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PurposeThe purpose of this study is to examine the role of trigger events and leadership crucibles in the lives of authentic leaders. The study was based on two theories: authentic leadership theory and born versus made theory.Design/methodology/approachParticipants were included in the study if they scored between 64 and 80 on the Authentic Leadership Questionnaire (ALQ). The qualified leaders were then asked to participate in a qualitative interview utilizing an interview guide born out of the relevant literature. The interview followed the guidelines of the Critical Incident Technique (CIT).FindingsThe data indicated that trigger events and leadership crucibles play a significant role in authentic leadership development.Practical implicationsPractitioners should emphasize the prominent themes of self-awareness, relational transparency, balanced processing and moral perspective and the connection with other themes that emerged from the current study when developing or training leaders. Furthermore, practitioners concerned with creating an authentic leadership culture may consider the findings of the current study to develop and employ hiring and promotion strategies that increase the probabilities of hiring and promoting leaders that exhibit authentic leadership behaviors.Originality/valueThe findings of the research indicate that trigger events and crucibles both affect authentic leadership development. The research findings confirm characteristics associated with authentic leadership theory were predominant in the participants. However, one theme that prevailed was that of spirituality, which may or may not be considered to be part of an authentic leader's moral perspective

Ionic transport through synthetic nanoporous membranes has received great attention in applications related to biosensing, fuel cell, and desalination. Past work has demonstrated that charge selectivity can be achieved by applying a potential across a metallized conductive membrane. However, challenges arise for improving charge selectivity as a result of irreversibility of the system from the anion adsorption at the membrane surface. This study demonstrates how charge selectivity can be improved with the presence of a well grown self-assembled monolayer (SAM), which can aid in applications that use chemical separation processes based on the surface charge of the nanopore. In this work, the transport and selectivity properties of gold-coated conductive nano-capillary-array-membranes (NCAMs) are studied using charged species methyl viologen paraquat, (MV2+) and napathalenedisulfonate disodium salt (NDS2−). The selectivity coefficients for MV2+ and NDS2− increased with the functionalization of undecanethiol on the gold-coated NCAM surface. With the presence of a SAM, the selectivity coefficients increased by 44% for MV2+ and 200% for NDS2−. The influence of ionic transport from the diffuse layer potential at the walls and surface of the nanopore is also discussed.

To treat wastewater containing paraquat, the interaction of the herbicide with unmodified and modified (i.e., chemically treated) proprietary silicas is explored using liquid chromatography—mass spectrometry and ultraviolet-visible spectrometry. Strong adsorption and rapid exchange kinetics (i.e., more than 80% within 30 s) of the contaminant onto both unmodified and modified silica surfaces indicate that paraquat adsorption is inherent to the unmodified silica. Although activated carbon sequesters paraquat more effectively than silica at long times (i.e., after 2 h), considering both constant mass and constant area approaches in loading the adsorbents, the best performance in the short-term (i.e., at least up to 150 s) interaction was achieved by using unmodified silicas. Comparison of data fitting to a competitive binding model with or without consideration of homogeneous solid diffusion indicates that, at least for times relevant to water-treatment applications, the competitive binding model is...

Interactions of supercritical water (SCW) with several carbon (including polycrystalline graphite, highly ordered pyrolytic graphite (HOPG), pyrolytic carbon, and diamond) and selected ceramic materials under oxic or anoxic conditions are investigated. Wettability and surface/material properties of samples, before and after the SCW exposure, are characterized with sessile drop contact angle measurement, profilometry, XPS, XRD, and ToF-SIMS. All tested ceramic materials became more hydrophilic during the SCW exposure, mainly due to hydrolysis reactions. Carbon samples exposed to oxic SCW became more hydrophilic as a result of surface oxidation. Carbon materials, except HOPG and diamond, became more hydrophobic when exposed to anoxic SCW because of degradation of hydrophilic oxygen functionalities. HOPG and diamond became more hydrophilic after anoxic SCW exposure mainly due to the removal of hydrophobic hydrocarbon contaminants. Hydrophobicity of different carbon samples exposed to SCW are explained based on the abundance of surface hydrophilic sites (i.e., oxygen functionalities, reactive carbon dangling bonds or defects), hydrocarbon impurities, and surface roughness.

Hydrogen sulphide is found in raw fuels such as natural gas and coal/biomass-derived syngas. It is poisonous to catalysts and corrosive to metals and therefore needs to be removed. This is often achieved using metal oxides as reactive adsorbents, but metal oxides perform poorly when subjected to repeated cycles of sulphidation and re-oxidation as a result of complex structural and chemical changes. Here, we show that Zn-Ti-O-based adsorbents with nanofibrous morphology can sustain their initial reactivity and sulphur removal capacity over multiple regeneration cycles. These nanostructured sorbents offer rapid reaction rates that overcome the gas-transport limitations of conventional pellet-based sorbents and allow all of the material to be used efficiently. Regeneration can be carried out at the same temperature as the sulphidation step because of the higher reactivity, which prevents sorbent deterioration and reduces energy use. The efficient regeneration of the adsorbent is also aided by structural features such as the growth of hierarchical nanostructures and preferential stabilization of a wurtzite phase in the sulphidation product.

An electrostatically driven valve-less peristaltic micropump for gas chromatography has been developed. A stepwise chamber was first fabricated using a three-dimensional (3D) fabrication technique known as detachment lithography; the stepwise design was intended to decrease the dead volume of the device and the operation voltage by inducing zipping action. The pump itself was fabricated with a silicon substrate and a polyimide (PI) diaphragm and operated by four electrodes with a 4-phase sequencing actuation. The pump was operated in a range starting from a voltage of 60 V and frequency of 4 Hz with a flow rate of 18.2 μl/min, up to a voltage of 90 V at a frequency of 6 Hz with a maximum flow rate of 33.1 μl/min. The results showed that the minimum operating voltage of the stepwise chamber was approximately 30% lower than that of a vertical chamber with the same depth, and the power consumption per unit flow rate was also decreased by about 10%.

A micro-flame ionization detector (micro-FID) design is presented that is targeted for use in a portable gas sensor. Our micro-FID is based on a diffusion flame and features a folded flame structure that is more sensitive than a counter-flow flame designs. Unlike conventional FIDs that use a premixed or open diffusion flame, an air–hydrogen diffusion flame is employed and tested in an encapsulated structure of Quartz–Macor–Quartz layers. Diffusion flames are generally known to be more controllable and stable than premixed flames, where the stability of the micro-FID plays an important role for portable gas sensors. Various channel designs for oxidant and fuel flows meeting with different angles at the burner cavity are tested to obtain a stable flame and high output sensitivity over methane test samples. To verify the empirically designed microchannel, we simulate the temperature distribution in the microchannel by using computational fluid dynamics (CFD) software. To gauge the sensitivity of the device, the collected electric charges per mole (C/mol) is calculated and taken as a reference value of ionization efficiency. The result of the folded flame design is 1.959 × 10 −2 C/mol for methane that is about 34 times higher than the result using a counter-flow flame, which is 5.73 × 10 −4 C/mol for methane, while one of the commercial macro FIDs’ is 10 −1 C/mol. This result shows that the micro-FID using the folded flame structure has higher ionization efficiency with less leakage of the analytes than of the classical counter-flow flame design.

This paper reports the integration of both electrical and thermal elements into the free end of an atomic-force microscope cantilever, where the electrode and heater-thermometer are electrically isolated by an NPN semiconductor back-to-back diode. The electrothermal cantilever can be self heated using an integrated solid-state heater to more than 600°C. The tip voltage can be measured or controlled independent of the tip temperature, either in the direct or the alternating current mode. To our knowledge, this setup is the first microcantilever to have a solid-state junction and heater integrated near a scanning probe tip.

This article introduces an on-demand microfluidic hydrogen generator that can be integrated with a micro-proton exchange membrane (PEM) fuel cell. The catalytic reaction, reactant circulation, gas/liquid separation, and autonomous control functionalities are all integrated into a single microfluidic device. It generates hydrated hydrogen gas from an aqueous ammonia borane solution which is circulated and exchanged between the microfluidic reactor and a rechargeable fuel reservoir without any parasitic power consumption. Ammonia borane is chosen instead of sodium borohydride because of its faster hydrogen generation rate, higher hydrogen storage capability, stability, and better catalyst durability. The self-circulation of the ammonia borane solution was achieved using directional growth and selective venting of hydrogen bubbles in micro-channels, which leads to agitation and addition of fresh solution without consumption of electrical power. The self-regulation mechanism ensures that hydrogen can be supplied to a fuel cell according to the exact demand of the current output of the fuel cell. The circulation flow rate of ammonia borane solution is also automatically regulated by the venting rate of hydrogen at the gas outlet. Design, fabrication, and testing results of a prototype system are described. The hydrogen generator is capable of generating hydrogen gas at a maximum rate of 0.6 ml/min (2.1 ml/min cm2) and circulating aqueous ammonia borane at a maximum flow rate of ~15.7 μl/min. The device has also been connected with a micro-PEM fuel cell to demonstrate the feasibility of its practical applications in a high-impedance system.

Herein, we discuss the synthesis as well as material and photochemical characterization of nanometer-sized Ta(2)O(5) decorated, in a controlled fashion, on top of 20 nm diameter SiO(2) particles to yield a composite oxide with a tunable band-gap width. Particular emphasis is paid to control of particle size, and control of the distribution of the overlying oxide. The nanoscale dimension imparts a high surface area and introduces quantum confinement effects that displace the conduction band more negatively and the valence band more positively on the electrochemical scale of potentials. This band shift results in an increase of the number of possible participants in photocatalytic reactions. The band shift is shown to result in an increase in driving force for thermodynamically feasible reactions. By decorating SiO(2) with smaller-sized Ta(2)O(5), the interplay of the Lewis acidity of SiO(2) and the contact area between Ta(2)O(5) and SiO(2) is utilized to develop a photocatalyst with higher photoactivity than pure Ta(2)O(5).

In this report, SrFeO 3 photocatalyst powder was synthesized by a high temperature solid state reaction method and the size of the particle was reduced with a high energy ball milling machine. The morphology, crystalline structure, particle size and size distribution of obtained samples were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV–vis spectrometer, scanning electron microscope (SEM), and transmission electron microscopy (TEM). Photocatalytic activity of the prepared samples was investigated by photodegradation of methylene blue (MB). The obtained results show that the SrFeO 3 sample works as photocatalyst and by reducing the particle size using high energy ball milling method for 5 h milling, particles with 19–25 nm crystallite size exhibit maximum activity due to larger surface area. The photocatalytic activities of the powders were investigated and kinetics of reaction was modeled by using high performance liquid chromatography (HPLC) and Mass spectroscopy. Photocatalytic activities of these powders increase with decreasing particle size.

An electrostatically driven valveless peristaltic micropump has been developed for pumping gases through microsystems, such as a micro-gas chromatography system. The pump was operated from 85 V up to 115 V, and a maximum flow rate of 40.3 μl/min was measured at 14 Hz and 95 V with an estimated power consumption of 0.87 mW /sccm. The peristaltic micropump has one long chamber and four electrodes that divide one chamber into four small chambers during operation.

Many microfabricated gas chromatography (micro-GC) column designs have been reported so far, but it is unclear how microcolumn design affects separation performance in the typical isothermal or temperature-programmed mode of operation. This paper compares the separation performance of microfabricated serpentine, circular-spiral and square-spiral columns in both modes of operation. Experimentally although all the geometries have similar gas permeability and unretained solute band broadening, it is shown that the serpentine columns show higher separation plate numbers (lower band broadening) for retained solutes in isothermal mode of operation compared to circular- or square-spiral configurations. Also in temperature-programmed mode of operation, the serpentine design yields higher separation numbers (peak–peak resolution) compared to spiral configurations. The advantage of using a serpentine configuration is clearly evident especially in the velocity range of 15–40 cm/s in either operation modes, and independent of the temperature programming rate in temperature-programmed mode. An exemplary mix of 33 chemicals was used to demonstrate the higher speed and resolution of practically relevant separations on serpentine column.

Nanosized TiO2 and nano-anatase TiO2 decorated on SiO2 spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO2 nano particle and TiO2 grafted on SiO2 sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO2/SiO2 particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO2 particles.

Microfuel cells (MFCs) can potentially power emerging technologies that require power sources in the microliter size range. The recent development of a microfluidic mechanism for self-regulated generation of hydrogen has enabled fabrication of MFCs orders of magnitude smaller than previously possible. In this study, we report an order of magnitude enhancement in the power density of a microliter-scale fuel cell incorporating a new microfluidic design. The microfluidic mechanism is part of an on-board hydrogen generator that uses a reaction between a metal hydride, LiAlH 4 , and water vapor to generate hydrogen. The hydrogen generated exits the hydride reactor through a porous silicon wall to reach a Nafion-based membrane electrode assembly (MEA). The microfluidic design increased the water vapor release rate to the hydride reactor by one order of magnitude over a previous design. A 9 μL device incorporating the enhanced microfluidic design delivered a power density of 92 W L −1 . Details of a parametric study conducted to improve the water vapor release rate of the microfluidic mechanism and performance analysis of the integrated device are presented in this paper.

Proton exchange membrane fuel cells have the potential for applications in energy conversion and energy storage, but their development has been impeded by problems with the membrane electrode assembly. Here, we demonstrate that a silicon-based inorganic-organic membrane offers a number of advantages over Nafion--the membrane widely used as a proton exchange membrane in hydrogen fuel cells--including higher proton conductivity, a lack of volumetric size change, and membrane electrode assembly construction capabilities. Key to achieving these advantages is fabricating a silicon membrane with pores with diameters of approximately 5-7 nm, adding a self-assembled molecular monolayer on the pore surface, and then capping the pores with a layer of porous silica. The silica layer reduces the diameter of the pores and ensures their hydration, resulting in a proton conductivity that is two to three orders of magnitude higher than that of Nafion at low humidity. A membrane electrode assembly constructed with this proton exchange membrane delivered an order of magnitude higher power density than that achieved previously with a dry hydrogen feed and an air-breathing cathode.

A technique to create arrays of micrometer-sized patterns of photosensitive polymers on the surface of elastomeric stamps and to transfer these patterns to planar and nonplanar substrates is presented. The photosensitive polymers are initially patterned through detachment lithography (DL), which utilizes the difference in adhesion forces to induce the mechanical failure in the film along the edges of the protruded parts of the mold. A polydimethylsiloxane (PDMS) stamp with a kinetically and thermally adjustable adhesion and conformal contact can transfer the detached patterns to etched or curved substrates, as well as planar ones. These printed patterns remain photochemically active for further modification via photolithography, and/or can serve as resists for subsequent etching or deposition, such that photolithography can be used on highly nonconformal and nonplanar surfaces. Various 3D structures fabricated using the process have potential applications in MEMS (micro-electromechanical systems) sensors/actuators, optical devices, and microfluidics.

Growing interest in small-scale, portable energy systems such as fuel cells has necessitated the development of small-scale fuel processing or reforming systems. Many fuel reforming systems require reliable heat sources as in some cases temperatures in excess of 600°C maybe required. Sub-millimeter combustors can provide such a heat source; however, a broader set of design rules are needed for constructing systematically engineered heat sources. In this article, experimental observations and computational fluid dynamics modeling results are presented for stable and steady confined flame structures within an alumina sub-millimeter combustor. Influence of inlet flow and thermal boundary conditions are evaluated through a parametric study. The inlet flow rates and relative gas composition, the thermal boundary conditions that include thermal conductivity of the walls, convection of heat to and from the walls, and radiation of heat energy through the walls all determine the position, structure, and temperature of the reacting fluid and combustor walls. The model shows the importance of radiative heat transfer in the formation of the steady-state flame structures within the microcombustor.

Micro-proton exchange membrane fuel cells are considered to be the next generation power sources for micro-scale power applications, but onboard hydrogen storage and generation with high energy density at the small scale is still a technical barrier. This paper introduces a hydrogen generation method based on an onboard hydride fuel and a byproduct water recovery mechanism for micro-hydrogen PEM fuel cells. The water recovery is carried out by water diffusion from the more humid cathode side to the less humid anode side through the proton exchange membrane. The micro-fuel cells based on this water recovery method were constructed and tested. The results demonstrate that the relative humidity has a significant affect on the fuel cell performance as well as the opening area on the cover layer, the type of hydrides, and the thickness of the Nafion membrane also can affect the fuel cell performance. A 10 mm 3 prototype water recovery micro-fuel cell has been built and tested, and the device has produced a maximum power density of 104 W L −1 and a maximum energy density of 313 W h L −1 .

Similar in both form and function to a classical circular membrane inflation experiment, cell-elastomer composite diaphragm inflation (CDI) experiments have recently been introduced as a methodology for exploring the mechanobiological properties of cell–cell anchoring junctions and cytoskeletal protein networks within a living epithelial sheet. Despite outward similarities, CDI experiments are unique from classical membrane inflation in that the loading associated with the inflation process, though axisymmetric, is inherently non-uniform. In order to better account for the effects of non-uniform loading in a CDI experiment, we introduce a model for the quasi-static inflation of a prestretched clamped circular isotropic incompressible hyperelastic membrane into a horizontally semi-infinite incompressible liquid reservoir of finite vertical depth. A set of coupled nonlinear first-order differential equations is shown to govern the inflation process. Assuming a Mooney–Rivlin (MR) constitutive model, the governing equations are formulated into a boundary value problem, and a procedure is developed for finding numerical solutions that quantify discrete membrane inflation states in terms of deformations, displacements, curvatures, stress resultants, and an inflation pressure distribution. Through iteration of the discrete state solution procedure, we further demonstrate how to generate a polynomial interpolating function that approximates the continuous volume–pressure response of a MR membrane. Select numerical examples are used to simulate the inflation response of a polydimethylsiloxane (PDMS) elastomer membrane used in an actual CDI experiment.

A method is introduced for estimating values of the hyperelastic material parameters and the residual membrane tension (prestretch) that best describe a set of volume-pressure inflation response data acquired during a cell-elastomer composite diaphragm inflation (CDI) experiment. Based on a model for the quasi-static inflation of a prestretched clamped circular isotropic incompressible hyperelastic membrane into a horizontally semi-infinite incompressible liquid reservoir of finite vertical depth, the fit methodology presented here is developed explicitly for a Mooney-Rivlin (MR) strain energy function. The parameter fit is formulated as a nonlinear least-squares optimization problem (NLSOP), and two empirical constraints are postulated to restrict the domain of model fit parameters to physically relevant values. A numerical least-squares regression analysis utilizing the Nelder-Mead simplex algorithm is proposed for solving the constrained NLSOP. To demonstrate the capabilities of the method, the fit procedure is utilized to estimate the residual membrane tensions and the MR constitutive parameters C 1 and C 2 that characterize the pseudoelastic loading and unloading responses of a polydimethylsiloxane elastomer membrane as observed in the context of a CDI experiment. The material parameter estimates are verified as being both accurate and repeatable, and the MR non-uniform inflation model is shown to produce better fits (in a least-squares sense) than direct polynomial fitting of the original data set. Extension of the fit methodology to volume-pressure data measured for cell-elastomer composite diaphragm specimens, though possible, requires the development of new constitutive models that can better account for the complex rheological behavior of a living epithelial sheet.

We report here a methodology to measure and characterize the interface properties of thin, insulating films that separate a gold electrode and an electrolyte solution, for cases when the electrolyte solution does not contain electro-active ions in appreciable amounts, by using experimental impedance data. Traditionally, in the absence of redox-active species either in the electrolyte or at the terminal headgroup, monolayer films on polycrystalline gold electrodes have been modeled as ideal dielectric capacitors. However, potential-dependent background currents are usually observed for gold−monolayer−electrolyte systems, even in the absence of redox-active moieties. A qualitative description of the background current density as a barrier-limited flux of charge that applies irrespective of the actual mechanism of charge transport through the monolayer film is proposed in this paper. The potential-dependent, low-frequency impedance data is shown to characterize the properties of this limiting energy barrier....

Capacitive (C) pressure sensors typically sense quadratic changes in C as a pressure difference (P) deflects a flexible conducting diaphragm near a rigid ground plane. Touch-mode capacitive pressure (C-P) sensors, where the conducting diaphragm touches a dielectric coated ground plane, often show a more linear response, but with less sensitivity, particularly at low-P. Initial contact of the diaphragm often occurs at a critical P. Until Pcrit is reached, the sensitivity is typically too low for accurate measurements. In this work, two different types of electrodes with ldquoparabolicrdquo and ldquodonutrdquo cavity-shapes have been designed, fabricated, and tested to achieve high-sensitivity at low-pressures. A flexible conducting diaphragm touches the bottom electrode smoothly, and both cavity shapes permit initial contact at a zero-pressure differential. This type of C-P sensors can have touch-mode and peeling-mode operations. The sensitivities of these sensors in two operation modes were measured, and their resolutions were smaller than 0.1 Pa at a mean pressure of 105 Pa. Both sensors in two modes have the resolution over total-pressure less than 106, which is difficult to achieve at atmospheric pressure.

This paper introduces and discusses the feasibility of millimeter scale powder packed-bed reactors using high energy density chemical hydrides for micro-PEM fuel cell applications. Two different reactors were designed and tested using LiBH4, LiAlH4, NaAlH4 and CaH2 hydride fuels. The mechanisms that limit the total yield of H2 generated and impact the performance of the hydrogen generator are investigated in this paper, including density, solubility and porosity of the reaction byproducts. The volume expansion of the byproducts has significant effect on the total energy density of micro-hydrogen generators because the byproducts are left in the millimeter scale reactor after the reactions and the micro-hydrogen generators have limited fuel storage space. The SEM images of the reaction byproducts indicates that the byproducts of LiBH4 can form a single solid mass that clogged the reaction vessel and limit the full utilization of the hydride. However, the byproducts of LiAlH4 and CaH2 reactions are non-agglomerated and they do not form impermeable mass. The experimental results show that the highest yield of hydrogen generation was achieved with LiAlH4 and CaH2 fuels.

We report microfabrication of a millimeter-scale fuel cell with onboard fuel and a passive control mechanism. This unique power source has a total volume of 9 muL (3times3times1 mm3), which makes it the smallest fully integrated fuel cell reported in the literature. The first generation of this device delivered an energy density of 254 Wmiddoth/L. The device uses a reaction between a metal hydride, LiAlH4, and water vapor to generate hydrogen in a reactor. The generated hydrogen exits the reactor through a nanoporous silicon wall to reach a hybrid silicon/Nafion membrane electrode assembly. A passive micro- fluidic control system regulates hydrogen generation through controlled delivery of water vapor to the metal hydride based on the reactor pressure. The development of this unique power source greatly benefits the portable electronics industry and enables future technologies that require significantly high energy density power sources such as cognitive arthropods ("thinking" insect- sized robots). This paper provides details of the device micro- fabrication processes, component integration, and performance analysis. [2008-0168].

Micro-power sources that are comparable to or smaller than the size of the micro-devices needing power are needed for many applications. This paper introduces an integrated millimeter scale power source based on a micro-silicon fuel cell and a MEMS hydrogen generator, with passive control. The integrated devices are fabricated from silicon wafers using conventional MEMS fabrication processes. In this design, the hydrolysis reaction of calcium hydride and water is used to generate hydrogen, and the hydrogen generation rate is controlled by a microfluidic self-regulating mechanism, which can control the hydrolysis reaction based on the load. Design, fabrication, and testing results of a prototype system are described. One of the devices can produce 90 μW for 6 h with a maximum power of 0.17 mW, and another one can produce 30 μW for 26 h with a total energy density of 100 Wh L −1 .

The ever-increasing power demands and miniaturization of portable electronics, micro-sensors and actuators, and emerging technologies such as cognitive arthropods have created a significant interest in development of micro fuel cells. One of the major challenges in development of hydrogen micro fuel cells is the fabrication and integration of auxiliary systems for generating, regulating, and delivering hydrogen gas to the membrane electrode assembly (MEA). In this paper, we report the development of a hydrogen gas generator with a micro-scale control system that does not consume any power. The hydrogen generator consists of a hydride reactor and a water reservoir, with a regulating valve separating them. The regulating valve consists of a port from the water reservoir and a movable membrane with via holes that permit water to flow from the reservoir to the hydride reactor. Water flows towards the hydride reactor, but stops within the membrane via holes due to capillary forces. Water vapor then diffuses from the via holes into the hydride reactor resulting in generation of hydrogen gas. When the rate of hydrogen consumed by the MEA is lower than the generation rate, gas pressure builds up inside the hydride reactor, deflecting the membrane, closing the water regulator valve, until the pressure drops, whereby the valve reopens. We have integrated the self-regulating micro hydrogen generator to a MEA and successfully conducted fuel cell tests under varying load conditions.

Microwave-assisted chemical vapor deposition has been used to generate high quality, high- k dielectric films on silicon at high deposition rates with film thicknesses varying from 50 nm to 110 μm using inexpensive equipment. Characterization of the post deposition products was performed by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy and Raman spectroscopy. Film growth was determined to occur via rapid formation and accumulation of tantalum oxide clusters from tantalum (v) ethoxide (Ta(OC 2 H 5 ) 5 ) vapor on the deposition surface.

Micron thick tantalum pentoxide (Ta2O5) films have been proposed as thermal insulating layers in microchemical systems, but so far it has been difficult to deposit thick enough films over complex substrates. So far sol–gel films cracked upon heating whenever the film thicknesses were above 350 nm. A 350 nm thick film is too thin for effective insulation. Other techniques are not suitable for coating the complex structures associated with microchemical systems. In this paper we report sol–gel synthesis of 1.6 μm thick tantalum pentoxide (Ta2O5) films. The films are almost crack free, and adhere to silicon surfaces even upon flashing to 900 °C. The key to the synthesis is the addition of Polyvinylpyrrolidine (PVP) to the sol. Films grown in the absence of PVP all show cracks upon calcination to 900 °C while few cracks are seen with PVP. X-ray diffraction and Fourier transform infra red analysis show that orthorhombic Ta2O5 is formed in all cases. X-ray photoelectron spectroscopy shows the O:Ta ratio to be 2.8:1. This shows that sol–gel is a viable process for making the micron thick films of Ta2O5 needed as insulators for microchemical systems.

Nanofluidics presents growing and exciting opportunities for conducting fundamental studies for processes and systems that govern molecular-scale operations in science and engineering. In addition, nanofluidics provides a rapidly growing platform for developing new systems and technologies for an ever-growing list of applications. This review presents a summary of the transport phenomena in nanofluidics with a focus on several systems and applications important to problems of public health and welfare. Special emphasis is afforded to the role of the electric double layer and the molecular-scale interactions that occur within confined nanoscale systems.

Microfluidic devices allow manipulation of reagents and fluids in a semi-automated fashion, ideal for performing multiple measurements or conditioning various reagents. Here, an enzyme assay has been performed in a multilayer poly(methyl methacrylate)-based microfluidic device, where the layers are fluidically connected via a nanocapillary array membrane serving as an effective injector and valve. As a model system, beta-glucuronidase from Escherichia coli and fluorescein di(beta-D-glucuronide) are used for the assay; offline mixing and online incubation of substrate and enzyme allow determination of the initial hydrolysis rates of the substrate under catalysis by beta-glucuronidase. The Michaelis constant Km was determined to be ~4.0 muM for the enzyme of 83 units/mL at ambient temperature. The 50% inhibitory concentration IC50 of D-saccharic acid-1,4-lactone to 167 units/mL was estimated to be 3.0 muM. These results demonstrate added functionality for a poly(methyl methacrylate)-based nanocapillary array membrane-containing microfluidic device for following enzyme reaction kinetics.

This article demonstrates how to prepare microfabricated columns (microcolumns) for organophosphonate and organosulfur compound separation that rival the performance of commercial capillary columns. Approximately 16,500 theoretical plates were generated with a 3 m long OV-5-coated microcolumn with a 0.25 microm phase thickness using helium as the carrier gas at 20 cm/s. Key to the advance was the development of deactivation procedures appropriate for silicon microcolumns with Pyrex tops. Active sites in a silicon-Pyrex microcolumn cause peak tailing and unwanted adsorption. Experimentally, we found that organosilicon hydride deactivation lowers adsorption activity in microcolumns more than silazane and silane treatments. But without further treatment, the phosphonate peaks continue to tail after the coating process. We found that heat treatment with pinacolyl methylphosphonic acid (PMP) eliminated the phosphonate peak tailing. In contrast, conventional resilylation employing N, O-bis(trimethylsilyl)acetamide, hexamethyldisilazane, and 1-(trimethylsilyl)imidazole does not eliminate peak tailing. Column activity tests show that the PMP treatment also improves the peaks for 2,6-dimethyl aniline, 1-octanol, and 1-decanol implying a decrease in the column's hydrogen bonding sites with the PMP treatment. FT-IR analysis shows that exposure to PMP forms a bond to the stationary phase that deactivates the active sites responsible for organophosphonate peak tailing.

Atomic force microscopy, attenuated-total-reflection Fourier-transform infrared (FTIR) spectroscopy, and sum-frequency vibrational spectroscopy (SFVS) were employed to study effects of heat treatment in different gas atmospheres on three different alumina crystalline surfaces (a, c and r) and subsequent hydroxylation. Samples heat-treated at a higher temperature (1550 °C) exhibited more surface roughening and faceting than those heated at 1000 °C. Also, the roughening and faceting depended on the gaseous atmosphere used during heat treatment. The SFVS and FTIR spectra showed clearer spectral features of hydroxylation and higher degree of hydroxylation for heat treatment at higher temperatures. Different crystalline surfaces displayed different spectral features upon hydration. Hydration of sample surfaces in water appears to be more effective than in humid air.

Details are presented for the formulation, fabrication, and mechanical characterization of mesoscopic freestanding polydimethylsiloxane (PDMS) elastomer membranes, 10.0 microm thick and 5.0 mm in diameter, used to probe the rheology of a living epithelial sheet. In what is described as a composite diaphragm inflation (CDI) experiment, freestanding PDMS membranes are utilized as substrates for the culture of a sheet of epithelial cells. Together, the cell layer and the PDMS elastomer form a composite diaphragm (CD) that is suitable for mechanical testing in an axisymmetric membrane inflation experiment. In order to distinguish the rheological behavior of the epithelial sheet from the mechanical response of the elastomer using inflation test data, freestanding PDMS membranes should exhibit a highly compliant yet mechanically invariant finite load-deformation response when subjected to multiple inflation cycles following intermittent periods of cell culture. Given these considerations, we describe a method for preparing freestanding PDMS elastomer membrane specimens that are optically transparent, tensed, and wrinkle-free. Surface modifications intended to facilitate cell culture, namely water vapor plasma and ultraviolet light treatments, were shown to dramatically stiffen the mechanical response of the membranes, rendering them unusable as CD substrates. In this study, only PDMS membranes with physiosorbed collagen demonstrated the mechanical compliance, fatigue resistance, and environmental stability necessary for reliable use in CDI experiments.

This paper describes a new bidirectional high-pressure gas electrostatic microvalve that opens and closes in 50 or less. The microvalve consists of a valve-closing electrode, a flexible movable membrane, and a valve-opening electrode that is directly opposed to the valve-closing electrode. The membrane contains an embedded electrode, so the valve can zip closed when a potential is applied between the membrane and the valve-closing electrode. The valve-opening electrode allows the valve to open again in a rapid discontinuous motion, without requiring a large applied potential. A pressure-balance port is used to enhance the microvalve switching speed and to allow the valve to close against applied pressures greater than 8.3 atm (840 kPa). The gas conductance through the valve is 2.8 nl/Pa ldr s (17 sccm/atm), and the fluid leakage measured zero over the entire pressure range up to a burst pressure of 10.8 atm (1.1 MPa). Measurements show that the valve can open or close in 50 or less for applied pressures up to 126 kPa. In an extended lifetime test, a sample microvalve has been opened and closed 47 million times before failure.

The objective of this paper is to report the recent progress in the development of porous silicon fuel cells for micro power generation. Previous work has demonstrated that an acid loaded porous silicon membrane could be a suitable proton conducting material that is compatible with silicon microfabrication technology. In this paper, we present recent improvements to our previously published micro fuel cell designs that achieve 94 mW cm−2 at room temperature. In addition, a percolation model is shown to be suitable for understanding the proton transport mechanism in acid loaded porous silicon membranes.

Non-premixed methane-oxygen flame dynamics and structures confined within an alumina combustor are described. Non-stabilized, transient flame dynamics and phenomena leading to the formation of a stable edge-like flame and distinct cellular structures that take place within combustor channels of dimensions 35 mm long, 5 mm wide, and 0.75 mm high (combustor volume ∼ 130 mm3) are discussed. These confined flames are surveyed by measuring the external wall temperatures, high-speed and still-frame visual flame imaging, recordings of emitted acoustics from the combustor, and capturing visible, CH*, and OH* chemiluminescence through a sapphire window. The observed dynamic flame structure is an oscillating edge-like flame accompanied by ignition-extinction events that precede the formation of a stable edge-like flame and flame cells in the reaction channel. The cellular flame structures in all cases exhibit a confined tribrachial structure with a folded or extinguished rich branch while the lean branch survives. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Advances in microelectromechanical systems have generated an ever-growing demand for novel insulating material applicable to high-temperature systems. Ta2O5 is appealing for such applications because of its high index of refraction, refractory nature, and negligible absorbance in the infrared region. The challenge faced in the realization of such materials is the synthesis of crack-free Ta2O5 films whose thickness is on the order of a quarter wavelength of the incident infrared radiation. This work seeks to investigate the effect of addition of polyvinyl pyrollidone (PVP) as a binder material in the presence of 2-methoxyethanol and acetylacetone in the sol−gel synthesis of thick, uniform, and crack-free Ta2O5 films. Incorporation of PVP into the sol precursor has enabled uniform and crack-free films with thicknesses of up to 2.4 μm to be realized. Chemical probing of the precursor was conducted via TGA, FTIR, and NMR analysis of the sol to elucidate the processes behind this film formation, showing that t...

We report here a technique to print small volumes of liquid on a hydrophobic substrate. This process is based on the control of the critical parameters that govern a quasi-equilibrium liquid transfer process from one surface to another. We present a qualitative model that describes the physics of a transfer printing process between hydrophobic surfaces, and we use the parameters outlined in this model to manipulate the amount of liquid transferred between surfaces. We demonstrate the printing of discrete, small volumes (approximately 70 fL) of different liquid inks on a polymer substrate starting with volumes that are 8 orders of magnitude larger (a droplet of approximately 10 microL) in a simple two-step procedure.

Dielectrophoretic separation of particles finds a variety of applications in the capture of species such as cells, viruses, proteins, DNA from biological systems, as well as other organic and inorganic contaminants from water. The ability to capture particles is constrained by poor volumetric scaling of separation force with respect to particle diameter, as well as the weak penetration of electric fields in the media. In order to improve the separation of sub-micron colloids, we present a scheme based on multiple interdigitated electrode arrays under mixed AC/DC bias. The use of high frequency longitudinal AC bias breaks the shielding effects through electroosmotic micromixing to enhance electric fields through the electrolyte, while a transverse DC bias between the electrode arrays enables penetration of the separation force to capture particles from the bulk of the microchannel. We determine the favorable biasing conditions for field enhancement with the help of analytical models, and experimentally demonstrate the improved capture from sub-micron colloidal suspensions with the mixed AC/DC electrostatic excitation scheme over conventional AC-DEP methods.

This paper reports on microscale silicon-based direct formic acid fuel cells (Si-DFAFCs) in which the fuel and the oxidant are supplied to the electrodes in a passive manner. Passive delivery of fuel and oxidant eliminates the need for ancillary components and associated parasitic losses. In this Si-DFAFC, an aqueous solution of formic acid is in direct contact with a Pd- or Pt-based anode and a Pt-based cathode is exposed to either a forced oxygen stream or quiescent air. In the presence of a forced oxygen flow on the cathode side the cell with Pd catalyst on the anode delivers a maximum power density of about 30 mW cm −2 at room temperature, limited mostly by mass transfer at the anode, while in an all-passive mode (quiescent air on the cathode side) a maximum power density of 12.3 mW cm −2 is obtained, limited by oxygen transport. This all-passive Si-DFAFC is fabricated using processes that are post-CMOS compatible, and thus can be integrated directly with envisioned MEMS applications, such as small sensors and actuators.

This paper reports on the development of a multi-layer microscale impedance measurement system with integrated working, counter, and reference electrodes that can be used to probe transport at the nanoscale. System fabrication and testing are carried out to demonstrate the feasibility of such a system for characterizing transport through nanocapillary array membranes (NCAMs). Results indicate that transport through NCAMs is a complex phenomenon, and impedance does not scale linearly with either pore diameter or ionic concentration. Use of a microscale construct for probing ionic transport at the nanoscale appears to be a promising path forward with further development.

Silicon-based fuel cells are under active development for chip-scale electrical power supply. One of the greatest challenges in micro-fuel-cell research is the development of a suitable proton conducting membrane material that is compatible with standard silicon microfabrication technology. In this paper, the use of nanoporous silicon as a novel proton conducting membrane material in a microscale fuel cell membrane electrode assembly (MEA) is demonstrated. The devices were fabricated by first creating 100-/spl mu/m-thick silicon windows in a standard silicon wafer, anodizing to create pores in the windows, and then painting catalyst layers and insulators onto the porous structures. Using 5 M formic acid and 0.5 M sulfuric acid as the fuel, the fuel cell peak power density reached about 30 mW/cm/sup 2/ at current density level of about 120 mA/cm/sup 2/. These results represent the successful integration of a new class of protonic conductor into a microfabricated silicon fuel cell.

Thin films (0.85 μm, 3 μm) of Ta 2 O 5 deposited on Si and SiO 2 were heated to 900 °C. Their reflectance in the infrared was measured using a Fourier transform infrared spectrometer equipped with a multiple angle reflectometer before and after exposure to the high-temperature heat treatment. An interfacial layer (TaSi X O y ) formed by the diffusion of Si from the substrate into the deposited film was observed using Auger depth profiling, and the effect of this interfacial layer on the reflectance was measured. Using a least squares optimization technique coupled with an optical admittance algorithm, the multiple angle reflectance data were used to calculate the optical constants of the as deposited Ta 2 Ο 5 film, crystalline Ta 2 Ο 5 , and the interfacial layer in the 1.6 to 10 μm range. The interfacial layer formed due to exposure to high temperature was found to be more absorptive than the crystalline Ta 2 Ο 5 .