Ultrafast and Parts-per-Billion-Level MEMS Gas Sensors by Hetero-Interface Engineering of 2D/2D Cu-TCPP@ZnIn2S4 with Enriched Surface Sulfur Vacancies.

The primary challenge for resonant-gravimetric gas sensors is the synchronous improvement of the sensitivity and response time, which is restricted by low adsorption capacity and slow mass transfer in the sensing process and remains a great challenge. In this study, a novel 2D/2D Cu-TCPP@ZnIn2S4 composite is successfully constructed, in which Cu-TCPP MOF is used as a core substrate for the growth of 2D ultrathin ZnIn2S4 nanosheets with well-defined {0001} crystalline facets. The Cu-TCPP@ZnIn2S4 sensor exhibited high sensitivity (1.5 Hz@50 and 2.3 Hz@100 ppb), limit of detection (LOD: 50 ppb), and ultrafast (9 s @500 ppb) detection of triethylamine (TEA), which is the lowest LOD and the fastest sensor among the reported TEA sensors at room temperature, tackling the bottleneck for the ultrafast detection of the resonant-gravimetric sensor. These above results provide an innovative and easily achievable pathway for the synthesis of heterogeneous structure sensing materials.

Anisotropic Growth of Centimeter-Size CsCu2 I3 Single Crystals with Ultra-Low Trap Density for Aspect-Ratio-Dependent Photodetectors.

Low-dimensional ternary copper iodide metal halide with strong quantum confinement effects has made great progress in optoelectronic fields. However, efficient regulation of anisotropic growth of metal halides single crystal still remains a great challenge. Herein, 2 cm size CsCu2 I3 single crystals with tunable aspect ratio and the trap states (ntrap ) as low as 5.38 × 109  cm-3 are fabricated by optimized anti-solvent vapor-assisted method, in which the growth cycle is shortened by half. Evidenced by real-time observation and the LaMer growth model, the rapid and anisotropic growth mechanism is ascribed to preferential 1D growth, promoted by high concentration and fast vapor rate. Furthermore, the aspect-ratio-dependent optoelectronic performance is observed, the on-off ratio for 2 cm CsCu2 I3 single crystal are enhanced 350 times compared with those of short and thick single crystal, which shows ultrahigh on-off ratio of 1570, D* of 1.34 × 1012  Jones, Rλ of 276.94 mA W-1 , t rise /t decay of 0.37 and 1.08 ms, and EQE of 95.53%, which are clearly at very high level among lead-free perovskite-based photodetectors. This study not only provides a new strategy for overcoming anisotropic growth limitations of low-dimensional metal halides, but also paves a way for high-performance optoelectronic applications.

Controlled preparation and gas sensitive properties of two-dimensional and cubic structure ZnSnO3.

Two-dimensional (2D) ZnSnO3 is a promising candidate for future gas sensors due to its high chemical response and excellent electronic properties. However, the preparation of 2D ZnSnO3 nanosheets by utilizing soluble inorganic salts and nonorganic solvents remains a challenge. In this work, 2D ZnSnO3 was synthesized via a facile graphene oxide (GO)-assisted co-precipitation method, in which inorganic salts in the aqueous phase replaced metal organic salts in a non-aqueous system. Meanwhile, a "dissolution and recrystallization" mechanism was proposed to explain the transformation from 3D nanocubes to 2D nanosheets. In comparison, the 2D ZnSnO3 nanosheets showed a higher response to formaldehyde (HCHO) at low operating temperature (100 °C). The response (Ra/Rg) of the 2D ZnSnO3 sensor to 10 ppm HCHO was as high as 57, which was approximately 5 times the response of the ZnSnO3 nanocubes sensor. However, the ZnSnO3 nanocubes sensor showed better gas sensing performance to ethanol at high temperature (200 °C). Different gas-sensitive properties were attributed to the different gas diffusion and adsorption processes caused by the morphology and nanostructure. Moreover, both sensors could detect either 0.1 ppm HCHO or ethanol at their optimum operating temperature. This work presents a relatively economical method to prepare 2D compound metal oxides, provides a novel "dissolution and recrystallization" mechanism for 2D multi-metal oxide preparation, and sheds light on the great potential of high-efficiency HCHO and/or ethanol gas sensors.

Wearable and Ultrasensitive Strain Sensor Based on High-Quality GaN pn Junction Microwire Arrays.

With the rapid growth in wearable electronics sensing devices, flexible sensing devices that monitor the human body have shown great promise in personalized healthcare. In the study, high-quality GaN pn junction microwire arrays with different aspect ratios and large-area uniformity are fabricated through an easy, repeatable fabrication process. The piezoelectric coefficient (d33 ) of GaN pn junction microwire arrays increases from 7.23 to 14.46 pm V-1 with the increasing of the aspect ratio, which is several times higher than that of GaN bulk material. Furthermore, flexible ultrasensitive strain sensor based on GaN microwires with the highest d33 is demonstrated to achieve the maximum open circuit voltage of 10.4 V, and presents excellent durability with stable output signals over 10 000 cycles with a response time of 50 ms. As a flexible and wearable sensor attached to the human skin, the GaN microwire pn junction arrays with such a high degree of uniformity can precisely monitor subtle human pulse and motions, which show great promise in future personalized healthcare.

Size-Controlled Graphene Nanodot Arrays/ZnO Hybrids for High-Performance UV Photodetectors.

Graphene nanodots (GNDs) are one of the most attractive graphene nanostructures due to their tunable optoelectronic properties. Fabricated by polystyrene-nanosphere lithography, uniformly sized graphene nanodots array (GNDA) is constructed as an ultraviolet photodetector (PD) with ZnO nanofilm spin coated on it. The size of GNDA can be well controlled from 45 to 20 nm varying the etching time. It is revealed in the study that the photoelectric properties of ZnO/GNDA PD are highly GNDA size-dependent. The highest responsivity (R) and external quantum efficiency of ZnO/GNDA (20 nm) PD are 22.55 mA W-1 and 9.32%, almost twofold of that of ZnO PD. Both ZnO/GNDA (20 nm) PD and ZnO/GNDA (30 nm) PD exhibit much faster response speed under on/off switching light and have shorter rise/decay time compared with ZnO PD. However, as the size of GNDA increase to 45 nm, the PD appears poor performance. The size-dependent phenomenon can be explained by the energy band alignments in ZnO/GNDA hybrids. These efforts reveal the enhancement of GNDs on traditional photodetectors with tunable optoelectronic properties and hold great potential to pave a new way to explore the various remarkable photodetection performances by controlling the size of the nanostructures.

Corrigendum: Superior Adsorption and Regenerable Dye Adsorbent Based on Flower-Like Molybdenum Disulfide Nanostructure.

This corrects the article DOI: 10.1038/srep43599.

Superior Adsorption and Regenerable Dye Adsorbent Based on Flower-Like Molybdenum Disulfide Nanostructure.

Herein we report superior dye-adsorption performance for flower-like nanostructure composed of two dimensional (2D) MoS2 nanosheets by a facile hydrothermal method, more prominent adsorption of cationic dye compared with anodic dye indicates the dye adsorption performance strongly depends on surface charge of MoS2 nanosheets. The adsorption mechanism of dye is analyzed, the kinetic data of dye adsorption fit well with the pseudo-second-order model, meanwhile adsorption capability at different equilibrium concentrations follows Langmuir model, indicating the favorability and feasibility of dye adsorption. The regenerable property for MoS2 with full adsorption of dye molecules by using alkaline solution were demonstrated, showing the feasibility of reuse for the MoS2, which is promising in its practical water treatment application.

Hierarchical MoS2 Nanosheet@TiO2 Nanotube Array Composites with Enhanced Photocatalytic and Photocurrent Performances.

A novel type of hierarchical nanocomposites consisted of MoS2 nanosheet coating on the self-ordered TiO2 nanotube arrays is successfully prepared by a facile combination of anodization and hydrothermal methods. The MoS2 nanosheets are uniformly decorated on the tube top surface and the intertubular voids with film appearance changing from brown to black color. Anatase TiO2 nanotube arrays (NTAs) with clean top surfaces and the appropriate amount of MoS2 precursors are key to the growth of perfect compositing TiO2 @MoS2 hybrids with significantly enhanced photocatalytic activity and photocurrent response. These results reveal that the strategy provides a flexible and straightforward route for design and preparation nanocomposites based on functional semiconducting nanostructures with 1D self-ordered TiO2 NTAs, promising for new opportunities in energy/environment applications, including photocatalysts and other photovoltaic devices.

Photocurrent enhancement mechanisms in bilayer nanofilm-based ultraviolet photodetectors made from ZnO and ZnS spherical nanoshells.

Hollow-sphere bilayer nanofilm-based ultraviolet light photodetectors made from ZnO and ZnS spherical nanoshells show enhanced photocurrent, which are comparable to or even better than those of other semiconductor nanostructures with different shapes. In this work, the photocurrent enhancement mechanisms of these bilayer nanofilm-based ultraviolet light photodetectors are explained, which could be attributed to the strong light absorption based on the whispering gallery mode resonances, the separation of the photogenerated carriers through the internal electric field within the bilayer nanofilms, the hopping-like electrical transport, and the effective charge injection from Cr/Au contacts to the nanofilms.