The facile synthesis of and light-driven water splitting on a hetero-metallic bismuth oxide catalyst.

The process of water photo-electrolysis possesses the capability to generate sustainable and renewable hydrogen fuels, consequently addressing the challenge of the irregularity of solar energy. Thus, developing highly-efficient and low-cost electrocatalysts for the use in contemporary renewable energy devices is critical. Herein, we report the fabrication of a novel BaCeFex-yBixO6 nanocrystalline material through a one-step solvothermal route using a post-annealing process at 500 °C. The synthesized material was investigated for its light-induced electrochemical HER and OER activities in alkaline media and the results revealed that the as-prepared BaCeFex-yBixO6-500 °C exhibited an excellent OER activity with an overpotential of 100 mV to achieve a current density of 10 mA cm-2, thus outperforming the IrO2 electrocatalyst. Besides its excellent water oxidation performance, the catalyst also demonstrated an admirable HER activity comparable to that of the Pt/C catalyst, indicating that the higher temperature treatment plays a significant role in achieving the maximum performance of the developed electrocatalyst. This work provides insights into the enhancement of light-induced OER and HER activities of bismuth oxides for a wide range of catalytic applications.

Bombax ceiba flower extract mediated synthesis of Se nanoparticles for antibacterial activity and urea detection.

Plant mediated synthesis of metallic nanomaterials has emerged as a non-toxic and economical approach to their applications in diverse fields especially in biomedical sciences. Herein, this study first time reporting the use of Bombax ceiba flower extract for synthesis of selenium nanoparticles (SeNPs). Initially, SeNPs were confirmed by turning the color of reaction mixtures from light yellow to brick-red. Scanning electron microscope (SEM) and Transmission electron microscopy (TEM) images showed spherical shaped nanoparticles with smooth surface, size ranges between 30 and 150 nm. Dynamic light scattering (DLS) showed 100-150 nm for the distribution of particle size. X-ray diffraction (XRD) analysis revealed SeNPs crystallinity and confirmed by matching with selenium JCPD card No. 06-362. Energy-dispersive X-ray (EDX) spectra showed presence of pure Se peaks that corroborate the conversion of selenium ions into its elemental form by bio-reduction. Fourier-transform infrared spectroscopy (FTIR) spectra demonstrated that involvement of -OH, C-H, C=C, and C=O functional groups for SeNPs formation. Raman Spectra peaks at 250 cm-1 represent asymmetric trigonal selenium (t-Se). Ultraviolet-visible spectrophotometer (UV-Vis) peaks at 296 and 306 nm which is an indication of surface plasmon resonance (SPR). Moreover, maximum antibacterial activity of SeNPs were observed against Staphylococcus aureus- a gram positive bacteria that possess zone of inhibition (ZOI) 20 mm and Klebsiella pneumonia and Pseudomonas aeruginosa-gram negative bacteria with ZOI 28 mm, respectively, at concentration 100 µg/ml. In addition, the surface functionalities induced through extract components adhere over Se binds with urea and give its detection up to 1mM in milk sample. Conclusively, synthesized SeNPs may function as a potential antibacterial pharmaceutical candidate.

Weak antilocalization effect of topological crystalline insulator Pb(1-x)Sn(x)Te nanowires with tunable composition and distinct {100} facets.

Pb(1-x)Sn(x)Te is a unique topological crystalline insulator (TCI) that undergoes a topological phase transition from topological trivial insulator to TCI with the change of Sn content and temperature. Meanwhile, the surface states properties of Pb(1-x)Sn(x)Te are strongly dependent on crystallographic plane orientation. In this work, we first reported controllable synthesis of rectangular prismatic Pb(x)Sn(1-x)Te nanowires by vapor deposition method. Rectangular prismatic Pb(x)Sn(1-x)Te nanowires exhibits distinct {100} surfaces. Furthermore, The Sn composition of Pb(1-x)Sn(x)Te nanowires can be continuously controlled from 0 to 1. Low temperature magnetotransport shows that PbTe nanowire exhibits weak localization (WL) effect, whereas Pb0.5Sn0.5Te and Pb0.2Sn0.8Te nanowires display pronounced weak antilocalization (WAL) effect. This transition is explained by the topological phase transform of Pb(1-x)Sn(x)Te from trivial to nontrivial insulator with Sn content (x) exceeding 0.38. Pb(x)Sn(1-x)Te nanowires synthesized in this work lay a foundation for probing spin-correlated electron transport and show great potentials for future applications of tunable spintronic devices.

High-performance flexible photodetectors based on GaTe nanosheets.

2D layered GaTe materials have attracted a great deal of attention for optoelectronic applications due to their direct band structure, whether in bulk or as a single layer. In this paper, for the first time, we have synthesized high quality, single crystalline GaTe nanosheets by employing a facile CVD method. The size of the GaTe nanosheets reached several tens of micrometers, and some of them even exceeded 100 µm. In particular, planar GaTe nanosheets were achieved on a mica substrate following a van der Waals epitaxial growth mechanism. Further, through a systematic comparison of the performances under various conditions, we found that adsorbates on the GaTe surface under ambient conditions strongly deteriorated the GaTe photodetector device performance. After removing the adsorbates in a ∼ 7 × 10(-5) torr vacuum, a flexible, fast response GaTe photodetector with a high photoresponse, high mechanical stability and an excellent linear input-output relationship was obtained. The results presented in this study suggest that the GaTe nanosheets grown by a CVD method are promising candidates for optoelectronic applications in the future.

Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets.

Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials.

Wide range photodetector based on catalyst free grown indium selenide microwires.

We first report the catalyst free growth of indium selenide microwires through a facile approach in a horizontal tube furnace using indium and selenium elemental powders as precursors. The synthesized microwires are γ-phase, high quality, single crystalline and grown along the [112̅0] direction. The wires have a uniform diameter of ∼1 µm and lengths of several micrometers. Photodetectors fabricated from synthesized microwires show reliable and stable photoresponse exhibiting a photoresponsivity of 0.54 A/W, external quantum efficiency of 1.23 at 633 nm with 4 V bias. The photodetector has a reasonable response time of 0.11 s and specific detectivity of 3.94 × 10(10) Jones at 633 nm with a light detection range from 350 to 1050 nm, covering the UV-vis-NIR region. The photoresponse shown by single wire is attributed to direct band gap (Eg = 1.3 eV) and superior single crystalline quality. The photoresponsive studies of single microwires clearly suggest the use of this new and facile growth technique without using catalysts for fabrication of indium selenide microwires in next-generation sensors and detectors for commercial and military applications.

Novel top-contact monolayer pentacene-based thin-film transistor for ammonia gas detection.

We report on the fabrication of an organic field-effect transistor (OFET) of a monolayer pentacene thin film with top-contact electrodes for the aim of ammonia (NH3) gas detection by monitoring changes in its drain current. A top-contact configuration, in which source and drain electrodes on a flexible stamp [poly(dimethylsiloxane)] were directly contacted with the monolayer pentacene film, was applied to maintain pentacene arrangement ordering and enhance the monolayer OFET detection performance. After exposure to NH3 gas, the carrier mobility at the monolayer OFET channel decreased down to one-third of its original value, leading to a several orders of magnitude decrease in the drain current, which tremendously enhanced the gas detection sensitivity. This sensitivity enhancement to a limit of the 10 ppm level was attributed to an increase of charge trapping in the carrier channel, and the amount of trapped states was experimentally evaluated by the threshold voltage shift induced by the absorbed NH3 molecular analyte. In contrast, a conventional device with a 50-nm-thick pentacene layer displayed much higher mobility but lower response to NH3 gas, arising from the impediment of analyte penetrating into the conductive channel, owing to the thick pentacene film.

Topological surface transport properties of single-crystalline SnTe nanowire.

SnTe has attracted worldwide interest since its theoretical predication as topological crystalline insulator. Because of promising applications of one-dimensional topological insulator in nanoscale electronics and spintronics device, it is very important to realize the observation of topological surface states in one-dimensional SnTe. In this work, for the first time we successfully synthesized high-quality single crystalline SnTe nanowire via gold-catalyst chemical vapor deposition method. Systematical investigation of Aharonov-Bohm and Shubnikov-de Haas oscillations in single SnTe nanowire prove the existence of Dirac electrons. Further analysis of temperature-dependent Shubnikov-de Haas oscillations gives valuable information of cyclotron mass, mean-free path, and mobility of Dirac electrons in SnTe nanowire. Our study provides the experimental groundwork for research in low-dimensional topological crystalline insulator materials and paves the way for the application of SnTe nanowire in nanoelectronics and spintronics device.

Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters.

We report the controlled growth of highly ordered and well aligned one-dimensional tellurium nanostructure arrays via a one-step catalyst-free physical vapor deposition method. The density, size and fine structures of tellurium nanowires are systematically studied and optimized. Field emission measurement was performed to display notable dependence on nanostructure morphologies. The ordered nanowire array based field emitter has a turn-on field as low as 3.27 V µm(-1) and a higher field enhancement factor of 3270. Our finding offers the possibility of controlling the growth of tellurium nanowire arrays and opens up new means for their potential applications in electronic devices and displays.