Christopher A. Apblett

Modeling of SiO2 deposition in high density plasma reactors and comparisons of model predictions with experimental measurements

High-density-plasma deposition of SiO2 is an important process in integrated circuit manufacturing. A list of gas-phase and surface reactions has been compiled for modeling plasma-enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar gas mixtures in high-density-plasma reactors. The gas-phase reactions include electron impact, neutral–neutral, ion–ion, and ion–neutral reactions. The surface reactions and deposition mechanism is based on insights gained from attenuated total reflection Fourier transform infrared spectroscopy experiments and includes radical adsorption onto the SiO2 surface, ion-enhanced desorption from the surface layer, radical abstractions, as well as direct ion-energy-dependent sputtering of the oxide film. A well-mixed reactor model that consists of mass and energy conservation equations averaged across the reactor volume was used to model three different kinds of high-density plasma deposition chambers. Experimental measurements of total ion densities, relative radical dens...

Fast lithium-ion conducting thin-film electrolytes integrated directly on flexible substrates for high-power solid-state batteries.

By utilizing an equilibrium processing strategy that enables co-firing of oxides and base metals, a means to integrate the lithium-stable fast lithium-ion conductor lanthanum lithium tantalate directly with a thin copper foil current collector appropriate for a solid-state battery is presented. This resulting thin-film electrolyte possesses a room temperature lithium-ion conductivity of 1.5 × 10(-5) S cm(-1) , which has the potential to increase the power of a solid-state battery over current state of the art.

Rational Redesign of Glucose Oxidase for Improved Catalytic Function and Stability

Glucose oxidase (GOx) is an enzymatic workhorse used in the food and wine industries to combat microbial contamination, to produce wines with lowered alcohol content, as the recognition element in amperometric glucose sensors, and as an anodic catalyst in biofuel cells. It is naturally produced by several species of fungi, and genetic variants are known to differ considerably in both stability and activity. Two of the more widely studied glucose oxidases come from the species Aspergillus niger (A. niger) and Penicillium amagasakiense (P. amag.), which have both had their respective genes isolated and sequenced. GOx from A. niger is known to be more stable than GOx from P. amag., while GOx from P. amag. has a six-fold superior substrate affinity (K M) and nearly four-fold greater catalytic rate (k cat). Here we sought to combine genetic elements from these two varieties to produce an enzyme displaying both superior catalytic capacity and stability. A comparison of the genes from the two organisms revealed 17 residues that differ between their active sites and cofactor binding regions. Fifteen of these residues in a parental A. niger GOx were altered to either mirror the corresponding residues in P. amag. GOx, or mutated into all possible amino acids via saturation mutagenesis. Ultimately, four mutants were identified with significantly improved catalytic activity. A single point mutation from threonine to serine at amino acid 132 (mutant T132S, numbering includes leader peptide) led to a three-fold improvement in k cat at the expense of a 3% loss of substrate affinity (increase in apparent K M for glucose) resulting in a specify constant (k cat/K M) of 23.8 (mM−1 · s−1) compared to 8.39 for the parental (A. niger) GOx and 170 for the P. amag. GOx. Three other mutant enzymes were also identified that had improvements in overall catalysis: V42Y, and the double mutants T132S/T56V and T132S/V42Y, with specificity constants of 31.5, 32.2, and 31.8 mM−1 · s−1, respectively. The thermal stability of these mutants was also measured and showed moderate improvement over the parental strain.

Neutron irradiation effects on domain wall mobility and reversibility in lead zirconate titanate thin films

The effects of neutron-induced damage on the ferroelectric properties of thin film lead zirconate titanate (PZT) were investigated. Two sets of PbZr0.52Ti0.48O3 films of varying initial quality were irradiated in a research nuclear reactor up to a maximum 1 MeV equivalent neutron fluence of (5.16 ± 0.03) × 1015 cm−2. Changes in domain wall mobility and reversibility were characterized by polarization-electric field measurements, Rayleigh analysis, and analysis of first order reversal curves (FORC). With increasing fluence, extrinsic contributions to the small-signal permittivity diminished. Additionally, redistribution of irreversible hysterons towards higher coercive fields was observed accompanied by the formation of a secondary hysteron peak following exposure to high fluence levels. The changes are attributed to the radiation-induced formation of defect dipoles and other charged defects, which serve as effective domain wall pinning sites. Differences in damage accumulation rates with initial film qual...

Direct Glucose Fuel Cell: Noble Metal Catalyst Anode Polymer Electrolyte Membrane Fuel Cell with Glucose Fuel

A 1 cm 2 constant flow glucose-oxygen fuel cell has been demonstrated using noble metal catalysis. The fuel cell is based on Pt―RuO 2 anode catalysts and Pt cathode. Operation of this cell under various concentrations of glucose has revealed the presence of a region of the polarization curve in which additional polarization leads to a decrease in current rather than the expected increase. We postulate that the appearance of this polarization loss is due to the adsorption of by-product lactones to the Pt―RuO 2 surface which is not desorbed under normal operating conditions, but instead decreases the number of catalytic sites over time, resulting in lower currents.

Design considerations for electrostatic microvalves with applications in poly(dimethylsiloxane)-based microfluidics†

Microvalves are critical in the operation of integrated microfluidic chips for a wide range of applications. In this paper, we present an analytical model to guide the design of electrostatic microvalves that can be integrated into microfluidic chips using standard fabrication processes and can reliably operate at low actuation potentials (<250 V). Based on the analytical model, we identify design guidelines and operational considerations for elastomeric electrostatic microvalves and formulate strategies to minimize their actuation potentials, while maintaining the feasibility of fabrication and integration. We specifically explore the application of the model to design microfluidic microvalves fabricated in poly(dimethylsiloxane), using only soft-lithographic techniques. We discuss the electrostatic actuation in terms of several microscale phenomena, including squeeze-film damping and adhesion-driven microvalve collapse. The actuation potentials predicted by the model are in good agreement with experimental data obtained with a microfabricated array of electrostatic microvalves actuated in air and oil. The model can also be extended to the design of peristaltic pumps for microfluidics and to the prediction of actuation potentials of microvalves in viscous liquid environments. Additionally, due to the compact ancillaries required to generate low potentials, these electrostatic microvalves can potentially be used in portable microfluidic chips.

Synthesis, Characterization, and Electrochemical Properties of a Series of Sterically Varied Iron(II) Alkoxide Precursors and Their Resultant Nanoparticles

A new family of iron(II) aryloxide [Fe(OAr)(2)(py)(x)] precursors was synthesized from the alcoholysis of iron(II) mesityl [Fe(Mes)(2)] in pyridine (py) using a series of sterically varied 2-alkyl phenols (alkyl = methyl (H-oMP), isopropyl (H-oPP), tert-butyl (H-oBP)) and 2,6-dialkyl phenols (alkyl = methyl (H-DMP), isopropyl (H-DIP), tert-butyl (H-DBP), phenyl (H-DPhP)). All of the products were found to be mononuclear and structurally characterized as [Fe(OAr)(2)(py)(x)] (x = 3 OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5); x = 2 OAr = DBP (6), DPhP (7)). The use of tris-tert-butoxysilanol (OSi(OBu(t))(3) = TOBS) led to isolation of [Fe(TOBS)(2)(py)(2)] (8). The new Fe(OAr)(2)(py)(x) (1-6) were found, under solvothermal conditions, to produce nanodots identified by PXRD as the γ-maghemite phase. The model precursor 3 and the nanoparticles 6n were evaluated using electrochemical methods. Cyclic voltammetry for 3 revealed multiple irreversible oxidation peaks, which have been tentatively attributed to the loss of alkoxide ligand coupled with the deposition of a solid Fe-containing coating on the electrode. This coating was stable out to the voltage limits for the acetonitrile solvent.

Control of pressure-driven components in integrated microfluidic devices using an on-chip electrostatic microvalve

Pressure-driven actuators play a critical role in many microfluidic technologies, but the ancillary equipment needed to operate pneumatic and hydraulic platforms has limited their portability. To address this issue, we created an electrostatic microvalve used to regulate pressures in hydraulic control lines. In turn, these control lines are able to actuate pressure-driven components, e.g., microvalves. The electrostatic microvalve is fabricated exclusively with soft-lithographic techniques, allowing it to be directly integrated in a microfluidic chip. The electrostatic microvalve also contains a passive structural element that balances the pressure on the top and bottom sides of the actuating membrane. This feature enables the microvalve to induce pressure changes up to 20 kPa with electric potentials less than 320 V. When the microvalve is integrated into a microfluidic “pressure amplifier” circuit, the pressure output of the circuit can be tuned with the voltage applied to the microvalve. This integration allows for different types of pressure-driven components to be actuated with variable pressures, and thus eliminates the need for off-chip pressure regulation. In the example reported here, only one actuator is required to adjust the pressure of a single hydraulic line.

Normally-Closed Electrostatic Microvalve Fabricated Using Exclusively Soft-Lithographic Techniques and Operated With Portable Electronics

We report an elastomer-based electrostatic microvalve that was fabricated using replica molding, micro-transfer printing, and plasma bonding. The microvalve can be actuated with an electric potential of ~ 220 V and can withstand pressures up to 3 kPa. Sixteen independently-operated valves were integrated on a single chip and operated with portable electronics.

Advanced inactive materials for improved lithium-ion battery safety.

This report describes advances in lithium-ion battery safety by use of alternative electrolytes and separators. Electrolytes based on hydrofluoro ether solvents and sulfonimide salts were characterized to determine electrochemical performance, thermal stability, and decomposition products. Flammability of these electrolytes was also tested under known cell failure mode conditions. Separators based on high melting temperature polymers and ceramics were developed by fiber spinning, casting, and vapor deposition techniques. Resulting high melt integrity separators show good electrochemical performance and improved thermal stability compared to commercial polyolefin separator materials.