Metastable MoS₂: Crystal Structure, Electronic Band Structure, Synthetic Approach and Intriguing Physical Properties

Abstract

The 2H molybdenum disulfide (MoS ), as a stable hexagonal phase, has been one of the most studied transition metal dichalcogenides over the past decades. In the last five years, the metastable phases of MoS (1T, 1T', 1T'', and 1T''') have seen a revival of interests. Different from the edge-sharing [MoS ] trigonal prisms in the 2H MoS phase, these metastable phases are composed of the edge-sharing [MoS ] octahedra, in which the neighboring Mo-Mo distances differ. Due to the various crystal structures and different electronic configurations of the building [MoS ] motifs, these metastable polytypes are endowed with intriguing physical properties and potential applications in diverse fields. In this Review, the recent research progress on metastable MoS is summarized, especially with an emphasis on the diverse synthetic approaches and the newly uncovered physical properties. The phase structures and electronic band structures are also outlined. In the end, a perspective of the future investigation on metastable MoS is discussed.

Atomic structure and defect dynamics of monolayer lead iodide nanodisks with epitaxial alignment on graphene

“…However, all PbI 2 flakes suspended on graphene, from smallest 3 nm to larger hundreds of nanometers in size (Supplementary Note 6), showed 1 H phase, attributed to epitaxial interactions with the underlying graphene support. Chemical vapor deposition (CVD)-grown graphene has grain boundaries with random orientation and hence, we saw that PbI 2 flakes within a region (1-5 µm) showed the same relative crystal orientation relative to the graphene crystal (Supplementary Note 7, Supplementary Note 8) 50,51 . To confirm the case of PbI 2 -graphene interactions, we deposited PbI 2 flakes directly on top of lacey carbon TEM grids without graphene, and observed PbI 2 flakes with 1 T structure instead (Supplementary Note 9).…”

“…The 1 T phase is expected to be more stable than the H phase with total energy 165 meV per unit cell lower 49 , unlike the other 2D materials such as MoS 2 , where the 1 H phase is generally known to be more stable than the 1 T phase 50 . However, all PbI 2 flakes suspended on graphene, from smallest 3 nm to larger hundreds of nanometers in size (Supplementary Note 6), showed 1 H phase, attributed to epitaxial interactions with the underlying graphene support.…”

Molybdenum Disulphide Heterointerfaces as Potential Materials for Solar Cells, Energy Storage, and Hydrogen Evolution

“…A lot of theoretical calculations have been conducted for these metastable monolayer phases to predict their physical/chemical properties, such as band structure, formation energy, spin‐orbit coupling, etc . For example, the electronic bandgap opening in the range of 50–570 meV has been expected . Because of unique structural modifications of these phases, exotic physical properties were theoretically predicted and some of these were experimentally confirmed.…”

“…For example, superconductivity at T c ≈ 4 K, topological, and ferroelectric effects were some more experimentally noted properties. Exhaustive details of these metastable phases, their formation, synthesis, along with their interesting physical/chemical properties can be found in recent articles …”

“…It is predicted that such materials can exhibit a high surface‐to‐volume ratio, high chemical activity, high stability, low toxicity etc . The QCE exhibits the size‐dependent optoelectronic properties as a result, these may find potential applications in numerous areas such as bioimaging, sensors, photodetectors, photocatalysts, energy‐conversion/storage and high‐performance electronic devices etc . As an example, MoS 2 QDs with a lateral size of ≈2.1 nm shows a larger direct bandgap (3.96 eV) compared with a monolayer 2D sheet with bandgap 1.89 eV, which is quite a significant change .…”