Core-shell Arrays Research Articles

Multispectral optical enhanced transmission of a continuous metal film coated with a plasmonic core-shell nanoparticle array

We propose and show multispectral optical enhanced transmission in the visible and near-infrared region in a continuous metal film coated with a two-dimensional (2D) hexagonal non-close-packed plasmonic array. The plasmonic array consists of metal/dielectric multilayer core-shell nanoparticles. The excitation of near-field plasmon resonance coupling between adjacent core-shell nanoparticles, plasmon resonance coupling between adjacent metal layers in the nanoparticle, and surface plasmon (SP) waves on the metal film are mainly responsible for the multispectral optical enhanced transmission behavior. The multispectral optical enhanced transmission response could be highly modified in the wavelength range, transparent bandwidth and transmission intensity by varying the geometry parameters including the gap distance between adjacent plasmonic nanoparticles, the size of metal core and the thickness of dielectric layer between the metal layers. In addition, the number of optical enhanced transmission bands increases with the number of metal layers in the plasmonic nanoparticle. The proposed structure shows many merits such as the deep sub-wavelength size, multispectral optical enhanced transmission bands as well as fully retained electric and mechanical properties of the natural metal. These merits may provide promising applications for highly integrated optoelectronic devices including plasmonic filters, nanoscale multiplexers, and nonlinear optics.

CdS/CdSe Core–Shell Nanorod Arrays: Energy Level Alignment and Enhanced Photoelectrochemical Performance

Novel CdS/CdSe core-shell nanorod arrays were fabricated by a chemical bath deposition of CdSe on hydrothermally synthesized CdS nanorods. The CdS rods were hexagonal phase faced and the top of the rod was subulate. After the chemical bath deposition approach, CdS nanorod arrays were encapsulated by a uniform CdSe layer resulting enhanced absorbance and extended absorption edges of the films. A tandem structure of the energy bands of CdS/CdSe was also formed as a result of the Fermi level alignment, which is a benefit to the efficient separation of photogenerated charges. CdS/CdSe core-shell arrays gave a maximum photocurrent of 5.3 mA/cm(2), which was 4 and 11 times as large as bare CdS and CdSe, respectively.

Electrochemical synthesis of ZnO/CdTe core-shell nanotube arrays for enhanced photoelectrochemical properties

ZnO/CdTe core–shell nanotube arrays are controllablly synthesized using a simple two-step electrochemical deposition strategy in this paper. The as-prepared ZnO/CdTe core–shell nanotube arrays are found to exhibit significantly enhanced photocurrent density for water splitting as compared to the ZnO nanorod arrays. This is mainly due to the lower the band gap or the lower density of oxygen vacancies and other defects states. Furthermore, the effect of CdTe loading on the photoelectrochemical performances of ZnO/CdTe core–shell nanotube arrays was also investigated.

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.

Epitaxial inversion on ferromagnetic (Fe,Zn)3O4 /ferroelectric BiFeO3 core-shell nanodot arrays using three dimensional nano-seeding assembly

We demonstrate an advanced fabrication method based on standard surface diffusion theory for preparation of core-shell nano-heterostructure arrays consisting of ferromagnetic (Fe,Zn)3O4 (FZO) and ferroelectric BiFeO3 (BFO) using a 3D nano-seeding-assembly technique. By adapting epitaxial spinel FZO nanodot arrays on a perovskite SrTiO3 substrate to templates, well-positioned selective epitaxial growth of FZO cores and BFO shells was spontaneously stimulated. This technique resolves the longstanding issues of the precise positional alignment and configuration inversion of materials that conventional self-assembly growth has faced.

Blood Clot Mechanical Properties measured with Arrays of Magnetically Actuated Core-Shell Microrods

Understanding blood clot formation and mechanical properties is vital, as clotting or bleeding disorders are a leading cause of morbidity and mortality in the world. One in four trauma patients admitted to the emergency room has an acute traumatic coagulopathy, requiring blood products and/or the management of specific clotting or fibrinolytic disorders. Such patients would be better served at or near the site of injury with a point-of-care diagnostic device capable of immediate coagulopathy detection and early diagnostic indications. We have developed arrays of magnetically actuated core-shell microrods able to assess the time evolution of fluid properties at the microscale. Here we describe their application to assessing the mechanical properties of a developing blood clot. Our core-shell post structures, 25 microns tall and 2.5 microns in diameter, consist of flexible poly(dimethylsiloxane) (PDMS) cores surrounded by 100 nm nickel shells. Packaged in a microfluidic channel, our arrays measure changes in fluid properties with less than 15 microliters of fluid and have the potential to become point-of-care devices. We present the use of these core-shell rod arrays as an assay for clot development, capable of producing clinically relevant clotting time measurements in animal plasmas, and will report on progress made in whole blood samples.

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell array electrode materials for supercapacitors

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell arrays (TiO2@MnO2 NBAs) have been fabricated on a Ti foil substrate by hydrothermal approach and further investigated as the electrode for a supercapacitor. Their electrochemical properties were examined using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. The experimental observations clearly show that the fabricated TiO2@MnO2 NBAs electrode possesses superior rate capability and outstanding cycling performance due to its rationally designed nanostructure. A specific capacitance as high as 557.6 F g−1 is obtained at a scan rate of 200 mV s−1 (454.2 F g−1 at a current density of 200 mA g−1) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 2 A g−1 are 7.5 Wh kg−1 and 1 kW kg−1 respectively, demonstrating its good rate capability. In addition, the composite TiO2@MnO2 NBAs electrode shows excellent long-term cyclic stability. The fabrication method presented here is facile, cost-effective and scalable, which may open a new pathway for real device applications.

Porous Ni@Pt Core‐Shell Nanotube Array Electrocatalyst with High Activity and Stability for Methanol Oxidation

Bimetallic core-shell nanostructures are emerging as more important materials than monometallic nanostructures, and have much more interesting potential applications in various fields, including catalysis and electronics. In this work, we demonstrate the facile synthesis of core-shell nanotube array catalysts consisting of Pt thin layers as the shells and Ni nanotubes as the cores. The porous Ni@Pt core-shell nanotube arrays were fabricated by ZnO nanorod-array template-assisted electrodeposition, and they represent a new class of nanostructures with a high electrochemically active surface area of 50.08 m(2) (g Pt)(-1), which is close to the value of 59.44 m(2) (g Pt)(-1) for commercial Pt/C catalysts. The porous Ni@Pt core-shell nanotube arrays also show markedly enhanced electrocatalytic activity and stability for methanol oxidation compared with the commercial Pt/C catalysts. The attractive performances exhibited by these prepared porous Ni@Pt core-shell nanotube arrays make them promising candidates as future high-performance catalysts for methanol electrooxidation. The facile method described herein is suitable for large-scale, low-cost production, and significantly lowers the Pt loading, and thus, the cost of the catalysts.

A novel semiconductor-sensitized solar cell based on P3HT@CdS@TiO2 core-shell nanotube array

In this paper, a novel semiconductor-sensitized solar cell with the photoanode based on poly (3-hexylthiophene) (P3HT)@CdS@TiO2 nanotube array was fabricated. Vertically oriented TiO2 nanotube arrays were prepared by a sol–gel based method using ZnO nanorod arrays as sacrificing template. CdS nanocrystals and a thin P3HT layer were electrodeposited onto the wall of TiO2 nanotube to prepare the photoanode of the semiconductor-sensitized solar cell. It has been demonstrated that the coating of P3HT on the surface of the CdS@TiO2 core-shell nanotube arrays could largely improve the photovoltaic performance of the solar cell. A power conversion efficiency of 1.16% was obtained with this type of solar cell.

Enhanced electron field emission properties of high aspect ratio silicon nanowire–zinc oxide core–shell arrays

The enhanced electron field emission (EFE) properties of high aspect ratio, vertically aligned SiNW-ZnO core-shell arrays are presented. These core-shell arrays are prepared by a thin, controlled, highly crystalline and conformal coating of zinc oxide as shell using the plasma assisted-atomic layer deposition (PA-ALD) route on vertically aligned silicon nanowire arrays core. The core-shell nanostuctures are confirmed by HRTEM imaging along with the individual elemental mapping demonstrating the conformal deposition of 10 nm ZnO on the SiNWs. EFE properties of va-SiNW-ZnO core-shell arrays showed a high emission current density of 51 μA cm(-2) and a low turn on field of 7.6 V μm(-1) (defined at a current density of 1 μA cm(-2)) compared to the 3.2 μA cm(-2) emission current density and 9.1 V μm(-1) turn on field for SiNWs. The field enhancement factor (β) of 4227 for the devices demonstrates that these core-shell nanowire arrays are excellent field-emitters. Such an enhancement in the field emission originates from the details of the band structure of this peculiar material combination resulting in good electron transport from SiNW to ZnO as evident from the band diagram of the core-shell material. This is further supported by the conducting AFM studies where lowering in threshold voltage by 1 eV confirms the role of ZnO coating in the enhancement of the emission characteristics.

Core-Shell Ni-NiO Nano Arrays for UV Photodetection without an External Bias

This work demonstrates a simple method for fabricating a nano-structured device that performs notable photodetecting capabilities. With a template of anodic aluminum oxide, highly ordered Ni-NiO nano core-shell arrays were fabricated by annealing the electroless-deposited Ni arrays at 300°C for 30 minutes. High-resolution transmission electron microscopy (HRTEM) demonstrated that a NiO layer with a thickness of ∼5 nm was developed on the surface of the Ni arrays. The effects of annealing time and temperature on NiO were probed by HRTEM. Results show that temperature has a greater effect on the development of NiO. The Ni/NiO interface forms naturally a Schottky nanojunction, which covers most of the array surface when patterned with an indium-tin oxide (ITO) electrode. The ITO/Ni-NiO/Si device was found to yield photocurrent when exposed to ultraviolet (UV) light without an external voltage bias. The device takes great advantage of the large junction area and one-dimensional configuration of the core-shell array, displaying rapid photoresponse to UV light and subsequent steady photocurrent. These features make the proposed device a viable alternative to the UV photodetector.

CoO/NiSix core–shell nanowire arrays as lithium-ion anodes with high rate capabilities

This paper describes a facile chemical vapor deposition (CVD) and subsequent radio-frequency (RF)-sputtering approach for the synthesis of CoO/NiSi(x) core-shell nanowire (NW) arrays on Ni foams. The metallic core (i.e., NiSi(x)) with high conductivity acts as a nanostructured current collector. The as-synthesized CoO/NiSi(x) core-shell NW arrays have been applied as anode materials for lithium-ion batteries, which deliver high cycle life and enhanced power performance compared to planar CoO electrodes on Ni foams. The high surface-to-volume ratio and improved electronic/ionic conductivity of the nanostructured electrodes may be responsible for the improved performance.

Fabrication and Photovoltaic Characteristics of Coaxial Silicon Nanowire Solar Cells Prepared by Wet Chemical Etching

Nanostructured solar cells with coaxial p-n junction structures have strong potential to enhance the performances of the silicon-based solar cells. This study demonstrates a radial junction silicon nanowire (RJSNW) solar cell that was fabricated simply and at low cost using wet chemical etching. Experimental results reveal that the reflectance of the silicon nanowires (SNWs) declines as their length increases. The excellent light trapping was mainly associated with high aspect ratio of the SNW arrays. A conversion efficiency of ∼7.1% and an external quantum efficiency of ∼64.6% at 700 nm were demonstrated. Control of etching time and diffusion conditions holds great promise for the development of future RJSNW solar cells. Improving the electrode/RJSNW contact will promote the collection of carries in coaxial core-shell SNW array solar cells.

Radial p-n Junction Solar Cells by Core-Shell Silicon Nanowire Arrays

ABSTRACTWe first fabricated a p-type single-crystalline SiNW array as the core by statistic electroless metal deposition (SEMD) method[1]. This structure exhibits per excellent absorption efficiency without increasing the diffusion path, indicating 1.75 times greater performance than Si-based planar solar cells under the same condition[2]. Next, we employed a method of spin-on dopant (SOD) to fabricate an n-type layer as an external thin shell, which benefits to decouple the absorption of light from charge transport by allowing lateral diffusion of minority carriers to the p-n junction rather than many microns away as in Si bulk solar cells, and is suitable for our SiNW array with a hydrophilic surface. Finally, our SiNW-based solar cell possesses strong broadband absorption and low reflection from visible light to near IR, in which the highly light trapping mechanism stems from the effective medium theory (EMT) to demonstrate only less than 3% of total reflectance in the range of 500-1100 nm. It also shows conversion efficiency improvement of 20% compared with the planar single-crystalline Si solar cell by the same fabrication processes. The proposed novel photovoltaic device by our core-shell SiNW array revolutionizes the current architecture of solar cells, promising niche points of (1) better absorption, (2) self-antireflection, and (3) low-cost process.

Ag–SiO2 Core–Shell Nanorod Arrays: Morphological, Optical, SERS, and Wetting Properties

Using the hydrolysis of tetraethylorthosilicate, a uniform and conformal layer of porous SiO(2) with controlled thickness has been coated onto the oblique angle deposited Ag nanorod (AgNR) array to form an aligned AgNR-SiO(2) core-shell array nanostructure. The morphology, optical property, SERS response, and surface wettability of the AgNRs with different SiO(2) shell thicknesses have been obtained by multiple characterization techniques. The morphological characterization shows that each AgNR on the array is coated with a uniform and porous silica shell independently and the growth of shell thickness follows a linear function versus the coating time. Thickening of the shell induces a monotonic decrease of the apparent contact angle, red-shift of the transverse mode of the localized surface plasmon resonance peak, and makes the SiO(2) shell more compact. The SERS response of 4-Mercaptophenol on these substrates exhibits an exponential decay behavior with the increasing coating time, which is ascribed to the decreasing Ag surface coverage of core-shell nanorods. Under the assumption that the Ag surface coverage is proportional to the SERS intensity, one can estimate the evolution of SiO(2) coverage on AgNRs. Such coverage evolution can be used to qualitatively explain the LSPR wavelength change and quantitatively interpret the contact angle change based on a double Cassie's law.

In Situ Surface-Enhanced Raman Spectroscopic Studies of Nafion Adsorption on Au and Pt Electrodes

Understanding interactions between Nafion (perfluorosulfonic acid) and Pt catalysts is important for the development and deployment of proton exchange membrane fuel cells. However, study of such interactions is challenging and Nafion/Pt interfacial structure remains elusive. In this study, adsorption of Nafion ionomer on Au and Pt surfaces was investigated for the first time by in situ surface-enhanced Raman spectroscopy. The study is made possible by the use of uniform SiO(2)@Au core-shell particle arrays which provides very strong enhancement of Raman scattering. The high surface sensitivity offered by this approach yields insightful information on interfacial Nafion structure. Through spectral comparison of several model compounds, vibration assignments of SERS bands were made. The SER spectra suggest the direct interaction of sulfonate group with the metal surfaces, in accord with cyclic voltammetric results. Comparison of present SERS results with previous IR spectra was briefly made.

Synthesis and magnetic characterization of Co-NiO-Ni core-shell nanotube arrays

Well-aligned Ni and Co-NiO-Ni core-shell nanotube arrays with an average outer diameter of about 200 nm have been synthesized in a porous anodic aluminum oxide (AAO) template by the direct electro-deposition method. The result shows that the nanotubes were polycrystalline phase. Angular dependent coercivity Hc(θ) indicates that the magnetization reversal mechanisms are mainly dominated by the “curling mode” for Ni nanotubes, while a transition from curling to transverse is observed in Co-NiO-Ni core-shell nanotubes at a large angle. A sharp increase in saturated magnetization (Ms) of Ni and Co-NiO-Ni core-shell nanotubes at 5 K was observed, due to dominance of the surface effect. Besides, the existed superparamagnetic nanoparticles also resulted in the increase of Ms for both cases. These structures have potential applications in the novel spintronics device, ultrasmall magnetic media, and other nanodevices.

Self-Assembled Vapor–Liquid–Solid Growth of Aligned Cu-SiO<SUB>2</SUB> Core–Shell Nanocable Arrays on Cu Substrates

The Cu-SiO2 core-shell nanocable arrays on the Cu wafers have been synthesized via a simple thermal evaporation of the SiO powder. The morphology and structure of the as-synthesized Cu-SiO2 core-shell nanocables are characterized by using scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray energy dispersive spectrometer. The growth of amorphous SiO2 shell follows a vapor-liquid-solid mechanism, and then molten metal Cu will be diffused into the SiO2 nanotubes, forming the Cu-SiO2 core-shell nanocable arrays. It is found that the aligned Cu-SiO2 core-shell nanocables prefer to grow along the grooves of the Cu substrate, and the density of the Cu-SiO2 core-shell nanocable arrays can be controlled by adjusting the growth temperature.

Composition-Tuned ZnO−CdSSe Core−Shell Nanowire Arrays

Vertically aligned ZnO--CdSSe core-shell nanocable arrays were synthesized with a controlled composition and shell thickness (10-50 nm) by the chemical vapor deposition on the pregrown ZnO nanowire arrays. They consisted of a composition-tuned single-crystalline wurtzite structure CdS1-xSex (x=0, 0.5, and 1) shell whose [0001] direction was aligned along the [0001] wire axis of the wurtzite ZnO core. The analysis of structural and optical properties shows the formation of Zn containing alloy in the interface region between the ZnO core and shell, which can facilitate the growth of single-crystalline shell layers by reducing both the lattice mismatch and the number of defect sites. In contrast, the TiO2 (rutile) nanowire array can form the polycrystalline shell under the same condition. The photoelectrochemical cell using the ZnO--CdS photoelectrode exhibits a higher photocurrent and hydrogen generation rate than that using the TiO2-CdS one. We suggest that the formation of the CdZnSSe intermediate layers contributes to the higher photoelectrochemical cell performance of the ZnO--CdSSe nanocables.

Fabrication of two-dimensional Au@FePt core-shell nanoparticle arrays by photochemical metal deposition

In this report, we experimentally demonstrate that single platinum nanoparticles exhibit the necessary catalytic activity for the optically induced reduction of H[AuCl4] complexes to elemental gold. This finding is exploited for the parallel Au encapsulation of FePt nanoparticles arranged in a self-assembled two-dimensional array. Magnetic force microscopy reveals that the thin gold layer formed on the FePt particles leads to a strongly increased long-term stability of their magnetization under ambient conditions.