A novel parylene-embedded carbon nanotube nanoelectrode array is presented for use as an electrochemical detector working electrode material. The fabrication process is compatible with standard microfluidic and other MEMS processing without requiring chemical mechanical polishing. Electrochemical studies of the nanoelectrodes showed that they perform comparably to platinum. Electrochemical pretreatment for short periods of time was found to further improve performance as measured by cathodic and anodic peak separation of K 3 Fe(CN) 6 . A lower detection limit below 0.1 µM was measured and with further fabrication improvements detection limits between 100 pM and 10 nM are possible. This makes the nanoelectrode arrays particularly suitable for trace electrochemical analysis.
Fully-integrated MEMS gaskets and O-rings made of SU8 and photosensitive silicone are described and tested under varying conditions of compressive stress. An analytical theory of microgasket sealing behavior is also presented. The theory shows the critical importance of device surface flatness. The microgasket is found to be capable of deforming approximately 25% of its initial thickness and forming leak-free fluidic seals at inlet pressures below 50 psi. The microgasket is incorporated into a modular microfluidic system that exhibits system leak rates lower than 2.3 nL/min for working pressures up to 250 psi. Fabricated chip-to-chip interconnects exhibit a low dead volume of approximately 9 nL while further optimization can reduce dead volume per interconnect to about 1 nL.
A 1 MW, 140 GHz gyrotron with diamond window for continuous wave operation and with a single-stage depressed collector has been designed and constructed in collaboration with CRPP Lausanne and TTE Velizy. It operates in the TE28,8 cavity mode and provides a linearly polarized TEM0,O beam. The gyrotron consists of a magnetron injection gun, an improved cavity, an optimized non-linear up-taper and an improved launcher. RF power measurements at short pulse lengths gave 0.65 MW output power. In long pulse operation (150111s) an output power of 0.6 MW was measured. Despite careful optimization it was not possible, to improve the output power. Measurements of the RF beam profile showed a strong shift of the beam by 30 mm downwards (design error). This deviation leads to power reflections of more than 20% back into the gyrotron, which causes a reduction of the generated power. The depressed collector could be operated up to 33 kV, which gives an improvement factor of 1.7 for the efficiency. The collector has been tested successfully in long pulse operation (30 s) without RF generation at 1 MW electron-beam power level. The measurements are currently continued, new results with a redesigned mirror system will be given. With the 165 GHz coaxial cavity gyrotron, an output power of 2.2 MW with an efficiency of 28% has been measured at a beam current of 84 A in short pulse operation. The maximum efficiency has been measured at 1.5 MW output power. With a voltage depression of about 35 kV an efficiency of 48% has been achieved (30% without SDC). Up to that depression voltage no reduction in output power has been observed. These results are in very good agreement with numerical calculations, if one includes internal losses of IO% and a velocity spread of 5% for the electron beam.
References:Forschungszentrum Kurlsruhe, IHM. G e m n y Tholes Electron Deviees, Frunre * Forschungszentrum Kadsruhe, Association Euratom-FZK. lnstitut luer Hochleistungsimpuls-und Mikrowellentechnik.A focussed Gaussian beam generated by an 83-GHz, 15-kW CW Gycom, Ltd. gyrotron is being applied to the processing of ceramic materials at the Naval Research Laboratory. Available microwave power densities of >I kW/cm2 enable rapid, localized heating of ceramic coatings and joints, provided adequate microwave-material coupling is achieved. This paper describes theoretical and experimental studies of microwave beam coupling to and propagation in multi-component ceramic systems corresponding to joints and coating configurations. Localized coupling enhancement using mixtures of ceramic and metal powders has been investigated. Techniques for minimization of reflection (important in a single-pass beam system) and beam polarization effects will be discussed, as well as the results of experiments designed to enhance heating rates based on these effects.References:
The authors demonstrate for the first time the injection of electrons across an n-type to p-type silicon junction and their subsequent tunneling from approximately 1 μm tall p-type silicon points into a vacuum gap. The diffusive flow of these minority carriers in the p-type material is controlled by the application of a bias voltage in the form of a base contact metallization contact on the p-type silicon, in analogy with a bipolar junction transistor. Using an array density of 4×106 tips/cm2, the authors measured a maximum average current of 1 nA per tip. Increasing the base contact bias voltage from 0 to ∼1 V changes the emission from a supply limited regime typically observed with p-type silicon emitters, bringing the emitted current back to a linear Fowler–Nordheim characteristic similar to that observed previously by photon generation of carriers in p-type silicon tips. The authors finally note that in our short tips, minority carrier flow should be a nondissipative largely adiabatic diffusive transport process which is followed by extraction into vacuum. A novel heat extraction mechanism for future cooling applications is thus anticipated.
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