Investigation on surface properties of TiO2 films modified by DC glow discharge plasma

In the present work, TiO₂ films deposited on polyethylene terephthalate substrates by dip coating technique were subsequently treated by DC glow discharge plasma as a function of discharge potential. Hydrophilicity of these TiO₂ film surfaces was analyzed by contact angle measurements. Atomic force microscopy (AFM) revealed changes in surface morphology of the plasma treated TiO₂ films. Modifications in structural and chemical composition of the TiO₂ films were detected by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The blood compatibility of TiO₂ films was studied by in vitro investigation which includes thrombus formation and whole blood clotting time analysis (WBCT). It was found that the plasma treatment results in blood compatibility enhancement attributed to the structural, chemical and morphological properties of the modified film surfaces.     

WO3 oxide film formation on tungsten in O2/H2 discharges

The features of tungsten oxidation in a flowing O₂ or O₂/H₂ mixture glow discharge with a hollow cathode are investigated in the cathode, plasma, and afterglow regions at T = 300–350 K. The structure and composition of the samples are analyzed via reflection high-energy electron diffraction, reflection X-ray diffraction, electron probe microanalysis, and X-ray photoelectron spectroscopy. The results of analysis show that the metal surface is covered by a thin film (5–10 nm thick) of amorphous porous hydrated tungsten oxide (WO₃) after its exposure to the discharge and storage in air. The study of the film composition using a time-of-flight mass spectrometer indicates that the WO₃ film contains (WO₃) _n (n = 1–6) clusters and water molecules adsorbed in the pores. After exposure of the polycrystals to the O₂/H₂ discharge, the selective intense oxidation of individual grains is detected in the cathode region; the surrounding areas are subjected to weaker oxidation. The thicknesses of the WO₃ films on neighbouring grains differ by more than tenfold. Such grains can be the source of tungsten dust in plasma installations.     

用PET薄膜覆盖金属丝网电极实现大气压空气中均匀放电

将325^#不锈钢丝网电极和0.1 mm厚的PET薄膜紧贴在一起,平整地固定在Rogowski电极基座上,用50 Hz工频电压源及并联稳压电容,在大气压下2 mm空气间隙中实现了均匀放电.实验表明：将放电电流和电荷量波形作为判断放电均匀性的依据并不是完全可靠的,它只能判断放电在时间上的一致性,而不足以判断放电在空间上的均匀性.只有拍摄曝光时间不大于100ns的放电图像,才能可靠地判断放电的均匀性.在金属丝网电极覆盖PET薄膜的大气压气体放电实验中,这种放电图像被拍摄到,并说明大气压空气中的均匀放电只是汤森放电,而非辉光放电. 关键词： 大气压辉光放电 金属丝网电极 驻极体 高速摄影     

Optical properties in binary Si: H alloy from disilane

Binary Si: H alloy films having a wide optical band gap have been prepared by r.f. glow discharge of disilane. The optical band gap and the infrared absorption spectrum have been measured for those binary alloy films. The infrared absorption strength for 850 cm^-1 peak and the vibrational freqcencies for all absorption peaks are increased with an increase in the optical band gap. This sugests the (SiH₂)_n group formation in a wide optical gap film.     

大气压辉光放电研究现状及应用前景

大气压辉光放电由于均匀性好、能量效率高并且不需要真空系统，正日益受到人们重视和研究．文章综述了大气压辉光放电的研究进展，包括实验条件、放电特征、放电机理以及最新的诊断方法，还介绍它在薄膜沉积、材料表面改性、污染物质的消毒去污等方面的应用前景．     

Electron impact ionization and excitation rate coefficients in the negative glow region of a glow discharge

Some easy to use reasonable approximations for electron impact rate coefficients have been considered. The most important rate coefficients for electron collisions in noble gases are electron-neutral ionization and electron impact excitation. Electron-neutral ionization besides electron impact excitation of some states of the argon and helium atom in direct current (dc) glow discharge plasma has been calculated. The plasma parameters of electron are significant factors for computing the rate coefficients. We present first results of probe diagnostic that includes the double probe measurements of the plasma parameters, namely, electron temperature (T_e) and electron density (n_e). Electron properties obtained from the double probe characteristic curves including T_e and n_e as well as the calculated rate coefficients (ionization and excitation) were studied as a function of the axial distance from the cathode while the discharge operating parameters of voltage and pressure were varied. Two regions of the glow discharge were investigated: cathode fall region and negative glow. Particular emphasis was placed on the negative glow region.     

Local Anodic Oxidation of Thin GeO Films and Formation of Nanostructures Based on Them

The process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide (R₀) significantly increases and the time of starting the oxidation (t₀) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.     

Generation of uniform atmospheric pressure argon glow plasma by dielectric barrier discharge

In this paper, atmospheric pressure glow discharges (APGD) in argon generated in parallel plate dielectric barrier discharge system is investigated by means of electrical and optical measurements. Using a high voltage (0–20 kV) power supply operating at 10–30 kHz, homogeneous and steady APGD has been observed between the electrodes with gap spacing from 0.5 mm to 2 mm and with a dielectric barrier of thickness 2 mm while argon gas is fed at a controlled flow rate of 1 l/min. The electron temperature and electron density of the plasma are determined by means of optical emission spectroscopy. Our results show that the electron density of the discharge obtained is of the order of 10¹⁶ cm^???3 while the electron temperature is estimated to be 0.65 eV. The important result is that electron density determined from the line intensity ratio method and stark broadening method are in very good agreement. The Lissajous figure is used to estimate the energy deposited to the glow discharge. It is found that the energy deposited to the discharge is in the range of 20 to 25 μJ with a discharge voltage of 1.85 kV. The energy deposited to the discharge is observed to be higher at smaller gas spacing. The glow discharge plasma is tested to be effective in reducing the hydrophobicity of polyethylene film significantly.     

Photo-resist ashing by atmospheric pressure glow discharge

Homogeneous glow plasma at atmospheric pressure without streamers and arcing was generated by making use of a radio-frequency (RF, 13.56 MHz) power supply. Oxygen gas was added to Ar/He gas as reactive agents for photo-resist (PR) ashing. The input power, flow rate, oxygen concentration, treatment time, substrate temperature are controlled for high ashing rate and uniform ashing. Thickness of PR film was measured by NANOSPEC (AFT200) and α-Step (P-10). An unstable discharge occurs destroying the uniformity, when the input power exceeds a threshold value determined from the distance between the substrate and plasma source. An increase of oxygen quantity or temperature increase makes high ashing rate, but the ashing surface is rugged. The PR ashing rate was related to oxygen atom in plasma. The number of treatment may not be important in PR ashing at the atmospheric pressure.     

Submillimeter-Wave Spectroscopy of HNC Produced in an Extended Negative Glow Discharge

Submillimeter-wave transitions of HNC are observed in an extended negative glow discharge. The measurements of the rotational lines in the ground state, as well as in the vibrational fundamentals, are extended to higher J values (up to J=9←8 in the 830-GHz region). The lines in the higher vibrational excited states ν₂+ν₃, 2ν₂, and 2ν₂+ν₃ are also observed and assigned, using the frequency-magnetic field double modulation technique. Dramatic enhancement of the signal intensity strongly suggests that HNC is predominantly produced in the extended negative glow discharge through the dissociative recombination of HCNH⁺ with electrons.     

Characteristics of DC discharge in a wire-cylinder configuration at high ambient temperatures

In the present work, the characteristics of direct-current (DC) discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C were studied by analyzing photographs of the discharging process and the corresponding V–I characteristics, with the aim of facilitating the application of plasma technology in the fields of energy and the environment. The influences of the ambient temperature, the inter-electrode gap, the gas medium and the cathode material on the DC discharge were investigated. The corona-onset threshold voltage (COTV) and the spark-breakdown threshold voltage (SBTV) decrease as the ambient temperature increases, and the SBTV decreases more rapidly. Increasing the inter-electrode gap enlarges the difference between the SBTV and the COTV. After spark breakdown, in an air atmosphere, glow discharge is more likely to take place under conditions of high ambient temperatures or small inter-electrode gaps. The values of the SBTV in different atmospheres have the following relation: air ≈ O₂ > CO₂. At an ambient temperature range of 350–850 °C and in an atmosphere of N₂, glow discharge and arc discharge occur successively as the output voltage of the power supply is increased, while in an atmosphere of O₂ and CO₂, only corona and arc discharge are successively observed. In an air atmosphere, when the inter-electrode gap is 29 mm, corona, glow and arc discharge occur successively with increasing output voltage when the ambient temperature is 850 °C, while only corona and arc discharge appear when the temperature is 350–750 °C. When the inter-electrode gap is 5 mm in an air atmosphere, corona, glow and arc discharge occur successively in an ambient temperature range of 350–850 °C. The cathode material has a minor influence on the COTV and a more significant influence on the SBTV. In a device using a cathode with a low work function, the SBTV is low, and the power to maintain arc discharge is small.     

有序结构氟聚合物压电驻极体的制备和压电性研究

描述了一种有序微孔结构压电聚合物功能膜的制备方法,利用模板的高度有序实现薄膜微孔结构的精确控制.将此制备方法用于氟聚合物压电驻极体薄膜的制备,通过扫描电子显微镜(SEM)对其微观结构的观察表明薄膜具有理想的有序结构.对氟聚合物压电驻极体压电性的研究则是利用正压电效应测量准静态压电系数d₃₃,通过等温衰减和压强依赖性的测量考察其压电性能.结果表明:有序结构氟聚合物压电驻极体的准静态压电系数d₃₃可高达300 pC/N;与无序结构氟聚合物     

Modification of surface layers of copper under the action of the volumetric discharge initiated by an avalanche electron beam in nitrogen and CO<Subscript>2</Subscript> at atmospheric pressure

The results of experimental investigations of the action of the volumetric discharge initiated by an avalanche electron beam on the surface of copper specimens are presented. The volumetric (diffuse) discharge in nitrogen and CO₂ at atmospheric pressure was initiated by applying high voltage pulses of nanosecond duration to a tubular foil cathode. It has been found that the treatment of a copper surface by this type of discharge increases the hardness of the surface layer due to oxidation.     

Effect of substrates on the morphology of Ba<Subscript>x</Subscript>Sr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> nanometer-scale films

The initial stages in the growth of Ba_xSr_1?xTiO₃ films on various dielectric substrates were studied using the middle-energy ion scattering spectroscopy, and the results obtained were used to analyze microdefects in the film. The character of film growth was found to depend on the shape, size, and electrostatic state of crystallographic unit cells of the substrate surface. The growth was epitaxial on an SrTiO₃ substrate. The film prepared on an LaAlO₃ substrate consists of slightly disordered crystallites. Films on MgO substrates demonstrated island-type growth up to a thickness of 20 nm, with foreign phases observed to form; as the film thickness increased, the growth acquired an epitaxial pattern. The film grown on the \(\alpha - Al_2 O_3 (1\bar 102)\) surface was polycrystalline and contained textured blocks.     

Structure of the glow of a nanosecond diffuse discharge in a strongly nonuniform electric field

The structure of the glow of a diffuse discharge in air under atmospheric pressure is studied in detail in the “rod (cathode)-plane” geometry for an electrode gap of 10 cm and a cathode tip radius from 3 cm to 2.4 μm. The amplitude of voltage across the gap was ～ 220 kV for voltage growth rate of ～10¹³ V/s and a pulse duration of 180 ns. It is found that the shape of the discharge glow strongly depends on the radius of the cathode tip. For large values of the radius, the multichannel form of the glow prevails, which is statistically transformed into a volume glow as the radius decreases from 5 mm to 60 μm. This transition is accompanied by a decrease in the amplitude of the discharge current from 440 to 140 A on the average. For ultrasmall radii of the cathode (2.4–7.7 μm), the multichannel form of the glow prevails again and the amplitude of the discharge current increases up to ～300 A.     

Breakdown mechanism of an atmospheric-pressure radio-frequency capacitive argon discharge in parallel-plate bare metal electrodes

The breakdown behavior of an atmospheric-pressure radio-frequency capacitively coupled argon plasma discharge at 13.56 MHz is investigated in order to produce a stable and homogeneous atmospheric-pressure argon glow discharge. It is found that the electrode separation distance plays a pivotal role in exciting argon discharge whether in mobility-controlled electric breakdown or in diffusion-controlled breakdown and the discharge mode (arc discharge, α-mode glow discharge, or γ-mode glow discharge) immediately following breakdown is closely related to the breakdown mechanism.     

Surface properties of silicon oxide films deposited using low-pressure dielectric barrier discharge

The deposition of SiO_X films from low-pressure dielectric barrier discharge plasmas has been investigated using tetraethoxysilane (TEOS)/O₂ as the feed gas. Films were analyzed using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), AFM-based nanoindentation/nanowear techniques, and conductive AFM. Film deposition rates and hydrocarbon incorporation in the SiO_X film decrease with addition of O₂. High-quality SiO_X films with extremely low surface roughness are deposited at high oxidant concertrations. Addition of oxidant to the feed gas leads to a change in the SiO_X film structure from precursor-like to a dense SiO_X structure. The SiO_X films deposited with TEOS/O₂ plasmas were found to have soft surface layers, 0.5-1.5 nm thick, which contribute to an improvement of their field emission properties. The effect of gas phase compositions on the surface properties of the conductive surface layer was discussed.     

Formation of ultrathin nanocomposite SiO2:nc-Au structures by Pulsed Laser Deposition

A method for the formation of Au nanocrystal (nc) arrays embedded in an ultrathin SiO₂ layer in one vacuum cycle is proposed. The method is based on the co-deposition in vacuum of ∼1 nm thick uniform Si-Au amorphous layer at a specific composition ratio by Pulsed Laser Deposition on the pre-oxidized Si(1 0 0) substrate, followed by its oxidation in the glow discharge oxygen plasma at room temperature, resulting in the precipitation of Au ncs at the bottom interface and/or at the surface of the forming SiO₂ layer. The capping SiO₂ layer is formed by the glow discharge plasma oxidation of further deposited ultrathin Si layer. Au ncs 2-5 nm in size and with the separation of ∼3-20 nm from each other segregate during the oxidation of Au-Si mixture as evidenced by transmission electron microscopy (TEM). The evolution of Au and Si chemical state upon each step of the SiO₂:nc-Au nanocomposite structure formation is monitored in situ by X-ray photoelectron spectroscopy (XPS). The metrology of nanocomposite SiO₂:nc-Au structures describing the space distribution of Au ncs as a function of Au/Si ratio is presented.     

Investigations on Plasma Assisted Surface Cleaning of Aluminum in an Oxygen Glow Discharge

Aluminum plates which are contaminated with hydrocarbon containing compounds (oil, grease) were treated in an Ar-, O₂- and Ar/O₂-plasma generated by a dc-discharge. Besides a variation of the macroscopic discharge parameters (power, pressure) also different modes (anomalous glow regime, hollow cathode regime) have been studied. In most cases the contaminated substrates served as cathodes of an anomalous glow discharge where the combined influence of chemically reactive radicals and energetic ions was very effective. During the plasma process the discharge was monitored by means of power variation and optical emission spectroscopy. The spectral line intensities of several species (etchants and products) have been measured as functions of the process duration. Simultaneously the removal of the contamination layers was observed by means of in-situ ellipsometry. The temporal change of the ellipsometric parameters ψ and δ during the cleaning process was taken as a measure for the state of the surface. The combination of spectroscopic and ellipsometric measurements which indicate the progress of the plasma treatment gave interesting results on the mechanisms at the surface. In addition, surface analysis was used to assess the quality of the substrates treated.     

Effect of laser irradiation on the structure and properties of dielectric column clusters in the YBaCuO superconducting films

The effect of laser irradiation on the structure and properties of the YBa₂Cu₃O_{7 ? δ} epitaxial super-conducting films (T _c = 90–91 K) that are grown on the SrTiO₃ and LaAlO₃ substrates is studied. The films exhibit a system of pyramidal peaks that are incorporated in the single-crystal structure of the film whose system of the (00l) planes is parallel to the surface of the substrate. It is demonstrated that the peaks represent growth defects that result from the relaxation of the accumulating strain due to the mismatch of the crystallographic parameters of the growing layers of the film and substrate. The island structures that are formed owing to the relaxation of strains acquire the (11l) or (10l) orientation and penetrate through the film layers in the course of growth. It is demonstrated that the irradiation using relatively short laser pulses makes it possible to modify the structure of the dielectric clusters and allows the smoothing of the film surface at an insignificant (5–10%) decrease in the concentration of the superconducting phase. An increase in the energy density to a level of greater than 100 mJ/cm² when the number of pulses is greater than five causes an increase in the volume of dielectric phases and the worsening of parameters.