Nanopatterning of silicon with use of self-organized porous alumina and colloidal crystals as mask

Nanopatterning processes based on a localized anodization of Si and the subsequent chemical etching of SiO₂ were developed to fabricate a dot array and a hole array on an Si surface using self-organized anodic porous alumina as a mask. Through the porous alumina mask, regularly arranged metal nanopatterns on the Si surface were fabricated by the electroless deposition of Cu nanodots in a CuSO₄/hydrofluoric acid (HF) solution. The periodicity of the Cu dot arrays was determined using the pore interval of the upper anodic alumina. Using self-assembled nanospheres as a mask for an electroless plating of metals such as Cu and Ag on the Si substrate, the patterning of an ordered honeycomb structure and a hexagonally arranged convex array of metals on Si was also developed by the combination of colloidal crystal patterning and wet chemical etching. The proposed patterning processes of the Si surface have potential technological applications in fields that need textured surfaces of controlled nanoscale periodicity and morphology owing to their relative simplicity and low cost.     

Fabricating colloidal crystals and construction of ordered nanostructures

Colloidal crystals of polymeric or inorganic microspheres are of extensive interest due to their potential applications in such as sensing, optics, photonic bandgap and surface patterning. The article highlights a set of approaches developed in our group, which are efficient to prepare colloidal crystals with ordered voids, patterned colloidal crystals on non-planar surfaces, heterogeneous colloidal crystals of different building blocks, colloidal crystals composed of non-spherical polyhedrons, and colloidal crystals of non-close-packed colloidal microspheres in particular. The use of these colloidal crystals as templates for different microstructures range from nanoscale to micron-scale is also summarized.     

(Ba0.5Sr0.5)TiO3 modification on etched aluminum foil for electrolytic capacitor

A new method was proposed to form (Ba_0.5Sr_0.5)TiO₃–Al₂O₃ composite oxide film on etched aluminum foils. The specimens were covered with (Ba_0.5Sr_0.5)TiO₃ (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating.     

Investigations on reducing microbiologically-influenced corrosion of aluminum by using super-hydrophobic surfaces

Electrochemical impedance spectroscopy, potentiodynamic polarization and scanning electron microscopy were carried out to determine the effect of super-hydrophobic surfaces on the marine bacterium Vibrio natriegens (V. natriegens) adhesion. Four different samples were prepared in order to investigate the anti-biocorrosion mechanism of super-hydrophobic surfaces. Potentiodynamic polarization suggested that the V. natriegens attached on the surface mainly enhanced the reaction kinetics of the anodic reaction and accelerated the dissolution of aluminum. EIS results were interpreted with different equivalent circuits to model the physicoelectric characteristics of the electrode/biofilm/solution interface. The results showed that neither anodization nor chemical modification could decrease the bacterial adhesion and corrosion rate individually. V. natriegens showed only weak attachment to the super-hydrophobic surface, and the biocorrosion mechanism was closely associated with surface energy and surface topography.     

Effects of addition of colloidal silica particles on TEOS-based stone protection using n-octylamine as a catalyst

Protective agents based on tetraethoxysilane (TEOS) have been widely used for the protection of stone heritages. However, TEOS-based protective agents suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developed capillary force, which is typical for TEOS-based protective agents. In this paper, we have prepared new TEOS-based protective agent containing flexible hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and colloidal silica particles (167 nm) using n-octylamine as a catalyst in order to reduce capillary force development and increase hydrophobicity, and have characterized them for the application of stone protective agent. The extent of surface hydrophobization depends on concentration of colloidal silica particles and reaches a maximum value of 123° at 0.2% (w/v) of colloidal silica particles for the case of treated with the modified composition. The presence of n-octylamine is a key factor which promotes the increase of the gel pore size. The protective performances were also evaluated by its ability to resist acid corrosion. The results reveal that the protective effects are satisfying.     

Controllable growth of aluminum nanorods using physical vapor deposition

This letter proposes and experimentally demonstrates that oxygen, through action as a surfactant, enables the growth of aluminum nanorods using physical vapor deposition. Based on the mechanism through which oxygen acts, the authors show that the diameter of aluminum nanorods can be controlled from 50 to 500 nm by varying the amount of oxygen present, through modulating the vacuum level, and by varying the substrate temperature. When grown under medium vacuum, the nanorods are in the form of an aluminum metal - aluminum oxide core-shell. The thickness of the oxide shell is ~2 nm as grown and is stable when maintained in ambient for 30 days or annealed in air at 475 K for 1 day. As annealing temperature is increased, the nanorod morphology remains stable while the ratio of oxide shell to metallic core increases, resulting in a fully aluminum oxide nanorod at 1,475 K.     

Fabrication of a novel electrochemical immunosensor based on the gold nanoparticles/colloidal carbon nanosphere hybrid material

The gold nanoparticles/colloidal carbon sphere hybrid material was used for the immobilization of protein, and was developed in biosensing. The hybrid material was fabricated by the assembly of gold nanoparticles onto the surface of colloidal carbon spheres, which constructed a 3D antibody immobilization matrix on the glass carbon electrode and made the immobilized biomolecules hold high stability and bioactivity. After the sandwich-type immunoreaction, the formed HRP-labeled immunoconjugate showed good enzymatic activity for the oxidation of o-phenylenediamine by H₂O₂. The approach provided a linear response range between 5 and 250 ng/mL with a detection limit of 1.8 ng/mL. The immunosensor showed good precision, acceptable stability and reproducibility and could be used for the detection of human IgG in real samples, which provided a potential alternative tool for the detection of protein in clinical laboratory.     

Effect of acid concentration and current density on DC etching of aluminum electrolytic capacitor foil

This work studies the effects of acid concentration and current density on etching morphology, microstructure and static capacity of the aluminum foils used in high-voltage electrolytic capacitors. The behavior associated with electrochemical etching was investigated with a potentiostat. The aluminum etching type of DC etching is greatly influenced by the etching potential. The static capacity increased to 0.65 uF/cm² with 540 V forming voltage by optimization of the etching parameters used in this work.     

Dense and square lattice-free colloid crystals of highly charged monodisperse latex particles on 3-aminopropyl trimethoxysilane-modified glass substrate

Two- and three-dimensional colloid arrays are fabricated using highly charged, monodisperse poly(styrene/sodium p-styrene sulfonate) particles and 3-aminopropyl trimethoxysilane (APTMS)-modified glass substrates at 20 °C. The colloidal array patterns were investigated by SEM, AFM, and UV-visible analyses, and the pattern on the APTMS-modified glass substrate shows a denser packing and square lattice-free pattern without any crevices, as compared with that of cleaned, bare glass substrates. The adhesion force curves obtained from AFM analysis proved a negligible attractive force between APTMS and the poly(St/NaSS) particles. The APTMS layer guaranteed the free-slipping condition to prevent scattered pinnings of drawing particles into the nuclei. Consequently, the free-slipping led to a denser hexagonal close packing and particle deformation by a stronger capillary force arising from the reduced interstices among the particles. As a result, a dense (packing density ∼ 0.80) fcc (or hcp) packing and narrower stop bands were obtained.     

Electrochemical synthesis of poly(o-anisidine) and its corrosion studies as a coating on aluminum alloy 3105

The synthesis of poly(o-anisidine) coatings on aluminum alloy 3105 (AA3105) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by reflection absorption infrared (RAIR) spectroscopy, UV–visible absorption spectrometry and scanning electron microscopy (SEM). Optical absorption spectroscopy reveals the formation of the emeraldine form of poly(o-anisidine). The anticorrosion performances of poly(o-anisidine) coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarization technique Tafle and electrochemical impedance spectroscopy (EIS). The corrosion rate of poly(o-anisidine)-coated AA3105 was found ∼330 times lower than bare AA3105 and potential corrosion increases from −0.85 V versus SCE for uncoated AA3105 to −0.65 V versus SCE for poly(o-anisidine)-coated AA3105 electrodes. The results of this study clearly ascertain that the poly(o-anisidine) has outstanding potential to protect the AA3105 against corrosion in a chloride environment.     

Local deposition of polypyrrole on aluminum by anodizing, laser irradiation, and electrolytic polymerization and its application to the fabrication of micro-actuators

Polypyrrole was deposited at selected areas on aluminum by anodizing, laser irradiation, and electrolytic polymerization, and the application of the technique for fabricating micro-actuators was attempted. Aluminum specimens covered with porous type anodic oxide films were irradiated with a pulsed Nd-YAG laser to remove the oxide films locally, and then thin Ni layers were deposited at areas where film had been removed. Polypyrrole could be successfully deposited only on the Ni layer by anodic polarization of the specimens in pyrrole monomer solution, and a polypyrrole/Ni bilayer structure could be obtained by dissolution of the aluminum substrate and anodic oxide film in NaOH solutions. The bilayer structure was found to be inactive to doping and dedoping of ions during anodic and cathodic polarization. A three-layer structure, nitrocellulose/Ni/polypyrrole, fabricated by electrolytic polymerization after nitrocellulose coating on a Ni layer detached from the aluminum substrate, showed ion-doping and -dedoping activity, suggesting the possibility of fabricating micro-actuators in this manner.     

Electroless plating of aluminum using diisobutyl aluminum hydride as liquid reducing agent in room-temperature ionic liquid

We investigated an electroless aluminum plating based on using AlCl₃–1-ethyl-3-methylimidazolium chloride (AlCl₃–EMIC) ionic liquid with diisobutyl aluminum hydride (DIBAH) as a liquid reducing agent. The plating film was analyzed by measurements of X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX) and glow discharge optical emission spectroscopy (GD-OES). Consequently, a thick aluminum plating film with high uniformity was prepared from AlCl₃–EMIC with DIBAH. No impurity phases were detected. Moreover, we discussed the reaction mechanism of the electroless aluminum plating.     

Effect of noble metal catalyst species on the morphology of macroporous silicon formed by metal-assisted chemical etching

Macroporous silicon with ordered pore intervals was fabricated by the site-selective chemical etching of a Si substrate using patterned noble-metal thin films as a catalyst. The morphology of the etched silicon surface and the etching rate was affected by the shape of deposits and metal catalyst species such as Pt-Pd, Au, and Pt. The etching rate increased in the following order: Au < Pt ≤ Pt-Pd. The pores of macroporous silicon prepared by using Pt-Pd catalyst were conical in shape because of the chemical dissolution of the surface of the macropores. On the other hand, by using Au catalyst, relatively straight pores with uniform diameter were formed in the direction of pore depth. The morphology of macroporous silicon was assumed to be affected by the difference in the shape of metal catalysts and the diffusion behaviour of injected positive holes at the silicon/metal interface.     

Cathodic disbondment of epoxy coating with zinc aluminum polyphosphate as a modified zinc phosphate anticorrosion pigment

As an approach to improve the resistance of protective coatings to the disbondment, modification of the formulation through incorporation of zinc aluminum polyphosphate anticorrosion pigment representing third generation phosphates was examined in this paper. The data obtained from cathodic disbonding test, electrochemical impedance spectroscopy and pull-off indicated that introduction of zinc aluminum polyphosphate within epoxy coating could provide improved resistance to cathodic disbonding as well as superior adhesion strength. The superiority in the presence of the modified pigment was connected to deposition of a layer at the disbonding front and locally controlled pH as well. The precipitation restricting active zone available for electrochemical reaction was confirmed by SEM.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

Nanofabrication on monocrystalline silicon through friction-induced selective etching of Si3N4 mask

A new fabrication method is proposed to produce nanostructures on monocrystalline silicon based on the friction-induced selective etching of its Si₃N₄ mask. With low-pressure chemical vapor deposition (LPCVD) Si₃N₄ film as etching mask on Si(100) surface, the fabrication can be realized by nanoscratching on the Si₃N₄ mask and post-etching in hydrofluoric acid (HF) and potassium hydroxide (KOH) solution in sequence. Scanning Auger nanoprobe analysis indicated that the HF solution could selectively etch the scratched Si₃N₄ mask and then provide the gap for post-etching of silicon substrate in KOH solution. Experimental results suggested that the fabrication depth increased with the increase of the scratching load or KOH etching period. Because of the excellent masking ability of the Si₃N₄ film, the maximum fabrication depth of nanostructure on silicon can reach several microns. Compared to the traditional friction-induced selective etching technique, the present method can fabricate structures with lesser damage and deeper depths. Since the proposed method has been demonstrated to be a less destructive and flexible way to fabricate a large-area texture structure, it will provide new opportunities for Si-based nanofabrication.     

Study on synthesis of low surface area activated carbons using multi-step activation for use in electric double layer capacitor

Low surface area activated carbon derived from compact mesocarbon microbeads (MCMB2010) was synthesized using a lower amount of KOH (1:1 weight ratio of KOH to MCMB) than normally used followed by electrochemical activation. The specific capacitance of the activated carbon heat treated at between 650 and 900 °C was increased up to ca. 118 F/cc (half cell base, 750 °C-heat treated sample) after electrochemical activation, even with a low surface area carbon (<50 m²/g). The morphology of low surface area activated MCMB determined by FE-SEM showed a smooth carbon surface without pores. The charge/discharge profiles were similar to those of conventional activated carbon. The specific capacitance of the activated samples increased with increasing heat treatment up to 850 °C after electrochemical activation. However, it was lower for the sample heat treated at 900 °C.     

Effect of NiS addition on nitridation of alumina to aluminum nitride using polymeric carbon nitride as a nitridation reagent

We investigated the effect of adding nickel(II) sulfide (NiS) on nitridation of alumina (Al₂O₃) to aluminum nitride (AlN) using polymeric carbon nitride (PCN), which was synthesized by polymerization of dicyandiamide at 500 °C. The product powders obtained from nitridation of a mixture of δ-Al₂O₃ and NiS powders (mole ratio of 1:0.01) at various reaction temperatures were characterized by powder X-ray diffraction, ²⁷Al magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. δ-Al₂O₃ began to convert to AlN at 900 °C and completely converted to AlN at 1300 °C. The as-synthesized sample powders contained nitrogen-doped carbon microtubes (N-doped CMTs) with a length of several tens of mm and thickness of ca. 3 µm. The addition of NiS to δ-Al₂O₃ resulted in the enhancement of the amount of N-doped CMTs and nitridation rate, which might be due to the catalytic action of Ni particles on the thermal decomposition of vaporized PCN. The change in Raman spectra with reaction temperatures indicated that the crystallinity of N-doped CMTs was increased by calcining at higher reaction temperatures.     

Structure,mechanical and corrosion properties of DC reactive magnetron sputtered aluminum nitride (AlN) hard coatings on mild steel substrates

Aluminum nitride (AlN) coatings of about 2 μm thick were deposited on mild steel (MS) by means of direct current (DC) reactive magnetron sputtering. AlN coatings were prepared in an Ar + N₂ gas mixture and their crystal structure, microstructure, and topography were analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. XRD revealed that the films are polycrystalline in nature and have a hexagonal wurtzite structure with a predominant peak observed along the (002) plane. SEM and AFM images showed the presence of continuously covered pebble like spherical grains on the surface. These coatings showed lower coefficient of friction and excellent wear resistance compared to the bare MS substrate. The potentiodynamic polarization studies showed lower corrosion current density and higher polarization resistance for the AlN/MS structure than the uncoated MS substrate.     

Characteristics of aluminum films prepared by metalorganic chemical vapor deposition using dimethylethylamine alane on the plasma-pretreated TiN surfaces

Aluminum films were prepared on H₂-plasma pretreated TiN substrates at deposition temperatures of 60-250 °C by metallorganic chemical vapor deposition using dimethylethylamine alane as a precursor. The films were highly pure and the growth rates were 3-50 nm/min, where the lowest deposition temperature was 60 °C. The resistivity was as low as 2.8 μΩcm. High substrate temperatures tended to favor a low resistivity and smooth surface morphology of the films, compared to films with a low temperature at a given thickness. Numerous empty pores appeared in the Al films deposited at a temperature below 150 °C when the film thickness exceeded 200 nm. The number of these pores tended to increase with decrease in temperature. However, in films deposited at temperatures above 200 °C, there were no pores and the large grains were interconnected to a high degree. Higher deposition temperatures yielded a greater preference of the (111) orientation of Al films.