Kotmool Komsilp, Kaewmaraya Thanayut, Hussain Tanveer, Ahuja Rajeev, Luo Wei, Bovornratanaraks Thiti
College of Advanced Manufacturing Innovation, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand.
Electronic and Optoelectronic Device Research Unit, School of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand.
Phys Chem Chem Phys. 2022 Jul 27;24(29):17862-17869. doi: 10.1039/d2cp02557d.
MXenes are a family of novel two-dimensional (2D) materials attracting intensive interest because of the rich chemistry rooted from the highly diversified surface functional groups. This enables the chemical optimization suitable for versatile applications, including energy conversion and storage, sensors, and catalysis. This work reports the study of the crystal energetics, electronic properties, and mechanical properties, and the impacts of strain on the electronic properties of tetragonal (1T) and hexagonal (2H) phases of MoC as well as the surface-terminated MoCT (T = O, F, and Cl). Our findings indicate that 2H-MoC is energetically more stabilized than the 1T counterpart, and the 1T-to-2H transition requires a substantial energy of 210 meV per atom. The presence of surface termination T atoms on MoC intrinsically induces variations in the atomic structure. The calculated structures were selected based on the energetic and thermodynamic stabilities (400 K). The O atom prefers to be terminated on 2H-MoC, whereas the Cl atom energetically stabilizes on 1T-MoC. Meanwhile, with certain configurations, 2H-MoCF and 1T-MoCF with slightly different energies could exist simultaneously. The MoCO possesses the highest mechanical strength and elastic modulus ( = 52 GPa at = 20% and = 507 GPa). The nature of the ordered centrosymmetric layer and the strong bonding between 4 d-Mo and 2 p-O of 2H-MoCO are responsible for its promising mechanical properties. Interestingly, the topological properties of 2H-MoCO at a wide range of strains (-10% to 12%) are reported. Moreover, 2H-MoCF is metallic through the range of calculation. Meanwhile, originally semiconducting 1T-MoCF and 1T-MoCCl preserve their features under the ranges of the strain of -2% to 10% and -1% to 5%, respectively, beyond which they undergo the semiconductor-to-metal transitions. These findings would guide the potential applications in modern 2D straintronic devices.
MXenes是一类新型二维（2D）材料，因其高度多样化的表面官能团所具有的丰富化学性质而备受关注。这使得其能够进行化学优化，以适用于多种应用，包括能量转换与存储、传感器和催化等。本文报道了对四方相（1T）和六方相（2H）的MoC以及表面端接的MoCT（T = O、F和Cl）的晶体能量学、电子性质和力学性质，以及应变对其电子性质影响的研究。我们的研究结果表明，2H-MoC在能量上比1T-MoC更稳定，从1T到2H的转变每个原子需要210 meV的大量能量。MoC表面端接的T原子的存在本质上会引起原子结构的变化。所计算的结构是基于能量和热力学稳定性（400 K）选择的。O原子更倾向于端接在2H-MoC上，而Cl原子在能量上使1T-MoC更稳定。同时，在某些构型下，能量略有不同的2H-MoCF和1T-MoCF可能同时存在。MoCO具有最高的机械强度和弹性模量（在应变 = 20%时为52 GPa，在应变 = 507 GPa时）。2H-MoCO有序中心对称层的性质以及4d-Mo和2p-O之间的强键合是其优异力学性质的原因。有趣的是，报道了2H-MoCO在很宽应变范围（-10%至12%）内的拓扑性质。此外，在计算范围内2H-MoCF是金属性的。同时，原本为半导体的1T-MoCF和1T-MoCCl分别在-2%至10%和-1%至5%的应变范围内保持其特性，超过该范围它们会发生半导体到金属的转变。这些发现将为现代二维应变电子器件的潜在应用提供指导。
