properties, borophene—a single-atom-layer-thick sheet of boron—is challenging to synthesize. Unlike its analog two-dimensional material graphene, which can be peeled away from innately layered graphite using something as simple as scotch tape, borophene cannot merely be peeled away from bulk boron. Instead, borophene must be grown directly onto a substrate.

And if growing one layer was difficult, growing multiple layers of atomically flat borophene seemed impossible. Because bulk boron is not layered like graphite, growing boron beyond single atomic layers leads to clustering rather than planar films.

"When you try to grow a thicker layer, the boron wants to adopt its bulk structure," said Northwestern's Mark C. Hersam, co-senior author of the study. "Rather than remaining atomically flat, thicker boron films form particles and clusters. The key was to find growth conditions that prevented the clusters from forming. Until now, we didn't think you could go beyond one layer. Now we have moved into unexplored territory between the single atomic layer and the bulk, resulting in a new playground for discovery."