Electronic Properties of Carbon Allotropes

Carbon exhibits a remarkable range of electronic behaviours across its allotropes, governed primarily by the hybridisation of its atomic orbitals and the topology of its crystal lattice. In the sp³-bonded diamond, a wide bandgap of approximately 5.5 eV renders it an electrical insulator with exceptional breakdown strength. By contrast, sp²-bonded graphitic forms such as graphene display a zero-gap semimetallic character arising from linear band crossings at symmetry points, yielding massless charge carriers and ultrahigh mobility. Between these extremes lie two-dimensional derivatives and three-dimensional networks—graphynes, biphenylene networks and various patterned graphene allotropes—that host tunable bandgaps, multiple Dirac points or narrow multigaps. The introduction of non-hexagonal rings, extended defects or periodic porosity can open or reshape electronic band structures, enabling semiconducting, semimetallic or topological behaviours. Charge-carrier effective masses, Fermi velocities and band dispersion can be modulated by lattice strain, chemical functionalisation and heteroatom substitution. These electronic characteristics underpin applications ranging from high-speed transistors and transparent electrodes to optoelectronic devices and energy conversion systems.

Research from Nature Portfolio

Recent computational work has identified new two-dimensional carbon networks formed by fusing azulene-derived macrocycles into a graphene matrix. Such azulenoid kekulene-based lattices exhibit unprecedented multigap semiconducting behaviour, with primary gaps of around 0.54 eV and secondary gaps of 0.80 eV that may enhance light–matter interaction in optoelectronic devices. One variant emerges as a narrow-gap semiconductor with exceptionally light electron and hole carriers, offering a promising platform for next-generation photodetectors and light-emitting materials. In parallel, first-principles studies on the recently synthesised biphenylene sheet have revealed its intrinsic metallicity and the presence of an n-type Dirac cone. This allotrope sustains high thermal stability and mechanical robustness, while its metallic conduction and catalytic activity for hydrogen evolution suggest multifunctional applications in nanocatalysis and carbon-based electronics.

Electronic Properties of Carbon Allotropes publication trend

The graph below shows the total number of articles in electronic properties of carbon allotropes across all publications each year (not limited to Nature Index journals).

Technical terms

Bandgap: Energy difference between the valence band maximum and conduction band minimum that determines a material’s electrical conductivity.

Dirac cone: Conical dispersion relation in the electronic band structure where conduction and valence bands meet at a point, yielding massless charge carriers.

Density functional theory (DFT): Quantum mechanical modelling framework used to calculate electronic structure and total energy of materials.

Multigap semiconductor: Material exhibiting more than one distinct energy gap between electronic bands, enabling tailored optical and transport properties.

Topological semimetal: Material in which band crossings are protected by crystal symmetry or topology, giving rise to robust surface or edge states and unconventional transport.

References

1. Prediction of highly stable 2D carbon allotropes based on azulenoid kekulene. Nature Communications (2024).
2. A first principles investigation on the structural, mechanical, electronic, and catalytic properties of biphenylene. Scientific Reports (2021).
3. The rare two-dimensional materials with Dirac cones. National Science Review (2015).
4. PAI-graphene: A new topological semimetallic two-dimensional carbon allotrope with highly tunable anisotropic Dirac cones. Carbon (2020).
5. Ultrahigh Electron Thermal Conductivity in T‐Graphene, Biphenylene, and Net‐Graphene. Advanced Energy Materials (2022).