Middle Frequency Magnetron Sputtering Research Articles

Influence of the Parameters of Middle Frequency Magnetron Sputtering on the Elemental Composition, Microstructure, and Mechanical Properties of Ti–Al–Ta–N Coatings

Influence of the Parameters of Middle Frequency Magnetron Sputtering on the Elemental Composition, Microstructure, and Mechanical Properties of Ti–Al–Ta–N Coatings

Structure and Mechanical Properties of Ti-Al-Ta-N Coatings Deposited by Direct Current and Middle-Frequency Magnetron Sputtering

Ti-Al-Ta-N coatings are characterized by attractive mechanical properties, thermal stability and oxidation resistance, which are superior to ternary compositions, such as Ti-Al-N. However, because of their open columnar microstructure, the Ti-Al-Ta-N coatings deposited by conventional direct current magnetron sputtering (DCMS) exhibit insufficient wear resistance. This work is focused on obtaining the Ti-Al-Ta-N coatings with improved microstructure and mechanical and tribological properties by middle-frequency magnetron sputtering (MFMS). The coatings are deposited by the co-sputtering of two separate targets (Ti-Al and Ta) using pure DCMS and MFMS modes as well as hybrid modes. It is found that the MFMS coating has a denser microstructure consisting of fragmented columnar grains interspersed with equiaxed grains and a smaller grain size than the DCMS coating, which is characterized by a fully columnar microstructure. The modification of the microstructure of the MFMS coating results in the simultaneous enhancement of its hardness, toughness and adhesion. As a result, the wear rate of the MFMS coating is less than half of that of the DCMS coating.

Influences of different sputtering current on the microstructure and electrical properties of silicon nitride thin films deposited on cemented carbide tools

Silicon nitride (SiNx) thin films, owing to their high hardness and great insulation performance, show a great prospect for application in smart temperature-measurement tools. However, their properties depend on the deposition conditions, and the high temperatures during cutting process affects the insulation function of these films. In the current work, SiNx thin films were prepared on YG8 cemented carbide by middle-frequency magnetron sputtering technology. Stylus profiler, atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM), and electrochemical analysis tester were applied to investigate the influence of various sputtering currents on microstructure, chemical composition, and electrical properties of SiNx thin films. The results revealed the amorphous structure of SiNx thin films. The sputtering current showed the impetus effect on the deposition rate and roughness of the films. As the sputtering current increased, the isolated islands, initially formed on the carbide substrates, transformed into the uniform and dense film structure. High sputtering current was conducive to the dissociation of N2 and to the formation of the SiNx phase in the films. Finally, annealing at 500 °C caused the failure of Si-N bonds in the film, which deteriorated the insulation performance of the latter at high temperatures at high temperatures.

Modulation of Si on microstructure and tribo-mechanical properties of hydrogen-free DLC films prepared by magnetron sputtering

Modulation of Si on microstructure and tribomechanical properties of hydrogen-free DLC films was studied by preparing Si-DLC films through a hybrid HiPIMS and middle-frequency magnetron sputtering deposition technique. Atomic force microscope, scanning electron microscope, transmission electron microscope, Raman spectrometer and X-ray photoelectron spectroscopy were used to investigate film chemical composition and microstructure. Hardness and elastic modulus were characterized by a nanoindenter. Friction coefficient was measured by a ball-on-disk tribometer. 3D surface profiler, optical microscope and Raman spectrometer were applied to study the tribological behaviors of Si-DLC films. Films surface roughnesses (Ra) are in the range of 1.18–3.15 nm. Si-DLC layer presents a Si-rich/Si-poor multilayer microstructure with a period of about 4 nm. With the rise of Si content in Si-DLC film, sp3 content, hardness and elastic modulus increase. Most Si atoms are interspersed in the amorphous carbon matrix and bond with carbon atoms forming Si-C bonds. The lowest wear rate of 3.5 × 10-7 mm3/Nm is obtained as Si content in Si-DLC film is 14.8%. Varying Si contents in Si-DLC films generated different bonding states of wear tracks, leading to the different wear behaviors of Si-DLC films.

Laser structured nitride and oxynitride coatings deposited by middle frequency magnetron sputtering

AbstractIm Rahmen dieser Untersuchungen galt es zu bestimmen, inwiefern die Variation der Laserstrahlparameter, wie z. B. Pulsenergie und Pulsanzahl, Einfluss auf die Eigenschaften von unbeschichteten Stahlsubstraten sowie von nitridischen und oxinitridischen Beschichtungen nimmt. Drei verschiedene Sauerstoff‐Gasflüsse j(O2) = 10 sccm, j(O2) = 15 sccm und j(O2) = 20 sccm im Beschichtungsprozess und entsprechend drei verschiedene resultierende Beschichtungszusammensetzungen mit xj(O2) = 10 sccm = (39,8±4,2) Atom‐%, xj(O2) = 15 sccm = (31,6±1,4) Atom‐% und xj(O2) = 20 sccm = (58,4±6,0) Atom‐% wurden untersucht. Die Analyse der Strukturtiefe mittels konfokaler Laserscanningmikroskopie zeigte, dass mit steigender Pulsenergie und Pulsanzahl die Strukturtiefe erhöht wird. Die linienartigen Interferenzstrukturen mit konstanter Periodizität wurden mittels Rasterelektronenmikroskopie erfasst. Zusätzlich sind bei allen beschichteten Oberflächen in vertikaler Richtung laserinduzierte periodische Oberflächenstrukturen mit höherer räumlicher Frequenz und kleinerer Periodizität deutlicher zu beobachten. Bei der Beschichtung mit xj(O2) = 20 sccm = (58,4±6,0) Atom‐% entstehen nach der Laserstrukturierung an den Flanken der Interferenzstruktur Mikrorisse.

The Effects of Precursor C₂H₂ Fraction on Microstructure and Properties of Amorphous Carbon Composite Films Containing Si and Ag Prepared by Magnetron Sputtering Deposition.

Hydrogenated graphite-like carbon composite films containing silicon (Si) and silver (Ag) (g-C:H:Si:Ag) were prepared by middle frequency magnetron sputtering deposition in argon (Ar) and acetylene (C2H2) mixture gases. The effects of precursor C2H2 fraction on the microstructure and properties were studied. The results of Raman and X-ray photoelectron spectroscope (XPS) revealed that the films were dominated by sp2 carbon sites. It was observed from transmission electron microscope (TEM) that the films contained nanoparticles mainly consisting of Ag, and their size increased with the decrease in the C2H2 fraction. Si was also found to aggregate in the areas where Ag nanoparticles formed in films with high Si content. The comparative studies on the frictional behaviors of films sliding against aluminum oxide were carried out in ambient air and saline solution. The g-C:H:Si:Ag films still exhibited outstanding frictional properties even when the test environment shifts from ambient air to saline solution.

Effects of bias voltage on the microstructure and properties of Al-doped hydrogenated amorphous carbon films synthesized by a hybrid deposition technique

Al-doped hydrogenated amorphous carbon films were deposited by a hybrid deposition technique combining middle-frequency magnetron sputtering and anode layer ion source. The evolution of chemical composition, surface morphology and chemical bonding state of the resultant films were investigated using XPS, SEM, TEM and Raman spectroscopy, respectively. It was found that the surface morphology of as-deposited films evolved from a rough surface with quasi-columnar characteristic to an ultra-smooth surface with the increasing of applied bias voltage from 0 V to −400 V. At the low bias voltage of 0 V to −50 V, a polymer-like structure was mainly formed. A diamond-like structure is dominated at the moderate bias voltage of −100 V to −300 V, while it transforms to graphite-like after a further increase of the applied bias voltage up to −400 V. The residual stresses and tribological behavior were characterized by stress-tester and ball-on-disk tribo-meter, respectively. The results suggested that tensile stress or compressive stress of the a-C:H(Al) film can be tailored by modifying the applied bias voltage. Particularly, the film deposited at −150 V exhibited a combination of superior properties, including low residual stress, high hardness, a low steady-state friction coefficient of 0.045 and wear rate of 2.7 × 10−7 mm3 N-1·m-1.

Superimposition of high power impulse and middle frequency magnetron sputtering for fabrication of CrTiBN multicomponent hard coatings

The combination of superimposition and hybrid target powers using a superimposed high power impulse magnetron sputtering (HiPIMS) power and middle-frequency (MF) power system, together with the hybrid of direct-current (DC) and radio-frequency (RF) powers was adopted in this work to grow CrTiBN hard coatings. The flexibility of tailoring the chemical composition, phase, deposition rate, microstructure and mechanical properties of CrTiBN coatings through the feedback control of reactive N2 gas flow rate and the corresponding Ti target poisoning status by a plasma emission monitoring (PEM) system was successfully illustrated in this work. Both the peak current and peak power density of Ti target increased with increasing poisoning ratio, i.e., decreasing PEM set point. The 1.64 times higher deposition rate of CrTiBN films can be obtained when the Ti target status changes from poisoning (PEM set point 30%) to transition regime (PEM set point 70%). Fine and compact film microstructure, and a very smooth surface are fabricated for all films. Each coating shows a low coefficient of friction and low wear rate ranging from 0.46 to 0.49 and from 2.06 to 5.73 × 10−6 mm3 N−1m−1, respectively. The highest hardness of 34.1 GPa, adequate adhesion and wear resistance can be found for the CrTiBN coating as deposited at PEM set point of 40% and Ti target poisoning ratio of 60%.

Superimposed high power impulse and middle frequency magnetron sputtering: Role of pulse duration and average power of middle frequency

The low deposition rate of the high power impulse magnetron sputtering (HiPIMS) somewhat limits its commercial applications in thin film and coating industries. In this work, an effective way to improve the deposition rate of TiN film by superimposing the middle-frequency (MF) pulses during off-time of HiPIMS pulsing was discussed. Superimposition of HiPIMS and MF fabricated TiN films with relatively smooth surface. All samples were found to have a single phase TiN according to the chemical composition and crystallographic analyses. The highest film hardness of ~31GPa, elastic modulus of 313GPa, and a density of 5.35g/cm3 were obtained in the sample grown at a MF pulse duration of 150μs in each superimposed cycle. The higher the deposition rate was achieved with longer MF pulse duration. This superimposition technique successfully improved the power-normalized deposition rate from 4.5 to 17.2nm/kW·min without significantly declining the mechanical properties and adhesion quality of deposited films. The role of MF pulse duration and average MF power were further studied in this work. It can be concluded that the MF pulse duration played a more significant role and showed a dominant influence on the plasma characteristics and resulting properties of deposited TiN films.

Enhanced replication ratio of injection molded plastic parts by using an innovative combination of laser-structuring and PVD coating

The properties of plastic products can be optimized by a suitable design of the component surface. One promising method for plastics processing by injection molding is the use of molding tools structured in the micro-meter range. Within the scope of this paper, laser micro-structuring was carried out on two injection molds. A chromium-based nitride coating was deposited on one of the micro-structured mold by means of middle frequency magnetron sputtering (mfMS). Commercial plastics polycarbonate (PC2245) and polymethyl methacrylate (PMMA 7N) were considered for all investigations. The coating contained xCr=51at.−% chromium, xAl=30at.−% aluminum and xN=19at.−% nitrogen exhibited a fine and dense columnar structure. It was experimentally seen that the coefficient of friction measured using a pin on disc tribometer reduces about 11% in case of PMMA 7N, and about 17% for PC2245, using PVD. By comparing coated and uncoated surfaces, a lower wettability in contact with the plastics melt of PC2245 and PMMA 7N analyzed by means of high temperature contact angle (CA) measurements was achieved for coated surfaces. This corresponds to the low amount of shear energy required for the separation of the solidified PC2245 and PMMA from the samples surfaces after the CA measurements. The influence of the temperature on coating property, roughness, after the CA measurements was observed as well. It was shown that the replication ratio of optical micro-structures can be increased significantly up to 20–30% by using a PVD coated in comparison to an uncoated mold.

Influence of titanium concentration on mechanical properties and wear resistance to Ti6Al4V of Ti-C:H on cemented carbide

Titanium doped hydrogenated amorphous carbon (Ti-C:H) was synthesized on silicon, YG8 cemented carbide by middle frequency magnetron sputtering technology. Doped Ti concentration was adjusted via allotting Ar/C2H2 flow rate to be 0–1.21 at.%. To investigate the influence of Ti concentration on mechanical properties and wear resistance to Ti6Al4V, stylus profiler, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and ball-on-disk friction test were applied. The results indicated that the incorporated Ti element existed as amorphous-like structure within the carbon network resulting in the decrease of sp3 fraction and increase of graphitization. The compressive stress of the film declined gradually along with the sacrifice of hardness and elastic modulus as the increase of Ti concentration. Compared with the none-doped and 1.21 at.% Ti-C:H, the friction coefficient of 0.32 at.% and 0.74 at.% Ti-C:H remained lower and more stable value of 0.07, which led to a lower wear rate of about 3.1 E-8 mm3/Nm as well. The worn surface of various Ti-C:H films after rubbing against Ti6Al4V exhibited three kinds of morphologies as adhesive wear, smooth and abrasive wear. The different morphologies and wear mechanism were discussed.

Effects of Sputtering Parameters on AlN Film Growth on Flexible Hastelloy Tapes by Two-Step Deposition Technique.

AlN thin films were deposited on flexible Hastelloy tapes and Si (100) substrate by middle-frequency magnetron sputtering. A layer of Y2O3 films was used as a buffer layer for the Hastelloy tapes. A two-step deposition technique was used to prepare the AlN films. The effects of deposition parameters such as sputtering power, N2/Ar flow rate and sputtering pressure on the microstructure of the AlN thin films were systematically investigated. The results show that the dependency of the full width at half maximum (FWHM) of AlN/Y2O3/Hastelloy on the sputtering parameters is similar to that of AlN/Si (100). The FWHM of the AlN (002) peak of the prepared AlN films decreases with increasing sputtering power. The FWHM decreases with the increase of the N2/Ar flow rate or sputtering pressure, and increases with the further increase of the N2/Ar flow rate or sputtering pressure. The FWHM of the AlN/Y2O3/Hastelloy prepared under optimized parameters is only 3.7° and its root mean square (RMS) roughness is 5.46 nm. Based on the experimental results, the growth mechanism of AlN thin films prepared by the two-step deposition process was explored. This work would assist us in understanding the AlN film’s growth mechanism of the two-step deposition process, preparing highly c-axis–oriented AlN films on flexible metal tapes and developing flexible surface acoustic wave (SAW) sensors from an application perspective.

Properties of a-C:H:Si thin films deposited by middle-frequency magnetron sputtering

The silicon doped hydrogenated amorphous carbon (a-C:H:Si) films were prepared on silicon substrates by middle-frequency magnetron sputtering silicon target in an argon and methane gas mixture atmosphere. The deposition rate, chemical composition, structure, surface properties, stress, hardness and tribological properties in the ambient air of the films were systemically investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscopy (AFM), nanoindentation and tribological tester. The results show that doped silicon content in the films is controlled in the wide range from 39.7at.% to 0.2at.% by various methane gas flow rate, and methane flow rate affects not only the silicon content but also its chemical bonding structure in the films due to the transformation of sputtering modes. Meanwhile, the sp3 carbon component in the films linearly increases with increasing of methane flow rate. The film deposited at moderate methane flow rate of 40–60sccm exhibits the very smooth surface (RMS roughness 0.4nm), low stress (0.42GPa), high hardness (21.1GPa), as well as low friction coefficient (0.038) and wear rate (1.6×10−7mm3/Nm). The superior tribological performance of the films could be attributed to the formation and integral covering of the transfer materials on the sliding surface and their high hardness.

Preparation of highly c-axis oriented AlN thin films on Hastelloy tapes with Y2O3 buffer layer for flexible SAW sensor applications

Highly c-axis oriented aluminum nitrade (AlN) films were successfully deposited on flexible Hastelloy tapes by middle-frequency magnetron sputtering. The microstructure and piezoelectric properties of the AlN films were investigated. The results show that the AlN films deposited directly on the bare Hastelloy substrate have rough surface with root mean square (RMS) roughness of 32.43[Formula: see text]nm and its full width at half maximum (FWHM) of the AlN (0002) peak is [Formula: see text]. However, the AlN films deposited on the Hastelloy substrate with Y2O3 buffer layer show smooth surface with RMS roughness of 5.46[Formula: see text]nm and its FWHM of the AlN (0002) peak is only [Formula: see text]. The piezoelectric coefficient d[Formula: see text] of the AlN films deposited on the Y2O3/Hastelloy substrate is larger than three times that of the AlN films deposited on the bare Hastelloy substrate. The prepared highly c-axis oriented AlN films can be used to develop high-temperature flexible SAW sensors.

Influence of Si contents on the microstructure, mechanical and tribological properties of Cr–Si–N coatings

Abstracts Cr–Si–N coatings with different Si contents were deposited by a hybrid coating system, where the Cr target was used for the arc ion plating (AIP) and the Si target for the middle frequency (MF) magnetron sputtering. The XRD, cross-sectional SEM and XPS results indicated that the Cr–Si–N coating exhibited a nanocomposite structure containing CrN nanocrystallines and amorphous Si 3 N 4 phase. Furthermore, the TEM results showed that all the CrN nano-crystals were embedded in an amorphous matrix of a-Si 3 N 4 . The thickness of the Cr–Si–N coatings was in the range of 2.1–2.4 μm while the Si content was in the range of 2.2–11.1 at%. The hardness of Cr–Si–N coatings first increased and then decreased with the increase of Si content and the highest value was approximately 2490 Hv at 6.94 at% Si content. For coatings with different Si content, the average friction coefficient was maintained around 0.35–0.45. The highest hardness of Cr–Si–N coatings with Si content of 6.94 at% can be attributed to limited dislocation activity in nano-crystals and suppression of grain boundary sliding.

Influences of CuO phase on electrical and optical performance of Cu2O films prepared by middle frequency magnetron sputtering

In the work, Cu2O films were prepared by middle frequency (mf) magnetron sputtering and subsequent anneals. CuO phase has been detected in a few Cu2O samples and its influences have been examined. The results show that the CuO phase can lead to a decrease of Hall mobility and change the surface morphology of the Cu2O films. The highest hall mobility of 43cm2V−1s−1 with the optical band gaps of about 2.5eV has been achieved in the Cu2O films where CuO is absent, which demonstrates the potential to fabricate high field-effected mobility Cu2O-based devices through this method.

Growth of c-axis oriented AlN thin films on titanium alloy substrate by middle frequency magnetron sputtering

A two-step deposition process was developed to deposit highly c-axis oriented AlN thin films on titanium alloy substrates by middle-frequency magnetron sputtering. Smooth AlN seed layer was first prepared on rough titanium alloy substrate at the first step. Then, c-axis oriented AlN films with small grain size were deposited at the second step. The effects of the growth time at the first and second step on the microstructure and the c-axis orientation of the AlN films were studied. It was found that the c-axis orientation of the AlN films is strongly dependent on the film thickness at the first step and the substrate temperature at the second step. With optimal process conditions, the full-width at half-maximum of the AlN (0002) peak rocking curve decreased to a minimum of 4.1° and the root-mean-square surface roughness of the prepared AlN films was 4.3 nm. The prepared AlN films have potential applications in piezoelectric microelectromechanical-systems and surface acoustic wave devices.

Effect of Methane Flow Rate on Growth and Properties of TiSi-C:H Films Deposited by Middle-frequency Magnetron Sputtering

Abstract The TiSi-C:H films were deposited on the silicon and the stainless steel substrates by middle-frequency magnetron sputtering Ti80Si20 targets using the methane gas as the precursor. The effects of the methane flow rate on the deposition rate, the structure, the mechanical and tribological properties were investigated. The results demonstrate that the structure, the mechanical and tribological properties of the films strongly depend on the methane flow rate. The deposited films exhibit a transition from a tapered columnar nanocomposite structure consisting of ~10 nm nanocrystallites and amorphous phases to an amorphous structure with increasing of methane flow rate. The films deposited at a low methane flow rate show high hardness, high internal stress and high wear rates, whereas the films deposited at high methane flow rate show a decrease in hardness and internal stress but an improvement in tribological performance. The variations on the mechanical and tribological properties may be attributed to the evolution of the microstructures of the films with increasing of methane flow rate.

Development of (Cr,Al)ON coatings using middle frequency magnetron sputtering and investigations on tribological behavior against polymers

Plastic processing is an enormous and expanding commercial sector. Injection molding and extrusion are common techniques for worldwide efficient mass production of plastic components with high shape accuracy and high surface quality for a broad variety of applications. Adhesive and abrasive wear as well as corrosion taking place during the production of plastic products and high deforming forces lead to the necessity of developing new material concepts. Ternary nitride and oxide hard coatings deposited by PVD (physical vapor deposition) find widespread application as hard protective coatings against wear and corrosion due to their outstanding tribological, mechanical and chemical properties. Besides ternary nitrides and oxides, quaternary chromium based oxy-nitride coating systems as (Cr1−xAlx)ON are promising candidates for tribological applications revealing high potential for decreasing adhesion and deforming forces between PVD coated tool and plastics melt during the production, e.g. of optical components or microstructered parts. The present work deals with the development of chromium based oxy-nitride hard coatings (Cr1−xAlx)ON on tool steel AISI 420 (X42Cr13, 1.2083) using middle frequency (mf) pulsed magnetron sputtering (MS) PVD technology. The aluminum content of the (Cr1−xAlx)ON coatings was varied in the range of 10.3at.-% and 68.0at.-%. By means of optical emission spectroscopy (OES) the deposition process was monitored regarding Cr/Cr+ and Al/Al+ ratios and the working points were varied via oxygen gas flow. Morphology, mechanical properties, phase and chemical composition were analyzed. Adhesion behavior between (Cr1−xAlx)ON coatings towards plastics by high temperature contact angle measurements revealed a significant impact of the coatings' chemical composition determined by depth resolved electron probe micro analysis (EPMA). Tribological model tests in a pin-on-disk-tribometer verified a positive influence of (Cr1−xAlx)ON coatings on the adhesion behavior towards polymers which is directly linked to lowering of deforming forces. This makes oxy-nitride (Cr1−xAlx)ON hard coatings a promising candidate for the production of optical components or microstructured parts by injection molding or extrusion.

CrN/AlN nanolaminate coatings deposited via high power pulsed and middle frequency pulsed magnetron sputtering

Nanolaminate coatings based on transition metal nitrides such as CrN, AlN and TiN deposited via physical vapor deposition (PVD) have shown great advantage as protective coatings on tools and components subject to high loads in tribological applications. By varying the individual layer materials and their thicknesses it is possible to optimize the coating properties, e.g. hardness, Young's modulus and thermal stability. One way for further improvement of coating properties is the use of advanced PVD technologies. High power pulsed magnetron sputtering (HPPMS) is an advancement of pulsed magnetron sputtering (MS). The use of HPPMS allows a better control of the energetic bombardment of the substrate due to the higher ionization degree of metallic species. It provides an opportunity to influence chemical and mechanical properties by varying the process parameters. The present work deals with the development of CrN/AlN nanolaminate coatings in an industrial scale unit by using two different PVD technologies. Therefore, HPPMS and mfMS (middle frequency magnetron sputtering) technologies were used. The bilayer period Λ, i.e. the thickness of a CrN/AlN double layer, was varied between 6.2nm and 47.8nm by varying the rotational speed of the substrate holders. In a second step the highest rotational speed was chosen and further HPPMS CrN/AlN coatings were deposited applying different HPPMS pulse lengths (40, 80, 200μs) at the same mean cathode power and frequency. Thickness, morphology, roughness and phase composition of the coatings were analyzed by means of scanning electron microscopy (SEM), confocal laser microscopy, and X-ray diffraction (XRD), respectively. The chemical composition was determined using glow discharge optical emission spectroscopy (GDOES). Detailed characterization of the nanolaminate was conducted by transmission electron microscopy (TEM). The hardness and the Young's modulus were analyzed by nanoindentation measurements. The residual stress was determined via Si microcantilever curvature measurements. The phase analysis revealed the formation of h-Cr2N, c-CrN and c-AlN mixed phases for the mfMS CrN/AlN coatings, whereas the HPPMS coatings exhibited only cubic phases (c-CrN, c-AlN). A hardness of 31.0GPa was measured for the HPPMS coating with a bilayer period of 6.2nm. The decrease of the HPPMS pulse length at constant mean power leads to a considerable increase of the cathode current on the Cr and Al target associated with an increased ion flux towards the substrate. Furthermore, it was observed that the deposition rate of HPPMS CrN/AlN decreases with shorter pulse lengths, so that a CrN/AlN coating with a bilayer period of 2.9nm, a high hardness of 40.8GPa and a high compressive stress (−4.37GPa) was achieved using a short pulse length of 40μs.