Optical Emission Spectroscopy Technique Research Articles

A calibration method for accurate prediction of amorphous to nanocrystalline transition from line intensities of optical emission spectrum

To be able to use the simple technique of optical emission spectroscopy (OES) for the prediction of the transition of growth from a-Si to nc-Si via the Hα/Si⁎ emission ratio, a regime-dependent correction factor is required to relate the measured Hα/Si⁎ emission ratio to the true flux (to the substrate) ratio of atomic hydrogen to deposited silicon radicals. Through an in-depth study in a very high frequency plasma enhanced chemical vapor deposition process, we obtained that the flux ratio of atomic hydrogen and deposited silicon radicals to the growing surface,ΓH/ΓSi, is related to the emission ratio of Hα and Si⁎, IradHα/IradSi*, by the relation, RradIradHαIradSi*/ΓHΓSi=a(pd)2/kTgas+b, where the parameters p (pressure), d (inter-electrode distance) and Tgas (gas temperature) are experimentally obtained quantities and Rrad is the ratio of the rate coefficients for radiation of Si⁎ and Hα. We obtained the calibration parameters a and b to be 1.9·10−21±2·10−22Pam−1 and 5.5±1.9 respectively which is valid in a broad range of power and pressure settings. With these parameters, it is easy to estimate the flux ratio of atomic hydrogen and silicon species at any deposition condition using the OES data and this will allow accurate prediction of the phase transition. According to simulations in the linear low-pressure regime, the amorphous to nanocrystalline phase transformation occurs at the flux ratio ΓH/ΓSi=12, which translates, using the factors a and b, to the required emission ratio.

OPTICAL CHARACTERIZATION OF 50 Hz ATMOSPHERIC PRESSURE SINGLE DIELECTRIC BARRIER DISCHARGE PLASMA

A low frequency (50Hz) dielectric barrier discharge (DBD) system with a single dielectric cover on copper coil anode is designed to generate and sustain the micro-discharge plasma which is very practical for material processing applications. The DBD system is powered by a high tension ac source consisting of a conventional step up transformer and variac. The dielectric barriers (quartz and glass) between the conducting electrodes appreciably influences the discharge plasma characterized by optical emission spectroscopy technique. Using intensity ratio method, the electron temperature and electron number density are determined from recorded spectra as function of ac input voltage, type and thickness of dielectric barrier and inter-electrode gap. It is observed that both the electron temperature and electron number density increase with the increase in ac input voltage and r/d ratio, while a decreasing trend is observed with increase in inter-electrode gap.

Hydroxyapatite Nanopowder Synthesis with a Programmed Resorption Rate

A microwave, solvothermal synthesis of hydroxyapatite (HAp) nanopowder with a programmed material resorption rate was developed. The aqueous reaction solution was heated by a microwave radiation field with high energy density. The measurements included powder X‐ray diffraction (PXRD) and the density, specific surface area (SSA), and chemical composition as specified by the inductively coupled plasma optical emission spectrometry technique (ICP‐OES). The morphology and structure were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A degradation test in accordance with norm ISO 10993‐4 was conducted. The developed method enables control of the average grain size and chemical composition of the obtained HAp nanoparticles by regulating the microwave radiation time. As a consequence, it allows programming of the material degradation rate and makes possible an adjustment of the material activity in a human body to meet individual resorption rate needs. The authors synthesized a pure, fully crystalline hexagonal hydroxyapatite nanopowder with a specific surface area from 60 to almost 240 m2/g, a Ca/P molar ratio in the range of 1.57–1.67, and an average grain size from 6 nm to over 30 nm. A 28‐day degradation test indicated that the material solubility ranged from 4 to 20 mg/dm3.

Experimental and theoretical study of dynamic effects in low-frequency capacitively coupled discharges

A low-frequency capacitively coupled radio-frequency (rf) discharge in Ar excited at 1.76 MHz is studied both experimentally and theoretically. Experimental measurements of electron concentration, discharge voltage and current are presented for a wide range of rf input powers. The rf current shape is nonsinusoidal, close to the triangle one. The evolution of Ar(2p1) emission excitation function in the interelectrode gap during an rf cycle is measured using the phase-resolved optical emission spectroscopy technique. Theoretical study is based on the particle-in-cell Monte Carlo collision numerical simulation. Specific dynamic features of the low-frequency discharge are discussed. The important role of secondary electrons in discharge maintenance and power balance is shown. This study is crucial for understanding dual-frequency discharges with a corresponding value of low frequency.

Free-flowing, transparent γ-alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

Nanoparticles of crystalline, phase-pure γ-alumina is synthesized in a supersonically expanded thermal plasma jet assisted experimental chemical reactor, with good control over the average particle sizes independently with respect to plasma current, oxygen flow rate and the ambient pressure in the sample collection chamber. Most of the synthesized particle samples were seen to be transparent, which gets more transparent with decrease in the particle sizes. The lowest achievable pressure in the chamber had produced particles with average 10 nm sizes, which was best also in terms of narrow size distribution. Another important observation was the absence of serious inter-particle agglomeration, producing free-flowing particles. Optical emission spectroscopic technique was used to study the plasma chemistry of the reaction zone as well as the plasma jet.

Luminescence during anodization of magnesium alloy AZ31

In this paper, we have presented our recent investigation of luminescence during anodization of magnesium alloy AZ31 at 100 mA/cm 2 in water solution containing 4 g/L Na 2SiO 3·5H 2O + 4 g/L KOH. Spectral characterization of anodic luminescence (galvanoluminescence GL) showed that there are wide GL bands in the range from 375 nm to 875 nm, with three spectral peaks around 430 nm, 600 nm and 780 nm. As the anodization voltage approaches the breakdown voltage, a large number of microdischarges appear superimposed on the GL. The microdischarges characteristics above breakdown (so-called plasma electrolytic oxidation PEO) were studied using real-time imaging. The spatial density of microdischarges is the highest in the early stage of PEO, while the percentage of oxide coating area covered by active discharge sites has maximum after about 120 s from the beginning of PEO and then stays almost constant. The elements present in PEO microdischares were identified using optical emission spectroscopy technique.

Preparation of high pure zinc for electronic applications using selective evaporation under vacuum

m6N pure (99.9999%) zinc (Zn) was obtained through multiple vacuum distillations using 99.9% (m3N) pure Zn as input material at 2 kg batch-size. The soaking (distillation) temperature and the time of distillation at a dynamic vacuum level of 2.1 * 10 −3 Torr were optimized to achieve the desired purity, distillation rate and yield. The detailed analysis of input as well as purified Zn was carried out by inductively coupled optical emission spectroscopy (ICP-OES) technique for 14 major impurity elements. This confirmed the reduction of total impurity content from ∼983 to <1.53 μg/g (∼m6N) upon three consecutive distillations. The major impurities separated from the distilled zinc were Al, Cu, Fe, Sn, Pb, Si, Ca, As, Ag, Sb, Ni, Bi, Mg, Mn, etc. The trace oxygen as determined by O–N analyzer reduced from (230–350) μg/g for raw Zn to (20–27) μg/g for distilled Zn and the nitrogen impurity from (34–45) to (15–19) μg/g. Carbon determined by GD-OES reduced from (60–70) to (5–8) μg/g on purification. The overall yield of distillation was found to be 67.5%. Analysis results, i.e. yield and purity are discussed with respect to vapor pressure of impurities and mean free path. ( λ) of Zn vapor. Crystalline structure of distilled Zn was studied by XRD.

Plasma electrolytic oxidation of titanium in heteropolytungstate acids

This article is a review of our recent research of plasma electrolytic oxidation (PEO) process of titanium in heteropolytungstate acids (12-tungstosilicic acid and 12-tungstophosphoric acid). It has been detected that spatial density of microdischarges is the highest in the early stage of the PEO process, while the percentage of oxide coating area covered by active discharge sites decreases with PEO time. The elements and their ionization stages present in PEO microdischarges are identified using optical emission spectroscopy technique. The spectral line shape analysis of hydrogen Balmer line Hβ (486.13nm) indicates presence of two types of microdischarges during PEO. The discharges are characterized by relatively low electron number densities of Ne≈0.8×1015cm−3 and Ne≈2.1×1016cm−3. Oxide coatings formed by PEO process were characterized by AFM, SEM–EDX and XRD. The elemental components of PEO coatings are Ti, W and O. The oxide coatings are partly crystallized and mainly composed of WO3 and anatase.

Characterization and properties of low-friction, multilayered Cr-doped diamond-like carbon coatings prepared by pulse biased filtered cathodic arc deposition

The aim of the article was to investigate the effect of pulsed high-voltage bias on phase composition, surface morphology, mechanical properties, and the tribological performance of the multilayered Cr/CrN/DLC coatings prepared by the filtered cathodic arc deposition (FCAD) process. The coatings were deposited using a laboratory arc source device equipped with two macroparticle filtering systems. All coatings were deposited at substrate temperatures below 200°C. Cr/CrN/DLC multilayered coatings were analysed using X-ray photoelectron spectroscopy, a glow discharge optical emission spectrometry technique, scratch testing, nano-indentation measurements (nano-hardness and Young's modulus), and optical microscopy. Tribological tests employing a ball-on-disc tribosystem were performed in dry friction conditions in an air-conditioned room (RH 50 per cent, 23°C). The results proved that the substrate bias voltage exerts a significant influence on the mechanical properties of the Cr/CrN/DLC multilayered coatings by the changing chemical composition of the DLC top layers. With an increase of bias voltage from 2 to 6 kV, the Cr content increases from 2 to 4 per cent and the sp2/sp3 ratio decreases from 1.06 to 0.44. The Cr-doped DLC multilayered coatings were characterized by a very smooth surface, a low friction coefficient (0.13–0.15), moderate hardness (8–11 GPa), and a Young's modulus of 95–130 GPa. Due to the moderate adhesion strength of DLC top layers, their wear resistance was not satisfactory for real applications. In each tribological test, the delaminating process of the DLC layers was observed after approximately 200–300 load cycles. To improve the mechanical properties and adhesion of a DLC layer, the optimization of the transition and DLC layers is achieved by changing the parameters of the physical vapour deposition process.

Elemental Identification of Materials Using Optical Emission Spectra during Electric Discharge Machining

Elemental identification of material is a prime most important in material science field. Electric discharge is used for material elemental identification with optical emission spectroscopy. During electric discharge machining between two electrodes plasma is generated which emits intense radiation in the UV-Visible region. The generated plasma captured by optical emission spectroscopic technique and elements are identified from recorded spectra by matching with standard NIST database. This method is simple, rapid, and inexpensive compared to all other elemental identification method. The elements of the metal, semiconductors, even insulators can be identified without much difficulty. The elemental identification of material has been investigated in macro and micro level.

Spectroscopic and real-time imaging investigation of tantalum plasma electrolytic oxidation (PEO)

We present the results of plasma electrolytic oxidation (PEO) of tantalum in 12-tungstosilicic acid at 70 mA/cm 2. For the characterization real-time imaging and optical emission spectroscopy (OES) were used. It has been detected that relatively small microdischarges (cross-sectional area < 0.1 mm 2) are dominant throughout the PEO, while the presence of medium-size microdischarges (cross-sectional area from 0.1 mm 2 to 0.2 mm 2) and large microdischarges (cross-sectional area > 0.2 mm 2) become noticeable only at later times of PEO. The elements and their singly charged positive ions present in PEO microdischarges are identified using standard OES technique. The spectral line shape analysis of first two hydrogen Balmer lines shows presence of two microdischarges during PEO. These discharges characterize relatively low electron number densities N e ≈ 0.9 × 10 15 cm − 3 and at N e ≈ 2.2 × 10 16 cm − 3 . A simple OES technique was introduced to test optical thickness of hydrogen Balmer lines emitted during PEO process.

Influence of dc Pulsed Atmospheric Pressure Plasma Jet Processing Conditions on Polymer Activation

AbstractPlasma treatments are widely used to activate polymer surfaces prior to adhesive bonding. This study investigates the influence of plasma treatment conditions on the surface activation of a range of polymers using the PlasmaTreat (Open Air) system. In this study the effect of dc pulse plasma cycle time, compressed air flow rate and the plasma jet nozzle to substrate distance on the plasma discharge was examined. The influence that the dc pulse plasma cycle time parameter has on the activation of polypropylene, polystyrene and polycarbonate was also investigated. The level of polymer surface activation was evaluated based on the change in water contact angle after plasma treatment. The polymer surface properties were also monitored using AFM and XPS measurements. The heating effect of the plasma was monitored using both infrared thermographic camera and thermocouple measurements. Plasma diagnostics measurements were obtained using the photo‐diode and optical emission spectroscopy techniques. From this study it was concluded that for the PlasmaTreat system the level of plasma activation was closely correlated with the dc pulsed plasma cycle time, which is a measure of the plasma intensity. For example, the more intense plasma obtained with shorter cycle times gave higher levels of polymer activation. The optimized pulsed plasma cycle times were found to be specific for a given polymer type and related to their thermal properties. The pulsed cycle times were also found to correlate with both the substrate and plasma gas temperatures. magnified image

Characterization of Doped Amorphous Silicon Thin Films through the Investigation of Dopant Elements by Glow Discharge Spectrometry: A Correlation of Conductivity and Bandgap Energy Measurements

The determination of optical parameters, such as absorption and extinction coefficients, refractive index and the bandgap energy, is crucial to understand the behavior and final efficiency of thin film solar cells based on hydrogenated amorphous silicon (a-Si:H). The influence of small variations of the gas flow rates used for the preparation of the p-a-SiC:H layer on the bandgap energy, as well as on the dopant elements concentration, thickness and conductivity of the p-layer, is investigated in this work using several complementary techniques. UV-NIR spectrophotometry and ellipsometry were used for the determination of bandgap energies of four p-a-SiC:H thin films, prepared by using different B2H6 and SiH4 fluxes (B2H6 from 12 sccm to 20 sccm and SiH4 from 6 sccm to 10 sccm). Moreover, radiofrequency glow discharge optical emission spectrometry technique was used for depth profiling characterization of p-a-SiC:H thin films and valuable information about dopant elements concentration and distribution throughout the coating was found. Finally, a direct relationship between the conductivity of p-a-SiC:H thin films and the dopant elements concentration, particularly boron and carbon, was observed for the four selected samples.

Effect of Excitation and Vibrational Temperature on the Dissociation of Nitrogen Molecules in Ar-N2 Mixture RF Discharge

ABSTRACT Non-equilibrium argon-nitrogen mixture plasma generated at 13.56 MHz is characterized by optical emission spectroscopy and Langmuir probe techniques. The excitation and vibrational temperature are studied as a function of argon percentage in the mixture, at 30-Pa filling pressure and input RF powers of 200 and 300 watt, to find out their role in dissociation of N2 molecules. In this work, the excitation temperature is determined from Ar-I emission line intensities by using the simple Boltzmann plot method and is found to increase with argon mixing in nitrogen plasma. In similar fashion, the vibrational temperature of second positive system has been determined and is found to also have increasing trend with argon addition. The effect of excitation and vibrational temperature on the nitrogen molecular dissociation level is also monitored. It is observed that N/N 2 ratio increases with increase in excitation and vibrational temperature and falls slightly at the end.

Substituent Effects of Porphyrin on Singlet Oxygen Generation Quantum Yields

The singlet oxygen photosensitizing efficiencies of the ortho-, meta-, and para-substituted free-base and zinc (II) tetraarylporphyrins have been investigated on the basis of the heavy atom effect, electronegativity, and spatial orbital overlap. Both the endocyclic and exocyclic heavy atom effects have been exploited to induce various degrees of spin-orbit coupling. The ground state and the lowest singlet excited electronic state of the porphyrins have been studied using optical absorption and fluorescence emission spectroscopic techniques. The experimental data suggest that implementation of the halogen substituent effect to enhance the photosensitizing properties of a chromophore from the excited triplet state should be done cautiously, as it may have negative implications.

Time-resolved optical emission spectroscopic measurements of He plasma induced by a high-power CO 2 pulsed laser

Laser-induced breakdown spectroscopy of helium plasma, initially at room temperature and pressures ranging from 12 to 101 kPa was investigated using a transverse excitation atmospheric CO 2 pulsed laser ( λ = 9.621 and 10.591 μm, a full width at half maximum of 64 ns, and an intensity from 1.5 to 5.36 GW cm −2). The helium breakdown spectrum is mainly due to electronic relaxation of excited He, He + and H. Plasma characteristics were examined in detail on the emission lines of He and He + by the time-integrated and time-resolved optical emission spectroscopy technique. Optical breakdown threshold intensities, ionization degree and plasma temperatures were obtained. An auxiliary metal mesh target was used to analyze the temporal evolution of the species in the plasma. The results show a faster decay of the continuum emission and He + species than in the case of neutral He atoms. The velocity and kinetic energy distributions for He and He + species were obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the laser pulse incidence. Temporal evolution of electron density has been used for the estimation of the three-body electron–ion recombination rate constant.

Optimization of La0.7Ba0.3MnO3−δ complex oxide laser ablation conditions by plume imaging and optical emission spectroscopy

The properties of thin films of complex oxides, such as La1−xDxMnO3−δ (D=Ba, Ca, Sr, etc.), produced by pulsed laser deposition depend critically on the experimental parameters in which laser ablation is carried out. Here, we report a comparative analysis of the pulsed laser ablation process of La0.7Ba0.3MnO3−δ, in oxygen background, in the ambient pressure range from 10−2 to 1 mbar, typically employed in pulsed laser deposition of manganites. The laser ablation plume was studied by using time-gated imaging and optical emission spectroscopy techniques. It was found that at a pressure of ≈10−2 mbar, the plume species arriving at the substrate are characterized by hyperthermal kinetic energy (≈10 eV), and high degree of excitation. On the contrary, at larger oxygen pressure (0.1–1 mbar), the velocity of plume species reaching the substrate, and their degree of excitation are much reduced by the confining effects of the background gas. These features explain why an appropriate choice of the experimental conditions in which the deposition process is carried out leads to better quality films, providing helpful indications to improve control over the growth process of both La1−xDxMnO3−δ and other perovskitic oxides.

The effect of potassium addition on plasma parameters in argon dc plasma arc

The effect of potassium addition on the radial distribution of temperature and electron number density in a U-shaped direct current (dc) argon plasma operating at different arc currents has been studied by optical emission spectroscopic techniques and the power interruption method. Spatially resolved electron number densities (ne) have been determined from measured radial profiles of Balmer-Hβ spectral line. The obtained electron number densities have been used for thermodynamic temperature (TLTE) evaluation with the assumption that the arc plasma is in a state of local thermodynamic equilibrium. The excitation temperatures (Texc) have been determined from the absolute integral emissivity of the argon line at 430.01 nm. For heavy particle temperature (Th) evaluations we have used a power interruption method. The obtained results have shown that an addition of KCl decreases both electron number density and temperature of the arc column. The magnitude of such an influence on plasma parameters increases with an increase in the KCl concentration and decreases with an increase in the arc current.

Understanding the mechanism of nano-aluminum particle formation by wire explosion process using optical emission technique

Nano-aluminum particles are produced by a wire explosion process in different inert gas ambience. It is observed that generated particles have different sizes and it follows log–normal probability distribution. The particle size produced by the wire explosion process varies depending on the thermal conductivity of the medium and the operating pressure of the gas. To understand the mechanism of nano-particle formation, the optical-emission spectroscopic technique is used for measuring characteristics of plasma generated during the wire explosion process. Strong emission lines were observed from the species formed during the wire explosion process. Plasma temperatures are estimated based on local thermal equilibrium principle and using Al emission lines. Plasma temperature of more than 8000 K is observed in an Ar ambient. The optical emission study clearly indicates that the intensity of plasma increases with an increase in the ambient pressure. Further, it is observed that an increase in the pressure of the gas, the plasma temperature also increases. The study shows that the plasma temperature in the He gas is lesser than in the Ar gas. The plasma temperature due to the discharge plays a significant role on nano-particle formation. In addition, it is observed that irrespective of polarity, emission characteristics are almost the same.

Spatial Structure of Emission Intensity in Capacitive RF Discharge of He:Ne Mixture at Moderate Pressures

The spatial structure of emission intensity in a capacitive radio frequency discharge at 13.56 Mhz in He:Ne mixture with total pressures of more than hundreds of Pascal was studied using the optical emission spectroscopy technique. The spectral line distributions at the axis of the discharge gap vs. the distance between two plane aluminium electrodes were found for: the line of 585.2 nm (Ne) and 447.15 nm (He) in 5:1 ratio of the mixture at pressure of 800 Pa for different driving powers 10, 20, and 30 W; the line of 585.2 nm in the range of 733–4393 Pa at power of 20 W in 10:1 ratio of the mixture; lines of 632.8 + 633.4 nm (Ne) at ratios of 5:1, 10:1, 15:1, a power of 20 W, under pressure of 1400 Pa; lines of 585.2 nm, 632.8 + 633.4 nm, 640.2 nm, and 703.2 nm (Ne) and 447.15 nm, 706.52 nm (He), at a pressure of 1467 Pa and a power of 20 W in ratio 10:1. Under chosen operational conditions, the measured relative spectral intensities for all studied lines in the middle of the discharge gap show the existence of the α-regime in the RF discharge. The dc-bias voltage vs. the total pressure and the dc-bias voltage–power characteristics were obtained at certain conditions.