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1.  Programmable nanoengineering templates for fabrication of three-dimensional nanophotonic structures 
Nanoscale Research Letters  2013;8(1):268.
Porous anodic alumina membranes (AAMs) have attracted great amount of attention due to their potential application as templates for nanoengineering. Template-guided fabrication and assembly of nanomaterials based on AAMs are cost-effective and scalable methods to program and engineer the shape and morphology of nanostructures and nanomaterials. In this work, perfectly ordered AAMs with the record large pitch up to 3 μm have been fabricated by properly controlling the anodization conditions and utilization of nanoimprint technique. Due to the capability of programmable structural design and fabrication, a variety of nanostructures, including nanopillar arrays, nanotower arrays, and nanocone arrays, have been successfully fabricated using nanoengineered AAM templates. Particularly, amorphous Si nanocones have been fabricated as three-dimensional nanophotonic structures with the characterization of their intriguing optical anti-reflection property. These results directly indicate the potential application of the reported approach for photonics and optoelectronics.
doi:10.1186/1556-276X-8-268
PMCID: PMC3685551  PMID: 23742170
Large-pitch anodic alumina membranes; Programmable nanoengineering templates; Nanocones; Three-dimensional nanophotonic structures
2.  Cobalt and Nickel Nanopillars on Aluminium Substrates by Direct Current Electrodeposition Process 
Nanoscale Research Letters  2009;4(9):1021-1028.
A fast and cost-effective technique is applied for fabricating cobalt and nickel nanopillars on aluminium substrates. By applying an electrochemical process, the aluminium oxide barrier layer is removed from the pore bottom tips of nanoporous anodic alumina templates. So, cobalt and nickel nanopillars are fabricated into these templates by DC electrodeposition. The resulting nanostructure remains on the aluminium substrate. In this way, this method could be used to fabricate a wide range of nanostructures which could be integrated in new nanodevices.
doi:10.1007/s11671-009-9351-5
PMCID: PMC2894324  PMID: 20596338
Nanoporous anodic alumina membranes; Transfer mask; Metallic nanopillars; Electrodeposition
3.  Cobalt and Nickel Nanopillars on Aluminium Substrates by Direct Current Electrodeposition Process 
Nanoscale Research Letters  2009;4(9):1021-1028.
A fast and cost-effective technique is applied for fabricating cobalt and nickel nanopillars on aluminium substrates. By applying an electrochemical process, the aluminium oxide barrier layer is removed from the pore bottom tips of nanoporous anodic alumina templates. So, cobalt and nickel nanopillars are fabricated into these templates by DC electrodeposition. The resulting nanostructure remains on the aluminium substrate. In this way, this method could be used to fabricate a wide range of nanostructures which could be integrated in new nanodevices.
doi:10.1007/s11671-009-9351-5
PMCID: PMC2894324  PMID: 20596338
Nanoporous anodic alumina membranes; Transfer mask; Metallic nanopillars; Electrodeposition
4.  Theoretical Simulation and Focused Ion Beam Fabrication of Gold Nanostructures For Surface-Enhanced Raman Scattering (SERS) 
This paper describes the fabrication of gold nanopillar and nanorod arrays and theoretical calculations of electromagnetic fields (EMFs) around ordered arrangements of these nanostructures. The EMFs of both single nanopillars and di-mers of nanopillars - having nanoscale gaps between the two adjacent nanopillars forming the di-mers - are simulated in this work by employing the Finite Difference Time Domain (FDTD) method. In the case of simulations for di-mers of nanopillars, the nano-scale gaps between the nanopillars are varied between 5 nm and 20 nm and calculations of the electromagnetic fields in the vicinity of the nanopillars and in the gaps between the nanopillars were carried out. Fabrication of gold nanopillars in a controlled manner for forming SERS substrates involves focused ion beam (FIB) milling. The nanostructures were fabricated on gold-coated silica, mica, and quartz planar substrates as well as on gold-coated tips of four mode and multimode silica optical fibers.
doi:10.1007/s12030-008-9017-x
PMCID: PMC3748982  PMID: 23976888
5.  Rapid fabrication of self-ordered porous alumina with 10-/sub-10-nm-scale nanostructures by selenic acid anodizing 
Scientific Reports  2013;3:2748.
Anodic porous alumina has been widely investigated and used as a nanostructure template in various nanoapplications. The porous structure consists of numerous hexagonal cells perpendicular to the aluminum substrate and each cell has several tens or hundreds of nanoscale pores at its center. Because the nanomorphology of anodic porous alumina is limited by the electrolyte during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. In this study, we report a new self-ordered nanoporous alumina formed by selenic acid (H2SeO4) anodizing. By optimizing the anodizing conditions, anodic alumina possessing 10-nm-scale pores was rapidly assembled (within 1 h) during selenic acid anodizing without any special electrochemical equipment. Novel sub-10-nm-scale spacing can also be achieved by selenic acid anodizing and metal sputter deposition. Our new nanoporous alumina can be used as a nanotemplate for various nanostructures in 10-/sub-10-nm-scale manufacturing.
doi:10.1038/srep02748
PMCID: PMC3782885  PMID: 24067318
6.  Ordered arrays of nanoporous silicon nanopillars and silicon nanopillars with nanoporous shells 
The fabrication of ordered arrays of nanoporous Si nanopillars with and without nanoporous base and ordered arrays of Si nanopillars with nanoporous shells are presented. The fabrication route is using a combination of substrate conformal imprint lithography and metal-assisted chemical etching. The metal-assisted chemical etching is performed in solutions with different [HF]/[H2O2 + HF] ratios. Both pore formation and polishing (marked by the vertical etching of the nanopillars) are observed in highly doped and lightly doped Si during metal-assisted chemical etching. Pore formation is more active in the highly doped Si, while the transition from polishing to pore formation is more obvious in the lightly doped Si. The etching rate is clearly higher in the highly doped Si. Oxidation occurs on the sidewalls of the pillars by etching in solutions with small [HF]/[H2O2 + HF] ratios, leading to thinning, bending, and bonding of pillars.
doi:10.1186/1556-276X-8-42
PMCID: PMC3570473  PMID: 23336430
Nanoporous Si; Pillars; Nanowires; Metal-assisted chemical etching; Nanoimprint lithography
7.  Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina 
Nanoscale Research Letters  2011;6(1):487.
Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting.
doi:10.1186/1556-276X-6-487
PMCID: PMC3212001  PMID: 21827683
superhydrophobic surfaces; surface modification; hexamethyldisilazane; nanoporous alumina
8.  High Efficiency Hybrid Silicon Nanopillar-Polymer Solar Cells 
ACS applied materials & interfaces  2013;5(19):9620-9627.
Recently, inorganic/organic hybrid solar cells have been considered as a viable alternative for low-cost photovoltaic devices because the Schottky junction between inorganic and organic materials can be formed employing low temperature processing methods. We present an efficient hybrid solar cell based on highly ordered silicon nanopillars (SiNPs) and poly (3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS). The proposed device is formed by spin coating the organic polymer PEDOT:PSS on a SiNP array fabricated using metal assisted electroless chemical etching process. The characteristics of the hybrid solar cells are investigated as a function of SiNP height. A maximum power conversion efficiency (PCE) of 9.65% has been achieved for an optimized SiNP array hybrid solar cell with nanopillar height of 400 nm, despite the absence of a back surface field enhancement. The effect of an ultrathin atomic layer deposition (ALD), grown aluminum oxide (Al2O3), as a passivation layer (recombination barrier) has also been studied for the enhanced electrical performance of the device. With the inclusion of the ultrathin ALD deposited Al2O3 between the SiNP array textured surface and the PEDOT:PSS layer, the PCE of the fabricated device was observed to increase to 10.56%, which is ~10% greater than the corresponding device without the Al2O3 layer. The device described herein is considered to be promising toward the realization of a low-cost, high-efficiency inorganic/organic hybrid solar cell.
doi:10.1021/am402598j
PMCID: PMC4142496  PMID: 24032746
Solar cell; light trapping; heterojunction; conductive polymer; silicon nanopillars; radial junction
9.  Swelling-Controlled Polymer Phase and Fluorescence Properties of Polyfluorene Nanoparticles 
Highly fluorescent nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) with distinct phases were prepared, and their photophysical properties were studied by steady state and time-resolved fluorescence spectroscopy. An aqueous suspension of PFO nanoparticles prepared by a reprecipitation method was observed to exhibit spectroscopic characteristics consistent with the glassy phase of the polymer. We demonstrate that controlled addition of organic solvent leads to partial transformation of the disordered polymer chains into the planarized conformation (β-phase), with the fractions of each component phase dependent on the amount of solvent added. Fluorescence spectroscopy of the PFO nanoparticles containing β-phase indicates efficient energy transfer from the glassy-phase regions of the nanoparticles to the β-phase regions. Salient features of the nanoparticles containing β-phase include narrow, red-shifted fluorescence and increased fluorescence quantum yield as compared to the glassy-phase nanoparticles. Fluorescence lifetime measurements indicate that the increased quantum yield of the β-phase PFO originates from a decrease in the nonradiative decay rate, with little change in the radiative rate. This decrease is likely due to exciton trapping by the β-phase, which leads to a reduction in the energy transfer efficiency to quencher species present within the nanoparticle.
doi:10.1021/la8000762
PMCID: PMC2517098  PMID: 18459748
10.  Investigation of size–dependent cell adhesion on nanostructured interfaces 
Background
Cells explore the surfaces of materials through membrane-bound receptors, such as the integrins, and use them to interact with extracellular matrix molecules adsorbed on the substrate surfaces, resulting in the formation of focal adhesions. With recent advances in nanotechnology, biosensors and bioelectronics are being fabricated with ever decreasing feature sizes. The performances of these devices depend on how cells interact with nanostructures on the device surfaces. However, the behavior of cells on nanostructures is not yet fully understood. Here we present a systematic study of cell-nanostructure interaction using polymeric nanopillars with various diameters.
Results
We first checked the viability of cells grown on nanopillars with diameters ranging from 200 nm to 700 nm. It was observed that when cells were cultured on the nanopillars, the apoptosis rate slightly increased as the size of the nanopillar decreased. We then calculated the average size of the focal adhesions and the cell-spreading area for focal adhesions using confocal microscopy. The size of focal adhesions formed on the nanopillars was found to decrease as the size of the nanopillars decreased, resembling the formations of nascent focal complexes. However, when the size of nanopillars decreased to 200 nm, the size of the focal adhesions increased. Further study revealed that cells interacted very strongly with the nanopillars with a diameter of 200 nm and exerted sufficient forces to bend the nanopillars together, resulting in the formation of larger focal adhesions.
Conclusions
We have developed a simple approach to systematically study cell-substrate interactions on physically well-defined substrates using size-tunable polymeric nanopillars. From this study, we conclude that cells can survive on nanostructures with a slight increase in apoptosis rate and that cells interact very strongly with smaller nanostructures. In contrast to previous observations on flat substrates that cells interacted weakly with softer substrates, we observed strong cell-substrate interactions on the softer nanopillars with smaller diameters. Our results indicate that in addition to substrate rigidity, nanostructure dimensions are additional important physical parameters that can be used to regulate behaviour of cells.
doi:10.1186/s12951-014-0054-4
PMCID: PMC4265325  PMID: 25477150
Nanotopography; Cell adhesion; Surface topography
11.  Templated growth of PFO-DBT nanorod bundles by spin coating: effect of spin coating rate on the morphological, structural, and optical properties 
Nanoscale Research Letters  2014;9(1):225.
In this study, the spin coating of template-assisted method is used to synthesize poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT) nanorod bundles. The morphological, structural, and optical properties of PFO-DBT nanorod bundles are enhanced by varying the spin coating rate (100, 500, and 1,000 rpm) of the common spin coater. The denser morphological distributions of PFO-DBT nanorod bundles are favorably yielded at the low spin coating rate of 100 rpm, while at high spin coating rate, it is shown otherwise. The auspicious morphologies of highly dense PFO-DBT nanorod bundles are supported by the augmented absorption and photoluminescence.
doi:10.1186/1556-276X-9-225
PMCID: PMC4019364  PMID: 24872806
PFO-DBT; Nanorods; Spin coating rate; Porous alumina template
12.  Stable White Light Electroluminescence from Highly Flexible Polymer/ZnO Nanorods Hybrid Heterojunction Grown at 50°C 
Nanoscale Research Letters  2010;5(9):1442-1448.
Stable intrinsic white light–emitting diodes were fabricated from c-axially oriented ZnO nanorods (NRs) grown at 50°C via the chemical bath deposition on top of a multi-layered poly(9,9-dioctylfluorene-co–N-(4-butylpheneylamine)diphenylamine)/poly(9,9dioctyl-fluorene) deposited on PEDOT:PSS on highly flexible plastic substrate. The low growth temperature enables the use of a variety of flexible plastic substrates. The fabricated flexible white light–emitting diode (FWLED) demonstrated good electrical properties and a single broad white emission peak extending from 420 nm and up to 800 nm combining the blue light emission of the polyflourene (PFO) polymer layer with the deep level emission (DLEs) of ZnO NRs. The influence of the temperature variations on the FWLED white emissions characteristics was studied and the devices exhibited high operation stability. Our results are promising for the development of white lighting sources using existing lighting glass bulbs, tubes, and armature technologies.
doi:10.1007/s11671-010-9659-1
PMCID: PMC2920425  PMID: 20730076
Hybrid technology; ZnO nanorods; Polymers; Large area lighting; Flexible low temperature LEDs
13.  Stable White Light Electroluminescence from Highly Flexible Polymer/ZnO Nanorods Hybrid Heterojunction Grown at 50°C 
Nanoscale Research Letters  2010;5(9):1442-1448.
Stable intrinsic white light–emitting diodes were fabricated from c-axially oriented ZnO nanorods (NRs) grown at 50°C via the chemical bath deposition on top of a multi-layered poly(9,9-dioctylfluorene-co–N-(4-butylpheneylamine)diphenylamine)/poly(9,9dioctyl-fluorene) deposited on PEDOT:PSS on highly flexible plastic substrate. The low growth temperature enables the use of a variety of flexible plastic substrates. The fabricated flexible white light–emitting diode (FWLED) demonstrated good electrical properties and a single broad white emission peak extending from 420 nm and up to 800 nm combining the blue light emission of the polyflourene (PFO) polymer layer with the deep level emission (DLEs) of ZnO NRs. The influence of the temperature variations on the FWLED white emissions characteristics was studied and the devices exhibited high operation stability. Our results are promising for the development of white lighting sources using existing lighting glass bulbs, tubes, and armature technologies.
doi:10.1007/s11671-010-9659-1
PMCID: PMC2920425  PMID: 20730076
Hybrid technology; ZnO nanorods; Polymers; Large area lighting; Flexible low temperature LEDs
14.  Controlling Film Morphology in Conjugated Polymer 
Journal of the American Chemical Society  2008;130(47):15916-15926.
We study the effects of patterned surface chemistry on the microscale and nanoscale morphology of solution-processed donor/acceptor polymer-blend films. Focusing on combinations of interest in polymer solar cells, we demonstrate that patterned surface chemistry can be used to tailor the film morphology of blends of semiconducting polymers such as poly-[2-(3,7-dimethyloctyloxy)-5-methoxy-p-phenylenevinylene] (MDMO-PPV), poly-3-hexylthiophene (P3HT), poly[(9,9-dioctylflorenyl-2,7-diyl)-co-benzothiadiazole)] (F8BT), and poly(9,9-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenyl-1,4-phenylendiamine) (PFB) with the fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We present a method for generating patterned, fullerene-terminated monolayers on gold surfaces, and use microcontact printing and Dip-Pen Nanolithography (DPN) to pattern alkanethiols with both micro- and nanoscale features. After patterning with fullerenes and other functional groups, we backfill the rest of the surface with a variety of thiols to prepare substrates with periodic variations in surface chemistry. Spin coating polymer:PCBM films onto these substrates, followed by thermal annealing under nitrogen, leads to the formation of structured polymer films. We characterize these films with Atomic Force Microscopy (AFM), Raman spectroscopy, and fluorescence microscopy. The surface patterns are effective in guiding phase separation in all of the polymer:PCBM systems investigated, and lead to a rich variety of film morphologies that are inaccessible with unpatterned substrates. We demonstrate our ability to guide pattern formation in films thick enough of be of interest for actual device applications (up to 200 nm in thickness) using feature sizes as small as 100 nm. Finally, we show that the surface chemistry can lead to variations in film morphology on length scales significantly smaller than those used in generating the original surface patterns. The variety of behaviors observed and the wide range of control over polymer morphology achieved at a variety of different length scales have important implications for the development of bulk heterojunction solar cells.
doi:10.1021/ja804088j
PMCID: PMC2702008  PMID: 18983150
15.  Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements 
Nature Communications  2015;6:5977.
Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. Here we show that a metamaterials approach, using a discrete physical geometry (conformation) of the segments of a polymer chain as the vector for a substantial refractive index change, can be used to enable visible wavelength, conjugated polymer photonic elements. In particular, we demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called β-phase conformation in poly(9,9-dioctylfluorene) thin films. This can be done on length scales ≤500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations.
The optoelectronic properties of semiconducting polymers are controlled by altering chemical structure and/or inter-chain order. Perevedentsev et al. propose a nanopatterning approach whereby the geometry of polymer chain segments is modified to engineer metamaterial structures for visible light.
doi:10.1038/ncomms6977
PMCID: PMC4309429  PMID: 25598208
16.  Parallel fabrication of magnetic tunnel junction nanopillars by nanosphere lithography 
Scientific Reports  2013;3:1948.
We present a new method for fabricating magnetic tunnel junction nanopillars that uses polystyrene nanospheres as a lithographic template. Unlike the common approaches, which depend on electron beam lithography to sequentially fabricate each nanopillar, this method is capable of patterning a large number of nanopillars simultaneously. Both random and ordered nanosphere patterns have been explored for fabricating high quality tunneling junctions with magnetoresistance in excess of 100%, employing ferromagnetic layers with both out-of-plane and in-plane easy axis. Novel voltage induced switching has been observed in these structures. This method provides a cost-effective way of rapidly fabricating a large number of tunnel junction nanopillars in parallel.
doi:10.1038/srep01948
PMCID: PMC3674430  PMID: 23739347
17.  Self-ordered TiO2 quantum dot array prepared via anodic oxidation 
Nanoscale Research Letters  2012;7(1):123.
The template-based methods belong to low-cost and rapid preparation techniques for various nanostructures like nanowires, nanotubes, and nanodots or even quantum dots [QDs]. The nanostructured surfaces with QDs are very promising in the application as a sensor array, also called 'fluorescence array detector.' In particular, this new sensing approach is suitable for the detection of various biomolecules (DNA, proteins) in vitro (in clinical diagnostics) as well as for in vivo imaging.
The paper deals with the fabrication of TiO2 planar nanostructures (QDs) by the process of titanium anodic oxidation through an alumina nanoporous template on a silicon substrate. Scanning electron microscopy observation showed that the average diameter of TiO2 QDs is less than 10 nm. Raman spectroscopic characterization of self-organized titania QDs confirmed the presence of an anatase phase after annealing at 400°C in vacuum. Such heat-treated TiO2 QDs revealed a broad emission peak in the visible range (characterized by fluorescence spectroscopy).
doi:10.1186/1556-276X-7-123
PMCID: PMC3305443  PMID: 22333295
quantum dots; biosensing; TiO2; template methods; nanoporous mask
18.  Enhancement of intrinsic emission from ultrathin ZnO films using Si nanopillar template 
Nanoscale Research Letters  2012;7(1):263.
Highly efficient room-temperature ultraviolet (UV) luminescence is obtained in heterostructures consisting of 10-nm-thick ultrathin ZnO films grown on Si nanopillars fabricated using self-assembled silver nanoislands as a natural metal nanomask during a subsequent dry etching process. Atomic layer deposition was applied for depositing the ZnO films on the Si nanopillars under an ambient temperature of 200°C. Based on measurements of photoluminescence (PL), an intensive UV emission corresponding to free-exciton recombination (approximately 3.31 eV) was observed with a nearly complete suppression of the defect-associated, broad-range visible emission peak. As compared to the ZnO/Si substrate, the almost five-times-of-magnitude enhancement in the intensity of PL, which peaked around 3.31 eV in the present ultrathin ZnO/Si nanopillars, is presumably attributed to the high surface/volume ratio inherent to the Si nanopillars. This allowed considerably more amount of ZnO material to be grown on the template and led to markedly more efficient intrinsic emission.
doi:10.1186/1556-276X-7-263
PMCID: PMC3460761  PMID: 22616734
Ultrathin films; ZnO; Nanopillars; Atomic layer deposition; Photoluminescence
19.  GaAs nanopillar-array solar cells employing in situ surface passivation 
Nature Communications  2013;4:1497-.
Arrays of III–V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p–n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm−2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode.
Arrays of III–V semiconductor nanopillars are promising photovoltaic materials due to their favourable optical properties, however, they show low power conversion efficiencies. Mariani et al. fabricate a GaAs nanopillar solar cell achieving an efficiency of 6.63% owing to surface passivation.
doi:10.1038/ncomms2509
PMCID: PMC3586731  PMID: 23422665
20.  Effect of the anodization voltage on the pore-widening rate of nanoporous anodic alumina 
Nanoscale Research Letters  2012;7(1):474.
A detailed study of the pore-widening rate of nanoporous anodic alumina layers as a function of the anodization voltage was carried out. The study focuses on samples produced under the same electrolyte and concentration but different anodization voltages within the self-ordering regime. By means of ellipsometry-based optical characterization, it is shown that in the pore-widening process, the porosity increases at a faster rate for lower anodization voltages. This opens the possibility of obtaining three-dimensional nanostructured nanoporous anodic alumina with controlled thickness and refractive index of each layer, and with a refractive index difference of up to 0.24 between layers, for samples produced with oxalic acid electrolytes.
doi:10.1186/1556-276X-7-474
PMCID: PMC3460793  PMID: 22916731
Anodization voltage; Alumina; Nanostructures; Nanoporous anodic alumina; Ellipsometry
21.  Preparation of electrochemically active silicon nanotubes in highly ordered arrays 
Summary
Silicon as the negative electrode material of lithium ion batteries has a very large capacity, the exploitation of which is impeded by the volume changes taking place upon electrochemical cycling. A Si electrode displaying a controlled porosity could circumvent the difficulty. In this perspective, we present a preparative method that yields ordered arrays of electrochemically competent silicon nanotubes. The method is based on the atomic layer deposition of silicon dioxide onto the pore walls of an anodic alumina template, followed by a thermal reduction with lithium vapor. This thermal reduction is quantitative, homogeneous over macroscopic samples, and it yields amorphous silicon and lithium oxide, at the exclusion of any lithium silicides. The reaction is characterized by spectroscopic ellipsometry for thin silica films, and by nuclear magnetic resonance and X-ray photoelectron spectroscopy for nanoporous samples. After removal of the lithium oxide byproduct, the silicon nanotubes can be contacted electrically. In a lithium ion electrolyte, they then display the electrochemical waves also observed for other bulk or nanostructured silicon systems. The method established here paves the way for systematic investigations of how the electrochemical properties (capacity, charge/discharge rates, cyclability) of nanoporous silicon negative lithium ion battery electrode materials depend on the geometry.
doi:10.3762/bjnano.4.73
PMCID: PMC3817651  PMID: 24205460
atomic layer deposition; electrochemistry; lithium ion battery electrode; silica thermal reduction; silicon nanotubes
22.  AFM, SEM and TEM Studies on Porous Anodic Alumina 
Nanoscale Research Letters  2010;5(4):725-734.
Porous anodic alumina (PAA) has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure.
doi:10.1007/s11671-010-9538-9
PMCID: PMC2894103  PMID: 20672104
Microscopy; Nanostructure; Porous; Anodic Alumina; Characterization
23.  AFM, SEM and TEM Studies on Porous Anodic Alumina 
Nanoscale Research Letters  2010;5(4):725-734.
Porous anodic alumina (PAA) has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure.
doi:10.1007/s11671-010-9538-9
PMCID: PMC2894103  PMID: 20672104
Microscopy; Nanostructure; Porous; Anodic Alumina; Characterization
24.  Structural tuning of photoluminescence in nanoporous anodic alumina by hard anodization in oxalic and malonic acids 
Nanoscale Research Letters  2012;7(1):228.
We report on an exhaustive and systematic study about the photoluminescent properties of nanoporous anodic alumina membranes fabricated by the one-step anodization process under hard conditions in oxalic and malonic acids. This optical property is analysed as a function of several parameters (i.e. hard anodization voltage, pore diameter, membrane thickness, annealing temperature and acid electrolyte). This analysis makes it possible to tune the photoluminescent behaviour at will simply by modifying the structural characteristics of these membranes. This structural tuning ability is of special interest in such fields as optoelectronics, in which an accurate design of the basic nanostructures (e.g. microcavities, resonators, filters, supports, etc.) yields the control over their optical properties and, thus, upon the performance of the nanodevices derived from them (biosensors, interferometers, selective filters, etc.)
doi:10.1186/1556-276X-7-228
PMCID: PMC3413565  PMID: 22515214
Photoluminescence; Hard anodization; Porous alumina; Pore widening; Heat treatment; Geometric characteristics
25.  1-D nanoporous anodic alumina rugate filters by means of small current variations for real-time sensing applications 
Nanoscale Research Letters  2014;9(1):315.
A rugate filter based on nanoporous anodic alumina was fabricated using an innovative sinusoidal current profile with small current variation. The resulting structure consisted of highly parallel pores with modulations of the pore diameter along the pore axis and with no branching. The effect of the period time and the pore widening post-treatment was studied. From reflectance measurements, it was seen that the position of the reflection band can be tuned by adjusting the period time and the width by pore-widening post-treatments. We tested one of the rugate filters by infiltrating the structure with EtOH and water in order to evaluate its sensing capabilities. This method allows the fabrication of complex in-depth modulated nanoporous anodic alumina structures that open up the possibility of new kinds of alumina-based optical sensing devices.
doi:10.1186/1556-276X-9-315
PMCID: PMC4082282  PMID: 25024680
Nanoporous anodic alumina; Rugate filter; Photonic crystal; Fabrication; Nanostructuring; Current control; Sensing

Results 1-25 (373697)