Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

This paper presents and explains the principle behind anelectrochemical method to enhance the antimicrobial action of plasma-activated hydrogel therapy (PAHT) in the context of wound decontamination. The process involves grounding and hydratingpoly(vinyl alcohol) (PVA) hydrogel films during treatment with a helium (He) plasma jet. This electrochemically enhances production of hydrogen peroxide (H2O2), which is amajor antibacterial agent produced in the PVA hydrogel. Production of H2O2 is shownto be electrically enhanced through electron dissociation reactions, and through reactions associated with excited state species, metastables and ultra-violet (UV) photolysis. H2O2 production is chemically enhanced through the He flow of the plasma jet dehydrating the PVA hydrogel, which fuels the electrochemical dependent reactions associated with H2O2 production. The electrochemical process produces an unprecedented 3.4 mM of H2O2 in the PVA hydrogel. Production of other molecules such as reactive nitrogen species (RNS) are also enhanced by the same method. The electrochemically enhanced PAHT is highly effective ateradicating common wound pathogens Escherichia coli and Pseudomonas aeruginosa and mildly effective against Staphylococcus aureus. Overall, this study shows that the new PAHT dressing offers a promising alternative to antibiotics and silver-based dressings for controlling infection and stimulating healing in wounds.

DOI： https://doi.org/10.1002/adfm.202314345

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Total reflection X-ray fluorescence (TXRF) analysis is used to determine the concentrations of trace elements in liquid samples. Solutions are generally added dropwise onto a flat substrate and dried. When liquids with low elemental levels are analyzed, a hydrophobic substrate is employed to prepare a small dome-shaped residue. In the analyses of high-level solutions (high elemental concentration solution), the quantitative accuracy and measurement sensitivity deteriorate because X-ray fluorescence (XRF) is absorbed inside the thick residue. By preparing a thin residue, it is possible to reduce this absorption effect. In our previous study, atmospheric pressure plasma jet (APPJ) treatment was used to prepare a superhydrophilic substrate. The time that super-hydrophilicity is maintained is not yet known and determining this value is important for performing TXRF analysis. Therefore, we measured the contact angles of the droplets and performed X-ray photoelectron spectroscopy of the substrate surfaces to determine the relationships between the experimental values and the elapsed time. The optimal APPJ-treated area has not yet been determined and is one of the most important factors for high-sensitivity analysis. In this study, we controlled the APPJ-treated area by preparing four polytetrafluoroethylene (PTFE) masks with different hole diameters and obtained recoveries, relative standard deviations, and minimum detection limits (MDLs) to identify the optimal APPJ-treated area. A PTFE mask with a diameter of 4 mm generated the best values, particularly for low-Z elements. By controlling the diameter of the dried residue to 4 mm, the MDL value in aluminum was improved by a factor of 1.7.

DOI： 10.1039/D3JA00168G

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Low-temperature atmospheric-pressure plasma jets are generally considered a safe medical technology with no significant long-term side effects in clinical studies reported to date. However, there are studies emerging that show plasma jets can cause significant side effects in the form of skin burns under certain conditions. Therefore, with a view of developing safer plasma treatment approaches, in this study we have set out to provide new insights into the cause of these skin burns and how to tailor plasma treatments to mitigate these effects. We discovered that joule heating by the plasma bullet currents is responsible for creating skin burns during helium plasma jet treatment of live mice. These burns can be mitigated by treating the mice at a further distance so that the visible plasma plume does not contact the skin. Under these treatment conditions we also show that the plasma jet treatment still retains its medically beneficial property of producing reactive oxygen species in vivo. Therefore, treatment distance is an important parameter for consideration when assessing the safety of medical plasma treatments.

DOI： https://doi.org/10.3390/plasma6010009

DOI： https://doi.org/10.3390/plasma6010009

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Applicability of precise Raman spectral analysis of a-C:H films deposited using a plasma chemical vapor deposition (CVD) method has been discussed based on the sensitivity to initial conditions in peak separation. The spectral analysis offers to deconvolute the spectra into five peaks, while the as-deposited films prepared by plasma CVD is difficult to the five-peak separation. We found the peak position and the peak height ratio of the D-band to the G+-band can be employed to discuss the structure of the as-deposited films. We examined the structural difference between the films deposited at the powered electrode and that at grounded electrode. We found graphene nanoribbon-like structures may be formed in the films deposited on the grounded substrate. This result suggests that the substrate position is an important factor to form the graphene nanoribbon-like structure.

DOI： https://doi.org/10.1557/s43580-022-00310-6

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Current methods used to treat non-muscle invasive bladder cancer are inadequate due to a high recurrence rate after surgery and the occurrence of adverse events such as interstitial pneumonia following intravesical instillation therapy. Low-temperature plasma is a new form of physical therapy that provides a rich source of reactive oxygen species (ROS). Oxidative solutions, created by pre-treatment of aqueous media with plasma before application to target cells, lead to the destruction of cancer cells through oxidative stress pathways. This study focuses on the effects of plasma-activated media (PAM) in bladder cancer cells. PAM treatment increases oxidative stress that leads to cell cycle arrest and concomitantly depolarises the mitochondrial membrane leading to increased mitochondrial ROS production. Cell cycle arrest and increased mitochondrial ROS production led to an increase in caspase 3/cytochrome c activity, which might explain the induction of apoptosis in bladder cancer cells in vitro and in a bladder cancer tumour in vivo. These observations highlight the potential of plasma activated solutions as a new adjuvant therapy in the clinical treatment of bladder cancer.

DOI： https://doi.org/10.3390/plasma5020018

DOI： https://doi.org/10.3390/plasma5020018

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Medical treatment using non-thermal atmospheric pressure plasma (NTAPP) is rapidly gaining recognition. NTAPP is thought to be a new therapeutic method because it could generate highly reactive species in an ambient atmosphere which could be exposed to biological targets (e.g., cells and tissues). If plasma-generated reactive species could stimulate bone regeneration, NTAPP can provide a new treatment opportunity in regenerative medicine. Here, we investigated the impact of NTAPP on bone regeneration using a large bone defect in New Zealand White rabbits and a simple atmospheric pressure plasma (helium microplasma jet). We observed the recovery progress of the large bone defects by X-ray imaging over eight weeks after surgery. The X-ray results showed a clear difference in the occupancy of the new bone of the large bone defect among groups with different plasma treatment times, whereas the new bone occupancy was not substantial in the untreated control group. According to the results of micro-computed tomography analysis at eight weeks, the most successful bone regeneration was achieved using a plasma treatment time of 10 min, wherein the new bone volume was 1.51 times larger than that in the plasma untreated control group. Using H&E and Masson trichrome stains, nucleated cells were uniformly observed, and no inclusion was confirmed, respectively, in the groups of plasma treatment. We concluded the critical large bone defect were filled with new bone. Overall, these results suggest that NTAPP is promising for fracture treatment.

DOI： 10.1371/journal.pone.0255861

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1039/D1JA00164G

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1361-6463/ab91eb

Other URL： https://iopscience.iop.org/article/10.1088/1361-6463/ab91eb/pdf

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/ppap.202000001

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ppap.202000001

Publishing type：Research paper (scientific journal)  

<p>PEDOT, which is widely used as a conductive polymer, is generally produced by oxidative polymerization of monomer (EDOT) over several hours. We investigated the possibility of EDOT polymerization using atmospheric pressure plasma as a simple and quick production method. In this work, measured infrared spectra of the EDOT before/after the plasma treatments. We discuss possibility of formation of PEDOT by our method through comparison to the IR spectrum of PEDOT given in a literature.</p>

DOI： 10.14886/jvss.2020.0_28

CiNii Article

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

Microplasma discharges in deionized water and artificial seawater were investigated using pin-to-plate electrodes with a gap of a several tens of microns. By using a pulse voltage source, microdischarge was operated in deionized water and diluted artificial seawater and compared with discharge in ambient air. To operate the microdischarge in undiluted artificial seawater, a pulse current source (impulse generator) was used to supply the breakdown voltage with sufficient current. Even in seawater with an electrical conductivity of 45 mS/cm, microplasma discharges were reproducibly ignited at applied voltages below 1 kV. In the optical emission spectrum for the microplasma in artificial seawater, the main components of Na, Mg, Ca, K, S, H, and O were observed as distinguishable isolated lines, including lines for Pd, Ag and Fe from the electrodes.

DOI： 10.34343/ijpest.2019.13.01.001

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

DOI： DOI: 10.1039/C9CP03520F

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1109/ACCESS.2019.2928419

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

DOI： 10.1002/ppap.201900055

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

This study assesses a potential use of the recently developed nonthermal atmospheric pressure plasma technology in hydroponic plant cultivation. Plasma‐activated liquid solutions were investigated, namely, L‐Phenylalanine (L‐Phe), which had a benzene ring structure. We found that the benzene ring structure in solution contributed to antimicrobial property. Further, colony forming unit (CFU) assay indicated that 99% of Escherichia coli (E. coli) were eliminated after 24‐h incubation and radish sprout growth increased by about 40% after 2 days of cultivation.

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： https://doi.org/10.3390/plasma2020010

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

DOI： 10.1002/ppap.201800185

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

DOI： 10.11470/oubutsu.88.8_507

CiNii Article

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

We employed UV–vis spectroscopy to monitor real-time changes in the oxygen tension and concentration of reactive oxygen and nitrogen species (RONS) in deionized (DI) water during treatments with helium (He) and argon (Ar) gas plasma jets. He and Ar gas jets are both shown to deoxygenate DI water with He being more efficient than Ar, whilst the plasma jets deliver and regulate the concentrations of hydrogen peroxide (H2O2), nitrite (NO2−) and nitrate (NO3−) in DI water. The H2O2 and NO3− production efficiency varied between He and Ar plasma jets, but was similar for NO2−. Whilst DI water fully equilibrated with ambient air prior to treatment (de-oxygenated by both plasma jets) when DI water was first de-oxygenated by an inert gas jet treatment, both plasma jets were found to be capable of oxygenating DI water. These insights were then used to show how different combinations of plasma jet and inert gas jet treatments can be used to modulate O2 tension and RONS chemistry. Finally, potential further improvements to improve control in the use of plasma jets in regulating O2 and RONS are discussed.

DOI： https://doi.org/10.7567/1347-4065/aaea6b

Publishing type：Research paper (scientific journal)  

J-GLOBAL

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

© 2018 IEEE. Chemical components induced in water by irradiation to atmospheric pressure He plasma jet in ambient air has been investigated using UV absorption spectroscopy. There appears a characteristic absorbance peak in UV range for deionized water after irradiation to plasma jet. The UV absorbance peak can be well deconvoluted to 4 characteristic components assigned as O2, NO2-, NO3-, and H2O2, and from the analysis, the absolute concentration can be determined.

DOI： 10.1109/IEECON.2018.8712335

DOI： 10.1109/IEECON.2018.8712335

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1063/1.4999256

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1186/s13068-017-0979-6

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：Domestic journal  

DOI： 10.7567/JJAP.57.0102B9

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

DOI： 10.1002/ppap.201700073

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1016/j.tibtech.2017.07.012

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：Domestic journal  

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1088/1361-6463/aa7501

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1039/c7cc02927f

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1088/1361-6463/aa61d7

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1038/srep41953

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.3389/fphy.2017.00001

Publishing type：Research paper (scientific journal)  

With ambient mass spectrometry, we followed the transport of neutral gas species and ionic species through a 3.2 mm thick agarose tissue model target during He non-thermal atmospheric pressure plasma (NT-APP) jet treatment. We found that the neutral gas species are unable to efficiently penetrate the agarose target. But both positively and negatively charged ionic species readily penetrate through the agarose target, following an initial time-lag period of several minutes. Interestingly, we also found that the ionic species are easily hydrated. The trends in the He NT-APP jet transport of ionic species observed in this study correlate well with the He NT-APP jet transport of reactive oxygen and nitrogen species (RONS) through agarose tissue model targets that was investigated in previous studies. Therefore, mass spectrometry might prove to be a useful tool in the future for analyzing the dosages of NT-APP-generated RONS in real biological tissues.

DOI： 10.2494/photopolymer.30.317

Publishing type：Research paper (scientific journal)  

The effect of oxidation, oxygenation, and de-oxygenation arising from He gas jet and He plasma jet treatments on the viability of skin cells cultured in vitro has been investigated. He gas jet treatment de-oxygenated cell culture medium in a process referred to as "sparging." He plasma jet treatments oxidized, as well as oxygenated or de-oxygenated cell culture medium depending on the dissolved oxygen concentration at the time of treatment. He gas and plasma jets were shown to have beneficial or deleterious effects on skin cells depending on the concentration of dissolved oxygen and other oxidative molecules at the time of treatment. Different combinations of treatments with He gas and plasma jets can be used to modulate the concentrations of dissolved oxygen and other oxidative molecules to influence cell viability. This study highlights the importance of a priori knowledge of the concentration of dissolved oxygen at the time of plasma jet treatment, given the potential for significant impact on the biological or medical outcome. Monitoring and controlling the dynamic changes in dissolved oxygen is essential in order to develop effective strategies for the use of cold atmospheric plasma jets in biology and medicine. Published by AIP Publishing.

DOI： 10.1063/1.4967880

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

The efficacy of helium (He) and argon (Ar) plasma jets are being investigated for different healthcare applications including wound and cancer therapy, sterilisation and surface disinfections. Current research points to a potential link between the generation of reactive oxygen and nitrogen species (RONS) and outcomes in a range of biological and medical applications. As new data accrue, further strengthening this link, it becomes important to understand the controlled delivery of RONS into solutions, tissue fluids and tissues. This paper investigates the use of He and Ar plasma jets to deliver three RONS (hydrogen peroxide-H2O2, nitrite-NO2- and nitrate-NO3- and molecular oxygen (O-2) directly into deionised (DI) water, or indirectly into DI water through an agarose target. The DI water is used in place of tissue fluid and the agarose target serves as a surrogate of tissue. Direct plasma jet treatments deliver more RONS and O-2 than the through-agarose treatments for equivalent treatments times. The former only deliver RONS whilst the plasma jets are ignited; the latter continues to deliver RONS into the DI water long after the plasmas are extinguished. The He plasma jet is more effective at delivering H2O2 and NO2- directly into DI water, but the Ar plasma jet is more effective at nitrating the DI water in both direct and through-agarose treatments. DI water directly treated with the plasma jets is deoxygenated, with the He plasma jet purging more O-2 than the Ar plasma jet. This effect is known as 'sparging'. In contrast, for through-agarose treatments both jets oxygenated the DI water. These results indicate that in the context of direct and indirect plasma jet treatments of real tissue fluids and tissue, the choice of process gas (He or Ar) could have a profound effect on the concentrations of RONS and O-2. Irrespective of operating gas, sparging of tissue fluid (in an open wound) for long prolonged periods during direct plasma jet treatment, could have implications for healthy tissue function; whilst through-tissue plasma jet treatment may provide a method to reperfuse oxygen-starved tissue. The assays described in this paper can be readily adopted (by others) and may support the future development of plasma sources to deliver specific (metered) doses of RONS.

DOI： 10.1088/0022-3727/49/30/304005

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

© 2016 The Japan Society of Applied Physics. Microplasma discharge in sea water for optical emission spectroscopy was investigated using a needle-to-plane electrode system. The electrodes of a Pd needle and a Pt plate were placed with a gap of 25 μm in typical artificial sea water or locally sampled natural deep sea water. A pulse current source, consisting of a MOSFET switch, a capacitor, an inductor and the resistance of the sea water between the electrodes, was used. The circuit parameters were optimized to decrease the breakdown voltage and the spark duration to suppress erosion of the electrodes. Using a microgap configuration, spark discharges were reproducibly ignited in the highly conductive sea water at low breakdown voltages. The ignition of spark discharges required not only a critical voltage sufficient for breakdown, but also a critical energy for preheating of the sea water, sufficient for bubble formation. The possibility of using optical emission spectroscopy of microplasma in water is shown for identifying elemental composition of sea water.

DOI： 10.7567/JJAP.55.07LC03

Publishing type：Research paper (scientific journal)  

Ozonated water was investigated using a conventional UV-Vis spectrophotometer. We compared the UV absorption spectra of ozone (O-3) in water generated by either O-2 or air plasma bubbling method. The results noted that the observing the entire absorption spectrum is important for understanding the composition of ozonated water. Using an in-situ with an O-2 plasma bubbling in water we monitored the time-resolved UV absorption spectrum of the ozonated water. It is well known that a typical UV absorption spectrum of ozonated water contains a broad absorption peak at 260 nm and a shoulder below 220 nm. In our time-resolved measurement, however, it initially contained a broad absorption at short wavelength range below 210 nm considerably from dissolved O-2. As increase of the ozonation time, it noted that the absorption spectrum indicated the presence of high concentration of H2O2 and O-2 as well as relatively lower concentration of O-3.

DOI： 10.2494/photopolymer.29.427

Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.54.01AD04

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4930874

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Using a versatile atmospheric-pressure helium plasma jet, diamond-like carbon (DLC) films were etched in ambientair. We observed that the DLC films are etched at a nominal rate of around 60 nm/min in the treated area (230 μm in diameter) during a 20-min exposure. The etching rate increased after the initial 10-min exposure. During this period, the flat DLC surface was structurally modified to produce carbon nanostructures with a density of ~2.4 × 10¹¹ cm⁻². With this increase in surface area, the etching rate increased. After 20 min, the DLC film had a circular pattern etched into it downto the substratewhere silicon nanostructureswere observed with sizes varying from 10 nm to 1 μm. The initial carbon nanostructure formation is believed to involve selective removal of the sp2-bonded carbon domains. The carbon etching results from the formation of reactive oxygen species in the plasma.

DOI： 10.1016/j.diamond.2014.08.009

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Ambient molecular beam mass spectrometry (MBMS) has been used to study how different capillary widths (530 µm and 2.4 mm) and excitation waveforms (continuous wave kHz and pulsed dc) affect the ionic composition of atmospheric pressure plasma jets. It is shown from time-averaged ion intensities that reducing the width of the jet capillary results in a significant increase in the variety of both positive and negative ions detected within the discharge. We discuss this in terms of changes in flow velocity and the onset of turbulence within the plasma plume. Changing the mode of excitation had little effect on the ionic species detected from the microplasma jet; however, there was a notable shift in dominance towards higher mass ions when operated in a continuous wave kHz mode. The temporal evolution of the ions within the microplasma jet was observed for both excitation sources, operated at 5 and 15 kHz. Positive ions were created during periods correlated with the positive and negative peaks in discharge current, while negative ions were predominantly created at times when the discharge current peak was negative. This phenomenon was independent of the driving waveform. For pulsed dc excitation, considerably fewer positive ions were created in periods related to the negative current peaks, especially at higher frequencies. We propose a simple explanation for these processes based on ideas of streamer propagation and the influence of self-induced electric fields in the plasma plume.

DOI： 10.1088/0022-3727/46/46/464018

Authorship：Lead author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

This paper reports the spatially resolved surface modification of polystyrene (PS) using an atmospheric-pressure microplasma jet. Treatment of PS surfaces using a microplasma jet with a 100 µm diameter is investigated using contact angle, XPS, AFM and lens epithelial cell (LEC) growth. Microplasma jet treatment creates a defined reduction in contact angle of approximately 60° in a circular pattern with a diameter of 1.5 mm or more. Spatially resolved XPS analysis demonstrates that a reduction in contact angle is related to an increase in O1s peak intensity. AFM confirms that microplasma jet treatment causes no significant change in surface roughness. LECs are confined to a treated area.

DOI： 10.1002/ppap.201300052

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

Using mass spectrometry we show that ion-molecule reactions in the gas phase produce heavy oligomers of the series [nM+H]⁺ (n up to 6) within the output plume of a heptylamine polymerizing plasma jet flowing into air and N₂ blankets. Optimal operating conditions for high yields of heavy oligomers are found.

DOI： 10.1002/ppap.201300042

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

A synthetic biological sensor was developed to monitor the interaction of plasma with soft, hydrated biological material. It comprises phospholipid vesicles in a hydrated proteinaceous environment comprising 5% (w/v) gelatin. The vesicles contained a self-quenched dye, which was activated by vesicle destruction giving a clear fluorescent switch on. The interaction of bacterial toxins with the sensor was measured in a proof of principle experiment, then the effect of atmospheric plasma jets with the sensor, was studied in order to assess the cytolytic effect of plasma jets in biological systems. When the plasma contacted the gelatin surface perpendicular to the surface, the treatment resulted in the formation of a star-shaped pattern of microchannels that radiated out from the centre of the treatment area within the gelatin matrix, and locally damaged vesicles within the microchannels at a depth of 150 µm below the gelatin surface. Plasma jets applied in parallel to the surface of the matrix resulted in the formation of a single microchannel with damage to the vesicles only evident at the walls of the channel, and a much reduced penetration depth within the gelatin. Our data show that the effects of plasma can be deep in the gelatin material and that the angle of treatment significantly influenced the nature and level of damage to the gelatin and vesicles. Potentially this gelatin model can be used to unravel the roles of different plasma species and the direct effect of whole plasma contact, from those of primary and secondary species—i.e. primary, those emanating directly from the plasma and secondary, those species created in the 'target' tissue. This type of insight could be useful in the future development of safe and effective plasma medical technologies.

DOI： 10.1088/0022-3727/46/18/185401

Authorship：Lead author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A commercial current monitor has been used to measure the current associated with plasma bullets created in both the positive and negative half cycles of the sinusoidal driving voltage sustaining a plasma jet. The maximum values of the positive bullet current are typically ∼750 µA and persist for 10 µs, while the peaks in the negative current of several hundred μA are broad, persisting for about 40 µs. From the time delay of the current peaks with increasing distance from the jet nozzle, an average bullet propagation speed has been measured; the positive and negative bullets travel at 17.5 km s⁻¹ and 3.9 km s⁻¹ respectively. The net space charge associated with the bullet(s) has also been calculated; the positive and negative bullets contain a similar net charge of the order of 10⁻⁹ C measured at all monitor positions, with estimated charged particle densities n_b of ∼10¹⁰–10¹¹ cm⁻³ in the bullet.

DOI： 10.1088/0963-0252/21/3/034020

Publishing type：Research paper (scientific journal)  

Time-resolved ICCD images of discharge and plasma bullet formation in a capillary dielectric barrier discharge at atmospheric pressure have been obtained across the whole period in the voltage cycle. The images clearly show that the capillary discharge ignites at the inner edges of both electrodes, when each electrode is working as a cathode, and this leads to the formation of afterglow plasma bullets traveling upstream and downstream.

DOI： 10.1109/TPS.2011.2160290

Authorship：Lead author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Using molecular beam mass spectroscopy, time-resolved measurements of the ionic species in the plasma plume of an atmospheric-pressure helium microplasma jet are made for a range of excitation frequencies (5, 10 and 25 kHz) and source–instrument orifice distances (1, 7 and 11 mm). Ionic species can only be observed in the visible plasma plume, with the main positive species being (65.26%) and (21.11%), and a few percentages of N⁺, O⁺, NO⁺ and He⁺. For the negative ions, the majority species are O₃^- (22.68%), O₂^-(H₂O) (10.49%) and a large range of minority species observed, namely O_n^-, OH_n^-, H₂O^-, CO_n^- and clusters, O_m^-(H₂O)_n, (OH)_m^-(H₂O)_n, O_n^-(CO₃) and CO₃^-(H₂O)_n. The flux of ions created from air species, such as NO⁺ and O₃^-, is seen to be maximized at a distance of several millimeters from the nozzle, whereas the He⁺ concentration continually decreases with distance from the exit orifice. The time-resolved measurements (time resolution down to 2 µs) show that positive ions appear twice in one full period of the voltage waveform, correlated directly with positive and negative current peaks. The rise and fall times of the positive ions are typically tens of us. In contrast, the appearance of negative ions is correlated only with the negative part of discharge current, with one main peak in the detected ionic flux seen per cycle. The rise time of the negative ions is about 10 µs, independent of mass; however, we observed longer decay times, from 100 to 150 µs, increasing with mass. With increased driving frequency, the time modulation in the ionic fluxes is reduced, particularly for the negative species that show almost constant fluxes at 25 kHz throughout the cycle. The observations can be understood through a simple picture of the interaction of the He jet and the moist ambient air. The results indicate that the discrete plasma 'bullets' and their afterglow tail, that forms the jet, carry an associated positive or negative current depending on the time of their creation in the voltage cycle.

DOI： 10.1088/0022-3727/44/36/365202

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Single Work   International / domestic magazine：International journal  

Time-resolved ICCD images of discharge and plasma bullet formation in a capillary dielectric barrier discharge at atmospheric pressure have been obtained across the whole period in the voltage cycle. The images clearly show that the capillary discharge ignites at the inner edges of both electrodes, when each electrode is working as a cathode, and this leads to the formation of afterglow plasma bullets traveling upstream and downstream.

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Single Work   International / domestic magazine：International journal  

Using Schlieren photography, the helium outflow configuration from a fine capillary-based microplasma jet discharge has been captured for free-stream conditions. The transition
from laminar to turbulent flow is clearly identified with and without operation of the plasma. At a flow rate of 2.3 L min⁻¹ with no plasma operating, this transition occurs 54 mm from the nozzle; however, with plasma struck (peak voltages of 8 kV_p−p), this reduces to 40 mm.

DOI： 10.1109/TPS.2011.2157940

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

This paper reports on the correlation between gas flow and plasma behaviour in the outflow of a micro-atmospheric pressure plasma jet operating in helium using both 2D optical imaging and Schlieren photography. Schlieren photography shows that the helium outflow changes from laminar to turbulent conditions after distances between 20 and 50 mm from the nozzle. Above a flow rate of 1.4 slm, the length of the laminar region decreases with increasing flow rate. However, by contrast the visible plasma plume increases in length with increasing flow rate until its extension just exceeds that of the laminar region. At this point, the plasma becomes turbulent and its length decreases. Exposing polystyrene (PS) samples to the plasma jet significantly alters the water contact angle in a defined area, with the hydrophobic PS surface becoming more hydrophilic. This modification occurs both with and without direct contact of the visible glow on the surface. The radius of the treated area is much larger than the width of the visible jet but much smaller than the area of the turbulence on the surface. The treated area reduces with increasing nozzle–substrate distance.

DOI： 10.1088/0022-3727/44/15/155206

Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms.131.344

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Single Work   International / domestic magazine：International journal  

The potential of using water-vapor plasmas excited by microwaves as a ultraviolet (UV) light source has been investigated by using various pressures and input powers. The UV irradiation power increased and saturated at a pressure range dependent on the input power. On the other hand, other visible and infrared emissions corresponding to four atomic lines, i.e., the Balmer series of hydrogen at 486.1 nm ( H beta) and 656.3 nm (H alpha) and oxygen atoms at 777.2 and 844.6 nm, were clearly decreased with an increase in the total gas pressure. It was found that pressures (1.4-2.0 kPa) near the saturated water-vapor pressure were found to give the most intense UV irradiation. With a vapor pressure of 1.6 kPa and a total microwave power of 300 W, the power density of UV (Gamma uv ) was measured to be 10.5 uW cm^-2 at a distance of 30 cm from the center of the discharge tube as measured through an optical viewing port on the cavity discharge applicator. This value for UV is comparable to that for a mercury lamp. However, the efficiency was estimated to be considerably lower than that of a mercury lamp.

DOI： 10.1109/TPS.2008.2007732

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

We have studied the effects of ternary gas mixtures of Xe(10%)–Kr(20% and 40%)–Ne on the luminous efficiency in ac plasma display panels. Spatiotemporal behaviors of near infrared (IR) emission was measured by an intensified charge-coupled device camera equipped with a narrow bandpass filter and absolute densities of excited Xe∗ and Kr∗ atoms in the lowest resonance (1s₄) and metastable (1s₅) levels were measured by a technique of microscopic laser absorption spectroscopy. We have found interesting features from both emission and absorption experiments, such as longer near-IR emission (0.3–0.4 us) and different temporal behaviors between the excited Kr^∗(1s₅) atoms and Xe^∗(1s₄,1s₅) atoms. We have also found that the order of magnitude of the peak density of excited Kr^∗(1s₅) atoms (∼10¹² cm⁻³) was ten times smaller than that of Xe^∗(1s₄,1s₅) atoms, and that their decay time was remarkably short (∼0.3 us). These results have then been compared with those for a binary gas mixture of Xe(10%)–Ne. At a certain range of the sustain voltage, the production rate of Xe^∗(1s₄,1s₅) atoms and the luminous efficiency have turned out to be slightly improved for the ternary gas mixtures, compared to the binary gas mixture.

DOI： https://doi.org/10.1063/1.2786609

Publishing type：Research paper (scientific journal)   Kind of work：Single Work   International / domestic magazine：International journal  

The effects of the driving frequency of the sustaining-voltage pulses on microplasmas in a cell of an ac plasma-display panel (ACPDP) were investigated using spectroscopic diagnostics [optical emission spectroscopy (OES) and laser-absorption spectroscopy (LAS)]. The unit discharge cell has a structure similar to that of a general commercial ACPDP, but it is prepared for three-dimensional (3-D) observation using a pair of micro-prisms. When the near-IR emission by OES and the absorption signal by LAS were observed in the front and side views simultaneously, it was determined that the discharge was concentrated at the center of the discharge space and quickly responded to an applied electrical potential as the sustaining frequency increases. The production efficiency of excited Xe^**(2p) atoms and vacuum-ultraviolet (VUV) photons, which was estimated from the spectroscopy results with the measured power dissipated in the discharges, increased as the frequency of the sustain pulses increases to 100 kHz. At 250 kHz, however, the efficiency remarkably decreased because of an inefficient time for excimer formation and, possibly, for wall-charge formation. From the quantitative analysis of the efficiency, the most-efficient frequency for the sustain voltage was around 100 kHz in the case of Xe(5%)–Ne at 500 Torr, i.e., the efficiency depended on both the priming particles [excited Xe^*(1s₅) atoms] in space and the charged particles on the dielectrics.

DOI： https://doi.org/10.1889/1.2739799

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

Performances of microplasmas in unit discharge cells with grooved structures in the dielectric layer covering the coplanar electrodes were investigated in alternating current (ac)-type plasma display panels filled with Ne-Xe(10%) mixture at 450 torr. The diagnostics are based on a microscopic laser-absorption spectroscopy technique for the spatiotemporally resolved measurements of absolute densities of Xe^*(1s₅,1s₄) atoms, from which the production rate and the efficiency of the vacuum ultraviolet photons were estimated. These results were compared with previously reported data obtained in conventional phosphor coated panels with the same structures for the dependences on the applied sustain voltages. As the result, the following conclusions were ascertained. The grooved structure does not help to improve the luminous efficiency but it helps to lower the firing and sustaining voltages by about 20 V if the electrode gap is kept constant. Therefore, it provides additional possibilities for the selection of other operating conditions such as the gas composition and pressure for the improvements of the luminance and the luminous efficiency.

DOI： 10.1109/TPS.2006.872431

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

Ne–Kr gas mixtures with high Kr concentrations were applied to ac plasma display panels. Spatiotemporal behaviors of excited Kr atoms in the 1s5 metastable state and the 1s₄ resonance state were measured by microscopic laser-absorption spectroscopy in the binary mixtures with Kr concentrations of 20% and 40%. A systematic comparison was done between the characteristics of Ne–Kr-filled panels and those of conventional Ne–Xe panels with the same structure but with lower Xe concentrations of 5% and 10%. For example, the total number of Kr^∗(1s₅) atoms in a unit cell ranged from 7.4×10⁷ to 2.0×10⁸, at the peak was apparently smaller than the value of Xe^∗(1s₅) atoms. However, when the difference in the decay rate of the excited atoms by three-body collision processes is taken into account, the production efficiency of vacuum-ultraviolet (VUV) emission from Kr^∗₂ excimers is as large as that from Xe^∗₂ excimers in a usual panel since these processes lead directly to the formation of excimers. From the measured density of Kr^∗(1s₄) atoms, it is estimated that the contribution of the atomic resonance line is smaller than the excimer band at those high Kr concentrations. In any case, by summing up those two contributions to the VUV emission, the overall efficiency in the Ne–Kr(40%) panel is estimated to be comparable to that in the Ne–Xe(10%) one.

DOI： http://dx.doi.org/10.1063/1.2131194

Publishing type：Research paper (scientific journal)  

We have investigated the influence of microscopic surface structures of the MgO protective layer on the ion-induced secondary electron emission coefficient in alternating-current plasma display panels (AC-PDPs). The microscopic surface structures of the MgO protective layer have been formed by using a mesh mask with an electron beam evaporation method. The ion-induced secondary electron emission coefficient γ of the MgO protective layer with mesh-patterned microscopic surface structures has been measured by the γ-FIB (focused ion beam) system. It is found that the MgO protective layer with microscopic surface structures has a higher γ than those without any surface structures.

DOI： https://doi.org/10.1143/JJAP.43.L1154

Publishing type：Research paper (scientific journal)  

The change in work function was studied on Indium-tin-oxide (ITO) surface after O-plasma treatment using γ-focused ion beam (γ-FIB). As the surface of ITO experienced more O-plasma treatment, both the surface resistivity and the work function got higher. Auger electron spectroscopy identified the increase of oxygen as well as the decrease of Sn. The rise of work function and surface resistivity is considered to be due to the change in oxygen and Sn on the surface of ITO

DOI： https://doi.org/10.1016/S0921-5107(03)00115-6

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The work functions of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary electron emission coefficient γ, respectively, using various ions with different ionization energies in a γ-focused ion beam system. The work function for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary electron emission coefficient γ for Xe+ ions, whose ionization energy is 12.13 eV.

DOI： http://dx.doi.org/10.1063/1.1581376

Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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