Pulsed Sputtering Deposition Research Articles

WITHDRAWN: Hard and superhard nanolaminate and nanocomposite coatings for machine elements based on Ti6Al4V alloy

Purpose: Verification of a series of hybrid treatments of Ti6Al4V alloy consisting of primary diffusion hardening of the substrate with subsequent deposition of wear resistant coatings. Design/methodology/approach: Different nanolaminate and nanocomposite coatings were deposited with use of four different methods including a newly developed high density gas pulsed plasma MS technique. After deposition the coatings were investigated using OM, SEM, HRTEM, XRD, XPS, nanoindentation, DaimlerBenz, ball-on-plate and scratch tests. Findings: Besides an important increase of Ti6Al4V alloy hardness much greater further increase of hardness was obtained due to coatings deposition up to 53 GPa in case of a nanolaminate coating and to 47 GPa in case of a nanocomposite nc-TiN/a-SiN coating. At the same time the volume wear coefficient decreases several orders of magnitude for all the coatings. Simultaneously the friction coefficient decreased to a great extent except for the nc-TiN/a-SiN coating. Research limitations/implications: High density gas pulsed plasma magnetron sputtering is an effective method for superhard coatings deposition, however the roughness of the deposited nc-TiN/a-SiN coating was greater than after conventional magnetron sputtering. This finding needs further experimental and theoretical investigation. Practical implications: Greater surface roughness and high resistance to wear of the coatings synthesized using the newly developed gas pulsed plasma magnetron sputtering deposition limits their application to wear protection of cutting tools rather than for friction reduction in tribological couples. Originality/value: Applicability of the broad spectrum of nanolaminate and nanocomposite coatings as well as different CVD and PVD techniques for an improvement of tribological properties of Ti6Al4V alloy was analyzed in the paper including a newly developed original high density gas pulsed plasma magnetron sputtering technique.

PULSED PLASMA DEPOSITION OF OXIDE HARD COATINGS

In the last years a variety of plasma sources have been developed for film deposition by magnetron sputtering. In addition to RF- and DC-sputter sources, pulsed plasma sources are gaining increased attention in sputter technology. This interest is driven by the wish of depositing coatings with superior properties as compared to those deposited by conventional techniques. One prominent example of coatings that are significantly enhanced by the usage of pulsed sputter deposition is alumina. Although crystalline α-alumina can be deposited by thermal CVD at temperatures above 1000° C for two decades, no process for the deposition of crystalline alumina at low temperatures is commercially available up to now. In this paper, the results of a detailed study of the plasma parameters during bipolar pulsed magnetron sputtering and their effect on the properties of alumina hard coatings is reported. Langmuir type voltage measurements at the substrate position, optical emission spectroscopy as well as mass spectroscopy were used to monitor the effect of target poisoning on the reactive deposition of alumina. Those principal observations were connected to easily available process parameters like discharge voltage and oxygen partial pressure. Based on these measurements, the deposition of crystalline γ-alumina with high hardness and good adhesion under technical conditions was achieved.

Transparent conducting impurity-doped ZnO thin films prepared using oxide targets sintered by millimeter-wave heating

The preparation of transparent conducting impurity-doped ZnO thin films by both pulsed laser deposition (PLD) and magnetron sputtering deposition (MSD) using impurity-doped ZnO targets sintered with a newly developed energy saving millimeter-wave (28GHz) heating technique is described. Al-doped ZnO (AZO) and V-co-doped AZO (AZO:V) targets were prepared by sintering with various impurity contents for 30min at a temperature of approximately 1250°C in an air or Ar gas atmosphere using the millimeter-wave heating technique. The resulting resistivity and its thickness dependence obtainable in thin films prepared by PLD using millimeter-wave-sintered AZO targets were comparable to those obtained in thin films prepared by PLD using conventional furnace-sintered AZO targets; a low resistivity on the order of 3×10−4Ωcm was obtained in AZO thin films prepared with an Al content [Al∕(Al+Zn) atomic ratio] of 3.2at.% and a thickness of 100nm. In addition, the resulting resistivity and its spatial distribution on the substrate surface obtainable in thin films prepared by rf-MSD using a millimeter-wave-sintered AZO target were almost the same as those obtained in thin films prepared by rf-MSD using a conventional powder AZO target. Thin films prepared by PLD using millimeter-wave-sintered AZO:V targets exhibited an improved resistivity stability in a high humidity environment. Thin films deposited with a thickness of approximately 100nm using an AZO:V target codoped with an Al content of 4at.% and a V content [V∕(V+Zn) atomic ratio] of 0.2at.% were sufficiently stable when long-term tested in air at 90% relative humidity and 60°C.

Coating material innovation in conjunction with optimized deposition technologies

Concentrating on physical vapour deposition methods several examples of recently developed coating materials for optical applications were studied for film deposition with optimized coating technologies: mixed evaporation materials for ion assisted deposition with modern plasma ion sources, planar metal and oxide sputter targets for Direct Current (DC) and Mid-Frequency (MF) pulsed sputter deposition and planar and rotatable sputter targets of transparent conductive oxides (TCO) for large-area sputter deposition. Films from specially designed titania based mixed evaporation materials deposited with new plasma ion sources and possible operation with pure oxygen showed extended ranges of the ratio between refractive index and structural film stress, hence there is an increased potential for the reduction of the total coating stress in High–Low alternating stacks and for coating plastics. DC and MF-pulsed sputtering of niobium metal and suboxide targets for optical coatings yielded essential benefits of the suboxide targets in a range of practical coating conditions (for absent in-situ post-oxidation ability): higher refractive index and deposition rate, better reproducibility and easier process control, and the potential for co-deposition of several targets. Technological progress in the manufacture of rotatable indium tin oxide (ITO) targets with regard to higher wall-thickness and density was shown to be reflected in higher material stock and coater up-time, economical deposition rates and stable process behaviour. Both for the rotatable ITO targets and higher-dense aluminum-doped zinc oxide (AZO) planar targets values of film transmittance and resistivity were in the range of the best values industrially achieved for films from the respective planar targets. The results for the rotatable ITO and planar AZO targets point to equally optimized process and film properties for the optimized rotatable AZO targets currently in testing.

Formation of TiOx films produced by high-power pulsed magnetron sputtering

Formation of thin TiOx films produced by pulsed planar magnetron sputtering deposition is reported in this paper. The formation process and layer growth were controlled by (i) the ratio of reactive O2 in Ar/O2 working gas mixture and (ii) the pressure in the vacuum chamber. The magnetron, operated in a high-power pulse mode with a low repetition frequency of 250 Hz, reached maxima peak current Ip ∼ 50 A and magnetron current density peaks at ip ∼ 1 A cm−2. Particular spectral lines (Ar = 420.07 nm, Ar+ = 487.98 nm, Ti = 518.96 nm) emitted by the discharge were investigated using time-resolved photon counting measurements. The phases of deposited TiOx films were determined by grazing incidence x-ray diffractometry and thickness and density were calculated from x-ray reflectometry measurements; in addition composition and chemical bounds were revealed by x-ray photoelectron spectroscopy. The film diagnostics survey the existence of different crystalline phases in the Ti–O system and their formation. Discharge properties for example, deposition rate and time evolution of discharge current are also discussed.

Time-resolved optical emission spectroscopy during pulsed dc magnetron sputter deposition of Ti and TiO2 thin films

Time-resolved optical emission spectroscopy is applied to analyse pulsed dc magnetron plasmas during sputter deposition of Ti and TiO2 thin films. The studies are focused on the temporal behaviour of emissions of selected atomic titanium, argon and oxygen during the ‘on-time’, when the magnetron plasma source is turned on, and during the ‘reverse-time’, when the magnetron plasma source is turned off. Single and double exponential decays of the optical emissions were found during the ‘reverse-time’. During the ‘on-time’, we observed a rapid increase in some emissions with a more or less pronounced overshoot and a slow increase in other emissions which follow the temporal evolution of the conduction current. The various time constants can be related to the dynamics of the fast electrons, the Ar metastables, the Ti atoms (metallic mode) and the O atoms (oxide mode).

Influence of substrate conditions on the temporal behaviour of plasma parameters in a pulsed dc magnetron discharge

Using time-resolved optical emission spectroscopy and Langmuir probing, the effect of substrate bias (and the absence of the substrate) on the energetics and concentrations of the plasma species at different phases of the pulse have been investigated in a bi-polar unbalanced pulsed dc magnetron. The discharge was operated in a range of frequencies, 25–100 kHz, and duty cycles, 60–90%, at a constant Ar pressure of 0.66 Pa. In the presence of an electrically grounded substrate at the transition from discharge on to off (when the plasma potential is raised to values over +150 V relative to ground), we have detected a short-lived burst in optical emissions from transitions in Ar and Ti (of duration 200 ns) in the plasma bulk. We also detect an associated elevation in the effective electron temperature measured with the Langmuir probe (Teff> twice that during the rest of the cycle). This phenomenon, we believe, is due to the liberation and increased confinement of electrons emanating from the substrate due to local ion bombardment. With an electrically floating substrate there is a much weaker associated optical flash, and none in the absence of the substrate. The Langmuir probe results also show that in the on phases of the pulse, a general increase in effective electron temperature and density is observed with decreasing frequency and duty cycle, i.e. increased reverse times. The implications of the observed transient bulk heating of electrons on the pulsed sputter deposition process are briefly discussed.

Effects of High D.C. Hias Voltage on the Properties of Diamond-Like Carbon Films

ABSTRACTDiamond-like carbon (DLC) films were synthesized using pulsed plasma sputtering deposition techniques. Microscope and Raman scattering techniques were used to study the effects of bias voltages on the properties of diamond-like carbon films. With d.c. bias voltage up to 1000V, the smooth and thick DLC films together with a few nanoparticles were obtained. An increase of the d.c. bias voltage up to 2000V yielded thicker DLC films but its surface became slightly rough and size of particles became large. The crystalline properties of these particles were studied. A tiny diamond peak from Raman spectrum was also observed.

Glass and glass ceramic materials obtained by pulsed laser deposition in the BaO–TiO 2–B 2O 3 system

We obtained glasses by using the classical method of melting in an electric furnace at 1100–1450 °C for 2 h. The obtained samples were characterized by differential thermal analyses and X-ray diffraction. By controlled thermal treatments the samples were crystallized. BaTiO 3 and other barium polititanates were identified. The thin layers were obtained by pulsed laser deposition and magnetron sputtering deposition. By controlled thermal treatments the glasses were transformed to partial and full crystalline materials. Atomic Force Microscopy and Electron Microscopy were used to characterize the materials.

Plasma characteristics in pulsed direct current reactive magnetron sputtering of aluminum nitride thin films

Plasma diagnostics is important to identify plasma parameters and generate reproducible plasma in magnetron sputtering. Langmuir probes have been used to measure local plasma parameters such as electron temperature (Te), charge densities (ne and ni), and plasma potential (Vp). Pulsed direct current (dc) power in the midfrequency range (50–250 kHz) has been used in growing insulating films without charging accumulations at target. Recent investigations showed increased energetic particle bombardment of the substrate in pulsed power. In this work, aluminum nitride thin films were fabricated by pulsed dc power sputter deposition. The argon and nitrogen plasma was characterized by Langmuir probe measurement. The electron temperature in argon and nitrogen plasma was observed to increased from 3.06 to 5.32 eV when the pulsed dc frequency increased from 75 to 250 kHz. The ion density and energy flux were found to increase with frequency. This is believed to be from the stochastic heating generated by the fast oscillation in the target voltage wave form. The measured plasma characteristics were correlated with the crystal orientation of AlN thin films. The crystal structure of AlN thin films changed to (002) preferred orientations as the ion and energy flux increased.

The Tribological Behavior of MoS2-Cr Films Sliding Against an Aluminum Counterface

ABSTRACTThe tribological performance of MoS2-Cr films in a pin-on-disk test sliding against an aluminum ball has been examined in this study. The MoS2-Cr films were deposited by pulsed laser deposition (MoS2) and simultaneous sputter deposition of Cr, giving a Cr content in the film of 10 mol. %. The results were also compared with films of MoS2 alone. The frictional behavior of MoS2-Cr films was not improved compared to the MoS2 alone, so SEM/EDS studies of the ball and flat were conducted to determine the nature of the transfer films and examine any interface reactions that occurred during the pin-on-disk (POD) test. In the early stages of the POD test (500 cycles) on the MoS2-Cr film, Al-oxide particles formed and caused cratering and scratching of the wear track, and the coefficient of friction neared 0.7. At later stages (9000 cycles), a thick oxide-based transfer film formed on the ball, but on the flat the track composition was closer to that of the original coating. For the films without Cr, after 104 cycles a smooth wear track was observed, and a thin transfer film of MoS2 was found within grooves on the ball wear scar along with Al oxide, which resulted in superior tribological performance.

Sputter deposition of crystalline alumina coatings

In the last years a variety of plasma sources have been developed for film deposition by magnetron sputtering. In addition to RF and DC sputter sources, pulsed DC and low-frequency plasma sources are gaining increased attention in sputter technology. This interest is driven by the wish of depositing coatings with superior properties as compared to those deposited by conventional techniques. One prominent example of coatings that are significantly enhanced by the usage of pulsed sputter deposition is alumina. Although crystalline α-alumina can be deposited by thermal CVD at temperatures above 1000 °C for two decades, no process for the deposition of crystalline alumina at low temperatures is commercially available up to now. In this paper, the results of a detailed study of the plasma parameters during bipolar pulsed magnetron sputtering and their effect on the properties of alumina hard coatings is reported. Langmuir type voltage measurements at the substrate position, optical emission spectroscopy as well as mass spectroscopy were used to monitor the effect of target poisoning on the reactive deposition of alumina. Those principal observations were connected to easily available process parameters like discharge voltage and oxygen partial pressure. Based on these measurements, the deposition of crystalline γ-alumina with high hardness and good adhesion under technical conditions was achieved.

Selective Surface Heat Treatment of Cr and CrN Coatings on Steel

Chromium and chromium nitride coatings on steels have been prepared with pulsed dc magnetron sputter deposition at a frequency of 185 kHz and a duty cycle of 96%. The coating process was carried out at 150 W with the substrate temperature maintained at 200°C. For nitride coatings, reactive sputter deposition was carried out in Ar with 3, 5, or 7%N2. Heat treatments were performed for coated steels with an infrared (IR) processing technique in an attempt to modify the interfaces and change coating properties. T he heat treatment was carried out at 400°C for 2 and 5 min. Characterisation of coated samples included X-ray diffraction (XRD), optical microscopy, and microhardness tests to verify the effect of the heat treatment. Results from XRD analysis indicated that IR heat treatment at 400°C for 2 or 5 min did not change the phases present in the coatings. Optical images of the coating microstructure show that cracks were developed on coatings deposited under 7%N2 even after only 2 min heat treatment at 400°C. Severity of cracking is reduced for coatings deposited under low nitrogen contents. No cracks were observed on coatings deposited without nitrogen. Microhardness measurements showed that for all coated specimens, 2 min IR treatment at 400°C gave the highest microhardness. For samples treated for 5 min, the microhardness decreased. X-ray diffraction analysis with slow scanning showed that CrN peaks were developed in the coatings deposited under 7%N2 and heat treated at 400°C for 2 and 5 min.

Pulsed low-energy ion-assisted growth of epitaxial aluminum nitride layer on 6H-silicon carbide by reactive magnetron sputtering

Epitaxial aluminum nitride thin films have been grown on silicon carbide (6H-SiC) substrates by pulsed low-energy ion-assisted reactive magnetron sputter deposition (+5/−20 V of bias pulses), with ion-assisted energy (Ei)≅22 eV, under ultrahigh-vacuum conditions. Surface ion interactions during the negative bias pulse gave rise to enhanced surface mobility of adatoms with beneficial effects, which extended over the limit of ion repelling in the positive pulse as the film thickness increased. High-resolution electron microscopy shows that a large (>90 nm) AlN domain width can form on the substrate. Domain-boundary annihilation and domain suppression during film growth have been observed. The growth rate also increased by a factor of ∼4 compared to growth conditions with no ion assistance (Ei=2 eV) and by a factor of 2 from dc ion-assisted growth. This indicates that the supply of nitrogen is a limiting factor for AlN formation and that the reactivity of nitrogen is increased on the growing AlN film surface for pulse ion-assisted deposition. High-resolution x-ray diffraction shows a reduction in the full width at half maximum of the rocking curve from 1490 to 1180 arcsec when pulsed ions are used. The cathodoluminescence shows high intensity of near-band edge emissions at wavelengths of 206 (6.02 eV) and 212 nm (5.84 eV) at a measured temperature of 5 K, with relatively low defect and oxygen and carbon impurity related emission, which is indicative of a high quality electronic material.

PULSED PLASMA DEPOSITION OF OXIDE HARD COATINGS

In the last years a variety of plasma sources have been developed for film deposition by magnetron sputtering. In addition to RF- and DC-sputter sources, pulsed plasma sources are gaming increased attention in sputter technology. This interest is driven by the wish of depositing coatings with superior properties as compared to those deposited by conventional techniques. One prominent example of coatings that are significantly enhanced by the usage of pulsed sputter deposition is alumina. Although crystalline a-alumina can be deposited by thermal CVD at temperatures above 1000 °C for two decades, no process for the deposition of crystalline alumina at low temperatures is commercially available up to now. In this paper, the results of a detailed study of the plasma parameters during bipolar pulsed magnetron sputtering and their effect on the properties of alumina hard coatings is reported. Langmuir type voltage measurements at the substrate position, optical emission spectroscopy as well as mass spectroscopy were used to monitor the effect of target poisoning on the reactive deposition of alumina. Those principal observations were connected to easily available process parameters like discharge voltage and oxygen partial pressure. Based on these measurements, the deposition of crystalline g-alumina with high hardness and good adhesion under technical conditions was achieved.

Ion-assisted pulsed magnetron sputtering deposition of ta-C films

The process of ion-assisted deposition of ta-C films by pulsed magnetron sputtering of a graphite target has been investigated. Probe measurements of the magnetron discharge plasma have been performed and its space- and time-dependent characteristics have been obtained as functions of the sputtering parameters and the bias voltage applied to the substrate. It has been shown that the density of the pulsed magnetron discharge plasma approaches values typical of pulsed laser or vacuum arc cathode sputtering of graphite (10 17−10 18 m −3). Raman scattering was used to examine the ta-C films produced at both low and high pulsed bias voltages applied to the substrate ( U sub<1 kV, τ=160 s and 1 kV< U sub<6 kV, τ=40 μs, respectively). It has been shown that in the first case the maximum content of diamond-like carbon in the coating (50–60%) is achieved at a lower energy per deposited carbon atom ( E C=100–300 eV) than in the second one (40–50% at E C=1100–1200 eV). Despite the lower diamond-like phase content in the coatings produced at a high bias voltage, they show better adhesion to the substrate due to the ion mixing between the film and the substrate and between the film layers. The use of shorter bias pulses is also important to prevent breakdowns of the deposited dielectric ta-C film.

Roll-to-roll pulsed dc magnetron sputtering deposition of WO 3 for electrochromic windows

This paper reports on the deposition conditions and properties of WO 3 films used as electrochromic layer in a monolithic device on a plastic substrate. The deposition technique employed was roll-to-roll pulsed dc magnetron sputtering. The oxide was deposited at room temperature in an argon and oxygen plasma on a transparent conducting ITO layer previously coated on a PET film. The influence of deposition parameters such as pulse mode, total pressure and oxygen partial pressure has been investigated, in order to obtain the best compromise between a high deposition rate and adequate electro-optical properties. As expected, the deposition rate increases with decreasing total pressure and oxygen partial pressure. To control the coloring/bleaching behavior, lithium ions from an aprotic electrolyte have been intercalated in films. Films with thickness around 400 nm exhibit a contrast ratio of 9:1. The optical efficiency increases slightly with increasing total pressure and lies between 30–40 cm 2 C −1. Further, the coloring and bleaching time decreases with increasing total pressure, coloring being faster than bleaching. This is consistent with UV–Vis ellipsometric measurements which reveal that the refractive index decreases with increasing total pressure. TEM investigations also confirm that films deposited at low total pressure exhibit a dense structure whereas those deposited at high-pressure exhibit a columnar structure.

The low-temperature electric conductivity of YBaCuO and LaSrMnO dielectric films obtained by a pulsed laser sputter deposition technique

We have studied the electric conductivity of YBaCuO and LaSrMnO dielectric films obtained by pulsed laser sputtering of targets possessing metallic conductivity. The plots of the sample resistance versus temperature R=R(T) measured at T<T cr(T cr=160–240 K) exhibit regions where R is independent of the temperature. This phenomenon is probably related to manifestations of the quantum confinement effects upon the conversion of small grains into quantum dots. In the region of T<T cr, the electric conductivity of the system is determined by a mechanism of the phononless electron tunneling with participation of the atomic-type states belonging to small grains (clusters) featuring metallic conductivity in the amorphous matrix.

In situ monitoring during pulsed laser deposition of complex oxides using reflection high energy electron diffraction under high oxygen pressure

A suitable in situ monitoring technique for growth of thin films is reflection high energy electron diffraction (RHEED). Deposition techniques, like pulsed laser deposition (PLD) and sputter deposition, used for fabrication of complex oxide thin films use relatively high oxygen pressures (up to 100 Pa) and are, therefore, not compatible with ultrahigh vacuum RHEED equipment. We have developed a RHEED system which can be used for growth monitoring during the deposition of complex oxides at standard PLD conditions. We are able to increase the deposition pressure up to 50 Pa using a two-stage differential pumping system. Clear RHEED patterns are observable at these high pressures. The applicability of this system is demonstrated with the study of homoepitaxial growth of SrTiO3 as well as the heteroepitaxial growth of YBa2Cu3O7−δ on SrTiO3. Intensity oscillations of the RHEED reflections, indicating two-dimensional growth, are observed up to several tens of nanometers film thickness in both cases.

Microstructural Study of CMR Films as a Function of Growth Temperature, As-Deposited and Annealed

AbstractThe properties encompassed by the family of complex metal oxides span the spectrum from superconductors to insulating ferroelectrics. Included in this family are the new colossal magnetoresistive perovskites with potential applications in advanced high density magnetic data storage devices based on single or multilayer thin films units of these materials fabricated by vapor phase deposition (PVD) methods. The realization of this potential requires solving basic thin film materials problems requiring understanding and controlling the growth of these materials. Toward this end, we have grown La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 on LaAlO3 single crystal substrates by pulsed laser and RF sputter deposition at temperatures from 500° C to 900° C and annealed at over 900° C for about 10 hours. The evolution of the microstructure of these films was studied by scanning probe microscopies and transmission electron microscopy (TEM).The results of SPM characterization showed that at the lower end of the growth temperature range, the as-grown films were polygranular with grain size increasing with temperature. The 500° C as-grown films appeared to be amorphous while the 750° C film grains were layered with terrace steps often one unit cell high. In contrast, films grown at 900° C consisted of coalesced islands with some 3-D surface crystals. After annealing, all films had coalesced into very large extended layered islands. The change in microstructure was reflected in a decreased resistivity of coalesced films over their unannealed granular precursors. Previous reported work on the growth of La0.84 Sr0.16MnO3 and La0.8Sr0 2CoO3 grown demonstrated the sensitivity of the microstructure to substrate and deposition conditions. Films grown on an “accidental” vicinal surface grew by a step flow mechanism.