•He detection by LIBS method was investigated in He containing Be coatings.•At optimized conditions, 2.8 % of He was confidently detectable with LOD 0.7 %•There was an upper limit of 20 mbar Ar ...background pressure for reliable He detection.•He detection was limited due to the He line broadening and increased noise.•Very high excitation energy of He atom complicates the application of CF-LIBS.
Laser Induced Breakdown Spectroscopy (LIBS) method is considered to be a promising tool for analyzing the retention of hydrogen isotopes (D and T) and helium (He) on the first walls and divertor regions of future fusion reactors. Helium will be produced in DT reactions but could also be used in the initial non-nuclear phases of DEMO concepts. The present study investigates the He detection by LIBS method in the Be coatings simulating the deposits on the divertor plasma-facing components of JET while the results are also relevant for He detection in the deposits of other wall materials. The study was carried out in a vacuum vessel filled with 2–40 mbar argon background gas. It was shown that 2.8 at. % of He was confidently detectable by LIBS at optimized measurement conditions and the estimated limit of detection at used experimental conditions is approximately 0.7 at. %. The intensity of the He emission line at 587.56 nm was the strongest at the center of the laser-induced plasma plume. The He line intensity increased with the pressure of Ar gas but the broadening of the He line and the increase of the background emission and noise set an upper limit to the Ar background pressure usable for He detection. The application of the calibration-free LIBS procedure resulted in the overestimation of the He/Be ratio by several orders of magnitude. The overestimation can be explained by the deviation of LIBS plasma from the local thermodynamic equilibrium, which is caused by the very high excitation energy of He atoms.
Direct current (DC) and radio frequency (RF) magnetron sputtering methods were selected for conducting the deposition of structural materials, namely ceramic and metallic co-depositions. A total of ...six configurations were deposited: single thin layers of oxides (Cr2O3, SiO2) and co-deposition configurations (50:50 wt.%) as structural materials (W, Be)—(Cr2O3, SiO2), all deposited on 304L stainless steel (SS). A comprehensive evaluation such as surface topology, thermal desorption outgassing, and structural/chemical state was performed. Moreover, mechanical characterization evaluating properties such as adherence, nano indentation hardness, indentation modulus, and deformation relative to yielding, was performed. Experimental results show that, contrary to SiO2 matrix, the composite layers of Cr2O3 with Be and W exhibit surface smoothing with mitigation of artifacts, thus presenting a uniform and compact state with the best microstructure. These results are relevant in order to develop future dense coatings to be used in the fusion domain.
Display omitted
•400nm nanocrystalline W thin films were deposited by dcMS and HiPIMS techniques.•HiPIMS was operated with different magnetic field and pulse configurations.•Presence of an additional ...magnetic field in HiPIMS leads to high deposition rates.•Topological, structural, mechanical and tribological properties were investigated.•Multi-pulse HiPIMS-films show the highest hardness and Young’s modulus.
Despite the tremendous potential for industrial use of tungsten (W), very few studies have been reported so far on controlling and tailoring the properties of W thin films obtained by physical vapor deposition techniques and, even less, for those deposited by High Power Impulse Magnetron Sputtering (HiPIMS). This study presents results on the deposition process and properties characterization of nanocrystalline W thin films deposited on silicon and molybdenum substrates (100W average sputtering power) by conventional dc magnetron sputtering (dcMS) and HiPIMS techniques. Topological, structural, mechanical and tribological properties of the deposited thin films were investigated. It was found that in HiPIMS, both deposition process and coatings properties may be optimized by using an appropriate magnetic field configuration and pulsing design. Compared to the other deposited samples, the W films grown in multi-pulse (5×3μs) HiPIMS assisted by an additional magnetic field, created with a toroidal-shaped permanent magnet placed in front of the magnetron cathode, show significantly enhanced properties, such as: smoother surfaces, higher homogeneity and denser microstructure, higher hardness and Young’s modulus values, better adhesion to the silicon substrate and lower coefficient of friction. Mechanical behaviour and structural changes are discussed based on plasma diagnostics results.
Display omitted
•Laser ablation of a Be target immersed in liquids leads to Be nanoparticles.•Liquid medium and laser fluences are important for Be dust size distribution.•High percentage of metallic ...Be (∼80%) bonds is obtained in heavy water.•Deuterium retention is observed in beryllium dust synthesized in heavy water.•New method to synthesize and incorporation deuterium into Be dust in one step.
In this paper, we describe a method to synthesize beryllium (Be) nanoparticles (NPs) by laser ablation of a solid target immersed in a liquid medium. Beryllium dust was successfully synthesized following the irradiation of a Be bulk target, which was immersed in water, acetone or heavy water, respectively, using the first and second harmonic (1064 and 532 nm) of a Nd: YAG laser source providing ns pulses, with a repetition rate of 10 Hz. The laser fluences used for Be target ablation were 8 and 15 J/cm2. In order to argue the successful obtaining of Be dust, scanning electron microscopy (SEM) was used for surface analysis. Colloidal solutions analysis by dynamic light scattering (DLS) supports the SEM analysis in terms of NPs size, whereas chemical analysis by X-ray photoelectron spectroscopy (XPS) was used in order to investigate the chemical composition. Moreover, thermal desorption spectroscopy (TDS) was performed on Be dust synthesized in heavy water to study the retention of deuterium (D). The key parameters for obtaining much sharper and regular size distribution were identified as being the liquid medium, laser fluence, and wavelength.
Bipolar Pulse High Power Impulse Magnetron Sputtering (BP-HiPIMS) was investigated and used in this work to control the ion bombardment process of growing thin films and to improve their structure ...and properties. Energy-resolving mass spectroscopy was used to investigate the effect of reverse target voltage on the ion energies and fluxes during BP-HiPIMS of a high-purity copper target, in argon gas. It was found that the reverse target voltage provides a wide range of ion energies and fluxes incident to the growing film, which, in turn, produce a wide variety of effects during the deposition process, improving the adhesion strength and influencing both surface and bulk properties. Fast ICCD imaging was used to investigate both HiPIMS and BP-HiPIMS plasma dynamics. The temporal and spatial distributions of plasma potential measurements were performed in order to explain the mechanisms for accelerating the ions. The topological, structural and mechanical properties of the deposited coatings were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), nanoindentation and scratch tests. The obtained results indicate an energy-enhanced deposition process during BP-HiPIMS, the deposited films being characterized by smooth surfaces, dense microstructure, small inert gas inclusions, high elastic strain to failure, scratch resistance and good adhesion to the substrate. These improvements in the films' structure and properties may be attributed to the intense and energetic ion bombardment taking place during the deposition process. During BP-HiPIMS operation, there is no net increase in the deposition rate as compared to the monopolar regime due to the re-sputtering process.
•Copper thin films were deposited on Si substrates by bipolar pulse HiPIMS technique.•The ICCD images reveal a plasma deconfinement process during bipolar HiPIMS.•The reverse target voltage provides a wide range of ion energies and fluxes.•The energy-enhanced deposition process occurs for reverse voltage above 100 V.•The films exhibit smooth surfaces, dense microstructure and good adhesion.
In ITER, the first mirrors would be vulnerable to deposition from the first wall materials, namely beryllium (Be) and tungsten (W) in mixed compositions. In this study we investigate the capactively ...coupled RF plasma sputtering of such mixed Be-W deposits on rhodium-coated substrates, using deuterium as the process gas, and track the enrichment of W during the sputtering process. Experiments were conducted on Be-W deposits with W concentration varying from 2 to 8.3 at.%, and maximal deuterium ion energies in the plasma of 70 and 220 eV. The evolution of the W concentration in the deposits during the plasma sputtering depended considerably on both deuterium ion energy as well as the initial concentration of W in the films. With 220 eV sputtering, a rapid enrichment of W was observed, with all the W changing from BexW before sputtering to metallic W and its oxides after sputtering. With 70 eV sputtering, there was no net change in the W concentration, as long as the initial concentration of W in the film was below 4 at.%. Moreover, the W remained considerably in the state of BexW after the sputtering as well. However, a W enrichment was also observed with 70 eV sputtering, when the W concentration in the films was higher (8.3 at.%). The rate of W enrichment was also observed to increase monotonically with the increase in the initial concentration of W in the deposits. SDTrimSP simulations performed with experimental parameters indicate that sputtering yield of Be increases with W concentrations in the Be-W layers due to backscattering of D projectiles off W atoms. These studies show that low energy deuterium sputtering of mixed Be-W layers with low W concentrations, allows for removal of Be without rapidly enriching W in the films, making it a promising option for ITER.
The thermionic vacuum discharge method is very effective in that the films obtained using this technology are characterised by a very high degree of adhesion, density and purity because the ...deposition technique is carried out in high, very high or, if possible, in ultra-very high vacuum conditions with no gas present. When the substrate is placed in vacuum, no heat transfer particles are present, the substrate being heated only by the ion incident on the surface. This advantage recommends the TVD method for deposits on plastics or other thermally sensitive materials. Additionally, this slow heat transfer reduces energy loss, making the deposition method industrially competitive. The paper aims to present theoretical aspects of this type of discharge, compared to typical or more popular plasmas but also to present the achievements of this method and its utility in the thin films production, layers that have specific imposed properties. The practical depositions and applications presented are in the nuclear fusion-related material science and also for obtaining materials for granular structures, used as magneto-resistive coatings.
Display omitted
•Polycrystalline WNx (x=0.4–1) thin films were deposited by reactive HiPIMS.•Nitrogen incorporation acts to reduce grain size and surface roughness.•D implantation was performed using ...a low-pressure deuterium plasma jet device.•D retention/release mechanisms depend on N content and films microstructure.•Nitrogen incorporation acts as diffusion barrier for D retention/desorption processes.
In this work, tungsten nitride coatings with nitrogen content in the range of 19–50 at% were prepared by reactive multi-pulse high power impulse magnetron sputtering as a function of the argon and nitrogen mixture and further exposed to a deuterium plasma jet. The elemental composition, morphological properties and physical structure of the samples were investigated by Rutherford backscattering spectrometry, atomic force microscopy and X-ray diffraction. Deuterium implantation was performed using a deuterium plasma jet and its retention in nitrogen containing tungsten films was investigated using thermal desorption spectrometry. Deuterium retention and release behaviour strongly depend on the nitrogen content in the coatings and the films microstructure. All nitride coatings have a polycrystalline structure and retain a lower deuterium level than the pure tungsten sample. Nitrogen content in the films acts as a diffusion barrier for deuterium and leads to a higher desorption temperature, therefore to a higher binding energy.
Silicon nitride (SiNx) and hydrogenated silicon nitride (SiN:H) thin films were deposited by reactive High Power Impulse Magnetron Sputtering (HiPIMS), at room temperature, in argon, nitrogen and ...hydrogen gas mixture. The long-term aim of our research is to obtain coatings for solar cell application, with improved optical properties, in a wide range of wavelength radiation. Anti-reflection, passivation and wear resistance properties are also considered for space mission application. Optical, compositional, structural, mechanical and tribological properties of the deposited films were characterized by UV–Vis–NIR spectroscopy, Glow Discharge Optical Emission Spectrometry (GDOES), thermal desorption spectroscopy (TDS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoscratch and nanoindentation. The obtained coatings show dense amorphous and amorphous to nanocrystalline structure, high packing density, very low surface roughness and very good adhesion to substrate and wear properties. Optical properties were optimized to obtain films of low effective reflectivity in a broad-band wavelength range, with good passivation properties and enhanced mechanical and tribological properties. The average reflectance measured in the range of 200–1800 nm is less than 5%, while the average transmittance is up to 93%. GDOES and TDS measurements of SiN:H coatings revealed a diffusion process of atomic H into the Si substrate. FTIR analysis of SiN:H films indicated the presence of numerous hydrogen bonds (Si − H and N − H) which could passivate structural defects and reduce the number of recombination centers in silicon bulk.
•SiNx and SiN:H thin films were obtained by reactive HiPIMS.•Anti-reflection, passivation and wear resistance properties were investigated.•Very low effective reflectivity in the wavelength range 200–1800 nm was obtained.•The deposited films show dense microstructure with high H/E ratios.•GDOES and TDS measurements revealed a diffusion process of H into Si substrate.
PDF
