Deposition Of Structured SiO_xC_yH_z Film In Dielectric Barrier Discharge At Atmospheric Pressure And Its Optical Performance

Dielectric barrier discharge(DBD)plasma at atmospheric pressure and its large-scale industrial application prospects are fantastic and promising.Efficient ways to realize the surface modification and functional structure construction are an important subject in this field.In this paper,the basic mechanism of DBD plasma etching and deposition is investigated,and the optical properties of the deposited thin films are studied.Polyimide(PI)film is firstly modified by DBD plasma and then be used as the substrate for deposition.Granular films,together with flatted and wrinkled ones can be achieved during the DBD enhanced chemical vapor deposition at atmospheric pressure.Mechanism of thin films' appearance and their evolution are discussed separately.Finally,optical response of wrinkled films to visible light is analyzed.The studies will path the way for application of DBD plasma in the industrial.Following four parts are included in this paper:Activation of PI Substrate by Plasma Etching Firstly,chemical composition,physical morphology and infiltration property of PI substrate under different discharge time are analyzed.Mechanism of plasma etching on the activation process of PI substrate is revealed.Secondly,the law of plasma etching under the change of power and O2 flow is discussed.In high-power pure Ar discharge,a large amount of uniformly distributed dandruff appears on the surface of the PI film,and the peeling effect is observed obviously.The relative absorption peak intensities of –C-O-and-C=O are increased compared with lower power discharge.Active particle concentration is increased when oxygen being introduced to the chamber,while the intensity of discharge being weaken.Many etching marks are observed on the surface of the PI film.Intensity and nonuniformity of etching are greatly improved.Finally,aging of surface properties of activated PI substrates are studied.It is found that the hydrophilic of the films decreases rapidly after samples being placed out of the plasma for 1 day,and then inclines to be stable.Plasma deposition of SiO_xC_yH_z granular/flattened filmsWhen the flow rate of Ar gas is lower,the evolution of the film is dominated by island growth,and granular films can be observed.When the Ar gas flow rate is higher,the film growth can be classified by step growth models and continuous growth rate can be 294 nm/min.Firstly SiO_xC_yH_z granular film is analyzed.Proportion of inorganic components in granular film increases,together with the nonuniformity of the polarity of the large particles as the introduction of O2.This will promote transformation from compact granular films to porous ones.Secondly,SiO_xC_yH_z flattened thin film is discussed.By observing the damage pattern of the flat film,it is found that the continuous SiO_xC_yH_z thin film owns multilayer structure.Proportion of the chemical elements on the surface of the thin film at different deposition time shows a big difference,which might lead to the difference of mechanical properties within layers.Si proportion increases and C accounts for gradually reduction from bottom to top in flattened thin films.Plasma Deposition of SiO_xC_yH_z FilmsThe SiO_xC_yH_z wrinkled film can be obtained under a certain plasma discharge.We investigate modulus and temperature of substrate and their influence to wrinkled film and find that intrinsic stress for wrinkles does not originate from internal stress accumulated between wrinkle and substrate.Chemical composition analysis on the front and back sides of the wrinkle shows that front side of the film owns more inorganic components while the back side owns more organic components,which might be the reason for wrinkled structure.In addition,the development of the wrinkled film is discussed.The results of SEM and AFM show that the wrinkled structure does not undergo a large secondary deformation during the plasma deposition process,but continues its basis structure.Usually the wrinkles are developed into more full folds from flat ones gradually.Optical properties of SiO_xC_yH_z wrinkled filmsThe optical response of different wrinkles as different orientations,zigzags,isotropy and large-scale wrinkles are discussed.It is found that the wrinkles of different morphologies show a strong spectroscopic effect and reflect the characteristics of the grating.All different wrinkles meet the basic grating equation.Furthermore,the theoretical calculation of the diffraction intensity of the zigzag is carried out,and the appearance of the diffraction dots are analyzed.For the isotropic wrinkles,the appearance of the circular diffraction pattern is analyzed.For large-scale wrinkles,there may be multi-level diffraction pattern.Wrinkle grating constants may need to be carefully considered.