Abstract
The renewed interest in two-dimensional materials, particularly transition metal dichalcogenides, has been explosive, evident in a number of review and perspective articles on the topic. Our ability to synthesize and study these 2D materials down to a single layer and to stack them to form van der Waals heterostructures opens up a wide range of possibilities from fundamental studies of nanoscale effects to future electronic and optoelectronic applications. Bottom-up and top-down synthesis and basic electronic properties of 2D chalcogenide materials have been covered in great detail elsewhere. Here, we bring attention to more subtle effects: how the environmental, surface, and crystal defects modify the electronic band structure and transport properties of 2D chalcogenide nanomaterials. Surface effects such as surface oxidation and substrate influence may dominate the overall transport properties, particularly in single layer chalcogenide devices. Thus, understanding such effects is critical for successful applications based on these materials. In this review, we discuss two classes of chalcogenides – Bi-based and Mo-based chalcogenides. The first are topological insulators with unique surface electronic properties and the second are promising for flexible optoelectronic applications as well as hydrogen evolution catalytic reactions.
Highlights
The renewed interest in two-dimensional materials, transition metal dichalcogenides, has been explosive, evident in a number of review and perspective articles on the topic
The topological surface state will be gapped if Bi2Se3 is less than 5 layers thick [18], and a single layer MoS2 becomes a direct bandgap semiconductor instead of an indirect bandgap semiconductor [19,20,21]
This review will look at how surface or parasitic effects play a role in 2D chalcogenide nanomaterials
Summary
SiOx substrate, suspended graphene, and hexagonal boron nitride Electron transport on graphene is subject to microscopic perturbations that can cause backscattering, greatly decreasing the electron mean free path as well as mobility. A theoretical model for weak anti-localization effects in thin Bi2Se3 or Bi2Te3 films shows that contribution from the 2D electron gas can lead to uncertainty related to the value of α [73], the parameter whose value can indicate how many topologically non-trivial states exist in the thin film [74]. Charge carrier transport of the 2D chalcogenides needs to be studied carefully, which is determined by intrinsic materials properties as well as extrinsic materials preparation methods Large uncertainty in both the intrinsic and extrinsic factors often leads to a huge variation in the performance of electronic devices based on these materials. We focus our discussion on MoS2, one of the most explored 2D chalcogenides, and discuss the followings: (1) extrinsic interfacial effects on MoS2 in contact with other medium such as metal contacts and dielectric substrates, and (2) intrinsic surface properties of MoS2 such as surface, electronic, and crystal defects
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