Computational Guide to Optimize Electric Conductance in MoS2 Films

TL;DR

This paper uses simulations to study how the structure of MoS2 films affects their electric conductance, helping optimize their use in nanoelectronics.

Contribution

The study introduces a computational method to optimize MoS2 film conductance by analyzing edge states and flake overlaps.

Findings

Edge states in MoS2 flakes behave like doped semiconductors, enabling control over charge carrier type.

Overlapping flakes reduce conductance, with a 6.5 nm overlap maximizing interflake conductance.

Flake geometry and chemical environment significantly impact conductance, with triangular flakes showing up to 58% reduction.

Abstract

Molybdenum disulfide (MoS2) is a high-potential
material
for nanoelectronic applications, especially when thinned to a few
layers. Liquid-phase exfoliation enables large-scale fabrication of
thin films comprising single- and few-layer flakes of MoS2 or other transition-metal dichalcogenides (TMDCs), exhibiting variations
in the flake size, geometry, edge terminations, and overlapping areas.
Electronic conductivity of such films is thus determined by two contributions:
the intraflake conductivity, reflecting the value of each single layer,
and charge transport across these overlapping flakes. Employing first-principles
simulations, we investigate the influence of various edge terminations
and the overlap between flakes on the charge transport in MoS2 film models. We identify characteristic electronic edge states
originating from the edge atoms and their chemical environment, which
resemble donor and acceptor states of doped semiconductors. This makes
either electrons or holes to majority carriers and enables selective
control over the dominant charge carrier type (n-type or p-type).
Compared to pristine nanosheets, overlapping flakes exhibit lower
overall conductance. In the best-performing hexagonal flakes occurring
in Mo-rich environments, the conductance is reduced by 18% compared
to the pristine layer, while the drop by 46% and 58% is predicted
for truncated triangular and triangular flakes, respectively, in S-rich
environments. An overlap of 6.5 nm is sufficient to achieve the highest
possible interflake conductance. These findings allow for rational
optimization of experimental conditions for the preparation of MoS2 and other TMDC semiconducting thin films.

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