Direct Current Unbalanced Magnetron Sputtering Research Articles

Impact of carbon content on the phase structure and mechanical properties of TiBCN coatings via direct current magnetron sputtering

Abstract In this study, unbalanced direct current magnetron sputtering was employed to develop TiBCN coatings on Si (100) wafers. The carbon (C) concentration was varied to manipulate the phase structure and mechanical properties of the coatings. The coatings were analyzed using Raman spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and nanoindentation. The results revealed that the TiBCN-2 coating, with a C concentration of 4.4 at.%, exhibited optimal hardness and elastic modulus values of 33 and 291 GPa, respectively. On the other hand, as the C content increased from 4.4 to 24.4 at.%, the hardness and elastic modulus values of the coatings decreased to 21 and 225 GPa, respectively, due to the formation of boron nitride and carbon phases within the coating matrix. Therefore, the inclusion of an ideal C concentration can considerably improve the properties of TiBCN coatings, thus rendering the coating a desirable material for cutting tools.

First Approach to Doping Silver into CrB2 Thin Films Deposited by DC/HiPIMS Technology in Terms of Mechanical and Tribological Properties

Doping of transition metal diborides (TMB2) films with soft metals (Ag, Au, Pt) can extend their application potential to tribological and biomedical fields. Here, a combination of direct current unbalanced magnetron sputtering (DC-UBMS) with high-power pulsed magnetron sputtering (HiPIMS) was used to synthesize silver-doped CrB2+x thin films on unheated substrates. All Ag–CrB2+x thin films were over-stoichiometric with a B/Cr ratio ranging from 2.05 to 2.30 and silver content varying from 3 at.% to 29 at.%. X-ray diffraction demonstrates the amorphous character of the structure in the case of films with silver content ranging from 0 at.% to 8 at.%. A nanocrystalline structure containing a cubic Ag phase is formed in the films with higher silver content. The highest hardness of 26.6 GPa accompanied by the highest value of elastic modulus of 362 GPa was measured in undoped CrB2.3 films. As the silver content in the Ag–CrB2+x thin films increases, the hardness and elastic modulus values gradually decrease to 7.8 GPa and 187 GPa, respectively. The friction properties of CrB2.3 films, expressed by the coefficient of friction against a steel ball of 0.72, are insufficient and limit their use in demanding industrial applications. However, silver doping significantly reduces the friction coefficient when the lowest value of 0.39 is measured in moderately hard Ag–CrB2+x films with an Ag content of 17 at.%. The scratch test shows satisfactory adhesion of films to substrates even without additional heating during deposition.

Thermal stability of Si/SiC/ta-C composite coatings and improvement of tribological properties through high-temperature annealing

We report the structure, mechanical properties, thermal stability, and durability of Si/SiC/ta-C composite (Si–ta-C) coatings fabricated using simultaneous filtered cathodic vacuum arc deposition and direct current unbalanced magnetron sputtering. Si concentration of 1.25–6.04 at.% was achieved by increasing the unbalanced magnetron sputtering power from 25 to 175 W. Si addition provided functionality to the coating, such as heat resistance, while retaining the high hardness of ta-C coatings. The Si–ta-C coatings were stable up to 600 °C regardless of the Si content, while the coating containing 3.85 at.% Si was stable up to 700 °C. The friction behavior and mechanical properties were dependent on the coating film before and after annealing at 100–200 °C; however, annealing at 300–400 °C decreased disk wear and increased counterpart wear due to an increase in film hardness on account of an endothermic reaction that increased the number of Si–C bonds. This indicates that the basic hardness characteristics of the ta-C coating and the high-temperature structural change of the Si–ta-C coating are important for ensuring high-temperature durability. These characteristics were verified through the low coefficient of friction and wear rate of the 1.25 at.% Si–ta-C coating after annealing at 500 °C.

TiN/NbN Nanoscale Multilayer Coatings Deposited by High Power Impulse Magnetron Sputtering to Protect Medical-Grade CoCrMo Alloys

This study describes the performance of nanoscale multilayer TiN/NbN coatings deposited on CoCrMo medical-grade alloys by utilising novel mixed high power impulse magnetron sputtering (HIPIMS) and direct current unbalanced magnetron sputtering (UBM) technique in an industrial size vacuum coater. Scanning electron microscopy analysis showed that these coatings were extremely dense without any intercolumnar voids. The coating exhibited high hardness of 28 GPa, as well as low friction and wear coefficient of 0.7 and 1.4 × 10−14 m3·N−1·m−1, respectively, as compared to the bare material. Scratch tests revealed superior coating to substrate adhesion due to the HIPIMS etching prior to coating deposition. Energy-dispersive X-ray analysis of the wear debris generated during the impact test together with focused ion beam cross-section analysis in different locations of the impact crater revealed the coating failure mechanism and further confirmed the excellent coating to substrate bonding strength. Potentiodynamic polarisation tests in NaCl and Hank’s solutions revealed the clear passivation behaviour, several orders of magnitude lower corrosion currents, and high pitting potentials of the coating, which guarantee excellent protection to the base alloy in such aggressive environments. Inductively coupled plasma mass spectrometry analysis of Hank’s solution containing corrosion debris of the coated sample revealed that the leaching of harmful metal ions from the base material was reduced to below the detection limit of the technique, thus demonstrating the high barrier properties of the coating.

Detailed study of the electrochemical behavior of low-reflectivity TiAlN coatings

Titanium aluminum nitride (TiAlN) is proposed as a coating to decrease the reflectivity of surgical instrumentation, thereby improving the field of vision of surgeons during procedures, although the corrosion resistance of the material against repeated sterilization processes must be guaranteed. The influence of aluminum (Al) on the microstructural and electrochemical properties of low-reflectivity titanium aluminum nitride coatings deposited by direct-current unbalanced magnetron sputtering was evaluated. The optical properties, chemical phases and composition were determined using the ultraviolet–visible spectroscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques. The microstructures were analyzed by atomic force microscopy, scanning electron microscopy and transmission electron microscopy–selected area electron diffraction. The corrosion resistance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization. It was found that an increase in the aluminum content reduced the coating reflectivity by 60%, showing a dense columnar crystalline structure with a grain size of 200–100 nm and roughness of 6.7–4.0 nm and the coexistence of titanium nitride (TiN), aluminum nitride (AlN), titanium aluminum nitride and aluminum oxide (Al2O3) phases. In comparison with AISI 420 steel, the TiAlN-1300W aluminum coating showed a more positive corrosion potential, as well as a current density two orders of magnitude lower, thus guaranteeing corrosion resistance.

Study of the effect of normal load on friction coefficient and wear properties of CNx thin films

The present study reports on the systematic analysis of the friction and the wear behaviors of carbon nitride (CNx) thin films deposited by direct current unbalanced magnetron sputtering. We focus on the normal load dependence on the friction coefficient and wear rate for the sliding friction of the SUJ2 ball with the CNx thin film. The friction coefficient was monitored using a ball-on-disc apparatus with various loads in ambient air. The friction coefficient (μ) increases linearly from ∼0.05 to 0.28 with increasing normal load, while the specific wear rate decreases with an increase in load. The wear rates of the SUJ2 ball ∼1.5 × 10−7 mm3/Nm for μ = 0.05 and ∼5.5 × 10−8 mm3/Nm for μ = 0.28 were observed in the deposited CNx films with the minimum and maximum normal load. The friction and wear mechanisms are discussed in relation to the surface morphology and microstructure of the CNx coatings.

Influence of Ag-Cu nanoparticles on the microstructural and bactericidal properties of TiAlN(Ag,Cu) coatings for medical applications deposited by Direct Current (DC) magnetron sputtering

Most medical instrumentation is manufactured using AISI 420 martensitic stainless steel, due to its acceptable biocompatibility, good hardenability, adequate hardness and resistance to corrosion. However, this steel can be susceptible to contamination with bacteria, representing a potential risk to the patient's health. This research work focused on the development of titanium‑aluminum-nitride coatings doped with silver and copper nanoparticles, TiAlN (Ag,Cu), with an appropriate bactericidal effect. TiAlN coatings doped with four different contents of Ag and Cu (11 at.% to 20 at.%) were deposited onto AISI 420 steel by means of DC unbalanced magnetron sputtering using two composite targets of Ti/Al and Ag/Cu. The diffusion of the Ag,Cu nanoparticles at the sample surface, as well as their quantity, size, shape and distribution, was controlled by appropriate adjustment of the power applied to the Ag/Cu- target, and the temperature and time of the deposition process. The mechanical, tribological and bactericidal properties of the compound depend on, among other factors, the above-mentioned characteristics of the nanoparticles. The microstructure, surface topography, and chemical and phase composition were analyzed by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. To evaluate the bactericidal effect of the coatings, in vitro inhibition and adhesion tests were carried out using selected Staphylococcus aureus and Escherichia coli, two of the major pathogens associated with infections frequently found in hospital environments. The coating without doping presented a structure of columnar growth, which became densified with the increase in the Ag-Cu content and took on a glassy appearance, accompanied by an increased size of the Ag-Cu particles and consequently also in the surface roughness. TiAlN(Ag,Cu) with 17 and 20 at.% Ag-Cu exhibited a higher bactericidal effect than TiAlN, showing high inhibition and less adhesion to both bacteria strains. Another series of techniques that comprehensively describe the relationship between external factors and the bactericidal response of the material were made. Based on the results obtained, the developed nanostructured coating system can be considered very promising for potential applications in surgical and dental instrumentation.

Six strategies to produce application tailored nanoscale multilayer structured PVD coatings by conventional and High Power Impulse Magnetron Sputtering (HIPIMS)

The application field of functional coatings produced by Physical Vapor Deposition, (PVD) is ever expanding. Consequently the demand for novel materials exhibiting extraordinary properties is growing intensively. The paper summarises the experience and the expertise gained at Sheffield Hallam University in UK through work dedicated to the development of such advanced materials spanning more than two decades. It discusses six strategies to produce PVD coatings where the main three steps followed in any coating development process namely material selection, structure selection and finally coating deposition method consideration have been application informed. All described coatings however, utilise nanoscale multilayer structure and have been deposited by Direct Current Unbalanced Magnetron Sputtering (DCMS) or the novel High Power Impulse Magnetron Sputtering (HIPIMS) techniques.

Studying the effects of plasma produced species on the optical characteristics and bonding structure of diamond-like carbon films deposited by direct current unbalanced magnetron sputtering

Abstract In the present study, the influence of target power and plasma produced species on optical, structural and morphological properties of diamond-like carbon thin films deposited by direct current unbalanced magnetron sputtering is investigated. Raman spectroscopy and spectroscopic ellipsometry are used to study the structural properties and optical characteristics, respectively. Additionally, optical spectroscopy is used to measure the optical band gap of the films and investigate the produced active species in the plasma. Optical emission spectroscopy of the plasma shows that increasing the target power from 60 W to 120 W, increases the hydrogen containing species in the plasma which was due to the water vapor remained in the vacuum chamber. Surface topography of the films illustrates that the surface roughness of the films decreases slightly which leads to the smoother surfaces. Raman spectroscopy shows that ID/IG ratio decreases and the G peak position shifts toward lower wavenumber. Indirect optical band gap also increases from 1.77 eV to 2.18 eV. Results of spectroscopic ellipsometry measurements illustrate that the refractive index decreases from 2.01 to 1.67 at 550 nm and the spectrum of the extinction coefficient decreases as well. These results indicate that increasing the sputtering power, increases the sp3 C H bonding more than C C bonding in the matrix of the film.

Ultra-low loading Pt-sputtered gas diffusion electrodes for oxygen reduction reaction

Ultra-low Pt-loaded (3–54 µg cm− 2) gas diffusion electrodes were prepared by a direct current unbalanced magnetron sputtering process. Pt films were deposited directly onto the microporous layer of the gas diffusion electrode and tested in a half-cell and proton exchange membrane fuel cell. While the apparent activity towards oxygen reduction reaction under half-cell conditions is dependent on Pt loading, mass activity is Pt loading independent, indicating constant catalyst utilization. Assuming the validity of the porous electrode model, kinetic parameters are extracted from the experimental data. Unlike the results from the half-cell study, the U–I curves of the proton exchange membrane fuel cell at different loadings show a decrease of the catalyst utilization at higher Pt loadings. The Pt structure on the gas diffusion electrode was investigated by electron microscopy, atomic force microscopy and X-ray diffraction.

Optical Properties of DLC:SiOx and Ag Multilayer Films: Surface Plasmon Resonance Effect

Diamond like carbon films containing silicon (DLC:SiO x ) and „conventional“ hydrogenated diamond like carbon (DLC) films were deposited by direct ion beam using anode layer ion source. Ag films were grown by unbalanced direct current magnetron sputtering. Structure of DLC:SiO x films was investigated by Raman scattering spectroscopy. In the case of DLC:SiO x film deposited on Ag layer surface enhanced Raman scattering effect was observed. Optical properties of the different diamond like carbon and silver multilayers were studied. Annealing effects were investigated. Influence of the thickness of the diamond like carbon and Ag layers was investigated. Position of the plasmonic absorbance peak maximum of DLC:SiO x and multilayers in all cases was redshifted in comparison with “conventional” diamond like nanocomposite films containing silver nanoclusters. It was explained by increase of the Ag nanoparticle size and/or increased probability of the oxidation of the embedded Ag due to the higher amount of oxygen in DLC:SiO x film in comparison with “conventional” diamond like carbon film. DOI: http://dx.doi.org/10.5755/j01.ms.22.4.13194

Optimization of process parameters to achieve spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO high temperature solar absorber coating

TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber was deposited on stainless steel substrate by using four cathode reactive direct current unbalanced magnetron sputtering system. The reactive gas flow rates (C2H2, N2 and O2) and thicknesses of each individual layers were varied to obtain the selective properties of the tandem absorber. The detailed effects of reactive gas flow rates and thicknesses of the individual layers on the optical properties were studied by using UV–vis–NIR spectrophotometer. Guiding factor in optimizing various process parameters was to achieve low reflectance in the solar spectrum region and high reflectance in the infrared region. The change in growth rate of the tandem absorber with reactive gas flow rate was studied using the thickness data, target voltage and target current. These results indicate a decrease in the growth rate of each individual layer of the tandem absorber with an increase in the flow rates of the reactive gases. The changes in bonding structure and chemical composition with reactive gas flow rates were studied by X-ray photoelectron spectroscopy. The optimized tandem absorber deposited on stainless steel substrate shows absorptance of 0.960 and emittance of 0.15. The thicknesses of the optimized individual layers were ∼62, 18, 20, 16, 27nm, respectively.

An experimental investigation on the machining characteristics of Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills

We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (vc) of 13m/min and a feed rate (fz) of 6mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation.

Effect of bias on the structure and properties of TiZrN thin films deposited by unbalanced magnetron sputtering

The objective is to investigate the substrate bias effect on the structure and properties of the TiZrN thin films. The TiZrN thin films were deposited by direct current unbalanced magnetron sputtering system with dual guns (Ti and Zr) targets onto Si (100) substrates at different substrate bias ranging from −35V to −150V. Experimental results indicated that all the specimens have strong (111) texture in X-ray Diffraction patterns. In this study, we discovered a transition bias of −35V, above which a significant improvement of properties was found, including high hardness, excellent brilliance, low resistivity and fine surface morphology. Within the bias range of −40 to −120V, the hardness of TiZrN films is around 35.5GPa, the resistivity is about 33.5μΩ-cm, and the brilliance is larger than 80. The roughness is between 0.5nm and 0.6nm. The TiZrN films maintain excellent properties through a large range of applying bias, indicating that the process window is considerably wide. However, structure damage and thin film delamination were found when substrate bias reached −150V. The Rutherford backscatterng spectrometry result and scanning electron microscope image further support the structure damage at −150V. For protective coatings, low residual stress is required to avoid delamination. By adjusting substrate bias, residual stress can be controlled to lower value. In this study, the residual stress of TiZrN films gradually decreases with decreasing the substrate bias ranging from −65V to −35V. The TiZrN thin films with high hardness, lower residual stress could be obtained simultaneously at low substrate bias of −40V and −45V, the hardness and residual stress are 33.4–34.5GPa and −2.7 to −3.7GPa, respectively.

TiN diffusion barrier failure by the formation of Cu3Si investigated by electron microscopy and atom probe tomography

The authors investigate the interdiffusion damage of Cu/TiN stacks deposited on Si(001) substrates by low-temperature unbalanced direct current magnetron sputtering. Pristine and diffusion-annealed samples are examined by x-ray diffraction, four-point-probe resistivity measurements, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and atom probe tomography. Two relevant diffusion processes are identified. The local diffusion of Cu through defects and grain boundaries in the TiN layer leads to the formation of the η″-Cu3Si phase at the barrier/substrate interface. Three-dimensional reconstructions obtained by atom probe tomography additionally reveal the outward diffusion of Si atoms from the substrate through the TiN bulk toward the Cu top layer, eventually also resulting in the formation of a discontinuous Cu3Si surface layer.

Improved thermal stability, mechanical and tribological properties of reactively sputtered Si doped TiAlC nanostructured hard coatings

The influence of different Si contents on TiAlSiC nanocomposite coatings deposited on stainless steel and silicon (100) substrates using reactive unbalanced direct current magnetron sputtering has been studied. A comprehensive study of microstructure, mechanical, tribological and thermal stability of Si doped TiAlC has been carried out. X-ray diffraction (XRD) analysis reveals that the TiAlSiC coating exhibits fcc NaCl type TiC phase. The presence of a-AlC and a-Si phases was observed by correlating the X-ray photoelectron spectroscopy and XRD data. Moreover, micro-Raman spectroscopy studies indicate the existence of graphitic rich layer of a-C in the coating which limits the columnar growth on account of a-Si. Friction coefficient, adhesion, toughness and mechanical properties of the TiAlSiC coatings were characterized by nanoscratch tester and nanoindentation measurements. A high hardness ~ 28 GPa and a friction co-efficient of ~ 0.49 was achieved for TiAlSiC coatings prepared at a Si contents of 8 at.%. The maximum toughness of 2.14 MPa m1/2 was obtained for the optimized coating due to grain boundary strengthening. Although, increase in the Si content deteriorates the mechanical and tribological performance, but it improves the thermal stability of the coatings. A remarkable thermal stability up to 1000 °C in air for 4 h has been observed for higher Si contents (> 12 at.%).

Air annealing effect on scratch behaviour of BCN films

Boron carbon nitride BCN films have been deposited by direct current unbalanced magnetron sputtering. The obtained amorphous films are annealed in air atmosphere with different temperatures from 200 to 800C. The composition, microstructure, mechanical properties and scratch behaviour of BCN films were studied. The microstructures do not change significantly and mechanical properties decrease slightly when the annealing temperatures are below 400C. The films are oxidised and mechanical properties decline rapidly when annealing temperature rises to 600C. The scratch depth decrease and the highest critical load increases after the films are treated by air annealing below the oxidation temperature. The dominant deformation changes from elastic deformation to plastic deformation with the increase in annealing temperature. The coefficient of friction rise and surface smoothness decreases after BCN films are oxidised. BCN amorphous films have good interfacial adhesion before and after oxidation.

Study on reactive sputtering of yttrium oxide: Process and thin film properties

This paper investigates the influence of deposition conditions on the properties of yttrium oxide thin films. The paper focuses on the texture, optical and mechanical properties. With this objective, a series of yttrium oxide thin films with different thicknesses were deposited by direct current (DC) unbalanced reactive magnetron sputtering at high and low pumping speed. By changing the oxygen flow, depositions were performed in the three characteristic deposition modes for reactive magnetron sputtering, i.e., metallic, transition and poisoned mode. By using an oxygen flow directed to the substrate, full oxidation of the samples, as shown by X-ray photoelectron spectroscopy (XPS), in the three modes is obtained. Crystallographic characterization by X-ray diffraction (XRD) shows that films crystallize in the cubic phase with a strong (222) out-of-plane orientation at low oxygen flow. As the oxygen flow increases a mixture of cubic and monoclinic phase is obtained. In poisoned mode, the films consist of the cubic phase with preferred (420) orientation. Scanning electron microscopy (SEM) cross sections show, with increasing oxygen flow, a loss of the columnar structure. As the oxygen flow rates increase through the metallic, transition, and the poisoned mode, the grain size becomes gradually smaller. An overview diagram of all experimental results uncovers that the textural changes are closely linked to the oxygen partial pressure rather than the oxygen flow. The optical properties of films were investigated by spectroscopic ellipsometry (SE). The films with a columnar structure demonstrate superior hardness and modulus as well as the high plasticity.

Structural and mechanical properties of reactively sputtered TiAlC nanostructured hard coatings

TiAlC nanostructured hard coatings have been deposited on Si(100) substrates by four-cathode reactive pulsed direct current unbalanced magnetron sputtering at various process conditions. The effects of Al and C on the compositional, mechanical and micro-structural properties of TiAlC coatings have been investigated using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy and nanoindentation hardness tester. Furthermore, the effect of substrate bias on the surface morphology, micro-structure and mechanical properties of TiAlC coatings is examined in detail. Formation of Ti3AlC(111) phase along with inclusion of TiC and amorphous carbon phases has been confirmed by XRD and micro-Raman spectroscopy studies. The optimized TiAlC coating exhibited a maximum hardness of ~30GPa and elastic modulus of 288GPa. Analysis of the nanoindentation data indicated that the resistance to plastic deformation (H3/E*2) and elastic strain to failure (H/E*) decrease with C and Al contents in the TiAlC coatings, whereas, these properties increase with an increase in the substrate bias due to grain size refinement. Lastly, fracture toughness of TiAlC coating has also been calculated using a cube corner indenter and the optimized coating exhibited a maximum toughness of ~1.38MPam1/2 at a load of 50mN.

Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for high-temperature solar thermal power applications

A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for high-temperature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82°C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325°C in air for 400h and up to 650°C in vacuum for 100h, thus demonstrating its suitability for high-temperature solar thermal power generation applications.