Electroosmotically induced hydraulic pumping with integrated electrodes on microfluidic devices

Electroosmotic manipulation of fluids was demonstrated using thin metal electrodes integrated within microfluidic channels at the substrate and cover plate interface. Devices were fabricated by photolithographically patterning electrodes on glass cover plates that were then bonded to polymeric substrates into which the channels were cast. Polymeric substrates were used to provide a permeable membrane for the transport and removal of gaseous electrolysis products generated at the electrodes. Electroosmotic flow between interdigitated electrodes was demonstrated and provided electric field-free pumping of fluids in sections of the channel outside of the electrode pairs. The resultant pumping velocities were shown to be dependent on the applied voltage, not on the applied field strength, and independent of the length of the electroosmotically pumped region.     

Protein analyses using differential ion mobility microchips with mass spectrometry

Differential ion mobility spectrometry (FAIMS) integrated with mass spectrometry (MS) is a powerful new tool for biological and environmental analyses. Large proteins occupy regions of FAIMS spectra distinct from peptides, lipids, or other medium-size biomolecules, likely because strong electric fields align huge dipoles common to macroions. Here we confirm this phenomenon in separations of proteins at extreme fields using FAIMS chips coupled to MS and demonstrate their use to detect even minor amounts of large proteins in complex matrixes of smaller proteins and peptides.     

The transport of ion bombardment induced ripples

It is demonstrated that a theory which predicts that ripples produced by ion bombardment are transported across the surface, as a result of the surface gradient dependence of the sputtering rate, is invalid and that its modification reveals their stationary behaviour. Other processes which could lead to such transport are examined.     

Differential ion transport induced electroosmosis and internal recirculation in heterogeneous osmosis membranes

Water and ion transport through a heterogeneous membrane separating two electrolyte solutions at different concentrations is investigated by using molecular dynamics simulations. The membrane features pairs of oppositely charged pores with identical diameters. Simulation results indicate that the differential transport of K(+) and Cl(-) ions through the membrane pores creates an electrical potential difference across the membrane, which then induces an electroosmotic water flux. The induced electroosmosis creates an internal recirculation loop of water between adjacent pores. The implications of these new observations are discussed.     

Nanoionics: ion transport and electrochemical storage in confined systems

The past two decades have shown that the exploration of properties on the nanoscale can lead to substantially new insights regarding fundamental issues, but also to novel technological perspectives. Simultaneously it became so fashionable to decorate activities with the prefix 'nano' that it has become devalued through overuse. Regardless of fashion and prejudice, this article shows that the crystallizing field of 'nanoionics' bears the conceptual and technological potential that justifies comparison with the well-acknowledged area of nanoelectronics. Demonstrating this potential implies both emphasizing the indispensability of electrochemical devices that rely on ion transport and complement the world of electronics, and working out the drastic impact of interfaces and size effects on mass transfer, transport and storage. The benefits for technology are expected to lie essentially in the field of room-temperature devices, and in particular in artificial self-sustaining structures to which both nanoelectronics and nanoionics might contribute synergistically.     

Indirect fluorescence detection of amino acids on electrophoretic microchips

Microfabricated devices enable rapid separations of a variety of clinically significant analytes, including DNA, proteins, and amino acids. However, absorbance detection has been difficult to achieve on these devices, prohibiting analysis of nonfluorophore-bearing or nonfluorescently tagged analytes. An alternative detection technique exploiting indirect fluorescence has been adapted to the electrophoretic microchip to provide fast analysis of amino acids, bypassing the need for absorbance detection or fluorescence derivitization procedures. Nineteen of the standard amino acids could be detected with an average detection limit of 32.9 microM (approximately 1.6 amol). Despite the fact that the detection sensitivity was lower than that achievable by labeling the amino acids with fluorescein isothiocyanate (approximately 1 nM), circumventing sample preparation and the difficulties inherent with tagging complex samples make this technique attractive for a variety of assays where sensitivity is not critical. To demonstrate the applicability to real sample matrixes, the analysis of urine with elevated amino acid levels is used as a model system where the elevated levels are indicative of a variety of pathologies including amino acid metabolism disorders and kidney malfunction. The minimal sample handling and rapid separations achievable by employing indirect detection on microchips provides the potential for high-throughput applications for certain amino acid analyses.     

Electrical transport in ion beam created InAs nanospikes

Ion beam irradiation has previously been demonstrated as a method for creating nanowire-like semiconductor nanostructures, but no previous studies have reported on the electrical properties of those structures. In this work we describe the creation and in?situ transmission electron microscopy electrical characterization of nanoscale InAs spike structures on both InAs and InP substrates fabricated using a focused ion beam erosion method. Those InAs 'nanospikes' are found to possess internal structures with varying amounts of ion damaged and single crystalline material. Nanospike electrical behavior is analyzed with respect to model electronic structures and is similar to cases of barrier limited conduction in nanowires. The different electrical responses of each nanospike are found to be the result of variation in their structure, with the conductivity of InAs nanospikes formed on InAs substrates found to increase with the degree of nanospike core crystallinity. The conductivity of InAs nanospikes formed on InP substrates does not show a dependence on core crystallinity, and may be controlled by the other internal barriers to conduction inherent in that system.     

Low-valence ion addition induced more compact passive films on nickel-copper nano-coatings

Ni-Cu nano-coatings were prepared by pulsed electroplating technique in the baths containing various amount of boric acid. Their microstructure, morphologies and corrosion resistance were characterized in detail. The addition of boric acid strongly influences on the microstructure of the Ni-Cu coatings. The coating with a grain size of 130 nm, obtained from the bath containing 35 g L⁻¹ boric acid, shows the highest corrosion resistance. This is attributed to the low-valence Cu ion (Cu⁺) additions in nickel oxide, which could significantly decrease the oxygen ion vacancy density in the passive film to form a more compact passive film. The higher Cu⁺ additions and the lower diffusivity of point defects (D₀) are responsible for the formation of more compact passive film on the coating obtained from the bath with 35 g L⁻¹ boric acid.     

Measurement of the gas-flow reduction factor of the KATRIN DPS2-F differential pumping section

The gas-flow reduction factor of the second forward Differential Pumping Section (DPS2-F) for the KATRIN experiment was determined using a dedicated vacuum-measurement setup and by detailed molecular-flow simulation of the DPS2-F beam tube and of the measurement apparatus. In the measurement, non-radioactive test gases deuterium, helium, neon, argon and krypton were used, the input gas flow was provided by a commercial mass-flow controller, and the output flow was measured using a residual gas analyzer, in order to distinguish it from the outgassing background. The measured reduction factor with the empty beam tube at room temperature for gases with mass 4 is 1.8(4) × 10⁴, which is in excellent agreement with the simulated value of 1.6 × 10⁴. The simulated reduction factor for tritium, based on the interpolated value for the capture factor at the turbo-molecular pump inlet flange is 2.5 × 10⁴. The difference with respect to the design value of 1 × 10⁵ is due to the modifications in the beam tube geometry since the initial design, and can be partly recovered by reduction of the effective beam tube diameter.     

Lithium ion transport in a model of amorphous polyethylene oxide

Summary We have made a molecular dynamics study of transport of a single lithium ion in a previously reported model of amorphous polyethylene oxide. New ab initio calculations of the interaction of the lithium ion with 1,2-dimethoxyethane and with dimethyl ether are reported which are used to determine force fields for the simulation. We report preliminary calculations of solvation energies and hopping barriers and a calculation of the ionic conductivity which is independent of any assumptions about the mechanism of ion transport. We also report some details of a study of transport of the trapped lithium ion on intermediate time and length scales.     

Rectified ion transport through concentration gradient in homogeneous silica nanochannels

We investigate the ionic rectifying effect through 4 and 20 nm thick silica nanochannels placed between two ionic solutions of different concentrations. The effect was observed when only a single side of the channel has electric double-layer overlap. The calculation based on Poisson-Nernst-Planck (PNP) theory and a simplified model suggests that the phenomenon result from the accumulation and depletion of both cations and anions in the nanochannels responding to different bias polarities. The model also elucidates that the basis of the rectifying effects in the nanofluidic devices reported to date is due to the asymmetric cation/anion ratios or equivalently built-in potentials on the two sides of the nanochannels. The study benefits the design of nanofluidic devices for attoliter-scale chemical delivery.     

Self-heating effect induced by ion bombardment on polycrystalline Al surface nanostructures evolution

We studied the self-heating effect during ion bombardment process on polycrystalline Al foils. An anisotropic surface morphology evolution has been observed. The adjacent peaks?? fusion along the direction perpendicular to the ion beam projection smoothen the surface. Fusion along the parallel direction has been suppressed due to Ar⁺ ion bombardment. It attributes to the result of the competition between the isotropic thermal effect, due to the self-heating effect by energy exchange between incident ions and Al surface, and the suppression by continuous ion bombardment with a certain incident angle. Varying the incident ion beam angle with the angular range 32°?<????<?82°, the ripple wave vector, ??, is found to be parallel to the ion beam direction, whereas for ?? > 82°, ?? is perpendicular to the beam direction. The critical angle, ?? _c , is close to 82°, which is different from Bradley and Harper??s prediction and attributes to the self-heating effect.     

Acousto-optical deflection-based laser beam scanning for fluorescence detection on multichannel electrophoretic microchips

Laser beam scanning driven by an acousto-optical deflector (AOD) is presented for multimicrochannel laser-induced fluorescence (LIF) detection during microchip-based electrophoresis. While fast laser beam scanning for LIF detection on capillary or microchannel arrays can been achieved with galvanometric scanning or a translating stage, it can also be accomplished by using acoustic waves to deflect the laser beam in a manner that is dependent on the acoustic frequency. AOD scanning differs from other approaches in that no moving parts are required, and the scan frequency is faster than conventional approaches. Using a digital/analog (D/A) converter to provide addressing voltages to a voltage/frequency converter, rapidly changing the frequency input to the AOD allows the laser beam to be addressed accurately on a microchip. With the ability to change the frequency on the nanosecond time scale, scanning rates as high as 30 Hz for Windows-based LabView programming are possible, with much faster scan rates achievable if a microprocessor-embedded system is utilized. In addition to spatial control, temporal control is easily attainable via raster scanning or random addressing, allowing for the scanning process to be self-aligning. Since the D/A output voltages drive the scanning of the laser beam over all channels, the software can define addressing voltages corresponding to the microchannel centers and, subsequently, fluorescence data can be collected from only those locations. This method allows for flexible, high-speed, self-align scanning for fluorescence detection in capillary or microchip electrophoresis and has the potential to be applied to a number of applications.     

Autostresses induced by point defects in sintering phenomena: effect on mass transport and sintering stress

States of anelastic strain can be associated with excess concentrations of point defects, as generated by mass transport in a sintering compact. Correspondingly, states of mechanical long-range self-equilibrated stresses (autostresses) can be produced. The relationships between anelastic strain and autostresses have been derived for a two-particle model. A generalized relation between chemical potentials and autostresses, including surface stresses, is provided, which allows derivation of local thermodynamic driving forces for mass transport. The concept of equivalent external sintering stress, assumed to be the driving force for the global densification process, is shown to correspond, approximately, to the material- and history dependent normal autostress component acting on the neck cross-sections. Predictions made from the model provide a new interpretation of experimental observations of the effect of gaseous phases, such as H₂O and CO₂, on the sintering of MgO and CaO powders.