Microscopic Mechanism of the Helix-to-Layer Transformation in Elemental Group VI Solids

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Bulk selenium (Se) and tellurium (Te) exist as intertwined alpha helices.
• Atomically thin two-dimensional (2D) allotropes of these elements are of significant interest.
• Understanding the conversion pathways from bulk to 2D materials is crucial for their application.

Purpose of the Study:

• To investigate the conversion mechanism of bulk Se and Te into 2D layers.
• To identify novel 2D allotropes of Se and Te.
• To determine the energetic barriers and conditions for this transformation.

Main Methods:

• Ab initio calculations were employed to simulate the conversion process.
• The study focused on atomic rearrangements at dislocation defects.
• Reaction paths and activation energies were analyzed.

Main Results:

• Previously unknown and stable delta (δ) and eta (η) 2D allotropes of Se and Te were identified.
• A multistep conversion process involving concerted atomic motion at dislocations was revealed.
• A zipper-like motion of dislocations facilitates the structural changes.
• Low activation barriers (≲0.3 eV) suggest the process can occur at moderate temperatures.
• All one-dimensional (1D) and 2D chalcogen structures studied were found to be semiconducting.

Conclusions:

• The conversion of bulk Se and Te to novel 2D allotropes is feasible through a defect-mediated process.
• The identified δ and η 2D allotropes represent new stable forms of these elements.
• The semiconducting nature of these 2D chalcogen structures opens possibilities for electronic applications.