Yewu Wang

Catalytic growth and photoluminescence properties of semiconductor single-crystal ZnS nanowires

Abstract Semiconductor single-crystal ZnS nanowires have been successfully synthesized in bulk quantities by a new, simple and low cost process based on thermal evaporation of ZnS powders onto a silicon substrate with the presence of Au catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) observations show that the ZnS nanowires have diameters about 30–60 nm and lengths up to several tens micrometers. The growth of ZnS nanowires is controlled by the conventional vapor–liquid–solid (VLS) mechanism. And the photoluminescence (PL) properties of these synthesized single-crystal ZnS nanowires have been presented in this Letter.

Flexible CuO nanosheets/reduced-graphene oxide composite paper: binder-free anode for high-performance lithium-ion batteries.

Flexible free-standing CuO nanosheets (NSs)/reduced graphene oxide (r-GO) hybrid lamellar paper was fabricated through vacuum filtration and hydrothermal reduction processes. A unique three-dimensional nanoporous network was achieved with CuO NSs homogeneously embedded within the r-GO layers. This hybrid lamellar composite paper was examined as a binder-free anode for lithium ion batteries, and demonstrated excellent cyclic retention with the specific capacity of 736.8 mA h g(-1) after 50 cycles. This is much higher than 219.1 mA h g(-1) of the pristine CuO NSs and 60.2 mA h g(-1) of r-GO film at the same current density of 67 mA g(-1). The high capacitance and excellent cycling performance were generated from the integrated nanoporous structure compose of CuO NSs spaced r-GO layers, which offered an efficient electrically conducting channels, favored electrolyte penetration, and buffered to the volume variations during the lithiation and delithiation process. These outstanding electrochemical capabilities of CuO NSs/r-GO paper holds great promise for flexible binder-free anode for lithium ion batteries.

Electrochemical synthesis of copper nanowires

Large-scale copper nanowires have been fabricated by potentiostatic electrochemical deposition (ECD) of copper sulphate solution within the nanochannels of porous anodic alumina templates. Scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction and x-ray diffraction techniques were used to characterize the copper nanowires obtained. It is found that the individual copper nanowires are dense and continuous, with uniform diameters (60 nm) along the entire lengths of the wires (30 µm). The single-crystal and polycrystal copper nanowires can be prepared by choosing suitable applied potentials in the copper ECD processes. Moreover, the formation of copper oxides in nanochannels is also discussed in detail. The investigation results reveal that a lower overpotential is necessary to fabricate copper nanowires with fine crystalline structures by the potentiostatic ECD technique.

Behind the change of the photoluminescence property of metal-coated ZnO nanowire arrays

The effect of metal coating on the photoluminescence (PL) properties of ZnO nanowire arrays has been investigated in detail in this letter. The Zn coating induces remarkable enhancement of the ultraviolet and green emissions of the nanowires, while the deposition of Ag leads to notable decrement of them. A model considering the type of contacts formed between metals and ZnO is proposed to interpret the change of the PL spectra. Also, this model is strongly supported by the PL variation of the nanowires after coating with other kinds of metals.

CuO nanosheets/rGO hybrid lamellar films with enhanced capacitance

CuO nanosheets (NSs)/reduced graphene oxide (rGO) hybrid lamellar films were prepared by vacuum filtration of CuO NSs/GO composite dispersions, followed by hydrothermal reduction. The CuO NSs/GO composite dispersions were assembled electrostatically by mixing a negatively charged GO sheets aqueous solution with a positively charged CuO NSs aqueous dispersion at room temperature. The prepared CuO NSs/rGO hybrid lamellar films exhibited a specific capacitance of 163.7 F g(-1), which is much higher than the 69.7 F g(-1) of CuO NSs and 66.0 F g(-1) of rGO. The effective specific capacitance was 82.5 F g(-1) after 1000 cycles, which was more than two times the 32.7 F g(-1) of CuO NSs electrodes. The synergistic redox activity of the CuO NSs, in combination with the high electronic conductivity of the rGO and the unique CuO NSs spaced sandwich-like porous structures, dominated the excellent capacitance of CuO NSs/rGO hybrid lamellar films. The sandwiched, lamellar, porous structures not only provide plenty of paths for electrolyte-ion access to the CuO NSs but also expose the rGO sheets to the electrolyte as much as possible. This process provides a potential way to synthesise metal oxide/GO composite electrodes for capacitors.

Quantum size effects in the volume plasmon excitation of bismuth nanoparticles investigated by electron energy loss spectroscopy

Quantum size effects in volume plasmon excitation of bismuth nanoparticles with diameters ranging from 5to500nm have been studied by electron energy loss spectroscopy. The Bi nanoparticles were prepared by reducing Bi3+ with sodium borohydride in the presence of poly(vinylpyrroldone). The volume plasmon energy and its peak width increase with decreasing nanoparticle diameter, due to the quantum size effect. For the particles with diameter less than 40nm, the increase of the volume plasmon energy is proportional to the inverse square of the nanoparticle diameter, confirming the semimetal to semiconductor transition in Bi nanoparticles.

Atomically Smooth p-Doped Silicon Nanowires Catalyzed by Aluminum at Low Temperature

Silicon nanowires (SiNWs) are powerful nanotechnological building blocks. To date, a variety of metals have been used to synthesize high-density epitaxial SiNWs through metal-catalyzed vapor phase epitaxy. Understanding the impact of the catalyst on the intrinsic properties of SiNWs is critical for precise manipulation of the emerging SiNW-based devices. Here we demonstrate that SiNWs synthesized at low-temperature by ultrahigh vacuum chemical vapor deposition using Al as a catalyst present distinct morphological properties. In particular, these nanowires are atomically smooth in contrast to rough {112}-type sidewalls characteristic of the intensively investigated Au-catalyzed SiNWs. We show that the stabilizing effect of Al plays the key role in the observed nanowire surface morphology. In fact, unlike Au which induces (111) and (113) facets on the nanowire sidewall surface, Al revokes the reconstruction along the [112] direction leading to equivalent adjacent step edges and flat surfaces. Our finding sets the lower limit of the Al surface density on the nanowire sidewalls at ∼2 atom/nm(2). Additionally, despite using temperatures of ca. 110-170 K below the eutectic point, we found that the incorporation of Al into the growing nanowires is sufficient to induce an effective p-type doping of SiNWs. These results demonstrate that the catalyst plays a crucial role is shaping the structural and electrical properties of SiNWs.

Nanodevices Based on Silicon Nanowires

Silicon nanowires (SiNWs) have been demonstrated as one of the promising building blocks for future nanodevices such as field effect transistors, solar cells, sensors and lithium battery; much progress has been made in this field during last decades. In this review paper, the synthesis and physical properties of SiNWs are introduced briefly. Significant advances of SiNWs-related nanodevices reported in recent literature and registered patents are reviewed. The latest development and prospects of SiNWs-related nanodevices are also discussed.

Binder-free three-dimensional porous Mn3O4 nanorods/reduced graphene oxide paper-like electrodes for electrochemical energy storage

This research demonstrates novel flexible and binder-free Mn3O4 nanorods (NRs)/reduced graphene oxide (rGO) hybrid papers with unique three-dimensional nanoporous networks were fabricated by filtration and a hydrothermal reduction process, where rGO acts not only as a flexible substrate but also as an electron conductor. The three-dimensional nanoporous networks were generated by the homogeneous intercalation of Mn3O4 NRs into the lamellar rGO layers, which exhibited excellent mechanical stability and provided electrically conducting channels to promote electrolyte penetration when used as electrodes for Li-ion batteries (LIBs) and supercapacitors. The prepared Mn3O4 NRs/rGO hybrid lamellar papers demonstrated excellent cyclic retention with the specific capacity of 669.6 mA h g−1 after 100 cycles in LIBs, which is 9 times higher than 65.8 mA h g−1 of γ-MnOOH/Mn3O4 mixed phase nanorods. Additionally, the three-dimensional porous hybrid Mn3O4 NRs/rGO papers also exhibit superior specific capacitance of 204.2 F g−1, two times higher than that of γ-MnOOH/Mn3O4 mixed phase nanorods, and only decreases by 10% after 2000 cycles in the supercapacitor. These Mn3O4 NRs/rGO papers hold promising potential for flexible electrochemical energy storage devices.

Anodic electrodeposition of a porous nickel oxide–hydroxide film on passivated nickel foam for supercapacitors

The response current of Ni foam in alkaline solutions can be reduced significantly by high-temperature annealing, making it more suitable for current collectors, and a porous NiO(OH) film deposited on the passivated 3D Ni foam by anodic electrodeposition shows an ultrahigh specific capacitance of 2302 F g−1 at 1 A g−1.