Spectroscopic Measurement of Electron Temperature and Density in an Argon Plasma Jet Based on Collisional‐Radiative Model

The present paper describes a spectroscopic method or determining electron temperature T_e and density N_e in an argon plasma jet on the basis of a Collisional‐Radiative model of argon. Electron temperature and density in the argon plasma were measured by the method developed, and comparison of them was discussed with those obtained with a Langmuir probe. The results or T_e and N_e obtained by the spectroscopic method agreed roughly with those by the probe.     

The dimension of the core and the tail of the plasma produced by laser ablating SiC targets

Optical emission of the plasma generated on SiC samples by pulsed laser beam from an Nd:YAG laser was used to investigate the spatial evolution of the electron temperature (Te) and density (Ne) of the plasma. The range and the profile of the plasma were characterized by the electron temperature Te and the electron density Ne, as functions of the distance from the SiC surface. It was found that the characterized spatial distribution closely coincided with the spatial images of the plasma recorded by a digital camera. The results obtained from the two different experimental measurements are consistent with other data from the literature, obtained either by models or experiments. The present result may give the insight to the complex physical phenomena in the thin film preparations using the pulsed laser deposition (PLD).     

Optical emission spectroscopy investigation of sputtering discharge used for SiOxNy thin films deposition and correlation with the film composition

The r.f. discharge of sputtering silicon target using argon-oxygen-nitrogen plasma was investigated by optical emission spectroscopy. Electronic temperature (T_e) and emission line intensity were measured for different plasma parameters: pressure (from 0.3 to 0.7 Pa), power density (0.6-5.7 W cm⁻²) and gas composition. At high oxygen concentration in the plasma, both T_e and the target self-bias voltage (V_b) steeply decrease. Such behaviour traduces the target poisoning phenomenon. In order to control the deposition process, emission line intensity of different species present in the plasma were compared to the ArI (λ = 696.54 nm) line intensity and then correlated to the film composition analysed by Rutherford Backscattering Spectroscopy.     

Electron impact ionization and excitation rate coefficients in the negative glow region of a glow discharge

Some easy to use reasonable approximations for electron impact rate coefficients have been considered. The most important rate coefficients for electron collisions in noble gases are electron-neutral ionization and electron impact excitation. Electron-neutral ionization besides electron impact excitation of some states of the argon and helium atom in direct current (dc) glow discharge plasma has been calculated. The plasma parameters of electron are significant factors for computing the rate coefficients. We present first results of probe diagnostic that includes the double probe measurements of the plasma parameters, namely, electron temperature (T_e) and electron density (n_e). Electron properties obtained from the double probe characteristic curves including T_e and n_e as well as the calculated rate coefficients (ionization and excitation) were studied as a function of the axial distance from the cathode while the discharge operating parameters of voltage and pressure were varied. Two regions of the glow discharge were investigated: cathode fall region and negative glow. Particular emphasis was placed on the negative glow region.     

Electron temperature determination in LTE and non-LTE plasmas

A method is presented for calculating electron temperatures (T_e) in dense plasmas, which does not assume equivalence with the excited level distribution temperatures (T_ex). The method involves the upper-level Saha ionization equation at the ionization limit, the limiting weighted population density (N_I/g_I) obtained from measured population densities and the experimentally obtained electron density. Electron temperatures calculated for 0.1-bar hydrogen and 1-atm helium and argon arcs are found to be up to twice as large as excited level distribution temperatures. For subatmospheric argon arcs, the calculated T_e are equivalent to the excitation temperature of the middle levels, but are two to three times smaller than the quoted T_ex for the highest levels. Reasons are discussed for the apparent invisibility of true electron temperatures and for differences between them and the excitation temperatures.     

Optical spectroscopic studies of titanium plasma produced by an Nd : YAG laser

We present optical emission characteristics of the titanium plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Q-switched Nd: YAG laser using laser induced breakdown spectroscopy (LIBS). The experimentally observed line profiles of neutral titanium (Ti I) have been used to extract the electron temperature (T _e ) using the Boltzmann plot method. The electron number density (N _e ) is calculated using the Stark broadening profile of 368.73 nm spectral line. Beside we have studied the spatial variation of electron temperature and number density as a function of laser energy for titanium plasma by placing the target material in air (at atmospheric pressure). We have determined the electron temperature and the electron number density along the axial position of the plasma plume.     

Quantitative surface analysis using ion-induced secondary ion and photon emission

The secondary ion and photon yield from a stainless steel target bombarded with Ar⁺ ions has been studied. The yields have been measured in a variety of oxygen background pressures. From the distribution of photon intensities, an effective arc temperature, T, for the bombarded surface has been derived. An empirical relationship has then been used to obtain the free electron density N_e, of the ion bombardment induced surface “plasma”. The derived values of (T, N_e) are then used in the Andersen-Hinthorne model, to calculate the changes in the Cr/Fe ratio as a function of the oxygen background pressure. The Cr/Fe ratio under the cleanest conditions available agrees very well with an electron microprobe measurement of the same ratio, while the changes in the Cr/Fe ratio as a function of oxygen pressure are consistent with electron spectroscopy studies of the changes in the Cr/Fe ratios in oxidised stainless steel.     

Electron density and temperature in the photoionized background gas (N2) surrounding a laser-produced plasma

An approach to obtain the electron density (N_e) and temperature (T_e) in nitrogen photoionized by radiation from a laser-produced plasma is described. The method is based on absolute intensities of the 3371 and 3914 Å bands and does not require quantitative knowledge of the photoionizing radiation. Applications are made using experimentally obtained data to find N_e and T_e.     

Optical emission studies of sulphur plasma using laser induced breakdown spectroscopy

We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T _e ) using the Boltzmann plot method, whereas the electron number density (N _e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased.     

Optical Emission Diagnostics of an U-Shaped Argon Stabilized d.c. Arc

The radial distribution of parameters has been measured by using the optical emission spectroscopy of an U-shaped argon stabilized low current arc at atmospheric pressure. All the measurements reported here were performed from a side-on observation direction by applying the Abel inversion routine. Radial distributions of apparent temperatures (T_exc., T_e, T_i, T_g) and of electron number density (n_e) for the plasma were measured, with and without presence of KCl (spectrochemical buffer). The measured data of n_e are compared to the theoretically calculated values of the equilibrium plasma composition. On the basis of the measured data, the validity of LTE concept is considered. It was found that deviation from LTE increases to the plasma periphery.     

Effect of neutral pressure on the He plasma flow measurement in a linear device

Axial and azimuthal flow velocities have been measured in a linear plasma device called NAGDIS-II (NAGoya DIvertor Simulator-II), along with plasma density and electron temperature, using a vector Mach probe composed of two Mach probes, one of which is for the axial flow, and the other is for the azimuthal flow. To study the effect of neutral pressure on the deduction of the Mach numbers, the ratio of upstream to downstream currents are measured by changing the neutral pressure for the deduction of flow velocities. Helium plasma was generated with pressure of 2–35 mTorr. Since the ion gyro-radius at the magnetic flux of 300 G is larger than the probe size, an unmagnetized collisionless Mach probe theory was used for the deduction of Mach numbers and their variations. In order to check the range of collisionality, plasma density (n_e = 10¹⁰–10¹¹ cm^?3) and electron temperature (T_e = 2–9 eV) are measured by a single electric probe using a conventional collisionless probe theory. Variations of Mach number, electron temperature and plasma density with collisionless models are to be compared with those using collisional models for different pressures where ionization and ion-neutral collision are included. Mach numbers by the collisionless model are found to be overestimated by 120% for the maximum difference even in weakly collisional plasmas. A clear flow reversal exists in the axial direction with higher pressure plasma, even in the linear machine. Azimuthal flows are also measured simultaneously along with axial flows, yet they seem to be very small in the present cold ion plasma (T_i/T_e << 1).     

Measurements of the spatially resolved electron temperature and plasma potential in ferrite-core side type Ar/He inductively-coupled plasmas

Spatial distributions of the effective electron temperature (T_eff) and plasma potential were studied from the measurement of an electron energy probability function in a side type ferrite-core inductively coupled plasma with an argon–helium mixture. As the helium gas was diluted at the fixed total gas pressure of 5 mTorr in an argon discharge, the distribution of the plasma density and plasma potential changed from a concave to a flat profile, and finally became a convex profile, while all spatial profiles of T_eff were hollow shapes with helium dilution in the argon discharge. This evolution of the plasma potential with helium gas could be explained by the increased energy relaxation length (λ_ε), indicating the transition of electron kinetics from local to non-local kinetics.     

Effect of ambient conditions on laser-induced breakdown spectra

The role of different ambient conditions on LIBS signal intensity was investigated for better understanding and performance of LIBS as a quantitative and qualitative analytical technique. For this purpose, the relative LIBS signal intensities were measured for a standard Cr line (520.8 nm) at different gas pressures of Ar, He, and air. The plasma was generated using a Q-switched pulsed Nd:YAG laser having wavelength of 1064 nm and pulse duration of 8 ns. The analysis revealed that the intensities of the spectral atomic Cr line (520.8 nm) were strongly enhanced under the argon environment in 10?C40 mbar range. The electron excitation temperature (T _e ) and number density (n _e ) were estimated by using a Boltzmann plot and a Stark broadening profile, respectively. For optimum dependence of LIBS, laser energy and pressure dependence was also studied. The electron temperature and number density showed an increase with increase in ambient gas pressure.     

Langmuir probe and optical emission spectroscopy studies for RF magnetron sputtering during TiON thin film deposition

Low-pressure plasma of gas mixture of Ar, O₂ and N₂ generated by RF magnetron sputtering was characterized by Langmuir probe and optical emission spectroscopy (OES). The electron temperature (T_e), ion density (n_i) and electron energy distribution function (EEDF) in Ar-O₂-N₂ plasma atmosphere were calculated from I-V characteristic of Langmuir probe. Boltzmann plot method was applied for calculating the vibrational temperature (T_vib) of the second positive system of N₂ (N₂SPS) in Ar-O₂-N₂ plasma. The T_e, n_i, EEDF and T_vib in Ar-O₂-N₂ plasma were studied as a function of O₂ percentages. It was found, the T_vib increased from 0.47 eV to 0.55 eV as the oxygen percentage in Ar-N₂-O₂ plasma increased from 10% to 40%. Further, the T_e increased from 1.6 eV to 3 eV as the O₂ concentration increased from 10% to 40%.     

Mode transition in magnetic pole enhanced inductively coupled argon plasmas

The electrical probe (Langmuir probe) diagnostics of different plasma parameters and operation regimes (E/H modes) of magnetic pole enhanced, inductively coupled (MaPE-ICP) argon plasmas are investigated. It is shown that uniform, high density (n _e ∼ 10¹² cm^-3) and low electron temperature (T _e ∼ 1.5 eV) plasma can be produced in low pressure argon discharges at a low power (100 W). It is found that an MaPE-ICP reactor operates in two different modes; capacitive (E mode) and inductive (H mode). No density jump or hysteresis are reported between these modes. The effect of pressure on transition power, where the mode changes from E to H mode at 20 sccm gas flow rate are studied and it is found that for all pressures tested (∼7.5 mTorr to 75 mTorr) the transition power remains same. In the inductive mode, the above plasma parameters show a smooth variation with increasing filling gas pressure at fixed power. The intensity of the emission line at 750.4 nm due to 2p ₁ → 1s ₂ (Paschen’s notation) transition, closely follows the variation of n _e with RF power and filling gas pressure. Measured electron energy probability function (EEPF) shows that electron occupation mostly changes in the high-energy tail, which enlightens close similarity of the 750.4 nm argon line to electron number density (n _e ). The behaviour of the electron energy probability function (EEPF) with regard to pressure and RF power in two operational modes is presented.     

电子回旋共振等离子体特性及其对生长氮化镓晶膜的影响

为了解并优化在电子回旋共振等离子体辅助化学汽相沉积GaN晶膜的工艺研究中的等离子体特性,利用朗缪尔探针及法拉第筒系统地测量了离子密度(N_i)、等离子体势(V_p)、电子温度(T_e)及离子流强(J_i)等多个等离子体参量随微波功率(P_w)及沉膜室气压(p)变化的关系.给出了在P_w＝850W,p＝0.22Pa时,上述等离子体参量的轴向及径向分布.GaN晶膜的生长速率、电学及晶体学性能 关键词：     

Supermode resonances in a multi-core holey fiber-based sensor

We report experimental research of the laser-produced indium plasma in hydrogen, argon and residual atmospheric ambient conditions. Note on general plasma behavior and morphology is presented. On the basis of intensity ratio of the two intense neutral resonance spectral lines (In I 410.2 nm and 451.1 nm), self-absorption was found to be almost negligible in case of argon environment at a pressure of 6650 Pa. Under these conditions, the first Stark widths (W) and shifts (d) measurements were performed as well. The resulting synthetic Lorentz profiles, based on the hyperfine structure of these two lines and corresponded W values, were calculated in order to reproduce measured W _m in case of particular electron temperature (T) and number density (N). These results should be of interest to the upcoming theoretical calculations concerning neutral indium spectral lines and also for various diagnostic applications.     

Optimal levels of oxygen deficiency in the visible light photocatalyst TiO2−x and long-term stability of catalytic performance

The dependence of the visible light-responsive photocatalytic activity of oxygen deficient TiO₂ (TiO_2−x) prepared by Ar/H₂ plasma surface treatment on the degree of oxygen deficiency (x) was assessed to determine the deficiency region associated with highest performance. The highest activity was obtained at x=0.06 (TiO_1.94). The maximum visible light activity for this material, estimated from the formaldehyde (HCHO) removal rate, was three times higher than that exhibited by nitrogen-doped TiO₂ (TiO_2−xN_x). The catalytic ability was found to decrease over the first week after fabrication of the material, after which it became stable, and the performance of TiO_2−x at this point was found to be nearly equal to that of TiO_2−xN_x. The results of ab initio calculations of density of states for TiO_2−x suggest that new oxygen deficiency states emerge at almost the exact center between the valence and conduction bands when x>0.06, which increases the recombination rate between electrons and holes. Therefore the declining performance of TiO_2−x at larger x values is attributed to the emergence of new oxygen deficient states.     

Hot-wire measurements of the electron thermal conductivity in a potassium plasma

The electron thermal conductivity λ_e of a potassium plasma is found by measuring the electron heat flux in a hot-wire device placed in a magnetic field. In the range 2300–3000 K, λ_e (W/mK) = 0.906 X 10¹⁰ T^-2_e exp(-3.2 X 10⁴/T_e) at a plasma pressure of 800 Pa and a gas temperature T_a = T_e/1.3.