Mechanical properties optimization of tungsten nitride thin films grown by reactive sputtering and laser ablation

Transition metal nitrides coatings are used as protective coatings against wear and corrosion. Their mechanical properties can be tailored by tuning the nitrogen content during film synthesis. The relationship between thin film preparation conditions and mechanical properties for tungsten nitride films is not as well understood as other transition metal nitrides, like titanium nitride. We report the synthesis of tungsten nitride films grown by reactive sputtering and laser ablation in the ambient of N₂ or N₂/Ar mixture at various pressures on stainless steel substrates at 400  C. The composition of the films was determined by XPS. The optimal mechanical properties were found by nanoindentation based on the determination of the proper deposition conditions. As nitrogen pressure was increased during processing, the stoichiometry and hardness changed from W₉N to W₄N and 30.8-38.7 GPa, respectively, for films deposited by reactive sputtering, and from W₆N to W₂N and 19.5-27.7 GPa, respectively, for those deposited by laser ablation.     

Properties of MoNxOy thin films as a function of the N/O ratio

The main purpose of this work is the preparation of single layer films of molybdenum oxynitride, MoN_xO_y. The films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure Mo target and varying the flow rate of reactive gases. This allowed tuning of the crystallographic structure between insulating oxides and metallic nitrides and consequently changes in the electronic, mechanical and optical properties of the material. X-ray diffraction (XRD) results revealed the presence of molybdenum nitride for the films with low oxygen fraction: face-centered cubic phases (γ-Mo₂N) for low nitrogen flow rate or cubic MoN_x and hexagonal phase (δ-MoN) for high nitrogen flow rate. The increase of oxygen content induces an amorphization of the nitride phases and the appearance of MoO₃ phases. The increase of the oxygen fraction in the films induces also a high decrease in the film's hardness. Residual stresses were compressive, in the range of very few tenths of GPa to − 2 GPa. These results will be presented as a function of the deposition parameters, the chemical composition and the structure of the films.     

Control of microstructures and properties of dc magnetron sputtering deposited chromium nitride films

Chromium nitride coatings have been prepared by a conventional DC magnetron reactive sputtering process in nitrogen-argon mixed atmospheres. The sputtering pressure and target voltage versus nitrogen flow rate curves were established in order to control the structures and properties of chromium nitride coatings. A good correspondence among the sputtering pressure, target voltage evolutions and the phase developments with respect to nitrogen flow rate has been found. The stoichiometric Cr₂N and CrN coatings were confirmed by EPMA and XRD analysis. Cryogenic fracture cross-section SEM images show columnar growth morphologies. Stoichiometric chromium nitrides present high hardness and elastic modulus as well as high H³/E² ratio in a nano-indenter test. Adhesion and tribological properties were evaluated by scratch and pin-on-disk tests, respectively. Chromium nitrides present normal adhesion failure critical load (Lc₂) between 10 and 20 N and friction coefficients ranging from 0.5 to 0.75.     

Preferentially oriented vanadium nitride films deposited by magnetron sputtering

Because of solid state lubricious properties of vanadium oxides, wear resistant coatings based on nitrides and carbides of that metal are still of interest for research teams. The aim of this report is to show phase composition evolution from metallic vanadium through intermediate phases up to δ-VN phase supersaturated with nitrogen in thin films deposited by reactive, pulsed magnetron sputtering from vanadium target. This analysis is completed by remarks on preferential orientation, lattice constant and crystallite size. Presented work is a part of research on composite hard coatings for woodworking tools where vanadium nitrides and carbides are considered as a component reducing friction.     

Deposition of hard wear-resistant coatings by reactive D.C. Plasmatron sputtering

Based on investigations on the reactive deposition of oxides and nitrides a review is given of the most important process parameters of reactive d.c. high rate sputtering. Knowledge of the possibilities to ensure a stable and reproducible regime is essential for the use of reactive d.c. plasmatron sputtering. Technical solutions are presented that use the principles of plasma emission spectroscopy. Also dealt with are oxides of CrSi and aluminium for use as wear-resistant coatings because they can be deposited in a self-stabilizing regime. Of particular interest is the production of TiN_x layers for various applications, especially to enhance the lifetime or productivity of cutting tools made from high speed steel. Hence the relationship between the process parameters and the properties of these coatings is outlined in more detail.     

Investigation of structural,optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO₂ anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10^?2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.     

Studies on thin film materials on acrylics for optical applications

Deposition of durable thin film coatings by vacuum evaporation on acrylic substrates for optical applications is a challenging job. Films crack upon deposition due to internal stresses and leads to performance degradation. In this investigation, we report the preparation and characterization of single and multi-layer films of TiO₂, CeO₂, Substance2 (E Merck, Germany), Al₂O₃, SiO₂ and MgF₂ by electron beam evaporation on both glass and PMMA substrates. Optical micrographs taken on single layer films deposited on PMMA substrates did not reveal any cracks. Cracks in films were observed on PMMA substrates when the substrate temperature exceeded 80°C. Antireflection coatings of 3 and 4 layers have been deposited and characterized. Antireflection coatings made on PMMA substrate using Substance2 (H2) and SiO₂ combination showed very fine cracks when observed under microscope. Optical performance of the coatings has been explained with the help of optical micrographs.     

Investigation of physicochemical and tribological properties of transparent oxide semiconducting thin films based on Ti-V oxides

In this paper investigations of structural and optical properties of nanocrystalline Ti-V oxide thin films are described. The films were deposited onto Corning 7059 glass using a modified reactive magnetron sputtering method. Structural investigations of prepared Ti-V oxides with vanadium addition of 19 at. % revealed amorphous structure, while incorporation of 21 and 23 at. % of vanadium resulted in V₂O₅ formation with crystallites sizes of 12.7 and 32.4 nm, respectively. All prepared thin films belong to transparent oxide semiconductors due to their high transmission level of ca. 60–75 % in the visible light range, and resistivity in the range of 3.3·10²–1.4·10⁵ Ωcm. Additionally, wettability and hardness tests were performed in order to evaluate the usefulness of the films for functional coatings.     

Reactively sputtered oxide optical coatings for inertial confinement fusion laser components

Results to date are presented for a study of reactively sputtered oxide optical coatings which are candidate materials for use in the NOVA Terawatt neodymium glass laser under development at Lawrence Livermore Laboratory, Livermore, California. Experimental details are described for the deposition of TiO₂ on fused silica substrates by r.f. diode sputtering of titanium in a reactive Ar-O₂ atmosphere. Specific deposition procedures are presented for variation of the phase composition and grain size of the coatings over wide ranges. High laser damage thresholds are reported for TiO₂, and glassy coatings appear to be more damage resistant than polycrystalline coatings. Phase composition appears to be less important to damage resistance than grain size. Application of the reactive sputtering process to preparation of damage-resistant oxides of In-Sn and tantalum is also described and damage thresholds obtained to date are reported.     

Structural and magnetic properties of transition metal doped ZnO films

Structural and magnetic properties have been studied for polycrystalline Zn_1 − xTM_xO films where transition metal (TM) = Fe, Cr. The Zn_1 − xTM_xO films were prepared by the radio frequency magnetron sputtering technique on Al₂O₃ (001) substrates. The microstructures of the films are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. TM in the films exists mainly in the form of TM²⁺, and the TM²⁺ ions have substituted for the Zn²⁺ ions bonded in TM-O in the ZnO lattice and do not change the wurtzite structure of ZnO. The result of magnetic measurement shows that the Zn_1 − xTM_xO films are ferromagnetic at 5 K and 300 K respectively. Subsequently, we discuss the origin of the ferromagnetism in the films.     

Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering

Radiofrequency magnetron sputtering deposition at low temperature (150°C) was used to deposit bioactive glass coatings onto titanium substrates. Three different working atmospheres were used: Ar 100%, Ar + 7%O₂, and Ar + 20%O₂. The preliminary adhesion tests (pull-out) produced excellent adhesion values (~75 MPa) for the as-deposited bio-glass films. Bioactivity tests in simulated body fluid were carried out for 30 days. SEM–EDS, XRD and FTIR measurements were performed. The tests clearly showed strong bioactive features for all the prepared films. The best biomineralization capability, expressed by the thickest chemically grown carbonated hydroxyapatite layer, was obtained for the bio-glass coating sputtered in a reactive atmosphere with 7% O₂.     

Structure, hardness and thermal stability of nanolayered TiN/CrN multilayer coatings

Nanolayered TiN/CrN multilayer coatings were deposited on silicon substrates using a reactive DC magnetron sputtering process at various modulation wavelengths (Λ), substrate biases (V_B) and substrate temperatures (T_S). X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of the TiN/CrN multilayers was 3800 kg/mm² at Λ=80  Å, V_B=−150 V and T_S=400°C. Thermal stability of TiN, CrN and TiN/CrN multilayer coatings was studied by heating the coatings in air in the temperature range (T_A) of 400-800°C. The XRD data revealed that TiN/CrN multilayers retained superlattice structure even up to 700°C and oxides were detected only after T_A?750°C, whereas for single layer TiN and CrN coatings oxides were detected even at 550°C and 600°C, respectively. Nanoindentation measurements showed that TiN/CrN multilayers retained a hardness of 2800 kg/mm² upon annealing at 700°C, and this decrease in the hardness was attributed to interdiffusion at the interfaces.     

Deposition of TiN/CrN hard superlattices by reactive d.c. magnetron sputtering

Multilayer superlattice coatings of TiN/CrN were deposited on silicon substrates using a reactive d.c. magnetron sputtering process. Superlattice period, also known as modulation wavelength (A), was controlled by controlling the dwell time of the substrate underneath Ti and Cr targets. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the films. The XRD data showed 1st and 2nd order satellite reflections along the principal reflection for films having 132 Å > Å > 84 Å, thus confirming the formation of superlattice. The multilayer coatings exhibited hardness(H) as high as 3200 kg/mm², which is 2 times the rule-of-mixtures value (i.e.)H _TiN = 2200 kg/mm² andH _CrN = 1000 kg/mm²). Detailed investigations on the effects of various process parameters indicated that hardness of the superlattice coatings was affected not only by modulation wavelength but also by nitrogen partial pressure and ion bombardment during deposition.     

Structure and mechanical properties of r.f. sputtered SiC films

Amorphous and polycrystalline SiC films were prepared on glass, sapphire and silicon substrates by r.f. sputtering of a SiC cathode in argon. From evaluation of their mechanical properties, it was found that the films have a Vickers hardness of 4000 kg mm^?2, similar to bulk SiC, and can be used to make hard surface coatings due to their high wear resistance. Mixed carbide (Si, B)C films prepared by r.f. sputtering exhibit a Vickers hardness of 4500 kg mm^?2 and are also usable for hard coatings.     

Reactive pulse magnetron sputtered SiOxNy coatings on polymers

Amorphous SiO₂, Si₃N₄ and SiO_xN_y single layers have been deposited on silicon, glass and glycol modified polyethylene terephthalate substrates by reactive pulse magnetron sputtering. Apart from the expected correlation between refractive index, coating density and nitrogen content in the reactive gas mixture further results have been found regarding mechanical stress and the humidity barrier property of these thin films. The lowest compressive stress was observed in the coatings deposited with nitrogen contents of around 30% to 50% in the reactive gas mixture. The humidity barrier effect of the thin films already begins to increase significantly at low nitrogen contents of below 20% in the reactive gas. Additional investigations regarding chemical composition, coating adhesion and environmental stability complement this work with the main focus on optimizing these materials for optical multilayer systems on polymer substrates.     

Magnetron sputtering of a vanadium-diboride target in Ar+N2 gaseous mixtures

The structure and composition of nanostructured multilayer V-B-N films, deposited by high-frequency magnetron sputtering of a composite VB₂ target in a gaseous mixture of argon and nitrogen, were studied by means of electron spectroscopy, X-ray diffraction and secondary ion mass-spectroscopy. The influence of the percentage ratio of nitrogen on the process of formation of films was investigated. On high-frequency reactive magnetron sputtering the composition of a superficial layer of a target changes. The influence of this change on structure and composition of coverings was described. The method of synthesis of multilayer films of borides and nitrides of vanadium is offered. Formation mechanisms of boride and nitride films are discussed.     

Structure and phase composition of thin TiO<Subscript>2</Subscript> films grown on the surface of metallized track-etched polyethylene terephthalate membranes by reactive magnetron sputtering

We have studied TiO₂, Ag, Ag/TiO₂, and Cu/TiO₂ coatings grown on track-etched polyethylene terephthalate membranes. The metals and oxides were deposited by reactive vacuum sputtering using a planar magnetron. The microstructure of the samples were examined by scanning and transmission electron microscopy techniques. The elemental composition of the coatings were determined by energy dispersive X-ray microanalysis, and their phase composition was determined by X-ray diffraction at different temperatures and by transmission electron diffraction. Titanium dioxide can be present on the surface of track-etched membranes (TMs) in three forms: nanocrystals of tetragonal anatase with orthorhombic brookite and amorphous TiO₂ impurities. The copper-metallized TM has been shown to contain cubic Cu₂O. The optical properties of the composite membranes and films have been studied by absorption spectroscopy. The energies of direct and indirect allowed optical transitions have been evaluated from measured absorption spectra of the TiO₂, Ag/TiO₂, and Cu/TiO₂ coatings.     

The effects of pre-implantation of steel substrates on the structural properties of TiN coatings

We have studied the effects of nitrogen pre-implantation of AISI C1045 steel substrates on the microstructure and microhardness of deposited TiN coatings. The substrates were implanted at 40 keV, to the fluences from 5 × 10¹⁶ to 5 × 10¹⁷ ions/cm², which was followed by deposition of 1.3-μm thick TiN coatings by reactive sputtering. Structural characterization of the samples was performed by standard and grazing incidence X-ray diffraction analysis, Rutherford backscattering spectroscopy and transmission electron microscopy. Microhardness was measured by the Vicker’s method. Nitrogen implantation up to 2 × 10¹⁷ ions/cm² induces the formation of Fe₂N phase in the near surface region of the substrates, which becomes more pronounced for higher fluences. Microstructure of the deposited TiN coatings shows a strong dependence on ion beam pre-treatment of the substrates. The layers grown on non-implanted substrates have a (200) TiN preferential orientation, and those grown on implanted substrates have (111) TiN preferential orientation. The change in preferred orientation of the layers is assigned to a developed surface topography of the substrates induced by ion implantation, and possible effects of distorted and altered crystalline structure at the surface. Ion implantation and deposition of TiN coatings induce an increase of microhardness of this low performance steel for more than eight times.     

Ein neues Wärmedämmsystem für Architekturglass

Vacuum coated glass plays an outstanding role for the energy saving of buildings. The basis of such low emissivity coatings is a 10 nm thick silver layer causing an effective reflexion of room temperature radiation. With conventional coatings k‐values of 1,3 W/m²K are realized. In the frame of a research project funded by the BMBF reactive mid frequency sputtering (Leybold TwinMag®) has been introduced for manufacturing of low e glass. The new developed system glass — TiO₂ — ZnO — Ag — NiCrO_x — Si₃N₄ enables a k‐value of 1,1 W/m²K and an improvement of optical properties.     

Magnetron sputter‐deposition on atom layer scale

For many applications there is an increasing request to control the deposition process on an atom layer scale. This offers a lot of advantages like in accuracy, layer homogeneity and tailoring of layer properties. On the other hand the speed and throughput of the process should not suffer from the control on an atom layer scale as it is the case for classical atom layer deposition (ALD). For optical applications especially high‐end interference filter coatings we developed a plasma assisted reactive magnetron sputtering process in combination with a high speed drive for the substrates. This combination allows controlling the layer thicknesses and layer properties on an atom layer scale while maintaining a high deposition rate. The advantages of this process are demonstrated on single layer results of SiO2, HfO2, ZrO2, Ta2O5 and mixed oxides of SiO2‐Nb2O5. Morphology, surface roughness, film stress, refractive index and losses are controlled by the oxygen partial pressure, the substrate temperature, the energy input by the sputtering ‐and assist process and by cosputtering. The outstanding performance of high‐end interference filter coatings like a multi notch filter for fluorescence microscopy is achieved by the very stable and reproducible deposition process in combination with an advanced thickness control strategy based on in‐situ optical thickness control and time control.