The Cd,Hg, -;re avalanche photodiodes present hole or electron majority mu!!iplicationi depending on the r valuesl with a ratio of infiizattion fa.ctQrs k = ?,I%, maximum for x = 0.6 and minimum for x = 0.4. This behaviour is explained by a simulation of the multiplication phenomenon. Monte Carlo electron traiectories are averaged to obtain ionization factors ah and G. This model introduces a linear relationship between the logarithm of k and the ionization energy difference for holes and electrons: AE, = E,, -E,-. We compute this energy difference in an empirical tight binding band structure and show that its variation versus x agrees with experimental k(x) variations. The hole multiplication maximum at x = 0.6 is explained as the effect of transitions issued from the
Potential oscillations of electronegative plasmas have been experimentally studied in a strongly asymmetric rf (13.56 MHz) discharge. Oscillation amplitudes in the plasma were found to increase suddenly from 10 to 60 V with increasing concentration of SF6 gas in He gas, while gradually from 10 to 40 V in CF4 mixed plasma. The electron energy distribution functions (EEDFs) measurement predicted an electron beam travelling from the plasma towards the rf electrode because of the potential double layer in the sheath picked up by an emissive probe. A clear difference in potential formation and EEDFs profiles in comparison to those in electropositive plasmas has been detected. A more marked gas concentration dependence was obtained in a SF6 gas than in a CF4 one due to the more active production of negative ions in a SF6 plasma.
Spatial structures of electronegative plasma were described in an inductively coupled discharge driven by an internal helical antenna in a uniform magnetic field. This new type of plasma source enables production of a high density (∼10 11 cm −3 ) electronegative plasma at a low pressure (2 mTorr). Good uniformity was measured for the plasma density and the electron temperature along the central axis. These same parameters formed respectively hill and valley profiles in the radial direction. Mode conversion of RF discharge from capacitively coupled to inductively coupled discharge that eventually might lead to a helicon discharge was observed at various gas pressures. The space potential was found to decline with introduction of the electronegative (SF 6 ) gas to the electropositive (Ar) gas, while the RF oscillating amplitude and the RF excited magnetic field increased. The electron energy distribution functions were found to be non-Maxwellian in electronegative plasma unlike in electropositive plasmas.
A direct current (DC) powered low-temperature atmospheric pressure plasma (LTAPP) jet device was built and used to sterilize Escherichia coli (E.coli) bacteria. The plasma jet's general properties, such as length and temperature, were first tested and found to be strongly related to the plasma jet's operational flow mode (laminar or turbulent flow). The optical emission spectra of various gas mixtures were measured to confirm the presence of active radicals, which is critical for sterilization success. Pure helium gas or a combination of helium with a small percentage of oxygen (6.25 %) was found to have the highest intensities of bactericidal species such as atomic oxygen (O) and hydroxide (OH). These mixtures were then used to treat E.coli bacteria previously grown in a Petri dish. Sterilization was accomplished by repeatedly treating the bacteria for 10 seconds for 5-10 rounds for short periods. The best results were obtained when the bacteria had enough time to rest between rounds.
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