Grating-assisted hot-electron photodetectors for S- and C-band telecommunication.

Although outstanding detectivities, InGaAs photodetectors for optic fiber communication are often costly due to the need for cooling. Therefore, cryogen-free and cost-effective alternatives working in telecommunication bands are highly desired. Here, we present a design of hot-electron photodetectors (HE PDs) with attributes of room-temperature operation and strong optical absorption over S and C bands (from 1460 to 1565 nm). The designed HE PD consists of a metal-semiconductor-metal hot-electron stack integrated with a front grating. Optical simulations reveal that mode hybridizations between Fabry-Pérot resonance and grating-induced surface plasmon excitation lead to high absorption efficiencies (≥0.9) covering S and C bands. Probability-based electrical calculations clarify that device responsivity is mainly determined by working wavelength on the premise of broadband strong absorption. Moreover, through comparison studies between the grating-assisted HE PD and purely planar microcavity system that serves as a reference, we highlight the design superiorities in average absorption and average responsivity with optimized values of 0.97 and 0.73 mA W-1, respectively. The upgraded peformances of the designed device are promising for efficient photoelectric conversion in optic fiber communication systems.

Planar hot-electron photodetection with polarity-switchable photocurrents controlled by the working wavelength.

Hot-electron photodetection is attracting increasing interests. Based on internal photoemission mechanism, hot-electron photodetectors (HE PDs) convert incident photon energy into measurable photocurrent. To obtain polarity-switchable photocurrent, one often applies electric bias to reverse the hot-electron flow. However, the employment of bias reduces the device flexibility and increasing the bias voltage degrades the detectivity of the device. Herein, we design a planar HE PD with the polarity-switchable photocurrent controlled by the working wavelength. Optical simulations show that the device exhibits two absorption peaks due to the resonances of two Tamm plasmons (TPs). Electrical calculations predict two corresponding TP-assisted responsivity peaks, but with opposite photocurrent polarities, which are determined by the hot-electron flows with opposite directions. We find that the hot-electron flows are closely related with the population differences of TP-induced hot electrons in two electrodes. We further demonstrate that the photocurrent polarity of the HE PD can be switched by altering working wavelength from one TP wavelength to the other. We believe that this approach paves a route to achieve flexible hot-electron photodetection for extensive applications.

Natural Products for Drug Discovery: Discovery of Gramines as Novel Agents against a Plant Virus.

Plant viral diseases seriously affect crop yield and quality. The natural product gramine (1) and its simple structural analogues 2-35 were synthesized from indoles, amines, and aldehydes in one step. The antiviral effects of these alkaloids were evaluated systematically. Most of these compounds were found to have higher antiviral effects than commercial ribavirin for the first time. Especially compounds 22, 30, and 31 exhibited significantly higher effects than ningnanmycin, thereby emerging as novel antiviral leads for further optimization. The preliminary implementation indicated that these compounds likely inhibit the assembly of tobacco mosaic virus (TMV) by cross-linking TMV capsid protein. Gramine analogues were also found to have broad-spectrum fungicidal effects. Although gramine has been reported to have influence on germination and development of Erysiphe graminis, these compounds displayed no fungicidal effects against Blumeria graminis f. sp. tritici on wheat in our test. Some of these compounds also exhibited certain insecticidal activities.

A new approach to understand the Cassie state of liquids on superamphiphobic materials.

A hierarchical structure is a prerequisite for a liquid super-repellent surface due to its capability to catch large numbers of fine air-pockets. In the present work, a series of hierarchical nanocomposites with anti-wettability were fabricated by in situ deposition of spherical SiO2 nanoparticles on Te@C nanofibers. N2 adsorption-desorption isotherms were used for the first time to characterize the air-pockets and relate them to the wettability of the nanocomposites. The results indicate that superamphiphobicity is a contribution of a delicate synergistic effect between a micro-scale structure and a nano-scale structure. Significant dominance of either of them led to reduced superamphiphobicity. The superamphiphobic "beads on a string" materials should meet the following features: higher SBET that ensures enough air-pockets (SBET value of the superamphiphobic sample is much higher than that of the superhydrophobic one); and the most important, a "continuous and balanced" distribution of micro and macro air-pockets derived from hierarchical structures.