7:43 PM - NM07.05.13
Salt-Assisted Growth of 2D Transition Metal Dichalcogenides
National Institute for Materials Science1
Chemical vapor deposition (CVD) of 2D transition metal dichalcogenides (TMDCs) always involves the conversion of vapor precursors to solid products in a vapor-solid-solid (VSS) growth mode (e.g., WO3 + S → WS2 + SO2). This often requires very high temperatures to sublimate metal oxide precursors (e.g., WO3).
Our pioneering work on salt-assisted CVD (Salt 1.0 technique) enables the growth of 2D WS2 and WSe2 monolayers in a mild condition (lower temperature and atmospheric pressure) [1,2]. In the last five years, the use of alkali (alkaline earth) metal halides (AH, A = Li, Na, K, Ba, Ca; H = F, Cl, Br, I) in CVD has demonstrated great success in growing tens of atomically thin metal chalcogenides, graphene & h-BN monolayers [3,4]. This is due to the formation of volatile MOuClv and non-volatile NaMyOz when alkali (alkaline earth) metal halides react with metal oxides. They are highly efficient precursors for growing 2D TMDC monolayers.
The recent discovery and use of non-volatile molten salts in CVD (Salt 2.0 technique) trigger the vapor-liquid-solid (VLS) growth of 1D/2D TMDC monolayers . The Salt 2.0 technique shows great improvements in the high-efficient and reproducible growth of large-area, uniform, and high-quality 2D TMDC monolayers. The Salt 2.0 technique also demonstrates great potentials in growing 2D TMDC materials in the following aspects: wafer-scale single crystals, patterns, heterostructure, and alloys . It represents a new trend in the CVD growth of 2D TMDC materials.
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