Mechanism On Electrostatic Focusing Of Plasma Jet And Its Application In Direct Writing

Atmospheric pressure plasma jet has a variety of applications ranging from modification,etching,to welding,in which the improvement of processing resolution is of importance in micro-nano fabrication.Meanwhile,in order to make flexible micro-nano structure patterned manufacturing process and surface modification technique compatible with traditional methods,it is necessary to develop a set of digitally controllable direct writing process via a focused plasma jet with continuously switchable beam diameter.Aiming at the application of atmospheric micro plasma jet in micro-nano fabrication,a plasma electrostatic focusing theory has been proposed in this paper,and a plasma electrostatic focusing nozzle was independently designed and manufactured.Before obtaining a stable process window and their associated mechanisms via collaborative optimization of process parameters,the process and principle of plasma direct writing etching and pattern modification have been studied thoroughly,which greatly broadens the application range of atmospheric pressure micro plasma jet in micro-nano fabrication and surface treatment,and the specific research content is as follow:(1)Establishment of plasma electrostatic focusing theory and related models.Firstly,based on the numerical model of plasma jet,a plasma electrostatic focusing theory and corresponding nozzle model have been proposed,and according to electrostatic field theory,theoretical potential distribution in the electrostatic lens were derived.Next,numerical simulation method was employed to analyze the distribution of electric field inside the nozzle and its focusing behavior,and it was found that when the potential of middle electrode U₁?0,upper/lower electrodes U₀?0,the potential ratio(|U₀|/|U₁|)was between 5-10,the beam could be focused elegantly,in which focal length was positively correlated with the lens radius and negatively correlated with the electrode spacing and potential ratio.Then,in order to effectively isolate the inner and outer layers of gas and optimize the jet length and its active species,the relationship between the diameter of inner and outer tube(d,D)and corresponding flow(q,Q)of the nozzle was calculated to meet the following requirements,namely D/d?7.5,Q/q?20,q/d?89.66,Q/D?22.36.Finally,according to the above researching results,a plasma electrostatic focusing nozzle has been designed and manufactured to provide support for the plasma direct writing experiment.(2)Investigation of atmospheric plasma-jet direct writing technique.Helium plasma jet had been employed 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(WCAs)from?160°to<10°ultimately,for the first time,to the best of our knowledge;in order to illuminate the principle of transformation,assisted by with Wenzel-Cassie theory,the relationships between the surface microstructure of carbon nanotube film and its surface chemistry and surface wettability of the film were expounded;"programmable"regulation of surface wettability and conductivity of carbon nanotube film has been successfully achieved via collaborative optimization of discharge parameters,working gas as well as thickness of the carbon nanotube film,and a flexible film with elegant conductivity,superhydrophobicity,translucency,and stretchability has been prepared as well.In plasma-jet etching process,the capability of etching of common materials(such as rosin film)on conductor,semiconductor and insulator substrates as well as their facility have been investigated;a minimal etching resolution of 50?m is realized by optimizing of parameters,and a set of techniques for making flexible conductive electrodes via plasma jet etching of rosin film were proposed and verified.(3)Preparation and application of flexible devices based on plasma jet direct writing.Direct writing of superhydrophobic(hydrophilic)patterns on superhydrophilic(hydrophobic)background has been successfully achieved,and corresponding resolution could be adjusted from?mm to 100?m scale;then,the influence and mechanism of direct writing speed and temperature on the recovery rate were investigated,at least 5 times of reversible writing and erasing achieved,and it has been found heating could exceedingly accelerate the evaporation rate of oxygen elements on the surface,thereby speeding up the erasability;background with stable superhydrophobicity was necessary for a stable superwetting pattern,which could bear tensile strain even up to 100%and 1000 cyclic stretching;finally,droplet manipulation,micro-channels,self-assembly of nano-materials,and reconfigurable patterns were demonstrated as the applications of erasable extreme wetting-contrast patterning.Furthermore,the as-prepared superhydrophobic,conductive surfaces could also bear tensile strain even up to 100%and 1000 cyclic stretching,and they also presented a distinguished enduring stability in terms of exposure to air and even extreme acidic/alkaline aqueous droplets.It has been shown that the excellent stretchability and corrosion resistance of the film is attributed to the synergistic effect of the chemical stability of the carbon nanotubes and a large number of carbon nanotube micro-nano structures that strongly adhering to PDMS,which was successfully employed for water repellent skin electronics and monitoring of human movement.In addition,a technique of fabricating self-adhesive water-repellent epidermal electronic devices has been proposed,providing a solution to monitor the data of human body,accurately and reliably.