Publications

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An electrochemical probe station (EPS) for automated electrochemical testing of electronic-grade thin films is presented. Similar in design to a scanning droplet cell, this modular system features a flexible probe tip capable of contacting both metallic and oxide surfaces. Using the highly sensitive Pt-H 2SO 4 system, it is demonstrated that the EPS obtains results equivalent to those of a traditional electrochemical cell. Further, electrical testing of thin film PbZr 0.52Ti 0.48O 3 shows that this system may be used to ascertain fundamental electrical properties of dielectric films. © 2012 The Electrochemical Society.

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We have demonstrated a novel microfluidic technique for aqueous media, which uses super-hydrophobic materials to create microfluidic channels that are open to the atmosphere. We have demonstrated the ability to perform traditional electrokinetic operations such as ionic separations and electrophoresis using these devices. The rate of evaporation was studied and found to increase with decreasing channel size, which places a limitation on the minimum size of channel that could be used for such a device.

Recent advances in nanoparticle inks have enabled inkjet printing of metal traces and interconnects with very low (100-200°C) process temperatures. This has enabled integration of printable electronics such as antennas and radio frequency identification (RFID) tags with polyimide, teflon, PCBs, and other low temperature substrates. We discuss here printing of nanoparticle inks for three dimensional interconnects, and the apparent mechanism of nanoparticle ink conductivity development at these low process temperatures.

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We have designed and built electrostatically actuated microvalves compatible with integration into a PDMS based microfluidic system. The key innovation for electrostatic actuation was the incorporation of carbon nanotubes into the PDMS valve membrane, allowing for electrostatic charging of the PDMS layer and subsequent discharging, while still allowing for significant distention of the valveseat for low voltage control of the system. Nanoparticles were applied to semi-cured PDMS using a stamp transfer method, and then cured fully to make the valve seats. DC actuation in air of these valves yielded operational voltages as low as 15V, by using a supporting structure above the valve seat that allowed sufficient restoring forces to be applied while not enhancing actuation forces to raise the valve actuation potential. Both actuate to open and actuate to close valves have been demonstrated, and integrated into a microfluidic platform, and demonstrated fluidic control using electrostatic valves.

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In light of difficulties in realizing a carbohydrate fuel cell that can run on animal or plant carbohydrates, a study was carried out to fabricate a membrane separated, platinum cathode, enzyme anode fuel cell, and test it under both quiescent and flow through conditions. Mediator loss to the flowing solution was the largest contributor to power loss. Use of the phenazine derivative mediators offered decent open circuit potentials for half cell and full cell performance, but suffered from quick loss to the solution which hampered long term operation. A means to stabilize the phenazine molecules to the electrode would need to be developed to extend the lifetime of the cell beyond its current level of a few hours. This is an abstract of a paper presented ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).

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There is a pressing need for miniaturized power systems for a variety of applications requiring a long life in the field of operations. Such power systems are required to be capable of providing power for months to years of operation, which all but eliminates battery technologies and technologies that bring their own fuel systems (except for nuclear fuel systems, which have their own drawbacks) due to constraints of having the all of the chemical fuel necessary for the entire life of the operational run available at the starting point of the operation. Alternatively, harvesting energy directly from the local environment obviates this need for bringing along all of the fuel necessary for operation. Instead, locally available energy, either in the form of chemical, thermal, light, or motion can be harvested and converted into electrical energy for use in sensor applications. The work from this LDRD is focused on developing a thermal engine that can take scavenged thermal gradients and convert them into direct electrical energy. The converter system is a MEMS based external combustion engine that uses a modified Stirling cycle to generate mechanical work on a piezoelectric generator. This piezoelectric generator then produced an AC voltage and current that can be delivered into an external load. The MEMS engine works on the conversion of a two phase working fluid trapped between two deformable membranes. As heat is added to the system, the liquid working fluid is converted to a gas, which exerts pneumatic pressure on the membranes, expanding them outward. This outward expansion continues after the heat input is removed when the engine is operated at resonance, since the membrane is expanded further due to inertial forces. Finally, the engine cools and heat rejection is accomplished through the membranes, closing the thermodynamic cycle. A piezoelectric generator stack is deposited on one of the membranes, and this generator extracts the strain energy work from the membrane expansion and generates electrical work. The overall system is pulsed by an electrical heater to generate the input heat pulse. Currently, the system has a resonant frequency that is in the low kilohertz regime, but operations under a dynamic damping have demonstrated operation at resonance and the existence of an open mechanical cycle of heat addition, expansion, and heat rejection. Power generation of direct thermal-to-electrical conversion show a 1.45W, 6mJ heat pulse can generate a 0.8 {micro}W power output pulse, and continuous operation generates a sustained power output of 0.8 {micro}W at 240Hz. Future improvements in the device will allow active heat rejection, allowing resonance with external damping to improve the thermal to electrical power efficiency.