Bottom-up approaches to form superatom-assembled 2D few-layered borophanes and carborophanes and 3D α-B12, γ-B28, and B4C based on icosahedral B12 and CB11

The discovery of monolayer graphene with a prototypical Dirac cone in 2004 has set up a new area in nanoscience and nanotechnology. Nevertheless, graphene has its intrinsic limitations to serve as semiconducting nanomaterials. The syntheses of supported monolayer borophene in 2015 and bilayer borophene in 2022 present the possibility of a new class of boron-based metallic and semiconducting nanomaterials. However, how to form stable freestanding few-layered borophenes in bottom-up approaches which can be peeled off from substitutes still remains unknown in both experiments and theory. A team of material scientists in the Nanoclusters & Nanomaterials Lab (NNL) led by Si-Dian Li from Shanxi University in Taiyuan, China recently established bottom-up approaches at DFT level to form a series of novel superatom-assembled 2D few-layered α-rhombohedral borophanes (B₁₂)_nH₆ (α-1–5) and (B₁₂)_nH₂ (α-7–11), γ-orthorhombic borophanes (B₁₂-B₂)_nH₈ (γ-1–5), and carborophanes (CB₁₁-CBC)_nH₈ (σ-1–5) and 3D α-B₁₂, γ-B₂₈, and B₄C crystals using the experimentally known aromatic icosahedral B₁₂H₁₂^2- and CB₁₁H₁₁^- as precursors by partial or complete dehydrogenations. The newly predicted freestanding few-layered 2D borophanes and carborophanes all appear to be semiconductors in nature, with the dangling bonds on the top and bottom of the 2D sheets satisfied by terminal hydrogen atoms.  

The team published their paper in Nano Research on March 28, 2025.

“Most profoundly, as both chemically and mechanically stable species, the freestanding trilayer, tetralayer, and pentalayer carborophanes (CB₁₁-CBC)_nH₈ (n=3-5) with the calculated band gaps between E_gap=1.32–1.26 eV are well compatible with traditional silicon semiconductors (E_gap=1.21 eV) in band structures. Such 2D boron-based nanomaterials are possible to be realized in future experiments with suitable dehydrogenation catalysts to produce semiconducting nanodevices well compatible with the nowadays widely used silicon devices in band gaps. Investigations on a general bottom-up strategy to form more complicated 2D few-layered borophanes and carborophanes following certain electron counting rules are currently in progress. Semiconducting pure boron or boron-carbon binary low-dimensional nanomaterials possess a huge potential in future nanodevice application and deserve further joint experimental and theoretical explorations.” Said Si-Dian Li, the corresponding author of the paper. Professor Li is the group leader and chief scientist in the Institute of Molecular Science at Shanxi University.

Extensive DFT calculations and Born-Oppenheimer molecular dynamics (BOMD) simulations indicate that these 2D few-layered borophanes and carborophanes are thermodynamically stable without imaginary phonon frequencies and highly dynamically stable even at 1200 K. These chemically stable 2D few-layered nanomaterials also appear to be mechanically stable, with both their maximum and minimum Young’s modulus (N/m) increasing almost linearly with the number of icosahedral layers in the systems. “These highly stable few-layered 2D borophanes and carborophanes based on icosahedral superatoms can be extended in vertical dimensions infinitely by complete dehydrogenations to form the experimentally known 3D α-B₁₂, γ-B₂₈, and CB₁₁-CBC, suggesting a general bottom-up strategy to form low-dimensional boron-based nanomaterials based on icosahedral B₁₂, CB₁₁, or C₂B₁₀ structural units.” said Si-Dian Li.

Detailed bonding pattern analyses indicate that each icosahedral B₁₂ or CB₁₁ building block in these 2D and 3D nanomaterials possesses 13 12c-2e locally delocalized chemical bonds in the universal superatomic electronic configuration of 1S²1P⁶1D¹⁰1F⁸ which matches the n+1 Wade's rule (n=12), accompanied by an interstitial B-B dumbbell or a C-B-C chain in the corresponding crystal lattice. Such bonding patterns render local spherical aromaticity and overall high stability to the systems. The locally delocalized 13 12c-2e chemical bonds on icosahedral B₁₂, CB₁₁, and C₂B₁₀ building blocks accompanied by necessary interstitial structural units provide the structural and bonding foundations to form semiconducting boron-based nanomaterials.

About the Authors

Professor Si-Dian Li is the group leader and chief scientist in the Institute of Molecular Science, Shanxi University, Taiyuan, China. His expertise mainly lies in the realms of structural chemistry, materials science, and computational chemistry. Over the past twenty years, in close collaboration with prof. Lai-Sheng Wang in Brown university, prof. Boris Yakobson in Rice university, and prof. Yan Li in Peking university, prof. Li’s group has been focusing on designing and discovering novel nanostructures that can serve as materials for energy and optoelectronic applications, including bare boron clusters, metal-doped boron clusters, low-dimensional boron-based nanomaterials, and boron/nitrogen-doped or pure carbon nanomaterials involving flash graphenes (FGs) and single-walled carbon nanotubes (SWCNTs). His group have published over 200 research papers in recent years in Nat. Chem., J. Am. Chem. Soc, Angew. Chem. Int. Ed., Acc. Chem. Res., ACS Nano, Nano Res., Nano Lett., Nanoscale, and Phys. Chem. Chem. Phys. et al.  

For more information about his research group, please visit their website: http://www.cluster-science.com.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 17 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2023 InCites Journal Citation Reports, its 2023 IF is 9.6 (9.0, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.