Two-Dimensional Haeckelite NbS₂ : A Diamagnetic High-Mobility Semiconductor with Nb⁴⁺ Ions

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Group 5 transition-metal dichalcogenide monolayers (MLs) typically exhibit metallic or semiconducting behavior with indirect band gaps.
• Metal centers in known MLs carry a spin, influencing their electronic and magnetic properties.

Purpose of the Study:

• To investigate the electronic and magnetic properties of Haeckelite polytype 1S-NbX2 and 1S-VX2 monolayers.
• To explore the potential of these novel MLs for optoelectronic applications.

Main Methods:

• First-principles calculations were employed to study the structural, electronic, and magnetic properties.
• Thermodynamic and dynamic stability analyses were performed.

Main Results:

• 1S-NbX2 (X=S, Se, Te) monolayers are identified as diamagnetic direct-band-gap semiconductors, distinct from other Group 5 MLs.
• 1S-VX2 MLs are antiferromagnetically coupled indirect-band-gap semiconductors.
• 1S phases are thermodynamically and dynamically stable, with minor energy differences compared to 1H and 1T phases.
• 1S-NbX2 MLs possess small band gaps (0.5–1 eV), suitable for optoelectronics.
• 1S-NbS2 exhibits exceptionally high hole mobility (2.68×10^3 cm^2 V^-1 s^-1), surpassing MoS2 and rivaling WSe2.

Conclusions:

• Haeckelite 1S-NbX2 monolayers represent a novel class of diamagnetic, direct-band-gap semiconductors.
• These materials hold significant promise for advanced optoelectronic devices due to their favorable electronic properties and high carrier mobility.