Raman spectroscopy

Phase (matter)

Engineering

Solid solution

Materials science

Semiconductor

Chemical engineering

Homojunction

Ohmic contact

Physical chemistry

Physics

Organic chemistry

Crystallite

Optics

X-ray photoelectron spectroscopy

Heterojunction

Crystallography

Chemistry

Electrode

Nucleation

Optoelectronics

Journal of the American Chemical Society

Among the Mo- and W-based two-dimensional (2D) transition metal dichalcogenides, MoTe2 is particularly interesting for phase-engineering applications, because it has the smallest free energy difference between the semiconducting 2H phase and metallic 1T′ phase. In this work, we reveal that, under the proper circumstance, Mo and Te atoms can rearrange themselves to transform from a polycrystalline 1T′ phase into a single-crystalline 2H phase in a large scale. We manifest the mechanisms of the solid-to-solid transformation by conducting density functional theory calculations, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The phase transformation is well described by the time–temperature–transformation diagram. By optimizing the kinetic rates of nucleation and crystal growth, we have synthesized a single-crystalline 2H-MoTe2 domain with a diameter of 2.34 mm, a centimeter-scale 2H-MoTe2 thin film with a domain size up to several hundred micrometers, and a seamless 1T′–2H MoTe2 coplanar homojunction. The 1T′–2H MoTe2 homojunction provides an elegant solution for ohmic contact of 2D semiconductors. The controlled solid-to-solid phase transformation in 2D limit provides a new route to realize wafer-scale single-crystalline 2D semiconductor and coplanar heterostructure for 2D circuitry.

Millimeter-Scale Single-Crystalline Semiconducting MoTe<sub>2</sub> via Solid-to-Solid Phase Transformation

Millimeter-Scale Single-Crystalline Semiconducting MoTe2 via Solid-to-Solid Phase Transformation

Millimeter-Scale Single-Crystalline Semiconducting MoTe₂ via Solid-to-Solid Phase Transformation