Two-dimensional transition metal carbides/nitrides, known as MXenes, have been recently receiving attention for gas sensing. However, studies on hybridization of MXenes and 2D transition metal dichalcogenides as gas-sensing materials are relatively rare at this time. Herein, Ti 3 C 2 T x and WSe 2 are selected as model materials for hybridization and implemented toward detection of various volatile organic compounds. The Ti 3 C 2 T x /WSe 2 hybrid sensor exhibits low noise level, ultrafast response/recovery times, and good flexibility for various volatile organic compounds. The sensitivity of the hybrid sensor to ethanol is improved by over 12-fold in comparison with pristine Ti 3 C 2 T x. Moreover, the hybridization process provides an effective strategy against MXene oxidation by restricting the interaction of water molecules from the edges of Ti 3 C 2 T x. An enhancement mechanism for Ti 3 C 2 T x /WSe 2 heterostructured materials is proposed for highly sensitive and selective detection of oxygencontaining volatile organic compounds. The scientific findings of this work could guide future exploration of next-generation field-deployable sensors.

Two-dimensional (2D) transition-metal carbides (Ti3C2T x MXene) have received a great deal of attention for potential use in gas sensing showing the highest sensitivity among 2D materials and good gas selectivity. However, one of the long-standing challenges of the MXenes is their poor stability against hydration and oxidation in a humid environment, limiting their long-term storage and applications. Integration of an effective protection layer with MXenes shows promise for overcoming this major drawback. Herein, we demonstrate a surface functionalization strategy for Ti3C2T x with fluoroalkylsilane (FOTS) molecules through surface treatment, providing not only a superhydrophobic surface, mechanical/environmental stability but also enhanced sensing performance. The experimental results show that high sensitivity, good repeatability, long-term stability, and selectivity and faster response/recovery property were achieved by the FOTS-functionalized when Ti3C2T x was integrated into chemoresistive sensors sensitive to oxygen-containing volatile organic compounds (ethanol, acetone). FOTS functionalization provided protection to sensing response when the dynamic response of the Ti3C2T x -F sensor to 30 ppm of ethanol was measured over in the 5 to 80% relative humidity range. Density functional theory simulations suggested that the strong adsorption energy of ethanol on Ti3C2T x -F and the local structure deformation induced by ethanol adsorption, contributing to the gas-sensing enhancement. This study offers a facile and practical solution for developing highly reliable MXene based gas-sensing devices with response that is stable in air and in the presence of water.

The realization of ultra-low power Si-based resistive switching memory technology will be a milestone in the development of next generation non-volatile memory. Here we show that a high performance and ultra-low power resistive random access memory (RRAM) based on an Al/a-SiNx:H/p+-Si structure can be achieved by tuning the Si dangling bond conduction paths. We reveal the intrinsic relationship between the Si dangling bonds and the N/Si ratio x for the a-SiNx:H films, which ensures that the programming current can be reduced to less than 1 μA by increasing the value of x. Theoretically calculated current-voltage (I–V ) curves combined with the temperature dependence of the I–V characteristics confirm that, for the low-resistance state (LRS), the Si dangling bond conduction paths obey the trap-assisted tunneling model. In the high-resistance state (HRS), conduction is dominated by either hopping or Poole–Frenkel (P–F) processes. Our introduction of hydrogen in the a-SiNx:H layer provides a new way to control the Si dangling bond conduction paths, and thus opens up a research field for ultra-low power Si-based RRAM.

achieved after 1000 cycles at 3.4 A g −1 (or 20 A g −1 ), with a capacity retention rate of ≈84% (≈88%), without the use of any binder or conductive agent. Remarkably, they can survive an extremely fast charging rate at 70 A g −1 for 35 runs (corresponding to one full cycle in 30 s) and recover 88% capacity. This novel alloy-nanotube structure could represent an ideal candidate to fulfi ll the true potential of Si-loaded LIB applications.

The ability to program highly modulated morphology upon silicon nanowires (SiNWs) has been fundamental to explore new phononic and electronic functionalities. We here exploit a nanoscale locomotion of metal droplets to demonstrate a large and readily controllable morphology engineering of crystalline SiNWs, from straight ones into continuous or discrete island-chains, at temperature <350 °C. This has been accomplished via a tin (Sn) droplet mediated in-plane growth where amorphous Si thin film is consumed as precursor to produce crystalline SiNWs. Thanks to a significant interface-stretching effect, a periodic Plateau-Rayleigh instability oscillation can be stimulated in the liquid Sn droplet, and the temporal oscillation of the Sn droplets is translated faithfully, via the deformable liquid/solid deposition interface, into regular spatial modulation upon the SiNWs. Combined with a unique self-alignment and positioning capability, this new strategy could enable a rational design and single-run fabrication of a wide variety of nanowire-based optoelectronic devices.

Producing ultra-stabilized radicals via light irradiation has raised considerable concern but remains a tremendous challenge in functional materials. Herein, optically actuating ultra-stable radicals are discovered in a sterically encumbered and large πconjugated tri(4-pyridyl)-1,3,5-triazine (TPT) ligands constructed photochromic compound Cu 3 (H-HEDP) 2 TPT 2 •2H 2 O (QDU-12; HEDP=hydroxyethylidene diphosphonate). The photogeneration of TPT• radicals is the photoactive behavior of electron transfer from HEDP motifs to TPT units. The ultra-long-lived radicals are contributed from strong interchain π-π interactions between the large π-conjugated TPT components, with the radical lifetime maintained for about 18 months under ambient conditions. Moreover, the antiferromagnetic couplings between TPT • radicals and Cu 2+ ions plummeted the demagnetization to 35% of its original state after light irradiation, showing the largest room temperature photodemagnetization in the current radicalbased photochromic materials.

Crystalline Si nanowire (SiNW) springs, produced via a low temperature (<350 °C) thin fi lm technology, are ideal building blocks for stretchable electronics. Herein, a novel cyclic crystallographic-index-lowering self-turning and twin dynamics is reported, during a tin-catalyzed in-plane growth of SiNWs, which results in a periodic zigzag SiNW without any external parametric intervention. More interestingly, a unique twin-refl ected interlaced crystaldomain structure has been identifi ed for the fi rst time, while in situ and realtime scanning electron microscopy observations reveal a new twin-triggering growth mechanism that is the key to reset a complete zigzag growth cycle. Direct "stress-strain" testing of the SiNW springs demonstrates a large stretchability of 12% under tensile loading, indicating a whole new strategy and capability to engineer mono-like SiNW channels for high performance stretchable electronics.

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