Comparison of fluorocarbon film deposition by pulsed/continuous wave and downstream radio frequency plasmas

Fluorocarbon (FC) films have been deposited using pulsed and continuous wave (cw) radio frequency (rf) plasmas fed with hexafluoroethane (C₂F₆), octafluoropropane (C₃F₈), or octafluorocyclobutane (C₄F₈). The effects of feed gases used, discharge pressure, rf power, substrate positions and discharge modes (pulsed or cw) on the deposited films are examined. Film properties are determined using X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. The contact angles of FC films are well related to their compositions and structures. Feed gases used, discharge pressure, rf power, substrate positions and discharge modes strongly affect the morphology of the resulting film, as revealed by atomic force microscopy. Optical emission spectrometry measurements were performed to in-situ characterize the gas-phase compositions of the plasmas and radicals’ emission intensities during film deposition. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. The film growth in pulsed or downstream plasmas was controlled by the surface migration of radicals, such as CF₂ towards nucleation centers, which result in the deposition of FC films with less cross-linked nature and rougher surfaces. These results demonstrate that it is possible to control film compositions and surface structure by changing deposition parameters.     

Hydrogen plasma diagnosis in penning ion source by optical emission spectroscopy

Penning-type discharge plasma ion source is a kind of powerful discharge device applied widely in many fields. In this paper, optical emission spectroscopy (OES) measurement is carried out to diagnose the parameters of hydrogen plasma in a miniature penning-type discharge ion source. The relative intensity of neutral atomic hydrogen emission spectral lines is used to evaluate the electron temperature of hydrogen plasma. The experiment results indicate that the relative intensity of Balmer-α, Balmer-β and Balmer-γ lines exhibits significant dependence on the filling gas pressure and the electron temperature is about 1.5-3 eV in the range of discharge current 30-180 μA when the anode voltage is fixed at 1.4 kV.     

In-situ optical emission spectroscopy of laser-induced vanadium oxide plasma in vacuum

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.     

Controlled synthesis of fullerenes and endohedral metallofullerenes in high frequency arc discharge

The article presents the high-frequency arc discharge setup operating in helium atmosphere and applicable for the syntheses of carbon condensate with different dispersion and structure, along with fullerenes and endohedral metallofullerenes. It also highlights how the change of helium pressure in chamber can control the amount and composition of products in carbon condensate. The setup can be applied for the purposes of analysis, for instance in order to obtain information about the process of fullerenes and endohedral met-allofullerenes formation. Also, the fact that the yield of higher fullerenes is increasing with the pressure rise, whereas the yield of endohedral metallofullerenes is decreasing suggests different formation mechanisms.     

Optical Emission Measurements of Rotational Temperature of C2 Radicals in Fullerene Processing

In this work, the results of optical emission study of C₂ radicals generated in carbon arc plasma are presented. It was found that a rotational temperature of carbon vapor depends significantly on carbon concentration and inert gas pressure. Experimentally obtained rotational temperature of C₂ emission spectra has been fitted with calculated spectra.     

Growth process observation of homoepitaxial ZnO thin films using optical emission spectra during pulsed laser deposition

Homoepitaxial ZnO thin films were prepared on the Zn-polar or O-polar ZnO substrates by pulsed laser deposition method. Optical emission spectroscopy of the plume was carried out to estimate O/Zn flux ratio under the various deposition conditions such as oxygen pressure, laser fluence, and the distance between target and substrate. It is revealed that the O/Zn flux ratio could be controlled by laser fluence, oxygen pressure, and target-substrate distance. Zn-rich O/Zn flux promotes pit formation and O-rich flux yields the three-dimensional growth. The difference of the growth process on Zn-polar or O-polar substrates is also discussed.     

Effects of plasma parameters on increasing the purity of nitrogen atom encapsulated fullerene in an RF plasma

Relatively high purity of nitrogen atom encapsulated fullerene (N@C₆₀) has been synthesized by an electron beam superimposed radio frequency (RF) discharge plasma method. Nitrogen species are characterized by an optical emission spectroscopy (OES); and a relationship between optical emission spectra and the purity of N@C₆₀ has been examined. It is observed that the increased amount of nitrogen molecule ions impinging on the sublimated fullerenes enhance the synthesis of N@C₆₀. Here, it is cleared that the efficient synthesis of N@C₆₀ is possible by controlling the parameters of electron beam superimposed RF plasma. As a consequence, comparatively high purity of about 0.08% of N@C₆₀ has been obtained.     

Characterization by optical emission spectroscopy of an oxygen plasma used for improving PET wettability

Polymers have excellent bulk physical and chemical properties but usually poor surface properties. For wettability improvement plasma technology is one of the most promising techniques. Several studies about surface modifications of polyethylene terephthalate (PET) exposed to an oxygen plasma have been already carried out. In this work an analysis of the plasma phase by optical emission spectroscopy (OES) has been employed in order to establish a correlation with the surface effects induced by plasma exposition on PET chemical composition and wettability, investigated by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements, respectively. The treatment has been carried out for a time of 60 s at a constant pressure (15 Pa) and at different process powers ranging from 20 to 200 W. As expected, the best performance has been obtained at a power of 200 W due to the larger presence of oxygen radicals (OI) with the assistance of ionic species (OII, O₂⁺) which create dangling bonds on the substrate surface.     

Surfactant effects on optical absorption spectra of iron phthalocyanine nanoparticles in water

Iron phthalocyanine (FePc) nanoparticles aqueous colloidal solutions were prepared by laser ablation in water, including surfactants. The Q band of FePc can be shifted to the longer or shorter wavelength widely by adjusting the concentration of surfactants on the basis of critical micelle concentration (CMC) with laser irradiation. The change in micelle structure of the surfactants surrounding the FePc nanoparticles may be the main reason for the shifting of the Q band.     

Process control of high rate microcrystalline silicon based solar cell deposition by optical emission spectroscopy

Silicon thin-film solar cells based on microcrystalline silicon (μc-Si:H) were prepared in a 30 × 30 cm² plasma-enhanced chemical vapor deposition reactor using 13.56 or 40.68 MHz plasma excitation frequency. Plasma emission was recorded by optical emission spectroscopy during μc-Si:H absorber layer deposition at deposition rates between 0.5 and 2.5 nm/s. The time course of SiH^? and H_β emission indicated strong drifts in the process conditions particularly at low total gas flows. By actively controlling the SiH₄ gas flow, the observed process drifts were successfully suppressed resulting in a more homogeneous i-layer crystallinity along the growth direction. In a deposition regime with efficient usage of the process gas, the μc-Si:H solar cell efficiency was enhanced from 7.9 % up to 8.8 % by applying process control.     

Silicon nitride films synthesized by reactive pulsed laser deposition in an electron cyclotron resonance nitrogen plasma

We report a film synthesis method called electron cyclotron resonance (ECR) plasma aided reactive pulsed laser deposition. Silicon nitride films were synthesized at low temperature by means of laser ablation of a silicon target in an ECR microwave discharge in pure nitrogen gas. It is found that silicon and nitrogen are well-distributed in the deposited films with a composition of near stoichiometric Si₃N₄. Optical emission spectroscopy indicated that nitrogen in the ECR plasma was highly activated. The presence of the ECR nitrogen plasma during the deposition is considered to lead to enhanced nitridation of the ablated silicon in the plume as well as at the substrate, and to be responsible for the effective incorporation of nitrogen in the films.     

ESR and TSL study of hole and electron traps in LuAG:Ce,Mg ceramic scintillator

The process of hole and electron localization in LuAG:Ce,Mg ceramics is studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL). Hole traps, which are created by UV irradiation, are detected in the form of O⁻ centers. Mg-perturbed variants of O⁻ centers are proposed to exist. The thermal stability of such defects is studied, proving that they are stable up to room temperature. The interaction between O⁻ centers and shallow electron traps is studied by thermally stimulated luminescence (TSL) and phosphorescence experiments, which reveal the occurrence of an a-thermal tunneling process between trapped electrons and randomly distributed Ce centers. By correlating the TSL-derived trap parameters and temperature dependent ESR intensities, it is found that O⁻ centers compete with Ce centers in free electron capture.     

Synthesis of carbon nanotubes at low temperature by filament assisted atmospheric CVD and their field emission characteristics

Multiwalled carbon nanotubes (MWNTs) were synthesized using a hot filament assisted chemical vapor deposition (CVD) at the atmospheric pressure at a substrate temperature of 550 °C. The size of nanotubes was controlled by changing the size of catalyst particles. The structure and composition of these nanotubes were investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The electron field emission current of MWNTs was also measured. It was found that the nanotubes with smaller the diameter had higher the emission current levels though synthesis conditions except catalyst particles were the same. These as-grown MWNTs had emission current densities of 6.5 mA/cm² and 2.5 mA/cm² at 1 V/μm for 5-8 nm and 20 nm size carbon nanotube samples, respectively. The results indicated that the MWNTs synthesized had low emission threshold voltages and high emission current levels that are favorable properties for field emission-based display device applications.     

Effect of Tb ions on X-ray-induced defect formation in phosphate containing glasses

The study of radiation-induced defect formation in glasses is of growing interest for applications in optics and photonics. The influence of Tb³⁺ ions on X-ray-induced defects has been examined in glasses with different phosphate contents. The defects have been characterized by optical absorption and ESR spectroscopy. (Tb³⁺)⁺ ions are formed by X-ray irradiation. They exhibit a broad charge transfer band at 370 nm. The formation of (Tb³⁺)⁺ hole centres suppresses the formation of intrinsic phosphate-related hole centres, absorbing in the visible region. PO₃ defects absorbing in the ultraviolet region contribute mainly to the electron centres corresponding to the (Tb³⁺)⁺ hole centres. Immediately after X-ray irradiation, 5–10% of the Tb³⁺ ions have been oxidized. The amount of (Tb³⁺)⁺ ions increases with increasing phosphate content. The stability of the (Tb³⁺)⁺ ions at room temperature depends on glass composition and melting conditions.     

Determination of trace bismuth in human serum by cloud point extraction coupled flow injection inductively coupled plasma optical emission spectrometry

A cloud point extraction method for the preconcentration of ultra-trace bismuth in human serum prior to its determination by inductively coupled plasma optical emission spectrometry had been developed in this paper. The cloud point extraction method was based on the complex of Bi(III) with 8-hydroxyquinoline and Triton X-114 was used as non-ionic surfactant. The main factors affecting cloud point extraction efficiency, such as pH of solution, concentration of complexing agent, concentration of non-ionic surfactant, equilibration temperature and time were investigated in detail. An enrichment factor of 81 was obtained for the preconcentration of Bi(III) with 25 mL solution. Under the optimal conditions, the detection limit of Bi(III) is 0.12 μg L⁻¹. The relative standard deviation (n = 7) of determination was 2.3%, values of recovery of bismuth were from 92.3% to 94.7% for three samples. This method is simple, accurate, sensitive and can be applied to the determination trace bismuth in human serum.     

Optimization of an open-focused microwave oven digestion procedure for determination of metals in diesel oil by inductively coupled plasma optical emission spectrometry

This work reports the optimization of a focused microwave assisted procedure for the wet acid dissolution of diesel oil in order to allow the determination of metals in the samples by inductively coupled plasma optical emission spectrometry (ICP-OES). The dissolution process was monitored by measuring residual carbon content (RCC), also by ICP-OES, in the final solutions obtained after application of digestion program. All experimental work was performed using a commercial sample of diesel oil containing 85.74+/-0.13% of carbon. The initial dissolution program comprised three steps: (i) carbonization with H(2)SO(4); (ii) oxidation with HNO(3) and (iii) final oxidation with H(2)O(2). During work it was verified that the first step played an important role on the dissolution process of this kind of sample. It is therefore, necessary to give a detailed optimization of such step. Employing the optimized conditions it was possible to digest 2.5 g of diesel oil with a 40 min-heating program. At these conditions, residual carbon content was always lower than 5%. Optimized methodology was applied in the determination of metals in three diesel oil samples by ICP-OES. Recovery tests were also performed by adding 10 microg of metals, as organic standards, to the samples before digestion. Recovery percentages always higher than 90% were obtained for the metals of interest (Al, Cu, Fe and Ni), except for Zn, which presented recoveries between 70 and 78%.     

Morphology design of highly oriented nonlinear optical Ba2TiSi2O8 crystals at the glass surface by crystallization in reduced atmosphere

The crystallization behavior of 40BaO–20TiO₂–40SiO₂ glass (mol%) in a reduced atmosphere (7%H₂/93%Ar) is examined to develop a new approach for the design and control of the morphology of nonlinear optical fresnoite (Ba₂TiSi₂O₈) crystals. It is found that the glass exhibits surface crystallization when heated in a reduced atmosphere, resulting in c-axis orientations of Ba₂TiSi₂O₈ crystals at the glass surface and enhanced second harmonic intensities. The formation of Ti³⁺ ions at the surface, through the reduction of Ti⁴⁺ ions in the reduced atmosphere, is confirmed from electron spin resonance spectra. It is clarified that the presence of Ti³⁺ ions at the surface induces the prominent change in the crystallization behavior from bulk nanocrystallization to surface crystallization of stoichiometric fresnoite.     

Spectroscopic study of an electrode microwave discharge in argon and argon-hydrogen mixtures

The results of an optical emission spectroscopy study of low-pressure microwave induced discharge in argon, argon-hydrogen (0.9% H₂) and hydrogen-argon (5% Ar) mixture are reported. At four different pressures the Boltzman plot of relative ArI line intensities is used to measure electron excitation temperature, which was close to 3000 K in argon and in argon-hydrogen mixture discharges. The spatial distributions of light emission from argon and hydrogen-argon discharges are recorded with CCD camera and compared with spectroscopically observed spatial distributions of the ArI 415.8 nm line intensity in argon and the H_β line intensity in hydrogen-argon mixture at three different pressures. The variation of light intensity with pressure for argon lines ArI 842.5 nm, ArI 750.3 nm and ArI 419.8 nm as well as for hydrogen H_β line is also studied. For high- and low-lying energy levels in argon and in argon-hydrogen mixture, a different dependence of spectral line intensity upon gas pressure is detected. In hydrogen-argon mixture, a non-linear decrease of argon and hydrogen spectral line intensity with an increase of gas pressure is observed.     

Elemental characterisation of aluminium used in reactors by optical emission spectroscopic methods

Using AC spark, AC arc and DC arc excitations in optical emission spectroscopic systems, the Al metal used in reactors can be characterised for its minor or trace element composition. The best precision of ± 6% is obtained with an AC spark in which the rod sample is taken as a self electrode and elements Cu, Fe, Mn, Si and Ti are determined in the concentration range 0·01–1%. The oxide powder sample with DC arc excitation provides best minimum detection limits of 10 ppm in general and 21 trace elements are determined by it. The AC arc method also uses oxide powder standards prepared synthetically and determines B and Mg in addition to the elements determined in AC spark excitation with a precision of ±9%.     

Investigation of emission location in top-emitting green organic light-emitting devices by optical analysis

A series of top-emitting organic light-emitting devices with different thicknesses of carrier transporting layers (N,N′-di(1-naphtyl)-N,N′-diphenylbenzidine, tris(8-hyroxyquinloine) aluminum (Alq₃)) and emitting layer (EML, 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)-doped Alq₃) were fabricated. C545T-doped Alq₃ was found to bring about double recombination peaks in EML. As the distance between EML and reflective anode was increased, the outcoupling efficiency greatly deviated from optically-simulated values due to charge imbalance in EML and optical loss at the EML/Alq₃ interface. The device with 30 nm of EML exhibited maximized outcoupling efficiency and further increase of EML thickness brought about decrease in efficiency due to decrease in hole-electron recombination at the EML/Alq₃ interface.