Optical Emission Spectroscopy Technique Research Articles

Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma

An established optical emission spectroscopy technique, laser-induced breakdown spectroscopy (LIBS), holds promise for detection and rapid analysis of elements relevant for nuclear safeguards, nonproliferation, and nuclear power, including the measurement of isotope ratios. One such important application of LIBS is the measurement of uranium enrichment (235U/238U), which requires high spectral resolution (e.g., 25pm for the 424.4nmU II line). High-resolution dispersive spectrometers necessary for such measurements are typically bulky and expensive. We demonstrate the use of an alternative measurement approach, which is based on an inexpensive and compact Fabry–Perot etalon integrated with a low to moderate resolution Czerny–Turner spectrometer, to achieve the resolution needed for isotope selectivity of LIBS of uranium in ambient air. Spectral line widths of ~10pm have been measured at a center wavelength 424.437nm, clearly discriminating the natural from the highly enriched uranium.

The optical emission spectroscopy of pulsed and pulse- periodic discharges initiated with runaway electrons

We report on the results of measurements of an electron Te and a gas Tg temperatures as well as a reduced electric field strength E/N in the plasma of a high-voltage nanosecond discharge initiated with runaway electrons in a gap with a strongly nonuniform electric field distribution. The foregoing plasma parameters were determined with optical emission spectroscopy techniques. The possibility of using the method for determining Te and E/N in thermodynamically nonequilibrium plasma, which is based on a determination of a ratio of a peak intensities of the ionic (λ = 391.4 nm) and molecular N2 (λ = 394 nm) nitrogen bands, is proved. To measure a gas temperature the optical emission spectroscopy technique based on the measurement of a relative radiation intensity of rotation structure of electronic-vibrational molecular transitions was used, as well.

Investigation of PtCo/Graphene and PtCoRu/Graphene Catalysts for Oxygen Reduction Reaction

In the present study a rapid microwave heating method was used to prepare the graphene supported PtCo and PtCoRu catalysts. The catalytic activity of the PtCo/graphene and PtCoRu/graphene catalysts for oxygen reduction reaction was investigated. Physical characterization of the catalysts was performed by Transmission Electron Microscopy and Inductively Coupled Plasma Optical Emission Spectroscopy techniques. It was found that the PtCo/graphene and PtCoRu/graphene catalysts show enhanced activity towards oxygen reduction as compared with that of bare Pt/graphene catalyst. The PtCo/graphene and PtCoRu/graphene catalysts show higher onset potentials, as well as higher current densities towards oxygen reduction reaction as compared with those at the bare Pt/graphene catalyst.

The measurement of electron number density in helium micro hollow gas discharge using asymmetric He I lines

The electron number density Ne in helium micro hollow gas discharge (MHGD) is measured by means of optical emission spectroscopy (OES) techniques. The structure of MHGD is a gold–alumina–gold sandwich with 250 μm alumina thickness and 100 μm diameter hole. The electron temperature Te and gas temperature Tg in the discharge is determined using the relative intensity of He I lines and R branch lines in the frame of BP technique, respectively. The simple procedure based on spectral line broadening theory was developed in MATLAB to generate synthetic neutral line asymmetric profiles. The synthetic profiles were compared with an experimental He I 447.1 nm and He I 492.2 nm line to obtain Ne from the centre of a micro hollow gas discharge (MHGD) source in helium. The Ne results were compared with Ne values obtained from the forbidden-to-allowed (F/A) intensity ratio technique. The comparison confirmed higher Ne determined using a F/A ratio due to large uncertainty of the method. Applying the fitting formula for a He I 492.2 nm line derived from computer simulation (CS) gives the same Ne values as the one determined using the MATLAB procedure in this study. The dependence of Ne on gas pressure and electric current is investigated as well.

Spectroscopic diagnostics of active screen plasma nitriding processes: on the interplay of active screen and model probe plasmas

In a reactor used for active screen plasma nitriding (ASPN) the interplay of two plasma types, (i) the plasma of the cylindrical active screen driven in a pulsed dc mode (f = 1 kHz, 60% duty cycle) and (ii) the plasma at an internal model probe driven in a cw dc mode, ignited in a low pressure H2–N2 gas mixture (p = 3 mbar) containing small amounts of CH4 and CO2 have been studied by tunable diode laser infrared absorption (TDLAS) and optical emission spectroscopy (OES) techniques. Applying in situ TDLAS the evolution of the carbon containing precursors, CH4 and CO2, and of the reaction products, NH3, HCN, CO and H2O, has been monitored. The degree of dissociation of the carbon containing precursor molecules varied between 70% and 92%. The concentrations of the reaction products were found to be in the range 1012…1015 molecules cm−3. By analyzing the development of the molecular concentrations at changes of gas mixtures and plasma power values, it was found that (i) HCN and NH3 are the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF(CH4) ≈ 1…2 × 1015 molecules J−1, RF(CO2) ≈ 0.5…1.0 × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power values, while the influence of probe and screen plasmas, i.e. the phenomena caused by the interplay of both plasma sources, was analyzed. The additional usage of the plasma at the model probe has a sensitive influence on the generation of the reaction products, in particular that of NH3 and HCN. With the help of OES the rotational temperature of the screen plasma could be determined, which increases with power from 770 K to 950 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0-0) band of the first negative system, increases strongly in relation to the intensity of the neutral component, represented by the N2-(0-0) band of the second positive system. In addition, the behavior of the emission of the plasma at the model probe has been studied during the off phase of the plasma of the active screen leading to a direct comparison of the emission characteristics of both plasma sources.

Investigation of PtCo/Graphene and PtCoRu/Graphene Catalysts for Oxygen Reduction Reaction

The electrocatalytic oxygen reduction reaction (ORR) is an important process in energy converting systems such as low temperature proton exchange membrane fuel cells (PEMFCs). Therefore, understanding the oxygen reduction mechanistic pathways in terms of developing an efficient and stable catalyst has been the main research interest over several decades. In the present study a rapid microwave heating method was used to prepare the graphene supported PtCo and PtCoRu catalysts with the different Pt:Co and Pt:Co:Ru molar ratios. The catalytic activity of the PtCo/graphene and PtCoRu/graphene catalysts, for oxygen reduction reaction was investigated by linear scan voltammetry in the cathodic direction at 5 mV s–1 in the 0.5 M H2SO4 solution saturated with O2 at a temperature of 25 oC. Physical characterization of the catalysts was performed by X-ray Diffraction, High Resolution Transmission Electron Microscopy, Energy Dispersive X-ray Analysis and Inductively Coupled Plasma Optical Emission Spectroscopy techniques. The cyclic voltammetry has been used to estimate the electrochemically active surface areas of the catalysts. It was found that the PtCo/graphene and PtCoRu/graphene catalysts prepared by means of microwave synthesis show enhanced activity towards oxygen reduction as compared with that at bare Pt/graphene catalyst. The PtCo/graphene and PtCo /graphene catalysts show higher onset potentials, as well as higher current densities towards oxygen reduction reaction as compared with those at the bare Pt/graphene catalyst.

Remarkable promotion effect of trace sulfation on OMS-2 nanorod catalysts for the catalytic combustion of ethanol

OMS-2 nanorod catalysts were synthesized by a hydrothermal redox reaction method using MnSO4 (OMS-2-SO4) and Mn(CH3COO)2 (OMS-2-AC) as precursors. SO42−-doped OMS-2-AC catalysts with different SO42− concentrations were prepared next by adding (NH4)2SO4 solution into OMS-2-AC samples to investigate the effect of the anion SO42− on the OMS-2-AC catalyst. All catalysts were then tested for the catalytic oxidation of ethanol. The OMS-2-SO4 catalyst synthesized demonstrated much better activity than OMS-2-AC. The SO42− doping greatly influenced the activity of the OMS-2-AC catalyst, with a dramatic promotion of activity for suitable concentration of SO42− (SO4/catalyst=0.5% W/W). The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), NH3-TPD and H2-TPR techniques. The results showed that the presence of a suitable amount of SO42− species in the OMS-2-AC catalyst could decrease the Mn–O bond strength and also enhance the lattice oxygen and acid site concentrations, which then effectively promoted the catalytic activity of OMS-2-AC toward ethanol oxidation. Thus it was confirmed that the better catalytic performance of OMS-2-SO4 compared to OMS-2-AC is due to the presence of some residual SO42− species in OMS-2-SO4 samples.

Conversion of a variety of high free fatty acid containing feedstock to biodiesel using solid acid supported catalyst

The present study explores the use of silicotungstic acid anchored to mesoporous siliceous support, Korean Institute of Technology-6 (KIT-6), as a catalyst to produce biodiesel. Silicotungstic acid loaded KIT-6 was synthesized and the physicochemical properties were characterized using scanning electron microscopy, surface area and pore size distribution analyzer, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and inductively coupled plasma – optical emission spectroscopy techniques. Efficiency of the silicotungstic acid loaded KIT-6 in the production of biodiesel from a variety of high free fatty acid containing feedstock was then evaluated. The composition of free fatty acids in all the feedstock oils (algae oil, coffee oil, palmitic acid and used cooking oil) and their biodiesel resulting from the feedstock were also analyzed. Compared with other solid acid catalysts, the resulting materials show stable and highly efficient catalytic performance in biodiesel production with the highest conversion reaching 99%. A sample containing 26 wt% of silicotungstic acid supported on KIT-6 was found to be the most active catalyst for esterification at 70 °C whilst stirring constantly, with an alcohol/acid volume ratio of 2 and 1.5 wt% loading catalyst for 3 h. Furthermore, the catalyst was reused for four cycles indicating recyclability of the catalyst.

The characterization of cathodic plasma electrolysis of tungsten by means of optical emission spectroscopy techniques

Cathodic plasma electrolysis (CPE) of tungsten is investigated by means of optical emission spectroscopy in order to measure the electron temperature Te and the electron number density Ne from CPE micro-arc discharges. The relative intensity of W I lines recorded from seven spectral ranges are used in conjunction with the Boltzmann plot (BP) technique to measure . For Ne diagnostics, the complex line shape of the and the lines are analyzed in the frame of the spectral line broadening theory. The results showed two Ne values, and , corresponding to different regions of CPE micro-arc discharges. The self-absorption effect on both studied H I lines was revealed and discussed as well. The SEM and XRD analysis showed a weak formation of rough oxide coating featured by the number of grains, channels, and holes.

Spectroscopic analysis of coal plasma emission produced by laser ablation

An analysis of plasma produced by laser ablation using 1,064 nm of laser radiation from a Q-switched Nd:YAG on coal mineral samples under air ambient, was performed. The emission of molecular band systems such as C2 Swan System , the First Negative System N2 (Band head at 501.53 nm) and different emission lines were investigated using the optical emission spectroscopy technique. The C2 molecular spectra (Swan band) were analyzed to determine vibrational temperature (0.62 eV). The density and electron temperature of the plasma have been evaluated using Stark broadening and the intensity of the nitrogen emission lines (N II). Values of 1.2 eV of electron temperature and 1.82×1019 cm-3 of electron density were found.

Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon**Supported by the National Natural Science Foundation of China under Grant Nos 11135002, 11075069, 91026021, 11075068 and 10975065, and the Scholarship Award for Excellent Doctoral Student by the Ministry of Education of China.

An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium (LTE), the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.

Methods Employed in Optical Emission Spectroscopy Analysis: a Review

In this work, different methods employed for the analysis of emission spectra are presented. The proposal is to calculate the excitation temperature (Texc), electronic temperature (Te) and electron density (ne) for several plasma techniques used in the growth of thin films. Some of these tecnniques include magnetron sputtering and arc discharges. Initially, some fundamental physical principles that support the Optical Emission Spec-troscopy (OES) technique are described; then, some rules to consider during the spectral analysis to avoid ambiguities are listed. Finally, some of the more frequently used spectroscopic methods for determining the physical properties of plasma are described.

Measurements of population densities of metastable and resonant levels of argon using laser induced fluorescence

We present a new approach to measure population densities of Ar I metastable and resonant excited states in low temperature Ar plasmas at pressures higher than 1 Torr. This approach combines the time resolved laser induced fluorescence technique with the kinetic model of Ar. The kinetic model of Ar is based on calculating the population rates of metastable and resonant levels by including contributions from the processes that affect population densities of Ar I excited states. In particular, we included collisional quenching processes between atoms in the ground state and excited states, since we are investigating plasma at higher pressures. We also determined time resolved population densities of Ar I 2 p excited states by employing optical emission spectroscopy technique. Time resolved Ar I excited state populations are presented for the case of the post-discharge of the supersonic flowing microwave discharge at pressures of 1.7 and 2.3 Torr. The experimental set-up consists of a pulsed tunable dye laser operating in the near infrared region and a cylindrical resonance cavity operating in TE111 mode at 2.45 GHz. Results show that time resolved population densities of Ar I metastable and resonant states oscillate with twice the frequency of the discharge.

Spectroscopic measurements of plasma temperatures and electron number density in a uranium hollow cathode discharge lamp

The plasma parameters including neutral species temperature, atomic excitation temperature and electron number density in a see-through type, homemade uranium hollow cathode discharge lamp with neon as a buffer gas have been investigated using optical emission spectroscopic techniques. The neutral species temperature has been measured using the Doppler broadening of a neon atomic spectral line. The atomic excitation temperature has been measured using the Boltzmann plot method utilizing uranium atomic spectral lines. The electron number density has been determined from the Saha-Boltzmann equation utilizing uranium atomic and ionic spectral lines. To the best of our knowledge, all these three plasma parameters are simultaneously measured for the first time in a uranium hollow cathode discharge lamp.

Diagnostics of laser-induced plasma by optical emission spectroscopy

The procedure for diagnostics of laser induced plasma (LIP) by optical emission spectroscopy technique is described. LIP was generated by focusing Nd:YAG laser radiation (1.064 nm, 50 mJ, 15 ns pulse duration) on the surface of pellet containing among other elements lithium. Details of the experimental setup and experimental data processing are presented. High speed plasma photography was used to study plasma evolution and decay. From those images optimum time for plasma diagnostics is located. The electron number density, Ne, is determined by fitting profiles of Li I lines while electron temperature, Te, was determined from relative intensities of Li I lines using Boltzmann plot (BP) technique. All spectral line recordings were tested for the presence of self-absorption and then if optically thin, Abel inverted and used for plasma diagnostic purposes.

Mechanisms and processes of arc propagation over an ice-covered surface

The general objective of this paper is to investigate the physical mechanisms and processes involved in the propagation of arc over the surface of ice. In the present research work, high-speed imaging and optical emission spectroscopy techniques were synchronized with the electrical measurements to study the various parameters of arc on an ice surface, i.e. channel radius, propagation velocities, arc column temperature and electron density. These results, together with observation of the propagation patterns and arc foot geometries, calculation of arc energy and the examination of the state of thermal equilibrium provide background information for understanding the ice-covered insulator flashover phenomenon. Arc root structure, current profile, propagation pattern and velocity were investigated under different type of applied voltage and different polarities. Water film conductivity and thickness, relative air humidity and the direction of arc propagation were also analyzed as influencing parameters of arc propagation. The effects of different possible mechanisms, e.g. collision and thermal ionization, buoyancy force and electrostatic force, on different stages of arc propagation has been discussed.

Investigation of H 2 /CH 4 mixed gas plasma post-etching process for ZnO:B front contacts grown by LP-MOCVD method in silicon-based thin-film solar cells

A new plasma post-etching method, H2/CH4 mixed gas plasma, is introduced to modify ZnO:B films grown by LP-MOCVD technique, successfully relaxing the double trade-offs, i.e., transparency/conductivity trade-off and surface texture/Voc and FF trade-off. To deeply evaluate the post-etching process, optical emission spectroscopy technique is applied to diagnose the plasma condition. Upon different etching power, three distinct possible etching mechanisms are identified by analyzing the evolution of Hα*, Hβ*, CH* emission species in the plasma space. It is demonstrated that Hβ* and CH* species are responsible for the physical etching process and chemical etching process, respectively, from which a new “soft” surface morphology is formed with a combination of micro- and nano-sized texture. Additionally, Hα* species can bond with ZnO and also passivate the grains boundaries, thereby making both the carrier concentration and hall mobility increase. This process is defined as chemical bonding process. Finally, pin-type a-Si:H single-junction solar cells with an optimized device structure is grown on the etched ZnO:B substrate. The corresponding electrical parameters, such as Jsc, Voc and FF, are simultaneously improved compared with the solar cell deposited on as-grown ZnO:B substrate with the same fabrication process. As a consequence, a noteworthy 8.85% conversion-efficiency is achieved with an absorber layer thickness only 160 nm.

Spectroscopic study of H2 microwave plasmas with small admixtures of CH4 and B2H6 used for doped diamond deposition

Microwave (MW) H2 plasmas with small admixtures of CH4 and/or B2H6 used for doped diamond deposition have been studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were carried out in order to analyze the dependence of the plasma chemistry on several parameters in the MW discharges, such as power, pressure and gas mixture, at relatively high pressures, i.e. up to 300 mbar, and power values, i.e. up to 4 kW. The evolution of the concentrations of five stable molecules, CH4, C2H2, C2H4, C2H6 and B2H6, was monitored in the plasma processes by in situ infrared tunable diode laser absorption spectroscopy. OES was used simultaneously to gather complementary information about the concentration of the boron atom. One target was the determination of the precursors' fragmentation rates and the conversion rates to the molecular reaction products. The analysis of correlations between the power and pressure of the plasma and molecular concentrations, and the differences found with CH4 and B2H6 admixtures were another focus of interest. The degree of dissociation of the carbon containing precursor molecule CH4 varied between 35% and 75%, while the decomposition of diborane, the boron precursor, varied between 85% and 97%. By analyzing the development of the molecular concentrations with changes of gas mixtures, pressure and plasma power values, it was found that (i) C2H2 is the most abundant reaction product in the plasma in the case of methane admixture and (ii) the boron atom concentration depends strongly on the presence of hydrocarbons in the plasma. The fragmentation efficiencies of methane and of diborane (RF(CH4) ≈ (1–2) × 1015 molecules J−1, RF(B2H6) ≈ (0.4–1.4) × 1013 molecules J−1) and the conversion efficiencies to the molecular products (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power, and pressure values. The boron atom balance, in relation to the dissociated B2H6 molecules was found to vary between 10% and 40% depending on the discharge conditions.

Spatial characterization of laser induced Yb plasma in argon using optical emission spectroscopy: Pressure effect

• Laser induced Yb plasma at different pressure of Argon is spatially investigated. • O-TOF profiles and excitation temperature are used to characterize the plasma. • At 100 Pa of argon background gas, shock wave begins to be formed. • Drag force expansion describes the plasma propagation at pressures bigger than 1 Pa. • Two components of velocity distribution of the Yb atoms are estimated. Spatial and temporal behavior of laser induced Ytterbium plasma plume is studied using optical emission spectroscopy technique. A third harmonic Nd:YAG nanosecond laser was used to generate Yb plasma plume at different Argon background pressures (1, 10, 10 2 , 10 3 and 10 4 Pa). The plasma dynamics was investigated based on the spatial behavior of the excitation temperature coupled with optical time of flight (O-TOF) profiles of neutral Yb emission line (555.65 nm) along the propagation axe of the plasma plume. Drag force model was appropriate to describe the propagation dynamics at all pressures except of the lowest one (1 Pa) where free expansion model is dominant. The velocity distribution of Yb I atoms were extracted using two terms of Shifted Maxwell–Boltzmann (SMB) distribution. The correlation between the spatial comportment of both excitation temperature and O-TOF profiles is discussed.

Spectroscopic study of emission coal mineral plasma produced by laser ablation

Spectroscopic analysis of plasma produced by laser ablation of coal samples using 1064 nm radiation pulses from a Q-switched Nd:YAG on different target under air ambient, was performed. The emission of molecular band systems such as C2 Swan System (d3Πg→a3Πu), the First Negative System N2 (Band head at 501,53 nm) and emission lines of the C I, C II, were investigated using the optical emission spectroscopy technique. The C2 molecular spectra (Swan band) were analyzed to determine vibrational temperature (0,62 eV); the density and electron temperature of the plasma have been evaluated using Stark broadening and the intensity of the nitrogen emission lines N II, the found values of 1,2 eV and 2,2 x1018 cm−3 respectively.