Ion-beam pore opening of porous anodic alumina: The formation of single nanopore and nanopore arrays

Anodized aluminium oxide (AAO) fabricated by electrochemical anodization of aluminium is used as the substrate for focused ion-beam (FIB) fabrication of single nanopore and nanopore arrays. The method is based on the controlled and selective removal of AAO barrier oxide film by FIB milling. FIB process with different milling conditions is applied to open single nanopores (diameter of 60 nm) or circular nanopore arrays with a different number of opened pores on AAO substrate. This process combines a low cost AAO substrate and FIB milling, and offers an economically viable alternative for the fabrication of nanopore devices with controlled dimensions for a range of applications in nanofluidics, molecular separations and biosensing.     

Large-area hard magnetic L10-FePt nanopatterns by nanoimprint lithography

Large-area hard magnetic L1(0)-FePt nanopatterns with out-of-plane texture were fabricated by using a top-down approach. For the fabrication process, ultraviolet nanoimprint lithography (UV-NIL) in combination with inductively coupled plasma reactive Ar-ion etching was used. By this technique a continuous L1(0)-Fe(51)Pt(49) film was nanostructured into a regular arrangement of nanodots over an area of 4 mm(2). The dot dimension and distribution was specified by the stamp, resulting in a dot size of 60 nm and a periodicity of 150 nm. For the large-scale L1(0)-FePt nanopatterns, huge coercivities up to 4.31 T could be achieved. By means of magnetic force microscopy it could be verified that the nanodots were magnetically decoupled from each other and occurred in the single-domain state with perpendicular magnetization.     

Versatile gradients of chemistry, bound ligands and nanoparticles on alumina nanopore arrays

Nanoporous alumina (PA) arrays produced by self-ordering growth, using electrochemical anodization, have been extensively explored for potential applications based upon the unique thermal, mechanical and structural properties, and high surface-to-volume ratio of these materials. However, the potential applications and functionality of these materials may be further extended by molecular-level engineering of the surface of the pore rims. In this paper we present a method for the generation of chemical gradients on the surface of PA arrays based upon plasma co-polymerization of two monomers. We further extend these chemical gradients, which are also gradients of surface charge, to those of bound ligands and number density gradients of nanoparticles. The latter represent a highly exotic new class of materials, comprising aligned PA, capped by gold nanoparticles around the rim of the pores. Gradients of chemistry, ligands and nanoparticles generated by our method retain the porous structure of the substrate, which is important in applications that take advantage of the inherent properties of these materials. This method can be readily extended to other porous materials.     

Hierarchical structural nanopore arrays fabricated by pre-patterning aluminum using nanosphere lithography

A highly ordered and hierarchical structural nanopore array is fabricated via anodizing a pre-patterned aluminum foil under an optimized voltage. A pre-patterned hexagonal nanoindentation array on an aluminum substrate is prepared via the nanosphere lithography method. This pattern leads to an elaborate nanochannel structure with seven nanopores in each nanoindentation after anodization treatment. The structure achieved in our study is new, interesting, and likely to be applied in photonic devices.     

Variation of nanopore diameter along porous anodic alumina channels by multi-step anodization

In order to form tapered nanocapillaries, we investigated a method to vary the nanopore diameter along the porous anodic alumina (PAA) channels using multi-step anodization. By anodizing the aluminum in either single acid (H3PO4) or multi-acid (H2SO4, oxalic acid and H3PO4) with increasing or decreasing voltage, the diameter of the nanopore along the PAA channel can be varied systematically corresponding to the applied voltages. The pore size along the channel can be enlarged or shrunken in the range of 20 nm to 200 nm. Structural engineering of the template along the film growth direction can be achieved by deliberately designing a suitable voltage and electrolyte together with anodization time.     

The fabrication of highly ordered silver nanodot patterns by platinum assisted nanoimprint lithography

Silver has been widely used for optical sensing and imaging applications which benefit from localized surface plasmon resonance (LSPR) in a nanoscale configuration. Many attempts have been made to fabricate and control silver nanostructures in order to improve the high performance in sensing and other applications. However, a fatal mechanical weakness of silver and a lack of durability in oxygen-rich conditions have disrupted the manufacturing of reproducible nanostructures by the top-down lithography approach. In this study, we suggest a steady fabrication strategy to obtain highly ordered silver nanopatterns that are able to provide tunable LSPR characteristics. By using a protecting layer of platinum on a silver surface in the lithography process, we successfully obtained large-area (2.7 × 2.7 mm(2)) silver nanopatterns with high reproducibility. This large-area silver nanopattern was capable of enhancing the low concentration of a Cy3 fluorescence signal (～10(-10) M) which was labeled with DNA oligomers.     

Nanopore domain growth behavior by nanopore changes near domain boundaries in porous anodic alumina

We investigate the nanopore changes near domain boundaries during the nanopore growth in porous anodic alumina (PAA) to understand the domain growth behavior with the anodization time. In order to observe the pore changes with the time, we analyze cleavage planes of PAA according to the nanopore length using a field emission scanning electron microscopy. The domain growth can be explained with three kinds of nanopore changes observed near domain boundaries: a change of pore diameter, a pore-branching, and a pore-movement.     

Defects analysis in self-organized nanopore arrays formed by anodization of aluminium at various temperatures

The self-organized anodization of aluminium in sulphuric acid was employed for formation of high-density nanostructures at various cell potentials and temperatures. The well-ordered arrangement of nanopores was obtained by two-step anodization process. The qualitative and quantitative analyses of defects were performed from SEM images of nanostructures. The Fourier transform (FFT) analyses showed that the uniformity of the triangular lattice increases gradually with increasing anodising potential independently of temperature. The order in the nanopore arrangement and size of well-ordered domains increase with increasing anodising potential for all studied temperatures. Quantitative analyses of defects, known as Delanuay triangulations, were performed for various anodising potentials and temperatures. The percentage of generated defects is constant at the cell potential between 15 and 23 V. At the temperature of 1 degree C, the percentage of defects equals to 20% while at temperatures of -8 or 10 degrees C reaches a value of about 30%. At the anodising potential of 25 V the percentage of generated defects in porous alumina is drastically reduced to about 10%, independently of the anodising temperature. The perfect nanopore arrangement on the anodised surface with the smallest number of defects can be obtained at 25 V.     

Fabrication of large number density platinum nanowire arrays by size reduction lithography and nanoimprint lithography

Large number density Pt nanowires with typical dimensions of 12 microm x 20 nm x 5 nm (length x width x height) are fabricated on planar oxide supports. First sub-20 nm single crystalline silicon nanowires are fabricated by size reduction lithography, and then the Si nanowire pattern is replicated to produce a large number of Pt nanowires by nanoimprint lithography. The width and height of the Pt nanowires are uniform and are controlled with nanometer precision. The nanowire number density is 4 x 10(4) cm(-1), resulting in a Pt surface area larger than 2 cm(2) on a 5 x 5 cm(2) oxide substrate. Bimodal nanowires with different width have been generated by using a Pt shadow deposition technique. Using this technique, alternating 10 and 19 nm wide nanowires are produced.     

Inherently reproducible fabrication of plasmonic nanoparticle arrays for SERS by combining nanoimprint and copolymer lithography

We present an inherently reproducible route to realizing high-performance SERS substrates by exploiting a high-throughput top-down/bottom-up fabrication scheme. The fabrication route employs self-assembly of amphiphilic copolymers to create high-resolution molds for nanoimprint lithography (NIL) spanning entire 100 mm Si wafers. The nanoporous polymer templates obtained upon NIL are subjected to galvanic displacement reactions to create gold nanorod arrays. Nanorods are subsequently converted to nanodiscs by thermal annealing. The nanodiscs were found to perform as robust SERS substrates as compared with the nanorods. The SERS performance of these substrates and its generality for catering to diverse molecules is demonstrated through the excellent Raman peak resolution and intensity for three different molecules, exhibiting different interaction modes on surface. Numerical simulations using FDTD shows plasmonic coupling between the particles and also brings out the influence due to size distribution. The approach combines distinct advantages of high-precision and repeatability offered by NIL with low-cost fabrication of high-resolution NIL molds by copolymer self-assembly.     

Improved sensing characteristics of dual-gate transistor sensor using silicon nanowire arrays defined by nanoimprint lithography

Abstract

This work describes the construction of a sensitive, stable, and label-free sensor based on a dual-gate field-effect transistor (DG FET), in which uniformly distributed and size-controlled silicon nanowire (SiNW) arrays by nanoimprint lithography act as conductor channels. Compared to previous DG FETs with a planar-type silicon channel layer, the constructed SiNW DG FETs exhibited superior electrical properties including a higher capacitive-coupling ratio of 18.0 and a lower off-state leakage current under high-temperature stress. In addition, while the conventional planar single-gate (SG) FET- and planar DG FET-based pH sensors showed the sensitivities of 56.7 mV/pH and 439.3 mV/pH, respectively, the SiNW DG FET-based pH sensors showed not only a higher sensitivity of 984.1 mV/pH, but also a lower drift rate of 0.8% for pH-sensitivity. This demonstrates that the SiNW DG FETs simultaneously achieve high sensitivity and stability, with significant potential for future biosensing applications.     

Patterned self-assembly of gold nanoparticles on chemical templates fabricated by soft UV nanoimprint lithography

Chemical templates for the patterned immobilization of gold nanoparticles were fabricated by soft UV nanoimprint lithography. The template structures were fabricated by means of the consecutively performed process steps of nanoimprint lithography, reactive ion etching, chemical functionalization with amino groups, and lift-off of imprint resist. These chemical templates were used for the defined assembly of 20 nm diameter citrate stabilized gold nanoparticles from aqueous solution. By reducing the ionic strength of the solution, one- and zero-dimensional particle assemblies were generated on sub-100-nm template structures. By this means, the pattern resolution predefined by the lithography process could be easily enhanced by dilution of the nanoparticle solution.     

微波辅助共沉淀法制备NiZnCu铁氧体纳米粉体研究

以硝酸铁、硝酸铜、硝酸镍和硝酸锌为原料,采用微波辅助共沉淀法制备了NiZnCu铁氧体纳米粉体,研究了微波的引入对纳米粉体制备的影响,通过XRD、TG-DTG、激光粒度分析和TEM表征了粉体的结晶性能,热性能,粒度以及粉体的形貌.研究表明,微波的引入可以明显加速晶化反应的进行,在较短时间内制得的纳米晶发育好于同温度下传统热处理方式制得的NiZnCu铁氧体纳米晶.研究表明,通过15min的微波辅助加热,可制得粒径在10nm左右的NiZnCu铁氧体纳米晶.     

Formation of uniform and square nanopore arrays on (100) InP surfaces by a two-step etching method

Uniform and square single-crystal InP nanopore arrays have been successfully fabricated on a (100) n-InP surface by a two-step etching method. The characteristic of slow etching rates in four equivalent crystalline (011) facets of (100) n-InP in a mixture of pure HCl and pure H(3)PO(4) has been found, which is the main reason for the formation of square single-crystal InP nanopores. The distribution of nanopores can be closely associated with the distribution of carriers in the semiconductor during the electrochemical etching process. An oscillating behaviour of current has been observed, which can probably be attributed to the oscillations in concentration of the electrolyte at the pore tips caused by diffusion of the electrolyte in the nanopore channels.     

Silica-sandwiched Au nanoparticle arrays by a soft PE-CVD/RF sputtering approach

This work is focused on the development of an innovative synthetic route to SiO(2)-sandwiched Au nanoparticle arrays. The adopted strategy consists of: (i) the radio frequency sputtering of gold on thermally oxidized Si(100) and silica substrates from Ar plasmas; (ii) the plasma enhanced chemical vapor deposition of a SiO(2) overlayer using tetramethoxysilane as precursor from Ar-O(2) plasmas. A common feature of both preparative stages is the use of very soft processing conditions at temperatures close to room temperature, in order to tailor the Au nanoparticle morphology and to preserve it upon SiO(2) coverage. In situ monitoring of gold deposition was accomplished by means of laser reflection interferometry. Valuable information on the system morphology before and after SiO(2) coverage was provided by field emission-scanning electron microscopy for samples with different Au content. Additional important information on the system chemical composition, structure and optical response was gained by the combined use of x-ray photoelectron spectroscopy, glancing incidence x-ray diffraction and UV-visible absorption spectroscopy. The results obtained highlight the formation of high-purity SiO(2)/Au/SiO(2)-sandwiched stacks, in which the gold content and distribution, as well as the nanoparticle morphology, could be tailored by the sole variation of the sputtering time, without any further ex situ treatment.     

Fabrication of metallic nanowire arrays by electrodeposition into nanoporous alumina membranes: effect of barrier layer

Deposition into nanoporous alumina membranes is widely used for nanowire fabrication. Herein using AC electrodeposition ternary Fe–Co–Ni nanowires are fabricated within the nanoscale-pores of alumina membranes. Using an electrodeposition frequency of 1,000 Hz, 15 V_rms, consistently and repeatably yield nanowire arrays over membranes several cm² in extent. Electrochemical Impedance Spectroscopy (EIS) is used to explain the effects of AC electrodeposition frequency. The impedance of the residual alumina barrier layer, separating the underlying aluminum metal and the nanoporous membrane, decreases drastically with electrodeposition frequency facilitating uniform pore-filling of samples several cm² in area. Anodic polarization studies on thin films having alloy compositions identical to the nanowires display excellent corrosion resistance properties.     

AlN nanorod and nanoneedle arrays prepared by chloride assisted chemical vapor deposition for field emission applications

Hexagonal AlN nanorod and nanoneedle arrays were synthesized through the direct reaction of AlCl(3) and NH(3) by chemical vapor deposition at about 750?°C. Both the AlN nanoneedle and nanorod samples were of wurtzite structure and grew preferentially along the c-axis. With an increase in the ratio of NH(3) to Ar, an evolution from nanorods to nanoneedles was observed. A growth model was proposed to explain the possible growth mechanism. Measurements in field emission show that AlN nanoneedle arrays have a much lower turn-on field (3.1?V?μm(-1)) compared to nanorod arrays (15.3?V?μm(-1)), due to their large curvature geometry. The AlN nanoneedle arrays have potential applications in many fields, such as electron-emitting nanodevices and field-emission-based flat-panel displays.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

Enhancement of light extraction efficiency of ultraviolet light emitting diodes by patterning of SiO2 nanosphere arrays

Here we introduce a simple and robust method to improve the light extraction efficiency of ultraviolet light emitting diodes (UV LEDs). Although many previous efforts have focused on etching the GaN surfaces, we employed a simple solution process to texture the GaN surface. Arrays of SiO₂ nanosphere monolayers were spun cast onto a polymer layer, consisting of benzocyclobutene (BCB) resins; subsequently, the bottom half of the SiO₂ nanospheres sunk into the BCB layer. The resulting array formed in a hexagonal-like pattern of ‘nano-lenses’ and the photoluminescence measurement exhibited that these patterns enhanced the light extracting efficiency of UV LEDs by 23%.