Pore Spacing Research Articles

Geometry-dependent band shift and dielectric modification of nanoporous Si nanowires

In order to obtain a detailed understanding of the modulation of electronic properties in nanoporous Si (np-Si) nanowires with containing ordered, nanometer-sized cylindrical pores, we propose a theoretical method to clarify the band shift and associated with the dielectric modification determined by the geometrical parameters, including nanowire diameter, pore size, pore spacing and porosity, in terms of size-dependent surface energy and atomic-bond-relaxation correlation mechanism. Our results reveal that the self-equilibrium strain induced by the atoms located at inner and outer surfaces with high ratio of under-coordinated atoms as well as elastic interaction among pores in np-Si nanowires play the dominant role in the bandgap shift and dielectric depression. The tunable electronic properties of np-Si nanowires with negative curvature make them attractive for nanoelectronic and optoelectronic devices.

Controlled synthesis of nanoporous tin oxide layers with various pore diameters and their photoelectrochemical properties

Porous anodic tin oxide films with various pore diameters were synthesized by one-step anodization of Sn foil in 1M NaOH followed by 2h of annealing at 200°C. When the potential of 2V was applied during anodization, oxide layers with ultra-small nanochannels having diameter slightly above 10nm were obtained, and an average distance between neighboring pores was ∼20nm. On the contrary, applying the potential of 4V resulted in the formation of anodic films with much wider channels (∼40nm in diameter) and larger pore spacing (∼55nm). The composition of as formed samples was examined by XRD and XPS measurements. The as obtained anodic films were amorphous even after annealing. However, the greater Sn2+ ion content was observed for the sample anodized at 4V. In consequence, the porous oxide layer grown at the higher potential exhibited a red-shifted absorption edge as well as the lower optical band-gap in comparison to the sample synthesized at 2V. This fact was ascribed to a higher content of Sn2+ defects which are mainly responsible for a significant enhancement of photoelectrochemical activity of the material in the visible range. However, photoelectrochemical activity in the visible range was noticeable for anodic tin oxide films independently of the anodizing potential. We believe that such kind of self-supported electrodes can be promising candidates for photocatalytic and photoelectrochemical applications.

The structure of mesoporous silica obtained by pseudomorphic transformation of SBA-15 and SBA-16

Mesoporous silica with bimodal pore size distributions was prepared by pseudomorphic transformation of SBA-15 and SBA-16 in the presence of hexadecyltrimethylammonium ions as a structure-directing agent. The characteristic particle morphology of the starting materials was retained after the transformation. Analysis of the products by gas sorption and small-angle X-ray scattering (SAXS) revealed hybrid pore structures, which featured – depending on the degree of transformation – variable contributions from the original and the newly introduced pore systems. In the case of SBA-15, it was found that a high degree of transformation leads to a seemingly complete conversion of the original pores with a diameter of 7.1 nm to pores with a diameter of 4.0 nm. The SAXS pattern of the product shows additional peaks that can be assigned to the original SBA-15 pore spacing. Similarly, a cubic phase could be observed in the samples prepared by pseudomorphic transformation of SBA-16, despite an almost complete conversion of the SBA-16 cavities. This leads to the conclusion that the pore structure of the starting material significantly affects the outcome of the pseudomorphic transformation, thus opening possibilities for the synthesis of new porous materials with complex pore systems.

Optimization of Anodic Porous Alumina Fabricated from Commercial Aluminum Food Foils: A Statistical Approach.

Anodic porous alumina is a known material based on an old industry, yet with emerging applications in nanoscience and nanotechnology. This is promising, but the nanostructured alumina should be fabricated from inexpensive raw material. We fabricated porous alumina from commercial aluminum food plate in 0.4 M aqueous phosphoric acid, aiming to design an effective manufacturing protocol for the material used as nanoporous filler in dental restorative composites, an application demonstrated previously by our group. We identified the critical input parameters of anodization voltage, bath temperature and anodization time, and the main output parameters of pore diameter, pore spacing and oxide thickness. Scanning electron microscopy and grain analysis allowed us to assess the nanostructured material, and the statistical design of experiments was used to optimize its fabrication. We analyzed a preliminary dataset, designed a second dataset aimed at clarifying the correlations between input and output parameters, and ran a confirmation dataset. Anodization conditions close to 125 V, 20 °C, and 7 h were identified as the best for obtaining, in the shortest possible time, pore diameters and spacing of 100–150 nm and 150–275 nm respectively, and thickness of 6–8 µm, which are desirable for the selected application according to previously published results. Our analysis confirmed the linear dependence of pore size on anodization voltage and of thickness on anodization time. The importance of proper control on the experiment was highlighted, since batch effects emerge when the experimental conditions are not exactly reproduced.

Design and Fabrication of Photonic Structured Organic Solar Cells by Electrospraying

Photonic architectures in optoelectronic devices are comprised of uniform periodic structural arrangement which aids in improved interaction with light. The processing of such photonic arrays generally involves several steps of fabrication. This work proposes single-step fabrication of an equal submicron size porous photonic structure array through electrospraying. This distinctive approach involves a continuous supply of material With simultaneous removal of solvent for fabricating large area samples, compared to other processing techniques. The process optimization is carried out to regulate the pore diameter and spacing. Morphological studies showed the continuity of porous arrays extending to large areas of the order of millimeters. Optical investigations demonstrated that this uniform periodic topography assisted in improved light scattering and a consequent enhancement of light absorption. Further, the incorporation of this array structure in the active layer of organic photovoltaic devices is evaluated through both experiments and modeling. Modeling and simulations suggest that the optimized range of 200-500 mm pore size aids in higher current density. Experiments reveal an improvement of 18% in the photocurrent density at short circuit in the periodic array architecture compared to the planar reference. Therefore, in this study, a facile single-step novel, method of obtaining photonic array structures with unproved device performances is demonstrated.

Micro-fabricated scaffolds lead to efficient remission of diabetes in mice.

Despite the clinical success of intrahepatic islet transplantation in treating type 1 diabetes, factors specific to this transplantation site hinder long-term insulin independence. The adoption of alternative, extravascular sites likely improve islet survival and function, but few locations are able to sufficiently confine islets in order to facilitate engraftment. This work describes a porous microwell scaffold with a well-defined pore size and spacing designed to guarantee islet retention at an extrahepatic transplantation site and facilitate islet revascularization. Three techniques to introduce pores were characterized: particulate leaching; solvent casting on pillared wafers; and laser drilling. Our criteria of a maximum pore diameter of 40μm were best achieved via laser drilling. Transplantation studies in the epididymal fat of diabetic mice elucidated the potential of this porous scaffold platform to restore blood glucose levels and facilitate islet engraftment. Six out of eight mice reverted to stable normoglycemia with a mean time to remission of 6.2±3.2 days, which was comparable to that of the gold standard of renal subcapsular islet grafts. In contrast, when islets were transplanted in the epididymal fat pad without a microwell scaffold, only two out of seven mice reverted to stable normoglycemia. Detailed histological evaluation four weeks after transplantation found a comparable vascular density in scaffold-seeded islets, renal subcapsular islets and native pancreatic islets. However, the vascularization pattern in scaffold-seeded islets was more inhomogeneous compared to native pancreatic islets with a higher vascular density in the outer shell of the islets compared to the inner core. We also observed a corresponding decrease in the beta-cell density in the islet core. Despite this, our data indicated that islets transplanted in the microwell scaffold platform were able to maintain a viable beta-cell population and restore glycemic control. Furthermore, we demonstrated that the microwell scaffold platform facilitated detailed analysis at a subcellular level to correlate design parameters with functional physiological observations.

Membrane Pore Spacing Can Modulate Endothelial Cell-Substrate and Cell-Cell Interactions.

Mechanical cues and substrate interaction affect the manner in which cells adhere, spread, migrate and form tissues. With increased interest in tissue-on-a-chip and co-culture systems utilizing porous membranes, it is important to understand the role of disrupted surfaces on cellular behavior. Using a transparent glass membrane with defined pore geometries, we investigated endothelial fibronectin fibrillogenesis and formation of focal adhesions as well as development of intercellular junctions. Cells formed fewer focal adhesions and had shorter fibronectin fibrils on porous membranes compared to non-porous controls, which was similar to cell behavior on continuous soft substrates with Young's moduli seven orders of magnitude lower than glass. Additionally, porous membranes promoted enhanced cell-cell interactions as evidenced by earlier formation of tight junctions. These findings suggest that porous membranes with discontinuous surfaces promote reduced cell-matrix interactions similarly to soft substrates and may enhance tissue and barrier formation.

The Correlation between Pore Structure and Macro Durability Performance of Road Concrete under Loading and Freeze-Thaw and Drying-Wetting Cycles

The grey correlation theory and multiple regression method are used to reveal macro performance degradation rules of road concrete under loading and freeze-thaw and drying-wetting cycles; then the correlation between mesoscopic pore structure and residual strength and antifreezing index of concrete is analyzed. Under the freeze-thaw and drying-wetting cycles with 50% loading level, the pore structure parameters that influence concrete strength show the following sequence: fractal dimension > most probable pore size > porosity > less harmful pore. The correlation between strength and pore parameters can be represented with multiple nonlinear equations. A negative correlation is shown between strength and fractal dimension and most probable pore size. Conversely, a positive correlation is shown between strength, porosity, and less harmful pore. Under the freeze-thaw and drying-wetting cycles with 80% loading level, the pore structure parameters that influence concrete strength show another sequence: fractal dimension > porosity > less harmful pore > most probable pore size. The correlation between antifreezing index and pore parameters should be described with multiple linear equations. The relative dynamic elastic modulus shows a positive correlation to most probable pore size, pore surface area, and porosity but a negative correlation to less harmful pore and pore spacing coefficient.

Suppression of Frost Nucleation Achieved Using the Nanoengineered Integral Humidity Sink Effect.

Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the mass transport mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concentration profile above periodically spaced pores is governed by the sink and source concentrations and two geometrical parameters: the nondimensional pore size and the ratio of the pore spacing to the boundary layer thickness. We demonstrate that when the ratio of the pore spacing to the boundary layer thickness vanishes, as for the nanoporous bilayer coatings, the entire surface concentration becomes uniform and equal to the concentration set by the hygroscopic liquid. In other words, the surface concentration becomes completely independent of the nanopore size. We identified the threshold geometrical parameters for this condition and show that it can lead to a 65 K decrease in the nucleation onset surface temperature below the dew point. With this fundamental insight, we use bilayer coatings to nanoengineer the integral humidity sink effect to provide extreme antifrosting performance with up to a 2 h delay in nucleation onset at 263 K. The nanoporous bilayer coatings can be designed to combine optimal antifrosting functionality with a superhydrophobic water repelling exterior to provide coatings that can robustly prevent frost, rime, and glaze accumulation. By minimizing the required amount of antifreeze, this anti-icing method can have minimal operational cost and environmental impact.

Scaling Resistance and Air Void Characteristics in Concrete Containing GGBS

AbstractIn this paper we discuss the test results for concretes containing various amounts of ggbs as compared to concretes made with Portland cement. The main objective of these tests is to evaluate the influence of varying air content in such mixtures on the structure and frost resistance of concrete. The authors suggest that the approach presented here allows for a safe design of concrete mixtures in terms of their frost resistance.The results indicate that concrete can be resistant to surface scaling even at the W/C ratio markedly higher than 0.45. Increased addition of ggbs leads to a decrease in concrete resistance to surface scaling. Proper air entrainment is the fundamental factor for frost-resistant concrete, and the air void system has to be assessed (micropore content A300, spacing factor $\overline L $). The addition of ggbs increases pore diameters, thus, to obtain the appropriate air pore spacing factor, micropore quantities introduced have to be increased.

Multiscale and multimodality computed tomography for cortical bone analysis

In clinical studies, high resolution peripheral quantitative computed tomography (HR-pQCT) is used to separately evaluate cortical bone and trabecular bone with an isotropic voxel of 82 µm3, and typical cortical parameters are cortical density (D.comp), thickness (Ct.Th), and porosity (Ct.Po).In vitro, micro-computed tomography (micro-CT) is used to explore the internal cortical bone micro-structure with isotropic voxels and high resolution synchrotron radiation (SR); micro-CT is considered the ‘gold standard’.In 16 tibias and 8 femurs, HR-pQCT measurements were compared to conventional micro-CT measurements. To test modality effects, conventional micro-CT measurements were compared to SR micro-CT measurements at 7.5 µm3; SR micro-CT measurements were also tested at different voxel sizes for the femurs, specifically, 7.5 µm3 versus 2.8 µm3.D.comp (r = −0.88, p < 10−3) was the parameter best correlated with porosity (Po.V/TV). The correlation was not affected by the removal of pores under 130 µm. Ct.Th was also significantly highly correlated (r = −0.89 p < 10−3), while Ct.Po was correlated with its counterpart Po.V/TV (r = 0.74, p < 10−3).From SR micro-CT and conventional micro-CT at 7.5 µm3 in matching areas, Po.V/TV and pore diameter were underestimated in conventional micro-CT with mean ± standard deviation (SD) biases of −2.5 ± 1.9% and −0.08 ± 0.08 mm, respectively. In contrast, pore number (Po.N) and pore separation (Po.Sp) were overestimated with mean ± SD biases of +0.03 ± 0.04 mm−1 and +0.02 ± 0.04 mm, respectively. The results from the tibia and femur were similar when the results of SR micro-CT at 7.5 µm3 and 2.8 µm3 were compared. Po.V/TV, specific surface of pores (Po.S/Po.V), and Po.N were underestimated with mean biases of −1.7 ± 0.9%, −4.6 ± 4.4 mm−1, and −0.26 ± 0.15 mm−1, respectively. In contrast, pore spacing was overestimated at 7.5 µm3 compared to 2.8 µm3 with mean biases of 0.05 ± 0.03 mm.Cortical bone measurements from HR-pQCT images provided consistent results compared to those obtained using conventional micro-CT at the distal tibia. D.comp was highly correlated to Po.V/TV because it considers both the micro-porosity (Haversian systems) and macro-porosity (resorption lacunae) of cortical bone. The complexity of canal organization, (including shape, connectivity, and surface) are not fully considered in conventional micro-CT in relation to beam hardening and cone beam reconstruction artifacts. With the exception of Po.V/TV measurements, morphological and topological measurements depend on the characteristics of the x-ray beam, and to a lesser extent, on image resolution.

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

Monolithic solar water splitting devices consist of photovoltaic materials integrated with electrocatalysts and produce solar hydrogen by water splitting upon solar illumination in one device. Upscaling of monolithic solar water splitting devices is obstructed by high ohmic losses in the electrolyte due to long ionic transport distances. A new design overcomes the problem by introducing micron sized pores in a silicon wafer substrate coated with electrocatalysts. A porous solar hydrogen device was simulated by applying a current corresponding to ca. 10% solar-to-hydrogen efficiency. Porous monoliths of 550 μm thickness with varying pore size and spacing were fabricated by laser ablation and electrochemically characterized. Ohmic losses well below 100 mV were reached at 14.4% porosity with 77 μm pores spaced 250 μm apart in 0.25 M KOH electrolyte. In 1 M KOH, 100 mV was reached at 6% porosity with 1 mm pore spacing. Our results suggest ohmic losses below 50 mV can be achieved when using 10 μm thick substra...

(Invited) Stress-Assisted Formation of Self-Organized Porous Anodic Oxides

Porous anodic oxide (PAO) films are grown by electrochemical polarization of Al, Ti, and other metals in baths that dissolve the oxide. Procedures to grow films with highly ordered and controllable arrangements of nanoscale pores have led to the extensive use of PAO films in nanofunctional devices. Experiments and calculations show that transport in the oxide occurs by electrical migration coupled with plastic flow driven by mechanical stress in the oxide, and suggest that flow may play a role in formation of self-ordered PAO (1-3). Pores initiate by a morphological instability at the oxide-solution interface when the initially formed barrier oxide reaches a critical thickness (4). Herein is reported a combined experimental and modeling investigation of the formation and self-ordering of PAO. Experiments were carried out to identify stress generation mechanisms during galvanostatic formation of Al barrier films in 0.4 M H3PO­4. Stress distributions in these films were measured by monitoring stress-induced sample curvature changes during oxide formation followed by open circuit dissolution of the films (5). Elevated compressive stress reaching several GPa was found to build up within a few nanometers of the oxide-solution interface, coinciding with high phosphorus contamination in the same layer revealed by GDOES (6). The compressive surface stress is likely due to electric field-induced phosphate incorporation. The experimentally characterized surface stress was incorporated in our anodizing model based on transport by coupled viscous flow and electrical migration (2). Morphological stability analysis of the model reveals pattern formation consistent with the well-established characteristic pore spacing to voltage relationship of PAO (7). Pore formation is governed by competition between stabilizing oxide formation at the solution interface and destabilizing flow driven by gradients of anion incorporation-induced surface stress. The model successfully predicts the critical threshold electric field and the narrow ranges of anodizing efficiency characterizing PAO formation on many metals (3,4). A compelling analogy exists between the mechanisms of PAO ordering and formation of hexagonally-ordered Marangoni patterns in thin liquid films.

Self-Organized Porous Anodic Oxide Formation: Role of Oxide Flow Driven By Surface Stress

Porous anodic oxide (PAO) films are grown by electrochemical polarization of Al, Ti, and other metals in baths that dissolve the oxide. Procedures to grow films with highly ordered and controllable arrangements of nanoscale pores have led to the extensive use of PAO films in nanofunctional devices. Experiments and calculations show that transport in the oxide occurs by electrical migration coupled with plastic flow driven by mechanical stress in the oxide, and suggest that flow may play a role in formation of self-ordered PAO (1-3). Pores initiate by a morphological instability at the oxide-solution interface when the initially formed barrier oxide reaches a critical thickness (4). Results of a combined experimental and modeling investigation of the formation and self-ordering of PAO are discussed. Experiments were carried out to identify stress generation mechanisms during galvanostatic formation of Al barrier films in 0.4 M H3PO4. Stress distributions in these films were measured by monitoring stress-induced sample curvature changes during oxide formation followed by open circuit dissolution of the films (5). Elevated compressive stress reaching several GPa was found to build up within a few nanometers of the oxide-solution interface, coinciding with high phosphorus contamination in the same layer revealed by GDOES (6). The compressive surface stress is likely due to electric field-induced phosphate incorporation. The experimentally characterized surface stress was incorporated in an anodizing model based on transport by coupled viscous flow and electrical migration (2). Morphological stability analysis of the model revealed pattern formation consistent with the characteristic pore spacing to voltage relationship of PAO (7). Pore formation is governed by competition between stabilizing oxide formation at the solution interface and destabilizing flow driven by gradients of anion incorporation-induced surface stress. The model successfully predicts the narrow ranges of anodizing efficiency characterizing PAO formation on many metals (3,4). A compelling analogy exists between the mechanisms of PAO ordering and formation of hexagonally-ordered Marangoni patterns in thin liquid films. Electrochemical impedance spectroscopy of steady-state porous anodic alumina formed in sulfuric and oxalic acid solutions are presented. It is shown that the characteristic inductive loop of impedance spectra of anodic oxide can be understood quantitatively in terms of electric field-induced homogeneous formation and annihilation of oxygen vacancies. We argue that this reaction can produce oxide displacement in the presence of sufficiently large stress gradients. The possible explanation of viscous oxide flow by such a vacancy creep mechanism is discussed.

Production of molecularly imprinted polymer particles with amide-decorated cavities for CO2 capture using membrane emulsification/suspension polymerisation

Highly uniform amide-based molecularly imprinted polymer (MIP) particles containing CO2-philic cavities decorated with amide groups were produced using membrane emulsification and subsequent suspension polymerisation. The organic phase containing acrylamide (functional monomer), oxalic acid (dummy template), ethylene glycol dimethacrylate (crosslinker) and azobisisobutyronitrile (initiator) dissolved in a 50/50 mixture (by volume) of acetonitrile and toluene (porogenic solvents) was injected through a microengineered nickel membrane with a pore diameter of 20μm and a pore spacing of 200μm into agitated 0.5wt% aqueous solution of poly(vinyl alcohol) to form droplets that have been polymerised at 60°C for 3h. The volume median diameter of the droplets was controlled between 35 and 158μm by shear stress at the membrane surface. The droplets maintained their physical stability during storage for 4 weeks and their size was independent of the dispersed phase content. The particle size after polymerisation was consistent with the initial droplet size. The particles were stable up to 210°C and had a specific surface area of 239m2/g and a CO2 capture capacity of 0.59mmol/g at 273K and 0.15bar CO2 partial pressure.

(Invited) 3D Pore-Scale Transport Model Incorporating Realistic Cathode Morphology and Intermediate Reactions in Lithium-Air Batteries

The lithium-air (Li-air) battery, with its usable energy density close to 1,700Wh/kg1, has captured worldwide attention as a promising battery solution for electric vehicles. However, a major hurdle facing the development of Li-air battery systems is their poor round-trip efficiency owing to the formation of electrically insulating lithium peroxide (Li2O2) at the cathode surface. Computational modeling has proven to be an indispensable tool in the analysis of battery systems, however, all existing simulations thus far treat the electrode/Li2O2 matrix as a homogenous continuum and utilize simply-shaped electrode morphologies, such as spheres and rods, to construct volume-averaged expressions (see Fig. 1a) for porosity and surface area and are insufficient to probe the effect of precise electrode microstructures and Li2O2 growth2,3. Utilizing a pore-scale transport-resolved model of the Li-air battery, the complex electrode and Li2O2morphologies can be directly incorporated and their effects on the system-level performance can be evaluated. In this work, we present a pore-scale transport resolved model (see Fig. 1b) of the Li-air battery that fully accounts for the electrode microstructure and peroxide growth4. This approach requires no empirical correlations regarding the electrode morphology. 3D reconstructed images of real carbon fiber cathode (Fig. 2) are used as geometric inputs to the model. Results obtained from our pore-scale model agree well with experiments and the validated model is then used to predict the galvanostatic discharge behavior of a Li-air cell for a variety of electrode morphologies and design parameters. Fig. 3 shows the cell voltage versus specific capacity curves for nanofiber electrodes of varying mean pore spacing from our 3D pore-scale model. The cell discharge capacity is limited by the spacing between nanostructures, which may lead to pore blocking and hence the reduction of active surface area. To capture the different growth morphologies two potential peroxide forming reactions, based on an intermediate oxygen reduction reaction where O2 reduces to becomes superoxide (O2 -), are incorporated as shown in Fig. 1c. Superoxide may form at the surface of the electrode and then follow one of two possible paths; reaction at the electrode surface to form lithium peroxide or diffusion into the bulk liquid to nucleate lithium peroxide in the electrolyte5. Lithium peroxide created at the electrode/electrolyte surface will produce a thin film growth morphology while peroxide particles generated further away in the electrolyte contributes to the formation of larger particle shaped or toroidal shaped growth. The competition between the different reactions can be explicitly accounted for in the pore-scale modeling framework. A discrete element method is used to simulate the nucleation and movement of lithium peroxide. Through extensive 3D simulations, we systematically examine the effect of drawing current, ORR rate coefficients, oxygen solubility, mean pore size and distribution on Li2O2growth and cell performance as to better understand the underlying physics of capacity fading during cycling. The methodology presented here can be applied to other electrochemical systems that include an insoluble product formation as a result of the reaction process and will be a valuable tool for rational design of electrode microstructures for improved cell performance.

The effect of electrolyte change on the morphology and degree of nanopore order of porous alumina formed by two-step anodization

The aim of this work was to verify if the quality, regularity and spacing of nanoconcaves formed on the Al surface during the first step of anodization (pre-texturing) have a significant effect on the morphology of AAO layers grown during the second anodization continued at the same potential but in different electrolytes. High purity (99.999%) aluminum substrates were anodized at 25V and 45V in sulfuric acid and oxalic acid, respectively. After chemical etching of initially formed oxide in a mixture of chromic and phosphoric acid, the samples were re-anodized under the same potentials, but in different electrolytes (sulfuric, oxalic, phosphoric acids). It was confirmed that the regular nanoporous structure formed on the Al surface during the first anodizing step is initially replicated at the beginning of the second anodization, independently of the electrolyte used. However, these initially formed oxide layers exhibit significantly different pore diameters but the same pore spacing, which is determined by the cell spacing on the Al surface. When phosphoric acid is used as an electrolyte, the prolonged anodization resulted in the formation of typical serrated nanochannels. However, we successfully obtained the almost ideally-ordered porous anodic alumina layer with a thickness of about 700nm, and the average diameter of nanochannels of ∼50nm after the second anodization carried out for 20min at 45V in 0.3M H3PO4, outside from the self-ordering regime for this electrolyte.

Electrochemistry at single molecule occupancy in nanopore-confined recessed ring-disk electrode arrays.

Electrochemical reactions at nanoscale structures possess unique characteristics, e.g. fast mass transport, high signal-to-noise ratio at low concentration, and insignificant ohmic losses even at low electrolyte concentrations. These properties motivate the fabrication of high density, laterally ordered arrays of nanopores, embedding vertically stacked metal-insulator-metal electrode structures and exhibiting precisely controlled pore size and interpore spacing for use in redox cycling. These nanoscale recessed ring-disk electrode (RRDE) arrays exhibit current amplification factors, AFRC, as large as 55-fold with Ru(NH3)62/3+, indicative of capture efficiencies at the top and bottom electrodes, Φt,b, exceeding 99%. Finite element simulations performed to investigate the concentration distribution of redox species and to assess operating characteristics are in excellent agreement with experiment. AFRC increases as the pore diameter, at constant pore spacing, increases in the range 200-500 nm and as the pore spacing, at constant pore diameter, decreases in the range 1000-460 nm. Optimized nanoscale RRDE arrays exhibit a linear current response with concentration ranging from 0.1 μM to 10 mM and a small capacitive current with scan rate up to 100 V s-1. At the lowest concentrations, the average pore occupancy is 〈n〉 ∼ 0.13 molecule establishing productive electrochemical signals at occupancies at and below the single molecule level in these nanoscale RRDE arrays.

A relationship of mesoscopic pore structure and concrete bending strength

Pore structure characteristics are important to improve the strength of concrete. Modified Image Photoshop Pro-plus method is proposed in the study to effectively classify the pore structure parameters. To assess bending strength through the mesoscopic pore structure based on the changing water-to-cement ratio, 10 samples with different water-to-cement ratio were obtained by changing water volume or cement content and Modified Image Photoshop Pro-plus was used to extract pore parameters. A better correlation between bending strength and pore parameters, including average pore diameter and spacing factor with different water-to-cement ratio, is obtained. The relationship of total porosity and bending strength can be linearly described as cement content change and water volume keep constant. Changing water-to-cement ratio obviously varies pore structure parameters' value accordingly.

Versatile Particle-Based Route to Engineer Vertically Aligned Silicon Nanowire Arrays and Nanoscale Pores.

Control over particle self-assembly is a prerequisite for the colloidal templating of lithographical etching masks to define nanostructures. This work integrates and combines for the first time bottom-up and top-down approaches, namely, particle self-assembly at liquid-liquid interfaces and metal-assisted chemical etching, to generate vertically aligned silicon nanowire (VA-SiNW) arrays and, alternatively, arrays of nanoscale pores in a silicon wafer. Of particular importance, and in contrast to current techniques, including conventional colloidal lithography, this approach provides excellent control over the nanowire or pore etching site locations and decouples nanowire or pore diameter and spacing. The spacing between pores or nanowires is tuned by adjusting the specific area of the particles at the liquid-liquid interface before deposition. Hence, the process enables fast and low-cost fabrication of ordered nanostructures in silicon and can be easily scaled up. We demonstrate that the fabricated VA-SiNW arrays can be used as in vitro transfection platforms for transfecting human primary cells.