A comparative study of the UV optical and structural properties of SiO2, Al2O3, and HfO2 single layers deposited by reactive evaporation, ion-assisted deposition and plasma ion-assisted deposition

Growing requirements for the optical and environmental stability, as well as the radiation resistance against high-power laser radiation, especially for optical interference coatings used in the ultraviolet spectral range, have to be met by new, optimised, thin-film deposition technologies. For applications in the UV spectral range, the number of useful oxide thin film materials is very limited due to the higher absorption at wavelengths near to the electronic bandgap of the materials. Applying ion-assisted processes offers the ability to grow dense and stable films, but in each case careful optimisation of the deposition process (evaporation rate, substrate temperature, bombarding gas, ion energy and ion current density) has to achieve a balance between densification of the layers and the absorption. High-quality coatings and multilayer interference systems with SiO₂ as the low-index material can be deposited by various physical vapour deposition technologies, including reactive e-beam evaporation, ion-assisted deposition and plasma ion-assisted deposition. In order to improve the degradation stability of dielectric mirrors for use in UV free-electron laser optical cavities, a comparative study of the properties of SiO₂, Al₂O₃ and HfO₂ single layers was performed, and was addressed to grow very dense films with minimum absorption in the spectral range from 200 to 300 nm. The films were deposited by low-loss reactive electron-beam evaporation, by ion-assisted deposition using a ‘Mark II’ ion source, and by plasma ion-assisted deposition using the advanced plasma source. Optical and structural properties of the samples were studied by spectral photometry, infrared spectroscopy, X-ray diffraction and reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energy values close to the bandgap was studied. For HfO₂ single layers, laser-induced damage thresholds at 248 nm were determined in the 1-on-1 and 1000-on-1 test modes as a function of the deposition technology and film thickness.     

Analysis of SAW properties of epitaxial ZnO films grown on R-Al2O3 substrates

ZnO thin films with a high piezoelectric coupling coefficient are widely used for high frequency and low loss surface acoustic wave (SAW) devices when the film is deposited on top of a high acoustic velocity substrate, such as diamond or sapphire. The performance of these devices is critically dependent on the quality of the ZnO films as well as of the interface between ZnO and the substrate. In this paper, we report the studies on piezoelectric properties of epitaxial (112¯0) ZnO thin films grown on R-plane sapphire substrates using metal organic chemical vapor deposition (MOCVD) technique. The c-axis of the ZnO film is in-plane. The ZnO/R-Al₂O₃ interface is atomically sharp. SAW delay lines, aligned parallel to the c-axis, were used to characterize the surface wave velocity, coupling coefficient, and temperature coefficient of frequency as functions of film thickness to wavelength ratio (h/λ). The acoustic wave properties of the material system were calculated using Adler's matrix method, and the devices were simulated using the quasi-static approximation based on Green's function analysis     

电沉积法可控制备纳米羟基磷灰石涂层的研究

采用电化学沉积法在医用金属钛表面制备钙磷盐涂层,通过XRD、FT-IR和SEM表征,侧重探索电化学沉积技术在温和条件下制备结晶结构优良的纯羟基磷灰石涂层的可控性.通过控制电流密度和反应时间,即研究在恒电量条件下羟基磷灰石涂层的电化学沉积规律性,并获得电化学沉积制备纳米有序结构羟基磷灰石涂层的最佳实验条件,同时对纳米有序结构羟基磷灰石涂层的电化学沉积机理进行讨论.     

Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (V_B) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (H) and Young’s modulus (Y) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100–250 V. Films deposited at |V _B| = 250 V exhibited hardness as high as 3300 kg/mm². This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure.     

Oxidation behaviour of TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings with Al2O3 topcoat deposited on γ-TiAl alloys

Abstract

TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings were deposited on γ-TiAl specimens using magnetron sputtering techniques. The nitride layers were manufactured by unbalanced magnetron sputtering (UBM) and high power impulse magnetron sputtering (HIPIMS). The CrAlYN/CrN coatings had an oxy-nitride overcoat. On some of the coated samples an additional alumina topcoat was deposited. The oxidation behaviour of the different coatings was investigated at 750 and 850°C performing quasi-isothermal oxidation tests in laboratory air. Mass change data were measured during exposure up to failure or the maximum exposure length of 2500 h. When exposed to air at 750°C, the Ti-based nitride films exhibited higher oxidation resistance than the Ti – 45Al –8Nb substrate material. The alumina topcoat enhanced the oxidation protection of this coating system, acting as diffusion barrier to oxygen penetration. At 850°C, the TiAlYN/CrN films exhibited poor stability and rapidly oxidised, and therefore were not applicable for long-term protective coatings on γ-TiAl alloys. The beneficial effect of the additional Al₂O₃ layer was less pronounced at this exposure temperature. The Cr-based nitride films exhibited high oxidation resistance during exposure at 850°C. HIPIMS deposition improved the oxidation behaviour of the CrAlYN/CrN nanoscale multilayer coatings in comparison to UBM coatings. For these coatings, the decomposed and partially oxidised nitride films were an effective barrier to oxygen inward diffusion. The alumina topcoat did not significantly increase the oxidation resistance of the γ-TiAl alloy coated with Cr-based nitride films.     

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.     

Liquid-phase deposition and the properties of thin zirconium dioxide films on different substrates

In recent years, the interest of the researchers to the methods of synthesis of inorganic thin oxide films from low-temperature liquid solutions permanently increases. This is explained by the recent achievements in the technology of deposition of the films, including, in particular, chemical deposition, sputtering, laser ablation, and evaporation. The liquid-phase deposition is an aqueous procedure of deposition of oxide films. In our investigation, we try to improve the adhesion and stability of zirconium-oxide coatings on polymers. Ceramic coatings (ZrO₂) protect the surface of the substrate against reactions with acids and oxidation. The deposition of ceramic coatings on polymers is connected with serious problems due to the sensitivity of polymers to the action of chemical reagents and high temperature. We make an attempt to explain the role of the substrate in the process of deposition of zirconium-oxide films from the liquid phase on the Kapton polymeric material with different types of surface treatment. It is shown that even insignificant variations of the pH value, temperature, and composition of the solution can noticeably affect the crystalline film, adhesion, and growth rate. Thin films are very smooth, homogeneous, and characterized by the presence of an insignificant number of cracks. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 2, pp. 53–56, March–April, 2008.     

Electrochemical evaluation of the reliability of plasma-polymerized methylcyclohexane films

Plasma-polymerized thin films are developed for electronic devices to satisfy the important requirement of a low dielectric constant in the interlayer dielectrics. Three types of methylcyclohexane coatings are deposited on copper as interlayer dielectrics by plasma-enhanced chemical vapor deposition at three different deposition temperatures. The coating performance is evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization testing in a 3.5 wt.% NaCl solution. The coatings are also analyzed by surface analyses, including atomic force microscopy, Fourier transform infrared spectroscopy, and contact angle measurements. The electrochemical behavior of the coatings is improved by increasing the deposition temperature. The methylcyclohexane films on the copper substrate show high protective efficiency, charge transfer resistance and low porosity, which indicate that the coating performance increased with increasing deposition temperature. Atomic force microscopy, Fourier transform infrared spectroscopy and contact angle measurements confirm the enhanced formation of C-H, C-C, and CC stretching configurations, improved surface roughness and wettability with increasing deposition temperature.     

Patterned superhydrophobic surfaces: toward a synthetic mimic of the Namib Desert beetle

The present study demonstrates a surface structure that mimics the water harvesting wing surface of the Namib Desert beetle. Hydrophilic patterns on superhydrophobic surfaces were created with water/2-propanol solutions of a polyelectrolyte to produce surfaces with extreme hydrophobic contrast. Selective deposition of multilayer films onto the hydrophilic patterns introduces different properties to the area including superhydrophilicity. Potential applications of such surfaces include water harvesting surfaces, controlled drug release coatings, open-air microchannel devices, and lab-on-chip devices.     

Sputtered tungsten-based ternary and quaternary layers for nanocrystalline diamond deposition

Many of today's demanding applications require thin-film coatings with high hardness, toughness, and thermal stability. In many cases, coating thickness in the range 2-20 microm and low surface roughness are required. Diamond films meet many of the stated requirements, but their crystalline nature leads to a high surface roughness. Nanocrystalline diamond offers a smoother surface, but significant surface modification of the substrate is necessary for successful nanocrystalline diamond deposition and adhesion. A hybrid hard and tough material may be required for either the desired applications, or as a basis for nanocrystalline diamond film growth. One possibility is a composite system based on carbides or nitrides. Many binary carbides and nitrides offer one or more mentioned properties. By combining these binary compounds in a ternary or quaternary nanocrystalline system, we can tailor the material for a desired combination of properties. Here, we describe the results on the structural and mechanical properties of the coating systems composed of tungsten-chromium-carbide and/or nitride. These WC-Cr-(N) coatings are deposited using magnetron sputtering. The growth of adherent nanocrystalline diamond films by microwave plasma chemical vapor deposition has been demonstrated on these coatings. The WC-Cr-(N) and WC-Cr-(N)-NCD coatings are characterized with atomic force microscopy and SEM, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and nanoindentation.     

SEM study of defects in PVD hard coatings

Hard coating defects are produced by foreign particle contamination on substrate surface before and during coating, or due to arcing. In this work, CrN, TiAlN and CrN/TiAlN multilayer hard coatings were prepared by thermoionic arc ion plating deposition system BAI 730 (Balzers) and by sputter deposition in CC800 (CemeCon). We investigated the concentration of defects, its size and structure after tool steel substrate surface pretreatment (polishing, ion etching) as well as after deposition by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM).     

Structure and morphology of TiB2 duplex coatings deposited over X40 CrMoV 5-1-1 steel by DC magnetron sputtering

The deposition of titanium diboride (TiB₂) films over tool steel substrates (AISI H13 premium/EN X40 CrMoV 5-1-1) is being investigated due to its excellent corrosion resistance and chemical stability against liquid aluminium. The use of nitrided steels as substrates for TiB₂ deposition may contribute to increase its adhesion and the overall steel resistance in applications such as forging, extrusion and die casting of aluminium. Duplex coatings were obtained by the PVD deposition of TiB₂ films over heat treated and nitrided steel using non-reactive DC magnetron sputtering from a TiB₂ target, varying the substrate bias voltage. Well structured and crystalline TiB₂ films were obtained for the selected deposition conditions, the best crystalline coatings being obtained for the positively biased substrates. Selected films produced over die-casting pins at a bias voltage of +50 V were tested for resistance to liquid aluminium soldering by immersion tests, and compared with the nitrided steel. The duplex TiB₂ coating has a much larger chemical resistance to attack by molten aluminium alloy than the just nitrided steel. Where there is soldering, steel is rapidly attacked and a complex Al-Fe-Si intermetallic forms.     

Dynamic aspects of films prepared by a sequential deposition of species: perspectives for smart and responsive materials

The deposition of surface coatings using a step-by-step approach from mutually interacting species allows the fabrication of so called "multilayered films". These coatings are very versatile and easy to produce in environmentally friendly conditions, mostly from aqueous solution. They find more and more applications in many hot topic areas, such as in biomaterials and nanoelectronics but also in stimuli-responsive films. We aim to review the most recent developments in such stimuli-responsive coatings based on layer-by-layer (LBL) depositions in relationship to the properties of these coatings. The most investigated stimuli are based on changes in ionic strength, temperature, exposure to light, and mechanical forces. The possibility to induce a transition from linear to exponential growth in thickness and to change the charge compensation from "intrinsic" to "extrinsic" by controlling parameters such as temperature, pH, and ionic strength are the ways to confer their responsiveness to the films. Chemical post-modifications also allow to significantly modify the film properties.     

Vacuum-deposited carbon coatings

In recent years, highly favorable results have been obtained using low temperature isotropic pyrolytic carbons in prosthetic devices requiring a high degree of thromboresistance. The development of vacuum-deposited carbon coatings was undertaken to extend the application of carbon to geometries and configurations that cannot be fabricated from low temperature isotropic carbon. Vacuum-deposited coatings have been produced on a variety of metallic and polymeric substrates.The different vacuum deposition processes which have been investigated include electron beam gun evaporation using high vacuum, gas scattering and ion- plating conditions. In addition, sputtering processes using ion beams and magnetically confined plasmas were studied.The surface morphology, structure and preferred orientation of the coatings produced by the different processes were characterized by scanning and transmission electron microscopy. Film purity and interfacial characteristics were examined by Auger electron spectroscopy.The scanning electron microscopy study shows that thin carbon films generally have a smooth and featureless surface morphology. However, other surface morphology features are obtained in thicker films, depending on the processing conditions. The transmission electron micrographs show the absence of structure and growth features. Electron diffraction indicates that the films consist of a turbostratic phase and a non-crystalline phase. The apparent crystallite sizes are small, and there is no three-dimensional ordering. Generally, the films are isotropic and consist of relatively pure carbon, with the degree of disorder dependent on the process conditions.     

Synthesis and surface acoustic wave properties of AlN films deposited on LiNbO3 substrates

The c-axis-oriented aluminum nitride (AlN) films were deposited on z-cut lithium niobate (LiNbO₃) substrates by reactive RF magnetron sputtering. The crystalline orientation of the AlN film determined by x-ray diffraction (XRD) was found to be dependent on the deposition conditions such as substrate temperature, N₂ concentration, and sputtering pressure. Highly c-axis-oriented AlN films to fabricate the AlN/LiNbO₃-based surface acoustic wave (SAW) devices were obtained under a sputtering pressure of 3.5 mTorr, N₂ concentration of 60%, RF power of 165 W, and substrate temperature of 400°C. A dense pebble-like surface texture of c-axis-oriented AlN film was obtained by scanning electron microscopy (SEM). The phase velocity and the electromechanical coupling coefficient (K²) of SAW were measured to be about 4200 m/s and 1.5%, respectively. The temperature coefficient of frequency (TCF) of SAW was calculated to be about -66 ppm/°C     

Low‐Vacuum Low‐Cost Deposition of Tribological Coatings

TiN coatings of some microns in thickness were deposited by different reactive plasma deposition technologies such as Magnetron Sputtering Magnetically Assisted, Arc Source Ion Plating and Sputter Ion Plating Plasma Assisted on various unheated metal parts. The source to substrate distances was between 8 and 25cm. Deposition were performed in specially designed plants in the pressure range between 10^‐3–10^‐1 mbar and under variable vacuum and plasma conditions. The experiments were carried out with the intention of obtaining isotropic coatings on substrates of complex geometry. Thickness distribution, morphology, hardness and tribological properties of these coatings were investigated and correlated with the gas pressures and the measured plasma parameters during deposition. The aim of this work was to find effective processes and conditions for the reliable low cost deposition of hard coatings at relatively high gas pressures. The investigations were supported by the European Union in the TIPCOAT‐Project: Brite EuRam BE‐3815/Contract BRPR‐CT97‐0397     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Morphological and structural characterisation of osseointegrable Mn2+ and CO32− doped hydroxylapatite thin films

We report a morphological and structural study of osseointegrable hydroxylapatite thin films doped with divalent manganese and carbonate ions. The films were grown by pulsed laser deposition on medical grade Ti substrates at low oxygen pressure (13 Pa). Deposition targets were prepared from powders obtained by precipitation. During deposition, the substrates were kept at constant temperature within the temperature range 350–450 °C and the obtained films were subsequently annealed in hot water vapours at the deposition temperature. The films were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). Film specimens for cross-section TEM were prepared by focused ion beam (FIB) machining. The inferred Ca/P atomic ratio in films varied between 1.6 and 1.8, depending on experimental conditions. XPS confirmed the presence of chemically bonded Mn²⁺. Cross-section TEM micrographs showed uniform thickness of the coatings, which consisted of amorphous and crystalline domains. Examination of the SEM micrographs revealed an increased smoothness of the surface with increase in substrate deposition temperature. XRD patterns of samples processed at temperatures over 400 °C showed well-crystallized hydroxylapatite, suggesting that deposition and annealing have to be performed at higher substrate temperature if highly crystalline coatings are required.     

化学气相沉积SiC涂层生长过程分析

以高纯石墨为沉积基体,MTS为先驱体原料,在负压条件下沉积了CVD SiC涂 层.利用SEM和XRD分别对涂层的形貌及晶体结构进行了表征,SiC涂层表面呈菱柱状, (111)面为择优取向面.利用高分辨透射电镜对涂层与基体的界面结构、涂层的显微结构进行 了研究,得出CVD SiC涂层生长过程如下:SiC最初是沿着石墨基体的晶面取向开始生长 的}随后经历一段取向淘汰及调整的过程后,开始(111)晶面的生长.     

Ultrafast thermal plasma physical vapor deposition of thick SiC films

Thick silicon carbide films have been successfully deposited at a deposition rate of 125 nm/s on stationary graphite substrates by the thermal plasma physical vapor deposition technique, with ultrafine SiC powder fed into a hybrid plasma jet and completely evaporated. The relationship between the processing parameters and the morphology, deposition rate, composition and crystal structure has been investigated under the typical conditions of substrate temperature in the range of 1400–1700 °C and chamber pressure of 250 Torr, and compared with the results of rotating substrate deposition at the substrate temperature of around 750 °C. It was found that the deposition rate and composition showed different processing parameter dependences for rotating substrate deposition and stationary substrate deposition. The films showed dense cross-sections or cauliflower-like structures depending on the deposition conditions.

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