Controlled CVD growth of ultrathin Mo2C (MXene) flakes

Abstract

MXenes combine distinctive properties, including high electrical conductivity, high thermal conductivity, and efficient absorption of electromagnetic waves, which allow them to be utilized in various applications such as electrical energy storage, sensors, and functional composites. This study aims to grow thin and large area Mo2C flakes in a controlled manner by using chemical vapor deposition, avoiding surface functionalization, and limited lateral dimensions. Herein, we investigate the effects of CH4 flow, the precursor/catalyst (Mo/Cu) ratio, and flow rates of carrier gas on the growth of two-dimensional Mo2C structures. This study examines the effects of the precursor/catalyst (Mo/Cu) ratio and flow rates of carrier gas on the growth of Mo2C structures. Our results show that when the flow rates of CH4, catalyst/precursor (Cu/Mo) ratio, and carrier gas (N2/H2) ratio are varied, we can control both thickness (from 7 to 145 nm) and coverage of the substrate surface (from 11% to 68%) of the Mo2C flakes. Therefore, this study reveals that it is possible to realize centimeter-scale surface coverage and controllable thicknesses by adjusting the process parameters. The deposited films and flakes are analyzed by optical microscopy, atomic force microscopy, and Raman scattering spectroscopy techniques. The Raman spectra are also compared with the theoretical calculations using density functional theory. Overall, the present work is expected to provide a significant impact for utilization of MXenes in various applications.

High yield and wide lateral size growth of α-Mo2C: exploring the boundaries of CVD growth of bare MXene analogues

“…Previous studies have shown that vertical stacking growth is preferrable at low CH 4 flow rates (0.3 sccm), while lateral crystal growth is more favored at high CH 4 flow rates (3 sccm) [50,52,56,58]. It is important to note here that the use of CH 4 flow rates of 3 sccm or higher has been found to result in the growth of graphene on the top Cu surface in tandem with Mo 2 C formation [50,59,60]. There is no clear reported evidence showing that Mo 2 C can grow laterally as a continuous film covering the entire growth substrate, and lateral merging between individual crystals to form large size crystals is not commonly observed.…”

Investigation of CVD Growth of 2D MoS2 on MXene Structures with Photoluminescence Mapping and Fluorescence Lifetime Imaging Microscopy

“…These peaks are in agreement with our previous study. [ 10 ] The peak at 183 cm −1 represents A g mode, while the peak at 144 cm −1 represents 2 E g mode.…”

“…The process parameters such as growth temperature, growth time, and gas flow rate were adjusted according to our previous study to obtain the desired Mo 2 C MXene structures. [ 10 ] H 2 gas was used as an activator for copper surface throughout the process. CH 4 gas was used as a carbon source when the tube reached the adjusted temperature.…”

Optically Active MXenes in Van der Waals Heterostructures

“…[222] It was revealed that the CH 4 adsorption on Mo 2 C is more favorable than the adsorption of C on the surface of Mo 2 C. Thus, Mo 2 C tends to grow along the c-axis, which results in relatively thick MXene layers ranging between 7 and 145 nm. [222,223] Lin et al prepared MoS 2 /WSe 2 /graphene and WSe 2 /MoSe 2 /graphene heterostructures through multistep CVD. However, some elemental exchange and intermixing regarding chalcogens and transition metals at high temperatures affected the resulting quality.…”

“…[ 222 ] It was revealed that the CH 4 adsorption on Mo 2 C is more favorable than the adsorption of C on the surface of Mo 2 C. Thus, Mo 2 C tends to grow along the c‐ axis, which results in relatively thick MXene layers ranging between 7 and 145 nm. [ 222,223 ]…”