A new thermistor, which shows an anomalously large positive temperature coefficient of electrical resistivity, has been found. The resistivity of the materials increases monotonically between 20°C and 85°C, and the resistivity at 85°C is 106∼108 times of that at 20°C. The sample is prepared by mixing graphite powder with a melted mixture of paraffin and polyethylene. The temperature sensitive electrical resistivity of the sample mainly depends on the resistivity of intergrain gaps between graphite particles. The resistance at the intergrain gaps is attributable to the tunneling current, because the field dependence of resistivity calculated theoretically based on the tunneling effect agrees well with the experimental data. The variation of electrical resistance of this mixture originates in the variation of the width of the intergrain gaps caused by the displacement of the graphite grains due to the rise of temperature.
The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively-coupled radio frequency (RF, 13.56 MHz) Ar/CF 4 discharge over a pressure range 3-30 mTorr by changing the CF 4 content from 0 to 20%, while keeping the power injected into the plasma at about 50 W. EEDFs measured at a pressure lower than 10 mTorr are bi-Maxwellian distributions over the measured CF 4 content, while those at a pressure of 30 mTorr are Druyvesteyn ones in the presence of a small amount of CF 4 . The average electron energy slightly increases with CF 4 content, while the electron density decreases. The decrease in the electron density with addition of CF 4 is more prominent as the total pressure increases. Dependences of the electron density and the averaged electron energy on CF 4 content are predicted in the global model.
A new method for evaluating negative ion and electron parameters from the current–voltage characteristics of electric probes is presented. A theoretical model and its related numerical procedures are established and errors included are estimated. Temperatures and densities of negative ions and electrons in a magnetic multipolar-confined plasma of Ar and Ar/SF6 mixtures are determined with allowable errors for various density ratios of the negative ion to the electron.
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Ar-N2 mixture positive columns of direct current glow discharges are experimentally and theoretically investigated. The electron energy distribution function of the column, which has a great deviation from the Maxwellian, is affected by the amount of N2. The N2 and Ar metastable species densities estimated from the rate equations are inversely proportional to N2 content. There is a large discrepancy between experimental and theoretical electron energy distribution functions, especially for N2 positive columns. The value of pR obtained experimentally is predicted from the measured electron energy distribution function, where p is the gas pressure and R the tube radius.
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