AlN/Al dual protective coatings on NdFeB by DC magnetron sputtering

AlN/Al dual protective coatings were prepared on NdFeB by DC magnetron sputtering in a home-made industrial apparatus. Comparing with Al coating, AlN/Al coatings have a denser structure of an outmost AlN amorphous layer following an inner Al columnar crystal layer. The coatings and NdFeB substrate combine well, and moreover, there is occurrence of metallurgy bonding in the interface layer. Both Al and AlN/Al coatings have a good protective ability to NdFeB. Especially, the corrosion resistance of AlN/Al coated NdFeB is improved largely. AlN/Al and Al protective coatings not only do not deteriorate the magnetic properties of NdFeB, but contribute to their slight increase.     

Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

A study of TiMoN nano-multilayer coatings deposited by CFUBMSIP using DC and HIPIMS power

TiMoN nano-multilayer hard coatings have been deposited using the closed field unbalanced magnetron sputter ion plating (CFUBMSIP) technique. In one set of experiments, standard DC power supplies were used on four magnetrons in the CFUBMSIP system (4DC magnetrons). The second set of experiments was also in the same magnetic field configuration of CFUBMSIP, but three magnetrons were as again powered with standard DC whilst one magnetron with Ti target was supplied by a high power impulse magnetron sputtering (HIPIMS) power generator (3DC + 1HIPIMS magnetrons). Two elemental titanium sputtering targets and two of molybdenum were used to produce the TiMoN nano-multilayer coatings. Analysis of the coatings was carried out to investigate the differences in terms of properties, compositions and microstructures of the coatings deposited by these two sets of experiments. It was found that the coatings deposited by both sets of the experiments exhibited similar properties of high hardness, good adhesion and exceptional wear resistance, with a lower sliding friction than more commonly used hard coatings including TiN, CrN, TiAlN, CrTiAlN etc. Although the initial TiN coating as formed at the coating-substrate interface using the process of 3DC + 1HIPIMS magnetrons appeared to show a less oriented microstructure in comparison with that of the coating produced by the process using 4DC magnetrons, the compositions and cross sectional microstructures of the bulk of the coatings did not show significant differences, as observed by the cross sectional Transmission Electron Microscopy microstructures of these two types of TiMoN coatings.     

Study of the plasmas produced during the deposition of TiC/SiC thin films in a hybrid magnetron-laser system

Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser (λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range 250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied. Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar⁺ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed emission of C, C⁺, C₂, Ar, Ar⁺. Spectra (c) showed presence of all previously mentioned species and further of Ti⁺ ions emission was detected. The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and Institutional Research Plan AV CR No. AV0Z 10100522.     

X-ray photoelectron spectroscopy of nano-multilayered Zr-O/Al-O coatings deposited by cathodic vacuum arc plasma

Nano-multilayered Zr-O/Al-O coatings with alternating Zr-O and Al-O layers having a bi-layer period of 6-7 nm and total coating thickness of 1.0-1.2 μm were deposited using a cathodic vacuum arc plasma process on rotating Si substrates. Plasmas generated from two cathodes, Zr and Al, were deposited simultaneously in a mixture of Ar and O₂ background gases. The Zr-O/Al-O coatings, as well as bulk ZrO₂ and Al₂O₃ reference samples, were studied using X-ray photoelectron spectroscopy (XPS). The XPS spectra were analyzed on the surface and after sputtering with a 4 kV Ar⁺ ion gun. High resolution angle resolved spectra were obtained at three take-off angles: 15°, 45° and 75° relative to the sample surface.It was shown that preferential sputtering of oxygen took place during XPS of bulk reference ZrO₂ samples, producing ZrO and free Zr along with ZrO₂ in the XPS spectra. In contrast, no preferential sputtering was observed with Al₂O₃ reference samples. The Zr-O/Al-O coatings contained a large amount of free metals along with their oxides. Free Zr and Al were observed in the coating spectra both before and after sputtering, and thus cannot be due solely to preferential sputtering.Transmission electron microscopy revealed that the Zr-O/Al-O coatings had a nano-multilayered structure with well distinguished alternating layers. However, both of the alternating layers of the coating contained of a mixture of aluminum and zirconium oxides and free Al and Zr metals. The concentration of Zr and Al changed periodically with distance normal to the coating surface: the Zr maximum coincided with the Al minimum and vice versa. However the concentration of Zr in both alternating layers was significantly larger than that of Al. Despite the large free metal concentration, the Knoop hardness, 21.5 GPa, was relatively high, which might be attributed to super-lattice formation or formation of a metal-oxide nanocomposite within the layers.     

Optical properties of La2O3 doped diamond-like carbon films

A novel kind of La₂O₃ doped diamond-like carbon (DLC) films with thickness of 100-120 nm were deposited by unbalanced magnetron sputtering. Raman spectra and photoluminescence properties were measured by Raman spectrometer operated by 325 nm He-Cd laser and 514 nm Ar⁺ laser, respectively. The intensities of Raman spectra and photoluminescence are higher than those of pure DLC films. The La₂O₃ doped DLC films have the potential promising for the application of solar cell coatings.     

Composition and structure-property relationships of chromium-diboride/molybdenum-disulphide PVD nanocomposite hard coatings deposited by pulsed magnetron sputtering

The composition and structure-property relationships of physical vapour deposited coatings containing mixtures of CrB₂ and MoS₂ are reported. The coatings were produced by pulsed magnetron sputtering of loosely-packed powder targets formed from a blend of chromium and boron powders, alloyed with 12.8, 18.9 and 24.0 atom percent MoS₂. Results of coating characterisation (by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and nanoindentation measurement of hardness and elastic modulus) revealed that increasing amounts of MoS₂ produced the following effects: frustration of crystallisation and phase separation; a decrease in average grain sizes (from ∼5.5 to ∼ 4.3 nm) and a decrease in coating hardness (from ∼15 to ∼ 10 GPa). Scratch testing also showed that the load-bearing capability of coatings was altered; coatings possessing an intermediate concentration of MoS₂ exhibited the best behaviour with no failure observed in mechanical testing, due to an optimal nanocomposite structure. The corrosion resistance (investigated by potentiodynamic polarisation tests) however tended to improve as more MoS₂ was introduced. An investigation of the effects of generating an amorphous structure by adding Ti and C into Cr-B-MoS₂ coatings revealed improved corrosion behaviour, which significantly exceeded that of uncoated stainless steel and CrB₂-coated samples. PACS 68.37.Lp; 68.55.A-; 68.55.Ln; 68.55.Nq; 68.60.Bs     

ISS measurement of surface composition of AuCu alloys by simultaneous ion bombardments with Ar+ and He + ions

Surface composition of Au-Cu(43 at%) alloy under 1.5–5 keV argon ion bombardment has been investigated by ion scattering spectroscopy (ISS). In this experiment, we adopted a specific technique to use mixed He⁺ and Ar⁺ ions as primary beam in order to perform sputtering (Ar⁺) and ISS measurement (He⁺) simultaneously. The outermost atom layer of Au-Cu alloys under Ar⁺ ion bombardment is Au-rich leading to the conclusion that Ar⁺ ion bombardment of AuCu alloys causes the preferential sputtering of Cu atoms, resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer due to ion-beam-enhanced surface segregation. This result explains the experimental results obtained by AES as well.     

Ion bombardment of ordered Zr3Al

The behaviour of the ordered alloy Zr₃Al was investigated by transmission electron microscopy following ion bombardments at temperatures ranging from 30 to 850 K. Utilizing high energy(0.5–2.0 MeV) C⁺, N⁺ and Ar⁺ ion bombardments, observations were made of the irradiation-induced transformation from the ordered → disordered → amorphous states. Information about individual damage cascades was also obtained using both high energy (C⁺. N⁺ and Ar⁺) and low energy (15–120 keV Cu⁺) ion bombardments.     

Preferential sputtering of TIC under keV Ar+ ion bombardment: Simultaneous sputtering-ISS measurement with He+ and Ar+ ions

The composition change of the outermost atom layer of TiC(110) under ion bombardment with 1.5–3 keV He⁺ and He⁺ + Ar⁺ ions has been measured by ion scattering spectroscopy with He⁺ ions at different sample temperatures. It has been found that the preferential sputtering of C atoms takes place for both the He⁺ and Ar⁺ ion bombardment, however the preferred sputtering is more pronounced for Ar⁺ ions than for He⁺ ions. The ion bombardment with He⁺ ions at elevated sample temperatures hardly results in any change in surface composition below ～800°C, while Ar⁺ ion bombardment results in C enrichment for elevated temperatures as reported so far.     

Development of protective metal coatings on aluminum by magnetron sputtering

Depositions of copper and titanium coatings on aluminum foils and polished aluminum plates for thier protection against corrosion in alkaline media were performed. The coatings were deposited in three different types of magnetron sputtering systems: a direct current (DC) magnetron discharge, a high current impulse magnetron discharge, and a DC magnetron discharge with melted cathode. Only aluminum foils coated with copper films obtained by combined ion-plasma technology, which included preliminarily sputtering of the aluminum surface with an ion beam, deposition of a dense interlayer in the DC magnetron discharge with ion assistance of initial stage of deposition, and deposition of additional layer in the magnetron discharge with melted cathode, were resistant against 30 wt % NaOH solution.     

Thermally oxidised rutile-TiO2 coating on stainless steel for tribological properties and corrosion resistance enhancement

In the present work, a novel process has been developed to improve the tribological and corrosion properties of austenitic stainless steels. Efforts have been made to deposit titanium coatings onto AISI 316L stainless steel by magnetron sputtering, and then to partially convert the titanium coatings to titanium oxide by thermal oxidation. The resultant coating has a layered structure, comprising of rutile-TiO₂ layer at the top, an oxygen and nitrogen dissolved α-Ti layer in the middle and a diffuse-type interface. Such a hybrid coating system showed good adhesion with the substrate, improved corrosion resistance, and significantly enhanced surface hardness and tribological properties of the stainless steel in terms of much reduced friction coefficient and increased wear resistance.     

Investigation on surface compositions of CuNi alloy under Ar+ ion bombardment by ISS and in situ AES measurements

Surface compositions of CuNi(50 wt%) alloy under 3 keV Ar⁺ ion bombardment were measured by Auger electron spectroscopy (AES) and ion scattering spectroscopy (ISS). In situ AES measurement of sputter-deposited layer and sputtered sample surface indicated that surface composition became Ni-rich due to Ar⁺ ion sputtering at steady state, in accord with previous reports of preferential sputtering. ISS measurements with 3 keV Ar⁺ ions, however, have suggested that the composition of the outermost atom layer is not Ni-rich but slightly copperrich. This leads to the conclusion that the degree of preferential sputtering is small and that the question of preferential sputtering, particularly, the ratio of the sputtering yields, $\text{S}{}_{\mathrm{<mtext>Cu</mtext>}}\text{S}{}_{\mathrm{<mtext>Ni</mtext>}}$, based on AES measurement requires further examination.     

A new technique for the measurement of sputtering yields

We have measured the yields of 90 keV ⁴⁰Ar⁺ and V⁴He⁺ sputtering of Mo and V samples by the use of a new radio-tracer technique. This technique involves activating the samples by high-energy charged-particle irradiation before sputtering, and using conventional γ-ray counting methods to analyze the material subsequently sputtered onto collector foils. We have also measured angular distributions of the sputtered material, and compared these results and our total sputtering yields with the predictions of Sigmund's sputtering theory. Further comparisons between our radiotracer results and those obtained for ⁴⁰Ar⁺ sputtering of unactivated Mo and V samples, determined from elastic backscattering measurements using 12 MeV ¹⁶O ions, show that the techniques give consistent results.     

Atomic excitations in sputtering studied with the use of composite targets

Atomic excitation phenomena in sputtering have been studied with the following combinations of projectile and target. (i) Be, B, Mg, Al, and Si bombarded with 80 keV Ar⁺ at UHV as well as with the target chamber backfilled with oxygen. (ii) Mg bombarded with 80 keV O⁺, F⁺, Ne⁺, Na⁺ Cl⁺, and Ar⁺. (iii) MgO, MgF₂, MgCl₂, MgSO₄, and several alkali halides bombarded with 80 keV Ar⁺ at UHV. Results are discussed. It is concluded that the excited-state formation takes place as electron tunneling at a fairly large separation between the target surface and the particle being sputtered. It is suggested with composite targets containing a metal element that excitation takes place predominantly at locations of the target surface where the work function is low, due to a thin, metallic surface layer, and that production of ground-state, positive secondary ions mainly takes place at target surface regions with high work function. For semiconductors, the changes caused by presence of oxygen are related to the change of the bonds in the solid from being of covalent nature to being fractionally ionic.     

Corrosion behavior and composition analysis of chromate passive film on electroless Ni-P coating

A passive film was formed on electroless Ni-P coating (ENPC) in a bath of K₂Cr₂O₇ 30 g/l. XPS and electrochemical methods were employed to analyze its chemical compositions and corrosion behaviors. The potentiodynamic polarization tests indicated the corrosion current of the passivated sample was 1/30 that of as-plated ENPC. The XPS analysis illustrated the film comprised Cr, Ni and O. The film thickness was evaluated to be a few nanometers according to the sputtering rate of Ar⁺ ion. High-resolution XPS spectra suggested that the detected Cr in film was in the form of trivalent compounds, Cr₂O₃ and Cr(OH)₃.     

Application of high-frequency magnetron sputtering to deposit thin calcium-phosphate biocompatible coatings on a titanium surface

Thin calcium-phosphate coatings were deposited on titanium substrates by high-frequency magnetron sputtering. The elemental composition of coatings and types of chemical bonds were studied by Rutherford backscattering (RBS) and Fourier transform infrared spectroscopy (FTIR), respectively. An analysis of the IR spectra detected absorption bands caused by vibrations of phosphate PO ₄ ^3? groups and pyrophosphate H₂PO ₄ ^? anions, which are typical of apatites. The RBS results showed that the coating contains elements typical of calcium phosphates, i.e., Ca, P, and O; 45.4 ± 1.1, 3.6 ± 0.5, and 41.1 ± 0.7 at %, respectively. The Ca/P atomic ratio depends on sputtering conditions and varies in the range 1.7–4.0. The physicomechanical characteristics of the coatings and their solubility in a biological liquid were studied. The grown coatings can significantly reduce dissolution of substrates and extraction of dopants into the surrounding solution.     

Enhanced optical properties of Al-doped TiO2 thin films in oxygen or nitrogen atmosphere

Al-doped TiO₂ (TiO₂:Al) films were deposited by simultaneous RF magnetron sputtering of TiO₂ and DC magnetron sputtering of Al. The advantage of this method is that the Al content could be independently controlled. By depositing in a mixed Ar-O₂ or a mixed Ar-N₂ atmosphere, the TiO₂:Al film became more stoichiometric and the nanocrystallinity was enhanced. The nonlinear refractive index of TiO₂:Al film deposited in a pure Ar, a mixed Ar-O₂ or a mixed Ar-N₂ atmosphere was measured by Moiré deflectometry, and was of the order of 10⁻⁸ cm² W⁻¹. For the TiO₂:Al film deposited in a pure Ar atmosphere, the porosity was higher corresponding to the lower transmission. However, the porosity of TiO₂:Al film decreased as the oxygen or nitrogen pressure increased. Especially, as the ratio of O₂ to Ar pressure increased to 0.22, TiO₂:Al film exhibited lower porosity, higher visible transmission, higher linear refractive index, lower stress and lower stress-optical coefficient.     

Sputtering of metals at ion-electron irradiation

It has been found that, in contrast to the commonly accepted opinion, simultaneous irradiation by 15-keV Ar⁺ ions and 2.5-keV electrons at temperatures above 0.5T _m (T _m is the melting temperature) induces much larger sputtering of metallic copper, nickel, and steel than irradiation only by Ar⁺ ions. The effect increases with the temperature. At T = 0.7T _m, the sputtering coefficients in the case of ion-electron irradiation are more than twice as large as the sputtering coefficients in the case of irradiation by Ar⁺ ions. The experiments on the sublimation of copper show that the sublimation rate in the case of the heating of a sample by an electron beam is higher than that in the case of heating in an electric vacuum oven. The revealed effects are explained by the electron-induced excitation of adatoms (atoms stuck over the surface, which appear owing to ion bombardment). Excited adatoms have a smaller binding energy with the surface and are sputtered more easily.     

Deposition of nanostructured crystalline and corrosion resistant alumina film on bell metal at low temperature by rf magnetron sputtering

Aluminium oxide films deposited by rf magnetron sputtering for protective coatings have been investigated. The alumina films are found to exhibit grainy surface microstructure. The grain size, structure and density depend on different system parameters such as argon and/or oxygen flow rate and applied rf power etc. The effect of transition of the discharge from metallic to reactive mode on the surface characteristics of the alumina film is studied. X-ray diffractometry reveals that in poisoned mode of sputtering and under optimized power and pressure, crystalline alumina film can be grown. Different system conditions are optimized for corrosion resistant aluminium oxide films with good adhesion properties. Nanostructured alumina film is obtained at lower pressure (8 × 10⁻⁴ to 9 × 10⁻⁴ Torr) by rf reactive magnetron sputtering.