A two-dimensional (2D) MoSi₂N₄ monolayer is an emerging class of air-stable 2D semiconductors possessing exceptional electrical and mechanical properties. Despite intensive recent research effort devoted to uncover the material properties of MoSi₂N₄, the physics of electrical contacts to MoSi₂N₄ remains largely unexplored thus far. In this work, we study van der Waals heterostructures composed of MoSi₂N₄ contacted by graphene and NbS₂ monolayers using first-principles density functional theory calculations. We show that the MoSi₂N₄/NbS₂ contact exhibits an ultralow Schottky barrier height (SBH), which is beneficial for nanoelectronics applications. For the MoSi₂N₄/graphene contact, the SBH can be modulated via the interlayer distance or via external electric fields, thus opening up an opportunity for reconfigurable and tunable nanoelectronic devices. Our findings provide insights into the physics of 2D electrical contacts to MoSi₂N₄ and shall offer a critical first step toward the design of high-performance electrical contacts to MoSi₂N₄-based 2D nanodevices.

Multiferroic van der Waals (vdW) heterostrucutres offer an exciting route toward high-performance nanoelectronics and spintronics device technology. Here we investigate the electronic and transport properties of multiferroic vdW heterostructures composed of a ferromagnetic ${\mathrm{FeCl}}_2$ monolayer and a ferroelectric ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ monolayer using first-principles density functional theory and quantum transport simulations. We show that ${\mathrm{FeCl}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ heterostructure can be reversibly switched from semiconducting to half-metallic behavior by electrically modulating the ferroelectric polarization states of ${\mathrm{Sc}}_2{\mathrm{CO}}_2$. Intriguingly, the half-metallic phase exhibits a type-III broken gap-band alignment, which can be beneficial for tunneling field-effect transistor applications. We perform a quantum transport simulation based on a proof-of-concept two-terminal nanodevice to demonstrate all-electric-controlled valving effects uniquely enabled by the nonvolatile ferroelectric switching of the heterostructure. These findings unravel the potential of ${\mathrm{FeCl}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ vdW heterostructures as a building block for designing the next generation of ultimately compact information processing, data storage, and spintronics devices.

We investigate the electronic transport properties for a molecular device model constructed by a phenylene ethynylene oligomer molecular with different side groups embedding in a carbon chain between two graphene electrodes. Using the first-principles method, the unusual dual conductance, negative differential resistance (NDR) behavior with large peak to valley ratio, and obvious rectifying performance are numerically observed in such proposed molecular device. The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals (MOs) as well as transmission coefficients under various external voltage biases gives an inside view of the observed results, which suggests that the dual conductance behavior and rectifying performance are due to the asymmetry distribution of the frontier MOs as well as the corresponding coupling between the molecule and electrodes. But the NDR behavior comes from the conduction orbital being suppressed at certain bias. Interestingly, the conduction properties can be tuned by introducing side groups to the molecule and the rectification as well as the NDR behavior (peak to valley ratio) can be improved by adding different side groups in the device model.