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We report on the fabrication and characterization of electrostatic gas micro-pumps integrated with polyimide check valves. Touch-mode capacitance actuation, enabled by a fixed silicon electrode and a metal/polyimide diaphragm, creates the suction and push-out of the ambient gas; the gas flow is rectified by the check valves located at the inlet and outlet of the pump. The fabricated pumps were tested with various actuation voltages at different frequencies and duty cycles; an emphasis was placed on investigating the effect of valve flow conductance on the gas pumping characteristics. The pump with higher valve conductance could increase the operating frequency of the pump and affect the pumping characteristics from a pulsating flow to a continuous flow, leading to a higher gas flow rate. This electrostatic pump has a flow control resolution of 1 &mgr;L min-1; it could generate a gas flow up to 106 &mgr;L min-1. [ABSTRACT FROM AUTHOR]

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 ∼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. [ABSTRACT FROM AUTHOR]

The effects of developer temperature on hydrogen silsesquioxane (HSQ) resist for the fabrication of ultradense silicon nanowires are reported. At higher developer temperatures, the contrast of HSQ significantly increased and sharply defined gratings were obtained. In addition, higher developer temperature provided larger processing windows for various grating periodicities. Pattern transfer with HSQ masks using both dry and wet etching processes to fabricate silicon nanowires on silicon-on-insulator substrates is demonstrated. 27-nm-period silicon nanowire arrays obtained using the high temperature development along with the two etching processes are presented and discussed. [ABSTRACT FROM AUTHOR]

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-μm-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/cm² at current density level of about 120 mA/cm². These results represent the successful integration of a new class of protonic conductor into a microfabricated silicon fuel cell. [ABSTRACT FROM AUTHOR]

Thin films (0.85 µm, 3 µm) of Ta2O5 deposited on Si and SiO2 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 (TaSixOy) 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 Ta2O5 film, crystalline Ta2O5, 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 Ta2O5. [ABSTRACT FROM AUTHOR]

Silicon-based fuel cells are under active development to supply chip-scale electrical power supply. In this paper, we demonstrate the use of sulfuric acid loaded nanoporous silicon as a proton electrolytic membrane (PEM) material for micro-fuel cell applications. Sulfuric acid loaded nanoporous silicon membranes with thickness of 40–70 μm have proton conductivities (0.0068–0.33 S/cm) comparable to, and in some cases better than, Nafion® (0.05 S/cm), which is the most commonly used commercial PEM material. Additionally, the permeability of formic acid at room temperature through nanoporous silicon membranes was found to be similar to that of Nafion® membranes, which increases with increasing anodization current density (4.3 × 10-8 to 3.9 × 10-7 mol/(s cm2) for nanoporous silicon as compared to 1.23 × 10-7 mol/(s cm2) for Nafion® 117). These results represent the discovery of a new class of protonic conductor that can be integrated into standard silicon microfabrication processes. [Copyright &y& Elsevier]