The synthesis mechanism of Mo₂C on Ag-Cu alloy substrates by chemical vapor deposition and the impact of substrate choice

Abstract

Two-dimensional (2D) transition metal carbides have shown promise for numerous applications because of their potential for a large surface area to volume ratio, while maintaining many of the useful properties of transition metal carbides. Recent work has explored the use of chemical vapor deposition on liquid metal substrates to controllably synthesize transition metal carbides. While alloys have been used to lower the required synthesis temperature, further understanding of the impact of these substrates on the synthesis mechanism is needed for future optimization. This work systematically analyzes the effects of using a Ag-Cu alloy as a substrate for Mo 2 C synthesis by chemical vapor deposition at a temperature below the melting point of Cu. The impact of parameters, such as time, cooling rate, composition of the alloy substrate, and methane partial pressure, on the synthesis and structure of Mo 2 C is studied. The results conclusively demonstrate that synthesis of Mo 2 C is controlled by Mo diffusion through the liquid alloy. Utilizing a Ag-Cu alloy as a substrate successfully reduced the necessary synthesis temperature below the melting point of Cu; however, Mo 2 C coalescence is limited due to the separation of the Ag and Cu components in the alloy upon cooling. The results show that Ag alone is not a suitable substrate for Mo 2 C synthesis, and Mo 2 C flake size decreased with increasing Ag concentration in the Ag-Cu alloy substrate. This is most likely due to the inability of Ag to dehydrogenate methane effectively. Thus, an optimal substrate for Mo 2 C synthesis should be able to dehydrogenate methane, have a low melting temperate, and, if an alloy, demonstrate solid solubility.

Advances and Promises of 2D MXenes as Cocatalysts for Artificial Photosynthesis

“…Since the first report of the CVD method used for preparing MXene, in 2015, 2D materials like Mo 2 C, Ti 4 C 3 , Ti 5 C 4 , Mo 2 C/graphene heterostructure have been successfully synthesized. [74][75][76] For example, large-area and uniform 2D orthorhombic-phased Mo 2 C film can be grown in situ on graphene using molten Mo-Cu alloy-catalyzed CVD strategy. [76] The role of graphene is to passivate the surface of the catalyst, thus preventing the segregated molybdenum from reacting with gaseous hydrocarbon.…”

“…Mo 2 TiC 2 , Cr 2 TiC 2 , Hf 3 C 2 , Mo 2 ScC 2 , (Ti 0.5 V 0.5 ) 3 C 2 , Ta 4 C 3 , Nb 4 C 3 , (Nb 0.8 Ti 0.2 ) 4 C 3 , (Nb 0.8 Zr 0.2 ) 4 C 3 , (Mo 2 Ti 2 )C 3 , V 4 C construction Chemical vapor deposition Mo 2 C, Ti 3 C 2 , Ti 4 C 3 , Ti 5 C 4[74][75][76] …”

Growth andin situcharacterization of 2D materials by chemical vapour deposition on liquid metal catalysts: a review

“…Shape and thickness engineering of Mo 2 C was further exhibited by precisely tuning CVD growth conditions. [151][152][153] The flow rate of the carbon source was found to play a crucial role in morphology evolution. Rectangular, pentagonal and flower-like Mo 2 C crystals were consecutively grown by gradually increasing the flow rate.…”

Growth Mechanism of 2D Mo2C on Cu via CVD

“…Although such materials may be suitable for applications such as energy storage and composite structures, they are not appropriate for electronic applications that require high purity and crystal perfection, especially in advanced electronic and microelectronic applications. Chemical vapor deposition (CVD) provides a promising solution for growing large area 2D crystals with fewer defects, without the presence of F or OH terminations in this context. − CVD-grown Mo 2 C crystals exhibit attractive properties, such as 2D superconductivity , and magnetoresistance. , …”