Fabrication Of Nanowire Arrays Research Articles

Block Copolymer-Templated, Single-Step Synthesis of Transition Metal Oxide Nanostructures for Sensing Applications.

The synthesis of transition metal oxide nanostructures, thanks to their high surface-to-volume ratio and the resulting large fraction of surface atoms with high catalytic activity, is of prime importance for the development of new sensors and catalytic materials. Here, we report an economical, time-efficient, and easily scalable method of fabricating nanowires composed of vanadium, chromium, manganese, iron, and cobalt oxides by employing simultaneous block copolymer (BCP) self-assembly and selective sequestration of metal-organic acetylacetonate complexes within one of the BCP blocks. We discuss the mechanism and the primary factors that are responsible for the sequestration and conformal replication of the BCP template by the inorganic material that is obtained after the polymer template is removed. X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (PXRD) studies indicate that the metal oxidation state in the nanowires produced by plasma ashing the BCP template closely matches that of the precursor complex and that their structure is amorphous, thus requiring high-temperature annealing in order to sinter them into a crystalline form. Finally, we demonstrate how the developed nanowire array fabrication scheme can be used to rapidly pattern a multilayered iron oxide nanomesh, which we then used to construct a prototype volatile organic compound sensor.

Constructing geometrically-ordered alumina nanoporous filters and alumina nanowire arrays by using ultrahigh voltage two step anodization

Abstract A simple ultrahigh voltage two-step anodization was developed to fabricate nanopore and nanowire arrays which can be utilized in various applications like water purification filter technology. Investigation of the electrolyte concentration effect on controlling the morphology and geometry of the alumina nanopore and nanowire (ANW) arrays has been done. The anodization was carried out in H2C2O4/H3PO4 mixture at about 0 °C to reach the best ordered nanopores array. In hard anodization step, the current density showed a peak shape profile so that its maximum was directly depended on the H3PO4 concentration. The SEM images of the arrays were studied by image histogram and fast Fourier transform (FFT). The model curves demonstrated direct dependency of the nanopores ordering on electrolyte concentration. The most ordered array was achieved by utilizing 0.3 M H2C2O4 and 0.35 M H3PO4. The SEM images showed that the pores became wider by etching the nanopores in an acidic solution. In addition, fast fabrication of nanowire arrays was achieved by managing the anodization process at 30 °C in a short time. The ANWs were obtained from nanopores etching through the anodization, without an extra etching step requirement. The studies on SEM images demonstrated succeeding high ordered ANWs bundle.

A comparative study on the shape-dependent biological activity of nanostructured zinc oxide

Monitoring and stimulating in biological systems are strongly dependent on the nature of the interfaces between biological systems and devices; in addition, one-dimensional nanostructures show high-charge accumulation at their surfaces which result in forming a conductive pathway between devices and cells. ZnO nanostructures because of their dual semiconducting properties and their piezoelectricity show a great potential to deploy in optoelectronic devices, biosensors and transducers in biological systems. For this purpose, we introduced a novel one-step hydrothermal nanowire array fabrication and compared it with ZnO nanorods array and ZnO compact film. Grazing incidence X-ray Diffraction (GIXRD), field-emission scanning electron microscope (FE-SEM), disperse X-ray spectroscopy (EDS) detector and inductively couples plasma optical emission spectrometry (ICP-OES) were used for physical and chemical characterizations of the arrays. In addition, we investigated the ability of zinc oxide nanostructures to control cell adhesion and viability of neuron-like PC12 cells. Furthermore, we examined the zinc oxide solubility and our results indicated that cytotoxicity were occurred in 2.23 ± 0.41 µg/ml concentration of zinc ions which was much less than the safe amount of zinc ions (10.23 ± 0.41 µg/ml) reported in previous studies. It is believed that ZnO dissociation behavior crucially affects cell fates even in rare amounts.

Thermoelectric property enhancement via pore confinement in template grown bismuth telluride nanowire arrays

Nanostructuring of thermoelectric materials can lead to thermal-to-electrical conversion efficiencies comparable with mechanical energy conversion. Theory predicts that characteristic length scales of <10 nm are necessary to achieve high thermoelectric figures of merit (zT > 3). While sub-10 nm diameter nanowire arrays have been difficult to fabricate, we present here a novel template for sub-10 nm thermoelectric nanowire array fabrication using anodized aluminum oxide followed by silica wall coating for pore confinement. Electrodeposited bismuth telluride nanowires displayed increasing electrical-to-thermal conductivity ratio as the pore diameter decreased, in agreement with theoretical predictions. Achieving the desired stoichiometric ratio of Bi2Te3 through electrodeposition was non-trivial, which limited the Seebeck coefficient of the nanowires. However, hydrolysis of the nanopore walls led to improved electrodeposition, achieving near stoichiometric bismuth-to-tellurium ratios and ultimately p-type thermoelectric nanowire arrays with a Seebeck coefficient of up to 79 μV K−1.

Top-down fabrication of silicon-nanowire arrays for large-scale integration on a flexible substrate for achieving high-resolution neural microelectrodes

In order to implement a nanowire-integrated device, well-aligned arrays of a silicon nanowires are necessary for scalable and repeatable mass production. Especially for biomedical applications in neural engineering, device flexibility robust to mechanical bending, without compromising the electrical performance, is a key issue to be resolved. In this paper, a simple fabrication method and the large-scale integration of silicon-nanowire arrays is proposed by combining top---down fabrication with nanowire transfer on flexible substrate for applications in high-resolution neural stimulation microelectrodes. The arrayed silicon nanowires are fabricated on a p-type, (111)-oriented, single-crystalline-silicon substrate by a top-down process that includes silicon dry etching, silicon wet etching, and wet oxidation. After the fabrication of nanowire arrays, the device is transferred to flexible substrate using polyimide coating, electrode formation, and substrate removal. In order to verify the feasibility of the proposed method, a silicon-nanowire field-effect transistor (FET) switch is implemented and evaluated. The results of the proposed method show an excellent potential for high-resolution neural stimulation microelectrodes.

Thin films of homopolymers and cylinder-forming diblock copolymers under shear.

We study thin films of homopolymers (PS) and monolayers of cylinder-forming diblock copolymers (PS–PHMA) under shear. To this end, we employed both experiments and computer simulations that correctly take into account hydrodynamic interactions and chain entanglements. Excellent quantitative agreement for static as well as dynamic properties in both the homopolymer and diblock copolymer cases was achieved. In particular, we found that the homopolymer thin films exhibit a distinct shear thinning behavior, which is strongly correlated with the disentanglement and shear alignment of the constituent polymer chains. For the PS–PHMA films, we show that shear can be employed to induce long-range ordering to the spontaneously self-assembled microdomains, which is required for many applications such as the fabrication of nanowire arrays. We found that the impact of chemical incompatibility on the viscosity is only minor in shear-aligned films. Once the domains were aligned, the films exhibited an almost Newtonian response to shear because the cylindrical microdomains acted as guide rails, along which the constituent copolymer chains could simply slide. Furthermore, we developed a model for predicting the onset of shear alignment based on equilibrium dynamics data, and found good agreement with our shear simulations. The employed computational method holds promise for a faster and more cost-effective route for developing custom tailored materials.

Engineered fabrication of ordered arrays of Au–NiO–Au nanowires

In the present paper, a novel method to fabricate ordered arrays of Au/NiO/Au nanowires is described, with the aim of filling the gap between the fundamental study of the electrical properties of scattered single nanowires and the engineered fabrication of nanowire arrays. This approach mainly consists of the following steps: (a) electrodeposition of Au/Ni/Au nanowires into an ordered porous anodic aluminum oxide template; (b) mechanical polishing of the sample to expose the gold tips of Au/Ni/Au nanowires to the template surface; (c) in situ annealing of the Au/Ni/Au nanowires without removing the template. The resulting structure consists in an ordered array of Au/NiO/Au nanowires slightly protruding out of a flat aluminum oxide template. Unlike current approaches, with the described method it is not necessary to remove the template in order to oxidize the middle metal, thus allowing the availability of an entire set of metal/oxide/metal nanowires ordered in a two-dimensional matrix and where single heterojunctions can be accessed individually.

Size and Temperature Dependence of the Magnetic Properties of Electrodeposited FeCoNiB Nanowires

Electrodeposited FeCoNiB nanowires with 10% boron in the electrolyte have been investigated. The focus is on studying the effect of their size on the magnetic characteristics. Both the coercivity and the squareness decreased with the increase in the nanowire diameter. The coercivity for out-of-plane (OOP) measurements varied from 41 to 277 Oe for nanowire arrays of different diameters. For nanowires of 20 and 200 nm in diameter the easy axis is in the OOP direction whereas it is in the in-plane (IP) direction for nanowires of 100 nm in diameter. For most of the samples, the OOP coercivity was higher than the IP coercivity, suggesting lower magnetostatic interactions amongst the nanowires. The OOP axis switched from easy to hard when the nanowire length increased beyond a critical value. EDX investigations showed that the atomic concentration of Fe and Co for the templates with pore diameters of 20 and 100 nm did not vary as much as the change observed for the template with a 200 nm pore diameter. The thermal stability of the FeCoNiB nanowires deposited at 9 mA pulsed current was studied over the temperature range 10–300 K. The OOP coercivity increases from 45 Oe at 300 K to 76 Oe at 10 K. Similarly, the squareness increased from 0.01 at 300 K to 0.023 at 10 K. The obtained results are important for the fabrication of nanowire arrays to be used in integrated microsystems.

Anodic Aluminum Oxide Templates for Nickel Nanowires Array Fabrication

This paper reports on the process developed to fabricate anodic aluminum oxide (AAO) templates suitable for the fabrication of nanowires arrays. Anodization process has been used to fabricate the AAO templates with pore diameters ranging from 15 nm to 30 nm. Electrodeposition of parallel arrays of high aspect ratio nickel nanowires were demonstrated using these fabricated AAO templates. The nanowires produced were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the orientations of the electrodeposited nickel nanowires were governed by the deposition current and electrolyte conditions.

Through-hole membranes of nanoporous alumina formed by anodizing in oxalic acid and their applications in fabrication of nanowire arrays

The nanopore arrays were fabricated by two-step self-organized anodization of aluminum carried out in 0.3 M oxalic acid at the temperature of 20 °C. This relatively high temperature shortens significantly the anodizing time and allows to fabricate quickly thick through-hole membranes without the additional operating cost of a cooling circuit. The structural features of anodic porous alumina such as pore diameter, interpore distance, porosity, pore density and pore circularity were investigated at various durations of pore opening/widening process carried out in 5% H 3PO 4. An excellent agreement of AAO structural features measured in FE-SEM images of the studied samples with results from software calculations was observed. The pore shape can be monitored qualitatively by fast Fourier transforms (FFTs) and quantitatively by calculation the percentage of pore circularity. Additionally, the regularity of the hexagonal arrangement of nanopores in through-hole AAO membranes was compared for various opening/widening time ranging from 40 to 100 min. It was shown that three-dimensional (3D) representations of FE-SEM images and their surface-height distribution diagrams provide interesting information about the surface roughness evolution during the pore opening/widening process. A template-assisted fabrication of Ag and Sn nanowire arrays by electrochemical deposition into the pores of the prepared AAO templates was also successfully demonstrated.

Generic nano-imprint process for fabrication of nanowire arrays

A generic process has been developed to grow nearly defect-free arrays of (heterostructured)InP and GaP nanowires. Soft nano-imprint lithography has been used to pattern goldparticle arrays on full 2 inch substrates. After lift-off organic residues remain on the surface,which induce the growth of additional undesired nanowires. We show that cleaning of thesamples before growth with piranha solution in combination with a thermal anneal at550 °C for InPand 700 °C for GaP results in uniform nanowire arrays with 1% variation in nanowire length, andwithout undesired extra nanowires. Our chemical cleaning procedure is applicable to otherlithographic techniques such as e-beam lithography, and therefore represents a genericprocess.

Ordered High‐Density Si [100] Nanowire Arrays Epitaxially Grown by Bottom Imprint Method

Ordered High‐Density Si [100] Nanowire Arrays Epitaxially Grown by Bottom Imprint Method

Template-free one-step electrochemical formation of polypyrrole nanowire array

Oriented polypyrrole nanowire (nanorod) array readily forms using one-step pyrrole electropolymerization without using a template. These nanostructures having diameter in the range of 40–120 nm are obtained by electrogenerating polypyrrole in the presence of jointly non-acidic and weak-acidic anions. The latter are essential, their presence leads to the formation of an overoxidized polypyrrole thin layer that surrounds the polypyrrole nanostructure base. This simple and convenient method allows direct polymer nanowire array fabrication on various conductive substrates, the length of nanostructures being controlled by the polymerization time . Finally, a reaction mechanism involving oxidation of pyrrole and water and polypyrrole overoxidation is discussed.

Silicon nanowire sensor array using top–down CMOS technology

The paper elaborates the silicon nanowire (SiNW) arrays fabrication using standard CMOS compatible technologies (top–down) with each array consisting of 100 wires, which are individually electrically measurable for their conductance and facilitating statistical analysis. To facilitate real-time analysis, the arrays are integrated with micro-fluidics for the delivery of various chemicals for surface modification, buffer solutions, bio-molecules/analytes, etc. The silicon nanowires are also presented as nano-temperature sensors in two configurations, i.e. as resistance temperature detector (RTD) and diode temperature detector (DTD) types. RTD type sensors have shown temperature coefficient of resistance (TCR) values ∼7500ppm/K which are enhanced beyond 10,000ppm/K by the application of back-bias. DTD type sensors using nanowires have recorded more than one order variation in reverse-bias current, in the temperature range of 293–373K. Both the types of nano-temperature sensors are highly sensitive and can be integrated with other bio-chemical sensors in lab-on-chip devices. Nanowire array fabrication details in particular as nano-temperature sensor are elaborated here along with their characterization.