Fabrication of nanostructure via self-assembly of nanowires within the AAO template

The novel nanostructures are fabricated by the spatial chemical modification of nanowires within the anodic aluminum oxide (AAO) template. To make the nanowires better dispersion in the aqueous solution, the copper is first deposited to fill the dendrite structure at the bottom of template. During the process of self-assembly, the dithiol compound was used as the connector between the nanowires and nanoparticles by a self-assembly method. The nanostructures of the nano cigars and structure which is containing particles junction are characterized by transmission electron microscopy (TEM). These kinds of novel nanostructure will be the building blocks for nanoelectronic and nanophotonic devices.      

硅基AAO模板法制备纳米阵列研究进展

硅基纳米材料结构与性能独特,在光学、半导体和材料科学等领域具有广阔的应用前景。本文介绍了硅基阳极氧化铝模板相对于铝基模板在集成纳米功能器件方面的优势及其制备方法,对阳极氧化工艺过程进行了分析,并对几种基于硅基AAO模板组装的纳米阵列进行了综述,总结了硅基纳米结构阵列性能的研究概况。     

Fabrication of nanowire network AAO and its application in SERS

In this paper, nanowire network anodized aluminum oxide (AAO) was fabricated by just adding a simple film-eroding process after the production of porous AAO. After depositing 50 nm of Au onto the surface, nanowire network AAO can be used as ultrasensitive and high reproducibility surface-enhanced Raman scattering (SERS) substrate. The average Raman enhancement factor of the nanowire network AAO SERS substrate can reach 5.93 × 10⁶, which is about 14% larger than that of commercial Klarite® substrates. Simultaneously, the relative standard deviations in the SERS intensities are limited to approximately 7%. All of the results indicate that our large-area low-cost high-performance nanowire structure AAO SERS substrates have a great advantage in chemical/biological sensing applications.     

Preparation of highly ordered ZnO nanowire arrays by paired-cell deposition

Highly ordered ZnO nanowire arrays were fabricated by paired cell method into nanoporous anodic alumina oxide (AAO) template. ZnO nanowires were uniformly assembled into the ordered channels of the AAO template. TEM and selected-area electron diffraction patterns indicated that the ZnO nanowires grow as a single crystal. The factors influencing the final filled density of ZnO nanowires, including the solution concentration and the diffusing temperature are discussed briefly. In addition, the possible mechanism is also proposed to account for the growth of the ZnO nanowires in the AAO template. This result has established that this paired cell method makes it possible to grow single-crystalline ZnO nanowires in the AAO template under appropriate conditions.     

Fabrication of Pd-Ni alloy nanowire arrays on HOPG surface by electrodeposition

Pd-Ni alloy nanowires with diameters 50-300 nm and lengths of over 250 μm have been obtained by electrochemical step edge decoration (ESED). The fabrication by ESED is accomplished on highly oriented pyrolytic graphite by applying three potential pulses in succession: an oxidizing “activation” pulse, a reducing “nucleation” pulse, and a reducing “growth” pulse. The alloy composition is controlled by adjusting the ion concentration ratio of palladium and nickel, and the deposition processes. The scanning electron microscopy (SEM) images reveal that the alloy nanowires fabricated by this procedure are separate, parallel, and continuous. The composition of alloy nanowires can be controlled in the range of 8-15 wt.% Ni when the ion concentration ratio of palladium and nickel is 7:3 in the solution containing 70 mmol dm⁻³ Pd(NH₃)₄Cl₂. The reaction mechanism involves nucleation at potential of −1.1 V_SCE to −2.0 V_SCE and growth at potential of −0.3 V_SCE to −0.5 V_SCE.     

Formation of Cu/Pd bimetallic crystals by electrochemical deposition

The early stages of the palladium electrodeposition process onto a vitreous carbon (VC) substrate as well as the deposition of Cu on such Pd/VC modified surface were investigated using classical electrochemical techniques, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Within the potential range considered the kinetics of the Pd electrodeposition from a PdCl₂ acid solution can be described by a model involving progressive nucleation on active sites and diffusion-controlled 3D growth. The nucleation rate constant, A₀, and the number of active sites of the substrate, N₀, were determined from the analysis of potentiostatic current transients on the basis of an existing theoretical model. The AFM images corroborated the progressive nucleation mechanism showing irregular palladium crystals randomly distributed over the VC surface, with different sizes and 3D morphological characteristics. The electrodeposition of Cu was carried out onto the characterized Pd/VC modified surface from a Cu²⁺ containing solution using a well defined polarization routine. The SEM/EDX images confirmed the formation of Cu/Pd bimetallic crystals uniformly distributed on the VC surface and the in situ AFM images obtained during this process corroborated that Cu formed a core-shell structure with the Pd crystals. Nevertheless, the subsequent anodic stripping produced only a partial dissolution of the Cu deposits, and therefore, the formation of a Cu/Pd alloy could be inferred.     

Fabrication of diameter-modulated and ultrathin porous nanowires in anodic aluminum oxide templates

Anodic aluminum oxide (AAO) membranes with modulated pore diameter were synthesized by pulse anodization in 0.3 M sulfuric acid at 1 °C. For AAO growth, a typical combination of alternating mild anodizing (MA) and hard anodizing (HA) pulses with applied potential pulses of 25 V and 35 V was applied. The control of the duration of HA pulses will provide an interesting way to tune the shape of pores and the structure of AAO channels. It was found that a non-uniform length of HA segments in cross section of AAO is usually observed when the HA pulse duration is shorter than 1.2 s. The pulse anodization performed with longer HA pulses leads to the formation of AAO templates with periodically modulated pore diameter and nearly uniform length of segments. Various diameter-modulated metallic nanowires (Au, Ag, Ni and Ag–Au) were fabricated by electrodeposition in the pores of anodic alumina membranes. A typical average nanowire diameter was about 30 nm and 48 nm for MA and HA nanowire segments, respectively. After a successful dealloying silver from Ag–Au nanowires, porous ultrathin Au nanowires were obtained.     

Fabrication of cobalt nanowires from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol using porous anodic alumina template

Porous anodic alumina template is synthesized by electrochemical anodization of aluminum and used to grow cobalt nanowires. The cobalt nanowires produced by direct current electrodeposition are characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and physical property measurement system. Test results indicate that the average diameter of cobalt nanowires is about 45 nm, which is generally the same as the pore diameter of porous anodic alumina template, and the cobalt nanowires electrodeposited from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol have a smoother surface and better magnetic properties than cobalt nanowires electrodeposited from aqueous solution, and they show a better squareness. Therefore it can be concluded that the cobalt nanowires electrodeposited from mixture of 1-ethyl-3-methylimidazolium chloride ionic liquid and ethylene glycol using porous anodic alumina template can be used as a perpendicular magnetic recording film.     

Fabrication of cobalt-nickel binary nanowires in a highly ordered alumina template via AC electrodeposition

Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO.     

Microstructures and enhanced flexural properties of single-crystalline HfC nanowires in-situ modified carbon/carbon composites by electrophoresis-thermal evaporation using CNTs as the template

To improve the mechanical properties of carbon/carbon (C/C) composites, in-situ synthetized single-crystalline hafnium carbide nanowires (HfCnws) were introduced into the carbon fiber preforms by electrophoresis-thermal evaporation method. The Multi-walled carbon nanotubes (MWCNTs) were utilized as the carbon source and templates for forming HfCnws. The microstructure, chemical composition and mechanical properties of the HfCnws modified carbon/carbon (HfCnws-C/C) composites were characterized. Results reveal that HfC is produced preferentially in the inner nodular parts and end parts of MWCNTs. The raising heat-treatment temperature would influence the diffusion rate of Hf atoms and then the number of nucleation sites, which further changed the aspect ratio and morphology of HfCnws. The HfCnws have refined the grain size of pyrolytic carbon (PyC), and significantly improve the flexural strength of C/C composites by 79.3%.     

Fabrication of TiO2 nanotubes by using electrodeposited ZnO nanorod template and their application to hybrid solar cells

Vertically aligned TiO₂ nanotubes have been fabricated on the indium-doped tin oxide (ITO) by a simple and versatile technique using the electrochemically deposited ZnO nanorods, oriented along the c-axis, as a template in the spin-on based sol-gel reaction of a Ti precursor. The diameter, length, and shape of TiO₂ nanotubes were controlled by changing the initial ZnO nanorod template and the spin conditions during sol-gel process of a Ti precursor. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) were used to confirm the successful formation of TiO₂ nanotubes and characterize their structure and morphology. Furthermore, as an application of the TiO₂ nanotubes, hybrid solar cells based on TiO₂ and poly[2-methoxy,5-(2′-ethyl-hexyloxy)1,4-phenylenevinylene] (MEH-PPV) were successfully fabricated.     

Studies of phase composition of Zn-Ni alloy obtained in acetate-chloride electrolyte by using XRD and potentiodynamic stripping

The phase composition of Zn-Ni alloy electrodeposited in acetate-chloride electrolyte has been studied as a function of ZnCl₂ concentration and cathodic current density (i_c) by the potentiodynamic stripping and XRD methods. It appeared to be dependent only on the Zn/Ni ratio in the alloy, irrespective of whether the result was attained by varying the cathodic current density or by changing the [Zn²⁺]/[Ni²⁺] ratio in electrolyte. A Zn-Ni alloy dissolving in the potential range of i_a peak D can be obtained by the method of cyclic voltammetry. This phase is a compact black coating. It has been determined by potentiodynamic stripping that pure Ni oxidizes only in the range of positive potentials, while Zn-Ni alloy containing some quantity of Zn oxidizes in the range of negative potentials. It was determined that the preciser data of potentiodynamic stripping were obtained in electrolyte containing Cl⁻ ions. Zn-Ni alloy can be chromated only in the case when the η-phase makes up a sufficiently large portion of Zn-Ni alloy.     

Picosecond carrier dynamics induced by coupling of wavefunctions in a Si-nanodisk array fabricated by neutral beam etching using bio-nano-templates

The picosecond carrier dynamics in a closely packed Si-nanodisk (Si-ND) array with ultrathin potential barrier fabricated by neutral beam etching using bio-nano-templates was investigated by time-resolved photoluminescence (PL). The PL decay curves were analyzed as a function of photon energy by the global fitting method. We show three spectral components with different decay times, where the systematic energy differences of the spectral peaks are clarified: 2.03 eV for the fastest decaying component with a decay time τ = 40 ps, 2.02 eV for τ = 300 ps, and 2.00 eV for τ = 1.6 ns. These energy separations ranging from 10 to 30 meV among the emissive states can be attributed to the coupling of wavefunctions of carriers between neighboring NDs.