First-Principles Calculations on Two-Dimensional Au₆X₂ (X = S, Se, or Te) Nanostructures for Device and Photocatalytic Applications

Two-dimensional (2D) transition-metal chalcogenides have been widely regarded due to their diverse properties and promising prospects in nanodevices and energy applications. In this paper, 2D group 11 chalcogenides (monolayer Au6X2, X = S, Se, or Te) with strain-induced indirect-to-direct band gap transitions and visible-light-driven overall water-splitting photocatalysts are predicted based on first-principles calculations. Au6X2 monolayers are semiconductors with band gaps ranging from 1.22 to 1.63 eV. Interestingly, strain-induced indirect-to-direct band gap transitions can be achieved in Au6X2 monolayers via enhancing in-plane interactions manipulated by reducing the height between chalcogens and the Au6 layer. Moreover, Au6Se2, SAu6Se, and SAu6Te have appropriate band edge levels and excellent optical absorptions, which are suitable for visible-light-driven overall water splitting. Notably, SAu6Te with a significant Janus-induced potential difference, which promotes the separation of photogenerated carriers and thus improves the efficiency of water splitting, still satisfies the conditions for visible-light-driven overall water splitting under −4∼4% uniaxial and biaxial strains. Our findings suggest that Au6X2 monolayers are potential materials for photoelectronic devices and photocatalytic applications.