Besides its promising high electron mobilities at room temperature, PtSe2 has a finite bandgap sensitively dependent on the number of monolayers combined by the van der Waals interaction according to our calculations based on the density functional theory. It was found that the frontier orbitals of the valence band maximum and the conduction band minimum are mainly contributed by pz and px+y orbitals of Se, which are sensitive to the out-of-plane and the in-plane lattice constants, respectively. The van der Waals force enhances the bonding out-of-plane, which in turn influences the bonding in-plane. We explain that the layer number dependent bandgap has the same electronic reason as the strain dependent bandgap based on the scenario above. This work shows the flexibilities of tuning the electronic and optical properties of PtSe2 in a wide range, which provides an advantage for applications of PtSe2 in sensors.
Zirconium (Zr) alloy is a promising fuel cladding material used widely in nuclear reactors. Usually, it is in service for a long time under the effects of neutron radiation with high temperature and high pressure, which results in thermomechanical coupling behavior during the service process. Focusing on the UO2/Zr fuel elements, the macroscopic thermomechanical coupling responses of pure Zr, Zr-Sn, and Zr-Nb binary system alloys, as well as Zr-Sn-Nb ternary system alloy as cladding materials, were studied under neutron irradiation. As a heat source, the thermal conductivity and thermal expansion coefficient models of the UO2 core were established, and an irradiation growth model of a pure Zr and Zr alloy multisystem was built. Based on the user material subroutine (UMAT) with ABAQUS, the current theoretical model was implemented into the finite element framework, and the consequent thermomechanical coupling behavior under irradiation was calculated. The distribution of temperature, the stress field of the fuel cladding, and their evolution over time were analyzed. It was found that the stress and displacement of the cladding were sensitive to alloying elements due to irradiated growth.
Two-dimensional transitional metal dichalcogenide (TMDC) field-effect transistors (FETs) are proposed to be promising for devices scaling beyond silicon-based devices. We explore the different effective mass and bandgap of the channel materials and figure out the possible candidates for high-performance devices with the gate length at 5 nm and below by solving the quantum transport equation self-constantly with the Poisson equation. We find that out of the 14 compounds, MoS2, MoSe2, and MoTe2 may be used in the devices to achieve a good subthreshold swing and a reasonable current ON-OFF ratio and delay. Our work points out the direction of further device optimization for experiments.
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