Frequency Glow Discharge Optical Emission Research Articles

Metal-ceramic diffusion barrier nanocomposite coatings on nickel based superalloys for corrosion and high temperature oxidation resistance

Ceramic diffusion barrier coatings are inevitable in high temperature aerospace and nuclear applications to protect superalloys from oxidation and hot corrosion. Compositionally graded coating (CGC) of Ni-YSZ with five layers was deposited on an Inconel-690 substrate through electron beam physical vapor deposition (EBPVD) method. After heat treatment, the phase formation and crystallite determination in each layer of the CGC were studied by X-ray diffraction. Pulsed radio frequency glow discharge optical emission spectroscopy (RF-GDOES) showed outward diffusion of Ni towards the surface of the CGC. High resolution transmission electron microscopy (HRTEM) studies of the cross-sectional region of the heat-treated coating at 1273 K revealed no secondary phases within the coating as well as at substrate-coating interface. The corrosion behavior of Ni-YSZ coating under 3 M HNO3 medium showed that the heat-treated CGC of Ni-YSZ exhibited better corrosion resistance due to the formation of NiO than as-deposited Ni-YSZ coating.

Focussing and defocussing effects at radio frequency glow discharge optical emission spectroscopy analyses of thin films with partly nonconductive components

Abstract The application of radio frequency glow discharge optical emission spectroscopy for the investigation of the stability of different diffusion barriers for microelectronic applications against thermal diffusion of Cu is presented. Difficulties in the interpretation of the glow discharge results are overcome by performing an additional special experiment, where conductive and nonconductive parts are sputtered intentionally at the same time. As a consequence of the investigations, care must be taken, if glow discharge spectrometry is applied to samples with conductive and nonconductive components.

Combined Pulsed RF GD-OES and HAXPES for Quantified Depth Profiling through Coatings

Chemical characterization at buried interfaces is a real challenge, as the physico-chemical processes operating at the interface govern the properties of many systems and devices. We have developed a methodology based on the combined use of pulsed RF GD-OES (pulsed Radio Frequency Glow Discharge Optical Emission Spectrometry) and XPS (X-ray Photoelectron Spectroscopy) to facilitate the access to deeply buried locations (taking advantage of the high profiling rate of the GD-OES) and perform an accurate chemical diagnosis using XPS directly inside the GD crater. The reliability of the chemical information is, however, influenced by a perturbed layer present at the surface of the crater, hindering traditional XPS examination due to a relatively short sampling depth. Sampling below the perturbed layer may, however, can be achieved using a higher energy excitation source with an increased sampling depth, and is enabled here by a new laboratory-based HAXPES (Hard X-ray PhotoElectron Spectroscopy) (Ga-Kα, 9.25 keV). This new approach combining HAXPES with pulsed RF GD-OES requires benchmarking and is here demonstrated and evaluated on InP. The perturbed depth is estimated and the consistency of the chemical information measured is demonstrated, offering a new route for advanced chemical depth profiling through coatings and heterostructures.

Quantification of High Resolution Pulsed RF GDOES Depth Profiles for Mo/B4C/Si Nano-Multilayers

Pulsed-radio frequency glow discharge optical emission spectrometry (Pulsed-RF-GDOES) has exhibited great potential for high resolution (HR) depth profiling. In this paper, the measured GDOES depth profile of 60 × Mo (3 nm)/B4C (0.3 nm)/Si (3.7 nm) was quantified by employing the newly extended Mixing-Roughness-Information depth (MRI) model. We evaluated the influences of the thickness and sputtering rate on the depth profile of very thin layers. We demonstrated that a method using the full width at half maximum (FWHM) value of the measured time-concentration profile for determining the sputtering rate and the corresponding thickness was not reliable if preferential sputtering took place upon depth profiling.

Aluminum coating of twinning-induced plasticity plates via plasma-enhanced magnetron sputtering as a potential industrial technique

Challenges are encountered in the use of the conventional hot-dip galvanization process to deposit a protective layer on the surface of twinning-induced plasticity (TWIP) steel due to the low wettability, which is caused by manganese oxidation on the surface of the steel. In a vacuum environment and after conducting etching on the surface to remove surface oxides, corrosion-resistant aluminum (Al) coatings were prepared on the surface of TWIP steel via the hot-wire plasma-enhanced magnetron sputtering (PEMS) technique under various target and wire discharge currents (Ihot-wires/Itarget). The substrate ion current density at −50 V was as high as 0.88 mA/cm2 under a high hot wire discharge current of 20 A and a low target current of 3 A (20 A/3 A), which was 4 times the ion current under Ihot-wires/Itarget of 5 A/3 A, respectively. According to an analysis of the coatings via pulsed radio frequency glow discharge optical emission spectroscopy, Al, Fe and Mn elements diffused at the interface between the coating and steel substrate. The diffusion layers on both sides of the interface resulted in the Al coating remaining well adhered to the surface of the TWIP steel after Rockwell indentation, scratch testing and Erichsen cupping tests. As the sacrificial and passivated anode, the self-corrosion potential of the dense Al coating increased from −0.770 V of the TWIP steel to −0.471 V, and the corrosion current decreased from 3.91 × 10−4 A/cm2 to 6.14 × 10−5 A/cm2. The dense coating remained undamaged after electrochemical corrosion. Additionally, the structure of the TWIP steel was not affected by the PEMS coating processes.

Experimental measurement of deuterium concentration and depth profiling in tungsten by radio frequency glow discharge optical emission spectroscopy

For a detailed understanding of fuel retention characterization, especially in-depth profile analysis of plasma-facing materials, radio frequency glow discharge optical emission spectroscopy (RF-GDOES) method was applied to determine the deuterium depth concentration. Tungsten or titanium targets were co-deposited in deuterium atmosphere by magnetron sputtering, and these deposited films with different deuterium contents and film thicknesses were used as the standard samples for RF-GDOES measurement. Rutherford backscattering spectroscopy (RBS) and thermal desorption mass spectrometry (TDS) were used to measure the metal and deuterium concentrations in the standard films, respectively. After the standardization of deuterium concentration and sample sputtering rate when tested by RF-GDOES, deuterium concentration and depth profiling of deuterium-exposed tungsten samples were obtained and subsequently verified by compared with results by TDS. Results showed the deuterium concentration in deuterium-exposed tungsten has a high concentration peak about 0.002–0.013 at.fr. within 125 nm near-surface, and then reduced by two orders of magnitude from surface to depth with a minimum concentration of few 10−5at.fr. With increasing the incident deuterium fluence, deuterium concentration increased obviously in the first 6 μm near the surface. Under low incident fluence, the total released deuterium amounts obtained from RF-GDOES and TDS methods agree within the experimental error. However, the total released deuterium amounts measured by RF-GDOES were smaller than those of the TDS method under high fluence due to reason of the increasing diffusion depth and inhomogeneity of deuterium in tungsten.

Characterization of recrystallized depth and dopant distribution in laser recovery of grinding damage in single-crystal silicon

A nanosecond pulsed Nd:YAG laser was irradiated on a boron-doped single-crystal silicon wafer with a diamond grinding finish to recover the grinding-induced subsurface damage. In order to visualize and measure the depth of the laser melted/recrystallized layer, small-angle beveled polishing was performed in pure water followed by KOH etching. It enabled the direct observation of the recrystallized region using a differential interference microscope and the measurement of its depth using a white light interferometer. Crystallinity analysis of the recrystallized region was carried out by using laser micro-Raman spectroscopy, and the dopant concentration profile was characterized by using radio frequency glow discharge optical emission spectrometry (rf-GD-OES). The results showed that the crystallinity and boron distribution in the recrystallized region changed after laser recovery. The dopant concentration becomes higher at the boundary of the recrystallized region and the bulk. This study demonstrates the possibility of boron concentration control by using suitable laser parameters.

Nanometer‐Scale Depth‐Resolved Atomic Layer Deposited SiO2 Thin Films Analyzed by Glow Discharge Optical Emission Spectroscopy

In this contribution, pulsed radio frequency (rf) glow discharge optical emission spectroscopy (GDOES) is used to investigate the film properties of SiO2 deposited by plasma enhanced atomic layer deposition (PEALD), for example, the chemical composition, structural properties and film thickness. The total sputtering time until the interface between the SiO2 layer and the Si substrate is ≈13 s. The main impurities in the film, that is, H, C, and N, are detected. It is observed that both C and N intensities decrease with increasing plasma power during deposition of the thin film. The higher plasma power seems to increase the reactivity of the PEALD process and consequently, it might reduce the concentration of impurities in the deposited film. Moreover, the deviation of the GDOES sputtering rates on the film are related to the film density. The thickness of one‐hundred‐nanometer range SiO2 film is calculated from the GDOES silicon and oxygen emission profiles, and its difference from ellipsometry and X‐ray reflectivity measurements highlights the challenges for the GDOES technique for transparent thin films.

A simple and rapid method for determination of boron in fast breeder reactor components

The present paper describes a new analytical method developed for direct determination of boron in steels using radio frequency glow discharge optical emission spectrometer. “Single parameter alternative method” technique has been used to optimize the various experimental conditions of glow discharge plasma such as forward power, gas pressure inside plasma chamber, pre-integration time, and integration time. Different emission lines for boron were studied and inter element interference effect is also discussed in the paper. A complete statistical analysis has been done to validate the developed method. A RSD of less than ±5% is achieved for boron in the range of 0.0010–0.020% in Steels using this method.

Rapid Elemental Analysis of Aerosols Using Atmospheric Glow Discharge Optical Emission Spectroscopy.

A new, low-cost approach based on the application of atmospheric radio frequency glow discharge (rf-GD) optical emission spectroscopy (OES) has been developed for near real-time measurement of multielemental concentration in airborne particulate phase. This method involves deposition of aerosol particles on the tip of a cathode in a coaxial microelectrode system, followed by ablation, atomization, and excitation of the particulate matter using the rf-GD. The resulting atomic emissions are recorded using a spectrometer for elemental identification and quantification. The glow discharge plasma in our system was characterized by measuring spatially resolved gas temperatures (378-1438 K) and electron densities (2-5 × 1014 cm-3). Spatial analysis of the spectral features showed that the excitation of the analyte occurred in the region near the collection electrode. The temporal analysis of spectral features in the rf-GD showed that the collected particles were continuously ablated; the time for complete ablation of 193 ng of sucrose particles was found to be approximately 2 s. The system was calibrated using 100 nm particles containing C, Cd, Mn, and Na, respectively. The method provides limits of detection in the range of 0.055-1.0 ng, and a measurement reproducibility of 5-28%. This study demonstrates that the rf-GD can be an excellent excitation source for the development of low-cost hand-held sensors for elemental measurement of aerosols.

Quantitative reconstruction of the GDOES sputter depth profile of a monomolecular layer structure of thiourea on copper

High-resolution depth profiles of a thiourea (CH4N2S) molecular monolayer on a copper substrate obtained by radio frequency glow discharge optical emission spectroscopy (rf-GDOES) are quantified by the Mixing-Roughness-Information depth (MRI) model. Based on the molecular structure of the self-assembled thiourea layer, the measured intensity-sputtering time profiles of N, S, C and Cu are fitted to the MRI model results with an appropriate depth resolution function. The sputtering rate is determined accordingly, using two different approaches based on constant sputtering rate and on composition dependent sputtering rate. While the first approach requires an additional background for a fairly acceptable solution, the approach using a newly developed multielement dependent sputtering rate results in a complete and consistent reconstruction of all the measured elemental depth profiles. It is demonstrated that for depth profiling of the first few monolayers with rf-GDOES, the depth resolution Δz can be as low as 0.5nm, which is of the order of the theoretical limit.

塩化物系電解採取浴からの電析 Ni の明度，表面性状に及ぼす電解条件の影響

To investigate the effect of current density and pH in solution on the lightness and surface morphology of deposited Ni, Ni electrodeposition was performed at current density 100 to 500 A・m-2 and the amount of charge 7.2×105 C・m-2 in unagitated chloride solution of pH 1 to 3 at 333 K. The composition and structure of the surface of the deposits were analyzed by radio frequency glow discharge optical emission spectroscopy and three dimensional SEM. The lightness of deposited Ni decreased with increasing pH, and became to be minimum at 300 A・m-2. The concentration of the surface oxide of deposits increased with pH, and became high at 300 A・m-2, which shows that the surface oxide of the deposits causes the decrease in the lightness. On the other hand, the surface of the deposited Ni was composed of both the pyramid microcrystals of several micrometers and the hill formed by the aggregations of pyramid microcrystals. To separate the two structural units of the pyramid microcrystals and the hill, the deposits were cut every 200 nm from the top to the thickness direction in three dimensional SEM, and the number and area of deposits in the cutting plane were measured, as a result, it was found that the lightness of the deposited Ni depended on the surface structure. The lightness of deposited Ni seems to depend on both the surface oxide and the microstructure of deposits. [doi:10.2320/jinstmet.J2014033]

Structural properties of hydrogenated microcrystalline silicon–carbon alloys deposited by Radio Frequency Plasma Enhanced Chemical Vapor Deposition: Effect of microcrystalline silicon seed layer and methane flow rate

Hydrogenated silicon–carbon thin films were deposited by Radio Frequency Plasma Enhanced Chemical Vapor Deposition using silane–methane gas mixtures highly diluted in hydrogen. The effects of the presence of a microcrystalline silicon seed layer and of the methane flow rate during deposition were investigated in order to find the optimal conditions for microcrystalline growth. The presence of a seed layer promotes the amorphous to microcrystalline transition at the interface with the substrate, reducing the incubation layer to a 5–10nm thickness. At the same time, an excessive increase in the CH4 flow rate suppresses crystalline growth, leading to extremely flat amorphous samples (root-mean-square surface roughness ρRMS~0.5nm), even with a seed layer. The total carbon content was measured by Radio Frequency Glow Discharge Optical Emission Spectroscopy. It was found that carbon is only incorporated in the amorphous tissue, and not in the crystalline phase. Thus, the increase of the crystalline fraction, directly linked to the increase of the seed layer deposition time, leads to a decrease of the carbon incorporation in the subsequent layer.

Sputter depth profiling of Mo/B4C/Si and Mo/Si multilayer nanostructures: A round-robin characterization by different techniques

A round-robin characterization is reported on the sputter depth profiling of [60×(3.0nm Mo/0.3nm B4C/3.7nm Si)] and [60×(3.5nm Mo/3.5nm Si)] stacks deposited on Si(111). Two different commercial secondary ion mass spectrometers with time-of-flight and magnetic-sector analyzers, a pulsed radio frequency glow discharge optical emission spectrometer, and a home-built time-of-flight low-energy ion scattering and quadrupole-based secondary ion mass spectrometer were used. The influence of the experimental conditions, especially the type and energy of sputter ions, on the depth profiles of Mo/Si nanostructures with and without B4C barrier layers is discussed in terms of depth resolution, modulation factor and rapidity of analysis. The pros and cons of each instrumental approach are summarized.

Optical Interference During rf-GDOES Depth Profiling of Anodized Aluminum-Tantalum Alloy Films

The optical interference effect observed in radio frequency glow discharge optical emission spectroscopy (rf-GDOES) depth profiles of anodic oxide films formed on several aluminum-tantalum alloys is investigated and then used to determine refractive index, thickness, and composition of the anodized Ta-Al alloy layer. Refractive indices at the tantalum wavelength (1.4-2.4) were found to increase approximately linearly with the Ta2O5/Al2O3 ratio in the inner layer of the anodic oxide film. The optical interference effect was used to determine the composition of the inner film layer from the intensity/time rf-GDOES depth profile with excellent agreement with RBS-derived values. Good accuracy is obtained for constant sputtering rates and hence good interfacial depth resolution and for intensity signals oscillating uniformly across the film. A procedure is also proposed for calculating the thickness of the transparent layer of the anodic oxide film using the refractive index value derived from calibration plots of refractive index versus Ta2O5/Al2O3 ratio. The quantified depth profile of anodized Ta-24at.%Al alloy is presented. There is excellent accuracy of the quantified composition. The accuracy of the film depth, however, has a strong correlation with calculated density.

Analysis of molecular monolayers adsorbed on metal surfaces by glow discharge optical emission spectrometry

The pioneering study of Shimizu et al. (J. Anal. At. Spectrom., 2004, 19, 692) on the examination of adsorbed organic molecules on a copper substrate by radio frequency glow discharge optical emission spectrometry (rf-GDOES) displayed the potential of GDOES for determination of the orientations of molecular monolayers. Here, the study has been extended to the examination of thiourea adsorbed on silver, gold and copper surfaces and metal-centred molecular wires (MCMWs) of 4–6 nm length, with cobalt atoms in the middle of the chain adsorbed on a gold surface. According to established data, these molecules are adsorbed onto a metal surface through a sulphur atom. Depth profiling of thiourea adsorbed on the copper surface confirmed the results of Shimizu et al., with a nitrogen peak followed by a sulphur peak in the depth profile revealed with sputtering time. However, in the case of silver and gold substrates, the positions of the sulphur and nitrogen peaks in the depth profiles were not as predicted from the orientation of the thiourea molecule, i.e. the nitrogen peak followed the sulphur peak with sputtering time or the peaks overlapped. In the depth profiles of the adsorbed MCMWs, the sulphur peak appeared prior to the cobalt peak with sputtering time. Further, the time required for sputtering of thiourea and the wires are comparable, whereas the lengths of thiourea and the wire molecules differ by more than one order of magnitude. Thus, in this case, no correlation between the orientation of the molecules and the peak sequence in the depth profiles has been observed.

Rf‐GDOES analysis of composite metal/ceramic electroplated coatings with nano‐ to microceramic particles' size: issues in plasma sputtering of Ni/micro‐SiC coatings

AbstractNi matrix composite coatings reinforced with nano‐ and microceramic particles were analyzed by radio frequency glow discharge optical emission spectrometry (Rf‐GDOES). An interesting phenomenon related to the sputtering and excitation modes of this technique was observed. During plasma sputtering with Rf‐GDOES, the micro‐SiC particles were detached from metal matrix and did not contribute to the analytical signals. The same was not found in composite coatings containing nanoceramic particles. This anomalous behavior was confirmed by atomic force microscopy (AFM) investigation and scanning electron microscope (SEM) observations into Rf‐GDOES craters that showed the presence of residual non‐sputtered microparticles. Various attempts were done in order to minimize this problem, mainly by varying the analysis parameters of the used instrumentation, but without any relevant success. Some suggestions were then proposed for explaining the observed phenomenon, moreover possible solutions (e.g. by using a strong magnetic field or changing plasma gas to be more energetic) are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

Influence of Substrate Dislocation on Passivation of Pure Iron in pH 8.4 Borate Buffer Solution

The influence of substrate dislocations on the passivation behavior of pure iron in a pH 8.4 borate buffer solution was investigated. Cold-rolling was employed to induce dislocation in the annealed substrate. The dislocation density on the cold-rolled substrate depended on the reduction ratio (Red) and was maximum at . The electric charge consumed in the passivation and the passivity-maintaining current increased with an increase in the dislocation density. Electrochemical impedance spectroscopy revealed that the dislocation exposed to the iron surface increased the donor density in the passive film and reduced the charge-transfer resistance for the film aging. It was also demonstrated by radio frequency–glow discharge optical emission spectroscopy that a thick passive film formed on the cold-rolled iron compared with that on annealed iron. These results suggest that substrate dislocations enhance the reactions at the substrate/film interface, resulting in the formation of a highly defective passive film.

18O/16O isotopic separation in anodic tantala films by glow discharge time‐of‐flight mass spectrometry

AbstractGlow discharge mass spectrometry has been widely used for trace and ultra‐trace element analysis of high‐purity alloys. A novel pulsed radio frequency glow discharge time‐of‐flight mass spectrometer (rf GD TOFMS) has been developed that retains the pulsed radio frequency analytical ion source to provide ion signal enhancement due to processes involving Penning ionisation. A time‐resolved detection mode has been implemented to sample the afterglow regime of the pulse profile, corresponding to the highest ion signal intensities. Here, the performance of rf GD TOFMS in isotope differentiation is discussed. Anodic tantala films, comprising 18O‐rich layers of controlled thicknesses and locations, were formed by appropriate combination of anodising of tantalum in electrolytes enriched with 18O isotopes and of natural O isotopic abundance. Transmission electron microscopy (TEM) and radio frequency glow discharge optical emission spectrometry (rf GD OES) analyses were performed to examine the morphology and elemental distributions of the specimens, while the content of 18O in the 18O‐rich layers was determined by elastic recoil detection analysis(ERDA). In pulsed rf GD TOFMS analysis, characteristic ionic species formed in the glow discharge allows differentiation of 18O‐rich layers. Particularly, the location of 18O‐rich layers was determined from the 16O18O and Ta18O ion signals at masses m/z 34 and 199, respectively. The locations of 18O‐rich layers in anodic films, controlled by the selected anodising conditions, were probed precisely. The 18O profiles in anodic tantala were directly compared with those obtained by dual beam time‐of‐flight SIMS. Copyright © 2009 John Wiley & Sons, Ltd.

Oxidation behaviour of PACVD TiBN coating at elevated temperatures

The elevated-temperature oxidation behaviour of a TiBN coating on a plasma-nitrided hot-work tool steel (DIN 1.2367) by means of plasma-assisted chemical vapour deposition (PACVD) was investigated under the condition where a coated die would be preheated prior to being mounted on the press for aluminium extrusion. The TiBN coating was found to possess good resistance to oxidation up to 400 °C. Rapid oxidation started to occur at 450 °C. Radio frequency glow discharge optical emission spectroscopy (rf-GDOES) indicated that the oxidised layer was thickened from 100 nm to 1.0 μm, as the soaking time at 500 °C was prolonged from 2 to 16 h, which was attributed to the high temperature that promoted the penetration of oxygen into the coating. rf-GDOES also showed that boron initially in the coating vanished from the oxidised layer when the temperature was 450 °C or higher. X-ray diffractometry confirmed that the oxidised layer was composed mainly of TiO 2. SEM revealed that the TiO 2 layer was pulverised, leaving many microcracks and cavities, as a result of the losses of boron oxide and nitrogen. The rapid oxidation at above 450 °C was attributed to the pulverised TiO 2 layer that was unable to hinder the diffusion of oxygen into the coating. It is therefore recommended to apply a protective gas during the preheating of the TiBN-coated die for aluminium extrusion. Alternatively, an advanced TiBN coating with enhanced resistance to oxidation must be developed, which will be conducive to its application for aluminium extrusion dies.