Properties of Individual Dopant Atoms in Single-Layer MoS2: Atomic Structure, Migration, and Enhanced Reactivity (1310.2366v1)

Abstract: The differences in the behavior of Re (n-type) and Au (p-type) dopant atoms in single-layered MoS2 were investigated by in situ scanning transmission electron microscopy. Re atoms tend to occupy Mo sites, while Au atoms exist as adatoms and show larger mobility under the electron beam. Re substituted to Mo site showed enhanced chemical affinity, evidenced by agglomeration of Re adatoms around these sites. This may explain the difficulties in achieving a high compositional rate of homogeneous Re doping in MoS2. In addition, an in situ coverage experiment together with density functional theory calculations discovered a high surface reactivity and agglomeration of other impurity atoms such as carbon at the Re doped sites.

• The paper demonstrates that Re dopants predominantly substitute Mo sites in single-layer MoS₂, showing 89% stability via STEM and DFT analysis.
• The paper reveals that Au dopants exhibit high mobility as adatoms, highlighting distinct energy barriers compared to Re substitutional incorporation.
• The paper indicates enhanced chemical reactivity at Re-doped sites, where carbon clustering signals promising catalytic applications.

Investigating the Properties of Dopant Atoms in Single-Layer MoS₂

This paper explores the properties of dopant atoms in single-layered molybdenum disulfide (MoS₂), specifically focusing on rhenium (Re) and gold (Au) using advanced techniques such as scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations. The differentiation between the behavior of Re (an n-type dopant) and Au (a p-type dopant) within the host MoS₂ matrix is thoroughly examined.

Atomic Structure and Dynamics of Dopants

Re atoms predominantly occupy the Mo sites in MoS₂, as verified by annular dark-field (ADF) imaging and energy-dispersive X-ray spectroscopy (EDX). Approximately 89% of Re dopants were substitutional, with minimal mobility observed during STEM examinations, suggesting a stable integration into the lattice. In contrast, Au atoms exhibited high mobility evident from their predominantly adatom status, leading to significant positional changes under the electron beam. This behavior aligns with DFT-calculated formation energies, where Re showed a strong preference for substitutional sites, while Au displayed a predilection for adatom configurations due to the higher energy barrier for substitutional incorporation.

Chemical Reactivity and Impurity Interaction

An intriguing aspect highlighted by the paper is the enhanced reactivity at Re-doped sites. In situ experiments exhibited agglomeration of carbon impurities around Re-dopant sites, an observation supported by DFT, which indicated a lower energy barrier for carbon clustering near Re atoms. This reactivity is attributed to the localized electronic environment altered by Re substitution.

Contrasting Behaviors of Re and Au

The authors provide a compelling case for the contrasting behaviors of Re and Au dopants through a combination of empirical data and theoretical modeling. Re's strong substitutional preference results in stable incorporation into MoS₂ and the creation of active sites for potential catalytic applications. On the other hand, Au's mobility suggests potential for dynamic processes on the MoS₂ surface, which could influence material properties such as photocurrent enhancement, as supported by observed mid-gap states and calculated magnetic moments.

Implications for Nanotechnology and Electronics

The findings carry significant implications for the use of doped MoS₂ in nanoelectronic devices. The stable incorporation and enhanced reactivity of Re make doped MoS₂ a promising candidate for catalytic applications, while the mobility of Au introduces potential for dynamic sensing applications. This delineation of the dopant behaviors could guide future experimental designs and optimization of 2D material properties for specific applications, particularly where predictable and tunable electronic properties are essential.

Conclusion and Future Prospects

In sum, this paper provides a detailed exploration of dopant behavior in MoS₂, contributing valuable insights into the fundamental science governing two-dimensional material properties. Future research directions may include the exploration of other dopant types or combinations thereof to further broaden the applicability of MoS₂ in multifunctional device applications. Such pursuits would entail a detailed understanding of how substitution and adatom dynamics influence both the local and extended properties of doped 2D material systems.