Eren Ismail, Akgenc Berna
Department of Physics, Izmir Institute of Technology, Izmir, 35430, Turkey.
Department of Physics, Kirklareli University, Kirklareli, 39100, Turkey.
Phys Chem Chem Phys. 2021 Sep 29;23(37):21139-21147. doi: 10.1039/d1cp01916c.
Based on density functional theory, the structural, electronic and vibrational properties of two-dimensional transition metal chalcogenides MX and their Janus type MXY, where M = Pd, Co and Ni and X = Se, S and Te, are investigated. Motivated by the successful synthesis of a 2D PdSe monolayer and the proof of the dynamical stability of NiSe and CoSe monolayers, in terms of the phonon band dispersions, we have systemically studied the fundamental physical properties of Janus transition metal chalcogenides, such as their structural, phonon and thermodynamic stability and their electronic and mechanical properties. Our results show that Janus structures of MXY are energetically favorable and dynamically stable. The molecular dynamic simulations (AIMD) results clearly prove that they kept their thermal stability at room temperature. We have demonstrated their structural, electronic and vibrational properties and Raman spectra. The electronic band dispersions show that monolayer CoSe shows half-metal properties with a moderate band gap (1.01 eV), PdSe has a 1.42 eV direct band gap, while NiSe has a 1.38 eV indirect band gap. PdSeS, PdSeTe and PdSTe are indirect band gap semiconductors with band gaps of 1.22 eV, 1.05 eV and 0.61 eV, respectively. NiSeS, NiSeTe and NiSTe are indirect band gap semiconductors with band gaps of 1.61 eV, 0.77 eV and 0.49 eV, respectively. While pristine CoSe is shown to have half-metallicity (HM), the HM behaviour of the Janus CoSeTe and CoSTe monolayers disappear and CoSeS remains a HM with a moderate band gap of 0.85 eV. In addition, the Raman spectra of these Janus materials are shown to exhibit totally distinctive features as compared to those of the pristine materials. This work reveals the important material properties of Janus type MXY monolayers, where M = Pd, Co and Ni and X = Se, S and Te, which could have wide applications in new functional devices.
基于密度泛函理论，研究了二维过渡金属硫族化合物MX及其Janus型MXY（其中M = Pd、Co和Ni，X = Se、S和Te）的结构、电子和振动性质。受二维PdSe单层成功合成以及NiSe和CoSe单层动力学稳定性证明的启发，根据声子能带色散，我们系统地研究了Janus过渡金属硫族化合物的基本物理性质，如它们的结构、声子和热力学稳定性以及电子和力学性质。我们的结果表明，MXY的Janus结构在能量上是有利的且动力学稳定。分子动力学模拟（AIMD）结果清楚地证明它们在室温下保持热稳定性。我们展示了它们的结构、电子和振动性质以及拉曼光谱。电子能带色散表明，单层CoSe表现出半金属性质，带隙适中（1.01 eV），PdSe具有1.42 eV的直接带隙，而NiSe具有1.38 eV的间接带隙。PdSeS、PdSeTe和PdSTe是间接带隙半导体，带隙分别为1.22 eV、1.05 eV和0.61 eV。NiSeS、NiSeTe和NiSTe是间接带隙半导体，带隙分别为1.61 eV、0.77 eV和0.49 eV。虽然原始CoSe显示出半金属性（HM），但Janus CoSeTe和CoSTe单层的HM行为消失，而CoSeS仍然是具有0.85 eV适中带隙的HM。此外，与原始材料相比，这些Janus材料的拉曼光谱表现出完全不同的特征。这项工作揭示了Janus型MXY单层（其中M = Pd、Co和Ni，X = Se、S和Te）的重要材料性质，其在新型功能器件中可能有广泛应用。
