Growth Mechanism of 2D Mo₂C on Cu via CVD

Abstract

This study investigates the growth of Mo2C crystals via chemical vapor deposition (CVD) in the presence of a carbon (H2/CH4 gas)-containing environment. The study employs both theoretical and experimental approaches to investigate the vertical and lateral (in-plane) growth of Mo2C crystals. A physico-mathematical consideration is applied to develop an analytical forward model, which incorporates bulk diffusivities, surface diffusivities, and solubility gradients for Mo2C crystal growth. Coupled nonlinear flow equations have been advanced for the Mo-, Cu-, Mo2C layer framework and effectively predicted the Mo2C crystal growth rate for both vertical and lateral directions. Forming the Mo2C crystal height and diameter was directly correlated with copper layer thickness and time using the forward model and then validated by the experiments together with SEM and AFM studies. Studies showed that the Cu layer thickness plays a crucial role in controlling the height of the Mo2C crystal while it is not that critical in changing the lateral dimension of the crystal. Beyond simply enhancing Mo2C crystal growth and property-processing relationship, this study demonstrated the synthesis of designer Mo2C, which can be tailored to the needs of specific applications. This forward model will enable us to further enhance and exploit the family of analogs of materials previously demonstrated by other methods.

Kinetic analysis of 2D Mo2C crystal growth via CVD

“…When graphene formation is not controlled, different scenarios depicted in figure 4 can occur simultaneously, a phenomenon that we have extensively discussed in our previous works [8,15,26,27]. If graphene forms on Cu surface before or simultaneously with Mo 2 C crystal formation (figures 4(b), (c), (e)), the lateral growth of Mo 2 C crystals involves a sequence of diffusion processes, including: As these processing steps occur sequentially, the activation energy is expected to primarily correspond to the rate-limiting step with the highest energy barrier.…”

“…Following the completion of the growth process, the supply of CH 4 was terminated, and upon the furnace temperature descending to 1358 K, the samples were rapidly cooled by moving them out of the heated zone, all while being exposed to N 2 and H 2 gases. Detailed information regarding the precleaning process and other specifics can be found elsewhere [8].…”

“…A set of coupled nonlinear flow equations has been formulated to describe the intricate dynamics within the Mo-, Cu-, and Mo 2 C layers. This innovative framework successfully anticipates the growth rate of Mo 2 C crystals, providing accurate predictions for both vertical and lateral growth directions [8].…”

“…For this CVD method, a Cu foil on top of the Mo substrate (Mo-Cu stack) is heated and used as substrate for Mo 2 C. At temperatures exceeding 1356 K, Cu melts, and Mo diffuses into Cu, forming a diluted Mo-Cu alloy. Concurrent to Mo-Cu alloy formation, CH 4 dissociates, depositing carbon atoms on the Mo-Cu alloy surface, where they combine with Mo atoms to form Mo 2 C crystals [8]. While several research groups have investigated the effects of processing parameters such as the type [9][10][11][12][13] and thickness of metals (mostly Cu) [11,12,[14][15][16], H 2 :CH 4 ratio [9,14,15,[17][18][19][20][21], and duration on crystal size and morphology [4,11,12,22], the growth dynamics of Mo 2 C using the CVD method have not been sufficiently studied, resulting in inadequate understanding in growth mechanism.…”

Strategic Insights for Bulk Production of MXene: A Review

“…Yet, there are obstacles, such as the need for regulated gas conditions and high temperatures, that restrict scalability and may affect the structure and characteristics of MXene. Substrate dependency, which might limit applications' adaptability, can also result from the deposition process [29]. Successfully navigating these obstacles, fine-tuning process parameters, and creating efficient, large-scale deposition techniques are crucial for the prospect of CVD bulk production.…”