Density Functional Theory Analysis of Electronic and Optical Properties of Two‐Dimensional Tantalum Carbides Ta_n+1C_n (n = 1, 2, 3)

Abstract

Using first principles methods based on the density functional theory, the electronic structure and optical properties of Ta‐containing MXenes (Tan+1Cn, n = 1, 2, 3) are theoretically studied. The results show that the monolayer thickness has a significant effect on the optical properties of Tan+1Cn. In the infrared region (<1.6 eV), the thickest Ta4C3 monolayer with seven atomic layers has highest values of absorption coefficients, reflectivity and refraction index. In the visible region, Ta4C3 exhibits different optical characteristics as compared to Ta2C and Ta3C2 due to the different structure configuration and electron interaction. Moreover, a high transmittance over 50% is demonstrated for both Ta2C and Ta3C2, while Ta4C3 monolayer exhibits selectively transmitting feature with a low transmittance of 35% at 1.65 eV and a high transmittance of 84% at 2.25 eV, making Ta4C3 monolayer highly responsive when exposed to visible light and favorable for optical detection.

Novel strong and tough Ta/TaHfC2 composites with multi‐scale laminated structure

“…65–3895), then the stack direction of the bright atomic columns is confirmed as (0001) in the combination of the EBSD results. Hence, based on the description of MXene, 26 the phases that possess general formulas M n+1 X n , and geometrical configurations of in‐plane hexagonal slabs with alternately arranged M and X atomic layers along c ‐axis, the nano‐lamellar Ta 2 C phases in layer 2 can be identified as 2D Ta 2 C MXene.…”

“…Since the concentration of carbon decreases gradually from the surface to the core of Ta phases, the Ta 2 C phases closer to Ta phase will preferentially reach the C/Ta ratio for the formation of that close‐packed phase and then stack in the sequence below along the c ‐axis: $$\begin{equation*}{ \ldots ^\alpha } \uparrow {\rm{A\gamma }}{{\rm{B}}^\alpha } \uparrow {\rm{A\gamma }}{{\rm{B}}^\alpha } \uparrow {\rm{A\gamma }}{{\rm{B}}^\alpha } \uparrow {{A\gamma B}} \ldots ,\end{equation*}$$where A and B are tantalum close‐packed atomic layers; α and γ are carbon close‐packed atomic layers; ↑ indicates an absence of the carbon atomic planes and formation of stacking faults between two tantalum adjacent h ‐layers. Moreover, Wang et al 26 . proposed that the monolayer thickness of close‐packed Ta 2 C phase is 0.243 nm, as such, so‐called Ta 2 C MXene (lattice structure as shown in Figure 9) with a nano‐lamellar structure formed.…”

“…where A and B are tantalum close-packed atomic layers; α and γ are carbon close-packed atomic layers; ↑ indicates an absence of the carbon atomic planes and formation of stacking faults between two tantalum adjacent h-layers. Moreover, Wang et al 26 proposed that the monolayer thickness of close-packed Ta 2 C phase is 0.243 nm, as such, so-called Ta 2 C MXene (lattice structure as shown in Figure 9) with a nano-lamellar structure formed.…”

“…65-3895), then the stack direction of the bright atomic columns is confirmed as (0001) in the combination of the EBSD results. Hence, based on the description of MXene, 26 the phases that possess general formulas M n+1 X n , and geometrical Figure 4 shows TEM results of the region between layers 1 and 2. For the dark gray phases in layer 1, a periodic columnar structure, which owns a Hf/Ta atom ratio between 84/16 and 80/20, was newly found in the HAADF image (Figure 4A,B), suggesting they are probably polycrystalline Ta 0.16∼0.2 Hf 0.8∼0.84 C. Corresponding to that periodic columnar structure, an interpenetrating grain boundary divides the HRTEM image of Ta 0.16∼0.2 Hf 0.8∼0.84 C into two parts (Figure 4C).…”

First-Principles Estimation of Core Level Shifts for Hf, Ta, W, and Re

“…Much of the early DFT-based modeling of MXenes considered structures of pure M it n +1 X n type as shown in Figure 4 a and 4 b without surface termination, 64 but recent experimental and computational work has addressed the question of termination by, for example, oxygen, fluorine, and hydroxyl groups. 65 , 66 Here, we do not aim to give an exhaustive study of the MXenes, but we demonstrate via the example material Ta 3 C 2 that we can again make predictions of the XPS spectra and, thus, that XPS is likely to be a very useful characterization tool.…”