Target Power Density Research Articles

Microstructure, mechanical and tribological characterization of magnetron sputtering ZrN and ZrAlN coatings

In this research paper, mechanical and tribological characterization of novel high wear-resistant ZrN-ZrAlN coatings are presented. The varying concentrations of AlN is chosen to evaluate the influence of AlN the surface morphological, nanomechanical, and tribological properties of the composite coating. The coatings were developed on D9 steel substrates using nitrogen reactive gas radio frequency (RF) magnetron sputtering of zirconium and aluminium targets in an argon plasma. Variable power density for the aluminium target and constant power density for zirconium, was used to obtain in a systematic way, the variable concentration of AlN in the coating. Surface morphological studies were carried out to evaluate composition and crystal structure using X-ray diffraction (GIXRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Coatings display a polycrystalline structure, but the level of crystallinity decreases with higher AlN concentration. Nanomechanical and nano scratch testing, along with tribological experimental studies were performed to comprehensively analyse performance of the developed coatings. Higher hardness of composite coating is achieved with optimal concentration of AlN in ZrN-ZrAlN coating. Adhesion strength of the coatings increased with the increase in the concentration of AlN. ZrN-ZrAlN coatings depicted low wear, however coatings containing AlN exhibits superior wear resistance.

Power-Law Scaling Relating the Average Charge State and Kinetic Energy in Expanding Laser-Driven Plasmas.

A universal power-law scaling z[over ¯]∝E^{0.4} in the correlation between the average ion charge state z[over ¯] and kinetic energy E in expanding laser-driven tin plasmas is identified. Universality here refers to an insensitivity to all experimental conditions: target geometry, expansion direction, laser wavelength, and power density. The power law is accurately captured in an analytical consideration of the dependence of the charge state on temperature and the subsequent transfer of internal to kinetic energy in the expansion. These analytical steps are individually, and collectively, validated by a two-dimensional radiation-hydrodynamic simulation of an expanding laser-driven plasma. This power-law behavior is expected to hold also for dense plasma containing heavier, complex ions such as those relevant to current and future laser-driven plasma light sources.

Characterisation of the Rigid Body Vibration Spectra of Road Transport Vehicles

ABSTRACTFor decades, numerous attempts at re‐creating realistic (vertical) vibrations that purport to represent typical conditions during road transport have been proposed and published. This has and continues to result in a significant number of target power density spectra (PDS) for use in laboratory simulation of vibrations despite the fact that the underlying parameters that influence the vibrations (road surface unevenness and vehicle dynamics) remain largely unchanged. This paper seeks to address this situation by analysing published and measured PDS (129 in total) from a variety of vehicles and road types with the aim of establishing typical PDS. Through the analysis of the frequency of the first natural mode of these PDS, it was found that there exist five typical response PDS (three for steel leaf suspension and two for air ride suspension) that can be considered as representative vibration response PDS for road transport in general. These representative PDS were matched with a two degree‐of‐freedom quarter‐car model representing the heave response of the rigid body motion of the vehicles. The analysis suggests that the higher frequency content of the measured data is not related to rigid body motion but emanates from drivetrain and, in some cases, structural vibrations. These usually comprise numerous harmonics of fixed and varying frequencies as well as transients. As these vibrations are impossible to classify based on vehicle type, it is recommended that the five quarter‐car representative spectral models proposed in this paper—namely, for steel leaf spring suspended vehicles with heavy, moderate and light loads and air ride type vehicles with heavy and light loads—be used for laboratory simulation for the purpose of evaluating the vibration resistance of products and packaged systems. It is suggested that, for most packaged product, this is sufficient to test their ability to survive road transport vibrations. These will yield more realistic vibrations than those endorsed by standards organisations and should have a positive impact on the optimisation of packaging designs and a corresponding reduction in packaging waste. Finally, the need for further work aimed at developing methods to identify and extract fixed and varying discrete frequency vibration as well as transient vibrations was identified.

Simulation study of a novel small animal FLASH irradiator (SAFI) with integrated inverse-geometry CT based on circularly distributed kV X-ray sources

Ultra-high dose rate (UHDR) radiotherapy (RT) or FLASH-RT can potentially reduce normal tissue toxicity. A small animal irradiator that can deliver FLASH-RT treatments similar to clinical RT treatments is needed for pre-clinical studies of FLASH-RT. We designed and simulated a novel small animal FLASH irradiator (SAFI) based on distributed x-ray source technology. The SAFI system comprises a distributed x-ray source with 51 focal spots equally distributed on a 20 cm diameter ring, which are used for both FLASH-RT and onboard micro-CT imaging. Monte Carlo simulation was performed to estimate the dosimetric characteristics of the SAFI treatment beams. The maximum dose rate, which is limited by the power density of the tungsten target, was estimated based on finite-element analysis (FEA). The maximum DC electron beam current density is 2.6 mA/mm2, limited by the tungsten target's linear focal spot power density. At 160 kVp, 51 focal spots, each with a dimension of 2times 20 mm2 and 10° anode angle, can produce up to 120 Gy/s maximum DC irradiation at the center of a cylindrical water phantom. We further demonstrate forward and inverse FLASH-RT planning, as well as inverse-geometry micro-CT with circular source array imaging via numerical simulations.

Holistic Approach toward a Damage-Less Sputtered Indium Tin Oxide Barrier Layer for High-Stability Inverted Perovskite Solar Cells and Modules.

The commercialization of perovskite solar cells (PSCs) requires the development of long-term, highly operational-stable devices. An efficient barrier layer plays a key role in improving the device stability of planar PSCs. Here, we focus on the use of sputtered indium tin oxide (ITO) as a barrier layer to stop major degradations. To mitigate efficiency losses of cells with the ITO barrier, we optimized various sputtering process parameters such as ITO layer thickness, target power density, and working pressure. The fabricated planar inverted PSCs based on the novel ITO barrier optimization demonstrate a power conversion efficiency (PCE) of 19.05% on a cell area of 0.09 cm2. The encapsulated cells retained >80% of their initial efficiency after 1400 h of continuous illumination at 55 °C and 94.5% of their initial PCE after 1500 h stored in air. Employing such a holistic stabilization approach, the PSC minimodules without encapsulation achieved an efficiency of 16.4% with a designated area of 2.28 cm2 and retained approximately 80% of the initial performance after thermal stress at 85 °C for 350 h under ambient conditions.

Numerical simulation of a high-power density 10 MW REBCO superconducting synchronous generator cooled by sub-cooled LN2 for low AC loss

Generators used in electric aircraft require a high-power density, and AC loss is also a significant problem. We designed 10 MW REBCO superconducting synchronous generators at 64 K to achieve a power density of 20 kW/kg and low AC loss. In this study, electromagnetic analyses were performed using finite element method software. Consequently, the thickness of the back yoke is 50 mm or less so that the generator can meet the target power density. The method of decreasing the magnetic field of the armature winding and increasing that of the field winding was used to effectively reduce the AC loss. As a result, the generator achieved a high-power density of 21.0 kW/kg, reducing the AC loss from over 600 kW to 415 kW.

Non-reactive HiPIMS deposition of NbCx thin films: Effect of the target power density on structure-mechanical properties

The exceptional mechanical properties of transition metal carbide coatings are known to be governed by the carbon content and its morphological distribution. Here, we verify the influence of the target peak power density on the chemical composition, microstructure, and mechanical properties of NbCx coatings grown by non-reactive high-power impulse magnetron sputtering (HiPIMS). By tuning the pulse parameters, the power density can be increased from 0.11 to 1.48 kW/cm2 leading to a decrease in the C/Nb ratio from 1.52 to 0.99 within the films – proven by combined elastic backscattering and time-of-flight elastic recoil detection analysis. This decrease in the C/Nb ratio is accompanied by microstructural changes from nanocomposite morphologies with an average grain size of 6.6 ± 2.5 nm at 0.13 kW/cm2 into more columnar structures with an average column width of 65.2 ± 18.7 nm at 1.48 kW/cm2. Independent from the C/Nb ratio, all films exhibit a single face-centered cubic structure. The mechanical properties correlate with the enhanced growth behavior dominated by ions at higher peak power densities and the varied C/Nb ratios. A maximum in hardness and fracture toughness of H = 38.7 ± 3.6 GPa and KIc = 2.78 ± 0.13 MPa∙m1/2 (at 3.2 GPa residual compressive stress), is obtained for the nearly stoichiometric NbC coating exhibiting C/Nb ratio of 1.06.

Effect of Al target power density on tribological properties of (Ti, Al)N coatings

(Ti, Al)N coatings with different Al target power densities on the surface of M2 high-speed steel were deposited by magnetron sputtering to study the tribological properties. The phase composition, microstructure, and element distribution of coatings were characterized by x-ray diffraction, field emission scanning electron microscopy, x-ray photoelectron spectroscopy, and energy dispersive spectrometry. The results showed that the tribological properties of the coatings were closely related to the power density of the Al target. With a gradual increase in the Al target power density, the microhardness increased from 1324.7 to 2819.2 HV. Meanwhile, when Al target power density was 7.9 W/cm2, the coatings exhibit the lowest coefficient of friction (COF = 0.23). By comparison, it was found that (Ti, Al)N coatings exhibited a smooth surface, uniformly dense columnar structures, and smaller grain sizes due to the addition of Al atoms. (Ti, Al)N coatings showed a unique microstructure that determined their excellent tribological properties.

Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition

Sn-added GeSbTe (GST) thin films were deposited using a co-magnetron sputtering technique. The effects of varying the Sn content through a variable Sn target sputtering power and post annealing at 673 K were investigated. The DC power density applied to the GST target was controlled at 50 W, while the power density of the Sn target was increased from 0 W to 40 W. The results demonstrate the coexistence of the fcc-GST, hcp-GST and SnTe phases in the Sn-added GST thin films. The substitution of Sn at the Ge-site increases the crystallization speed and leads to defects and lattice disordered local arrangement in the GST films, causing the Seebeck coefficient to increase. The SnTe phase was created as a result of the high Sn content in the sample due to the over-doping limit of Sn into the GST structure. The presence of SnTe in Sn-doped GST films increased the electrical conductivity. The maximum power factor of 17.0 μW/cmK2 at 450 K was obtained at an Sn content of 14.7 at%. These results indicated that the thermoelectric properties of Sn-doped GST films were improved via the formation of an appropriate amount of SnTe composite.

Multiparameter Influence Analysis of the Target Spot Power Distribution of Airborne Laser

With the continuous improvement of the power and miniaturization of high-energy laser weapons, the airborne laser may become the active defense weapon of the next-generation fighter. However, in order to achieve hard damage to the target, there has been a lack of comprehensive quantitative method as a reference in the parameter design of airborne laser. This paper establishes the high-altitude, slope-down, and short-range laser transmission process models based on the laser transmission simulation platform Easylaser to analyze the effect of the airborne laser weapons system parameters on the power distribution to the target spot. The simulation results show that the laser power, wavelength, laser emission aperture, tracking accuracy, and transmission distance have significant impact on the power distribution to the target spot, whereas the atmospheric mode, slanted angle, and adaptive optics almost no impact on that. On the basis of the simulation results, the response sensitivity of some parameters’ variations to the power distribution to the target spot are analyzed. The response sensitivity variations of the tracking accuracy and transmission distance to the target spot power density varies greatly, while the response sensitivity variations of the laser power and emission aperture to the target power density varies little. These quantifiable outcomes can provide a basis for parameter optimization of airborne laser in the future.

Composition, dielectric breakdown, and bandgap of ultra-thin amorphous boron oxynitride produced by magnetron sputtering

Ultra-thin amorphous boron oxynitride films were deposited at room temperature on silicon and polymer substrates using radio frequency magnetron sputtering of a hexagonal boron nitride target in varied argon-nitrogen background gas ratios. The effects of nitrogen content in the sputtering gas, changes in target-to-substrate distance, and magnetron power density on the film composition were investigated with X-ray photoelectron spectroscopy and correlated to the dielectric breakdown strength and bandgap obtained from current-voltage measurements and Tauc plots. Films grown in pure Ar atmosphere at a large target-to-substrate distance displayed compositions containing metallic boron, which led to a decrease in the dielectric breakdown strength. The use of Ar:N2 mixtures and pure N2 eliminated metallic boron bonding. Decreasing the target-to-substrate distance and target power density during reactive sputtering resulted in B:N stoichiometry ratio closer to one and about 25–30 at.% oxygen. Smooth surface morphology films grown in pure N2 at a small target-to-substrate distance exhibited dielectric breakdown strength of 2.1–2.4 MV cm−1at 30 nm film thickness and bandgap of 5.4 eV. The results show the suitability of amorphous boron oxynitride for application as an insulator or gate dielectric in thin-films flexible transistors and other electronics when a low processing temperature is required.

Synergy of experiment and model for reactive HiPIMS: effect of discharge parameters on WOx composition and deposition rate

Reactive high-power impulse magnetron sputtering of tungsten oxide films using metallic tungsten target (72 mm in diameter) in argon-oxygen atmosphere (total pressure of 0.75 Pa) was carried out. The effect of various discharge parameters on the deposition rate and film oxygen concentration was investigated. Moreover, a model combining a reactive high-power impulse magnetron sputtering model and a discharge plasma model for the ionization region was successfully used for deeper insight into the effect of particular discharge parameters such as voltage pulse length (from 100 –800 µs), oxygen partial pressure (from 0.25–0.50 Pa) or the value of pulse-averaged target power density (from 2.5–500 W cm−2). The results of the presented model, most notably trends in the target- and substrate oxide fraction, composition of particle fluxes onto the substrate, degree of W atom ionization or degree of O2 molecule dissociation are discussed and put into context with experimentally measured quantities.

Three-dimensional numerical simulation of full-scale proton exchange membrane fuel cells at high current densities

Improving the maximum power density of proton exchange membrane fuel cells (PEMFCs) requires very high current density and downsizing. Challenging targets, such as 0.66 V at 3.8 A/cm2, have been proposed to achieve a power density of 6.0 kW/L. The internal distributions of PEMFCs are not well understood at such densities; they must be analyzed because cell performance and durability relate to distributions such as temperature, the water content of a proton exchange membrane (PEM), and water saturation in gas diffusion layers. We conducted three-dimensional numerical simulations of a full-scale PEMFC and its short stack at high current densities. Model parameters in the simulations were fitted to reproduce experimental results of common PEMFCs. The material properties of the PEM, cathode catalyst layer, and gas diffusion layers (GDLs) were numerically modified to achieve the target power density. Modifying the GDL markedly improved the cell performance. The simulations estimated in- and through-plane distributions at high current densities; results indicate that gas diffusivity and thermal conductivity of GDLs considerably affect the distributions of PEM temperature and water saturation in the GDL, which relate to cell performance and durability.

Effect of target peak power density on the phase formation, microstructure evolution, and mechanical properties of Cr2AlC MAX-phase coatings

The applicability of Cr2AlC MAX-phases as protective coatings in energy conversion or aerospace applications requires a dense, single-phase structure. Therefore, we study the effect of target power density and substrate bias on phase formation, microstructure evolution, and mechanical properties of Cr2AlC coatings utilizing direct current (DCMS) and high-power pulsed magnetron sputtering (HPPMS). Generally, HPPMS results in coatings with superior density and hence larger elastic moduli compared to DCMS, indicating that ion bombardment by ionized film-forming species is beneficial. However, decreasing the substrate bias to −200 V for DCMS and −100 V for HPPMS favors the ion bombardment induced formation of the disordered (Cr,Al)2Cx solid solution. It is evident that there is an optimum moderate ion energy for the formation of dense Cr2AlC coatings. Too low energy results in the formation of under-dense coatings. Too high energy yields the formation of (Cr,Al)2Cx in addition to Cr2AlC.

Angular resolved mass-energy analysis of species emitted from a dc magnetron sputtered NiW-target

A Ni81W19 target was dc sputter eroded at constant target power density from a tiltable magnetron at different Ar pressures. The combination with a stationary mass-energy analyzer allowed investigating the abundance of different species within the plasma as well as the ion energy distribution functions of 40Ar+, 58Ni+, and 184W+ at any given angle θ between 0° and 90° from the target normal. Ar+ ions are detected at θ angles close to the target normal, whereas metal atoms are observed at larger θ angles. Ni is emitted at smaller θ angles compared to W. Both investigated metal ion energy distributions exhibit a high energy tail with energies up to 50 eV. Increasing the Ar pressure first affects the trajectories of Ni before W atoms. This can be understood by considering the smaller mass difference between Ni and Ar compared to W and Ar. This enables more effective energy transfer and larger scattering angles of Ni undergoing collisions with Ar compared to W. Subsequent film depositions on a spherical-shell substrate holder, covering angles between 0° and 80° from the target normal, allowed for a comparison of the angular dependent film- and plasma-compositions. This correlative analysis suggests that selective resputtering of Ni by energetic Ar neutrals, reflected from the target, leads to the observed difference between the target and film composition during sputter deposition from a multielement NiW target.

Effects of power per pulse on reactive HiPIMS deposition of ZrO2 films: A time-resolved optical emission spectroscopy study

Time-resolved optical emission spectroscopy was carried out during controlled reactive high-power impulse magnetron sputtering of ZrO2 films in argon–oxygen gas mixtures. The effects of increased target power density (up to 3.0 kW cm−2) applied in voltage pulses shortened from 200 to 50 μs were studied at a nearly constant deposition-averaged target power density (close to 50 W cm−2) and a fixed repetition frequency of 500 Hz. The trends in time evolution of the local ground-state densities of Zr, Ar, and O atoms and that of the Zr+, Zr2+, Ar+, and O+ ions during a voltage pulse were deduced from the time evolution of the corresponding excited-state populations and the excitation temperature. It was found that the sputtered Zr atoms are much more ionized (with a high fraction of Zr2+ ions) and the Ar atom density is more decreased near the target during the shorter (50 μs) high-power pulses. These shorter pulses produce a four times higher pulse-averaged target power density oscillating between 1.7 and 2.1 kW cm−2 during deposition. Under these conditions, much higher densities of O atoms and Zr2+ ions were measured in the plasma bulk. The higher backward flux of the Zr+ and Zr2+ ions onto the target during this high-power discharge regime contributed significantly to a 34% decrease in the efficiency of the magnetron sputter deposition of ZrO2 films.

Synergistic enhancement of antibacterial activity of Cu:C nanocomposites through plasma induced microstructural engineering

This study presents magnetron plasma co-sputtering process for the synthesis of carbon thin films embedded with Cu nanoparticles (NPs). Varying the working pressure and power density of Cu target, induces control over morphology as well as the amount of Cu ions release while interacting with bacterial aliquots. The crystallographic observations present the formation, growth and orientation of crystals in Cu NPs. Raman spectroscopy depicts that increase in working pressure contributes to the development of carbon matrix structure dominating sp3 hybridizations. The variation in chemical structure with varying the plasma conditions is studied by high resolution x-ray photoelectron spectroscopy. The antibacterial activity, observed against staphylococcus aureus (S. aureus) and Escheria coli (E. coli), is strongly related to the release of Cu ions from the films. The nanocomposite films releasing Cu ions ∼1.68 µg/g of the aliquot, completely inhibit the bacterial growth. Obtained excellent antibacterial activity of presented Cu embedded nanostructured carbon films proves these films as a promising candidate in bio-medical applications.

High-rate reactive high-power impulse magnetron sputtering of transparent conductive Al-doped ZnO thin films prepared at ambient temperature

Reactive high-power impulse magnetron sputtering was used for high-rate (deposition rate of 60 nm/min) deposition of conductive (resistivity of 3 × 10−3 Ωcm) and optically transparent (extinction coefficient at the wavelength of 550 nm of 0.01) ZnO:Al thin films at ambient temperature (< 40 °C). We used planar Zn:Al target (3.09 at.% of Al) with diameter of 100 mm and thickness of 6 mm mounted on strongly unbalanced magnetron. The films were deposited in argon‑oxygen atmosphere at constant argon and oxygen partial pressure of 2.0 Pa and 0.1 Pa, respectively. An average target power and voltage pulse length were kept constant to 1.9 Wcm−2 and 200 μs, respectively. A pulse-averaged target power density was varied in the range of 190 Wcm−2–940 Wcm−2. Optical emission spectroscopy was used for better understanding of correlations between plasma discharge properties and structural, electrical and optical properties of prepared films.

Tribological and Electrical Properties of Chromium-Doped Carbon Films Fabricated by Unbalanced Magnetron Sputtering for Medical Stents.

Chromium-doped carbon (Cr:C) films were fabricated by using unbalanced magnetron sputtering with chromium (Cr) and graphite (C) targets. We investigated the structural, tribological, and electrical properties of the Cr:C films fabricated with various target power densities. The surface of all the Cr:C films was smooth and uniform, and the cross section showed a more compact and clear columnar structure as the target power density increased. The root mean square surface roughness increased and the contact angle on the film surface increased with the increase in target power density. Furthermore, the hardness and elastic modulus of the Cr:C films showed improvements, while the resistivity decreased with the increase in target power density. These results are associated with the ion bombardment and resputtering owing to the effects of the applied target power density.

Structure, Mechanical and Optical Properties of Silicon-Rich Al–Si–N Films Prepared by High Power Impulse Magnetron Sputtering

This article reports on the influence of the sputtering parameters (discharge voltage, average target power density) of a high power impulse magnetron discharge (HiPIMS) on the structure, mechanical and optical properties of silicon-rich Al–Si–N films. We show that with the change of a discharge target power density in the range of 30–120 W/cm2, the hardness of the sputtered Al–Si–N films nonlinearly changes in the range of 22–29 GPa, while the concentration of the absorption centers changes in the range of 1018–1020/cm3. The optical spectra of the HiPIMS sputtered films are completely different from the Al–Si–N films prepared by a direct current magnetron sputtering, with an absence of “monoenergetic” optical absorption centers, which are attributed to point defects.