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The long-term stability and superior device reliability through the use of delicately designed metal contacts with two-dimensional (2D) atomic-scale semiconductors are considered one of the critical issues related to practical 2D-based electronic components. Here, we investigate the origin of the improved contact properties of alloyed 2D metal-semiconductor heterojunctions. 2D WSe2-based transistors with mixed transition layers containing van der Waals (M-vdW, NbSe2/WxNb1-xSe2/WSe2) junctions realize atomically sharp interfaces, exhibiting long hot-carrier lifetimes of approximately 75,296 s (78 times longer than that of metal-semiconductor, Pd/WSe2 junctions). Such dramatic lifetime enhancement in M-vdW-junctioned devices is attributed to the synergistic effects arising from the significant reduction in the number of defects and the Schottky barrier lowering at the interface. Formation of a controllable mixed-composition alloyed layer on the 2D active channel would be a breakthrough approach to maximize the electrical reliability of 2D nanomaterial-based electronic applications.

A three-dimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but with linear energy dispersion in all (three) momentum directions. 3D DSs have been a fertile playground in discovering novel quantum particles, for example Weyl fermions, in solid state systems. Many 3D DSs were theoretically predicted and experimentally confirmed. We report here the results in exfoliated ZrTe5 thin flakes from the studies of aberration-corrected scanning transmission electron microscopy and low temperature magneto-transport measurements. Several unique results were observed. First, a π Berry phase was obtained from the Landau fan diagram of the Shubnikov-de Haas oscillations in the longitudinal conductivity σxx. Second, the longitudinal resistivity ρxx shows a linear magnetic field dependence in the quantum limit regime. Most surprisingly, quantum oscillations were also observed at fractional Landau level indices N = 5/3 and 7/5, demonstrating strong electron-electron interaction effects in ZrTe5.

The electronic properties of colloidal quantum dots (CQDs) have shown intriguing potential in recent years for implementation in various optoelectronic applications. However, their chemical and photochemical stabilities, mainly derived from surface properties, have remained a major concern. This paper reports a new strategic route for the synthesis of surface-treated CQDs, the CdSe/CdS core/shell heterostructures, based on low-temperature coating of a shell constituent, followed by a programmed annealing process. A comprehensive follow-up of the stability and the optical properties through the various synthesis stages is reported, suggesting that the low-temperature coating is responsible for the formation of a sharp interface between the core and the shell, whereas a postcoating annealing process leads to the generation of a thin alloy interfacial layer. At the end of the process, the CdSe/CdS CQDs show a significant improvement of the photoluminescence quantum yield, as well as an exceptional photostability. Consequently, the work reported here provides a convenient generic route to the formation of core/shell CQDs to be employed as a procedure for achieving various other heterostructures.

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In this study, MoS nanosheets are vertically grown on the inside and outside surfaces of the carbonized corn stalks (CCS) by a simple hydrothermal reaction. The vertically grown structure can not only improve the transmission rate of Li and electrons but also avoid the agglomeration of the nanosheets. Meanwhile, a new approach of biomass source application is presented. We use CCS instead of graphite powders, which can not only avoid the exploitation of graphite resources, but also be used as a matrix for MoS growth to prevent the electrode from being further decomposed during long cycles and at high current densities. Meanwhile, lithium-ion batteries show remarkable electrochemical performance. They demonstrate a high specific capacity of 1409.5 mA g at 100 mA g in the initial cycle. After 250 cycles, the discharge capacity is still as high as 1230.9 mAh g. Even at 4000 mA g, they show a high specific capacity of 777.7 mAh g. Furthermore, the MoS/CCS electrodes show long cycle life, and the specific capacity is still up to ∼500 mAh g at 5000 mA g after 1000 cycles.

A unique reversible conversion-type mechanism is reported in the amorphous molybdenum polysulfide (a-MoS) cathode material. The lithiation products of metallic Mo and LiS rather than Mo and LiS species have been detected. This process could yield a high discharge capacity of 746 mAh g. Characterizations of the recovered molybdenum polysulfide after the delithiaiton process manifests the high reversibility of the unique conversion reaction, in contrast with the general irreversibility of the conventional conversion-type mechanism. As a result, the a-MoS electrodes deliver high cycling stability with an energy-density retention of 1166 Wh kg after 100 cycles. These results provide a novel model for the design of high-capacity and long-life electrode materials.

Plasma reactions are very effective in preparation of both silicon and carbon materials. However, Si/C composites, which are highly attractive as the anode material in lithium ion batteries, are difficult to be prepared using plasma due to the strong tendency of silicon carbide (SiC) formation. Here we effectively inhibit the SiC formation by generating reactive Si and C species in separated plasma zones and by using a solid graphite carbon precursor. Homogeneous Si/C nanocomposites with excellent lithium storage performance are obtained from one step plasma deposition at room temperature, which retain high capacity of 1760 and 1460 mAhg -1 after more than 400 cycles at charge/discharge rate of 2.0 and 4.0 Ag -1 , respectively. Electronic Supplementary Information (ESI) available: [A cross section SEM image, EDS spectrum, CV curves and voltage-capacity curves of the Si/C-graphite sample; a TEM image, elemental mapping and CV curves of the Si/C-CH4 sample ]. See