Optical Emission Spectroscopy Spectra Research Articles

Nanosecond pulsed laser cleaning of titanium alloy oxide films: Modeling and experiments

Nanosecond pulsed laser cleaning is an indispensable green technology. A three-dimensional (3-D) finite element model (FEM) was used to predict the surface temperature during laser cleaning. Then, the macroscopic morphology of the FEM that was obtained was verified using digital ultra-depth-of-field microscopy (OM). Finally, the variation in the surface morphology with the maximum power density (F), x-axis spot overlap ratio (Ux), and y-axis spot overlap ratio (Uy) was determined using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The change in surface composition was analysed using X-ray photoelectron spectroscopy (XPS), and optical emission spectroscopy (OES) was used to monitor laser cleaning. Transmission electron microscopy (TEM) was used to analyse the surface secondary oxidation thickness. The original surface consisted of titanium oxides (Ti4+ and Ti3+) and organics. The Ti0 peak was enhanced, and the O content was reduced after laser cleaning. Therefore, the laser-cleaning effect was clear. The surface was smooth without cracks when the maximum power density and the spot overlap ratio were set to 31.85 MW/cm2 and 80 %, respectively. A dense and uniformity oxide film, 29 nm thickness, was formed on the surface of TA15 titanium alloy after laser cleaning. Changes in F, Ux, and Uy caused noticeable changes in the Ti I and Ti II peaks in the OES spectra, which were used to monitor laser cleaning.

The Correlation of Plasma Characteristics to the Deposition Rate of Plasma Polymerized Methyl Methacrylate Thin Films in an Inductively Coupled Plasma System

A plasma system attached with one internal coil (for generating inductively coupled plasma) and two sputtering carbon targets was set up to deposit PP-MMA (plasma polymerized methyl methacrylate) thin films. PP-MMA was used as a model material in the present study. In the experiment, the working pressure and Ar/MMA flow ratio were varied, which resulted in the change in plasma conditions as well as the deposition rates. The optical emission spectroscopy (OES) method was applied to identify the presence of the excited species related to the fragmented monomer. In addition, the electron temperature and electron density were determined using the modified Boltzmann plot and line-ratio method, according to the measured OES spectra. The deposition rate of the PMMA film was then correlated with the determined plasma characteristics. To determine the vibrational modes of the deposited PP-MMA films, Fourier transformed infrared spectrometry (FTIR) was used. The highest deposition rate of PP-MMA could be obtained with the optimized working pressure and Ar/MMA volume ratio. This could be related to the plasma characteristics that contribute to the fragmentation of the monomer in the plasma.

Application of Spectroscopic Analysis for Plasma Polymerization Deposition onto the Inner Surfaces of Silicone Tubes

In the current study, plasma-polymerized methyl methacrylate (PP-MMA) generation on the inner surface of a silicone tube was performed in a capacitively coupled discharge reactor. The possibility of generating plasma inside the tube was analyzed and calculated by using optical emission spectroscopy (OES). A hollow cathode model was first proposed to determine whether plasma discharge would be generated inside the tube in the low-pressure regime. Since the ignition of plasma inside the tube is necessary for the initiation of polymerization processes, the sheath thickness was calculated analytically. To achieve the goal, the electron temperature and density of plasma should be determined beforehand. In this study, the electron temperature and plasma density were measured and calculated according to OES spectra using both the modified Boltzmann plot and the line-ratio method. The results reveal that the occurrence of plasma inside the tube can be achieved if the tube’s inner diameter is greater than two times the thickness of the sheath. The effect of methyl methacrylate (MMA) monomer concentration on sheath thickness, and, hence, plasma generation and deposition, was investigated in the presence of argon plasma and MMA monomer. According to the study, one could control the ignition of plasma discharges inside the tube followed by plasma polymerization deposition. The OES method was also applied to identify the presence of the excited species related to the fragmented monomer. The deposition of PP-MMA films on the inner surface of the tube was confirmed via attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy.

Optical Emission Spectroscopy as a Diagnostic Tool for Characterization of Atmospheric Plasma Jets

A suitable technique for localized surface treatment of solid materials is an atmospheric pressure plasma jet (APPJ). The properties of the APPJ plasma often depend on small details like the concentration of gaseous impurities what influences the surface kinetics. The simplest and often most useful configuration of the APPJ is presented, characterized by optical emission spectroscopy (OES), and results are discussed in view of various papers. Furthermore, results of additional recent papers on the characterization of the APPJ by OES are presented as well. Because the APPJ is operating at atmospheric pressure, even the water vapor traces may significantly alter the type and concentration of reactive species. The APPJ sustained in noble gases represents a source of vacuum ultraviolet (VUV) radiation that is absorbed in the surface of the treated material, thus causing bond scission. The addition of minute amounts of reactive gases causes significant suppression of VUV radiation and the formation of reactive radicals. These radicals such as OH, O, N, NO, O3, and alike interact chemically with the surface causing its functionalization. Huge gradients of these radicals have been reported, so the surface finish is limited to the area reached by the radicals. Particularly OH radicals significantly prevail in the OES spectra, even when using very pure noble gas. They may cause suppression of other spectral features. OH radicals are especially pronounced in Ar plasmas. Their density decreases exponentially with a distance from the APPJ orifice.

In vitro antiproliferative activity of cold atmospheric plasma on small-cell lung carcinoma

Background: Cold plasma is shown to inhibit the cancer cell growth. Manipulation of different plasma parameters might have influence on the production of major reactive species which leads to killing of the cancer cells. Antiproliferative activity of cold atmospheric pressure plasma jet was investigated on small-cell lung carcinoma BHY cell line (squamous cell carcinoma) under different in vitro conditions. Methods: A homemade plasma jet was designed and created using pure helium gas. To identify the species created by the plasma jet, optical emission spectroscopy (OES) was employed. Next, the effect of plasma jet was examined on lung cancer cell survival by MTT assay and the effects of main parameters were evaluated on plasma performance. In this favor, various treatment times including 60, 90, 120, 180, and 300 s in combination with different voltages of 5, 11, and 14 kV were investigated, and the results were analyzed at 2, 24, and 48 h after exposure to plasma. Results: Predominant species of OES spectra were O, OH, N2+, and N2. Results of MTT assay indicated a dramatic reduction in cell viabilities in both dose- and time-dependent manners, and more than 75% of cancer cells were died after 48 h at 180 s of plasma treatment. Conclusion: The homemade plasma jet can chiefly contribute to the production of reactive oxygen and nitrogen species (reactive oxygen species and reactive nitrogen species) and can induce apoptosis in small-cell lung carcinoma BHY cell line.

Synthesis of fluorescent carbon via atmospheric pressure plasma pyrolysis of waste expanded polystyrene

The lack of proper waste management systems in various countries often results in a continual volume increase of plastic waste which when left unkempt may be detrimental to the environment. Plasma pyrolysis provides a possible solution to the problem of increasing polymeric waste by transforming polymers into reusable hydrocarbons and residual carbon at much lower temperatures compared to high temperature pyrolysis methods. The study analyses the resultant carbon as a result of the plasma pyrolysis of waste expanded polystyrene (WEPS) via industrial nitrogen plasma exposure for 20 min under varied flow rates (10, 13, 15 standard cubic feet per hour). From the optical emission spectroscopy spectra, the presence of C, O, and N ions were identified which indicates the possible presence of light-weight hydrocarbons as well as CO in the plasma. The residual solids were analyzed using X-ray diffraction, scanning electron microscope, and Raman spectroscopy which showed that the process was able to successfully produce carbon at lower temperatures and fluorescent carbon at higher temperatures from the decomposition of WEPS.

Effects of hydrogen addition in nitrogen atmospheric pressure plasma on its optical and electrical properties and silicon-based deposits compositions

Si-based coatings were deposited with a cold plasma jet (Plasmabrush® PB1 from Reinhausen Plasma) at atmospheric pressure with nitrogen as main carrier gas and hexamethyldisilazane (HMDSN) as precursor. Effects of hydrogen addition on the plasma characteristics and the coatings compositions have been evidenced with optical emission spectroscopy (OES), power measurements and XPS in-depth analyses. The intensity evolution of the nitrogen line (at 315.9 nm) with the applied voltage has a sigmoid shape for the pure nitrogen plasma but a quite linear one with hydrogen addition (up to 3%). Based on OES spectra, the presence of the NH specie in the nitrogen-hydrogen plasmas has been evidenced (around 336.0 nm) but not in the pure nitrogen plasmas. Although the plasma power is similar for both gases, the nitrogen atomic concentrations in the films as evidenced by XPS were lower with the nitrogen-hydrogen plasmas than with the pure nitrogen plasmas indicating a chemical effect of the presence of hydrogen in the plasma.

Analysis of the impact of different additives during etch processes of dense and porous low- k with OES and QMS

The focus of this paper is the impact of CF 4 based plasma etch processes with the additives argon and C 4F 8 on material properties and geometrical parameters of etched trenches using dense and porous SiCOH. Argon and C 4F 8 were added to change the radical to ion composition and to shift the carbon to fluorine ratio, respectively. With several techniques, FTIR, spectral ellipsometry and contact angle measurements, modifications in the structure of the materials and their surface conditions were analyzed. To understand the influences of the additives on the plasma conditions, optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS) were used to estimate the composition of the plasma in situ. For the additive argon, a slightly enhanced etch rate and an increased refractive index due to serious plasma damage for porous SiCOH was observed. At higher Ar flow rates peaks of Si 2O 4H x clusters in the QMS spectra and increased CO and O lines, measured with OES, indicate a higher sputter yield on the SiCOH network. SEM cross-sections show, that argon has no effect on the sidewall geometry of etched trenches. A higher CH/CN line in the OES spectra indicates an enhanced sputter effect of the SiCN films in via bottoms. For C 4F 8 addition results of spectral ellipsometry show a decreased etch rate and refractive index. Using FTIR the formation of a polymer film on the surface was observed. Higher C 2 lines in the OES spectra are indications of enhanced polymerization efficiency. Finally, the addition of C 4F 8 decreases the etch rate in the trench sidewalls and therewith assumedly the sidewall damage.

Characteristics of nitrogen-incorporated silicon oxycarbide films and plasmas for plasma enhanced chemical vapor deposition with TMOS/N 2/NH 3

Plasma enhanced chemical vapor deposition of nitrogen-incorporated silicon oxycarbide thin films obtained from the gas mixture of TMOS (tetramethoxysilane), N 2, and NH 3 is studied. The effects of the TMOS to N 2 pressure ratio on the properties of the film and the plasma are investigated. The deposited films are analyzed by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy (FTIR), and by X-ray photoelectron spectroscopy (XPS). The plasma is characterized by using optical emission spectroscopy (OES). The mass spectra of the constituents in the plasma are obtained by quadrupole mass spectroscopy. The correlation between the film properties and the plasma characteristics is explained wherever possible. As the partial pressure of N 2 is decreased, the refractive index begins to decrease, reaches a minimum, and then saturates. The FTIR absorption bands are observed from about 850 to 1000 cm −1 and from 1000 to 1250 cm −1, and can be attributed to the formation of a nitrogen-incorporated silicon oxycarbide thin film. The variation of the refractive index is discussed in relationship with the deposition rate, the OES spectra, the mass spectra of the plasma, the film composition obtained by XPS, and FTIR spectra.

Electrical and structural properties of nano-crystalline silicon intrinsic layers for nano-crystalline silicon solar cells prepared by very high frequency plasma chemical vapor deposition

Thin silicon intrinsic layers were deposited in the amorphous to nano-crystalline transition regime to investigate their structural and optoelectrical properties using the very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique. Optical emission spectroscopy (OES) was primarily used to monitor the plasma properties during the deposition. The ratio H α / Si * , estimated from OES spectra, is closely related to the microstructure of the films. With the increasing plasma power from 10 to 50 W, the ratio H α / Si * increases leading to nano-crystalline films. The ratio H α / Si * decreases with the increase of process gas pressure at constant power of 15 and 30 W. The films were nano-crystalline at low pressure and became amorphous at high pressure.

Modification of ink-jet paper by oxygen-plasma treatment

A study on oxygen-plasma treatment of ink-jet paper is presented. Paper was exposed to a weakly ionized, highly dissociated oxygen plasma with an electron temperature of 5 eV, a positive-ion density of 8 × 1015 m−3 and a density of neutral oxygen atoms of 5 × 1021 m−3. Optical emission spectroscopy (OES) was applied as a method for detection of the reaction products during the plasma treatment of the paper. OES spectra between 250 and 1000 nm were measured continuously during the plasma treatment. The wettability of the samples before and after the plasma treatment was determined by measuring the contact angle of a water drop. The appearance of the surface-functional groups was determined by using high-resolution x-ray photoelectron spectroscopy (XPS), while changes in the surface morphology were monitored with scanning electron microscopy (SEM). Already after 1 s of the plasma treatment the surface, which was originally hydrophobic, changed to hydrophilic, as indicated by a high absorption rate of a water drop into the paper. The OES showed a rapid increase of the CO and OH bands for the first few seconds of the plasma treatment, followed by a slow decrease during the next 40 s. The intensity of the O atom line showed reversed behaviour. The XPS analyses showed a gradual increase of oxygen-rich functional groups on the surface, while SEM analyses did not show significant modification of the morphology during the first 10 s of the plasma treatment. The results were explained by degradation of the alkyl ketene dimer sizing agent during the first few seconds of the oxygen-plasma treatment.

Optical and electrical characterization of an atmospheric pressure microplasma jet for Ar∕CH4 and Ar∕C2H2 mixtures

A rf microplasma jet working at atmospheric pressure has been characterized for Ar, He, and Ar∕CH4 and Ar∕C2H2 mixtures. The microdischarge has a coaxial configuration, with a gap between the inner and outer electrodes of 250μm. The main flow runs through the gap of the coaxial structure, while the reactive gases are inserted through a capillary as inner electrode. The discharge is excited using a rf of 13.56MHz, and rms voltages around 200–250V and rms currents of 0.4–0.6A are obtained. Electron densities around 8×1020m−3 and gas temperatures lower than 400K have been measured using optical emission spectroscopy for main flows of 3slm and inner capillary flows of 160SCCM. By adjusting the flows, the flow pattern prevents the mixing of the reactive species with the ambient air in the discharge region, so that no traces of air are found even when the microplasma is operated in an open atmosphere. This is shown in Ar∕CH4 and Ar∕C2H2 plasmas, where no CO and CN species are present and the optical emission spectroscopy spectra are mainly dominated by CH and C2 bands. The ratio of these two species follows different trends with the amount of precursor for Ar∕CH4 and Ar∕C2H2 mixtures, showing the presence of distinct chemistries in each of them. In Ar∕C2H2 plasmas, CHx species are produced mainly by electron impact dissociation of C2H2 molecules, and the CHx∕C2Hx ratio is independent of the precursor amount. In Ar∕CH4 mixtures, C2Hx species are formed mainly by recombination of CHx species through three-body reactions, so that the CHx∕C2Hx ratio depends on the amount of CH4 present in the mixture. All these properties make our microplasma design of great interest for applications such as thin film growth or surface treatment.

Optical emission spectroscopy characterization of oxygen plasma during treatment of a PET foil

Optical emission spectroscopy (OES) analysis of inductively coupled RF oxygen plasma during plasma treatment of a 23 µm thick polyethylene terephthalate (PET) foil is presented. Plasma was generated in pure oxygen at a pressure of 75 Pa with a RF generator at a frequency of 27.12 MHz and an output power of 300 W. The electron temperature was about 6 eV, the density of charged particles about 1016 m−3 and the density of neutral O atoms about 1022 m−3. Spectra were measured in the range from 250 to 950 nm by means of an optical spectrometer. For the first 10 s of plasma treatment the OES showed the presence of oxygen radicals only. Later, the OES spectra became richer with significant emission from CO and OH, which was attributed to PET oxidation. Simultaneously, the O peaks decreased significantly. After prolonged plasma treatment, the O peaks recovered, the CO band vanished while the OH and H peaks still persisted. In the final period of the treatment only atomic oxygen lines remained. The results showed that OES analysis was a powerful method for studying the evolution of PET oxidation by plasma treatment.

Characterization of remote inductively coupled CH4–N2 plasma for carbon nitride thin-film deposition

We investigated reaction characteristics in a CH4∕N2 plasma for deposition of amorphous CNx thin films (a-CNx) by evaluating the change in electron density using the wave cutoff method, and the behavior of ions and radicals with an optical emission spectroscopy (OES). An inductively coupled plasma source that was 30cm away from the substrate stage was used for the discharge. The change in electron density in the substrate region and OES spectra in the plasma-source region were evaluated to investigate both the reaction mechanism and the remote effect while varying process conditions such as rf power, pressure, and gas-mixing ratio. We found that the electron density in the remote CH4∕N2 plasma was closely related to recombination reactions of major ions such as N2+, CH4+, CH3+, and H2+ during diffusion from the plasma source to the substrate. The electron density and optical emission of major ions and radicals in the CH4∕N2 plasma increase at higher rf power. The ratio [N]∕([N]+[C]) in a-CNx films, as measured by auger electron spectroscopy, also increases with rf power since more excited N and C species are generated. For increasing pressure, the change in electron density and emission spectra showed different behavior, which arose from recombination of ions that generated more CH4, Nx (x=1,2), and CN radicals. The majority of positive ions generated from N2 species are greatly affected by the remote effect, while the majority of positive ions generated from CH4 species are not significantly influenced, since each species has different losses dependent on the pressure. A higher N2 gas fraction in the gas mixture generated more CN radicals, which resulted not only in more N incorporated into a-CNx films but also to a reduction of H passivation that retards formation of hybrid bonding between C and N in the films. These results suggest that efficient H abstraction is required to achieve more NC triple bonding in CH4∕N2 plasma deposition.

Optical-quality diamond growth from CO2-containing gas chemistries

Abstract From interpretation of the Bachmann diagram, it is conceivable that there may be some advantage to be gained by moving up the H–CO tie line for optical-quality diamond deposition. A convenient system for achieving this are gas chemistries containing CO 2 , which, when combined with gases such as CH 4 and C 2 H 4 (ethylene), enables the diamond deposition region to be traversed and, with the addition of hydrogen, to move along the H–CO tie line. The fabrication of free-standing diamond wafers using combinations of these feed-stock gases with a high-pressure, 2.45-GHz microwave source reactor (HPMS) able to operate at up to 140 Torr and 6 kW has been investigated. The FWHM line width of the 1332 cm −1 Raman peak is found to be predominately a function of the gas composition. The growth rate is also dependent on the input power and the deposition pressure. The deposition plasmas are bright green in colour, and optical emission spectroscopy (OES) of the plasma reveals distinctive C 2 and H α peaks. In some cases, it is possible to correlate characteristics of the deposited diamond layer to features in the OES spectra.

Optical emission spectroscopy of H2–CO and H2O–CH3OH plasmas for diamond growth

Optical emission spectroscopy (OES) was used as a diagnostic tool to determine diamond growth in our rf plasma chemical vapor deposition systems. Diamond was grown with a conventional H2–CO source gas and in a low pressure system using a water–methanol source. Optical emission spectra were recorded between the wavelengths of 2000 and 8000 Å for both the systems. The OES spectral peak ratios of Hα to certain carbon radicals are an indicator of diamond growth in H2–CO plasmas. In particular, both the growth rate and morphology showed a correlation with Hα to certain carbon radical ratios in H2–CO discharges. The OES spectra in the water–methanol plasma are quite different than in the H2–CO plasma. Different species are represented and the intensity of the common peaks is much higher than in the H2–CO plasma.