Thermal properties of natural quartz slightly irradiated by fast neutrons are reported between 50 m K and 4 K. The different kinds of defects responsible for the lowtemperature properties of irradiated quartz are discussed. A well defined peak in the specific heat at 2 K is not affected by the origin of quartz samples (natural or synthetic) and characterises an intrinsic structural defect of the crystalline host. Below 1 K. the thermal conductivity shows a 'glass-like' T' behaviour and defines the existence of low-energy excitations associated with the disordering process of the quartz lattice. The dielectric and electron spin resonance properties obtained after different thermal treatments are also discussed. t Present address: Instituto Venezolano de Investigaciones Cientificas.
Articles you may be interested inInvestigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge Phys. Plasmas 19, 073521 (2012); 10.1063/1.4740508Langmuir probe data analysis for a magnetized inductive radio-frequency discharge Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited Production of high-density capacitively coupled radio-frequency discharge plasma by high-secondary-electronemission oxide Appl. Phys. Lett. 85, 4875 (2004); 10.1063/1.1827353Ion fluxes and energies in inductively coupled radio-frequency discharges containing CHF 3 A full wave or lambda resonator ͑-R͒ is a capacitively balanced radio-frequency ͑rf͒ inductive plasma source. It has three separate inductive excitation zones with opposite magnetic momenta strictly located at their axial positions. The 2 kW, 27 MHz, 1.4 Torr pressure discharge in oxygen was studied by means of movable single rf compensated fine cylindrical Langmuir probes. Flat wall probes were also used to reveal the distribution of positive ion flux and floating potentials on the chamber wall. The electron density in the -R discharge varies from 10 7 -10 8 cm Ϫ3 at 5-10 mm distance from the wafer to 2ϫ10 11 cm Ϫ3 in the central plasma toroid. One of the main problems of the probe operation is high gas temperature of ϳ1500 K in the plasma toroid and high-power dissipation on the probe surface. That is why not only fine cylindrical but also 100-130 m diam spherical probes were used. The probe technique and preliminary results are presented.
A preliminary study on the 1–4.5 kW power industrial scale 27.12 MHz rf lambda-resonator oxygen asher is presented. Contact probes of several types, including single Langmuir and flat wall probes, thermocouples, and optical emission spectroscopy, are mainly used to diagnose plasma in the inductive source area, downstream chamber and in the vicinity of wafers. Electron density in a 200 mm wafer asher at 2 kW rf power varies from 2×1011 in the plasma source to 5×107 cm−3 in a downstream chamber 5–10 mm from a wafer. The ion density exceeds the electron density 10–60 times. The plasma space potential varies in a range of 14–22 V, while the floating potential of the bulk plasma and wall surface varies from +9 to −17 V. The minimum surface floating potential of −17 V exists at the maximum of the rf voltage standing wave distributed along the full lambda inductor. The wafer surface floating potential is in the range of 3–5 V depending on the reactor configuration and is constant within ±1 V on the 200 mm wafer. Positive ion current density on the wafer and downstream chamber surface is less than 1 μA/cm−2. The typical resist ashing nonuniformity is ⩽2%–5% (range, not sigma) for both 200 and 300 mm ashers at about a 6–8 μ/min ashing rate.
We have been researching manufacturing methods of catalyst layers in order to improve the effective utilization rate of Pt in polymer electrolyte fuel cells. In our previous research1-3, we demonstrated experimentally that an electrospray (ES) method was able to make great progress in the interface formation between the electrolyte polymer ionomer and the Pt supported on carbon1,3 or conductive ceramics2, and that the immediate drying of the catalyst layer ink also greatly contributes to the improvement of Pt effectiveness. Since the ink droplets had already dried when these were deposited on the membrane, we proposed that the ink drying process can be reduced and that the cost of producing the catalyst layer is also greatly reduced. However, since the amount of catalyst applied is very small with a single nozzle, we also proposed that a multi-nozzle system is indispensable in order to adapt to the actual catalyst layer formation process.Therefore, we are jointly developing the ES manufacturing system with a multi-nozzle device (Fig. 1a) in a collaboration between the University of Yamanashi and Meiko Co., Ltd. We developed the first prototype machine, MES-Lab.α, for R & D, which features options such as nozzle material, multi-nozzle structure, coating treatment of nozzle tip, nozzle fixing adhesive, suck-back method, and ink energization method, among others. We have completed a new design for a basic 72-nozzle block (Fig. 1b), which incorporates all of the above new materials and new structures and is compatible with the production of industry-standard electrodes (5 cm x 5 cm).The performance of the PEFC cell using the cathode catalyst layer produced by this ES device was superior to that of a cell using the conventional pulse-swirl-spray device (PSS). We prepared the catalyst layer according to two different ionization methods (positive (ESP), and negative (ESN) ionization), and compared these with that prepared by the PSS method.3 The catalyst layers prepared by ESN successfully mitigated oxygen transport resistance. The highest porosity, which induced better water management, revealed superior performance at high current. Moreover, we confirmed the importance of the proton conduction in the catalyst layer through the ionomer contents. Thinly coated ionomer film on the catalyst surface revealed that lower resistance originates from the ionomer film on the Pt surface, RCL, film , but poor σ H+cath. , as evaluated for low contents of ionomer in the catalyst layer. These results also suggest that we will be able to achieve superior actual cell performance for catalyst layers prepared via ES using modified ionomer chemical structures, for which there is enhanced H+ conductivity, σ H+cath. , via, e.g., increased ion exchange capacity, and oxygen permeability3 (Fig. 2). Acknowledgement This work was partially supported by funds for the “Superlative, stable, and scalable performance fuel cell” (SPer-FC) and the “Electrolytes, catalysts and catalyst layers with extraordinary efficiency, power and durability for PEF...
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