Abstract: Electrical conductivity of , as a function of temperature and oxygen partial pressure, is measured with a complex impedance method. The increase of electrical conductivity with reducing oxygen partial pressure can be described well by a model that assumes constant mobility of both oxygen vacancies and electrons, based on an ideal‐solution model of non‐stoichiometry of Gd‐doped ceria. Ionic conductivity is calculated, and its activation energy is discussed. Electronic conductivity is discussed also. © 2000 The Electrochemical Society. All rights reserved.

Abstract: The stability of the (100) MoS2 surface has been studied using periodic DFT calculations taking into account various parameters such as the temperature and the partial pressure ratios of H2 and H2S...

Abstract: Acceptor and donor doped SrTi1−xFexO3−δ materials for novel temperature independent resistive oxygen sensors for lean-burn engine exhaust gases were prepared and characterized by X-ray diffraction. Their electrical resistance, R, was investigated in the oxygen partial pressure range from 10−4 to 1 bar between 700°C and 1000°C. Doped and undoped samples with x=0.3 obey an R∝pO2−1/5 power law. Undoped samples show negligible temperature dependence in a small oxygen partial pressure (pO2) range between 10−2 and 3×10−2 bar. Acceptor (Ga) doping shifts the pO2 range of negligible temperature dependence to lower pO2, whereas donor (La) doping results in a right-hand shift to higher pO2. Combined acceptor and donor doping leads to an extended pO2 range of negligible temperature dependence. At pO2=10−1 bar the temperature coefficient of resistance (TCR) of this material composition is always below 250 ppm/K in the complete investigated temperature range. At about 725°C and 975°C TCR=0 can be found.

Abstract: The effect of nitrogen addition on the properties of tetrahedral amorphous carbon (ta-C) has been studied. The ta-C is deposited by a filtered cathodic vacuum arc. The effect of introducing nitrogen on its plasma was measured by a retarding field analyzer and optical emission spectroscopy. The ta-C:N films were studied as a function of nitrogen content, ion energy, and deposition temperature. The incorporation of nitrogen was measured over the range of 10−2–10 at. % by secondary ion mass spectrometry and elastic recoil detection analysis. The N content was found to vary slightly sublinearly with the N2 partial pressure during deposition. A doping regime was found for N contents of up to 0.4 at. %, in which the conductivity changes while the sp3 content and the optical band gap remain constant. For 0.4%–8% N, the sp3 fraction remains above 80% but the optical gap closes due to a clustering of sp2 sites. Only above about 10% N, the sp3 fraction falls. The influence of nitrogen on the a-C was found to be independent of ion energies between 20 and 220 eV. Deposition above 200 °C causes a sudden loss of sp3 bonding. Raman and optical gap data show however that existing sp2 sites begin to cluster below this temperature.

Abstract: A 3-liter culture vessel has been developed for the growth of animal cells in suspension at controlled pH and dissolved oxygen partial pressure (pO2). The culture technique allows metabolically produced CO2 to be measured; provision can be made to control the dissolved CO2 partial pressure. In cultures containing a low serum concentration, gas sparging to control pO2 was found to cause cell damage. This could be prevented by increasing the serum concentration to 10%, or by adding 0.02% of the surface-active polymer Pluronic F68. The growth of mouse LS cells in batch culture without pO2 control was found to be limited by the availability of oxygen. Maximum viable cell populations were obtained when dissolved pO2 was controlled at values within the range 40–100 mm Hg.

Abstract: Fluorinated amorphous-carbon films (a-C:F:H) were deposited by low-power rf capacitively coupled plasma-enhanced chemical-vapor deposition using CH4–CF4 gas mixtures. Different series of films were deposited, changing one parameter at a time: the CF4 partial pressure from 0% to 100%, the self-bias voltage from −50 to −700 V, and the total deposition pressure from 5 to 15 Pa. The composition was determined by ion-beam analysis (IBA): Rutherford backscattering spectrometry, elastic recoil detection analysis, and nuclear reaction analysis. The atomic density of the films was evaluated by combining the IBA results with the thickness value measured by stylus profilometry. Film structure was investigated by infrared transmission and Raman scattering spectroscopies. The internal stress and Vickers hardness were also measured. For a fixed self-bias, the increase of the CF4 partial pressure leads to a higher fluorine incorporation and the decrease of both hardness and internal stress. The film microstructure chang...

Abstract: Nanocluster carbon films grown using a cathodic arc process at room temperature in the presence of background gases such as He are found to be good electron emitters. The variation in the surface morphology and the corresponding emission characteristics of the films with change in helium partial pressure (5×10−4–50 Torr) during the film growth are reported. The effect of helium partial pressure on clustering was studied for films grown at nitrogen partial pressures of 10−4 and 10−3 Torr. The surface morphology of the films grown, varied from smooth through clusters (with sizes 50–200 nm), to fibrous films. The threshold field varied from 1 to 10 V/μm for an emission current density of 1 μA/cm2. These films exhibit an emission site density of ∼104–105/cm2 at an applied field of 5 V/μm.

Abstract: Thin tungsten films were produced by magnetron sputtering at room temperature in Ar and O 2 gas mixture. The influences of oxygen impurities by varying oxygen partial pressures on the formation and stability of the A15 β-W phase were investigated. The films were analyzed by X-ray photoelectron spectroscopy (XPS), electron energy-loss spectrometry (EELS), X-ray diffraction (XRD), and energy-filtered electron diffraction (EFED). It was found that the formation of the body-centered-cubic (bcc) α-W structure was favored when the oxygen content in the films was less than 3 at.%, while the A15 β-W phase was formed between 6 and 15 at.% oxygen. At higher oxygen partial pressures, the films deposited in this manner were found to be essentially amorphous. Phase transformation from A15 W to bcc W by higher temperature annealing (∼900 K) was accompanied by reduction of oxygen in the films. The driving force for the irreversible phase transition process, A15 β-W→bcc α-W by anneal, is discussed.

Abstract: The influence of hydrogen contained in a sample or otherwise introduced into a glow discharge source (GDS) is here extensively experimentally presented for the case of copper as a sample by means of the addition of small quantities of molecular hydrogen (<1% relative partial pressure) to the argon carrier gas. The progressive addition of molecular hydrogen causes different intensity changes particular to the individual lines of different species such as atomic (Cu I) and ionic (Cu II) copper, and also atomic (Ar I) and ionic (Ar II) argon. Some interesting features of the emission spectrum of hydrogen such as its line, band and even continuum spectrum are observed. It was also found that the depth resolution becomes worse even at very low concentrations of hydrogen.

Abstract: Polycrystalline CeO 2 with a relative density in excess of 97% was prepared The specimens contained a lower concentration of impurities than those examined previously Oxygen diffusion experiments were performed for the temperature range from 800 to 1300°C, in an oxygen partial pressure of 66 X 10 3 Pa The concentration profile of 18 O in the specimens following diffusion annealing was measured by secondary ion mass spectroscopy (SIMS) In the high-temperature region (intrinsic region, above 1000°C), the oxygen self-diffusion coefficient obtained using SIMS was observed to agree reasonably with that obtained by gas phase analysis in a previous study, but the activation energy was found to be slightly smaller The present result, D = 316 X 10 -4 exp(-226 kJ mol -1 /RT) m 2 s -1 (T = I 100-1300°C), is thought to represent the intrinsic behavior of undoped CeO 2 In contrast, in the low temperature region (extrinsic region, less than 1000°C), the activation energy was smaller than that in the high temperature region Comparison with data reported in the literature for CeO 2 doped with Y and Gd, suggests that the low-temperature oxygen diffusion region is controlled by a trivalent impurity The surface exchange coefficients obtained from gas phase analysis and SIMS agreed very well with each other and were represented by k = 193 X 10 -3 exp(-136 kJ mol -1 /RT) m s -1 (T = 800-1300°C) The data were also in good agreement with the surface exchange coefficient in ThO 2 , suggesting that the oxygen surface exchange reaction is insensitive to cation species