2D materials and van der Waals heterostructures.

K S Novoselov,A Carvalho,A Mishchenko,A H Castro Neto

doi:10.1126/science.aac9439

K S Novoselov, A Carvalho + Show 2 more

Open Access

https://doi.org/10.1126/science.aac9439

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Abstract

The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear (for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices--such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes--are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.

Highlights

Heterostructures of 2D materials offer a way to study these phenomena, but open unprecedented possibilities of combining them for technological use
Moiré structure for graphene on hexagonal boron nitride leads to the formation of the secondary Dirac points[5,6,7,8,9], commensurateincommensurate transition in the same system leads to surface reconstruction[10] and gap opening in the electron spectrum[8], spin-orbit can be induced in graphene by neighboring transition metal dichalcogenide (TMDC)(11, 12)
We provide a review of 2D materials, analyzing the physics that can be observed in such crystals

Summary

Transition metal dichalcogenides

TMDCs, with formula MX2, where M is a transition metal and X a chalcogen, offer a broad range of electronic properties from insulating or semiconducting (e.g. Ti, Hf, Zr, Mo and W dichalcogenides) to metals or semimetals (V, Nb and Ta dichalcogenides). Metallic TMDC As one can see, the DoS of metallic TMDC has two main properties: the Fermi level of the undoped material is always crossing a band with d-orbital character, implying that the electrons move mostly in the metal layers; the DoS at the Fermi level is usually quite high which hints to a common explanation for the phase transitions which are observed in these materials[18] The interest in these materials comes from the existence of CDW and superconductivity in their phase diagram[19]. Group-IV monochalcogenides SnS, GeS, SnSe and GeSe are isoelectronic with phosphorene and share its orthorhombic structure, but the two atom types break the inversion symmetry of the monolayer As a consequence, they feature spin-orbit splitting (19-86 meV)(40) and piezoelectricity with large coupling between deformation and polarization change in plane (with piezoelectric coefficient e33=7-23 10-10 C/m, largely exceeding those of MoS2 and hBN) [41]. Few-layer hybrid perovskite have been isolated by mechanical exfoliation, and found to be stable in air in the timescale of minutes

Novel van der Waals heterostructures

Growing van der Waals heterostructures

Van der Waals epitaxy

Lateral heterostructures

Conclusion