Optimization of the implosion phase on TC-I by light emission analysis

The best operation condition on the field-reversed theta-pinch TC-I at UNICAMP is studied by analysis of the helium-plasma light emission and electromagnetic signals observed during the preionization and implosion phase of FRC plasma. The TC-I device can be operated with a crowbar switch on the preionization and main capacitor banks, in order to fix the number of oscillations as well as the time interval between the end of the preionization and the main discharge phase. A detailed study of the plasma implosion has been carried out by changing the above parameters and also the working gas pressure by using a photodiode, a visible spectrometer, magnetic probes, a Faraday cup and a streak camera.     

D.C. cathode sputtering: influence of the oxygen content in the gas flow on the discharge current

A qualitative physical model is proposed to explain the influence of the oxygen content in the gas flow on the discharge current for reactive cathode sputtering in a d.c. diode system. According to this model the increase in the oxygen content affects the discharge current density in two main ways: (i) by a sharp change in the coefficient of secondary ion-electron emission from the target surface as a result of its oxidation; and (ii) by the influence of the oxygen content on the elementary ionization processes in the discharge region near the cathode as a result of the transition from a glow discharge in a noble gas to a glow discharge in oxygen.The results of the experimental investigations with targets of different materials under different sputtering conditions were in good agreement with the conclusions from the proposed physical model. Experiments aimed at elucidating the mechanism of formation of an oxide layer by sputtering of a silicon target have also been carried out. The conclusions can be useful for thin film deposition as well as for investigations of secondary emission from surfaces in a glow discharge.     

Microstructure and physical properties of nanofaceted antimony doped tin oxide thin films deposited by chemical vapor deposition on different substrates

Antimony doped tin oxide SnO₂: Sb thin films have been fabricated by atmospheric pressure chemical vapour deposition at substrate temperature varying between 350 °C and 420 °C in a horizontal reactor, from a mixture of hydrated SnCl₂, SbCl₃ and O₂ gas. The films were grown on glass substrates and onto polished and porous n-type silicon. Doped films fabricated with various Sb (Sb/Sn %) contents ranging from undoped 0% to 4% were characterised employing different optical characterisation techniques, like X-ray diffraction, transmittance and reflectance in the wavelength range of 300 to 2500 nm and ellipsometry. The films exhibit the usual cassiterite diffraction pattern with high crystalline structure. Examination of the surface by scanning electron microscopy (SEM) showed that the films are textured made up of many pyramidal crystallites with nanofaceted surfaces, indicating highly stabilised material. The presence of inverted pyramids indicates that the crystallites grown by coalescence. The surface morphology was found to be independent on the kind of the substrate. From X-Ray spectra and SEM observations we get the texture the lattice constant and the grain size. The optical results provide information on film thickness, optical parameters and transmittance upon antimony concentration. The microstructure of the films, the grain growth topics (nucleation, coalescence…) depend strongly on deposition conditions and doping concentration. The observed variations of both the resistivity ρ and transmittance T are correlated to antimony atoms concentration which induced variation in the microstructure and in the size of SnO₂ nanograins (typically 20-40 nm). In this work, we have determined the feasibility of incorporating the correct amount of Sb atoms in tin oxide film by means of resistivity and transmission. SEM observations showed that the substrate do not affect the morphology.     

Reactive sputtering of magnesium oxide thin film for plasma display panel applications

A magnesium oxide thin film deposition process based on reactive magnetron sputtering for plasma display panel applications has been developed. The sputtering system was manufactured with a vertical In-Line type of 1067 mm, which has a length of 563 mm and a width of 982 mm. Reactive magnetron discharge was generated using a 7.5 kW unipolar pulsed power supply. The power supply was operated at a maximum constant voltage of 500 V and a constant current of 15 A. The frequency and the duty were changed 10–100 kHz and 10–60%, respectively. Magnesium oxide films were prepared using various deposition conditions: 0.4–1.33 Pa pressure, the ratio of O₂/(O₂+Ar)=0.1–0.5, 50% duty and 0.5–1.7 kW peak power. The deposition rates of a static state and a moving state were measured to be approximately 45 nm/min and 6 nm/min at the distance of 50 mm between the target and the substrate, respectively. The texture of the sputtered magnesium oxide thin film was characterized by X-ray diffraction. Secondary electron emission coefficient was measured to be 0.1 at 100 V of ion acceleration voltage. The transmittance was observed to be approximately 90% at the wavelength of 300–800 nm. The density and hardness were measured as 93.2%, and 800–900 kg/mm², respectively. When the prepared magnesium oxide film applied to the 6-inch plasma display panel, discharge phenomena of the plasma display panel occurred at 200 V.     

The effect of Fe-doped magnesium oxide thin film in alternative current plasma display panel

In order to improve the discharge characteristics of MgO thin film as a protective layer in an alternative current plasma display panel, Fe-doped MgO thin films was introduced. Both the surface characteristics of the deposited thin films and the electro-optical properties of 4 inch test panels were investigated. It has been demonstrated experimentally that ac PDP with Fe-doped MgO protective layer has lower discharge voltage than that of undoped MgO film, which corresponds to measured secondary electron emission coefficients. The crystallinity and surface roughness of thin films were determined by XRD patterns and AFM images.     

Growth of ITO thin films by magnetron sputtering: OES study,opticaland electrical properties

In this work tin doped indium oxide (ITO) thin films were deposited onto soda lime glass substrates by the direct current magnetron sputtering system analyzing process of deposition with optical emission spectroscopy (OES). The dependence of electro-optical characteristics of the deposited films on the sputtering pressure, O₂/Ar working gas flow ratio and the discharge power was investigated. Transparency of the ITO films was measured using the ultraviolet and visible light spectrometer (UV–vis). The X-Ray photoelectron spectroscopy (XPS) method was applied for analysis of thin films surface chemical composition. It was found that in-situ measurement of plasma emission spectra allowed prediction and control of parameters of ITO thin films, namely resistivity and transparency. The correlation between the thin films resistivity, optical transparency and kinetics of deposition was examined.     

Effect of a thin silver sublayer on the growth of antimony films deposited in vacuum of 10-5 Pa

The growth of antimony films on collodion covered with a predeposited thin silver sublayer was studied by electron microscopy. The mean thickness of the sublayer, which was composed of silver islands, ranged from 0.03 to 0.30 nm. The oblique angle φ of the antimony vapour beam with respect to the substrate surface was varied from 0° to 80°. The surface coverage of the substrate by the antimony film is markedly increased, independently of φ, by the predeposition of silver because the silver islands act as excess nucleation centres to capture antimony molecules, absorbing the momenta of the molecules along the substrate surface. The crystallization thickness d_c for Sb/Ag/collodion is much smaller than that for Sb/collodion and no sensitive dependence of d_c on φ is observed for the former system.     

Structural, electrical and optical characteristics of SnO2:Sb thin films by ultrasonic spray pyrolysis

Antimony-doped tin oxide (SnO₂:Sb) thin films were fabricated by an ultrasonic spray pyrolysis method. The effect of antimony doping on the structural, electrical and optical properties of tin oxide thin films were investigated. Tin(II) chloride dehydrate (SnCl₂·2H₂O) and antimony(III) chloride (SbCl₃) were used as a host and a dopant precursor. X-ray diffraction analysis showed that the non-doped SnO₂ thin film had a preferred (211) orientation, but as the Sb-doping concentration increased, a preferred (200) orientation was observed. Scanning electron microscopy studies indicated that the polyhedron-like grains observed for the non-doped SnO₂ thin films became rounder and decreased in size with the Sb-doping concentration. The lowest resistivity (about 8.4 × 10^− 4 Ω·cm) was obtained for the 3 at.% Sb-doped films. Antimony-doping led to an increase in the carrier concentration and a decrease in Hall mobility. The transmittance level in the near infrared region was lowered with the Sb-doping concentration.     

Active species characterization in RF remote oxygen plasma using actinometry OES and electrical probes

Actinometry optical emission spectroscopy (AOES), single cylindrical Langmuir probe and electrostatic planar probe were used to investigate the active species (electrons, ions and atomic oxygen) of remote oxygen plasma in an RF (13.56 MHz) hollow cathode discharge system, as a function of applied power and gas pressure. The electron density and electron temperature were determined from Langmuir probe. The atomic oxygen (AO) density was measured using argon actinometry method. Positive ion flux rate was estimated from the positive ion saturation current of the planar probe, and the combination of the planar and Langmuir probes enabled the determination of the negative ion fraction in the discharge. The explanation of the behavior of the different active plasma species was performed on the basis of the main kinetic reactions of oxygen plasma.     

Characterization of silicon oxide gas barrier films with controlling to the ion current density (ion flux) by plasma enhanced chemical vapor deposition

Silicon oxide gas barrier films were deposited on polyethylene terephthalate (PET) substrates by plasma enhanced chemical vapor deposition (PE-CVD) for applications to transparent barrier packaging. The barrier properties of the silicon oxide coated film were optimized by varying the bias conditions and input power in the radio frequency plasma. The plasma diagnostics, ion current density and substrate temperature were characterized by optical emission spectrometry (OES), an oscilloscope and thermometer, respectively. The coating properties were examined by Fourier transform infrared (FT-IR) spectroscopy and the water vapor transmission rate (WVTR). A high intensity of O and H ions and a high ion current density (ion flux) with a low temperature plasma process were found to be suitable for improving the barrier properties of the silicon oxide film coatings. The Si-O cage-like structure adversely affected the gas barrier properties of the deposited coating. The energy provided by ion bombardment (ion flux) can induce changes in the film density and composition similar to those that may occur by the increase in deposition temperature through rf bias. In addition, the film properties depend not only on a high ion current density (ion flux) and input power, but are also related to a silicon oxide film with a widely distributed planar ring size.     

Effects of additive gases and plasma post-treatment on electrical properties and optical transmittance of ZnO thin films

A zinc oxide (ZnO) thin film as a channel layer in an oxide thin film transistor (TFT) has been characterized by investigating the effects of additive gases (such as hydrogen and oxygen) during growth and plasma treatment (using argon or hydrogen) after growth on its electrical, optical, and structural properties. By decreasing the additive gas ratio of O₂/H₂ or by increasing the treatment time of hydrogen plasma, the electrical resistivities of ZnO films were significantly reduced, and their transmittances and optical bandgap energies were blue-shifted in wavelength. These results were considered to be closely related to the passivation of oxygen vacancies as well as the formation of shallow donors that were induced by the injection of hydrogen in ZnO via gas addition and plasma treatment. In addition, the injection of hydrogen-including additive gas resulted in a decrease in grain size and crystallinity of ZnO films, whereas the plasma treatment hardly affected their crystalline structures.     

真空蒸镀法制备Sb膜电极及其性能

采用真空蒸镀法制备了金属Sb膜电极, 通过XRD、SEM、恒流充放电循环、循环伏安(CV)等方法, 研究了Sb膜电极的结构、形貌和电化学性能, 并对嵌脱锂机理进行了分析. 结果表明: 蒸镀后, 金属Sb为六方晶体, (003)晶面择优取向. Sb膜电极与基底铜箔的微观形貌接近, Sb金属以片层颗粒堆积在Cu箔颗粒上面. 在首次嵌锂过程中, 能观察到Li₃Sb合金的生成和Sb相的消失, 在脱锂之后, 能观察到Sb相的重新出现和Li₃Sb合金的消失, 且Sb相还是回复到(003)面择优相. Sb膜电极的首次充放电比容量分别为652和454 mAh/g, 循环16周后放电比容量还为300 mAh/g, 性能远优于Sb粉电极.     

Properties of plasma-produced amorphous silicon governed by parameters of the production,transport and deposition of Si and SiHx

Amorphous silicon thin films, which are a fundamental material for photovoltaic applications, can be prepared by plasma chemical processes. Four types of gas discharges, namely r.f. sputtering, d.c. glow discharge, arc and corona discharge, have been investigated to determine their particular characteristics as plasma chemical processes for the deposition of amorphous silicon. By determining the parameters of the plasmas and the conditions of the specific discharge by optical emission spectroscopy and by mass spectroscopy we can control the reproducibility of the plasma state and obtain defined variations in the generated species Si and SiH which constitute the layer. Analyses of film properties show high reproducibility. Moreover, the properties of the films reflect the plasma parameters as well as the deposition conditions.     

Quantitative modeling of reactive sputtering process for MgO thin film deposition

Reactive sputtering process of magnesium target in d.c. planar magnetron discharge using argon and oxygen gases as buffer and reactive gases, respectively, has been investigated. A drastic mode transition between metallic and oxide modes has been observed due to a large difference in the secondary electron emission coefficients of magnesium and magnesium oxide. To describe the experimental results quantitatively, a new reactive sputtering model has been developed. The model is fundamentally based on a simple reactive gas balance model proposed by Berg et al. in 1988, but includes the change in the secondary electron emission coefficient of target. The modified model can deal with the change of plasma properties through the change of ion to electron current ratio at the target, and can quantitatively describe experimental results such as oxygen flow rate dependence of deposition rate and discharge voltage, which were obtained at a constant discharge current.     

Generation of intense soft X-rays from capillary discharge plasmas

X-ray lasing through high voltage, high current discharges in gas filled capillaries has been demonstrated in several laboratories. This method gives highest number of X-ray photons per pulse. The fast varying current and the jxB magnetic force compress the plasma towards the axis forming a hot, dense, line plasma, wherein under appropriate discharge conditions lasing occurs. At Laser Plasma Division, RRCAT, a program on high voltage capillary discharge had been started. The system consists of a 400 kV Marx bank, water line capacitor, spark gap and capillary chamber. The initial results of the emission of intense short soft X-ray pulses (5–10ns) from the capillary discharge are reported.     

Antimony surfactant effect on green emission InGaN/GaN multi quantum wells grown by MOCVD

An improvement in the optical and structural properties of green emitting InGaN/GaN Multi Quantum Wells (MQWs) was obtained by using antimony (Sb) as a surfactant during InGaN growth. Keeping the growth conditions for InGaN constant, Sb was introduced during InGaN growth while varying the [Sb]/([In]+ [Ga]) flow ratio from 0 to 0.16%. The analysis results suggest that using the optimum [Sb]/([In]+[Ga]) ratio (0.04%-0.1%) during InGaN growth greatly improves the optical and structural properties of the MQWs without incorporating much Sb into the growing film and that the emission wavelength is also maintained with a slight blue shift. Under the optimum conditions of 0.05% Sb addition, the PL intensity was increased by as much as 3.3 times compared to the sample without Sb addition. The root mean square (RMS) roughness was reduced from 2.2 nm to 1.9 nm and the pit density was decreased from 2.0 x 10(10) cm(-2) to 1.2 x 10(10) cm(-2) when the amount of Sb was increased from 0% to 0.05%.     

Mechanism of carbon film formation in a discharge with crossed electric and magnetic fields in neon and argon

The process of carbon-film formation in a discharge with crossed electric and magnetic fields in neon and argon has been studied in a system with a cylindrical geometry of electrodes. Radial profiles of the film thickness on an edge substrate have been measured using an interferometric technique. A diffusion model of film formation is proposed, which takes into account the inert gas ion charge exchange and gas heating processes. Experimental data are compared to the results of model calculations.     

Influence of additional magnetic field on plasma parameters in magnetron sputtering

With three additional magnetic rings being assembled outside the discharge room and connected with the magnetic field of the conventional unbalanced magnetron sputtering, a closed magnetic field configuration distribution had been formed in the whole discharge room and which can confine discharge plasma more effectively. The spatial distribution of the newly designed magnetic field configuration was simulated using the ANSYS software. Plasma potential, electron temperature, electron density and ion density in the discharge plasma were diagnosed by Langmuir probe and the optical emission line intensity ratios of Ar⁺/Ar and Cu⁺/Cu were studied by optical emission spectroscopy. The structure and morphology of the Cu films are measured by scanning electron microscopy. A comparative study of the new magnetic field configuration with the conventional unbalanced magnetic field configuration was conducted. The results showed that the application of the additional magnetic field can increase the plasma density, enhance the ionization degree of the sputtered Cu and decrease the plasma potential effectively. The characteristics of the deposited Cu film were also influenced by the new magnetic field configuration greatly.     

Influence of non-axial magnetic field in a 3D3V Particle-In-Cell plasma model

In this article we report on results obtained using a newly developed self-consistent fully 3D Particle-In-Cell code for modelling of plasma-solid interaction.The model presented here involves a hollow cylindrical chamber opened to the plasma, with a thin cylindrical guard at the inlet and a strong external magnetic field limiting access of charged particles to the cylindrical wall. This model layout might provide more insight into processes taking place during magnetron deposition of thin films onto porous media. It is also a basis for probe diagnostics in fusion plasma research.The magnetic field is either parallel or slightly inclined with respect to the cylindrical axis. The results presented are axial and azimuthal ion current densities and cumulative distribution functions of ions impinging on the cylindrical surface for several angles of magnetic field inclination. They confirm the importance of proper alignment with magnetic field in certain geometries.Efficiency and possibilities of further extensions to the 3D model are also briefly discussed.     

Synthesis of nitrogen-rich carbon nitride thin films via magnetic field-assisted inductively coupled plasma sputtering

Carbon nitride (CN_x) thin films were synthesized by magnetic field-assisted inductively coupled plasma (ICP) sputtering. The electron density, electron temperature and optical emission intensity of the plasma state were significantly changed by varying the external magnetic field applied. The CN_x thin film with the highest nitrogen content (N/C=1.16) was obtained when the electron density was at its highest and the electron temperature at its lowest. Additionally, the optical emission from atomic nitrogen was the strongest under the same condition.