Nanostructured Hexaborides and Their Emission Properties

Metal hexaborides, notably lanthanum and cerium hexaboride, feature an octahedral boron framework interspersed with metal atoms. Nanostructuring these compounds into wires, rods, tubes and particles refines their surface-to-volume ratio, enhances electron emission and tunes optical absorption bands. Their intrinsically low work function, high thermal stability and robust mechanical properties render them exemplary candidates for thermionic and field emission cathodes, as well as plasmonic absorbers in solar-energy harvesting. At the nanoscale, quantum size effects, surface defects and doping strategies enable precise modulation of emission turn-on fields and spectral selectivity. Advances in synthesis—ranging from chemical vapour deposition to mechanochemical routes—have yielded high-aspect-ratio nanowires and doped nanoparticles with tailored emission characteristics and infrared plasmon resonances. The global appeal of these materials spans electron microscopy sources, high-brightness X-ray tubes and concentrating solar power systems, where concurrent thermal and electron emission can simplify device architecture and drive energy-efficient technologies.

Research from Nature Portfolio

Recent studies have demonstrated that bulk lanthanum hexaboride materials, when optimally consolidated and surface-textured, achieve solar absorbance comparable to advanced silicon carbide absorbers while exhibiting superior spectral selectivity at elevated temperatures. Concurrent measurements of thermal emittance at temperatures around 1100 K have revealed that these materials can function dually as high-temperature solar absorbers and efficient electron sources through thermionic emission, suggesting a pathway to integrated solar thermionic systems with reduced complexity and enhanced energy conversion efficiency.

Nanostructured Hexaborides and Their Emission Properties publication trend

The graph below shows the total number of articles in nanostructured hexaborides and their emission properties across all publications each year (not limited to Nature Index journals).

Technical terms

Nanostructure: A material having at least one dimension in the nanometre scale, typically below 100 nm, which exhibits size-dependent properties.

Hexaboride: A class of compounds with a chemical formula MB₆, where M is a metal and B₆ indicates an octahedral boron cluster.

Thermionic emission: The release of electrons from a heated material when thermal energy overcomes its work function.

Field emission: The extraction of electrons from a surface under a high electric field, often enhanced by nanoscale geometry.

Plasmon resonance: Collective oscillation of free electrons in a material, leading to strong absorption or scattering at specific optical frequencies.

Work function: The minimum energy required to remove an electron from the surface of a solid to a point immediately outside the solid.

References

1. Lanthanum hexaboride for solar energy applications. Scientific Reports (2017).
2. Tuning the Surface Plasmon Resonance of Lanthanum Hexaboride to Absorb Solar Heat: A Review. Materials (2018).
3. Fabrication of vertically aligned single-crystalline lanthanum hexaboride nanowire arrays and investigation of their field emission. NPG Asia Materials (2013).
4. Thermally assisted photoemission effect on CeB6 and LaB6 for application as photocathodes. Physical Review Accelerators and Beams (2017).