First-principles simulation of monolayer hydrogen passivated Bi2O2S2-metal interfaces.

Monolayer (ML) MoS2 is one of the most extensively studied two-dimensional (2D) semiconductors. However, it suffers from low carrier mobility and pervasive Schottky contact with metal electrodes. 2D semiconductor Bi2O2S, a sulfur analogue of 2D Bi2O2Se, has been prepared recently. ML fully hydrogen-passivated Bi2O2S2 (Bi2O2S2H2) posseses a comparable band gap (1.92 eV) with ML MoS2 (1.8 eV), but probably has a better device performance than ML MoS2. Based on the density functional theory, the electron and hole mobilities of ML Bi2O2S2H2 at 300 K are calculated to be 16 447-26 699 and 264-968 cm2 V-1 s-1, respectively. Then we firstly characterize the contact properties of ML half hydrogen-passivated Bi2O2S2 (Bi2O2S2H) with four bulk metal electrodes (Ti, Sc, Pd, and Pt) based on ab initio quantum transport simulation. In the lateral direction, a p-type Schottky contact is found in Pd and Pt electrodes, and the corresponding hole Schottky barrier heights (SBHs) are 0.54 and 0.99 eV, respectively. Remarkably, a coveted n-type Ohmic contact appears in Sc and Ti electrodes. Finally, the current on-off ratio of the ML hydrogen-passivated Bi2O2S2 field effect transistor with a Ti electrode reaches 105. Hence, the good intrinsic properties, contact properties, and large switching ability put ML hydrogen-passivated Bi2O2S2 in the rank of potential channel candidates for post-silicon era field effect transistors.

Sub-5 nm Ultrathin In2O3 Transistors for High-Performance and Low-Power Electronic Applications.

Ultrathin oxide semiconductors are promising candidates for back-end-of-line (BEOL) compatible transistors and monolithic three-dimensional integration. Experimentally, ultrathin indium oxide (In2O3) field-effect transistors (FETs) with thicknesses down to 0.4 nm exhibit an extremely high drain current (104 µA/µm) and transconductance (4000 µS/µm). Here, we employ ab initio quantum transport simulation to investigate the performance limit of sub-5 nm gate length (Lg) ultrathin In2O3 FETs. Based on the International Technology Roadmap for Semiconductors (ITRS) criteria for high-performance (HP) devices, the scaling limit of ultrathin In2O3 FETs can reach 2 nm in terms of on-state current, delay time, and power dissipation. The wide bandgap nature of ultrathin In2O3 (3.0 eV) renders it a suitable candidate for ITRS low-power (LP) electronics with Lg down to 3 nm. Notably, both the HP and LP ultrathin In2O3 FETs exhibit superior energy-delay products as compared to those of other common 2D semiconductors such as monolayer MoS2 and MoTe2. These findings unveil the potential of ultrathin In2O3 in HP and LP nanoelectronic device applications.

Performance Limit of Ultrathin GaAs Transistors.

High-electron-mobility group III-V compounds have been regarded as a promising successor to silicon in next-generation field-effect transistors (FETs). Gallium arsenide (GaAs) is an outstanding member of the III-V family due to its advantage of both good n- and p-type device performance. Monolayer (ML) GaAs is the limit form of ultrathin GaAs. Here, a hydrogenated ML GaAs (GaAsH2) FET is simulated by ab initio quantum-transport methods. The n- and p-type ML GaAsH2 metal-oxide-semiconductor FETs (MOSFETs) can well satisfy the on-state current, delay time, power dissipation, and energy-delay product requirements of the International Technology Roadmap for Semiconductors until the gate length is scaled down to 3/4 and 3/5 nm for the high-performance/low-power applications, respectively. Therefore, ultrathin GaAs is a prominent channel candidate for devices in the post-Moore era. The p-type ML GaAsH2 MOSFETs with a 2% uniaxially compressive strain and the unstrained n-type counterparts have symmetrical performance for the high-performance application, making ultrathin GaAs applicable for complementary MOS integrated circuits.

Improvement of alkali metal ion batteries via interlayer engineering of anodes: from graphite to graphene.

Interlayer engineering of graphite anodes in alkali metal ion (M = Li, Na, and K) batteries is carried out based on the first-principles calculations. By increasing the interlayer spacing of graphite, the specific capacity of Li or Na does not increase while that of K increases continuously (from 279 mA h g-1 at the equilibrium interlayer spacing to 1396 mA h g-1 at the interlayer spacing of 20.0 Å). As the interlayer spacing increases, the electrostatic potential of graphite becomes smoother, and the ability to buffer the electrostatic potential fluctuation becomes poorer in M ions. These two effects jointly lead to minima of the diffusion barrier of M ions on graphite (0.01-0.05 eV), instead of strictly monotonous declines with the increasing interlayer spacing. To perform the interlayer engineering of anode candidates more efficiently, a set of high-throughput programs has been developed and can be easily applied to other systems. Our research has guiding significance for achieving the optimal effect in interlayer engineering experimentally.

Can ultra-thin Si FinFETs work well in the sub-10 nm gate-length region?

Fin field-effect transistors (FinFETs) dominate the present Si FETs. However, when the gate length is scaled down to the sub-10 nm region, the experimental Si FinFETs suffer from poor performance due to a large fin width (the minimum value is 3 nm). In this paper, an ultra-thin Si FinFET with a width of 0.8 nm is investigated for the first time by utilizing ab initio quantum transport simulations. Remarkably, even with the gate length down to 5 nm, the on-state current, delay time, power dissipation, and energy-delay product of the optimized perfect ultra-thin Si FinFET still meet the high-performance applications' requirements of the International Technology Roadmap for Semiconductors in the next decade. The overall performance of the simulated ultra-thin Si FinFET is even comparable with that of the typical two-dimensional FETs. Such a good performance can be significantly degraded by the defect. Hence, Si FinFETs have the potential to be scaled down to the sub-10 nm gate length as long as the width is scaled down while keeping a perfect structure.

Polylysine and cysteine functionalized chitosan nanoparticle as an efficient platform for oral delivery of paclitaxel.

A novel chitosan-based multifunctional nanoparticle (PY-CS-PLA) using cationic polylysine (PL) polymer and L-cysteine has been developed and investigated for the oral delivery of paclitaxel (PTX). As amphiphilic polymer, PY-CS-PLA presented good capability in self-assembling into spherical nanoparticle with mean size of 165 nm, and encapsulating PTX into the hydrophobic core. The encapsulated PTX was observed to be sustainedly released from the functionalized chitosan nanoparticle, and with a positive correlation to the pH value of the medium in the range of 1.2 to 7.4. The in vitro studies indicated that PY-CS-PLA/PTX could effectively enhance the cellular uptake of the PTX in Caco-2 cells. Pharmacokinetic result indicated that the oral bioavailability of PY-CS-PLA/PTX in rats was determined to be 5.63-fold to that of Taxol. Moreover, PY-CS-PLA/PTX improved the distribution of PTX in tumor site and presented better antitumor efficacy in Heps tumor-bearing mice and with less toxicity than other formulations. In conclusion, the PY-CS-PLA/PTX nanoparticle might be developed as a promising delivery vehicle for improving the oral bioavailability and therapeutic effect of hydrophobic antitumor drugs.