Pressure Radio Frequency Plasma Research Articles

Inactivation of Staphylococcus aureus on the beef jerky by radio-frequency atmospheric pressure plasma discharge treatment

Abstract Radio-frequency atmospheric pressure plasma discharge as an inactivation technique was tested to reduce Staphylococcus aureus on the surface of polystyrene, agar, and beef jerky. S. aureus ATCC12600 was reduced by 3–4 log colony forming unit on the polystyrene and agar after 2 min treatment, but on beef jerky sample after 10 min treatment. It suggests that the surface feature can significantly affect the inactivation of S. aureus by plasma. The scanning electron microscopy analysis showed that the S. aureus cells were disintegrated into pieces and many holes were created. The analysis of optical emission spectrum suggests that reactive oxygen species, especially the singlet state of oxygen at 777 nm are mainly responsible for the inactivation and cellular deformation of S. aureus. No significant change was found in the fatty acid composition, color and shear force of the beef jerky samples (p > 0.05). This study shows that radio-frequency atmospheric pressure plasma is effective in inactivation of S. aureus on the food samples such as beef jerky with little changes in nutritional and sensory qualities. Industrial relevance Inactivation of S. aureus on polystyrene, agar, and beef jerky samples using radiofrequency atmospheric pressure plasma is presented. The plasma treatment was a useful technology to reduce a microbial contamination on the surface of thin and dehydrated food products such as beef jerky. It is promising in the industrial application since no significant change was found in the fatty acid composition, color, and shear force of the beef jerky after the plasma treatment.

Inactivation of Campylobacter jejuni using Radio-frequency Atmospheric Pressure Plasma on Agar Plates and Chicken Hams

Radio-frequency driven atmospheric pressure plasma using argon gas was studied in the inactivation of Campylobacter jejuni in order to investigate its applicability. First, the inactivation study was conducted on an agar surface. C. jejuni NCTC11168 was reduced by more than 7 Log CFU after an 88 s treatment. Another strain, ATCC49943, was studied; however, the inactivation was less efficient, with a 5 Log CFU reduction after a 2 min treatment. Then, chicken breast ham was studied at the <TEX>$10^6$</TEX> CFU inoculation level. The inactivation efficiency was much lower for both strains compared to that on the agar plates. C. jejuni NCTC11168 and ATCC49943 were reduced by 3 Log CFU after a 6 min treatment and by 1.5 Log CFU after a 10 min treatment, respectively. The scanning electron microscopy analysis indicated that C. jejuni cells were deformed or transformed into coccoid form under the plasma treatment. During the plasma treatment, the temperature of the samples did not rise above <TEX>$43^{\circ}C$</TEX>, suggesting that heat did not contribute to the inactivation. Meanwhile, water activity significantly decreased after a 10 min treatment (p<0.05). This study conveyed that radio-frequency atmospheric pressure plasma can effectively inactivate C. jejuni with strain-specific variation.

Comparison of a global model to semi-kinetic fluid simulations for atmospheric pressure radio-frequency plasmas

A global model of a homogeneous plasma bulk oscillating between electron-free radio-frequency (rf) sheaths is developed. Particle and power balance, including ohmic heating loss for bulk-electrons and ions in the sheaths, yield the bulk electron temperature and density. Explicit time dependence of the reduced bulk electric field and correspondingly of the total ionization rate and electron transport coefficients is accounted for. Results for a gas mixture of 0.5 vol% oxygen in helium at atmospheric pressure within a 1 mm discharge gap as a function of the 13.56 MHz rf power density are presented and compared with a semi-kinetic 1D-fluid simulation. The quality of agreement is critically analyzed and correlated with the individual global model assumptions.

Determination of the elemental composition of micrometric and submicrometric particles levitating in a low pressure Radio-Frequency plasma discharge using Laser-Induced Breakdown Spectroscopy

The LIBS (Laser-Induced Breakdown Spectroscopy) technique has shown its potential in many fields of applications including that of aerosol analysis. The latter is usually carried out on the particle flow, thereby allowing quantitative detection in various experimental conditions such as ambient air analysis or exhaust stack monitoring, to name but a few. A possible alternative method for particle analysis has been experimented combining a low pressure RF (Radio-Frequency) plasma discharge with the LIBS technique. Such approach has two peculiar features in comparison to the usual LIBS analysis. First, the particles injected in the RF plasma discharge are trapped in levitation. Second, the analysis is performed at a reduced pressure of around 1mbar. LIBS detection at such low pressure has this peculiarity that particle vaporization is assumed to be achieved through direct laser particle interaction whereas it is caused by laser-induced plasma ignited in the gas at atmospheric pressure. The use of such particle trap could allow improving particle sampling, making organic particle analysis possible (by using an inert gas for RF plasma ignition) and even (depending on the pressure) obtaining a better signal to noise ratio. Detection of the elements of nanoparticle agglomerates made following their injection in the RF discharge has demonstrated the feasibility of such approach. Future experiments are intended to explore its potentialities when tackling issues such as process control or ambient air monitoring.

Two-photon absorption laser-induced fluorescence measurements of atomic nitrogen in a radio-frequency atmospheric-pressure plasma jet

The first direct measurements of atomic nitrogen species in a radio-frequency atmospheric-pressure plasma jet (APPJ) are presented. Atomic nitrogen radicals play a key role in new plasma medicine applications of APPJs. The measurements were performed with a two-photon absorption laser-induced fluorescence diagnostic, using 206.65 nm laser photons for the excitation of ground-state N atoms and observing fluorescence light around 744 nm. The APPJ was run with a helium gas flow of 1 slm and varying small admixtures of molecular nitrogen of 0–0.7 vol%. A maximum in the measured N concentration was observed for an admixture of 0.25 vol% N2.

Surface plasmon resonance investigation of optical detection in plasma-modified phospholipid layers

We herein report on a study of surface plasmon resonance (SPR) in thin gold (Au) films coated with thin layers of phospholipid material, which had been exposed to an atmospheric pressure (AP) plasma containing both pure Ar and Ar mixed with O2 (Ar/O2, 0.8%). The phospholipid material that we used for the SPR experiments was lecithin, and the AP plasma system was applied in air by means of a radio-frequency (RF) plasma generator. A thin (∼60 nm) film of Au and a thin (∼15 nm) layer of lecithin were deposited and attached to the face of a prism, and surface plasmon modes were excited along the interfaces of the prism-Au-lecithin-air system by means of prism coupling using a He-Ne Laser (632.8 nm). The experimental SPR reflectance curves of the Au-lecithin-air modes were found to be shifted towards those of the Au-air mode with increasing applications of AP RF plasma treatment. From the shifts in the SPR curves, we found that the estimated thickness of the lecithin layer treated with a pure Ar plasma showed a linear decrease with etching rate of about 3 nm per treatment while the thickness of the lecithin layer treated with a mixed Ar/O2 plasma showed a tendency to saturate following a large initial decrease (ca. 14 nm). All these results demonstrate that the use of SPR sensing could facilitate the detection of extremely small variations in plasma-treated films of biomaterials.

Study on mechanism of etching in low pressure radio-frequency plasmas

In order to investigate the mechanism of etching in low pressure radio-frequency (rf) plasmas, we adopt a two-dimensional Monte-Carlo (MC) cellular method to simulate the profile evolution, in which the ion reflection, the ion angular distribution (IAD) etc. are considered. It is found that the phenomenon of microtrenching results from the reflection of particles on the sidewall and the IAD is responsible for round corners at the bottom of the trench. The deeper the trench is, the more easily microtrenching or notching appear. In addition, the neutral particles can destroy the anisotropic etching of the trench and lead to bowling. On the other hand, by means of solving the Laplace equation near and in the trench with an iterative procedure, we obtain a stable or periodic stable electric field biased by a dc or rf source, in which the charging effect on the photoresist sidewall of the trench is considered. It is observed that both the dc and rf biases applied to the substrate can influence the profiles of etching, and the better etching profiles on the sidewall of the trench can be obtained with the rf bias than those with the dc bias.

Diagnostic of Capacitively Coupled Low Pressure Radio Frequency Plasma: An Approach through Electrical Discharge Characteristic

Diagnostic of Capacitively Coupled Low Pressure Radio Frequency Plasma: An Approach through Electrical Discharge Characteristic

Influence of p-layer on the performance of n-i-p μc-Si:H thin film solar cells

The high pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to prepare the n-i-p microcrystalline silicon solar cells, the influence of p-type layers on the performance of the solar cells was investigated, and the optimum p layer suited to the n-i-p microcrystalline silicon solar cells was obtained. The experimental results demonstrate that the performance of the solar cells can be highly affected by the structural and optical properties of the p-layers, and the performance of solar cells can be greatly improved by optimizing p layers. We have achieved an initial active-area efficiency of 8.17% (Voc=0.49 V, Jsc=24.9 mA/cm2, FF=67%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.93% (Voc=1.31 V, Jsc=13.09 mA/cm2, FF=64%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells.

Poly(ethylene glycol) Films Deposited by Atmospheric Pressure Plasma Liquid Deposition and Atmospheric Pressure Plasma‐Enhanced Chemical Vapour Deposition: Process, Chemical Composition Analysis and Biocompatibility

AbstractPoly(ethylene glycol) (PEG) films are known to be protein‐repelling and to reduce biofilms attachment. We use a simple, easy to set up, versatile atmospheric pressure radiofrequency plasma to deposit plasma‐polymerized poly(ethylene glycol) films onto polyvinylfluoride (PVF) and gold surfaces, using liquid or gaseous tetraglyme (CH3O(CH2CH2O)4CH3) as precursor. The chemical composition of the films was studied using infrared reflection absorption spectroscopy, X‐ray photoelectron spectroscopy and secondary ions mass spectroscopy. Bovine Serum Albumin adsorption has revealed good biocompatible properties that are correlated to the surface composition. magnified image

Decontamination of VX Surrogate Malathion by Atmospheric Pressure Radio-frequency Plasma Jet

Decontamination of the VX surrogate (malathion) by the atmospheric pressure radio-frequency plasma jet (APPJ) was investigated. Optical emission spectroscopy was used to identify the active species and measure the neutral gas temperature. The effects of RF input power and exposing time on the decontamination efficiency and neutral gas temperature were investigated. The thermal effect and volatilization could be ignored from the APPJ decontamination mechanism in our processing conditions. The degradation products were identified by gas chromatograph coupled with mass spectrometers (GC–MS). Besides the trace amount of the oxidation product (malaxon), the main degradation products were formed by breaking the S–C bond of malathion. In the end, the main degradation mechanism was drawn out.

An Indirect Method for Measuring Electron Density of Atmospheric Pressure Plasma Jets

An indirect method for measuring the electron density of radio frequency atmospheric pressure plasma jets (RF-APPJ) based on the discharge voltage and current waveforms is presented. An equivalent circuit of the plasma discharge is assumed by taking into account the electrode capacitance, serial resistance and inductance of the bulk plasma, as well as the sheath impedance. Based on the circuit model, the electron density can be obtained according to Ohm's law. By using this method, the effects of the electrode shape and discharge gap on the electron density are discussed.

Enhanced inactivation of bacterial spores by atmospheric pressure plasma with catalyst TiO2

Both atmospheric pressure plasma and photo-catalyst metal oxide titanium dioxide (TiO2) are well known for their microorganism inactivation and chemical material decomposition abilities. In this work, radio-frequency atmospheric pressure plasma and TiO2 are used together to inactivate Bacillus subtilis spores that have a very high degree of environmental resistance to ultra-violet (UV) photons and heat. The combinational use of the plasma and TiO2 demonstrates an enhanced performance of B. subtilis spore inactivation by showing a decrease in the decimal reduction time of as large as 40% compared with the use of plasma alone. A significant increase of hydroxyl (OH) and excited oxygen atomic emission line (O I) intensities in the presence of TiO2 suggests that the atmospheric pressure plasma assisted by TiO2 is very effective at generating reactive oxygen radicals, which is known to be a dominant factor in bacterial spore inactivation. Possible TiO2 activation mechanism by the plasma is investigated.

Performance improvement of n-i-p μc-Si:H solar cells by gradient hydrogen dilution technique

High pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to investigate the effect of constant hydrogen dilution technique and gradient hydrogen dilution technique on the structural evolution of intrinsic films and the performance of n-i-p microcrystalline silicon solar cells. The experiment results demonstrated that the grain size and crystalline volume fraction along the growth direction of intrinsic films can be controlled and the performance of solar cells can be greatly improved by gradient hydrogen dilution technique. An initial active-area efficiency of 5.7% (Voc=0.47 V, Jsc=20.2 mA/cm2, FF=60%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.12% (Voc=1.2 V, Jsc=12.05 mA/cm2, FF=70%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells has been achieved.

Comparison of Low- and Atmospheric-Pressure Radio Frequency Plasma Treatments on the Surface Modification of Poly(methyl methacrylate) Plates

In this article, the effects of RF (radio frequency) atmospheric pressure plasma (APP), and low pressure plasma (LPP) treatment were compared on the surface of the poly(methyl methacrylate) (PMMA) plate. The APP was proved to be able to improve the surface free energy of the PMMA faster and higher than the LPP under similar treatment condition. Atomic force microscopy revealed extraordinary surface roughness and morphology generated only on the APP-treated PMMA, where the cracks appeared. The surface temperature increased very quickly and exceeded quickly the glass transition temperature (Tg) of PMMA on the APP-treated surface, while it showed a little increase below the Tg on the LPP-treated surface. X-ray photoelectron spectroscopy analysis revealed a novel reaction mechanism is proposed for the formation of the nitrogen-containing groups. It was believed that the generation of new oxygen- and nitrogen-containing groups was dependent on the plasma treatment environment, which provided necessary active s...

The Design of an Atmospheric Pressure Plasma Torch Used for Polishing Ultra-Smooth Surfaces

As there are always certain defects on the final surface of large-scale lightweight mirrors, which are formed in traditional mechanical polishing process, such as microcracks, lattice disturbances, plastic deformation, and so on, an atmospheric pressure plasma polishing method is a good solution to this problem. As a key component, the design of the capacitance coupling atmospheric pressure radio-frequency plasma torch is introduced. The designed torch uses water cooled coaxial aluminium electrodes with special treatment to avoid arcing between them. In normal machining process, the mixture of reaction gas and plasma gas with optimum ratio is input into the plasma torch. Then, excited by radio-frequency power, reaction gas is ionized in the plasma so as to create high density and energy reactive radicals under atmospheric pressure. The radicals cause chemical reactions with the atoms on the part surface, which performs an effective atomscale removal process. As the machining process is chemical in nature, this method avoids surface/subsurface defects mentioned above. Furthermore, initial experiment data analysis has proved that the atmospheric pressure plasma polishing method is effective and reliable, as well as demonstrates the validity of the designed plasma torch.

Radio-frequency plasma transducer for use in harsh environments

We describe a compact transducer used to generate and modulate low-intensity radio-frequency atmospheric pressure plasma (RF-APP) for high temperature gap measurement and generation of air-coupled ultrasound. The new transducer consists of a quarter-wave transmission line where the ground return path is a coaxial solenoid winding. The RF-APP is initiated at the open end of the transmission line and stabilized by passive negative feedback between the electrical impedance of the plasma and the energy stored in the solenoid. The electrical impedance of the plasma was measured at the lower-voltage source end of the transducer, eliminating the need to measure kilovolt-level voltages near the discharge. We describe the use of a 7 MHz RF-APP prototype as a harsh-environment clearance sensor to demonstrate the suitability of plasma discharges for a common nondestructive inspection application. Clearance measurements of 0-5 mm were performed on a rotating calibration target with a measurement precision of 0.1 mm and a 20 kHz sampling rate.

Atmospheric Pressure Plasma Deposition of Polyfuran

The atmospheric pressure radiofrequency (RF) plasma polymerization of furan was carried out with the objective of synthesizing polyfuran thin film. The structure, compositions and morphology of the plasma deposited polyfuran film were investigated by Fourier transform infrared (FTIR), atomic force microscopy (AFM), ultraviolet‐visible absorption spectroscopy (UV‐vis) and thermogravimetric analysis (TGA). The formation of polyfuran was confirmed using FTIR and UV‐visible analysis. The properties of plasma‐deposited polyfuran were compared with those of chemically synthesized polyfuran. Although the plasma deposited thin film polyfuran shows lower thermal stability than that of chemically synthesized polyfuran. It has better solubility in CHCl3, also. Thin uniform polyfuran films are obtained in plasma assisted polyfuran deposition, while particles are obtained in chemical polyfuran polymerization.

06/01132 Coupling and reforming of methane by means of low pressure radio-frequency plasmas: Patino, P. et al. Fuel, 2005, 84, (16), 2008–2014

06/01132 Coupling and reforming of methane by means of low pressure radio-frequency plasmas: Patino, P. et al. Fuel, 2005, 84, (16), 2008–2014

Self-excited instability occurring during the nanoparticle formation in an Ar–SiH4 low pressure radio frequency plasma

An experimental investigation of an instability occurring during dust nanoparticle formation is presented in this paper. The present study has been performed in radio frequency low pressure plasma in an argon-silane mixture. The formation and growth of nanoparticles is followed, thanks to the analysis of the amplitude of the third harmonics (40.68MHz) of the discharge current and the self-bias voltage (Vdc). In some cases, at the end of the accumulation phase of the nanocrystallites an instability occurs. It seems to be an attachment induced ionization instability as observed in electronegative plasmas. A detailed study of the influence of different operating conditions (injected power, gas temperature, and silane flow rate) on this instability behavior and frequencies is presented. The paper concludes by examining a very particular case of the instability.