Zhenyu Zhang

Highly aligned SnO2 nanorods on graphene sheets for gas sensors

Highly aligned SnO2 nanorods on graphene 3-D array structures were synthesized by a straightforward nanocrystal-seeds-directing hydrothermal method. The diameter and density of the nanorods grown on the graphene can be easily tuned as required by varying the seeding concentration and temperature. The array structures were used as gas sensors and exhibit improved sensing performances to a series of gases in comparison to that of SnO2 nanorod flowers. For nanorod arrays of optimal diameter and distribution, these structures were proved to exert an enhanced sensitivity to reductive gases (especially H2S), which was twice as high as that obtained using SnO2 nanorod flowers. The improved sensing properties are attributed to the synergism of the large surface area of SnO2 nanorod arrays and the superior electronic characteristics of graphene.

A General Approach for the Growth of Metal Oxide Nanorod Arrays on Graphene Sheets and Their Applications

In the fabrication of flexible devices, highly ordered nanoscale texturing, such as semiconductor metal oxide nanorod arrays on flexible substrates, is critical for optimal performance. Use of transparent conducting films, metallic films, and polymer substrates is limited by mechanical brittleness, chemical and thermal instability, or low electrical conductivity, low melting point, and so on. A simple and general nanocrystal-seed-directed hydrothermal route has now been developed for large-scale growth of nanorod arrays of various semiconductor metal oxides (MO), including TiO(2), ZnO, MnO(2), CuO, and ZrO(2) on both sides of flexible graphene (G) sheets to form sandwichlike MO/G/MO heterostructures. The TiO(2)/G/TiO(2) heterostructures have much higher photocatalytic activity than TiO(2) nanorods, with a photocatalytic degradation rate of methylene blue that is four times faster than that of the TiO(2) nanorods, and are thus promising candidates for photocatalytic decontamination.

Phase-controlled synthesis and gas-sensing properties of zinc stannate (ZnSnO3 and Zn2SnO4) faceted solid and hollow microcrystals

Well-defined faceted zinc stannate, including cubic ZnSnO3 and octahedral Zn2SnO4, microcrystals were synthesized in a large scale by a one-step chemical solution route, in which the phase control was simply accomplished by only changing stannic precursors. These faceted cubic ZnSnO3 and octahedral Zn2SnO4 microcrystals are easily converted to faceted hollow structures with a shape preserved through an acid etching process. Possible growth and etching mechanisms of these faceted microcrystals have been proposed. The hollow structures of zinc stannate were exploited as gas sensors and exhibit improved sensing performances to a series of gases (especially with regard to H2S and C2H5OH); moreover, the sensitivity and recovery time of Zn2SnO4 hollow octahedral structures to H2S and C2H5OH are both higher than those of the cubic structures, which may find potential industrial applications in detecting gases.

A Zn2GeO4-ethylenediamine hybrid nanoribbon membrane as a recyclable adsorbent for the highly efficient removal of heavy metals from contaminated water.

Zn(2)GeO(4)-ethylenediamine (ZGO-EDA) hybrid nanoribbons have been synthesized on a large-scale and directly assembled to membranes, which exhibit an excellent recyclability, high selectivity, and good thermal stability for highly efficient removal of heavy metal ions, i.e., Pb(2+), Cd(2+), Co(2+), and Cu(2+), from contaminated water.

Morphology-selective synthesis and wettability properties of well-aligned Cu2-xSe nanostructures on a copper substrate

The morphology-selective synthesis of well-aligned Cu2-xSe nanostructures including nanosheets, nanoribbons, and heterostructures on copper substrate has been achieved by a simple hydrothermal route; the micropatterned assembly of Cu2-xSe nanostructures has been realized using a copper grid to direct the growth on prescribed arbitrary patterns with unprecedented control and selectivity. The control experimental conditions, such as hydrothermal temperature and time, and concentration of NaOH have been found to be important parameters for the growth process of the Cu2-xSe nanostructures. So-called “coordination assembly” has shown to be dominant in the formation of the Cu2-xSe nanostructures, consisting of an initial nucleation and subsequent vertical growth on the copper substrate. The wettability properties of the Cu2-xSe nanostructures have been investigated, and the water contact angle from these nanostructured materials has been measured to be up to 160°, showing a superhydrophobicity. These results might provide a facile route for the preparation of novel micropatterned and high assemblies of nanostructures on other metal substrates (e.g.Al, Zn, Mg, etc.), for which a number of promising applications in microelectronic fields can be envisioned.

Oriented Free-Standing Ammonium Vanadium Oxide Nanobelt Membranes: Highly Selective Absorbent Materials

Highly selective, absorbent, free-standing, paper-like membranes made of ammonium vanadium oxide (NH(4)V(4)O(14)) nanobelts have been engineered by taking advantage of the nanoscaled self-assembly of architectures that display a mesh structure with an average periodic pore size of about 5 to 10u2005nm. The NH(4)V(4)O(14) nanobelts are synthesized by using a simple hydrothermal process, and exhibit the same orientation and assemble into bundles, each about 40 to 80u2005nm in width, 3 to 5u2005nm in thickness, and up to several millimeters in length. Importantly, the as-obtained NH(4)V(4)O(14) nanobelt membranes can highly selectively absorb a variety of organic solvents, covering both polar and non-polar solvents, for example, the absorbent capacity of glycol is 28 times as high as the initial weight of the membrane, and it can even separate organic solvents with similar polarities and absorb solid contaminants in organic solvents. These highly selective, absorbent membrane materials can be an ideal candidate for the separation and removal of pollution in industrial and environmental applications.

SnO2 nanoribbons: excellent field-emitters

Nanoribbon structures have the feature of sharp edges, providing the marked geometrical field enhancement for field emitters even in a randomly arranged thin film structure. In this work, the field emission of SnO2 nanoribbons with thin walls (10–30 nm) prepared on a large scale via a rapid oxidation reaction is investigated. It is found that macroscopically, thin films made of SnO2 nanoribbons have an extremely low electron threshold field as low as 1.23 V μm−1. The SnO2 nanoribbon field emitter also exhibits excellent emission stability, with a degradation lower than 2.7% and a huge field enhancement factor as high as 2680. Furthermore, the emission current decrease slightly, while the stability remains excellent even for a poor vacuum of 10−4 Pa. These field emission properties of the present SnO2 nanoribbons surpass any other reported SnO2 nanostructures. This work opens the avenues for SnO2 nanoribbon structures as promising thin film field emitters.

Recent Research on One-Dimensional Silicon-Based Semiconductor Nanomaterials: Synthesis, Structures, Properties and Applications

The field of silicon nanowires (SiNWs) and silicon-based 1D nanostructured heterostructures represent one of the most important research subjects within the nanomaterials family. A series of synthesis approaches of SiNWs and silicon-based 1D nanostructured heterostructures have been developed, and have garnered the greatest attention in the past decades for a variety of applications. This article provides an overview on recent research on the synthesis, properties and applications of SiNWs, silicon nanotubes (SiNTs) and complex silicon-based 1D nanostructures.

Melting of Metallic Electrodes and Their Flowing Through a Carbon Nanotube Channel within a Device

Evidence is presented of a new cause of Joule heating within a simple electronic device involving a multiwalled carbon nanotube (CNT) mounted on two metal electrodes forming an electrical circuit. This time-resolved, high-resolution in situ observation of metal electrode material melting and its flow driven by the thermomigration and electromigration forces through the CNT channel sheds an additional light on the effects affecting the real electrical performance of the CNT-based devices.

A Mobile Sn Nanowire Inside a β-Ga2O3 Tube: A Practical Nanoscale Electrically/Thermally Driven Switch

Nanoelectromechanical system switches are seen as key devices for fast switching in communication networks since they can be switched between transmitting and receiving states with an electrostatic command. Herein, the fabrication of practical, nanoscale electrically/thermally driven switches is reported based on a mobile Sn nanowire inside a β-Ga2 O3 tube. The melting point of Sn inside the Ga2 O3 tube is found to be as low as 58 °C-far below the value of bulk Sn (231.89 °C)-and its crystal phase (β-Sn) remains unchanged even at temperatures as low as -170 °C. Thus a miniaturization of the unique wide-temperature-range thermometer based on the linear thermal expansion of liquid Sn fillings in the Ga2 O3 tube is realized. In addition, the electrical properties of the Sn-nanowire-filled β-Ga2 O3 tubes are carefully determined: importantly, the resistance demonstrates a sudden drop (rise) when two Sn nanowires contact (separate), due to the thermally driven motion of the liquid Sn fillings inside the tube. Thus this structure can be switched between its on and off states by controlling the motion, merging or splitting, of the Sn nanowires inside the tube, either electrically, by applying a current, or thermally, at a predetermined temperature.