Xiong-Ying Ye

Controlled assembly of zinc oxide nanowires using dielectrophoresis

A structure similar to a field effect transistor with two isolated top electrodes comprising the source and drain and a lower substrate electrode as the gate was used for the dielectrophoresis-based assembly of zinc oxide nanowires. The results reveal that the assembly of nanowires is significantly affected by the gap distance between the two top electrodes as well as the magnitude and frequency of the applied electric field. Gate assisted assemblies using direct current and alternating current dielectrophoresis were also investigated and determined to improve the assembly effect of nanowires.

Synergistic effect of Cu2+-coordinated carbon nanotube/graphene network on the electrical and mechanical properties of polymer nanocomposites

A novel hybrid nanofiller system, in which oxidized multi-walled carbon nanotubes (MWCNTs) and chemically modified graphene (CMG) are coordinated by copper ions, is fabricated. The CMG sheets are efficiently isolated and bridged by MWCNTs through copper ion coordination to form a uniform network, and the Cu2+-coordinated MWCNT/CMG network can be easily introduced to a variety of polymer matrices by solution mixing. For example, the Cu2+-coordinated MWCNT/CMG network is successfully incorporated in poly(styrene-co-butadiene-co-styrene) (SBS), one of the most widely used synthetic rubbers. The molecular-level dispersion of the nanofillers in the SBS matrix facilitates efficient electron and load transfer. The Cu2+-coordinated MWCNT/CMG network demonstrates a synergistic effect that cannot be achieved by simple physical mixing of the two nanofillers. The obtained SBS nanocomposites have much better electrical and mechanical properties than those filled with MWCNTs, CMG or a non-coordinated hybrid nanofiller system at the same loading. This fabrication method may open the door to a new class of high-performance polymer-matrix composites.

Constructing Novel Si@SnO2 Core–Shell Heterostructures by Facile Self-Assembly of SnO2 Nanowires on Silicon Hollow Nanospheres for Large, Reversible Lithium Storage

Developing an industrially viable silicon anode, featured by the highest theoretical capacity (4200 mA h g(-1)) among common electrode materials, is still a huge challenge because of its large volume expansion during repeated lithiation-delithiation as well as low intrinsic conductivity. Here, we expect to address these inherent deficiencies simultaneously with an interesting hybridization design. A facile self-assembly approach is proposed to decorate silicon hollow nanospheres with SnO2 nanowires. The two building blocks, hand in hand, play a wonderful duet by bridging their appealing functionalities in a complementary way: (1) The silicon hollow nanospheres, in addition to the major role as a superior capacity contributor, also act as a host material (core) to partially accommodate the volume expansion, thus alleviating the capacity fading by providing abundant hollow interiors, void spaces, and surface areas. (2) The SnO2 nanowires serve as a conductive coating (shell) to enable efficient electron transport due to a relatively high conductivity, thereby improving the cyclability of silicon. Compared to other conductive dopants, the SnO2 nanowires with a high theoretical capacity (790 mA h g(-1)) can contribute outstanding electrochemical reaction kinetics, further adding value to the ultimate electrochemical performances. The resulting novel Si@SnO2 core-shell heterostructures exhibit remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1869 mA h g(-1)@500 mA g(-1) after 100 charging-discharging cycles.

Multi-dimensionally ordered, multi-functionally integrated r-GO@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures for ultrafast lithium storage

TiO2(B) is an attractive new anode candidate for lithium-ion batteries (LIBs) due to its unique and highly desirable properties, including high structural integrity, long cycle life, and low cost. However, despite these merits, its inherent slow lithium and electron transport kinetics hinder its practical application to LIBs. Here, we propose a novel, simple route towards multi-dimensionally ordered, multi-functionally integrated reduced graphene oxide (r-GO)@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures in which r-GO nanosheets, TiO2(B) nanosheets, and Mn3O4 nanoparticles are hierarchically organized to achieve remarkable synergistic interactions. This hybridization design is fundamentally bilateral in nature, aiming to overcome the conductivity and capacity deficiencies of TiO2(B) simultaneously. The resulting r-GO@TiO2(B)@Mn3O4 yolk–membrane–shell superstructures have great potential as advanced anode materials for ultrafast lithium storage, delivering a strikingly high reversible capacity of 662 mA·h·g−1 at 500 mA·g−1 after 500 charge–discharge cycles.

h-BN Nanosheets as 2D Substrates to Load 0D Fe3O4 Nanoparticles: A Hybrid Anode Material for Lithium-Ion Batteries.

h-BN, as an isoelectronic analogue of graphene, has improved thermal mechanical properties. Moreover, the liquid-phase production of h-BN is greener since harmful oxidants/reductants are unnecessary. Here we report a novel hybrid architecture by employing h-BN nanosheets as 2D substrates to load 0D Fe3O4 nanoparticles, followed by phenol/formol carbonization to form a carbon coating. The resulting carbon-encapsulated h-BN@Fe3O4 hybrid architecture exhibits synergistic interactions: 1) The h-BN nanosheets act as flexible 2D substrates to accommodate the volume change of the Fe3O4 nanoparticles; 2) The Fe3O4 nanoparticles serve as active materials to contribute to a high specific capacity; and 3) The carbon coating not only protects the hybrid architecture from deformation but also keeps the whole electrode highly conductive. The synergistic interactions translate into significantly enhanced electrochemical performances, laying a basis for the development of superior hybrid anode materials.

Facile and Green Production of Impurity-Free Aqueous Solutions of WS2 Nanosheets by Direct Exfoliation in Water.

To obtain 2D materials with large quantity, low cost, and little pollution, liquid-phase exfoliation of their bulk form in water is a particularly fascinating concept. However, the current strategies for water-borne exfoliation exclusively employ stabilizers, such as surfactants, polymers, or inorganic salts, to minimize the extremely high surface energy of these nanosheets and stabilize them by steric repulsion. It is worth noting, however, that the remaining impurities inevitably bring about adverse effects to the ultimate performances of 2D materials. Here, a facile and green route to large-scale production of impurity-free aqueous solutions of WS2 nanosheets is reported by direct exfoliation in water. Crucial parameters such as initial concentration, sonication time, centrifugation speed, and centrifugation time are systematically evaluated to screen out an optimized condition for scaling up. Statistics based on morphological characterization prove that substantial fraction (66%) of the obtained WS2 nanosheets are one to five layers. X-ray diffraction and Raman characterizations reveal a high quality with few, if any, structural distortions. The water-borne exfoliation route opens up new opportunities for easy, clean processing of WS2 -based film devices that may shine in the fields of, e.g., energy storage and functional nanocomposites owing to their excellent electrochemical, mechanical, and thermal properties.

Single semiconducting zinc oxide nanowire based device for thermal and airflow sensing

This paper reports a technology for fabricating a novel nanostructure-based device comprised of a single semiconducting zinc oxide (ZnO) nanowire suspended between two micro Au electrodes for sensor applications. The electric characteristics of the device before and after processed by Pt deposition using focused ion beam microscope were comparatively studied. Furthermore, the potential applications by using the device for thermal and airflow sensing were also investigated. The temperature coefficient of resistance of the ZnO nanowire was estimated to be about -2.61 times 10-3degC-1. The airflow sensitivity of the device is about 3 kOmega/m/s. Compared with conventional sensors, this device takes advantages of high sensitivity and ultra-low power.

Current-voltage and Optoelectronic Properties of Semiconducting ZnO Nanobelts

We report on electrophoretic alignment of ZnO nanobelt bunches and their electrical and optical properties. The nanobelts were trapped onto a pair of electrodes by using alternating electrical current at frequency between 5 ~ 50 MHz and peak-to-peak amplitude from 2 to 20 V. Their electrical transport properties associated with the photoelectricity were studied at room temperature in the air ambient by using a xenon arc lamp source. Three typical IV characteristics were observed: asymmetry, symmetry and infinite impedance. The photoconductivity measurements show that the photocurrent through ZnO nanobelts increases as about 1.6 power of light intensity. The electron concentration Delta n is estimated to be 3.3times107 cm-1 at a bias voltage of -3V. Photocurrent decay was also studied through the experiment of photoresponse to illumination, and the decay time was estimated to be about 3 s. Collectively, ZnO nanobelts are demonstrated to be a remarkable optoelectronic material that holds wide applications for nanoscale photonic devices.

The analysis of microtoroid cavity coupling system based on fullwave

The parameters of coupling system composed by microtoroid cavity and fiber-taper such as coupling distance, the size of the microtoroid cavities and the wavelength of the input light directly affect its coupling property. It has been fabricated in our laboratory and Rsoft Fullwave based on FDTD is used to simulate different size of micro-cavities, coupling distance from 0.1µm to 0.5µm, and the wavelength of input light around 0.85µm, 1.31µm and 1.55µm corresponding to individual optical-windows of optical fiber. It shows that the relationship among parameters mentioned can get an analysis through evanescent wave theory.

Field Emission Characteristics of Carbon Nanotube Films Fabricated by Different Methods

In order to improve the performance of field emitters nowadays, carbon nanotubes are used instead of conventional materials such as silicon and metals. In this paper, field emission characteristics of three different multi-wall carbon nanotube films have been compared, which are fabricated by different methods, including direct growth, evaporation coating and flow assembly. The field emission current-voltage property of each film has been characterized experimentally, and the electric field enhancement factor has been analyzed using Fowler-Nordheim theory. Moreover, emission stability of each film has been measured too. It can be concluded that the direct-grown vertical multi-wall carbon nanotube array has turn-on field of 0.603 V/mum and current density fluctuation less than 5%, which is much lower than the other films by post-treatment processes.