Core-shell Nanowire Arrays Research Articles

(Invited) Oxygen Evolution At Vertically Aligned Core-Shell Ion-Iron Oxide Nanowire Arrays

not Available.

Improved performance of three-dimensional Ni–TiO2 core–shell nanowire photoanodes in dye-sensitized solar cells

Abstract

Spatial Mapping of Efficiency of GaN/InGaN Nanowire Array Solar Cells Using Scanning Photocurrent Microscopy

GaN-InGaN core-shell nanowire array devices are characterized by spectrally resolved scanning photocurrent microscopy (SPCM). The spatially resolved external quantum efficiency is correlated with structure and composition inferred from atomic force microscope (AFM) topography, scanning transmission electron microscope (STEM) imaging, Raman microspectroscopy, and scanning photocurrent microscopy (SPCM) maps of the effective absorption edge. The experimental analyses are coupled with finite difference time domain simulations to provide mechanistic understanding of spatial variations in carrier generation and collection, which is essential to the development of heterogeneous novel architecture solar cell devices.

The fabrication of large-scale sub-10-nm core-shell silicon nanowire arrays.

A combination of template-assisted metal catalytic etching and self-limiting oxidation has been successfully implemented to yield core-shell silicon nanowire arrays with inner diameter down to sub-10 nm. The diameter of the polystyrene spheres after reactive ion etching and the thickness of the deposited Ag film are both crucial for the removal of the polystyrene spheres. The mean diameter of the reactive ion-etched spheres, the holes on the Ag film, and the nanowires after metal catalytic etching exhibit an increasing trend during the synthesis process. Two-step dry oxidation and post-chemical etching were employed to reduce the diameter of the silicon nanowires to approximately 50 nm. A self-limiting effect was induced by further oxidation at lower temperatures (750°C ~ 850°C), and core-shell silicon nanowire arrays with controllable diameter were obtained.

ZnO/ZnO Core–Shell Nanowire Array Electrodes: Blocking of Recombination and Impressive Enhancement of Photovoltage in Dye-Sensitized Solar Cells

A multistep wet-chemistry route was developed, by combining electrodeposition, colloidal synthesis and spin coating, to obtain arrays of ZnO nanowires (NWs) coated by a ZnO nanocrystalline layer (i.e., ZnO/ZnO core–shell NWs). They were integrated as anodes in dye-sensitized solar cells. With the use of an iodide-based electrolyte, photovoltages as impressive as 870 mV were obtained with an enhancement of more than 250 mV with respect to devices based on bare NWs. A comprehensive device characterization study by means of impedance spectroscopy (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) reveals a significant blockage of recombination upon NW shell deposition. To study the generality of this multistep method, electrodes of core–shell nanostructures based on commercial ZnO nanoparticles were also prepared. A decrease of recombination rate is also detected, although it is much more moderate than the observed for nanowire-based electrodes. The present ZnO synthetic approach allows obtaining nanowire-based dye-sensitized solar cells which exhibit longer electron lifetimes than nanocrystalline analogues. This finding implies a significant improvement of photovoltage with respect to the state of the art ZnO-based dye-sensitized solar cells.

Physisorption-induced electron scattering on the surface of carbon-metal core-shell nanowire arrays for hydrogen sensing

Palladium is sputtered on multi-walled carbon nanotube forests to form carbon-metal core-shell nanowire arrays. These hybrid nanostructures exhibited resistive responses when exposed to hydrogen with an excellent baseline recovery at room temperature. The magnitude of the response is shown to be tuneable by an applied voltage. Unlike the charge-transfer mechanism commonly attributed to Pd nanoparticle-decorated carbon nanotubes, this demonstrates that the hydrogen response mechanism of the multi-walled carbon nanotube-Pd core-shell nanostructure is due to the increase in electron scattering induced by physisorption of hydrogen. These hybrid core-shell nanostructures are promising for gas detection in hydrogen storage applications.

ZnO/TiO2 core–shell nanowire arrays for enhanced dye-sensitized solar cell efficiency

We present a new method of synthesizing ZnO/TiO2 core–shell nanowire (NW) arrays for the fabrication of dye-sensitized solar cells (DSSCs). Vertically aligned ZnO NW arrays were obtained on Si substrates, and modified by a TiO2 shell in order to solve the recombination problems via a cost-effective spin-coating method. The structure of the ZnO/TiO2 composite NW arrays was characterized. The experimental results indicate that the TiO2 shell enhances the performance of the DSSCs, through improving the stability of the ZnO NWs and decreasing the recombination of photogenerated electrons on the NW surface. The highest overall conversion efficiency of the cell reaches about 3.0 %.

High Performance Core-Shell Nanowire Array Devices Prepared by Atomic Layer Deposition

Atomic layer deposition (ALD) is a promising nanomaterial synthesis technique due to its excellent confomality over complicated nanostructure. We fabricated ALD semiconducting oxide/semiconductor core-shell nanowire array and characterized the device performances as a photodiode. Si nanowires array with about 100~300 nm diameter were prepared using electroless etching technique. Nitrogen doped ALD ZnO was carried out using diethylzinc (DEZ) and diluted NH4OH various growth temperature. We measured responsivity and external quantum efficiency of the fabricated device as a function of wavelength of incident light and compared with thin film based photodiode. For NW array device, the photocurrent density and responsivity were significantly enhanced compared to thin film based device. Also, by combining self-assembly process, well ordered core-shell ZnO/Si nanowire arrays were prepared. The device performance made of ordered core-shell NW arrays was significantly enhanced. In addition, ZnO homojunction NW photodiode as well as ALD TiO2 outer shell NW photodiodes were fabricated and their device characterizations were compared to the planar type device.

Optical and electrical simulations of two-junction III-V nanowires on Si solar cell

A coupled optoelectronic simulation was used to theoretically assess the performance of core-shell GaInP nanowires array (NWA)/Si thin-film two-junction solar cell. Outstanding light harvesting rooted from the strong light trapping and the formation of Fabry-Pérot optical cavity in the NWA enables the cell to produce high photocurrent. From the detailed balance calculation, above 32% of efficiency could be obtained at the current matching geometries. Coupled optoelectronic simulation shows that current matching can be easily achieved even under relatively high recombination rate. A promising efficiency of 27.1% is obtained for the proposed cell with appropriate nanowires surface passivation.

Self-powered spectrum-selective photodetectors fabricated from n-ZnO/p-NiO core–shell nanowire arrays

Self-powered, highly spectrum-selective photodetectors have been fabricated from n-ZnO/p-NiO core–shell nanowire arrays. In the structure, the outer-layer of the p-NiO acts as a “filter” which can filter out the photons with short wavelength. In this way, highly spectrum-selective photodetectors that only respond to a narrow spectrum range have been obtained.

SnO2@Si core–shell nanowire arrays on carbon cloth as a flexible anode for Li ion batteries

In this communication, 3D hierarchical SnO2@Si nanowire arrays on carbon cloth are synthesized by a combination of the chemical vapour deposition (CVD) method for SnO2 nanowires and a subsequent Si thin film coating with a plasma-enhanced CVD (PE-CVD) route. The as-prepared SnO2@Si nanowire arrays are further tested as a flexible and binder-free anode for Li ion batteries. A high areal capacity (e.g. 2.13 mA h cm−2 at a current density of 0.38 mA cm−2) and good cycling performance are demonstrated for the core–shell SnO2@Si nanowire/carbon cloth electrode, which could be attributed to the 3D structural design and a synergistic effect between Si and SnO2.

Diffusion-controlled evolution of core–shell nanowire arrays into integrated hybrid nanotube arrays for Li-ion batteries

Controlled integration of multiple semiconducting oxides into each single unit of ordered nanotube arrays is highly desired in scientific research for the realization of more attractive applications. We herein report a diffusion-controlled solid-solid route to evolve simplex Co(CO3)0.5(OH)0.11H2O@TiO2 core-shell nanowire arrays (NWs) into CoO-CoTiO3 integrated hybrid nanotube arrays (NTs) with preserved morphology. During the evolution procedure, the decomposition of Co(CO3)0.5(OH)0.11H2O NWs into chains of CoCO3 nanoparticles initiates the diffusion process and promotes the interfacial solid-solid diffusion reaction even at a low temperature of 450 °C. The resulting CoO-CoTiO3 NTs possess well-defined sealed tubular geometries and a special "inner-outer" hybrid nature, which is suitable for application in Li-ion batteries (LIBs). As a proof-of-concept demonstration of the functions of such hybrid NTs in LIBs, CoO-CoTiO3 NTs are directly tested as LIB anodes, exhibiting both a high capacity (~600 mA h g(-1) still remaining after 250 continuous cycles) and a much better cycling performance (no capacity fading within 250 total cycles) than CoO NWs. Our work presents not only a diffusion route for the formation of integrated hybrid NTs but also a new concept that can be employed as a general strategy to fabricate other oxide-based hybrid NTs for energy storage devices.

Hierarchical NiCo2O4@MnO2core–shell heterostructured nanowire arrays on Ni foam as high-performance supercapacitor electrodes

An advanced integrated electrode for high-performance supercapacitors has been designed by growing hierarchical NiCo(2)O(4)@MnO(2) core-shell heterostructured nanowire arrays on nickel foam. Such unique array nanoarchitectures exhibit remarkable electrochemical performance with high capacitance and desirable cycle life at high rates.

Synthesis of NixSiy–SiGe core–shell nanowire arrays on Ni foam as a high-performance anode for Li-ion batteries

We demonstrate the large-area synthesis of NixSiy–SiGe core–shell nanowire arrays on a Ni foam via chemical vapor deposition and subsequent co-sputtering methods. When used as the anode of Li-ion batteries, the NixSiy–SiGe nanowire arrays show high reversible capacity and good rate capability compared to planar SiGe layers and NixSiy–Si core–shell nanowires. The good adhesion and contact of the core–shell nanowires with the current collector, and the integration of Ge which can greatly improve the conductivity and lithium-ion-diffusivity in the SiGe layer, may be responsible for the enhanced performance.

ZnO dense nanowire array on a film structure in a single crystal domain texture for optical and photoelectrochemical applications

A single crystal domain texture quality (a unique in-plane and out-of-plane crystalline orientation over a large area) ZnO nanostructure of a dense nanowire array on a thick film has been homogeneously synthesized on a-plane sapphire substrates over large areas through a one-step chemical vapor deposition (CVD) process. The growth mechanism is clarified: a single crystal [] oriented ZnAl2O4 buffer layer was formed at the ZnO film and the a-plane sapphire substrate interface via a diffusion reaction process during the CVD process, providing improved epitaxial conditions that enable the synthesis of the high crystalline quality ZnO nanowire array on a film structure. The high optoelectronic quality of the ZnO nanowire array on a film sample is evidenced by the free exitonic emissions in the low-temperature photoluminescence spectroscopy. A carrier density of ∼1017 cm−3 with an n-type conductivity of the ZnO nanowire array on a film sample is obtained by electrochemical impedance analysis. Finally, the ZnO nanowire array on a film sample is demonstrated to be an ideal template for a further synthesis of a single crystal quality ZnO–ZnGa2O4 core–shell nanowire array on a film structure. The fabricated ZnO–ZnGa2O4 sample revealed an enhanced anticorrosive ability and photoelectrochemical performance when used as a photoanode in a photoelectrochemical water splitting application.

Comparison of optical properties of Si and ZnO/CdTe core/shell nanowire arrays

Abstract The systematic computations of the short-circuit current density have been performed for Si and ZnO/CdTe core shell nanowire arrays of 1 μm height in order to optimize the structural morphology in terms of nanowire diameter and period. It is found that the best structural configuration for Si leading to the ideal short-circuit current density of 19.6 mA/cm 2 is achieved for a nanowire diameter and period of 315 nm and 350 nm, respectively. In case of ZnO/CdTe, the ideal short circuit current density is of 24.0 mA/cm 2 , the nanowire diameter and period is of 210 nm and 350 nm, respectively. It is shown that the optimal configuration is more compact in the case of Si nanowire arrays than in the case of ZnO/CdTe nanowire arrays. Since Si has a smaller absorption coefficient than CdTe, a larger amount of material is needed and thus more compact nanowire arrays are required. It is also revealed that core–shell nanowire arrays made of ZnO/CdTe more efficiently absorb light than that of Si, making this device a good candidate for the next generation of nanostructured solar cells.

High Performance Core-Shell Nanowire Array Devices Prepared by Atomic Layer Deposition

not Available.

Structure and Photoluminescence of Metal Oxide Core-Shell Nanowire Arrays

Metal oxide core-shell nanowire arrays composed of electrodeposited ZnO nanowires and atomic layer deposited Al2O3, ZnO, and TiO2 shells were fabricated at low process temperatures. The structural and photoluminescence (PL) properties of the core-shell structures were investigated and distinctive features were induced by the shell coatings. Due in part to their low temperature deposition, the effects of annealing on the core-shell nanowires were also studied in detail. The room temperature and low temperature PL of the nanowire cores are affected by the annealing treatments and the shell layers, with diverse effects observed depending on the shell material. Evidence for solid state reactions between the ZnO core and metal-oxide shell at increased annealing temperatures was also observed, leading to further changes in their optical properties.

Cu–Si1−xGex core–shell nanowire arrays as three-dimensional electrodes for high-rate capability lithium-ion batteries

We demonstrate the synthesis of new Cu–Si1−xGex core–shell nanowire array electrodes by directly depositing Si1−xGex layer on the surface of pre-synthesized Cu nanowire arrays via co-sputtering method. When used as anodes of lithium-ion batteries, the Cu–Si1−xGex (x=0.4) nanowire array electrodes show excellent electrochemical performance in terms of cycle stability and rate capability, which is much better than that of planar electrodes. The improved performance can be attributed to the good strain accommodation, fast electron transport and good electrical contact of the nanowire array electrodes. The effect of Ge content and the thickness of alloy film on the electrochemical performance of the three-dimensional electrodes have also been investigated.

Synthesis of ZnO@TiO2 core–shell long nanowire arrays and their application on dye-sensitized solar cells

Long ZnO nanowire arrays (NAs) grown on fluorine-doped tin oxide (FTO) glasses have been synthesized via a facile hydrothermal method without refreshing the reaction solution and applied as the precursor. By adjusting growth conditions, ZnO NAs with tunable lengths can be achieved. A nanocomposite made of ZnO nanowire core and TiO2 shell was further realized by a novel “fast-dip-coating” method conducted in a Ti(OC4H9)4-dissolved ethanol solution. The formed ZnO@TiO2 core–shell NAs on FTO substrates were applied as electrodes for dye sensitized solar cells (DSSCs). It is found that both the TiO2 coating and NAs length play important roles in the enhancement of photoelectric conversion efficiency (PCE) of DSSCs. When the length of ZnO@TiO2 NAs reaches up to 14μm, the electrode can exhibit a maximum PCE as high as 3.80%, which is 2.6 times higher than that of pure ZnO NAs.