Two-Dimensional Boron Materials and Their Properties

Two-dimensional boron materials, most notably borophene and hydrogen boride sheets, stand out among elemental monolayers for their remarkable combination of electronic, mechanical and chemical characteristics. Unlike graphene’s uniform honeycomb lattice, boron monolayers adopt a range of polymorphic structures defined by arrangements of triangular motifs interspersed with hollow hexagons. This flexibility gives rise to strong anisotropy in thermal and electrical transport, with ultrahigh electron mobility, Dirac-like charge carriers and tunable metallic or semiconducting behaviour under chemical functionalisation or charge doping. Mechanically, borophene exhibits exceptional in-plane rigidity alongside regions of negative Poisson’s ratio and high fracture strength. Its unique σ-bond network underpins stability and guides the rational design of new allotropes. Optical bandgaps can be opened by defect introduction or surface passivation, offering routes to optoelectronic devices. In tandem, hydrogen boride sheets demonstrate photoinduced hydrogen release and reversible H₂ storage, pointing to transformative applications in clean energy. Collectively, the interplay of polymorphism, bond resonance and low-dimensional physics in two-dimensional boron materials underlies their rapid emergence as versatile platforms for nanoelectronics, catalysis, sensing and energy technologies.

Research from Nature Portfolio

Recent studies have developed a σ-bond resonance framework for flat boron sheets, enabling intuitive prediction of two- and three-centre bond distributions without resorting to extensive quantum calculations. This theory explains the exceptional stability of particular hole concentrations and informs targeted design of novel boron allotropes. Complementing this, advanced microscopy using functionalised atomic probes has directly visualised the hollow hexagon arrangements in multiple borophene polymorphs, establishing a comprehensive phase diagram across growth conditions. These images confirm the structural models for v1/5 and v1/6 phases and reveal transitions between rotationally commensurate and incommensurate lattices. In related work, hydrogen boride nanosheets have been shown to release molecular hydrogen under mild photoirradiation by promoting electrons from σ-bonding to antibonding states. This process delivers a reversible H₂ output of approximately 8 wt %, demonstrating a promising avenue for solid-state hydrogen storage and on-demand release under ambient conditions.

Two-Dimensional Boron Materials and Their Properties publication trend

The graph below shows the total number of articles in two-dimensional boron materials and their properties across all publications each year (not limited to Nature Index journals).

Technical terms

Borophene: A monolayer of boron atoms forming polymorphic two-dimensional lattices with mixtures of triangular motifs and hollow hexagons.

σ-bond resonance: A theoretical model describing the distribution of two-centre and three-centre σ-bonds in boron sheets, analogous to aromatic resonance in carbon systems.

Polymorphism: The ability of a material to adopt multiple distinct crystal structures or lattice arrangements.

Dirac fermions: Charge carriers in a material that behave as massless relativistic particles, leading to high mobility and linear energy dispersion.

Phonon dispersion: The relationship between phonon frequency and wavevector, governing thermal transport in crystalline materials.

References

1. Theory of sigma bond resonance in flat boron materials. Nature Communications (2023).
2. Geometric imaging of borophene polymorphs with functionalized probes. Nature Communications (2019).
3. Photoinduced hydrogen release from hydrogen boride sheets. Nature Communications (2019).
4. Strain effects on borophene: ideal strength, negative Possion’s ratio and phonon instability. New Journal of Physics (2016).
5. Exploring the charge localization and band gap opening of borophene: a first-principles study. Nanoscale (2018).
6. Two-Dimensional Borophene: Properties, Fabrication, and Promising Applications. Research (2020).
7. Recent progress in boron nanomaterials. Science and Technology of Advanced Materials (2017).