Two-dimensional (2D) semiconductors are attractive channels to shrink the scale of field-effect transistors (FETs), and among which the anisotropic one is more advantageous for a higher on-state current (I_on). Monolayer (ML) SnSe₂, as an abundant, economic, nontoxic, and stable two-dimensional material, possesses an anisotropic electronic nature. Herein, we study the device performances of the ML SnSe₂ metal-oxide-semiconductor FETs (MOSFETs) and deduce their performance limit to an ultrashort gate length (L_g) and ultralow supply voltage (V_dd) by using the ab initio quantum transport simulation. An ultrahigh I_on of 5,660 and 3,145 µA/µm is acquired for the n-type 10-nm-L_g ML SnSe₂ MOSFET at V_dd = 0.7 V for high-performance (HP) and low-power (LP) applications, respectively. Specifically, until L_g scales down to 2 and 3 nm, the MOSFETs (at V_dd = 0.65 V) surpass I_on, intrinsic delay time ( $\tau$), and power-delay product (PDP) of the International Roadmap for Device and Systems (IRDS, 2020 version) for HP and LP devices for the year 2028. Moreover, the 5-nm-L_g ML SnSe₂ MOSFET (at V_dd = 0.4 V) fulfills the IRDS HP device and the 7-nm-L_g MOSFET (at V_dd = 0.55 V) fulfills the IRDS LP device for the year 2034.

Moore's law is approaching its physical limit. Tunneling field-effect transistors (TFETs) based on 2D materials provide a possible scheme to extend Moore's lawdown to the sub-10-nm region owing to the electrostatic integrity and absence of dangling bonds in 2D materials. We report an ab initio quantum transport study on the device performance of monolayer (ML) black phosphorene (BP)TFETs in the sub-10-nm scale (6–10 nm). Under the optimal schemes, the ML BP TFETs show excellent device performance along the armchair transport direction.The on-state current, delay time, and power dissipation of the optimal sub-10-nm ML BP TFETs significantly surpass the latest International Technology Roadmap for Semiconductors (ITRS) requirements for high-performance devices. The subthreshold swings are 56–100 mV/dec, which are much lower than those of their Schottky barrier and metal oxide semiconductor field-effect transistor counterparts.

Semiconducting monolayer (ML) blue phosphorene (BlueP) shares similar stability with ML black phosphorene (BP), and it has recently been grown on an Au surface. Potential ML BlueP devices often require direct contact with metal to enable the injection of carriers. Using ab initio electronic structure calculations and quantum transport simulations, for the first time, we perform a systematic study of the interfacial properties of ML BlueP in contact with metals spanning a wide work function range in a field effect transistor (FET) configuration. ML BlueP has undergone metallization owing to strong interaction with five metals. There is a strong Fermi level pinning (FLP) in the ML BlueP FETs due to the metal-induced gap states (MIGS) with a pinning factor of 0.42. ML BlueP forms n-type Schottky contact with Sc, Ag, and Pt electrodes with electron Schottky barrier heights (SBHs) of 0.22, 0.22, and 0.80 eV, respectively, and p-type Schottky contact with Au and Pd electrodes with hole SBHs of 0.61 and 0.79 eV, respectively. The MIGS are eliminated by inserting graphene between ML BlueP and the metal electrode, accompanied by a transition from a strong FLP to a weak FLP. Our study not only provides insight into the ML BlueP–metal interfaces, but also helps in the design of ML BlueP devices.

Phosphorene has attracted much attention recently as an alternative channel material in nanoscale electronic and optoelectronic devices due to its high carrier mobility and tunable direct bandgap. Compared with monolayer (ML) phosphorene, few-layer (FL) phosphorene is easier to prepare, is more stable in experiments, and is expected to form a smaller Schottky barrier height (SBH) at the phosphorene-metal interface. Using ab initio electronic structure calculations and quantum transport simulations, we perform a systematic study of the interfacial properties of three-layer (3L) phosphorene field effect transistors (FETs) contacted with several common metals (Al, Ag, Au, Cu, Ti, Cr, Ni, and Pd) for the first time. The SBHs obtained in the vertical direction from projecting the band structures of the 3L phosphorene-metal systems to the left bilayer (2L) phosphorenes are comparable with those obtained in the lateral direction from the quantum transport simulations for 2L phosphorene FETs. The quantum transport simulations for the 3L phosphorene FETs show that 3L phosphorene forms n-type Schottky contacts with electron SBHs of 0.16 and 0.28 eV in the lateral direction, when Ag and Cu are used as electrodes, respectively, and p-type Schottky contacts with hole SBHs of 0.05, 0.11, 0.20, 0.30, 0.30, and 0.31 eV in the lateral direction when Cr, Pd, Ni, Ti, Al, and Au are used as electrodes, respectively. The calculated polarity and SBHs of the 3L phosphorene FETs are generally in agreement with the available experiments.

Diameter- and chirality-dependent interactions between aromatic molecule-based nanotweezers and single-walled carbon nanotubes (SWNTs) are revealed by density functional theory calculations. We found that the threshold diameter of selected SWNTs is determined by the end-to-end distance of the nanotweezer. Large-diameter SWNTs are preferred by a nanotweezer with an obtuse folding angle, whereas small-diameter SWNTs are favored by a nanotweezer with an acute folding angle. The adsorption can be further stabilized by the orientational alignment of the hexagonal rings of the nanotweezer and the SWNT sidewall. Therefore, by taking advantage of the supramolecular recognition ability of the aromatic molecule-based nanotweezer, SWNTs can be enriched with both controllable diameter and chirality.

A magnetic ground state is revealed for the first time in zigzag-edged carbon nanoscrolls (ZCNSs) from spin-unrestricted density functional theory calculations. Unlike their flat counterpart—zigzag-edged carbon nanoribbons, which are semiconductors with spin-degenerate electronic structure—ZCNSs show a variety of magnetic configurations, namely spin-selective semiconductors, metals, semimetals, quasi-half-metals, and half-metals. To the best of our knowledge, this is the first discovery of quasi-half-metals and half-metals in a pure hydrocarbon without resort to an external electric field. In addition, we calculated the spin-dependent transportation of the semiconducting ZCNSs with 12 and 20 zigzag chains, and found that they are 13% and 17% at the Fermi level, respectively, suggesting that ZCNS can be an effective spin filter.