Atomic Defects and Doping of Monolayer NbSe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Monolayer niobium diselenide (NbSe2) is a promising two-dimensional material with unique electronic and magnetic properties.
• Understanding atomic defects is crucial for controlling and optimizing the performance of NbSe2-based devices.
• Previous studies have not fully characterized the types and frequencies of atomic defects in encapsulated monolayer NbSe2.

Purpose of the Study:

• To investigate the atomic structure and types of defects present in monolayer NbSe2 encapsulated in graphene.
• To determine the relative frequencies and formation energies of different atomic defects.
• To understand the influence of impurities on defect stabilization in NbSe2.

Main Methods:

• Atomic resolution transmission electron microscopy (TEM) for high-resolution imaging of atomic structures.
• Density functional theory (DFT) calculations to determine defect formation energies.
• Geometric phase analysis (GPA) for precise strain mapping within the material.

Main Results:

• Stable niobium (Nb) and selenium (Se) monovacancies were observed in monolayer NbSe2.
• Selenium monovacancies were identified as the most frequent defects, aligning with DFT predictions.
• Adventitious impurities (C, N, O) were found to substitute into the NbSe2 lattice, stabilizing Se divacancies. Platinum (Pt) substitution was also observed.

Conclusions:

• The study provides a comprehensive understanding of atomic defect types and their frequencies in encapsulated monolayer NbSe2.
• Knowledge of defect character and prevalence is essential for tailoring the electronic and magnetic properties of NbSe2.
• This work lays the foundation for defect engineering to enhance the functionality of this significant two-dimensional material.