Optical Emission Spectroscopy Measurements Research Articles

Tailoring the Surface Functionalities of Radio Frequency Magnetron-Sputtered ZnO Thin Films by Ar/NH3 Gas Mixture Surface-Wave Plasmas.

The surface functionalization of radio frequency magnetron-sputtered zinc oxide (ZnO) thin films tailored by low-pressure Ar/NH3 mixture surface-wave plasmas (SWPs) is discussed based on the results of photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectrophotometric measurements. At an Ar/NH3 gas mixture ratio of 70%/30%, both the PL intensity of the near-band-edge emission and the XRD intensity of the ZnO(002) reflection peak were enhanced by about 5.5 and 8 times, respectively, compared to the values for the as-grown sample. Furthermore, the XPS and spectrophotometric analyses using the fluorescent dye showed that the amine group functionalization over the surface of the ZnO films reached their maximum values at the same gas ratio. From the results of optical emission spectroscopic and ion mass spectrometric measurements in the Ar/NH3 mixture SWPs, it is inferred that the nitrogen-containing reactive species, such as NH x+ ( x = 1-4) ions and NH y ( y = 1, 2) molecules in addition to H radicals might crucially interact with the defective ZnO surface lattices to repair the ZnO thin films from compressive to strain-free crystallized structures, enhance the PL intensity, and producethe amine group surface functionalization.

Monitoring bone changes due to calcium, magnesium, and phosphorus loss in rat femurs using Quantitative Ultrasound

Bone mineral density is an important parameter for the diagnosis of bone diseases, as well as for predicting fractures and treatment monitoring. Thus, the aim of the present study was to evaluate the potential of Quantitative Ultrasound (QUS) to monitor bone changes after calcium, phosphorus, and magnesium loss in rat femurs in vitro during a demineralization process. Four quantitative ultrasound parameters were estimated from bone surface echoes in eight femur diaphysis of rats. The echo signals were acquired during a decalcification process by Ethylenediaminetetraacetic Acid (EDTA). The results were compared to Quantitative Computed Tomography (QCT) and inductively coupled plasma optical emission spectrometry measurements for validation. Integrated Reflection Coefficient (IRC) reflection parameters and Frequency Slope of Reflection Transfer Function (FSRTF) during demineralization tended to decrease, while the backscattering parameter Apparent Integrated Backscatter (AIB) increased and Frequency Slope of Apparent Backscatter (FSAB) showed an oscillatory behavior with no defined trend. Results indicate a clear relation between demineralization and the corresponding decrease in the reflection parameters and increase in the scattering parameters. The trend analysis of the fall curve of the chemical elements showed a better relationship between IRC and QCT. It was possible to monitor bone changes after ions losses, through the QUS. Thus, it is an indication that the proposed protocol has potential to characterize bone tissue in animal models, providing consistent results towards standardization of bone characterization studies by QUS endorsing its use in humans.

Tuning of Conversion and Optical Emission by Electron Temperature in Inductively Coupled CO2 Plasma

This paper focuses on how the electron temperature and other plasma properties affect optical emission and CO2 conversion in CO2 plasma. Such plasma-mediated reactions can enable efficient CO2 reuse. We study CO2 and CO plasmas generated by inductively coupled radiofrequency power (30–300 W) at low pressures (6–400 Pa). By varying the argon admixture, we can study the effect of the electron temperature, Te, on the conversion and emission properties using optical emission spectroscopy, mass spectrometry, and electrical probe measurements. Importantly, we can observe several parameters simultaneously: Te, CO2 conversion, chemiluminescence from CO2, and dissociation products and optical emission from several atomic and CO transitions and from the C2 Swan system. On the basis of these results, we establish a correlation between Te, the CO2 conversion, and the optical emission spectra. A low Te enhances CO2 conversion and Swan band emission. In contrast with published studies, our results show that the CO2 and C2 vibrations are not in local equilibrium. This means that the vibrational temperatures of CO2 and C2 should differ.

Towards the fluorescence retention and colloidal stability of InP quantum dots through surface treatment with zirconium propoxide

ABSTRACTThrough the synthetic development of sophisticated core/shell heterostructures, the fluorescent properties of quantum dots (QDs) have been steadily improved to a level that can ultimately meet the industrial demands, but their reliability is still insufficient, particularly showing low fluorescence stability against degradable conditions. As one solution to this issue, an additional physical barrier typically with an oxide phase has been introduced to protect the QD surface from the environment. In this work, a strategy for improving the stability of QDs involving the passivation of their surfaces with zirconium propoxide (Zr(PrO)4) is suggested. Multi-shelled green QDs of InP/ZnSeS/ZnS were first synthesized, and then their surfaces were in-situ-treated with Zr(PrO)4. To confirm the presence of Zr(PrO)4-derived species on the QD surfaces, chemical analyses of the Zr(PrO)4-treated QDs were performed through Fourier transform infrared, X-ray photoelectron, and inductively coupled plasma optical emission spectroscopic measurements. A photostability test of two comparative InP/ZnSeS/ZnS QDs – one treated without and one with Zr(PrO)4 – was performed by exposing their dispersions to ultraviolet (UV) irradiation for prolonged periods of time, up to 120 h. It was revealed that Zr(PrO)4 treatment is highly effective in improving fluorescence retention and colloidal stability.

Experimental and Numerical Investigations on Interdiffusion Profiles in Compounds Produced by Sinter-Cladding

Tools used for mineral processing applications are affected by strong abrasive wear and high dynamic loads. This results in opposing demands on the mechanical properties of these tools. Therefore, modern concepts for the manufacturing of mineral processing tools include a composite tool concept consisting of a low-alloyed substrate and a high-alloyed, wear-resistant cladding material. These coatings can be applied using different production processes such as composite casting, deposit welding, and HIP cladding. During the deposition of the cladding, interdiffusion between the substrate and cladding material occurs. This interdiffusion may have a negative impact on the compound, since characteristics such as wear resistance, mechanical properties, and the local microstructure are influenced. This article is focused on the investigation and simulation of interdiffusion processes in supersolidus-sintered compounds using computational thermodynamics, diffusion calculations, optical emission spectrometry, hardness profiles, and microstructural investigations. It is shown that the interdiffusion processes between the solid substrate and the semisolid cladding can be simulated using a dispersed phase model to give results with a close concordance to optical emission spectrometry measurements.

Time-resolved optical emission spectroscopic studies of picosecond laser produced Cr plasma

Time-resolved optical emission spectroscopic measurements of a plasma generated by irradiating a Cr target using 60 picosecond (ps) and 300 ps laser pulses are carried out to investigate the variation in the line width (δλ) of emission from neutrals and ions for increasing ambient pressures. Measurements ranging from 10−6 Torr to 102 Torr show a distinctly different variation in the δλ of neutrals (Cr I) compared to that of singly ionized Cr (Cr II), for both irradiations. δλ increases monotonously with pressure for Cr II, but an oscillation is evident at intermediate pressures for Cr I. This oscillation does not depend on the laser pulse widths used. In spite of the differences in the plasma formation mechanisms, it is experimentally found that there is an optimum intermediate background pressure for which δλ of neutrals drops to a minimum. Importantly, these results underline the fact that for intermediate pressures, the usual practice of calculating the plasma number density from the δλ of neutrals needs to be judiciously done, to avoid reaching inaccurate conclusions.

Characteristics of a novel nanosecond DBD microplasma reactor for flow applications

We present a novel microplasma flow reactor using a dielectric barrier discharge (DBD) driven by repetitive nanosecond high-voltage pulses. Our DBD-based geometry can generate a non-thermal plasma discharge at atmospheric pressure and below in a regular pattern of micro-channels. This reactor can work continuously up to about 100 min in air, depending on the pulse repetition rate and operating pressure. We here present the geometry and main characteristics of the reactor. Pulse energies of 1.46 and 1.3 μJ per channel at atmospheric pressure and 50 mbar, respectively, have been determined by time-resolved measurements of current and voltage. Time-resolved optical emission spectroscopy measurements have been performed to calculate the relative species concentrations and temperatures (vibrational and rotational) of the discharge. The effects of the operating pressure and flow velocity on the discharge intensity have been investigated. In addition, the effective reduced electric field strength has been obtained from the intensity ratio of vibronic emission bands of molecular nitrogen at different operating pressures and different locations. The derived increases gradually from about 550 to 4600 Td when decreasing the pressure from 1 bar to 100 mbar. Below 100 mbar, further pressure reduction results in a significant increase in up to about 10000 Td at 50 mbar.

GDOES analysis of niobium de-hydrogenation after electropolishing processes

Niobium, as pure metal and alloying element, is used in a variety of applications, among them in nuclear industries. Niobium is incorporated into nuclear fission reactors due to its enormous strength and relatively low density. Surface finishing of niobium is often performed in electrochemical polishing processes in view of improving its smoothness, corrosion resistance and its surface cleanability. However, the presently used electropolishing process (EP) is intrinsically linked to the subsurface hydrogenation of niobium, which measurably degrades its properties. The annealing operation, which is used to remove hydrogen from electropolished niobium, is quite a costly and time-consuming process. The traditional electrolyte consisting of a mixture of 96% H2SO4/49% HF acids by volume in a 9:1 ratio has been substituted for the new one, being a mixture of 70% methanesulfonic acid with 49% hydrofluoric acid by volume in a 3:1 ratio. The additional imposition of a magnetic field during the electropolishing process – magnetoelectropolishing (MEP) further increases hydrogen removal, when compared to the hydrogen content achieved by the electropolishing process (EP) alone.The aim of the study is to reveal a methodic approach and showing decreasing hydrogenation of niobium samples after consecutive steps of electrochemical polishing. Glow-Discharge Optical Emission Spectroscopy (GDOES) measurements were used to measure the hydrogen content in the surface layer of as-received (AR) niobium and in the samples after EP and MEP processes, and prove its close-to-zero content after MEP.

Effects of helium concentration on microcrystalline silicon thin film solar cells deposited by atmospheric-pressure plasma deposition at 13.3 kPa

An atmospheric-pressure plasma deposition system was developed and used to deposit intrinsic hydrogenated microcrystalline silicon (μc-Si:H) thin films for μc-Si:H thin film solar cells. The helium (He) gas concentration in plasma increased Raman crystallinity (Xc) of μc-Si:H, which was a critical parameter to determine photovoltaic performance. In addition, dependence of Xc on the He concentration is shown to be closely related to the atomic hydrogen flux during film growth, which is evidenced by plasma diagnostics derived from in situ optical emission spectroscopy measurements. Those analysis contributed to achieve impressive photovoltaic performance – namely, a power conversion efficiency of 4.60%, an open-circuit voltage of 0.52 V, a short-circuit current density of 13.62 mA/cm2, and a fill factor of 0.65, which is the first experimental demonstration of μc-Si:H thin film solar cells fabricated with the atmospheric-pressure plasma deposition under very high working-pressure regime at 13.3 kPa.

Characteristics of meso-pressure six-phase alternative current arc discharge plasma jet: Experiments

During the re-entry process of a supersonic vehicle in near space, the interaction between the flying vehicle and surrounding air is violent due to the hypersonic relative speed.As a consequence, the shock-heated air in the vicinity of the vehicle surface is ionized.Thus, the formed plasma layer operates in strong collision, non-uniform and nonequilibrium states.One of the serious system operation problems resulting from this non-equilibrium plasma layer is the so-called communication blackout.Physical simulation of the near-space plasma environment in laboratory based on various plasma sources is a much lower cost method than the in-situ measurements in the vehicle re-entry process.In this paper, based on the ideas for designing the dual jet direct current arc plasma and the muti-phase alternating current discharge plasma, a physical design on the multi-phase alternating discharge apparatus is proposed for generating a large volume plasma arc-jet.And a multi-phase gas discharge plasma experimental platform-2015(MPX-2015) is established with the image recording/processing, electrical and optical emission spectroscopy measurement system in this laboratory. The preliminary experimental observations show that under a typical operating condition with a 500 Pa background pressure, a large volume plasma jet with a maximum diameter of 14.0 cm and a maximum length of 60.0 cm is obtained on this newly developed platform.The influences of the gas flow rate, the chamber pressure, the electrode gap spacing and the arc current on the characteristics of the plasma free jet and impinging jet are also studied.The experimental results show that within the parameter ranges studied in this paper, the chamber pressure has a very significant influence on the size of the plasma jet, i.e., both the diameter and length of the plasma free jet increase with chamber pressure decreasing, and a similar variation trend is also observed for the thickness and length of the plasma layer surrounding a bluff body.In addition, the size of the plasma layer also increases with the increase of the plasma working gas flowrate and the discharge current.These results are helpful in the more in-depth investigating of the aerodynamic heat effect and blackout issue of the re-entry process of supersonic vehicle in near space in future.In the future research, we will modify the structures of the plasma generators in order to obtain supersonic plasma arc-jets, and study both the quasi-steady and transient characteristics of the arc plasmas, as well as the strong interactions among the plasma jet, the surrounding air and the solid bluff body.

Ethylene Ignition and Flameholding by Electrical Discharge in Supersonic Combustor

This study examined the ignition and flameholding effects of the quasi-direct-current discharge on a directly injected hydrocarbon fuel (ethylene) in a supersonic combustion chamber without mechanical flameholders (plane walls). Tests were performed in supersonic wind tunnel SBR-50 at the University of Notre Dame at a Mach number of while varying the air pressure (), an air temperature of , and a fuel mass flow rate of . The sensitivity of the ignition dynamics to the plasma power was also explored. The pressure distribution over the test section, schlieren visualization, and camera imaging were used for combustion intensity and combustion front identification. Optical emission spectroscopy and electrical measurements were employed to characterize the quasi-direct-current discharge. Previously, ignition and flameholding of hydrogen were demonstrated in a wide range of parameters. In the case of ethylene injection, it was shown under current test conditions that lower pressure and lower air temperature were beneficial for flameholding. A preliminary explanation of these unobvious effects is proffered.

Optical Emission Spectroscopic Studies on Atmospheric Electrodeless Microwave Plasma in Carbon Dioxide–Hydrogen Mixture

Optical emission spectroscopic measurements were performed on atmospheric pressure electrodeless microwave plasmas produced in a 95% carbon dioxide–5% hydrogen mixture. The rotational and vibrational temperatures of the plasma were determined by measuring the C2 Swan band spectra at wavelengths in the ranges of 500–517 and 548–565 nm. The electron number density of the plasma was deduced by measuring the Stark broadening of the hydrogen Balmer- $\beta $ line shape at 486.13 nm. The microwave power was fixed at 2 kW, and the flow rate was varied from 5 to 20 standard liter per minute. The difference between the rotational and vibrational temperatures was found to be negligible. The temperatures reached 6200 (±200) K and were independent of the flow rate. The electron number densities of the plasmas were estimated to be approximately 2.06 (±0.12) $\times 10^{14}$ cm−3. Thermodynamic-equilibrium calculations indicated that the temperature corresponding to the measured electron density was 6221 (±200) K, which is almost the same as the temperatures measured according to the C2 Swan band spectra. Therefore, the electron temperature was nearly the same as the gas temperature, and the plasma was in local thermal equilibrium.

Roll-to-roll deposition of silicon oxynitride layers on polymer films using a rotatable dual magnetron system

High performance permeation barrier coatings are usually multilayer stacks consisting of inorganic and organic layers. Besides the water vapor transmission rate, the optical properties of such layers have a high importance. This contribution focuses on the deposition of silicon oxynitride as an inorganic layer. This material attracts a widespread interest due to its varying refractive index depending on its oxygen and nitrogen content. The experiments were carried out in a roll-to-roll coating machine using a rotatable magnetron system. The layers were deposited by reactive pulse magnetron sputtering using targets of 1m length. It was established that the ratio of oxygen to nitrogen in the layer was not only determined by the reactive gas mixture but also by the chosen set point of the closed loop control. Both the Secondary Ion Mass Spectrometry and the Glow Discharge Optical Emission Spectroscopy measurements revealed a vertically different composition of the SiOxNy layers. This could be supported by the simulation of the optical properties of the layers.

Enhanced power coupling efficiency in inductive discharges with RF substrate bias driven at consecutive harmonics with adjustable phase

Inductive discharges with radio-frequency (RF) substrate bias are frequently used for various technological applications. We operate such a hybrid discharge with a phase-locked RF substrate bias at twice the frequency of the inductive coupling with fixed but adjustable phase between both RF sources in neon at low pressures of a few Pa. The ion flux to the substrate is found to be a function of this relative phase in the H-mode at constant RF powers as long as some residual capacitive coupling of the planar coil is present. For distinct choices of the phase, Phase Resolved Optical Emission Spectroscopy measurements show that energetic beam electrons generated by the expanding boundary sheaths (i) are well confined, (ii) are accelerated efficiently, and (iii) propagate vertically through the inductive skin layer at the times of maximum azimuthal induced electric field within the fundamental RF period. This enhances the inductive stochastic electron heating, the power coupling efficiency, and finally the ion flux.

Assessment of optical emission analysis for in-process monitoring of powder bed fusion additive manufacturing

ABSTRACTDeveloping methods which allow real-time monitoring of powder bed fusion (PBF) additive manufacturing (AM) processes is key to enabling in situ assessments of build quality (e.g. lack of fusion and porosity). Here, we investigate the use of optical emission spectroscopy and high-speed (100 kHz) measurement of select wavelength emissions, based on a line-to-continuum approach, to determine if a correlation between PBF AM process inputs, sensor outputs, and build quality exists. Using an open protocol system interfaced with a 3D Systems ProX 200 machine, sensor data were synchronised with the scanner position and the laser state during the buildup of Inconel-718 components under varying powers, scan speeds, and hatch spacing parameters. Sensor measurements were then compared against post-build computed tomography scans. We show evidence that sensor data, when combined with appropriate analyses, are related to both processing conditions and build quality.

Al-Si-N thin films deposited by laser ablation: Effect of plasma parameters on mechanical and optical properties

Al-Si-N thin films were deposited using simultaneous laser ablation of silicon and aluminum targets in a nitrogen atmosphere at a substrate temperature of 200°C. The silicon content of the films was studied as a function of the plasma parameters (mean ion kinetic energy and plasma density), produced by the ablation of the silicon target. The plasma parameters were measured by means of a planar Langmuir probe and optical emission spectroscopy. The chemical composition of the films was determined by X-ray photoelectron spectroscopy. The results showed a dependence between the silicon content and the silicon plasma density. Optical emission spectroscopy measurements showed that variations of the working pressure produced changes in the intensity of excited species (N2+, Si2+, Al+ and Al0), and in the incorporation of these elements into the films. For a working pressure of 0.6Pa, hardness measurements gave a maximum of 30±1.5GPa for a silicon content of 4at.%. The optical constants (refractive index and extinction coefficient) and direct band gap were evaluated as a function of the silicon content in the films.

Ultraviolet Raman spectroscopy of N2 in a recombining atmospheric pressure plasma

We report ultraviolet spontaneous Raman scattering measurements of temperature in a recombining nitrogen plasma. The plasma source is an atmospheric pressure RF torch facility. A mixture is injected into the torch and heated to approximately 6800 K at the torch exit. Raman scattering measurements are in agreement with optical emission spectroscopy measurements of temperature at the torch exit. A 15 cm water-cooled tube is then mounted at the torch exit to rapidly cool the gas and produce a recombining plasma. Raman scattering measurements indicate a temperature of approximately 3300 K at the tube exit, significantly lower than previous emission spectroscopy estimates. The Raman measurements were confirmed via separate Rayleigh scattering measurements. The lack of agreement between emission spectroscopy, which only yields information on excited states, and Raman scattering measurements shows that the plasma is far from equilibrium at the exit of the recombining tube. These experiments provide a basis for studying recombining plasmas which, among other applications, are important for atmospheric reentry applications and plasma processing.

A fully-implicit Particle-In-Cell Monte Carlo Collision code for the simulation of inductively coupled plasmas

We present a fully-implicit electromagnetic Particle-In-Cell Monte Carlo collision code, called NINJA, written for the simulation of inductively coupled plasmas. NINJA employs a kinetic enslaved Jacobian-Free Newton Krylov method to solve self-consistently the interaction between the electromagnetic field generated by the radio-frequency coil and the plasma response. The simulated plasma includes a kinetic description of charged and neutral species as well as the collision processes between them. The algorithm allows simulations with cell sizes much larger than the Debye length and time steps in excess of the Courant–Friedrichs–Lewy condition whilst preserving the conservation of the total energy. The code is applied to the simulation of the plasma discharge of the Linac4 H− ion source at CERN. Simulation results of plasma density, temperature and EEDF are discussed and compared with optical emission spectroscopy measurements. A systematic study of the energy conservation as a function of the numerical parameters is presented.

Novel Prospects for Plasma Spray–Physical Vapor Deposition of Columnar Thermal Barrier Coatings

Plasma spray–physical vapor deposition (PS-PVD) is an emerging coating technique that can produce columnar thermal barrier coatings from vapor phase. Feedstock treatment at the start of its trajectory in the plasma torch nozzle is important for such vapor-phase deposition. This study describes the effects of the plasma composition (Ar/He) on the plasma characteristics, plasma–particle interaction, and particle dynamics at different points spatially distributed inside the plasma torch nozzle. The results of calculations show that increasing the fraction of argon in the plasma gas mixture enhances the momentum and heat flow between the plasma and injected feedstock. For the plasma gas combination of 45Ar/45He, the total enthalpy transferred to a representative powder particle inside the plasma torch nozzle is highest (~9828 kJ/kg). Moreover, due to the properties of the plasma, the contribution of the cylindrical throat, i.e., from the feed injection point (FIP) to the start of divergence (SOD), to the total transferred energy is ~69%. The carrier gas flow for different plasma gas mixtures was also investigated by optical emission spectroscopy (OES) measurements of zirconium emissions. Yttria-stabilized zirconia (YSZ) coating microstructures were produced when using selected plasma gas compositions and corresponding carrier gas flows; structural morphologies were found to be in good agreement with OES and theoretical predictions. Quasicolumnar microstructure was obtained with porosity of ~15% when applying the plasma composition of 45Ar/45He.

Optical Emission Spectroscopy-Based Tomography for Compact Low-Pressure Microwave Plasma in a Multicusp

Microwave-induced argon and hydrogen plasmas confined in a compact multicusp (MC) are studied in the pressure range of 0.2–2 mtorr and at microwave powers of 216–324 W. Plasma parameters such as electron temperature ( $\text{T}_{\text{e}}$ ) and density ( $\text{N}_{\text{e}}$ ) are evaluated using optical emission spectroscopy (OES) and Langmuir probe (LP) measurements. The estimated $\text{T}_{\text{e}}$ and $\text{N}_{\text{e}}$ from OES measurements lie in the range of 5–13 eV and $0.6 \times 10^{\mathrm {{10}}}$ – $4.0 \times 10^{\mathrm {{10}}}$ cm $^{-\mathrm {{3}}}$ , respectively, for the Ar and H2 plasmas, and are comparable to the values obtained from the LP measurements. The objective of this paper is to develop an emission tomographic measurement system for plasma confined in a compact MC. In general, OES is carried out to determine the wavelength of the most intense emitted light from the plasma, which is then applied to design the tomographic system to finally obtain a 2-D emission profile of light from the whole plasma cross section. Tomographic reconstruction of the plasma emission indicates two bright rings, one at the core and another near the plasma boundary, which are influenced by higher electron density at the core region and higher electron temperature near the electron cyclotron resonance zone.