Lutfi Oksuz

One Atmosphere Uniform Glow Discharge Plasma

Summary form given only. Production of a stable atmospheric pressure glow discharge is always problem. Parallel plate dielectric barrier system is built in order to examine the physics of the atmospheric pressure discharge. The gap distance, frequency and voltage characteristics of atmospheric pressure plasma discharge are experimentally investigated with and without the addition of the helium. Optical characteristics, time-dependent and spatiallv resolved ICCD pictures will be given.

Elimination of Aspergillus parasiticus from nut surface with low pressure cold plasma (LPCP) treatment

Low pressure cold plasma (LPCP) using air gases and sulfur hexafluoride (SF(6)) was developed and tested for anti-fungal efficacy against Aspergillus parasiticus on various nut samples. Artificially A. parasiticus contaminated hazelnuts, peanuts, and pistachio nuts were treated with air gases plasma and SF(6) plasma for up to 20 min duration. The sterilizing effect of LPCP on A. parasiticus was higher during the early treatment period than the later treatment period. Air gases plasma treatment for 5 min resulted in 1-log reduction of A. parasiticus and a further 5 min treatment resulted in additional 1-log reduction. SF(6) plasma application was more effective resulting in approximately a 5-log decrease in fungal population for the same duration. When effectiveness of plasma treatment against aflatoxins were tested, 20 min air gases plasma treatment resulted in a 50% reduction in total aflatoxins (AFB1, AFB2, AFG1, and AFG2), while only a 20% reduction in total aflatoxin was observed after 20 min SF(6) plasma treatment. In this study, a rapid, functional clean-up method for the elimination of aflatoxin producing fungus from shelled and unshelled nuts was investigated as a suitable fungal decontamination method.

Laser induced fluorescence of argon ions in a plasma presheath

The characteristics of presheaths near an electrically floating plate in weakly collisional argon multidipole plasmas are investigated with a combination of data from laser induced fluorescence using a diode laser, Mach probes, emissive probes, and Langmuir probes. It is shown that ion–neutral collisions result in an increase in ion temperature from approximately room temperature in the bulk plasma to 0.13 eV, 0.5 cm from the plate, the location of the closest measurement. In addition, at that point, the presheath plasma potential drop is greater than Te/2, and the drift velocity is equal to 0.5 cs, where cs is the ion sound velocity.

RF hydrazine plasma modification of chitosan for antibacterial activity and nanofiber applications

Chitosan nano powders were modified using RF hydrazine plasma produced at low pressure (26.66Pa) with 13.56MHz frequency at a power of 100W for 30min. Characterization and investigation of the properties of plasma-modified chitosan (PMCh) and non-modified chitosan (Ch) were carried out using an optical monochromator, FTIR, florescence analysis, TGA, SEM, and X-ray techniques. FTIR spectra of PMCh indicated a band broadening at 3436cm(-1) that confirmed increasing functional groups based on H-bonding. The number of NH(2) groups was determined from fluorescence analysis. TGA analysis shows that the moisture absorption is three times higher in the PMCh structure. Ch and PMCh in PVA solutions were used to produce nanofibers by the electrospinning method; average fiber diameters were 480 and 280nm for Ch and PMCh, respectively. It was found that the antibacterial effect of PMCh is better than the Ch for Gram-positive strains.

Plasma, presheath, collisional sheath and collisionless sheath potential profiles in weakly ionized, weakly collisional plasma

Potential variations in bulk plasma, presheath and sheath describe the plasma potential profile responsible for ion acceleration out of weakly ionized, weakly collisional plasma. Experiments with emissive probes, Langmuir probes, laser induced fluorescence (LIF) and Mach probes in a multi-dipole plasma show that the presheath potential near a negatively biased plate scales as and is insensitive to the value of the plate bias. Plasma parameters were chosen so that ? = ?D/?? 0.02 ? 0.06 and 0.2 < ?/L <0.6, where ? is the ion?neutral mean free path, ?D is the Debye length and L is the plasma length. A Child?Langmuir-like sheath with width scaling as ?D(e/Te)3/4 with a Te/?D initial boundary electric field has been measured. A transition region, in which the plasma starts to deviate from being quasi-neutral, is observed between the presheath and the Child?Langmuir sheath. The transition region is approximately 2?D or ?1/5?d4/5. Mach probe data, calibrated by LIF data, suggest that the average ion velocity reaches the Bohm velocity inside the transition region and significantly exceeds the Bohm velocity at the Child?Langmuir sheath/transition boundary.

Laser-induced fluorescence measurements of argon ion velocities near the sheath boundary of an argon–xenon plasma

The Bohm sheath criterion in single- and two-ion species plasma is studied with laser-induced fluorescence using a diode laser. Xenon is added to a low pressure unmagnetized dc hot filament argon discharge confined by surface multidipole magnetic fields. The Ar II transition at 668.614 nm is adopted for optical pumping to detect the fluorescence from the plasma and to measure the argon ion velocity distribution functions with respect to positions relative to a negatively biased boundary plate. The structures of the plasma sheath and presheath are measured by an emissive probe. The ion concentrations of the two-species in the bulk plasma are calculated from ion acoustic wave experiments. Results are compared with previous experiments of Ar–He plasmas in which the argon ions were the heavier ion species. Unlike the previous results, the argon speed is slower than its own Bohm velocity near the sheath–presheath boundary in the Ar–Xe plasma where argon ions are the lighter ion species. We argue that this result is consistent with the behaviour of the helium ion required by the generalized Bohm criterion in the previous experiments with Ar–He plasmas. Further, our results suggest that the measured argon ion speed approaches the ion sound speed of the system.

Analysis of uncompensated Langmuir probe characteristics in radio-frequency discharges revisited

Measurements of the electron temperature, plasma density, and floating and plasma potentials with Langmuir probes in radio-frequency discharges often represent a challenge due to rf oscillations of the plasma potential. These oscillations distort the probe characteristic, resulting in wrong estimates of the plasma parameters. Both active and passive rf compensation methods have previously been used to eliminate rf fluctuation effects on the electron current drawn by an electrostatic probe. These effects on an uncompensated probe have been theoretically and experimentally studied by Garscadden and Emeleus [Proc. Phys. Soc. London 79, 535 (1962)], Boschi and Magistrelli [Nuovo Cimento 29, 487 (1963)], and Crawford [J. Appl. Phys. 34, 1897 (1963)]. They have shown theoretically that, assuming a Maxwellian distribution and sinusoidal plasma-potential oscillation, the electron temperature can be deduced directly from an uncompensated Langmuir probe trace, by taking the natural logarithm of the electron current...

Microdischarge propagation and expansion in a surface dielectric barrier discharge

We have recorded light emission from a surface dielectric barrier discharge with one exposed and one insulated electrode using an intensified digital camera. The discharge was operated in atmospheric pressure air. When the voltage to the exposed electrode is increasing, streamers form and propagate away from the exposed electrode in tens of nanoseconds. When the voltage is decreasing, more diffuse microdischarges form in a few nanoseconds. The qualitative behaviors of the plasma agree well with two-dimensional fluid simulations. Expansion in the average length of microdischarges as the applied voltage changes in both half-cycles of the waveform is also observed.

Electrospun chitosan/PEDOT nanofibers.

Plasma-modified chitosan and poly(3,4-ethylenedioxythiophene) were blended to obtain conducting nanofibers with polyvinyl alcohol as a supporting polymer at various volumetric ratios by electrospinning method. Chemical compositions and molecular interactions among nanofiber blend components were determined using Fourier transform infrared spectroscopy (FTIR). The conducting blends containing plasma-modified chitosan resulted in a superior antibacterial activity and thinner fiber formation than those containing chitosan without plasma-modification. The obtained nanofiber diameters of plasma-modified chitosan were in the range of 170 to 200 nm and those obtained from unmodified chitosan were in the range of 190 to 246 nm. The electrical and electrochemical properties of nanofibers were also investigated by four-point probe conductivity and cyclic voltammetry measurements.

Understanding Mach probes and Langmuir probes in a drifting, unmagnetized, non-uniform plasma

The effects of non-uniform drifting plasmas (in presheaths) on planar Langmuir probes and Mach probes are investigated in an unmagnetized argon plasma. Mach probe data are compared with double-sided Langmuir probe data. The calculated plasma potential from the Langmuir probe is found to be approximately equal to the average of the plasma potentials calculated from data on each side of the Mach probe. A new method is presented to determine the ion drift velocity using the electron saturation currents for um < 1 where um is the Mach number. This approach has the advantage that it uses much higher currents. It is shown that a single-sided planar probe gives information about the plasma almost an ion–neutral collision length away from the probe and should not be used in drifting plasma. The one-sided Langmuir probe on the downstream side of the Mach probe indicates the plasma potential where the ion drift velocity is zero and a one-sided Langmuir probe on the upstream side of the Mach probe also indicates the plasma potential where the ion drift velocity is zero.