Mechanical properties of pristine and defective carbon-phosphide monolayers: a density functional tight-binding study

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Carbon-phosphide (CP) monolayers are emerging 2D materials with potential applications.
• Understanding their mechanical properties under strain is crucial for device integration.
• Defects, such as vacancies, can significantly alter material behavior.

Purpose of the Study:

• To investigate the elastic, deformation, and failure properties of pristine and defective CP monolayers.
• To analyze the influence of carbon and phosphorus vacancies on mechanical behavior.
• To compare the tensile response along armchair (AC) and zig-zag (ZZ) directions.

Main Methods:

• Density functional tight-binding (DFTB) theory was employed.
• Simulations involved uniform uniaxial tensile strain.
• Two CP allotropes (α-CP and β-CP) and single/double vacancies were considered.

Main Results:

• CP monolayers show strong mechanical anisotropy; ZZ direction is much stiffer and stronger than AC.
• Carbon monovacancies have the lowest formation energy, while P divacancies have the highest.
• Vacancies significantly reduce Young's modulus, failure stress, and strain, especially along the AC direction.
• Fracture mechanisms involve P-P bond rupture (AC) and C-P bond rupture (ZZ) in pristine monolayers.
• Defective CP monolayers exhibit brittle-like failure initiated at vacancies.

Conclusions:

• Mechanical properties of CP monolayers are highly anisotropic and sensitive to vacancy defects.
• Phosphorus vacancies predominantly affect AC direction failure, while both C and P vacancies impact ZZ direction.
• Findings offer insights for designing CP-based nanoelectromechanical systems (NEMS).