Atmospheric Microplasma Jet Research Articles

Plasma-jet-induced programmable wettability on stretchable carbon nanotube films

Stretchable surfaces with site-selective and degree-controlled wettability are indispensable for various applications ranging from self-cleaning to droplet manipulation and drag reduction; however, superwettable surfaces or patterns with robust stretchability are seldom demonstrated to date. To address such challenging issue, herein, we proposed a facile approach to programmatically realize extreme wetting-contrast patterning of stretchable carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) using atmospheric micro-plasma jet (μPJ). The μPJ had been used to engineer both superhydrophobicity and superhydrophilicity through exploiting surface hierarchical roughness under a shielding nitrogen gas and oxygenic functional groups in atmosphere, respectively, tailoring the water contact angles from ~160° to <10° ultimately. The as-prepared superhydrophobic, conductive surfaces could bear tensile strain even up to 100% and demonstrated no noticeable wettability deterioration after 1000 cyclic stretching from ε = 0% to ε = 50%. And they also presented a distinguished enduring stability in terms of exposure to air and even extreme acidic/alkaline aqueous droplets. As the randomly entangled CNTs film could respond to tensile strain, the superhydrophobic films had been successfully applied to water-repellent epidermal sensors. And hydrophilic patterns had been fabricated on the superhydrophobic surfaces as well. It can be envisioned that a variety of novel applications ranging from water/blood-repellent human-machine interfaces to in-plane microfluidic can be implemented via this powerful wettability regulation paradigm.

Plasma-jet-assisted maskless, erasable, extreme wetting-contrast patterning on stretchable carbon nanotubes film

We present a mask-free approach to fabricate patterned surfaces with extreme wetting-contrast on carbon nanotubes/polydimethylsiloxane films using atmospheric micro-plasma jet, merely through exploiting surface hierarchical roughness for superhydrophobic background and oxygenic functional groups for superhydrophilic patches in sequence. Such high-contrast wetting behavior can be fast erased upon low-temperature thermal annealing and recovered by direct plasma jet writing in atmosphere for five cycles. The superwettable patterns also exhibit rather excellent mechanical stability against tensile strain up to 100% and 1000 cyclic stretching under 50% strain. These appealing features endow their versatile potential in liquid manipulation and self-assembly applications towards flexible/stretchable device.

Spatio-temporal distribution of absolute densities of argon metastable 1s5 state in the diffuse area of an atmospheric pressure nanosecond pulsed argon microplasma jet propagating into ambient air

Atmospheric microplasma jets (MPJs) sustained in rare gases have gained increased attention due to their potential to generate highly reactive species. In this paper, we present space- and time-resolved argon metastable densities, Ar(1s5), measured in an atmospheric pressure MPJ operated in Ar and propagating into ambient air using tunable diode laser absorption spectroscopy (1s5 → 2p9 optical transition). The MPJ was produced using a dielectric barrier discharge energized by short duration (230 ns) high-voltage positive pulses (4.2–6.2 kV) at a repetition frequency of 20 kHz. The spectral absorption line profile was recorded and allowed measurements of the absolute metastable Ar(1s5) density integrated in the line-of-sight of the laser beam under various operating conditions of the MPJ. The results reveal a sensitive dependence of the Ar(1s5) density on spatial coordinates, i.e., distance from the exit of the capillary tube of the discharge and from the axis of the argon jet. The highest Ar(1s5) densities of about 3 × 1013 cm−3 were measured at the axis of the argon jet at longitudinal distances between 4 and 5.5 mm downstream from the nozzle of the tube. The temporal distribution of the Ar(1s5) density, which presents three maxima, is thoroughly discussed in this paper. The spatial distribution of the effective Ar(1s5) lifetime (&amp;lt;250 ns) is also reported, giving some insight into the surrounding environment of the argon metastable atoms. The determined spatiotemporal distributions of the Ar(1s5) density can be useful for the optimization of argon MPJs for different applications like surface or biomedical processes.

Microplasma jet cleaning of Langmuir probes for methane-air premixed flame diagnostics

This paper presents the use of an atmospheric microplasma jet to preserve the measurement integrity of Langmuir probes for ion density measurements of an atmospheric methane-air premixed flame. Soot produced from incomplete combustion is able to deposit on the probe filaments and alter measurement characteristics over time. The effect of argon microplasma probe cleaning on current measurements was investigated, with probe flame exposure of 2–30 s and 20 s of microplasma cleaning. In the noncleaned probes, a decrease in the current measurements (up to 64% reduction) was observed in subsequent tests of probes at all exposure times. The probe cleaning experiments yielded a near constant current reading, even after subsequent flame exposures. The resulting plasma densities showed similar trends.

Low temperature atmospheric microplasma jet array for uniform treatment of polymer surface for flexible electronics

In this paper, the uniformity of polymer film etching by an atmospheric pressure He/O2 microplasma jet array (μPJA) is first investigated with different applied voltage. Plasma characteristics of μPJA were recorded by optical discharge images. Morphologies and chemical compositions of polymer film etched by μPJA were analyzed by optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). By increasing the applied voltage from 8.5 kV to 16.4 kV, the non-uniformity of the luminous intensity of the plasma jets increases. It is interesting that the plasma treated regions are actually composed of an etched region and modification region, with distinct morphologies and chemical compositions. The diameters of the etched parylene-C film show the increase of non-uniformity with higher applied voltage. SEM results show that the non-uniformity of surface morphologies of both the modification regions and etched regions increases with the increase of applied voltage. EDS and XPS results also present the significant effect of higher applied voltage on the non-uniformity of surface chemical compositions of both modification and etched regions. The Coulomb interaction of the streamer heads and the hydrodynamic interaction between the plasma jets and the surrounding air are considered to be responsible for this phenomenon. The results shown in this work can help improve the processing quality of polymer film etched by an atmospheric pressure microplasma jet array and two applications are demonstrated to illustrate the uniform downstream surface treatment.

Use of thermocouples and argon line broadening for gas temperature measurement in a radio frequency atmospheric microplasma jet.

This paper presents the use of thermocouples and line broadening of argon 2p-1s emission lines for the measurement of gas temperature of an atmospheric argon microplasma jet. The measured temperatures are compared with rotational spectra fitting of OH (A-X) and N2 (C-B) emission. An rf microplasma jet with two electrical configurations and different temperature ranges was used. The calculated gas temperatures with thermocouples, argon lines, and OH ranged from 290 to 423 K and 393-510 K for the two configurations, depending on the rf power. The temperature from fitting the N2 spectra overestimated the gas temperatures in both configurations (593-680 and 664-853 K). The non-nitrogen temperature measurements agree well with each other within the measurement uncertainty. The results show that not all optical emission temperature methods are appropriate and the accuracy of argon line broadening is dependent on the device configuration. The results also show that conventional thermocouples are surprisingly accurate and viable for these plasmas.

A Portable Plasma Sterilizer

An atmospheric microplasma jet system powered by an commercial transformer is developed for investigating the sterilizing efficiency of Escherichia coli in different conditions. The device can be hand-held and operated in the open air. The effect of carrier gas, gas flow rate, distance and treatment time of inactivation is studied. According to the experiment, plasma jet is able to inactivate all the bacteria on the surface in 20 s when the air flow rate is 5 L/min and the distance is 2.0 cm. Besides, the sterilization efficacy with different carrier gas follows an order as bellow: N2 > air > O2 > Ar. The measurements of malondialdehyde content, protein leakage quantity and Mg content are performed as well. In addition, the SEM after plasma treatment reveals that the integrity of E. coli cells is damaged and intracellular particles are excreted into the extracellular space. With discussions upon the mechanisms of surface sterilization, it is found that during the treatment of microplasma, it is mainly the etching actions of electrons and ions on the bacilli that kill the E. coli. Chemical effects rather than physical ones that are responsible for inactivation. Furthermore, the experiment results suggest that there may be better sterilization effect with gas mixture as carrier gas.

(Invited) Atmospheric Pressure Microplasma Jet: Properties and Applications in Synthesis of Nanoparticles

Atmospheric pressure microplasma jet: properties and applications in syntheses of nanoparticles (invited) Xiao-Xia Zhong State Key Laboratory of Advanced Optical Communication Systems and Networks and key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China. Atmospheric pressure microplasma jets are usually characterized with vacuum free, high electron temperature (several eV), and low gas temperature (room temperature). Being with the clear advantages such as clean or environmental friendly, fast, more and more attentions have been paid on atmospheric pressure microplasma assisted electrochemistry and its application in nanofabrication. In this talk, non-equilibrium properties, instability and nonlinearity of atmospheric microplasma jet are presented. [1-6] The non-equilibrium state of microplasma was studied as a function of capillary size, gas distance, gas flux and composition, etc. The unstability and nonlinearity of microplasma was discussed with water acting as anode and cathode respectively. The understanding of the thermodynamics and the nonlinearity of the plasma will help us to get an atmospheric pressure microplasma jet with controllable plasma density and temperature. Ecofriendly syntheses of Au Nps, Ag Nps, Au-Ag nanoalloys, carbon nanodots are also presented. [7-10] Experimental parameters such as plasma power, solution composition, process time, etc. play an important role in the syntheses of nanoparticles and deep investigations are still under way.

Generation of Silicon Nanostructures by Atmospheric Microplasma Jet: The Role of Hydrogen Admixture

Silicon nanostructures are synthesized with a DC atmospheric pressure microplasma jet using an Ar/SiH4/H2 gas mixture. The plasma is characterized by OES and imaged using an EMCCD camera. The effect of hydrogen admixture to the formed structures is studied by transmission electron microscopy. Under specific conditions, crystalline silicon nanoparticles grow in an amorphous matrix investigated by electron energy loss spectroscopy. As-grown silicon nanoparticles are collected in ethanol for dynamic light scattering and photoluminescence measurements. The size distribution peaks at 4 nm. The silicon nanocrystals exhibit roomtemperature photoluminescence that peaks at ∼415 and ∼465 nm.

Atmospheric microplasma-functionalized 3D microfluidic strips within dense carbon nanotube arrays confine Au nanodots for SERS sensing

An atmospheric microplasma jet produces three-dimensional (3D) microfluidic channels on dense arrays of vertically aligned carbon nanotubes, which confines Au nanodot aqueous solution. The resulting hybrid 3D nanostructure is exploited as an effective microscopic area-selective sensing platform based on surface-enhanced Raman scattering.

Degradation of adhesion molecules of G361 melanoma cells by a non-thermal atmospheric pressure microplasma

Increased expression of integrins and focal adhesion kinase (FAK) is important for the survival, growth and metastasis of melanoma cells. Based on this well-established observation in oncology, we propose to use degradation of integrin and FAK proteins as a potential strategy for melanoma cancer therapy. A low-temperature radio-frequency atmospheric microplasma jet is used to study their effects on the adhesion molecules of G361 melanoma cells. Microplasma treatment is shown to (1) cause significant cell detachment from the bottom of microtiter plates coated with collagen, (2) induce the death of human melanoma cells, (3) inhibit the expression of integrin α2, integrin α4 and FAK on the cell surface and finally (4) change well-stretched actin filaments to a diffuse pattern. These results suggest that cold atmospheric pressure plasmas can strongly inhibit the adhesion of melanoma cells by reducing the activities of adhesion proteins such as integrins and FAK, key biomolecules that are known to be important in malignant transformation and acquisition of metastatic phenotypes.