Nanosurface-confined nucleation and patterned growth of Pt and TiO2

The nanosurface-confined nucleation and growth processes of Pt and TiO2 were investigated when Pt was sputter deposited and TiO2 was sol-gel coated on a unique surface-designed substrate. The substrate was an anodic aluminum oxide (AAO) film with self-assembled grouped nanopores (SGNPs). The SGNPs gave rise to unique nucleation sites comprising very small-sized boundaries and nanopores. Pt sputter deposition onto the SGNPs showed restricted growth of nanogranules. The TiO2 sol-gel coating onto the SGNPs resulted in unique formations of nanopore and network structures. The unique nucleation phenomena of Pt and TiO2 on the nanometer-sized surfaces are explained by a combination of two effects: confinement of the degree of freedom at the nucleation sites and growth direction. This is different from conventional surface nucleation that yields the growth of islands, layer-by-layer deposition, and epitaxy.     

Fabrication and magnetic characteristics of vertical feco nanowire arrayed in Al2O3 insulator of honeycomb bulkhead structure

High-density and uniform-sized FeCo alloy nanowires were prepared by electro deposition of Fe2+ and Co2+ into Anodic aluminum oxide (AAO) templates with two different diameters. These templates were fabricated with three-step anodization method. The additional anodization after the 2nd anodization step resulted in the decrease of the thickness of bottom barrier layer. It found an optimum condition to obtain a successful electrodeposition of Fe2+ and Co2+ into AAO templates. The nanowires with the diameters of 25 nm and 80 nm were homogeneously embedded in the AAO templates and their magnetic properties were strongly affected by diameters of nanowire.     

交流电化学沉积FeCo合金纳米线阵列及其磁性能研究

采用二步阳极氧化法制备孔结构高度有序的多孔氧化铝(AAO)模板。在不同Fe2+/Co2+摩尔比的电解液中,利用交流电化学沉积,在模板孔内成功制备了FeCo合金纳米线阵列。分别采用透射电子显微镜(TEM),场发射扫描电子显微镜(FE-SEM),X射线衍射仪(XRD)和震动样品磁强计(VSM)对样品的形貌,结构及磁学性能进行了表征。结果表明,制备的FeCo合金纳米线排列有序,粗细均匀;其直径与模板孔径一致,填充率较高,且具有明显的[110]择优取向。VSM测试结果表明,不同溶液浓度下制备的FeCo合金纳米线阵列均具有良好的垂直磁各向异性,易磁化轴沿着纳米线轴线方向。随着电解液Fe2+/Co2+摩尔比的不同,可在一定范围内对FeCo合金纳米线阵列的磁性进行调控,并对其原因进行了讨论。     

Realignment of slanted Fe nanorods on silicon substrates by a strong magnetic field

Slanted Fe nanorods prepared by glancing angle deposition on silicon substrates exhibited easy magnetization along their growth axis. By using a thin gold film on a silicon substrate as a buffer layer, slanted Fe nanorods can be realigned towards the substrate surface normal by a strong magnetic field. After realignment, the Fe nanorods retained the easy magnetization axis along their growth axis. The effects of the realignment by the strong magnetic field on the properties of the slanted Fe nanorods were also investigated. This study provides a possible way to fabricate magnetic nanostructures for perpendicular recording applications.     

Composition controlling of KNbO3 thin films prepared by pulsed laser deposition

The composition of KNbO₃ thin films prepared by pulsed laser deposition is crucially influenced by the deposition configuration. In the present study, the composition of KNbO₃ thin films grown on Si (100) substrates by pulsed laser ablation was tried to be controlled by adjusting the target-substrate distance and the oblique angle of substrate from the plume axial direction. It was found that the K deficiency in the films can be effectively avoided by setting the substrate at an appropriate oblique angle from the plume axial direction. The stoichiometric KNbO₃ thin films with a K/Nb molar ratio of 0.98 were successfully obtained, where the substrates were set at an oblique angle of 3-12° from the plume axis while the target-substrate distance was kept at 40 mm.     

Fe:O:C grown by focused-electron-beam-induced deposition: magnetic and electric properties

We systematically study the effect of oxygen content on the magneto-transport and microstructure of Fe:O:C nanowires deposited by focused-electron-beam-induced (FEBID) deposition. The Fe/O ratio can be varied with an Fe content varying between ～ 50 and 80 at.% with overall low C content (≈16 ± 3 at.%) by adding H(2)O during the deposition while keeping the beam parameters constant as measured by energy dispersive x-ray (EDX) spectroscopy. The room-temperature magnetic properties for deposits with an Fe content of 66-71 at.% are investigated using the magneto-optical Kerr effect (MOKE) and electric magneto-transport measurements. The nanostructure of the deposits is investigated through cross-sectional high-resolution transmission electron microscopy (HRTEM) imaging, allowing us to link the observed magneto-resistance and resistivity to the transport mechanism in the deposits. These results demonstrate that functional magnetic nanostructures can be created, paving the way for new magnetic or even spintronics devices.     

Role of AAO template filling process parameters in controlling the structure of one-dimensional polymer nanoparticles

Solution template wetting is a common technique used to fabricate elongated polymer nanostructures; however, the parameters controlling the resulting morphology remain unclear. The purpose of this investigation was to elucidate the effects of process variables on the types of nanostructures obtained and to understand the physical mechanisms associated with structure development. 1 wt% polystyrene-THF solutions were infiltrated into commercial and homemade anodized aluminum oxide (AAO) templates. The wetting interaction between the AAO template and the polymer solution was examined through contact angle measurements. In general, for moderate dipping times (<18 h), the morphology of the nanopolymer was rod-like at low molecular weights, while tubes were observed at high molecular weight, even at this low concentration. Nanorods were obtained for all molecular weights for extended dipping times. The data suggest that phase separated layers may grow sequentially from the pore walls and yield nanotubes if the growth is interrupted or produce nanorods for unhindered deposition over long periods.     

The heterostructured AAO/CeO2 nanosystem fabricated by electrodeposition for charge storage and hydrophobicity

Tilted cathode was adopted to prepare porous anodic alumina membrane (PAAM) during the second aluminum anodic oxidation (AAO). A heterostructured AAO/CeO₂ nanosystem was fabricated by filling CeO₂ into the PAAM by electrochemical deposition. The larger the intersection angle of the cathode, the more the charge storage of the fabricated system. A lower potential scan rate is beneficial to the electrochemical charge storage of the system. With the cathode intersection angle increasing, the hydrophobicity of the AAO/CeO₂ system is greatly improved. As the 40° is the optimum angle, the charge storage and hydrophobicity of the system increase with the increasing cathode intersection angle up to 40°. The AAO/CeO₂ system could be utilized in both charge storage and self-cleaning.     

Fabrication of ZnO nanostructure within the AAO template by electrochemical deposition

This paper presents a simple and efficient method to prepare ZnO nanostructure by anodic aluminum oxide (AAO) template-assisted growth combined with DC electrochemical deposition. Scanning electron microscopy results indicate that the morphology of the AAO basically present highly ordered hexagonal distribution, and the pore size and inter-pore distance is 55 and 100 nm, respectively. X-Ray diffraction reveals that the AAO template is amorphous, and the ZnO nano-particles within the AAO have wurtzite structure. Photoluminescence spectra demonstrate that ZnO/AAO has a strong blue emission at 419 nm compared with AAO, the intensity is about 8 times stronger than that of AAO template.     

Assembly of Colloidal Nanoparticles into Anodic Aluminum Oxide Templates by Dip-Coating Process

In this paper, the assembly behavior of colloidal nanoparticles into anodic aluminum oxide (AAO) templates is investigated. Approximately 20-nm-diameter iron oxide ($hbox{Fe}_{2}hbox{O}_{3}$ ) particles stabilized by oleic acid and 5-nm-diameter CdSe coated by thin ZnS and stabilized by trioctylphosphine oxide and dispersed in octane solvent are integrated into AAO pores with an average pore diameter of $sim$30–100 nm by dip-coating process. The particles assemble selectively at the bottom of pores. Also, the multiple stacks of particles are obtained selectively inside the pores by sequentially repeating dip coating and removing the surfactants (oleic acid) from the particle layer. The nanoparticles integrated into nanometer-scale AAO templates produce the nanostructures for potential applications such as high-density patterned magnetic media, patterned nanoparticle layers for memory device, seeds for nanowire growth, and so on.      

Fabrication and magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline nanotubes

Aligned NiFe₂O₄ polycrystalline nanotubes have been successfully fabricated inside the nanochannels of porous anodic aluminum oxide (AAO) templates by wetting chemical deposition. A mixture of Fe nitrate and Ni nitrate, which was thermally decomposed at no less than 400 °C, was used to yield NiFe₂O₄ tubes. By varying the deposition conditions and the parameters of the templates, we could tailor the lengths and the outer as well as the inner diameters of the tubes. Transmission electron microscopy (TEM) images reveal that the nanotubes are uniform and well isolated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) demonstrate that the as-obtained nanotubes can be indexed to polycrystalline cubic spinel. The Mössbauer spectra show that the magnetic hyperfine field is reduced with the decrease of the metrical temperature as well as the decrease of the size of nanoparticles.     

Metal-Containing Poly(tetrafluoroethylene): A Novel Material

A method is described for preparing isolated Fe nanoparticles on the surface of poly(tetrafluoroethylene) (PTFE) nanogranules. The composition and atomic structure of the nanoparticles are investigated by transmission electron microscopy and EXAFS, x-ray emission, and Mössbauer spectroscopic techniques. The nanoparticles have a complex composition and structure and contain -Fe (15%). The majority phase in the nanoparticles is iron carbide (48%). On the surface of the PTFE nanogranules, the nanoparticles react with fluorine, forming Fe–F bonds (12% FeF₂). The free surface of the nanoparticles, noninteracting with fluorine, is oxidized by oxygen to form Fe₂O₃ (25%). A model for the structure of the nanoparticles is described.     

Fabrication of highly ordered anodic aluminium oxide templates on silicon substrates

The controlled fabrication of highly ordered anodic aluminium oxide (AAO) templates of unprecedented pore uniformity directly on Si, enabled by new advances on two fronts - direct and timed anodisation of a high-purity Al film of unprecedented thickness (50 mum) on Si, and anodising a thin but pre-textured Al film on Si, has been reported. To deposit high-quality and ultra-thick Al on a non-compliant substrate, a prerequisite for obtaining highly ordered pore arrays on Si by self-organisation while retaining a good adhesion, a specially designed process of e-beam evaporation followed by in situ annealing has been deployed. To obtain an AAO template with the same high degree of ordering and uniformity but from a thin Al film, which is not achievable by the self-organisation alone, pre-patterning of the thin Al surface by reactive ion etching using a freestanding AAO mask that was formed in a separate process was performed. The resultant AAO/Si template provides a good platform for integrated growth of nanotube, nanowire or nanodot arrays on Si. Template-assisted growth of carbon nanotubes (CNTs) directly on Si was demonstrated via a chemical vapour deposition method. By controllably removing the AAO barrier layer at the bottom of the pores and partially etching back the AAO top surface, new CNT/Si structures were obtained with potential applications in field emitters, sensors, oscillators and photodetectors.     

Nanomechanical and surface behavior of polydimethylsiloxane-filled nanoporous anodic alumina

In this article, the mechanical and wetting behavior of anodic aluminum oxide (AAO) and nanoporous-filled AAO were investigated using nanoindentation and contact angle measurements. The results showed that the nanoporous AAO was hydrophobic with a contact angle of 105°. The polymer filling affected the surface property and reduced the contact angle to 84°. The effects of the nanoporous filling on the Young’s modulus and the hardness are investigated and discussed. A three-dimensional finite element model was also successfully developed to understand the nanoindentation-induced mechanism. A maximum von Mises stress of 1058 MPa occurred beneath the indenter.     

Niobium and hafnium grown on porous membranes

In this work we report on a method for fabricating highly ordered nanostructures of niobium and hafnium metals by physical vapour deposition using two different templates: anodized aluminum oxide membranes (AAO) and zirconium onto AAO membranes (Zr/AAO). The growth mechanism of these metal nanostructures is clearly different depending on the material used as a template. A different morphology was obtained by using AAO or Zr/AAO templates: when the metal is deposited onto AAO membranes, nanospheres with ordered hexagonal regularity are obtained; however, when the metal is deposited onto a Zr/AAO template, highly ordered nanocones are formed. The experimental approach described in this work is simple and suitable for synthesizing nanospheres or nanoholes of niobium and hafnium metals in a highly ordered structure.     

Finite-size effect on magnetic properties in iron sulfide nanowire arrays

We report the size effect on the magnetic properties in Fe(7)S(8) nanowire arrays. Samples with diameters in the range of 50-200?nm have been prepared by electrodeposition with AAO films. The M?ssbauer measurement results show that four parameters (hyperfine fields, isomer shift, quadrupole splitting, full width at half-maximum) increased with decreasing the diameter of the nanowires. The magnetic properties were investigated. The hysteresis loop shape and the magnetization are dependent on the diameter of the nanowires. The thermomagnetic measurements on the as-synthesized nanowire samples and the corresponding bulk display a mixed-type curve and a Weiss-type curve, respectively.     

Influence of different conducting substrates on magnetic properties of electrodeposited Ni–Fe thin films

Electrodeposition of Ni–Fe soft magnetic alloy on copper and stainless steel substrates was performed in chloride bath. The deposition parameters such as current density, pH, temperature and deposition time have been investigated. From the investigation the optimized deposition parameters were current density 3.5 mA/cm², pH 3, temperature 30 °C and deposition time 15 min. The Ni–Fe magnetic alloys deposited on copper and stainless steel substrates under optimized deposition parameters are subjected to various characterizations. The structural and surface morphology of the Ni–Fe films were detected by using X-ray diffractogram (XRD) and scanning electron microscope (SEM) respectively. The constituents in the films were determined by energy dispersive X-ray spectroscopy (EDAX) technique. The magnetic properties such as the coercivity (H_c) and saturation magnetization of the films were studied with the help of vibrating sample magnetometer (VSM). From the magnetic studies it is concluded that the grain size are create a considerable impact on magnetic behavior of the films on both the substrates. The films prepared on stainless steel substrate of 0.1 M concentration at optimized deposition parameters exhibits higher coercivity (5010 Oe) which seems to be ideal for magnetic sensor applications.     

Growth, structure, and properties of BiFeO3/-BiCrO3 films obtained by dual cross beam PLD

The properties of epitaxial Bi(2)FeCrO(6) thin films, recently synthesized by pulsed laser deposition, have partially confirmed the theoretical predictions (i.e., a magnetic moment of 2 micro(B) per formula unit and a polarization of approximately 80 microC/cm(2) at 0 K). The existence of magnetic ordering at room temperature for this material is an unexpected, but very promising, result that needs to be further investigated. Because magnetism is assumed to arise from the exchange interaction between the Fe and Cr cations, the magnetic behavior is strongly dependent on both their ordering and the distance between them. We present here the successful synthesis of epitaxial Bi(2)Fe(x)CryO(6) (BFCO x/y) films grown on SrTiO3 substrates using dual crossed-beam, pulsed-laser deposition. The crystal structure of the films has different types of (111)-oriented superstructures, depending on the deposition conditions. The multiferroic character of BFCO (x/y) films is proven by the presence of both ferroelectric and magnetic hysteresis at room temperature. The oxidation state of Fe and Cr ions in the films is shown to be 3+ only, and the difference in macroscopic magnetization with Fe/Cr ratio composition could only be due to ordering of the Cr(3+) and Fe(3+) cations to the modification of the exchange interaction between them.     

Nanopore gradients on porous aluminum oxide generated by nonuniform anodization of aluminum

A method for surface engineering of structural gradients with nanopore topography using the self-ordering process based on electrochemical anodization of aluminum is described. A distinct anodization condition with an asymmetrically distributed electric field at the electrolyte/aluminum interface is created by nonparallel arrangement between electrodes (tilted by 45°) in an electrochemical cell. The anodic aluminum oxide (AAO) porous surfaces with ordered nanopore structures with gradual and continuous change of pore diameters from 80 to 300 nm across an area of 0.5-1 cm were fabricated by this anodization using two common electrolytes, oxalic acid (0.3 M) and phosphoric acid (0.3 M). The formation of pore gradients of AAO is explained by asymmetric and gradual distribution of the current density and temperature variation generated on the surface of Al during the anodization process. Optical and wetting gradients of prepared pore structures were confirmed by reflective interferometric spectroscopy and contact angle measurements showing the ability of this method to generate porous surfaces with multifunctional gradients (structural, optical, wetting). The study of influence of pore structures on cell growth using the culture of neuroblastoma cells reveals biological relevance of nanopore gradients and the potential to be applied as the platform for spatially controllable cell growth and cell differentiation.     

Synthesis of metallic nanotube arrays in porous anodic aluminum oxide template through electroless deposition

Ordered Co, Ni and Cu nanotubes embedded in a porous anodic aluminum oxide (AAO) membrane were fabricated by electroless deposition. The results show that the length of the nanotubes is determined by the thickness of the AAO template and the outside diameter of the nanotubes is determined by the pore size of the AAO template. The factors that impact on the growth of metallic nanotubes are also discussed.