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.     

Plasma dynamics from laser ablated solid lithium

Emission plasma plume generated by pulsed laser ablation of a lithium solid target by a ruby laser (694 nm, 20 ns, 3 J) was subjected to optical emission spectroscopy: time and space resolved optical emission was characterised as a function of distance from the target surface. Propagation of the plume was studied through ambient background of argon gas. Spectroscopic observations can, in general, be used to analyse plume structure with respect to an appropriate theoretical plasma model. The plume expansion dynamics in this case could be explained through a shock wave propagation model wherein, the experimental observations made were seen to fit well with the theoretical predictions. Spectral information derived from measurement of peak intensity and line width determined the parameters, electron temperature (T _e) and electron number density (n _e), typically used to characterise laser produced plasma plume emission. These measurements were also used to validate the assumptions underlying the local thermodynamic equilibrium (LTE) model, invoked for the high density laser plasma under study. Some interesting results pertaining to the analysis of plume structure and spatio-temporal behaviour of T _e and n _e along the plume length will be presented and discussed.     

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.     

Influence of the plasma parameters on the properties of aluminum oxide thin films deposited by laser ablation

The plasma produced by the ablation of a high purity Al₂O₃ target, using the fundamental line (1064 nm) of a Nd:YAG laser, was characterized. The laser fluence was varied in order to study its effect on the characteristics of the produced plasma as well as on the properties of the material deposited. Optical emission spectroscopy (OES) was used to determine the type of excited species present in the plasma. The mean kinetic energy of the ions and the maximum plasma density were determined from the time of flight (TOF) curves, obtained with a planar Langmuir probe. The obtained results reveal that the fast peak in the probe curve could be attributed to Al III, while the slow peak corresponds to the Al II. Aluminum oxide thin films were then deposited under the same conditions of the diagnosed plasma, in an attempt to correlate the plasma parameters with the properties of the deposited material. It was found that when Al II ion energies are lower than 461.0 eV the films deposited have structural characteristics similar to that of α-Al₂O₃, whereas at ion energies greater than 461.0 eV amorphous material was obtained.     

Pressure effects during pulsed-laser deposition of barium titanate thin films

2 , Ar) in a broad pressure range (10^-7–1 mbar) are correlated to the plasma expansion dynamics. It is found that the deposited films present an excess of Ba in the intermediate pressure range (10^-2<P<10^-1 mbar) and a peaked distribution of Ba to Ti atoms ratio, that is not related to either the substrate temperature or the nature of the gas environment. The results are discussed in terms of the dependence of the plume length (L_P) on the gas pressure and the existence of scattering processes for distances (d) from the target lower than L_P and the diffusion of the ejected species for L_P<d. Received: 7 November 1997/Accepted: 8 November 1997     

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.     

Experimental transition probabilities for several spectral lines arising from the 5d 6s{8s, 7p, 5f, 5g} electronic configurations of Pb III

Transition probabilities for 30 spectral lines, arising from the 5d¹⁰ 6s{8s, 7p, 5f, 5g} electronic configurations of Pb III (20 measured for the first time), have been experimentally determined from measurements of emission line intensities in a plasma lead induced by ablation with a Nd:YAG laser. The line intensities were obtained with the target placed in molecular argon at 6 Torr, recorded at a 400 ns delay from the laser pulse, which provides appropriate measurement conditions, and analysed between 200 and 700 nm. They are measured when the plasma reaches local thermodynamic equilibrium (LTE). The plasma under study had an electron temperature (T) of 21,400 K and an electron number density (N_e) of 7×10¹⁶ cm⁻³. The influence of self-absorption has been estimated for every line, and plasma homogeneity has been checked. The values obtained were compared with previous experimental values and theoretical estimates where possible.     

Diagnostics of Tin Plasma Produced by Visible and IR Nanosecond Laser Ablation

We present the optical emission spectroscopic studies of the Tin (Sn) plasma, produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Q switched Nd: YAG pulsed laser having pulse duration of 5 ns and 10 Hz repetition rate which is capable of delivering 400 mJ at 1064 nm, and 200 mJ at 532 nm using Laser Induced Breakdown Spectroscopy (LIBS). The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of four neutral tin (Sn I) lines at 231.72, 248.34, 257.15 and 266.12 nm were used to extract the electron temperature (T_e) using the Boltzmann plot method and determined its value 6360 and 5970 K respectively for fundamental and second harmonics of the laser. Whereas, the electron number density (N_e) has been determined from the Stark broadening profile of neutral tin (Sn I) line at 286.33 nm and determined its value 5.85 x 10¹⁶ and 6.80 x 10¹⁶cm^–3 for fundamental and second harmonics of the laser respectively. Both plasma parameters (T_e and N_e) have also been calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of laser-induced plasma plume: Comparison between Al and Al2O3 targets

Characterization of the plasma plume produced by laser ablation from Al and Al₂O₃ targets was carried out on the basis of the line profile analysis of Al(I) (²P°–²S) emission. The spatial distribution and density parameters of electrons and Al atoms in the plume were obtained by comparing observed spectral line profiles with a theoretical calculation. The results showed different behavior for the Al and Al₂O₃ targets. The Al atoms from the Al₂O₃ target were populated in a smaller region than those from the Al target. PACS 52.38.MF; 52.70.Kz; 52.25.Os     

Laser-based optical emission studies of barium plasma

We present the optical emission characteristics of the barium plasma produced at the surface of barium hydroxide Ba(OH)₂, also known as baryta, generated by the first harmonic (1,064 nm) of a Q-switched Nd:YAG laser. The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of neutral barium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density 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 energy. Besides, we have studied the variation of number density as a function of laser energy as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increase as laser energy increases.     

Kinetische Diagnose des Helium-Niederdruckfunkens

In a short spark discharge (energy release time < 0,5 μs) at pressures between 10 and 100 Torr a pure helium plasma was created and investigated by spectroscopic techniques. The following time dependent plasma parameters could be determined (0,5 ≦ t ≦ 5 μs): pressure p from hydrodynamic considerations, electron density n_e from the line profiles and gas temperature T_g from the Boltzmann population of the higher levels, i ≧. The population densities of the levels 3 and 4 deviated from the Boltzmann-T_g-straight line and thus indicated a strong disturbance of thermal equilibrium. For the determination of the electron temperature T_e an ionization rate equation was formulated, which took into consideration electron impact ionization, three body recombination and radiation recombination. The deviation from thermal equilibrium of the spark plasma was nearly constant in the investigated pressure-time region: the ratio T_g/T_e gave ≈ 0,06; the ration n_e/n_o was about 7 orders of magnitude below the corresponding Saha ratio.     

Direct observation of population inversion between Al+11 levels in a laser-produced plasma

Measured X-ray intensities of the resonance line series of Al⁺¹¹ in a laser-produced plasma shows population inversion between the n = 4,5 levels and the n =3 level at a plasma density N_e～10²⁰ cm^-3. The cooling of the expanding plasma leading to inversion is enhanced by a special target configuration. The gain coefficient in the 4 → 3 transition at 129.7 Å is estimated to be ～ 10 cm^-1, using both measured line intensities and numerical simulation.     

Lattice damage and Al-metal precipitation in 2.5 MeV-electron-irradiated AlH3

AlH₃ powder was bombarded with energetic electrons at 20 K and at room temperature and investigated by EPR, NMR, X-ray diffractometry, and microwave dielectric-constant measurements. The EPR spectra of the irradiated powder and of a selected single crystal cuboid of mm edge show a complex asymmetric line centered at g = 2.009, with a Curie-like temperature dependence, attributed to radiation-induced color centers and/or their agglomerates. At the same time, the grains, which have become shiny black after irradiation, exhibit an increase of both the real and the imaginary part of . ²⁷Al-NMR spectra of the irradiated powder present a Knight-shifted line at 1600(50) ppm, close to the position of bulk metallic Al, and corresponding to a concentration of c(Al) . In addition, the main hydride line differs from that before irradiation, demonstrating an alteration of environmental symmetry. The irradiation induces also a change in shape and width of the ¹H-NMR line, another indication of symmetry change in the lattice. Finally, a refined X-ray single-crystal structure analysis of the irradiated cuboid indicates a change of structure from trigonal R -3 c to R -3, with a loss of mirror symmetry for the two Al sites caused by the introduction of Al-defects in the vicinity of one of them. Received: 20 October 1997 / Revised: 24 December 1997 / Accepted: 30 January 1998     

Experimental Stark broadening studies of the CI transition 3s1P1o ? 3p1S0 at 833.5 nm

Experimental Stark broadening studies of the infrared CI transition 3s ¹ P ₁ ^o − 3p ¹ S ₀ at 833.5 nm are reported for the first time. A high-current wall-stabilized arc, operated in a mixture of helium, argon, carbon dioxide and hydrogen, was applied as the plasma source. Radiation emitted from homogeneous and optically thin plasma layers was analyzed. Stark broadening studies of the selected CI transition and the hydrogen Balmer β line were performed. As expected from theoretical considerations, the CI line width depends linearly on the electron density of the plasma. Applying theoretical Stark broadening data for the H _gb line, the measured Stark widths of the CI line were calibrated for the purpose of electron density determination in low temperature plasmas.     

Radio frequency excited waveguide CO2 lasers on sequence-band transitions

2 lasers based on either a quartz or an alumina waveguide were studied on the 00°2 - [10°1,02°1]_I,II sequence bands. A compact multisegment RF excitation with capacitive coupling was used for pumping the gain section of the laser waveguide. The use of a separate intracavity hot CO₂ waveguide suppresses the regular-band transitions. The quartz waveguide laser has a total of 62 lines lasing on both the 9.4 and 10.4 μm sequence bands. The alumina waveguide laser has 40 lines lasing on the 10.4 μm sequence band. These lasers can be either pulsed or continuous-wave (CW) operated on the selected line without a line jumping problem. Received: 29 September 1997/Revised version: 2 December 1997     

Evaluation of plasma produced by first and second harmonic nano-second laser for enhancing the capability of laser induced breakdown spectroscopy technique

Evaluation of plasmas produced and optimized for improving the capability of convenential laser induced breakdown spectroscopy (LIBS) for analytical purposes of solid samples is the main goal of the present work. The plasma produced in the present study was generated by focusing a single nano-second Nd:YAG laser at the fundamental wavelength of 1064 nm and at the second harmonic wavelength of 532 nm on an Al target in air at atmospheric pressure. The emission spectrum was recorded time resolved over the whole UV-NIR (200–1000 nm) spectral range. This work describes an extension of previously reported studies and focuses now on the determination of the plasma parameters at the optimum condition – highest signal-to-noise ratio (SNR) and minimum limit of detection (LOD) — of the LIBS technique, which is now widely applied to the elemental analysis of materials in atmospheric air. Parameters of the produced plasma in the time interval from 0 to 10 μs are determined for to further understanding the LIBS plasma dynamics. O I and Mn I spectral lines are used in the present work as thermometric lines for the determination of the plasma temperature based on Boltzmann plots. Stark broadening of lines yields the electron density. The widths of the H _α -line at 656.27 nm, of the O I line at 844.65 nm, of Al II lines at 281.65 nm and 466.30 nm and of the Si I line at 288.15 nm has been utilized for that. The plasma temperature ranged from 0.73 eV to around 1 eV for the different laser energies with both laser wavelengths for the optimized plasma used for LIBS analysis. This temperature is very close to that well known for the other spectrochemical analytical techniques or in excitation sources such as inductively coupled plasma-optical emission spectrometry (ICP-OES).     

EPR investigation of endofullerenes in solution

82 and Lu@C₈₂ were prepared by arc burning and subsequent HPLC purification. EPR spectra of Lu@C₈₂ could be interpreted as arising from unresolved hyperfine interaction with the I=7/2 nuclear spin of ¹⁷⁵Lu. At temperatures above 250 K, a thermally activated process, which is tentatively attributed to a hopping process of the encapsulated ion or to time-dependent population of close-lying electronic states, leads to pronounced line broadening. For the Ho@C₈₂ sample, no EPR signals could be detected, indicating a high spin state of this molecule. Spin relaxation data of N@C₆₀, which was prepared by ion bombardment, could be interpreted by assuming that collision-induced deformation of the carbon shell leads to a fluctuating zero-field splitting, sensed by the quartet spin state of the central encapsulated nitrogen atom. Received: 25 August 1997/Accepted: 6 October 1997     

Development of a target for laser-produced plasma EUV light source using Sn nano-particles

Nano-structured and tin-based targets have been fabricated by the pulsed-laser ablation method, in order to develop efficient and debris-free targets for the laser-produced plasma extreme ultraviolet (EUV) light source at 13.5 nm. Characteristic spectra that have the radiation peak around 13.5 nm were obtained from CO₂ laser produced plasma using the films as a target. A nano-structured target produced EUV light as intense as a bulk target and a narrower line spectrum at 13.5 nm than a bulk target. PACS 32.30.Rj; 52.38.-r; 52.38.Mf; 61.46.+w; 68.37.-d     

Temporal and spatial TaO emission generated from UV laser ablation of Ta and Ta2O5 in oxygen ambient

2 O₅ targets in oxygen ambient are presented. Line assignments indicate the presence of the excited Ta(I), Ta(II), and TaO in the plume. At higher oxygen pressure, a single peak appears in the TaO emission spectrum from the laser ablation of Ta while two peaks corresponding to a fast and a slow component of TaO emission are observed from the laser ablation of the Ta₂O₅ target by time-resolved emission spectroscopy. The delay times after laser pulse corresponding to two components of TaO emission from the laser ablation of Ta₂O₅ have been investigated as a function of oxygen pressure, laser fluence, and observation distance from the target surface. The two components of TaO emission could be attributed to different pathways for the generation of excited TaO molecules. A blast wave model is proposed to describe the behavior of the excited TaO in the plume of laser ablation of Ta₂O₅. Received: 1 February 1997/Accepted: 12 March 1997     

Spectroscopic studies of sodium nitrate plasma produced by nanosecond laser ablation

We present the optical emission characteristics of the sodium plasma produced at the surface of sodium nitrate (NaNO₃) also known as Chile saltpeter. We used a Q-switched Nd:YAG (Quantel Brilliant) pulsed laser having a pulse duration of 5?ns and 10?Hz repetition rate which is capable of delivering 400?mJ at 1064?nm and 200?mJ at 532?nm. The target material was placed in front of laser beam in air (atmospheric pressure). The experimentally observed line profiles of neutral sodium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying the distance from the target surface along the line of propagation of the plasma plume and also by varying the laser irradiance. Besides, we have studied the variation of number density as a function of laser irradiance as well as its variation with the distance from the target surface. It is observed that electron temperature and electron number density increase as the laser irradiance is increased.