Ultrashort Channel Length Black Phosphorus Field-Effect Transistors

This paper reports high-performance top-gated black phosphorus (BP) field-effect transistors with channel lengths down to 20 nm fabricated using a facile angle evaporation process. By controlling the evaporation angle, the channel length of the transistors can be reproducibly controlled to be anywhere between 20 and 70 nm. The as-fabricated 20 nm top-gated BP transistors exhibit respectable on-state current (174 μA/μm) and transconductance (70 μS/μm) at a <i>V</i>_DS of 0.1 V. Due to the use of two-dimensional BP as the channel material, the transistors exhibit relatively small short channel effects, preserving a decent on–off current ratio of 10² even at an extremely small channel length of 20 nm. Additionally, unlike the unencapsulated BP devices, which are known to be chemically unstable in ambient conditions, the top-gated BP transistors passivated by the Al₂O₃ gate dielectric layer remain stable without noticeable degradation in device performance after being stored in ambient conditions for more than 1 week. This work demonstrates the great promise of atomically thin BP for applications in ultimately scaled transistors

Fully Printed Stretchable Thin-Film Transistors and Integrated Logic Circuits

This paper reports intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits directly printed on elastomeric polydimethylsiloxane (PDMS) substrates. The printed devices utilize carbon nanotubes and a type of hybrid gate dielectric comprising PDMS and barium titanate (BaTiO₃) nanoparticles. The BaTiO₃/PDMS composite simultaneously provides high dielectric constant, superior stretchability, low leakage, as well as good printability and compatibility with the elastomeric substrate. Both TFTs and logic circuits can be stretched beyond 50% strain along either channel length or channel width directions for thousands of cycles while showing no significant degradation in electrical performance. This work may offer an entry into more sophisticated stretchable electronic systems with monolithically integrated sensors, actuators, and displays, fabricated by scalable and low-cost methods for real life applications

Air-Stable Humidity Sensor Using Few-Layer Black Phosphorus

As a new family member of two-dimensional layered materials, black phosphorus (BP) has attracted significant attention for chemical sensing applications due to its exceptional electrical, mechanical, and surface properties. However, producing air-stable BP sensors is extremely challenging because BP atomic layers degrade rapidly in ambient conditions. In this study, we explored the humidity sensing properties of BP field-effect transistors fully encapsulated by a 6 nm-thick Al₂O₃ encapsulation layer deposited by atomic layer deposition. The encapsulated BP sensors exhibited superior ambient stability with no noticeable degradation in sensing response after being stored in air for more than a week. Compared with the bare BP devices, the encapsulated ones offered long-term stability with a trade-off in slightly reduced sensitivity. Capacitance–voltage measurement results further reveal that instead of direct charge transfer, the electrostatic gating effect on BP flakes arising from the dipole moment of adsorbed water molecules is the basic mechanism governing the humidity sensing behavior of both bare and encapsulated BP sensors. This work demonstrates a viable approach for achieving air-stable BP-based humidity or chemical sensors for practical applications

Vertically Stacked and Self-Encapsulated van der Waals Heterojunction Diodes Using Two-Dimensional Layered Semiconductors

van der Waals heterojunctions using 2D semiconducting materials could overcome the defect issues included by lattice mismatch in conventional epitaxially grown heterojunctions with bulk materials and could enable a much wider palette for choice of materials and more sophisticated device design. Such 2D heterojunction devices are of great interest for important functional devices such as diodes, bipolar junction transistors, light-emitting diodes, and photodetectors. In this paper, we demonstrate a truly vertical p–n heterojunction diode built from 2D semiconductors (MoS₂ and BP) and compare its performance against conventional lateral 2D heterojunction devices (partially overlapped 2D heterostructures). Both vertical and lateral p–n heterostructure diodes exhibit a strong rectification ratio even with no gate voltage applied. More importantly, the results show that the vertical diode delivers 70 times higher current density under forward bias than a conventional lateral device design and the improved device performance can be attributed to the complete elimination of series resistance. Low-temperature measurements and TCAD simulations are used to determine the barrier height at the junctions. Moreover, the vertical device structure allows certain ambiently unstable 2D semiconductors to be fully encapsulated by the materials on top, preventing the material from degradation. This work demonstrates the potential of using the vertically stacked 2D semiconductors for future nanoelectronic and optoelectronic devices with optimal performance

Discovery of Novel Urea-Based Hepatitis C Protease Inhibitors with High Potency against Protease-Inhibitor-Resistant Mutants

The macrocyclic urea <b>2</b>, a byproduct in the synthesis of benzoxaborole <b>1</b>, was identified to be a novel and potent HCV protease inhibitor. We further explored this motif by synthesizing additional urea-based inhibitors and by characterizing them in replicase HCV protease-resistant mutants assay. Several compounds, exemplified by <b>12</b>, were found to be more potent in HCV replicon assays than leading second generation inhibitors such as danoprevir and TMC-435350. Additionally, following oral administration, inhibitor <b>12</b> was found in rat liver in significantly higher concentrations than those reported for both danoprevir and TMC-435350, suggesting that inhibitor <b>12</b> has the combination of anti-HCV and pharmacokinetic properties that warrants further development of this series

Novel macrocyclic HCV NS3 protease inhibitors derived from a-amino cyclic boronates

A novel series of P2-P4 macrocyclic HCV NS3/4A protease inhibitors with a-amino cyclic boronates as warheads at the P1 site was designed and synthesized. When compared to their linear analogs, these macrocyclic inhibitors exhibited a remarkable improvement in cell-based replicon activities, with compounds 9a and 9e reaching sub-micromolar potency in replicon assay. The SAR around a-amino cyclic boronates clearly established the influence of ring size, chirality and of the substitution pattern. Furthermore, X-ray structure of the co-crystal of inhibitor 9a and NS3 protease revealed that Ser-139 in the enzyme active site traps boron in the warhead region of 9a, thus establishing its mode of action