Plasma Microjet Research Articles

Atmospheric-Pressure Plasma Microjet of Argon–Nitrogen Mixtures Directed by Dielectric Flexible Tubes

Herein, a plasma microjet of argon-nitrogen mixtures is produced at atmospheric pressure. The device operation is based on a dielectric-barrier discharge generated by high-voltage positive pulses. We show the possibility to direct the excited species of the jet into flexible silicone tubes and to drastically modify the reactivity at the tube's downstream end by varying the gas composition of the jet. The induced modifications are illustrated by aesthetically pleasing images which unveil the existence of an optimum proportion of nitrogen to argon in order to achieve increased reactivity.

Microplasma Jets Generated by Arrays of Microchannels Fabricated in Flexible Molded Plastic

Novel microplasma jet devices have been fabricated in a moldable polymer that is resilient, transparent, and flexible. With a layer-by-layer assembly process involving a mold and initially undercured polymer, arrays of plasma microjets as large as 5 × 2 have been constructed and demonstrated to date. Having a channel diameter of 340 ± 5 μm and a single gas feed 4 mm in diameter for the entire array, the microchannel jets extend ~3.6 mm into laboratory air for a He gas flow rate of ~4.6 standard liters per minute.

Guided Propagation of Excited Species Produced by Microjet Plasma

The outlet of a plasma microjet system operating with noble gases at atmospheric pressure is connected to dielectric guides, and the transfer of excited species to long downstream regions is demonstrated by means of photography. Both straight and curved particle propagation paths are achieved and illustrated by imaginative images. The latter justify the potential use of this atmospheric-pressure plasma device to biomedical applications.

Laminar-to-Turbulent Transition of a DC Helium/Oxygen (2%) Plasma Microjet

A direct current plasma microjet is generated from a microhollow cathode discharge device in air with helium and oxygen (2%) as working gas. With the increase of the gas flow rate, a laminar-to-turbulent transition was found at a flow rate between 2.5 and 3.0 slm. The corresponding critical Reynolds number is calculated to be between 639 and 768. A stable bifurcation of the jet tip is observed with a transition flow when a nozzle with a 400- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> diameter opening is used.

Inactivation of Bacillus subtilis Spores in Water by a Direct‐Current, Cold Atmospheric‐Pressure Air Plasma Microjet

AbstractBacillus subtilis spores suspended in distilled water was effectively inactivated in 6 min by a direct‐current atmospheric pressure non‐thermal air plasma microjet. Scanning electron microscopic images show clear distortion and debris of spores after plasma treatment. Direct contribution by temperature and pH change of water as well as relatively long lived species in plasma activated water (PAW) is excluded. Short lived species (such as •OH, •O and O2(1Δg)) are detected in the plasma‐water system by electron spin resonance spectroscopy, and are considered to be the most important agents in the inactivation process.magnified image

Inactivation of Staphylococcus aureus in Water by a Cold, He/O2 Atmospheric Pressure Plasma Microjet

AbstractA direct‐current, atmospheric pressure, cold plasma microjet (PMJ) sustained in a quasi‐steady gas cavity in liquid was used to inactivate Staphylococcus aureus suspended in distilled water. While helium gas (with 2% O2 as additive) was used as working gas, an effective inactivation (&gt;99%) was achieved in 6 min. The inactivation of bacteria was further verified by surface morphology examination and LIVE/DEAD Baclight bacterial viability test (fluorescence microscopy). The overall pH and temperature of the liquid were monitored during the plasma treatment and were found to be below the critical values for the survival of S. aureus. Hydroxyl radical (•OH) was detected via electron spin resonance (ESR) spectroscopy, and alongside other intermediate reactive species, is attributed to the effective inactivation of S. aureus. End‐on optical emission spectroscopy show strong atomic oxygen emission both in air and in water.magnified image

High-rate reduction of copper oxide using atmospheric-pressure inductively coupled plasma microjets

Reduction of copper oxide was performed using an atmospheric-pressure inductively coupled plasma (AP-ICP) microjet while varying the input power P between 15 and 50 W. Cuprous oxide (Cu 2O) and cupric oxide (CuO) were formed on the sputtered Cu surface by thermal annealing. Dynamic behavior of the microplasma jet, optical emission from H atoms, the substrate temperature, chemical bonding states of the treated surface, and the thickness of the reduced Cu layer were measured to study the fundamental reduction process. Surface composition and the thickness of the reduced Cu layer changed significantly with P. Rapid reduction of CuO and Cu 2O was achieved at a rate of 493 nm/min at P = 50 W since high-density H atoms were produced by the AP-ICP microjet.

Atmospheric pressure cold plasma as an antifungal therapy

A microhollow cathode based, direct-current, atmospheric pressure, He/O2 (2%) cold plasma microjet was used to inactive antifungal resistants Candida albicans, Candida krusei, and Candida glabrata in air and in water. Effective inactivation (&amp;gt;90%) was achieved in 10 min in air and 1 min in water. Antifungal susceptibility tests showed drastic reduction of the minimum inhibitory concentration after plasma treatment. The inactivation was attributed to the reactive oxygen species generated in plasma or in water. Hydroxyl and singlet molecular oxygen radicals were detected in plasma-water system by electron spin resonance spectroscopy. This approach proposed a promising clinical dermatology therapy.

The Effect of an Atmospheric Pressure, DC Nonthermal Plasma Microjet on Tooth Root Canal, Dentinal Tubules Infection and Reinfection Prevention

A direct current, cold, atmospheric-pressure Ar/O 2 (2%) plasma microjet (PMJ) was used to disinfect root canals in single-rooted extracted human teeth. Results showed that 98.8% Enterococcus faecalis (E. faecalis) was inactivated in 8 min. However, the seemingly cleaned root canal was reinfected after a week, possibly due to the hard-to-reach infected dentinal tubules. It was found that a 30-min PMJ treatment could effectively prevent the re- infection. This presents a simple yet effective alternative to traditional treatment of root canal infections in endodontic therapy.

A Novel Method of Tooth Whitening Using Cold Plasma Microjet Driven by Direct Current in Atmospheric-Pressure Air

We reported in this paper the tooth-whitening effect by a direct-current cold atmospheric-pressure air plasma microjet (PMJ) and saline solution (0.9%). All teeth were randomly divided into three groups, treated for 20 min with an air blow and saline solution, a PMJ and saline solution, and 35% hydrogen peroxide gel, respectively. Compared with the other groups, the teeth treated with the PMJ and saline solution showed the best tooth-whitening effect. The microhardness of the tooth enamel measurement showed no apparent differences among the three groups. A minor enamel surface morphological change was observed via SEM but was considered acceptable. Singlet oxygen ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and hydroxyl (*OH) radicals were detected by electron spin resonance spectroscopy. Atomic oxygen (O) was observed in the optical emission spectra of the PMJ. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , *OH, and O were considered to be the key agents during the tooth-whitening process. This novel method of tooth whitening has the potential to revolutionize the clinical tooth-whitening procedure.

Optical and electrical characterization of pulse-modulated argon atmospheric-pressure inductively coupled microplasma jets

The critical parameters determining the generation of the pulse-modulated argon atmospheric-pressure inductively coupled plasma (AP-ICP) microjet were studied by varying the power, P, pulse-modulation frequency, f, and duty ratio, DR. The temporal changes in the net output power, Pnet, monitored between the very high frequency power supply and matching network by an rf sampler, and ArI 4s′[1/2]1O–4p′[1/2]0 emission from the antenna were measured to elucidate the behavior of this plasma. The AP-ICP microjet, which produces high-density (0.9–1.1×1015 cm−3) nonequilibrium plasma, consists of an alumina discharge tube with the inner diameter of 0.8 mm. The generation diagram of the pulse-modulated plasma was created by having f as the horizontal axis and DR as the vertical axis while varying P up to 50 W. At f≤10 kHz, the plasma was generated at above the linear lines of f and DR, which indicated the existence of the critical power-off period of approximately 80 μs. At f&amp;gt;10 kHz, the pulse-modulated plasma was produced above constant DR and almost independent of f. The time-averaged power, P¯, which is the product of P and DR, had to be more than 8–10 W to sustain the pulse-modulated plasma. From the measurement of the temporal changes in the net power and ArI emission, the dynamic behavior of the pulse-modulated plasma was revealed as follows. The prebreakdown period was present for ∼5 μs after the power was turned on. Once the plasma was generated, the impedance was changed and the reflected power gradually decreased. A strong emission peak was observed immediately after the breakdown, followed by the gradual increase up to the steady state. Finally, the intense afterpeak was observed at 0.8 μs after the power was turned off.

Tooth Whitening With Hydrogen Peroxide Assisted by a Direct-Current Cold Atmospheric-Pressure Air Plasma Microjet

A tooth-whitening process using hydrogen peroxide (H2O2) enhanced by a direct-current cold atmospheric-pressure plasma microjet (PMJ) is presented. Compared with the conventional clinical method of using H2O2 alone, a significant improvement of the tooth-whitening process was observed when the PMJ was used in the process. The tooth-surface temperature was monitored for safety considerations and did not exceed 37°C at a distance of 1 cm between the exit nozzle of the plasma source and the tooth for a treatment time of 20 min. No apparent differences in the tooth-surface morphology and microhardness were observed between teeth treated with and without the PMJ. The use of the PMJ with H2O2 resulted in an enhanced production of reactive hydroxyl (OH) radicals. This plasma-enhanced tooth-whitening method may be a promising new method for clinical applications.

Inactivation of Staphylococcus aureus and Enterococcus faecalis by a direct-current, cold atmospheric-pressure air plasma microjet

Objective A direct-current, cold atmospheric-pressure air plasma microjet (PMJ) was performed to inactivate Staphylococcus aureus (S. aureus) and Enterococcus faecalis (E. faecalis) in air. The process of sterilization and morphology of bacteria was observed. We wish to know the possible inactivation mechanisms of PMJ and explore a potential application in dental and other temperature sensitive treatment. Methods In this study, we employed a direct current, atmospheric pressure, cold air PMJ to inactivate bacterias. Scanning electron microscopy was employed to evaluate the morphology of S. aureus and showed rupture of cell walls after the plasma treatment and Optical emission spectrum (OES) were used to understand the possible inactivation mechanisms of PMJ. Results The inactivation rates could reach 100% in 5 min. When the distance between the exit nozzle of the PMJ device and Petri dish was extended from 1 cm to 3 cm, effective inactivation was also observed with a similar inactivation curve. Conclusion The inactivation of bacteria is attributed to the abundant reactive oxygen and nitrogen species, as well as ultroviolet radiation in the plasma. Different life spans and defensibilities of these killing agents may hold the key to understanding the different inactivation curves at different treatment distances.

Inactivation of Bacteria in an Aqueous Environment by a Direct‐Current, Cold‐Atmospheric‐Pressure Air Plasma Microjet

AbstractA direct‐current, cold‐atmospheric‐pressure air plasma microjet (PMJ) sustained in a quasi‐steady gas cavity in a liquid medium is used to inactivate Staphylococcus aureus (S. aureus) suspended in the liquid. The temperature and the pH value of the liquid change to steady‐state values of about 40 °C and 3.0–4.5, respectively, after 10 min of plasma treatment. The decrease in the pH is attributed to the reaction of NOx produced in the air plasma with water at the gas–liquid interface. The concentrations of NO and NO are measured to be 37 mg · L−1 and 21 mg · L−1, respectively, after a 20 min of plasma treatment. Effective inactivation of S. aureus is found to start after the pH values decreases to about 4.5. This is attributed to the high oxidizing potential of the perhydroxyl radical (HOO•) on the fatty acid in the cell membranes of the microorganisms in the liquid.magnified image

Reduction of Copper Oxide Films by an Atmospheric-Pressure Inductively Coupled Plasma Microjet

Satomi Tajima*, Shouichi Tsuchiya, Masashi Matsumori, Shigeki Nakatsuka, and Takanori Ichiki 3, 4 1 Department of Bioengineering, School of Engineering, The University of Tokyo *Fax: 81-3-5841-7781, e-mail: satomi@bionano.t.u-tokyo.ac.jp 2 Panasonic Factory Solutions Co., Ltd. 3 Center for NanoBio Integration (CNBI), The University of Tokyo 4 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency

On/off Pulse Modulation of Atmospheric-Pressure Helium/Argon Inductively Coupled Plasma Microjet for Plasma Processing of Polymers

On/off Pulse Modulation of Atmospheric-Pressure Helium/Argon Inductively Coupled Plasma Microjet for Plasma Processing of Polymers

The Interaction of a Direct-Current Cold Atmospheric-Pressure Air Plasma With Bacteria

A direct-current cold atmospheric-pressure air plasma microjet (PMJ) based on the microhollow cathode discharge design is used to inactivate six types of bacteria within a small well-defined area on a large Petri dish. We show that the PMJ is very effective in inactivating bacteria in their vegetative state as well as in the spore state within the area of plasma exposure. We also observed that bacteria in their vegetative state were inactivated efficiently outside the area of direct plasma exposure. Different bacteria responded differently to an increase in the plasma exposure (dose). Lastly, we observed two types of colony forming unit (CFU) distributions after plasma treatment; one distribution is diffusionlike with a gradual increase of the surviving CFU as one moves radially away from the area of direct plasma exposure, and the other distribution shows an essentially uniform reduction in surviving CFU across the entire Petri dish.

Possible Reasons of Degradation of Elements of Space Vehicle Control-Systems

It was shown experimentally that super-deep penetration (SDP) effect occurs due to collision of a microparticles clot with a metallic thick-walled shell. It has been established that this process is accompanied by plasma microjets ejection from an internal surface of a protective shell. Plasma microjets are highly injurious in relation to elements (microcircuits) of electronic control systems.

Hollow cathode sustained plasma microjets: Characterization and application to diamond deposition

Extending the principle of operation of hollow cathode microdischarges to a tube geometry has allowed the formation of stable, high-pressure plasma microjets in a variety of gases including Ar, He, and H2. Direct current discharges are ignited between stainless steel capillary tubes (d=178 μm) which are operated as the cathode and a metal grid or plate that serves as the anode. Argon plasma microjets can be sustained in ambient air with plasma voltages as low as 260 V for cathode-anode gaps of 0.5 mm. At larger operating voltage, this gap can be extended up to several millimeters. Using a heated molybdenum substrate as the anode, plasma microjets in CH4/H2 mixtures have been used to deposit diamond crystals and polycrystalline films. Micro-Raman spectroscopy of these films shows mainly sp3 carbon content with slight shifting of the diamond peak due to internal stresses. Optical emission spectroscopy of the discharges used in the diamond growth experiments confirms the presence of atomic hydrogen and CH radicals.

Plasma Micro-Jet Apparatus for Thermo-Chemical Treatment of Refractory Films

An r.f plasma micro-jet apparatus of transferred type for thermal and chemical treatment of re-fractory films has been developed. The plasma micro-jet generator is characterized by highly focusing plasma spot and making ready to generate and stabilize the plasma arc. Rf supply of 4 MHz was used. The operating characteristics, especially the dimension and temperature of plasma spot have been investigated as a function of rf voltage, argon flow rate, stand-off distance, composition of plasma gas, and other parameters of operation.The spot temperature above 3300°C and the spot diameter smaller than 0.3 mm was obtained on operating at the optimum conditions. Heating treatments of sputtered films of TiC and TiN were carried out by scanning with argon plasma micro-jet and argon-nitrogen one, respectively. The development of crystal growth in the film specimens by plasma irradiation were verified by the observation with an electron microscope and an X-ray micro-diffractometer.