Laser Physical Vapor Deposition Research Articles

A study on the wear and corrosion resistance of high-entropy alloy treated with laser shock peening and PVD coating

A cross-scale study on the effect induced by laser shock peening (LSP) and physical vapor deposition (PVD) coating on the wear and corrosion resistance of FeCoCrNiAl high entropy alloys (HEA) has been made in this work. The nano scale FeCoCrNiAl HEA coating on substrate 304 steel and microscale FeCoCrNiAl HEA has been acquired through PVD nanocoating and LSP, respectively. The micro hardness, friction and corrosion properties have been investigated to evaluate the reliability of the material in application. The results of microhardness and wear test indicate that both approaches have increased the surface hardness of HEA through grain refinement. And the results for corrosion test reveal a competing effect between grain refinement and compressive stress. As the enhancement brought by PVD nano coating is not comparable to the cast sample, due to the side effect brought by grain refinement which will reduce the corrosion resistance. Surprisingly, specimens treated with LSP have better performance in corrosion resistance, as the compressive residual stress induced by LSP enhanced the adhesion between the substrate and modified layer, forming dense passive films to inhibit corrosion ions in the environment and successfully neutralized the side effect brought by grain refinement. Therefore, the modified layer induced by LSP on the surface contributes to the improvement of both wear resistance and corrosion resistance.

Wear behaviours of PVD-TiN coating onTi-6Al-4V alloy processed by laser powder bed fusion or conventionally processed

Ti-6Al-4V alloy is the most preferred alloy used in laser powder bed fusion (LPBF) and physical vapour deposition (PVD) coating may often be needed. However, whether the wear performance of the coating on the high hardness LPBF Ti-6Al-4V substrate may perform differently to that on the conventionally processed (CP) and significantly lower hardness alloy substrate has not been clear. In this study, dry sliding wear tests have been conducted on PVD TiN-coated Ti-6Al-4V samples processed either by LPBF or by CP, using WC-Co as counter material. It has been found that local fracturing of coating after being thinned to 0.4–0.5μm in both coated LPBF and CP samples is similar. The major wear mechanism leading to a gradually rapid increase in wear rate of the coated samples will be demonstrated and explained through a wear process described as thickness reduction and local fracturing of the coating before the widening of the wear track. It will be shown that the local fracturing of coating was accompanied by the local deformation in CP substrate due to its low hardness. For the LBPF substrate, the deformation was not readily observed. That the higher amount of deformation underneath the coating for the case of CP substrate has affected little the overall wear rate will be illustrated.

Effect of MoS2 film on memristor characteristics of ZnO film

Memory resistive devices using a ZnO dielectric layer are promising due to the transparent nature, lower operating voltage, synthesis compatible with semiconductor processing, and ability to control using magnetic fields. In the present work, niobium incorporated MoS2 films in combination with ZnO are used to form diode-resistor devices with memory. The two device structures p-Si-SiO2/Pt/MoS2(Nb)/ZnO/Ag and p-Si-SiO2/Pt/ZnO/Ag are grown using laser physical vapor deposition. The resistive characteristics are investigated as a function of temperature for comparison. The unipolar I-V characteristics of Pt/ZnO/Ag device films were found to be nonreproducible, and the temperature dependence was irregular for negative polarity. The unipolar I-V characteristics of Pt/MoS2(Nb)/ZnO/Ag device films were found to be reproducible. The temperature dependence of the I-V characteristics was regular for both polarities. The presence of a MoS2 film is found to improve and distinguish the effect of the polarity of the applied field on the unipolar device characteristics by the formation of a p-n device configuration. The conductance in the transition from a low resistance state to a high resistance state was found to follow the Schottky emission with the apparent barrier height being influenced by the p-n junction.

Low resistance metal contacts on MoS2 films deposited by laser physical vapor deposition

Niobium doped MoS2 films were grown on sapphire and SiO2-p-Si substrates by laser physical vapor deposition at 600 °C. The nature of conductivity in MoS2 film on sapphire was found to be n-type while that in the film on SiO2-p-Si was p-type. Metal contacts with Al, Mo, Ta and Au were deposited by laser physical deposition on the MoS2 films. Applied current versus voltage measurements were made at room temperature. In addition, applied voltage versus current measurements were made as a function of temperature from 270 to 400 K. The two sets of measurements were used to determine the ideality factor, series resistance and Schottky barrier height for the four metal contacts. Lower resistance contacts were found to form with Ta and Mo for n-type films on sapphire and with Al and Mo for p-type films on SiO2-p-Si. The value of Schottky barrier height for the four metal films on SiO2-p-Si remained closer but differed for films on sapphire. The Schottky barrier height was found to increase with applied voltage indicating the influence of interface states and defects present in the films.

Laser-structured high performance PVD coatings

Structured plastic components, which are used for flow-optimization, self-cleaning surfaces and optical applications, are usually produced by injection molding using structured tools. A suitable technique for structuring these tools on macro and nanometer scales is laser ablation, which offers a high level of accuracy and flexibility. The influence of laser treatments for the fabrication of nanostructures on the surface properties of steel has been extensively investigated. In contrast, there are only few studies dealing with the cause-effect mechanisms between a corresponding laser treatment and PVD (physical vapor deposition) hard coatings.This work deals with the influence of a laser nanostructuring on the properties of different CrAl-based PVD hard coatings. For this purpose, three coatings, one nitride (Cr,Al)N and one oxynitride (Cr,Al)ON, as well as one CrN/AlN nanolaminate were deposited on steel AISI 420 (X42Cr13, 1.2083) using a PVD process. The coatings were structured by means of an ultra-short pulsed (USP) laser with a varying laser pulse energy (Ep) ranging from Ep1=0.005mJ over Ep2=0.011mJ to Ep3=0.018mJ. On the one hand, an increasing laser pulse energy leads to significantly greater structural depths. This was quantified by confocal laser scanning microscopy (CLSM). On the other hand, it has been found that, in excess of a certain laser pulse energy, the universal hardness of the coatings decreases. By means of microstructural investigations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), this effect was investigated and characterized. It was found that thermal effects induced during laser structuring lead to an increasing ratio of amorphous to crystalline domains of the PVD coating, causing the reduction in hardness. Finally, suitable combinations of PVD hard coatings and laser structuring parameters are recommended.

Initial stages of delamination of the aluminum film from silicon wafer

Aluminum films of thickness 0.5 µm were deposited on silicon substrates by pulsed laser physical vapor deposition. The substrate with the film was subjected to laser pulses from the backside of the wafer to initiate delamination of the film. Subsequently, the front side of the film was examined by atomic force, and optical and scanning electron microscopy, and found to contain blisters of different sizes. In addition, larger regions of the film debonded but did not spall. Transient thermo-reflectance was used to study the acoustic oscillations generated in the larger regions of the debonded film using the incidence of a pulsed laser beam with wave length of 532 nm and pulse repetition frequency 10 Hz. The periodicity of the acoustic oscillations was used to determine the size of the film that oscillated. The periods varied from 0.088 to 1.900 µs and the corresponding radii of the oscillating film from 296 to 6384 µm. The work of adhesion was found to reach a maximum value at blister radius close to 25 µm. There were no acoustic oscillations from the delaminated film in the blisters. Acoustic beats were also generated from larger debonded film by superposition of two acoustic oscillations. These results were used to investigate the initial stages of delamination of the films from the substrates.

Nature of electrical conduction in MoS2 films deposited by laser physical vapor deposition

Molybdenum disulfide (MoS2) films with n- and p-type conductivity are considered to be important for potential use in next generation devices. Laser physical vapor deposition is used in the present work to deposit undoped, niobium (Nb)-doped and tungsten (W)-doped films on sapphire (Al2O3), silicon oxide (SiO2)-n-Si and silicon oxide (SiO2)-p-Si substrates maintained at 600 °C. The films are characterized for the nature of charge carriers, composition, lattice orientation and phonon signature. Results from Seebeck and Hall measurements corroborate to show that all films on sapphire and SiO2-n-Si are n-type whereas films on SiO2-p-Si are p-type with a higher activation energy for conduction. The reasons for the difference in nature of conductivity in the films are investigated. Sulfur deficient films are predominantly n-type; however, the presence of adsorbed oxygen and molybdenum trioxide (MoO3) in the films on SiO2-p-Si is found to be responsible for p-type conductivity.

Zinc Oxide Nanoparticles: chemical, physical and Biosynthesis Synthesis and its some Applications

This review article described the major synthesis of Zinc oxide nanoparticles with various ways, such as physical synthesis, chemical synthesis and Biosynthesis. Chemical synthesis as Hydrothermal Technique, Vapor Transport, Precipitation Method, Self-Combustion technique, Sol-gel method and microemulsion method. Physical synthesis as high-energy ball milling method, laser ablation method and Physical vapor deposition method. Biosynthesis Includes synthesis through fungi, plants, bacteria Some applications of zinc oxide nanoparticles have been listed.

Development of new duplex treatments on 100Cr6steel combining Thermochemical Treatments, Laser Shock Peening and Physical Vapour Deposition

100Cr6 steel (AISI 52100) is one of the most used steel grades in the manufacturing of through hardening bearings mainly due to its properties: controlled impurities during steel making process, high hardenability and well known mechanical properties such as wear and fatigue resistance on clean environments. These characteristics play an important role on the performance of a bearing together with the bearing design, loads and environment. However, there is an increasing set of demanding applications where the above mentioned steel does not fulfil the required needs and thus, bearing manufacturers continuously work on the development of technologies to improve the bearing performance.Nowadays thermochemical treatments (TCT), such as carbonitriding are being applied to this steel in order to enhance the performance of such pieces in contaminated environment, where particles can produce defects on the raceway, increasing the onset of defects that eventually lead to premature fail. These treatments induce the formation of carbides and nitrides which are directly related to the enhancement of the wear resistance and also to increasing the amount of Retained Austenite (RA) in the surface which may have a beneficial effect as it delays the crack propagation on subsurface regions, then increasing bearing fatigue life.In this work, different TCTs have been applied to 100Cr6 steel flat samples. Using a tribometer (ball-on-disc configuration) and a grinding machine, surface and in-depth wear resistance measurements have been carried out, obtaining wear resistance profiles that have been correlated with the microstructure, microhardness profiles and RA content.The most promising TCT has been combined either with Laser Shock Peening (LSP) treatments or carbonaceous Physical Vapour Deposition (PVD) coatings with the aim of improving not only the wear resistance but also the CoF of the duplex treated sample.The results obtained on flat samples are promising; the combination of treatments produces long-lasting low CoF and a reduction of 60% in the wear rate. However, the treatments should be applied on real pieces and tested in a test bench in order to obtain more appropriate data about the lifespan of duplex treated bearings.

Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu)

Molybdenum disulfide (MoS2) films were deposited on sapphire (0001), Si (001) and graphene on Cu by laser physical vapor deposition at 600°C for different time periods to achieve control of thickness. MoS2 film was found to grow on all the substrates in the (0002) orientation. Films are found to be S-deficient and a free Mo peak was observed in the x-ray diffraction. Raman spectroscopy showed the characteristic peaks of MoS2 film with decreasing separation between the A1g and E 2g 1 peaks for a shorter time of deposition or smaller thickness of the film. MoS2 films on sapphire substrate showed additional peaks due to MoO3 and Mo4O11 phases. Films on Si substrate and graphene on Cu contained only the characteristic peaks. MoS2 films on graphene suppressed the graphene peak as a result of large fluorescence background in the Raman spectrum. Interfacial effects and the presence of an oxygen impurity are considered responsible for the large fluorescence background in the Raman spectrum. X-ray photoelectron spectroscopy indicated substrate interaction with the films on sapphire and Si. Coverage of the film on the substrates is uniform with uniform distribution of the Mo and S as evidenced from the x-ray maps. Atomic force microscopy image revealed the surface of the film on sapphire to be very smooth. Electrical conductance measurements showed the MoS2 film on sapphire is semiconducting but with much lower activation energy compared to the bandgap. The presence of excess Mo in the film is considered responsible for the lower activation energy.

Thermal conductivity and interface thermal conductance of thin films in Li ion batteries

Abstract Laser physical vapor deposition is used to deposit thin films of lithium phosphorous oxynitride in nitrogen and lithium nickel manganese oxide in oxygen ambient on Si substrate. LIPON film is also deposited on LiNiMnO film that is deposited on Si. Graphene films consisting of graphene platelets are deposited on Si substrate from a suspension in isopropyl alcohol. Li-graphene films are obtained after Li adsorption by immersion in LiCl solution and further drying. Transient thermo reflectance signal is used to determine the cross-plane thermal conductivity of different layers and interface thermal conductance of the interfaces. The results show that LIPON film with lower thermal conductivity is a thermal barrier. The interface thermal conductance between LIPON and Au or Si is found to be very low. Thermal conductivity of LiNiMnO is found to be reasonably high so that it is not a barrier to thermal transport. Film with graphene platelets shows a higher value and Li adsorbed graphene film shows a much higher value of cross-plane thermal conductivity. The value of interface thermal conductance between graphene and Au or Si (100) substrate is also much lower. The implications of the results for the thermal transport in thin film Li batteries are discussed.

Thermal Conductivity and Interface Thermal Conductance of Titanium Silicide Films on Si

Titanium silicide films were prepared by magnetron sputtering of Ti on B-doped Si (100) and annealing at different temperatures up to 700 °C in argon atmosphere. Films were also prepared by laser physical vapor deposition (LPVD) of Ti at 500 °C and 600 °C on B-doped Si (100) followed by in situ annealing. The films were characterized by X-ray diffraction for phase identification, scanning electron microscopy for interface microstructure and oxygen level, atomic force microscopy for interface roughness, transient thermoreflectance for thermal conductivity and interface thermal conductance of the interface with Si. Annealing at 700 °C for 1 h was responsible for the complete formation of C54 phase. LPVD at 500 °C and 600 °C was responsible for C54 formation with smaller grain size, but unreacted Ti and other silicide phases were also present. The interface in all the films was continuous with the absence of voids. The thermal conductivity of the films increased for higher processing temperature. The interface thermal conductance for films prepared below 700 °C was lower. Film annealed at 700 °C significantly showed higher interface thermal conductance and lower effective thermal resistance. Comparison of thermal properties of the TiSi2 films with that of WSi2 films prepared previously showed that the effective thermal resistance of the C54 phase is lower.

Fabrication and tribological properties of Al2O3/TiC ceramic with nano-textures and WS2/Zr soft-coatings

To improve the tribological properties of the solid contact surfaces, the surface micro/nano-texturing and thin film lubrication are two effective ways to alleviate adhesion, friction and wear of the counter-parts. In this paper, the nano-textures and WS2/Zr soft-coatings were made on the Al2O3/TiC ceramic surface by femtosecond laser technology and physical vapor deposition (PVD) method. The microstructural and fundamental properties of the nano-textures and WS2/Zr soft-coatings were examined, and the friction and wear properties of nano-textures, WS2/Zr soft-coatings and a combination of nano-textures and WS2/Zr soft-coatings on Al2O3/TiC ceramic surface were investigated by carrying out sliding friction tests. Results show that nano-textures increase the adhesion strength between the coatings and substrate; the friction coefficient and wear are reduced by the nano-textures and WS2/Zr soft-coatings, a combination of nano-textures and WS2/Zr soft-coatings shows the best efficiency in improving the tribological properties; meanwhile, the nano-textures significantly increase the wear life of initial WS2/Zr lubricant coatings. The possible effect mechanism of the nano-textures and WS2/Zr soft-coatings was discussed.

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

ABSTRACTIn this work, we report on ion‐implanted, high‐efficiency n‐type silicon solar cells fabricated on large area pseudosquare Czochralski wafers. The sputtering of aluminum (Al) via physical vapor deposition (PVD) in combination with a laser‐patterned dielectric stack was used on the rear side to produce front junction cells with an implanted boron emitter and a phosphorus back surface field. Front and back surface passivation was achieved by thin thermally grown oxide during the implant anneal. Both front and back oxides were capped with SiNx, followed by screen‐printed metal grid formation on the front side. An ultraviolet laser was used to selectively ablate the SiO2/SiNx passivation stack on the back to form the pattern for metal–Si contact. The laser pulse energy had to be optimized to fully open the SiO2/SiNx passivation layers, without inducing appreciable damage or defects on the surface of the n+ back surface field layer. It was also found that a low temperature annealing for less than 3 min after PVD Al provided an excellent charge collecting contact on the back. In order to obtain high fill factor of ~80%, an in situ plasma etching in an inert ambient prior to PVD was found to be essential for etching the native oxide formed in the rear vias during the front contact firing. Finally, through optimization of the size and pitch of the rear point contacts, an efficiency of 20.7% was achieved for the large area n‐type passivated emitter, rear totally diffused cell. Copyright © 2014 John Wiley & Sons, Ltd.

Laser physical vapor deposition of nanocrystalline dots using nanopore filters

Nanocrystalline dots of n-type Bi2Te2.7Se0.3 thermoelectric compound and of silicon were deposited by laser physical vapor deposition using polycarbonate or alumina nanopore filters as templates. The films were characterized by scanning electron microscopy and transmission electron microscopy. Using a pore size of 0.2 μm in the nanopore filters, a uniform distribution of crystallites with size 3 to 4 nm and separated from each other was observed by high-resolution transmission electron microscopy. The dots were all single crystals, as seen by the resolved crystal lattice planes. The compositions of the crystallites, of both the thermoelectric compound and silicon, were analyzed by energy dispersive X-ray analysis. The composition of the thermoelectric compound nanocrystals differed significantly from that of the bulk target, likely due to vapor pressure differences of the constituent elements. The results are promising for synthesis of nanocrystalline dots with controlled size but compositional control is a different task that is not carried out. The observations illustrate that nonstoichiometry is a result of difference in the vapor pressure of different elements in the compound. The method of synthesis is found to be suitable for deposition of quantum dots below certain size determined by the size of the pores in the porous filter.

Laser physical vapor deposition of boron carbide films to enhance cutting tool performance

Laser physical vapor deposition was used to deposit thin films of boron carbide on Si (100) and WC–Co substrates at 550 °C under different pressures of methane atmosphere. Grazing incidence X-ray diffraction was used to identify a boron carbide phase, which exhibited weak peaks. The presence of particulates in the size range of 50 nm–3 µm embedded in an amorphous matrix was observed by scanning electron microscopy. Raman spectroscopy indicated that as methane partial pressure was increased during deposition, the amount of disorder with the boron carbide structure also increased. Also, the nanoindentation hardness decreased, while the coefficient of friction and scratch adhesion strength increased. These effects are attributed to an increase in amorphous phase/disorder in the films. Wear tests conducted by machining particleboard using boron carbide coated WC–Co tools in the absence of methane showed the same wear rate as tools coated under higher methane pressures.

Evolution of Ag nanocrystal films grown by pulsed laser deposition

We have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare metal-on-insulator growth morphology in Pulsed Laser Deposition (PLD) and Physical Vapor Deposition (PVD). Such films deposited from a thermal vapor are known to exhibit a characteristic morphological progression beginning with isolated three-dimensional islands and ending with a percolating, continuous film that conducts electrically. We have studied this progression for Pulsed Laser Deposition, a technique that differs from PVD in that depositing species arrive in short bursts (<10 microseconds) with kinetic energy typically of 10–100 eV. Kinetic Monte Carlo (KMC) simulations that take into account only the pulsed nature of the flux predict that PLD films should advance to percolation with relatively less deposition compared with PVD under otherwise identical conditions. Our experiments, with PLD and PVD performed in the same chamber, reveal that PLD films actually require more deposition to reach percolation. We conclude that energetic effects are important in determining morphology evolution.

Deposition and Characterization of Carbon Nitride Films by Laser Processed Methods

AbstractLaser assisted methods such as laser physical vapor deposition (LPVD) and laser induced chemical vapor deposition (LCVD) have been utilized to grow carbon nitride (CNx) films on various substrates. It has been shown that the both techniques produce good quality thin films of CNx. In LPVD, a laser beam (λ= 248 nm) has been used to ablate the pyrolytic graphite target in nitrogen atmosphere, where as CO2 laser was to irradiate carbon-nitrogen containing mixtures such as C2H2/N2O/NH3 in LCVD method. A comparative analysis will be presented in terms of structural properties of CNx films prepared by both techniques.

Comparison of microstructural features of diamond composite coatings with polycrystalline diamond or boron nitride brazed on tungsten carbide tools

We have investigated microstructure and properties of diamond composite coatings on cemented tungsten carbide tool substrates, and compared wear resistance of these coatings with that of polycrystalline diamond (PCD) and polycrystalline boron nitride (PCBN) tools brazed on to cemented tungsten carbide substrates. The diamond composite coatings consist of layers of discontinuous diamond, TiC, and continuous diamond. In these composite layers, diamond is deposited by hot filament chemical vapor deposition and TiC by pulsed laser physical vapor deposition. Thermal stresses in the composite layer and the substrate are reduced and thereby help to improve the adhesion of diamond to the tool substrate. These tool coatings are characterized by scanning electron microscopy, Raman spectroscopy, secondary ion mass spectroscopy, and x-ray diffraction. The results of microstructural characterization and analysis of chemical composition are correlated with wear resistance. The present results demonstrate the advantages associated with composite diamond coatings compared to PCD and PCBN tool coatings.

Multilayer diamond coatings on silicon carbide

Multilayer composite diamond coatings on SiC substrates with improved adhesion and wear resistance have been developed. The coatings consist of a first layer of discontinuous diamond crystallites which are anchored to the SiC substrates by an interposing layer of TiC or TiN films. A top layer of continuous diamond film is grown epitaxially on the first layer. The diamond films and TiC or TiN films were deposited using hot filament chemical vapor depostion and laser physical vapor deposition, respectively. The diamond films were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion of the diamond coatings to SiC seal ring substrates was investigated by using overlap polishing with diamond paste or by wear test against Al-12.5%Si alloy. The results show that, after introducing an interposing layer, the internal thermal stresses are reduced so that the adhesion of diamond coatings on the SiC substrates is improved significantly.