Xincun Dou

Kinetic versus thermodynamic control over growth process of electrodeposited Bi/BiSb superlattice nanowires.

The growth mechanism of the electrodeposited single crystalline nanowires is generally considered to follow a three-dimensional to two-dimensional (2D) transition mode, and as for the 2D growth, it is ordinarily considered as a plane growth mode (layer-by-layer growth mechanism). We report in this Letter the growth of Bi/BiSb superlattice nanowires by adopting a charge-controlled pulse electrodeposition technique, and to our best knowledge, different growth modes of the nanowires, the 2D plane growth mode, the tilted plane growth mode, and the curved plane growth mode, were first observed. These growth modes were gathered and analyzed from the perspectives of crystal growth as well as kinetics and thermodynamics. It is shown that the superlattice nanowires are good structures for studying the growth mechanism of electrodeposited nanowires. This work will deeply benefit the understanding of the growth process of the electrodeposited nanowires and provide important experiment data to crystal growth theory.

Nanostructure-based optoelectronic sensing of vapor phase explosives – a promising but challenging method

Optoelectronic sensing of gas phase hazardous chemicals is a newly explored field, which shows great advantages towards low concentration sensing when compared to normal gas sensing in the dark. Here, based on the recent progress on nanostructured vapor phase explosive gas sensors operated in dark conditions, the attractiveness of developing optoelectronic sensors for vapor phase explosive detection was highlighted. Furthermore, we try to propose some new insights to enhance optoelectronic sensing of vapor phase explosives. We suggest employing photocatalysis principles to enhance the sensitivity and employing a molecular imprinting technique (MIT) to enhance the selectivity.

Magnetic properties of single crystalline Co nanowire arrays with different diameters and orientations

Single crystalline Co nanowire arrays with different diameters and orientations were grown within porous anodic alumina membranes by a pulsed electrodeposition technique and the magnetic properties of the nanowire were systematically studied. It was found that the magnetization behavior of the Co nanowire arrays is anisotropic and their magnetic properties can be effectively modulated through tuning either the diameter or the orientation of the nanowires. The magnetic properties of the Co nanowires were discussed qualitatively by using the classical magnetization theory and single domain model.

Transition‐Metal‐Doped p‐Type ZnO Nanoparticle‐Based Sensory Array for Instant Discrimination of Explosive Vapors

The development of portable, real-time, and cheap platforms to monitor ultratrace levels of explosives is of great urgence and importance due to the threat of terrorism attacks and the need for homeland security. However, most of the previous chemiresistor sensors for explosive detection are suffering from limited responses and long response time. Here, a transition-metal-doping method is presented to remarkably promote the quantity of the surface defect states and to significantly reduce the charge transfer distance by creating a local charge reservoir layer. Thus, the sensor response is greatly enhanced and the response time is remarkably shortened. The resulting sensory array can not only detect military explosives, such as, TNT, DNT, PNT, PA, and RDX with high response, but also can fully distinguish some of the improvised explosive vapors, such as AN and urea, due to the huge response reaching to 100%. Furthermore, this sensory array can discriminate ppb-level TNT and ppt-level RDX from structurally similar and high-concentration interfering aromatic gases in less than 12 s. Through comparison with the previously reported chemiresistor or Schottky sensors for explosive detection, the present transition-metal-doping method resulting ZnO sensor stands out and undoubtedly challenges the best.

Template Epitaxial Growth of Thermoelectric Bi/BiSb Superlattice Nanowires by Charge-Controlled Pulse Electrodeposition

Bi/BiSb superlattice nanowires SLNWs with a controllable and very small bilayer thickness and a sharp segment interface were grown by adopting a charge-controlled pulse electrodeposition. The deposition parameters were optimized to ensure an epitaxial growth of the SLNWs with a preferential orientation. The segment length and bilayer thickness of the SLNWs can be controlled simply by changing the modulating time, and the consistency of the segment length can be well maintained by our approach. The Bravais law in the electrodeposited nanowires is verified by the SLNW structure. The current‐voltage measurement shows that the SLNWs have good electrical conductance, particularly those with a smaller bilayer thickness. The Bi/BiSb SLNWs might have excellent thermoelectric performances.

Surface Superoxide Complex Defects-Boosted Ultrasensitive ppb-Level NO2 Gas Sensors

Sn(4+) -O2 (-•) centers are intentionally created in SnO2 nanoflowers by a thermodynamically instable synthetic process. The resulting SnO2 nanoflower-based sensor is confirmed to be the most sensitive ppb-level chemiresistor NO2 sensor to date. The Sn(4+) -O2 (-•) centers with strong gas-adsorbing and high eletron-donating capability towards NO2 molecules decisively determine the sensor sensitivity.

Initial Growth of Single-Crystalline Nanowires:From 3D Nucleation to 2D Growth

The initial growth stage of the single-crystalline Sb and Co nanowires with preferential orientation was studied, which were synthesized in porous anodic alumina membranes by the pulsed electrodeposition technique. It was revealed that the initial growth of the nanowires is a three-dimensional nucleation process, and then gradually transforms to two-dimensional growth via progressive nucleation mechanism, which resulting in a structure transition from polycrystalline to single crystalline. The competition among the nuclei inside the nanoscaled-confined channel and the growth kinetics is responsible for the structure transition of the initial grown nanowires.

Artificial Olfactory System for Trace Identification of Explosive Vapors Realized by Optoelectronic Schottky Sensing

A rapid, ultrasensitive artificial olfactory system based on an individual optoelectronic Schottky junction is demonstrated for the discriminative detection of explosive vapors, including military explosives and improvised explosives.

Simple metal/SiO2/Si planar photodetector utilizing leakage current flows through a SiO2 layer

Silicon wafers covered with a thermally grown high-quality SiO2 layer were often used as the substrate to house different nanostructures to fabricate photodetection devices. No reports have ever challenged directly fabricating photodetectors utilizing leakage current through non-high-quality SiO2 films and the intrinsic light absorption properties of Si. Herein, we show that metal/SiO2/Si planar photodetectors could be easily fabricated by simply depositing two metal electrodes (such as, Au, Ag and Al) on top of SiO2/Si wafer in which the SiO2 layer is of non-high quality. The responsivity, stability, photoresponse characteristics and light intensity sensitivity are systematically evaluated. Our results clearly show that the present conveniently and cost-effectively fabricated metal/SiO2/Si planar photodetectors are of great advantage as compared to many of the nanostructure-based photodetectors constructed on SiO2/Si substrate.

Thermal Contraction of Electrodeposited Bi/BiSb Superlattice Nanowires

The lattice parameter of Bi/BiSb superlattice nanowire (SLNW) has been measured using in situ high-temperature X-ray diffraction method. The single crystalline Bi/BiSb SLNW arrays with different bilayer thicknesses have been fabricated within the porous anodic alumina membranes (AAMs) by a charge-controlled pulse electrodeposition. Different temperature dependences of the lattice parameter and thermal expansion coefficient were found for the SLNWs. It was found that the thermal expansion coefficient of the SLNWs with a large bilayer thickness has weak temperature dependence, and the interface stress and defect are the main factors responsible for the thermal contraction of the SLNWs.