Optical Emission Intensity Research Articles

Variation of luminescence properties of Na 2O–CaO–SiO 2: Nd 3+ glass with crystallinity

The optical absorption and emission intensities of Nd 3+-doped transparent glass-ceramics with high crystallinity in Na 2O–CaO–SiO 2 (NSC) system were studied. The transmittance of NCS decreases with increasing degree of crystallinity, however it still remains 65.5% at λ = 710 nm when the crystallization is almost completed. Judd–Ofelt theory is performed to evaluate the radiative transition probability as well as quality factor, branching ratio and emission cross section. The maximum values of Ω 2 and emission cross section ( 4F 3/2 → 4I 11/2) of NCS are obtained after nucleating at 630 °C for 10 h. The quality factor increases with increasing crystallinity, while branching ratio for 4F 3/2 → 4I 11/2 is opposite. The results show that transparent glass-ceramic with high crystallinity is a potential laser host for 1.06 μm emission.

Thermal, chemical, optical properties and structure of Er 3+-doped and Er 3+/Yb 3+-codoped P 2O 5–Al 2O 3–ZnO glasses

This study was explored in series of the optical, thermal, and structure properties based on 60P 2O 5–10Al 2O 3–30ZnO (PAZ) glasses system that doped with varied rare-earth (RE) elements Yb 2O 3/Er 2O 3. The glass transition temperature, softening temperature and chemical durability were increased with RE-doping concentrations increasing, whereas thermal expansion coefficient was decreased. In the optical properties, the absorption and emission intensities also increase with RE-doping concentrations increasing, When Er 2O 3 and Yb 2O 3 concentrations are over than 3 mol% in the Er 3+-doped PAZ system and Yb 3+-doped concentration is over than 3 mol% for Er 3+/Yb 3+-codoped PAZ system, the emission intensity significantly decreases presumably due to concentration quenching, formation of the ions clustering, and OH − groups in the glasses network. It is suggested that the maximum emission cross-section ( σ e ) is 7.64 × 10 − 21 cm 2 at 1535 nm is observed for 3 mol% Er 3+-doped PAZ glasses. Moreover, the maximum σ e × full-width-at-half-maximum is 327.8 for 5 mol% Er 3+-doped PAZ glasses.

The role of oxygen in analytical glow discharges: GD-OES and GD-ToF-MS studies

The influence of up to 0.8% volume fraction of oxygen on the argon plasma in a direct current analytical glow discharge was studied for iron, titanium, copper and gold samples using both time-of-flight mass spectrometry and high resolution optical UV-Vis Fourier transform spectrometry. A sudden decrease in sputtering rates, optical emission intensities and ion signals is observed at a current and material dependent threshold fraction of oxygen, and is attributed in part to the formation of an oxide layer on the surface. Beyond the threshold oxygen fraction, a further large continuing decrease in ion signals is observed as the oxygen fraction is increased. This smooth decrease of the observed ion signals is attributed to quenching of ions and argon metastable atoms by oxygen in the flowing afterglow in the flow tube used to promote ion transport to the mass spectrometer sampling orifice. At the threshold oxygen fraction, signals from the mass spectrometer decrease by orders of magnitude more than the optical emission observed from analyte and gas ions. This disproportionate decrease is also likely to be due to reactions in the flow tube. The negative mass spectra were also measured for iron, titanium and copper samples and a significant increase in ion signals is observed at material dependent critical oxygen concentration. Results of studies using calamine (a sample with oxide layer) in pure argon are reported and compared with argon/oxygen mixtures.

Combination of RF-plasma jet and Laser-induced plasma for breakdown spectroscopy analysis of complex materials

Laser-induced breakdown spectroscopy method is modified using an external radiofrequency (RF) plasma jet that overlaps spatially with the laser-induced plasma. Short UV laser pulses (wavelength 193 nm) are employed to ablate iron oxide ceramics, zinc oxide ceramics and polyethylene pressed pellets in ambient air background. An RF generator (frequency 13.56 MHz, power ≤1 kW) and a gas nozzle system are employed to generate a continuous jet of argon and nitrogen plasma expanding into air. The optical emission of the overlapped plasma is analyzed using an Echelle spectrometer equipped with an intensified CCD camera. The time dependence of optical emission intensities and of plasma parameters is investigated by varying the spectrometer delay time with respect to the laser pulse. The emission intensities of major (Fe, Zn) and minor (Mn, Al) elements are moderately increased with the RF plasma jet (≤2×). The intensities of atomic lines and molecular bands from ablated polymer material are increased also.

Effects of phase explosion in pulsed laser deposition of nickel thin film and sub-micron droplets

Nickel (Ni) thin films were deposited on glass substrates in high vacuum and at room temperature with third-harmonic or 355-nm output from a nanosecond Nd:YAG laser. At low laser fluence of 1J/cm2, the deposition rate was about 0.0016nm/shot which increased linearly until 4J/cm2. Above 4J/cm2, the onset of phase explosion in the ablation abruptly increased the optical emission intensity from laser-produced Ni plume as well as thin-film deposition rate by about 6×. The phase explosion also shifted the size distribution and number density of Ni droplets on its thin-film surface. On the other hand, the surface structures of the ablated Ni targets were compared between the scan-mode and the fixed-mode ablations, which may suggest that droplets observed on the thin-film surface were caused by direct laser-induced splashing of molten Ni rather than vapour-to-cluster condensation during the plume propagation.

Influence of excitation voltage waveform on dielectric barrier discharge plasma aerodynamic actuation characteristics

Plasma flow control, based on the plasma aerodynamic actuati on generated by air discharge, is an active field in aerodynamics due to its potential application in performance improvement of future aircraft. In order to better understand the underlying physical mechanism of plasma flow control, it is i mportant to investigate the relationship between the operating parameters and the plasma aerodynamic actuation characteristics. This paper reports the electrical, optical and mech anical characteristics of surface dielectric barrier discharge p lasma aerodynamic actuation excited by microsecond and nanosecond high voltage waveforms. The nanosecond discharge is more diffuser than the microsecond discharge and the discharge current is much larger at the same applied voltage amplitude. The optical emission intensity of the nanosecond discharge plasma is stronger than that of the microsecond discharge plasma, while the rotational and vibrational temperatures of N2 in the nanosecond discharge plasma are less. In addition, the relative intensity of the first negative system of N + 2 (B 2 � + u ! X 2 � + g ) and the second positive system of N2(C 3 �u ! B 3 �g) is much less in the nanosecond discharge plasma. The velocity measurements indicate that the air flow induced by the nanose cond discharge plasma aerodynamic actuation is vertical to the dielectric surface, while that induced by the microsecond discharge actuation is parallel to the dielectric surface.

High performance InGaN LEDs on Si (1 1 1) substrates grown by MOCVD

We report high performance InGaN multiple-quantum well (MQW) light-emitting diodes (LEDs) grown on Si (1 1 1) substrates using metalorganic chemical vapour deposition (MOCVD). A high-temperature thin AlN layer and AlN/GaN multilayers have been used for the growth of a high-quality GaN-based LED structure on Si substrates. Reduction of the high-temperature AlN layer thickness promotes the formation of a tunnel junction at the AlN/Si interface which reduces the LED operating voltage. Optical output power of the LED on Si saturates at a higher injected current density due to higher thermal conductivity of Si than that of a sapphire substrate. At a high injection current, output power of the LED on Si is higher than that of the LED on sapphire. Cross-sectional transmission electron microscopy (TEM) indicates that the active layer of these LEDs consists of a dislocation-free pyramid-shaped (quantum-dot-like) structure. Additionally, the crack-free thin-film LED epilayer region was transferred onto a copper carrier using metal-to-metal bonding and the selective lift-off technique. A LED with high output power, low operating voltage and low series resistance was realized by this technique. Furthermore, optimization of LED on Si by insertion of an Al0.06Ga0.94N/GaN strained-layer superlattice underlayer into the structure exhibits improved internal quantum efficiency (ηiqe) in the MQW, higher optical emission intensity with higher saturation current, lower operation voltage of 3.2 V at 20 mA and a series resistance of 16 Ω, as well as narrower electroluminescence spectra.

Optical-transition properties of the Nd 3+ ion in KLu(WO 4) 2 crystal

Optical absorption and emission intensities of Nd 3+ ion in KLu(WO 4) 2 crystal were investigated. Based on the Judd-Offelt theory, we calculated the following spectral parameters: phenomenological intensity parameters Ω 2=5.567×10 −20, Ω 4=3.597×10 −20, and Ω 6= 3.800×10 −20 cm 2. The radiative lifetime of levels 4F 3/2 was 182.58 μs. The fluorescence branching ratio for the transition 4F 3/2→ 4I 11/2 was 46.98%. In addition, the radiative transition probabilities A J,J', oscillator strengths P J,J' and the values of integrated emission cross sections were also calculated. In comparison with those of other laser crystals, these results indicated that Nd: KLuW is a promising efficient laser material.

Analysis of Plasma Wall Reactions Using Virtual Optical Emission Spectrometry Signal during Dielectric Etching

We confirmed that the SiN etch rate uniformity depends on not only the spatial distribution of the H radical density which is strongly affected by loss rates on chamber walls but also time-dependence of the loss rates. We developed a numerical simulation method for plasma–wall reactions to predict both the spatial distribution of the H radical density and the optical emission intensity observed from the view port during dielectric etching. In comparing experimental optical emission spectrometer (OES) data with virtual OES (our simulation), loss probabilities of the H radical on the Si, SiO2, and C–F polymer surfaces were estimated to be 0.5, 0.06, and 0.1, respectively. We successfully predicted SiN etch rates under various wall conditions by considering the spatial distribution and time-dependence of the loss probabilities.

Transient effects caused by pulsed gas and liquid injections into low pressure plasmas

The fast injection of liquid droplets into a glow discharge causes significant time variations in the pressure, the chemical composition of the gas and the phases present (liquid and/or solid along with gas). While the variations can be large and important, very few studies, especially kinetic studies, have been published. In this paper we examine the changes brought about in argon plasma by injecting Ar (gas), N2 (gas) hexane (gas) and hexane (liquid droplets). The changes in the RF capacitively coupled power (forward and reflected), electron and ion density (ne, ni), electron temperature (Te) and optical emissions were monitored during the injections. It was found that the Ar injection (pressure change only) caused expected variations. The electron temperature reduced, the plasma density increased and the optical emission intensity remained nearly constant. The N2 and hexane gas injections (chemical composition and pressure changes) also followed expected trends. The plasma densities increased and electron temperature decreased while the optical emissions changed from argon to the injected gas. These all serve to highlight the fact that the injection of evaporating hexane droplets in the plasma caused very little change. This is because the number of injected droplets is too small to noticeably affect the plasma, even though the shift in the chemical composition of the gas caused by evaporation from those same droplets can be very significant. The net conclusion is that using liquid droplets to inject precursors for low pressure plasmas is both feasible and controllable.

Experimental investigations on the propagation of the plasma jet in the open air

The fundamental of the generation and propagation of the atmospheric pressure nonequilibrium plasma jets has recently attracted significant interests. In this paper, investigations on the effects of the parameters of the pulsed dc voltages on the optical emission intensity of the plasma jet and the bullet propagation behavior are carried out based on the temporal-spatial resolved optical emission spectroscopy measurements and the high-speed photography. It is found that, with the increase in the applied voltage, the bullet propagates out from the nozzle earlier and accelerates to higher peak-velocities. The increase in the pulse frequency exerts no significant influences on the optical emission of the plasma jet and the bullet propagation velocity. But it can induce the bullet propagates out from the nozzle earlier. Besides, it is interesting to notice that, with the increase in the pulse width in the beginning, the bullet propagates out from the nozzle with longer delay time. However, when the pulse width is increased to be more than 100 μs, the delay time of the bullet propagating out from the nozzle becomes much shorter. On the other hand, with the increase in the pulse width, the optical emission intensity of the plasma jet drops and the maximum bullet velocity decreases too. Detailed analysis shows that it may be due to the accumulation of the charges and radicals, which can shorten the prebreakdown of the discharge inside the syringe and result in the bullet propagating out earlier from the nozzle.

Low-pressure indium-halide discharges for fluorescent illumination applications

Low-pressure gas discharges of molecular radiators were studied for fluorescent lighting applications with a goal of reducing the energy loss due to the large Stokes shift in phosphors of conventional mercury-based fluorescent lamp technology. Indium halides (InCl, InBr, and InI) were chosen as the molecular radiators that generate ultraviolet to blue light emissions. The electrical characteristics and optical emission intensities were measured in discharges containing gaseous indium halides (InCl, InBr, and InI) as molecular radiators. The low-pressure discharges in indium halide vapor showed potential as a highly efficient gas discharge system for fluorescent lighting application.

Controllable optical emission spectroscopy diagnostic system for analysis of process chemistries

Optical emission spectroscopy (OES) diagnostics have been employed for many years in plasma etch end point detection schemes. Unfortunately some newer process systems have much lower optical emission or limited optical access. To overcome such limitations, an OES diagnostic system making use of variable e-beam has been developed. That system is described and initial experimental results are presented. A strong correlation is observed between the optical emission intensity and e-beam current, a measurable electrical parameter. This correlation offers means to normalize optical signal and to be used as a feedback input to the electronics that control the plasma source. In addition there is a measurable response from the different lines due to energy of the electrons, indicating a new degree of freedom in the diagnostic that can be tapped for more precise analysis of end point.

Effect of neutron irradiation on electrical and optical properties of InGaN/GaN light-emitting diodes

InGaN/GaN multiquantum well light-emitting diodes (LED) with emission wavelength of 450 nm were irradiated with average energy of 9.8 MeV and dose of 5.5×1011 cm−2 neutrons. Right after irradiation, the forward current of the irradiated LEDs was decreased as a result of the creation of deep levels by the neutron-induced lattice displacement. However, unstable lattice damages resulting from the collisions with the incoming neutrons were removed at room temperature 6 days after the irradiation. The diode turn-on voltage, ideality factor, and optical emission intensity were recovered to preirradiated state by self-annealing process at room temperature.

Formation of ZnO nanostructures in energy-controlled hollow-type magnetron RF plasma

In this study, we investigated how zinc, sputtered from a zinc target, reacts with oxygen on the substrate to form ZnO nanostructures when the discharge parameters, such as gas flow ratio and target bias voltage, are controlled in O 2/Ar plasma. The deposits were estimated by SEM and Raman spectroscopy. Under conditions of a Zn to Ar optical emission intensity ratio of 2/1, a target voltage of − 550 V, a total pressure of 40 Pa, a substrate temperature of 150 °C, an RF power of 50 W, and a deposition time of 30 min, many vertically aligned ZnO nanorods were observed to be deposited on the substrate. The diameter of the rods was typically 50 nm. It was found that the film morphology can be controlled by the sputtering rate of zinc varied by the target bias voltage and gas flow rate.

The trend of electron temperature and electron density in the process of microcrystalline silicon solar cells

We measured the trend of the electron temperature in the SiH4/H2 plasma by monitoring the optical emission intensity ratio between Si ∗ (288 nm) and SiH ∗ (414 nm) and estimated the averaged electron density through plasma impedance measurement with a current–voltage monitor (ENI.INC, V–I probe). The plasma was generated between parallel plates by using VHF (40.68 MHz) power for Plasma Enhanced Chemical Vapor Deposition (PECVD). For various pressures and input powers, we analyzed the relation between the plasma parameters and the characteristics of the H 2-diluted silane plasma. From the analysis, the optimization of the μc-Si:H CVD process was suggested.

A two-dimensional cold atmospheric plasma jet array for uniform treatment of large-area surfaces for plasma medicine

For plasma treatment of inanimate surfaces and living tissues in medicine, it is important to control plasma–sample interactions and to mitigate non-uniform treatments of usually uneven sample surfaces so that effectiveness of application can be reproduced for different biological samples, relatively independently of their varying surface topologies and material characters. This paper reports a scalable two-dimensional (2D) array of seven cold atmospheric plasma (CAP) jets intended to achieve these two important requirements as well as to address the unique challenge of jet–jet interactions. While the CAP jet array can be configured to interact with a biological sample in either a direct mode (used with an in situ sample) or a remote mode (used as an afterglow), this study focuses on the direct mode. Using a downstream planar electrode as a sample model, the spatial distribution of reactive species and electrons delivered by individual jets of the 2D CAP jet array attains excellent uniformity. Specifically, the spatial variation over 100 μs is 5.6 and 7.9%, respectively, for wavelength-integrated optical emission intensity, and for atomic oxygen emission intensity at 845 nm when the oxygen admixture is 0.5% of the helium carrier gas. It is also shown that the highest emission intensity at 845 nm occurs at O2/He=0.5% under the best jet–jet uniformity conditions for O2/He=0.3–0.7%. These results indicate the potential of 2D CAP jet arrays for uniform treatment and for effective control of jet–jet interactions. Furthermore, spatial uniformity is accompanied by rich dynamics of jet–jet interactions and jet–sample interactions. Of the honeycomb-arranged seven CAP jets, the central jet is strongest in the negative half cycle, whereas the six surrounding jets (of uniform strength) are strongest in the positive half cycle. These dynamic features offer possible insights with which to better control jet–jet interactions and plasma–surface interactions in future.

In situ observation of nucleation by optical emission spectra in CVD diamond

Optical emission spectroscopy (OES) was used to in situ detect the intensity variation of C 2 radical with the deposition time in the boundary layer during homo-nucleation of CVD diamond by DC Arcjet Plasma. The obvious drop and fluctuation of the optical emission intensity were found during the early growth stage. The samples grown after selected deposition time were characterized by micro-structural probes (transmission electron microscope (TEM), high resolution electronic microscope (HREM), selected area diffraction (SAD) and electron energy loss spectra (EELS)), in order to determine the occurrence of the diamond nucleation. Based on the results of the OES and the micro-structural probes, it was revealed that the variation of the optical emission intensity corresponded to the diamond nucleation. The incubation period and the lasting time of nucleation were thus deduced as 6–8 min and 20–60 s depending on the concentration of CH 4 in H 2. The incubation period decreased and the lasting time of nucleation increased with the increase of the concentration of CH 4 in H 2.

Al-doped ZnO (AZO) films deposited by reactive sputtering with unipolar-pulsing and plasma-emission control systems

Al-doped ZnO (AZO) films were deposited on fused silica glass substrates unheated or heated at 200 °C by reactive dc sputtering using a Zn–Al alloy target with mid-frequency pulsing (50 kHz) and the plasma control unit with a feedback system of the optical emission intensity of the atomic O* line at 777 nm to control oxygen gas flow. The stable and reproducible depositions were successfully carried out in the transition region. The deposition rates attained in this study were about 10–20 times higher than the one by conventional sputtering using oxide targets. The AZO films with the lowest resistivity of 3.8 × 10 − 4 Ω cm was deposited on the substrate heated at 200 °C with a sputter power of 4 kW, where the deposition rate was 385 nm/min.

The effect of the CH 4 level on the morphology, microstructure, phase purity and electrochemical properties of carbon films deposited by microwave-assisted CVD from Ar-rich source gas mixtures

Carbon thin films were deposited on Si substrates by microwave-assisted chemical vapor deposition (CVD) using variable CH 4 levels in an Ar/H 2 (Ar-rich) source gas mixture. The relationship between the CH 4 concentration (0.5 to 3 vol.%) in the source gas and the resulting film morphology, microstructure, phase purity and electrochemical behavior was investigated. The H 2 level was maintained constant at 5% while the Ar level ranged from 92 to 94.5%. The films used in the electrochemical measurements were boron-doped with 2 ppm B 2H 6 while those used in the structural studies were undoped. Boron doping at this level had no detectable effect on the film morphology or microstructure. Relatively smooth ultrananocrystalline diamond (UNCD) thin films, with a nominal grain size of ca. 15 nm, were only formed at a CH 4 concentration of 1%. At the lower CH 4 concentration (0.5%), faceted microcrystalline diamond was the predominant phase formed with a grain size of ca. 0.5 µm. At the higher CH 4 concentration (2%), a diamond-like carbon film was produced with mixture of sp 2-bonded carbon and UNCD. Finally, the film grown with 3% CH 4 was essentially nanocrystalline graphite. The characteristic voltammetric features of high quality diamond (low and featureless voltammetric background current, wide potential window, and weak molecular adsorption) were observed for the film grown with 1% CH 4, not the films' grown with higher CH 4 levels. The C 2 dimer level in the source gas was monitored using the Swan band optical emission intensity at 516 nm. The emission intensity and the film growth rate both increased with the CH 4 concentration in the source gas, consistent with the dimer being involved in the film growth. Importantly, C 2 appears to be involved in the growth of the different carbon microstructures including microcrystalline and ultrananocrystalline diamond, amorphous or diamond-like carbon, and nanocrystalline graphite. In summary, the morphology, microstructure, phase purity and electrochemical properties of the carbon films formed varied significantly over a narrow range of CH 4 concentrations in the Ar-rich source gas. The results have important implications for the formation of UNCD from Ar-rich source gas mixtures, and its application in electrochemistry. Characterization data by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), visible-Raman spectroscopy and electrochemical methods are presented.