GaAs IGFET digital integrated circuits

To obtain a better understanding of the short term reactions between sulfate and hydrous alumina the relationships between the amount of sulfate retained by the alumina and reaction time, concentration, ligands displaced by sulfate, and changes in surface charge were studied. Experimental conditions were 3 hours reaction time, 0.01 M NaCl medium, pH 5.0, 30°C, and nitrogen atmosphere. Sulfate adsorption was very rapid and about 90% of the reaction was over in 10 min. There was little change in adsorption after 3 hours. The adsorption increased with increasing final solution concentration up to about 6 µeq/ml after which it decreased. Sulfate adsorption resulted in the release of OH ‐ from, and the neutralization of positive charge on the surface. From the quantitative relationships between sulfate adsorbed, the ligands displaced, and the changes in surface charge it is proposed that sulfate is adsorbed on hydrous alumina as SO 4 2‐ bridging across two aluminum atoms, forming a six‐membered ring. At low concentrations sulfate preferentially displaces aquo groups (Al‐OH 2 ) from the positive sites. With increasing concentration, increasing proportions of hydroxo groups (Al‐OH) from the neutral sites are displaced. The decrease in adsorption above 6 µeq/ml of sulfate concentration is inexplicable at this stage.

AlGaN/GaN high electron mobility transistors (HEMTs) with a polarized polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an ink-jet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change in surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors.

: Stimulus-induced changes in surface properties of nanoassemblies have been of interest in a variety of applications. One such change involves change in surface charge. Changes in surface charge can be conveniently assayed using interaction of the nanoassemblies with cells. We have utilized the nanoassembly-cell interaction to investigate the pH-induced changes in surface properties. Similarly, surface functionalization of nanoparticles and host-guest properties of nanoassemblies are two critical features in the utilization of nanostructures in a variety of applications in materials, chemical, and biological nanotechnology. However, simultaneously incorporating these two features in one nanoparticle design is a rather challenging task. We were interested in developing a simple approach for functionalizable polymer nanoparticles, where we stipulated that: (i) the precursor polymer is based on a random copolymer, which is synthetically accessible; (ii) the polymer self-assembles in a solvent, which can then be converted to nanoparticle in one step without the need for any additional processing; (iii) the nanoparticle contains a surface functional group, which can be further manipulated easily; (iv) the size of the nanoparticle is tunable; and (iv) the interior of the nanoparticle is capable of sequestering guest molecules.

Large pressures can induce detrimental deformation in micro- and nanofluidic channels. Although this has been extensively studied for systems driven by pressure and/or capillary forces, deflection in electrokinetic systems due to internal pressure gradients caused by non-uniform electric fields has not been widely explored. For example, applying an axial electric field in a channel with a step change in conductivity and/or surface charge can lead to internally generated pressures large enough to cause cavitation, debonding, and/or channel collapse. Finite electric double layers within nanofluidic channels can further complicate the physics involved in the deformation process. In order to design devices and experimental procedures that avoid issues resulting from such deformation, it is imperative to be able to predict deformation for given system parameters. In this work, we numerically investigate pressures resulting from a step change in conductivity and/or surface charge in micro- and nanofluidic channels with both thin and thick double layers. We show an explicit relation of pressure dependence on concentration ratio and electric double layer thickness. Furthermore, we develop a numerical model to predict deformation in such systems and use the model to unearth trends in deformation for various electric double layer thicknesses and both glass and PDMS on glass channels. Our work is particularly impactful for the development and design of micro- and nanofluidic-based devices with gradients in surface charge and/or conductivity, fundamental study of electrokinetic-based cavitation, and other systems that exploit non-uniform electric fields.

The immobilization of thiol-derivatized DNA on a Au (111) single crystal surface by self-assembly has been investigated by electrochemical scanning tunneling microscopy (EC-STM). Continuous potential-dependent orientation changes of double-stranded oligodeoxynucleotides (ODN) have been observed in a certain potential range from 200 to 600 mV (versus SCE). It is suggested that the DNA duplexes stand straight on the gold surface at potentials negative of the potential of zero charge (pzc) and then lay down on the surface when the potential shifts positively. These results are in agreement with the expectation based on the Coulombic interaction consideration between negatively charged DNA helices and gold surface. As the applied potential shifts positively, the surface charge changes from negative to positive, that is, the Coulombic force between negatively charged DNA helices and gold surfaces changes from repulsion to attraction. However, for the single-stranded oligodeoxynucleotides, no distinct changes in the surface structure were observed with the applied potential.

Change in surface charge density and membrane potential of intact mitochondria during energization

The luminal plasmalemma of regenerating mesothelial cells was examined by transmission electron microscopy and the concentration of microvilli at various stages of healing was quantified. Charged tracer and lectin binding techniques were also employed to investigate electrostatic and chemical changes in mesothelial glycocalyx. In uninjured mesothelium and at all stages of healing, the concentration of microvilli at the cellular periphery was greater than over the main cell mass (P < 0.05). Furthermore, there was an increase in the concentration of microvilli in all regions by day 4, which reached a maximum at day 6, then at days 10-15 returned to values closer to uninjured mesothelium (P < 0.01). These changes were associated with an alteration in surface charge. In all lesions, the surface charge on microvillar membranes was greater than for flat membranes, but the difference was only significant at days 4, 6, and 15 (P < 0.001). The changes in surface charge may reflect a differential expression of mucopolysaccharides on the surface membrane. In addition, concanavalin A bound avidly to mesothelial surface membranes, suggesting the presence of alpha-methyl-D-mannoside residues. These findings suggest an association between microvillar formation and surface charge, the former protecting the healing mesothelium by enhancing entrapment of serosal fluid and its contents.

Modelling of PFAS-surface interactions: Effect of surface charge and solution ions

In oxide semiconductors, defect chemistry and hydrogen can influence free carrier concentration and these materials can have strong interactions with the atmosphere and contaminents.[1,2] An inverted staggered structure is commonly used for oxide TFTs and a high-quality passivation layer is needed to provide protection and minimize back channel surface charge changes.[2,3] Negative shifts in turn-on and threshold voltage after passivation with inorganic thin films have been reported by several groups.[4,5] We have previously reported weak oxidant plasma enhanced atomic layer deposition (PEALD) ZnO TFTs with an ALD-based Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation layer [6]. Before passivation the TFT has a turn-on voltage near 0 V, but significant hysteresis (often > 0.5 V). A 32 nm thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer deposited by ALD eliminates the hysteresis, but causes a negative shift in turn-on and threshold voltage (~3 V). A 32 nm thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer deposited by PEALD also removes the hysteresis, but shifts the device turn-on and threshold voltage negative by more than 10 V [6]. We have developed a tri-layer process for bottom-gate, top contact TFTs. An Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -ZnO-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> tri-layer is deposited sequentially at 200°C and provides effective passivation and reduced turn-on voltage shift.

Concentration polarization-enhanced radical graft polymerization, a facile surface modification technique, was examined as an approach to reduce bacterial deposition onto RO membranes and thus contribute to mitigation of biofouling. For this purpose an RO membrane ESPA-1 was surface-grafted with a zwitterionic and negatively and positively charged monomers. The low monomer concentrations and low degrees of grafting employed in modifications moderately reduced flux (by 20-40%) and did not affect salt rejection, yet produced substantial changes in surface chemistry, charge and hydrophilicity. The propensity to bacterial attachment of original and modified membranes was assessed using bacterial deposition tests carried out in a parallel plate flow setup using a fluorescent strain of Pseudomonas fluorescens. Compared to unmodified ESPA-1 the deposition (mass transfer) coefficient was significantly increased for modification with the positively charged monomer. On the other hand, a substantial reduction in bacterial deposition rates was observed for membranes modified with zwitterionic monomer and, still more, with very hydrophilic negatively charged monomers. This trend is well explained by the effects of surface charge (as measured by ζ-potential) and hydrophilicity (contact angle). It also well correlated with force distance measurements by AFM using surrogate spherical probes with a negative surface charge mimicking the bacterial surface. The positively charged surface showed a strong hysteresis with a large adhesion force, which was weaker for unmodified ESPA-1 and still weaker for zwitterionic surface, while negatively charged surface showed a long-range repulsion and negligible hysteresis. These results demonstrate the potential of using the proposed surface- modification approach for varying surface characteristics, charge and hydrophilicity, and thus minimizing bacterial deposition and potentially reducing propensity biofouling.

&lt;p&gt;Plasmalemmal phosphatidylinositol (PI) 4,5-bisphosphate (PI4,5P(2)) synthesized by PI 4-phosphate (PI4P) 5-kinase (PIP5K) is key to the polymerization of actin that drives chemotaxis and phagocytosis. We investigated the means whereby PIP5K is targeted to the membrane and its fate during phagosome formation. Homology modeling revealed that all PIP5K isoforms feature a positively charged face. Together with the substrate-binding loop, this polycationic surface is proposed to constitute a coincidence detector that targets PIP5Ks to the plasmalemma. Accordingly, manipulation of the surface charge displaced PIP5Ks from the plasma membrane. During particle engulfment, PIP5Ks detached from forming phagosomes as the surface charge at these sites decreased. Precluding the change in surface charge caused the PIP5Ks to remain associated with the phagosomal cup. Chemically induced retention of PIP5K-gamma prevented the disappearance of PI4,5P(2) and aborted phagosome formation. We conclude that a bistable electrostatic switch mechanism regulates the association/dissociation of PIP5Ks from the membrane during phagocytosis and likely other processes.&lt;/p&gt; &lt;p&gt; &lt;/p&gt;

[This retracts the article DOI: 10.1021/acsomega.0c02518.].

Influence of Nanopolymers with Different End-Functionalities on Platelet Function and the Coagulation Cascade - An Ex-Vivo Study.

ABSTRACTHybrid organic/inorganic nanostructures are engineered to function as two terminal devices with enhanced functionality. The devices are the building blocks for designing hybrid organic/inorganic circuits in the nanoscale. In our work, we have demonstrated the sensing capabilities of polymer nanocomposite thin films for designing nanoweb devices towards detection of biomolecules. Biomolecules with surface charge such as troponin-T were detected on this device by interfacing them with the polymer/metal composites. The change in electrical properties due to modulation in charge transport at the crossbar junction was identified as the measured electrical signal for designing switch based sensors. Nanotextured surface offers strong charge carrier transport and hence enhances the strength of the detected signal. The antibodyantigen interactions at the junction effectively modulate the charge transfer kinetics and modify the junction characteristics due to the surface potential associated with the organic molecules. The net change in surface charge can be measured either as changes in the diode current in the two terminal configuration or as changes in the source- drain current in the three terminal configuration. Detection sensitivity in the order of pg/mL was targeted by measuring the voltammetric current response (in microamperes).

Plasmalemmal phosphatidylinositol (PI) 4,5-bisphosphate (PI4,5P(2)) synthesized by PI 4-phosphate (PI4P) 5-kinase (PIP5K) is key to the polymerization of actin that drives chemotaxis and phagocytosis. We investigated the means whereby PIP5K is targeted to the membrane and its fate during phagosome formation. Homology modeling revealed that all PIP5K isoforms feature a positively charged face. Together with the substrate-binding loop, this polycationic surface is proposed to constitute a coincidence detector that targets PIP5Ks to the plasmalemma. Accordingly, manipulation of the surface charge displaced PIP5Ks from the plasma membrane. During particle engulfment, PIP5Ks detached from forming phagosomes as the surface charge at these sites decreased. Precluding the change in surface charge caused the PIP5Ks to remain associated with the phagosomal cup. Chemically induced retention of PIP5K-gamma prevented the disappearance of PI4,5P(2) and aborted phagosome formation. We conclude that a bistable electrostatic switch mechanism regulates the association/dissociation of PIP5Ks from the membrane during phagocytosis and likely other processes.