Structure, optical properties and defects in nitride (III-V) nanoscale cage clusters.

Area of Science:

• Computational Materials Science
• Quantum Chemistry
• Nanotechnology

Background:

• Cage-structured nitrides (BN, AlN, GaN, InN) are crucial in materials science.
• Understanding their nanoscale properties is key for advanced applications.
• Previous studies often focused on bulk properties, leaving nanoscale cluster behavior less explored.

Purpose of the Study:

• To investigate the structural, energetic, and optical properties of sub- and low-nanosize stoichiometric clusters of BN, AlN, GaN, and InN.
• To determine the stability of these clusters relative to their bulk phases.
• To explore the influence of defects on cluster stability and properties.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Two octahedral symmetry families (T(d) and T(h)) were considered.
• Time-Dependent Density Functional Theory (TD-DFT) was used for optical absorption spectra of BN clusters.

Main Results:

• BN clusters demonstrate high stability compared to bulk phases.
• Cluster formation energy includes a constant term attributed to curvature and tetragonal defects.
• The (BN)(60) double-bubble structure is unstable, unlike single/double shell cages of other nitrides.
• One-electron band gaps show weak size dependency, contradicting quantum confinement predictions.
• Point defects, particularly interstitials, exhibit the lowest formation energy.

Conclusions:

• Nanoscale BN clusters possess unique stability characteristics influenced by curvature and defects.
• DFT and TD-DFT provide valuable insights into the electronic and optical properties of these nanoclusters.
• The findings challenge existing theories like quantum confinement for these specific nanostructures and highlight the role of defects in stability.