Samples of nanocrystalline tungsten trioxide with an enhanced surface area were fabricated by oxidation of nanostructured tungsten films. These samples demonstrated a substantial photochromic response when exposed to ultraviolet radiation. The UV-induced absorption bands demonstrated a gradual drift toward the spectrum of the original annealed state. The kinetics of this process were studied by analyzing the light backscattered from the sample as it transitioned through coloration states. This approach revealed the time-dependent evolution of polaron-related absorption bands and the optical band gap of WO3. The absorption band located just below the band edge is associated with an apparent blue shift of the optical absorption edge, consistent with a Burstein-Moss-like contribution. Our study illustrates that an optically thick sample with a nanostructured surface can serve as a relevant model for understanding the mechanism of WO3 photochromism and for predicting the optical responses of tungsten trioxide upon hydrogenation.

Effects of substrate biasing on deuterium content in W-D layers co-deposited at 380 K was investigated for biasing potentials from +5 V to-500 V. The mean deuteron implantation energy at 500 V was similar to 100 eV. It was found that deuterium content increased with increase of the bias voltage absolute value with no clear sign of saturation, and approximately a 2-fold increase was observed at -500 V. Co-deposited deuterium was suggested to be trapped both from three sources: from gas, largely unaffected by substrate biasing, from atomic particles formed in the plasma near the substrate, also mostly unaffected by substrate biasing, and by ion implantation due to bias applied. Deuterium trapped by implantation desorbs at higher temperatures as TDS demonstrated.

A new facility based on a HiPIMS (high-power impulse magnetron sputtering) discharge plasma with a hot tungsten (W) target for the investigation of co-deposition of W with helium (He) and hydrogen (H2, D2) isotopes on W substrate was developed. To find the ion fluxes from He/H2 and He/D2 plasma together with W ions from W target incident on installed samples, the ion mass spectrometric study of a HiPIMS plasma was performed. The results reveal a mixed composition of ion fluxes consisting mainly of monoatomic H+(D+) and He+, diatomic H2 +(D2 +) and HeH+, and triatomic H3+ ions. The content of tungsten ions does not exceed 2 % in any of the explored discharge regimes. The contributions of different species to the total flux are strongly affected by the discharge pulsing parameters, especially pulsed power density. For pulsed power densities below 200 W/cm2, H3+ ions in the He/H2 or D3+ in He/D2 gas mixtures dominate in the ion flux. The opposite situation of monoatomic ion fraction (H+ and D+) prevailing over molecular ions is observed in the case of the pulse power density above the values: 400 W/cm2 for prevailing of H+ in He/H2 gas mixture discharge, and 900 W/cm2 for prevailing of D+ in He/D2 gas mixture discharge. The most suitable discharge modes are selected for future simulation of W co- deposition processes with He/H2 and He/D2 gas mixtures. Preliminary data on the thickness of co-deposits in various regimes have been obtained. The He retention in W irradiated at the HiPIMS facility in hydrogen plasma with V- 10 % He ion seeding was validated by comparison with the experimental data after irradiation of W under the same conditions in a linear plasma device.

Direct current (DC) reactive magnetron discharge in Ar + O2 mixtures with an aluminum (Al) target was investigated. Electrical measurements of the discharge voltage and current along with the deposition rate trends observed with varying the oxygen flow rate indicated the presence of hysteresis, typical to when using a DC power supply. The transition between metallic and oxide (compound) modes was analyzed in more detail by measuring the mass-resolved fluxes of positively and negatively charged ions together with the optical emission spectra of plasma. The dependence of constituent ion fluxes (Ar+, Ar2+, Al+, O+, O2+, O−, and O2−) on the reactive oxygen gas flow rate was revealed, indicating the transition (in 1.2–1.8 sccm O2 flow range) from a metallic regime to a poisoned regime. The optical diagnostics indicated a nonlinear hysteresis loop pattern of dependence for various constituents (ions and neutrals) of the magnetron discharge plasma. The comparison between the particle and optical measurements, though exhibiting a pronounced correlation, demonstrated individual features of both methods, which need to be taken into account when interpreting the results. The hysteresis patterns were further discussed by comparing the experimental data with the calculation results from the Berg model. An approach of adapting the model results to the case of a power-regulated magnetron power supply is expressed.

Tungsten fuzz layers formed on the plasma-facing material surfaces of thermonuclear facilities due to helium ion irradiation are known to promote the initiation of electrical discharges on the first wall. Previous studies have indicated increased arcing probability under helium ion irradiation in steady plasmas with increasing ion energy to several hundred eV. Here, we experimentally consider the growth of nanostructures on tungsten surfaces in an RF He plasma and the spontaneous initiation of arcs when applying the pulsed bias voltage to the sample, up to several keV. The arc current and voltage waveforms were obtained, and the scanning electron images of the arc traces were analyzed. The behavior of the arc at the smooth/fuzzy surface boundary directly demonstrated the beneficial arcing conditions of the nanostructured layer. The proposed approach of pulsed biasing enables controlling the amount and duration of arcs for better analysis of their dimensions and dynamics. From the experimental results, the total arc trace length and arc velocity were calculated and compared with literature data, giving a good agreement both between experiments and theoretical data and between experiments in different arc initiation conditions.

The enhancement of cutting tools' performance by properly engineering their surfaces is one of the most demanded fields of applications for plasma-based coating deposition methods. While tungsten carbide (WC-Co) cutting tools are usually processed by chemical vapor deposition techniques, their treatment by magnetron sputtering-based physical vapor deposition is promising since it allows one to fine-tune the surface properties by controlling the charged particle flux onto the surface. In this work, the mechanical properties (hardness and Young's modulus) were studied for the CrAlN coatings deposited onto WC-Co (P10) substrates in a pulsed DC magnetron discharge. The discharge was operated in reactive mode by sputtering of Cr and Al targets in the Ar/ N2 atmosphere, and the ratio of Cr/Al discharge power values was selected to optimize the Al content in the resulting films. The bias voltage applied to the samples during the deposition was varied from -100 V to +100 V with respect to the grounded anode. The coatings were studied by means of scanning electron microscopy, X-ray diffraction, nano- and microindentation. The results show the improvement in surface hardness up to 28 GPa for the CrAlN coatings fabricated at -100 V bias voltage, with Young's modulus lower than the substrate's for all studied deposition modes. The deformation behavior of coatings during the indentation tests was additionally investigated using a finite element modeling approach, and the simulated load-displacement curves are in good agreement with the experimentally measured curves. Both experiments and simulations demonstrate that CrAlN coatings are plastically deformed during indentation with the absence of cracking behavior.

The modes of maintaining a pulsed magnetron discharge with a hot thermally insulated silicon target during operation in oxygen-containing gas mixtures (Ar + O 2 ) have been studied. The range of the average power density at the target was 60–120 W/cm 2 at a pulse duration of 100–300 µs and a repetition rate of 0.5–2 kHz. Maps of stable operating modes of the sputtering system have been determined. Si x O y coatings were prepared on single-crystal silicon substrates at different values of the oxygen fraction in the gas flow and various parameters of the magnetron pulsed power supply and diagnosed.

This paper aims to investigate the quality of thin alumina films deposited on glass samples using magnetron sputtering in the reactive modulated pulsed power mode (MPPMS) and evaluate the process productivity. The aluminum target was sputtered in Ar/O2 gas mixtures with different fractions of oxygen in the total gas flow, in the fixed pulsed voltage mode. The pulse-on duration was varied between 5 and 10 ms, while the pulse-off time was 100 or 200 ms. The dependences of mass deposition rate and discharge current on the oxygen flow were measured, and the specific deposition rate values were calculated. Prepared coatings had a thicknesses of 100–400 nm. Their quality was assessed by scratch testing and by measuring density, refractory index, and extinction coefficient for different power management strategies. The strong influence of pulse parameters on the coating properties was observed, resulting in a maximum density of 3.6 g/cm3 and a refractive index of 1.68 for deposition modes with higher duty cycle values. Therefore, adjusting the pulse-on and pulse-off periods in MPPMS can be used not only to optimize the deposition rate but also as a tool to tune the optical characteristics of the films. The performance of the studied deposition method was evaluated by comparing the specific growth rates of alumina coatings with the relevant data for other magnetron discharge modes. In MPPMS, a specific deposition rate of 200 nm/min/kW was obtained for highly transparent Al2O3, without using any dedicated feedback loop system for oxygen pressure stabilization, which makes MPPMS superior to short-pulse high-power impulse magnetron sputtering (HiPIMS) modes.

We report the implementation of a method for non-destructive remote diagnostics of the content of gas impurities retained in a material surface layer. The technique is based on the laser-induced heating of a surface layer and associated desorption of gas species in the presence of background inductively coupled plasma (ICP). The analysis of released gas species is made by optical emission spectroscopy (OES). The procedure of optimizing the signal efficiency by changing the spectrometer observation path with respect to the laser beam and the delay of spectrum acquisition is discussed. The applicability of laser-induced desorption spectroscopy (LIDS) was examined by studying the release of hydrogen from a Ti-V test sample exposed to Nd:glass laser pulses (λ = 1064 nm, duration 0.5 ms, energy 1–14 J), in a background argon plasma, by measuring the intensity of Balmer spectral lines. The demonstrated dependence of Hα intensity on the laser pulse energy enables implementing the LIDS technique for diagnostics of retained hydrogen. The lower limit of the laser pulse energy range suitable for diagnostics is associated with spectrometer sensitivity. The higher limit is governed by distortion of plasma conditions, which is detected as a deviation in argon emission intensity from constant value when the laser pulse energy exceeds 6 J.

The deformation and failure behavior of any coating governs the performance of the resulting coating system. In the present work, we numerically and experimentally examine the fundamental deformation mechanisms of CrAlN coating on Si substrate, particularly its cracking behavior under indentation processes. For this purpose, CrAlN coatings deposited on monocrystalline Si substrates by pulsed DC magnetron sputtering were subject to indentation procedures with different depths. Subsequent characterization of top surface and cross-sectional morphologies demonstrates a strong dependence of coating profile and microstructures on the initial surface condition of the substrate. Specifically, uniform CrAlN coatings with a thickness of 1.1 μm and densified columnar microstructures were prepared on a polished Si substrate. Berkovich nanoindentation test with an indentation depth of 530 nm derives the mechanical properties of the prepared CrAlN coating. The corresponding finite element simulation reveals the propensity of cracking initiation accompanied by the stress concentration at three edge corners of the dent. Subsequent microindentation test with an indentation depth of 1.09 μm demonstrates the coexistence of plastic deformation and brittle fracture of CrAlN coating. In particular, surface radial cracks within CrAlN coating are experimentally and theoretically observed, and the cracking processes are analyzed in detail by finite element simulations.

We theoretically consider the joint influence of hot-target effects and the pulsed nature of the discharge on the state of the target surface. The system of equations describes the state of the target in terms of poisoned area fractions theta(1) and theta(2), where index 1 corresponds to the monoatomic surface layer, and index 2 - to the layer beneath the surface (subsurface layer). The processes of chemisorption on target and substrate surfaces, sputtering of reactive gas atoms from target, im-plantation of reactive gas ions to the sub-surface layer, material evaporation, and transfer between the layers are considered. A separate equation connects the atomic fluxes of reactive gas associated with target and substrate surfaces with the volumetric characteristics, such as gas injection rate and pumping speed. The system of equations is solved numerically, and test results are presented. Temporal evolutions of the compound fraction of target surface and subsurface layers as well as the substrate surface in a high-power impulse magnetron sputtering process with uncooled target have been studied numerically. The repetitive fashion of HiPIMS process has been taken into account by introducing current waveform in the shape of rectangular pulses with 50-500 mu s duration and 0.1-1 kHz frequency. The model predicts strong influence of initial target poisoning conditions on the behavior of sputtering process on the timescale of 20 ms. The compound fractions on target and substrate surfaces demonstrate larger magnitude of oscillations when increasing the pulse-off period, even if the duty factor remains constant.

Исследованы режимы существования импульсного магнетронного разряда с горячей теплоизолированной кремниевой мишенью при работе в газовой смеси, содержащей кислород (Ar + O 2 ). Рассмотрен диапазон средней плотности мощности на мишени 60…120 Вт/см 2 при длительности импульсов 100…300 мкс и частоте повторения 0.5…2 кГц. Построены карты стабильных режимов работы распылительной системы. Получены и продиагностированы покрытия Si x O y на подложках из монокристаллического кремния при различных значениях доли кислорода в газовом потоке и различных параметрах импульсного питания магнетрона.

An overview of the MEPhIST-0 educational and research small-scale spherical tokamak project is presented including the vacuum vessel, magnetic field systems, and diagnostics. In contrast to other small machines, it is an advanced tokamak with D-shaped plasma equipped with an electron-cyclotron resonance pre-ionization system for plasma startup and an ion-cyclotron resonance system for plasma heating and wall conditioning. The design choices taken are discussed from the perspective of a primarily educational installation. The machine design is simplified while remaining relevant to larger devices. First plasma results obtained in 2021 are presented.

Tribological parameters of samples of bronze substrates coated with MoS2 were investigated. The friction tests were carried out at load 7N, temperature of 250°C in vacuum according to ASTM G133. Magnetron sputtering was used to deposit MoS2 coatings. A 100Cr6 steel ball was used as a counter-sample. Based on the results of the experiments, the values of the friction coefficient of the coatings and their comparative service lifetime were obtained. The results can be used in the manufacturing of devices operating in similar conditions.

The electrical parameters of a high-power impulse magnetron sputtering (HiPIMS) discharge operating in H2/He mixtures were studied using different values of the pulse width, repetition frequency, and power. Deposition of tungsten (W) coatings was carried out in a magnetron discharge with a thermally insulated W target in two regimes at different pulse widths (80 and 500 µs) and frequencies (2 and 0.5 kHz). The average discharge power was fixed at Pd = 1500 W. Fusion-relevant molecular deuterium/helium (He) and hydrogen/He gas mixtures with a 90/10 flow ratio were used in the experiments.

We examined the feasibility of alumina substrate metallization by magnetron deposition of copper coatings with thickness of several tens µm for its prospective applications in production of ceramic PCBs and packaging. The films were prepared in magnetron sputtering systems with cooled and thermally insulated (hot) targets. Substrates with different geometries were used, including those with through-holes. Thickness, adhesive properties, and electrical resistivity of produced coatings were analyzed. If the film thickness exceeded ~20 µm, we observed its systematic delamination, unless the dedicated CuxOy sub-layer of was introduced between the substrate and the main Cu film. Intermediate copper oxide films were investigated separately by SEM, EDS, and XRD methods, and deposition conditions for predominant growth of favorable tenorite CuO were determined. Prepared composite two-layer CuO + Cu coatings with total thickness of ~100 µm demonstrated good adhesion to alumina substrates in scratch-testing and performed much better than Cu-only films both in soldering and thermal cycling tests. We discuss an approach for constructing a reliable metallizing coating by plasma-assisted PVD methods that could be beneficial for complex-shaped ceramic PCBs and packaging.

A group of high-energy positive O+ ions in a plasma flow from a high-current pulsed magnetron discharge with a hot target in an Ar/O2 gas mixture. The mechanism of occurrence of accelerated O+ ions is the conversion of negative ions accelerated in the cathode layer O– → O+ in the processes of charge exchange or ionization by electron impact.

Electrical parameters of a high-power impulse magnetron sputtering (HiPIMS) discharge operated in H2/He mixtures were studied for different values of pulse width, repetition frequency, and power. Deposition of W coatings was carried out in a magnetron discharge with a thermally insulated W target in two regimes with different pulse width (80 μs or 500 μs) and frequency (2 kHz or 0.5 kHz, respectively). Average discharge power was fixed Pd = 1500 W. Fusion-relevant D2/He and H2/He gas mixtures with 90/10 flow ratio were used in the experiments.

The arrival of highly energetic (near 1000 eV) positive atomic oxygen ions at the substrate region has been detected in a unipolar reactive high-power impulse magnetron sputtering process operated with an uncooled copper target in argon–oxygen mixtures. Examination of the ion fluxes from discharge plasma was performed with a magnetic sector mass-spectrometer and an electrostatic energy analyzer. The energy of fast positive O + ions is close to the value of eV d ( e —elementary charge, V d —discharge voltage), which indicates their connection to the well-studied fraction of negative O − ions, which undergo acceleration in the cathode sheath. After switching the oxygen gas supply off, the flux of energetic O + species decreases gradually as the poisoned target surface layers become depleted of oxygen due to sputtering in pure argon. Presumably, the observed energetic O + ions originate as a result of low-angle scattering of fast negative O − ions from other charged or neutral species in the plasma followed by electron detachment, ionization, or charge exchange.