Template-assisted Electrochemical Deposition Research Articles

Magnetometry of Individual Polycrystalline Ferromagnetic Nanowires.

Ferromagnetic nanowires are finding use as untethered sensors and actuators for probing micro- and nanoscale biophysical phenomena, such as for localized sensing and application of forces and torques on biological samples, for tissue heating through magnetic hyperthermia, and for microrheology. Quantifying the magnetic properties of individual isolated nanowires is crucial for such applications. Dynamic cantilever magnetometry is used to measure the magnetic properties of individual sub-500 nm diameter polycrystalline nanowires of Ni and Ni80 Co20 fabricated by template-assisted electrochemical deposition. The values are compared with bulk, ensemble measurements when the nanowires are still embedded within their growth matrix. It is found that single-particle and ensemble measurements of nanowires yield significantly different results that reflect inter-nanowire interactions and chemical modifications of the sample during the release process from the growth matrix. The results highlight the importance of performing single-particle characterization for objects that will be used as individual magnetic nanoactuators or nanosensors in biomedical applications.

Fabrication of hierarchically ordered porous scheelite-related monoclinic BiVO4 nanotubes by electrochemical deposition

Scheelite-related monoclinic BiVO4 is one of the most promising metal oxide photoanode materials. It is therefore highly desirable to explore its new nanostructured morphologies in order to achieve higher performance. We present a new method for the fabrication of porous BiVO4 nanotubes. Powder XRD experiments show that the electrodeposited BiVO4 nanotubes crystallize in the scheelite-related monoclinic phase. The produced BiVO4 nanotubes are highly hierarchically ordered and aligned perpendicular to the electrically conductive substrate. The nanostructures were produced by template-assisted electrochemical deposition inside porous anodized alumina oxide. Our method may be extended to other semiconductor materials used in photoelectrochemical systems, such as Bi2WO6 and [Formula: see text]-Bi2MoO6.

Morphology Dependence on Surface-Enhanced Raman Scattering Using Gold Nanorod Arrays Consisting of Agglomerated Nanoparticles

Highly ordered arrays of vertically aligned Au nanorod arrays consisting of agglomerated nanoparticles are fabricated by porous anodic aluminum oxide (AAO) template-assisted electrochemical deposition. The Au nanorod arrays with rough surfaces are then transformed to smooth surfaces by a subsequent thermal annealing step. The surface-enhanced Raman scattering (SERS) intensity of the Au nanorod arrays with rough and smooth surfaces was compared to investigate the morphology dependence of SERS. The Au nanorod arrays with agglomerated structures demonstrated a highly active SERS effect as abundant nanogaps are created uniformly by combination of hot spots caused by both agglomerated porous structures on each nanorod and inter-rod gaps.

Magnetocaloric effect at cryogenic temperature in gadolinium oxide nanotubes

We have synthesized fascinating nano-structure of Gadolinium oxide (Gd2O3) using controlled template-assisted electrochemical deposition technique which showed interesting anisotropic magnetic behavior. The nanotubes of Gd2O3 with average diameter 200nm, length 10µm and wall thickness 20nm are constituted of nanoclusters with average diameter 7.5nm. The tubes are aligned and are almost uniform throughout their length. Detailed magnetic measurements of aligned Gd2O3 nanotubes have been performed for both parallel and perpendicular magnetic field orientations with respect to the axis of the Gd2O3 nanotube array. Significant differences in magnetization values have been observed between the parallel and perpendicular orientations. Experimental results indicate the superparamagnetic nature of the nanomaterial. Large magnetocaloric effect, associated with the sharp change in magnetization of the Gd2O3 nanotubes, has been observed in the cryogenic temperature regime that shows anisotropic behavior.

Effect of morphology on the magnetic properties of Gd2O3 nanotubes

Gadolinium oxide (Gd2O3) nanotubes of micron length and average diameter 100nm have been synthesized by a controlled template-assisted electrochemical deposition technique. Structure and morphology of the synthesized nanotubes have been well characterized by using microscopy and spectroscopy analyses. HRTEM and XRD analysis revealed the crystalline planes of Gd2O3 nanotubes. Magnetic measurements of the aligned Gd2O3 nanotubes have been performed for both parallel and perpendicular orientations of the magnetic field with respect to the axis of the Gd2O3 nanotube array. Large bifurcation in ZFC–FC over the regime of 2–320K without any signature of long range magnetic ordering confirms the presence of SPM clusters in Gd2O3 nanotubes. Also, large magnetocaloric effect is observed in the cryogenic temperature regime. No anisotropy is seen at the low temperature region but is found to evolve with temperature and becomes significant ~300K. These nanotubes can be considered as promising candidates for magnetic refrigeration at cryogenic temperature.

Electrochemical Synthesis and Characterisation of BiTe-Based Nanowire Arrays as Thermoelectric Nanogenerators

Thermoelectric (TE) nanogenerators are solid state devices that can directly convert thermal energy into electrical power. The family of bismuth telluride (BiTe)-based semiconductor materials is a good candidate for room-temperature thermoelectric applications. This work aims to synthesize the binary and ternary TE nanowire arrays from BiTe and BiSbTe using template-assisted electrochemical deposition. The compositions and lengths of the nanowires fabricated were precisely tuned by controlling the deposition conditions, while their diameters were confined by the pore sizes of the anodized alumina oxide (AAO) templates used. Chemical compositions of the nanowires were evaluated using Energy Dispersive X-ray (EDX) Spectroscopy and their microstructures were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), conventional transmission electron microscopy (CTEM) and high resolution transmission electron microscopy (HRTEM). TE nanogenerator modules comprising of BiTe and BiSbTe nanowires/AAO composite arrays were fabricated for TE performance evaluation on the basis of their power outputs.

Magneto-Acoustic Hybrid Nanomotor.

Efficient and controlled nanoscale propulsion in harsh environments requires careful design and manufacturing of nanomachines, which can harvest and translate the propelling forces with high spatial and time resolution. Here we report a new class of artificial nanomachine, named magneto-acoustic hybrid nanomotor, which displays efficient propulsion in the presence of either magnetic or acoustic fields without adding any chemical fuel. These fuel-free hybrid nanomotors, which comprise a magnetic helical structure and a concave nanorod end, are synthesized using a template-assisted electrochemical deposition process followed by segment-selective chemical etching. Dynamic switching of the propulsion mode with reversal of the movement direction and digital speed regulation are demonstrated on a single nanovehicle. These hybrid nanomotors exhibit a diverse biomimetic collective behavior, including stable aggregation, swarm motion, and swarm vortex, triggered in response to different field inputs. Such adaptive hybrid operation and controlled collective behavior hold considerable promise for designing smart nanovehicles that autonomously reconfigure their operation mode according to their mission or in response to changes in their surrounding environment or in their own performance, thus holding considerable promise for diverse practical biomedical applications of fuel-free nanomachines.

Novel dye-sensitized solar cell architecture using TiO2-coated Ag nanowires array as photoanode

With the aim of reducing series resistance and increasing dye loading, novel dye-sensitized solar cell architecture was designed with TiO2 nanoparticle-coated Ag nanowires array as the photoanode. Ag nanowire array was prepared by anodic aluminum oxide (AAO) template-assisted electrochemical deposition route. Then, Ag nanowires were coated by TiO2 nanoparticles in hydrothermal process. The structures of the photoanode were characterized by field emission scanning electron microscopy (FESEM). Ag nanowires are covered by a layer of very fine nanoparticles with a diameter of less than 5 nm. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) show that Ag nanowires have a strong preferred orientation in (220) direction and the TiO2 coating layer is a polycrystalline structure. With this photoanode, 3.2 % conversion efficiency is achieved for the cell sensitized with N3 dye.

Geometry Controlled Growth of Single Crystalline CdS Nanopillar Arrays and the Investigation of Their Electrical Properties

Recently, one dimensional semiconductor nanomaterials have been extensively explored as building blocks for nanoscale electronic devices such as field-effect transistors (FETs), optoelectronic devices such as solar cells, light emitting diodes, and lasers. Apart from their advantageous small dimensions for device miniaturization, semiconductor nanowires (NWs) and nanopillars (NPLs) have shown intriguing properties that promise high device performance. Notably, many of these intriguing properties have shown strong geometry dependence, in terms of length, diameter, pitch, cross-section shape etc. Past studies have shown that well organized nanostructure arrays exhibit unique photon management ability, which further resulted in the potency to demonstrate light absorption exceeding conventional limits. Therefore, the capability to program and engineer the shape and morphology of NWs and NPLs is of paramount importance and in urgent need. However, conventional bottom-up growth of NWs in free space using a catalytic process lacks precise control over NW length and diameter. Template-assisted electrochemical deposition can produce NWs/NPLs with designed geometry. Nevertheless, the typically low crystalline quality of its products places them into disadvantageous situation for high performance electronic and opto-electronic devices. Herein, we utilize a template-assisted, Vapor-Liquid-Solid (VLS) growth process for the fabrication of regular and single-crystalline NW/NPL arrays with tunable shapes. Self-organized and perfectly ordered Anodized Alumina Membranes (AAMs) have been fabricated by properly controlling the anodization conditions in combination with the utilization of nanoimprint technique. With these nanoengineered AAM as templates, a variety of nanostructures, including nanopillar arrays, nanotower arrays, and nanocone arrays, have been successfully fabricated. It is worth noting that due to the capability of programmable structural design and fabrication of the AAM templates, the semiconductor arrays can be well defined as desired. ZnO nanostructures were also prepared with the same method. This is to demonstrate that the process is applied for the growth of CdS NPLs, but can be easily extended to other materials. All in all, the process reported here presented a generic platform toward the controlled growth of nanostructures with tunable shape and geometry. In addition, we have investigated the electrical properties of the CdS NPLs from AAM assisted growth. Vertical NPL array devices and horizontal individual NPL field-effect transistors have been fabricated and characterized. The intrinsic CdS NPLs showed poor conductivity and weak gate dependent performance, which is not desirable for device applications. Thus, Indium was chosen as dopant to tailor the electrical and optical properties of CdS NPLs. Specifically, in-situ Indium doping was conducted with 80 mg of Indium metal pellet. The measurements showed that the location of the Indium doping source significantly affected carrier concentration, conductivity and field-effect mobility of the prepared CdS NPLs. Particularly, it was found that conductivity could be improved by 4 orders of magnitude and field-effect mobility could be enhanced up to 50 cm2/Vs via proper doping control. These results enable further applications of CdS nanopillars for nano-optoelectronic applications such as photodetection and photovoltaics in the future.

A visible metamaterial fabricated by self-assembly method

A visible negative-index metamaterial was fabricated by adopting a template-assisted and self-assembled electrochemical deposition method. Originating from the inherent characteristic of bottom-up fabrication, it has been demonstrated by the effective medium theory that the metamaterial resonance could realize a negative index at visible wavelengths if the degree of asymmetry is kept in a moderate range. This was experimentally substantiated by fabricating an asymmetric Ag–polyvinyl alcohol (PVA)–Ag multilayer nanostructure with two apertured silver films on the opposite sides of PVA film. The extraction of constitutive parameters shows negative index in the wavelength range from 535 to 565 nm, with a minimum value close to −0.5. Simultaneously, an optically active medium Rhodamine B was incorporated into the PVA layer, which readily changed the transmission peak through control experiments. Finally, the enhanced transmission was realized through a flat sample.

Synthesis of Silicon and Germanium Nanowire Assemblies by Template-Assisted Electrodeposition from an Ionic Liquid

We report on the template-assisted synthesis of silicon and germanium nanowires from the air- and water-stable ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4] TFSA). The synthesis was done by electrochemical deposition in the pores of a commercial track-etched polycarbonate membrane. After chemical dissolution of the polycarbonate membrane in dichloromethane, nanowire assemblies with a regular arrangement were obtained. Different lengths of nanowires can be obtained by varying the applied potential and the time of deposition. The nanowire assemblies were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX). Our results show that the template-assisted electrochemical deposition approach in ionic liquids has the potential to easily synthesise germanium and silicon nanowire assemblies.

Three-dimensionally porous Fe3O4 as high-performance anode materials for lithium–ion batteries

This paper describes the synthesis of three-dimensionally porous Fe3O4 via template-assisted and subsequent electrochemical deposition methods. When used as anode materials of lithium–ion batteries, the porous Fe3O4 electrodes show better cyclability and enhanced rate capabilities compared to planar Fe3O4 electrodes. The superior performance can be attributed to improved electrical contact, fast electron transport and good strain accommodation of the porous electrodes. The effect of the thickness of the porous Fe3O4 electrodes on the lithium–ion battery performance has also been investigated.

Direct deposition of inorganic–organic hybrid semiconductors and their template-assisted microstructures

A straight forward method is developed to deposit new class of self-organized inorganic–organic (IO) hybrid, (C12H25NH3)2PbI4. These IO hybrid structures are stacked-up as natural multiple quantum well structures and exhibit strong room-temperature exciton emission and other multifunctional features. Here it is successfully demonstrated that these materials can be directly carved into 2D photonic structures from the inexpensive template-assisted electrochemical deposition followed by solution processing. The applicability of this method for many such varieties of IO-hybrids is also explored. By appropriately controlling the deposition conditions and the self-assembly templates, target structures are achieved for new-generation low-cost photonic devices.

Enhanced photoluminescence of ordered macroporous germanium electrochemically prepared from ionic liquids

Recently we reported our results on the successful synthesis of 3-D highly ordered macroporous (3DOM) structure of germanium via the template-assisted electrochemical deposition from air- and water stable ionic liquids. Herein we report our new results on the photoluminescence (PL) properties of the obtained ordered macroporous Ge and the Ge/polystyrene composite opal structure. The latter showed a strong green emission compared to a Ge film and a Ge inverse opal. The enhancement of PL intensity was ascribed to the disorder multiple scattering in polystyrene colloidal crystal structure which increased both the excitation light absorption efficiency and the light extraction efficiency. The X-ray photoelectron spectroscopy (XPS) results suggested that the ordered macroporous Ge was capped with an oxide layer including a considerable amount of GeO(2). The observed green emission (539 nm) was related to GeO(2), likely resulting from the Ge-O bond related intrinsic defects.

Surface Plasmon Polaritons of Two-Dimensional Three-Order Dendritic Structures

We study surface plasmon polaritons excited on two-dimensional three-order dendritic structures. Previous studies show that split ring resonators (SRRs) can be used to obtain magnetic resonance, thus sustaining surface waves behaving like surface plasmon polaritons (SPPs). In this paper, we obtain detailed results on surface plasmon polaritons of several different grating structures and theoretically prove that this kind of structures can sustain SPPs. Besides, since dendritic structures can be fabricated by double template-assisted electrochemical deposition, it is worth noting that fabrication of SPP-based materials might be much easier.

Enhancing Ni–Sn nanowire lithium-ion anode performance by tailoring active/inactive material interfaces

Nanowire arrays have attracted great attention due to their great potential to improve the performance of Li-ion batteries. In this work, we studied anode performance of lithium-ion batteries using Ni–Sn nanowire arrays. A versatile method through a porous anodic alumina (PAA) template-assisted electrochemical deposition process was developed to directly synthesize Ni–Sn nanowire arrays on copper current collectors. This method presents significant advantage that the as-prepared Ni–Sn nanowire arrays can be directly used as anode electrode without any binder or conductive materials. However, the formation of a continuous Ni–Sn film at the base of the nanowires result in quick loss of electrical contact between the active material and the current collector because of the large strain mismatch at the large continuous active/inactive material (A/I) interface. By growing short Cu nanoscrews as a buffer layer before Ni–Sn nanowire growth, the formation of Ni–Sn film was inhibited and the A/I interface was scaled down to nanoscale islands. The strain mismatch is thus significantly reduced, which results in enhanced structural stability and battery performance. The effect of the composition and the length of Ni–Sn nanowire arrays on the electrochemical performance of lithium ion batteries are also systematically studied.

Visible light metamaterials based on the double-fishnet structure

A novel method was proposed to fabricate double-fishnet structure metamaterials working at visible frequencies. Via template-assisted electrochemical deposition, silver nanonets with different lattices were fabricated, which were used to achieve final double-fishnet structures. It was revealed that the passband of the silver nanonet structure was shift to shorter wavelength when changing the lattice of structure smaller, according to the transmission spectra. Silver nanonet with lattice of 420 nm was used to achieve double-fishnet structure, which has novel effects at 610 nm wavelength, such as enhanced transmission and planar focusing. Furthermore, it is possible to fabricate double-fishnet structure metamaterials working at shorter wavelengths even for blue light when using template with smaller lattice.

Electrodeposition of Multi-Segmented CoNiP-Au Nanowires for Bio-Barcodes

One-dimensional nanowires with a number of readily distinguishable hard magnetic (CoNiP) and non-magnetic (Au) multi-segments were synthesized via template-assisted sequential electrochemical deposition in single batch procedure. The Co, Ni and P contents of CoNiP composition have been measured to be 80.6, 13.2, and 6.2 at%, respectively, where both Co-fcc and Co-hcp phases were observed. The CoNiP exhibits a hard magnetic property with a coercive force of 103 kA/m and a remanent magnetization of 1.98 × 10−1 T, where the combinations of CoNiP and Au segments could be assigned as digital codings of “1” and “0”, respectively. A selective Cytochrome-c protein and Green Fluorescent Protein (GFP) immobilization on Au-segments of the nanowires has been demonstrated for the feasibility of barcode applications in future multiplexed bioassays.

Electrodeposition of Ni/Co and Ni Magnetic Nanowires Using Allumina Template

Nickel and nickel-cobalt alloy nanowires were fabricated through template-assisted electrochemical deposition method and sandwiched between two caps of electrodeposited pure gold. Free standing porous alumina templates were prepared and used for the synthesis of the ordered nanowires. The morphology and composition of as-deposited nanowires were determined by scanning electron microscope. Nanowires were characterized by a diameter of 70 nm, as the alumina template pores diameter, and by a length in the range of 2-3 μm. Backscattered electron signal showed the presence of Au and Ni or Ni-Co sandwich, highlighting a well defined and void free interface between the gold caps and the Ni or Ni-Co layer. Particular optimization has been considered for the subsequent magnetoresistance characterization of nanowires. Angular dependence of magnetoresistance has been measured as a function of temperature from in-plane to perpendicular magnetic field configuration. Anisotropic magnetoresistive measurements suggested a magnetization process by magnetization rotation from nanowire axis towards in-plane orientation.

Planar focus effect of visible light metamaterials

In this paper are described three composite structures of visible light metamaterials, i.e. dendritic structures and dendritic structures, dendritic structures and silver film, dendritic structures and indium tin oxide slice, based on the physical model of “double-fishnet” structure. By double template-assisted electrochemical deposition, silver dendritic structure arrays and silver films are fabricated, which is useful for achieving the above three composite structures. It is revealed that all of the three composite structures have the same effects according to the transmission spectra and reverberation spectra.A comparison among all of the three composite structures clealy shows that the composite structure of dendritic structures and indium tin oxide slice has the best performance, such as low loss and distinct planar focus effect. Through adjusting the experiment conditions, three kinds of visible light metamaterials are prepared which can realize planar focus effects at red, green and blue light frequencies, separately.