Properties Of Thin-film Coatings Research Articles

Effect of B2O3 additive on the properties of ZnS-Ge system and the resulting thin-film coatings

The effect of B2O3 additive to ZnS and ZnS-Ge system on their properties and parameters of thin-film coatings obtained from them has been studied. The essence of the additive is the binding of ZnO in Zinc sulfide, which has a negative effect due to the interaction with the evaporator material. According to X-ray diffraction, the introduction of B2O3 additive to ZnS results in the disappearance of the wurtzite phases (β-ZnS and ZnO). There is also a change in the IR spectra, in which reveal the bands at ≈300 cm−1 and 415 cm−1, which correspond to the valence vibrations of the Zn-S and Zn-O bonds, respectively. It is established that the addition of B2O3 noticeable improves the technological mode of evaporation in vacuum of materials due to the increase of their volatility. The reflection spectra of thin films of undoped and doped ZnS indicate a certain increase in the refractive index of the latter, while in the ZnS-Ge system such a difference is not observed. The mechanical durability of coatings increases especially significantly - more than 10 times for ZnS and more than 2 times - for the ZnS-Ge system. Therefore, the use of B2O3 as an additive has proved to be an effective method for minimizing the effects of oxide impurities in chalcogenide materials on the properties of thin-film coatings.

Structures, morphological control, and antibacterial performance of tungsten oxide thin films

The present work describes structural, morphological, and antibacterial properties of thin film coatings based on tungsten oxide material on stainless-steel substrates. Thin films were prepared by RF magnetron sputtering of W targets in the oxygen/argon plasma environment in 60 W sputtering power. The characterization of the specimens was made on the basis of microstructure and antibacterial properties of the thin films surface. The effect of O2/Ar ratio on the structure, morphology, and antibacterial properties of the tungsten oxide thin films was studied. Methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) were used to assess the properties of deposited thin films. XRD peak analysis indicates (100) and (200) of WO3 phase with hexagonal structure. Moreover, the micro-strain, grain size, and dislocation density were obtained. It is noteworthy that by increasing the oxygen percentage from 10% to 20%, the grain size decreases from 81 to 23 nm while the film micro-strain and dislocation density increases. The SEM results illustrates that tungsten oxide thin films are made of interconnected nano-points in a chain shape with sphere-shaped grains with diameter variation from 10 to 100 nm. The FTIR spectra displays four distinct bands corresponds to O–W–O bending modes of vibrations and W–O–W stretching modes of the WO3 films. The antibacterial effects of tungsten oxide thin films on steel stainless substrate against Escherichia coli bacteria are also examined for the first time and our observation shows that the number of bacteria on all tungsten oxide samples decreases after 24 h. The samples exhibit an excellent antibacterial performance. This paper renders a strategy through which the tungsten oxide thin films for antibacterial purpose and proposes that WO3 thin films are ideal for various medical applications including stainless steel medical tools, optical coatings, and antibacterial coatings.

Implementation of the new minimum resultant error approach to extract elastic-plastic properties of titanium nitride thin film by nanoindentation, finite element analysis, and modified dimensional analysis

Obtaining the plastic properties of thin film coatings has been the main challenge for decades. Implementing the hybrid methods seems to be an applicable way to address this issue. Unfortunately, limitations of nonunique answers together with the need for enormous amount of calculations are counted as the main challenges. To overcome such difficulties, a modified dimensional analysis method is proposed, which is able to reduce the number of dimensionless parameters. Another novel algorithm named “minimum resultant error method” is developed to provide proper criteria to investigate the compliance of the analytical results with empirical data. With this algorithm, yield stress, strain hardening exponent, and strain hardening coefficient are extracted as unique values by using a single indenter nanoindentation results. The simulation results are processed with combined modified dimensional analysis method and minimum resultant error method algorithms. The effects of interlayer, friction coefficient, and indenter tip radius are investigated. Error analysis to the modulus of elasticity is undertaken and the results show less than 2% error for the infimum point, while the individual dimensionless functions errors are below 3.4%. According to the results, this new approach is well-coped with the earlier studies.

Photocatalytic methylene blue degradation on multilayer transparent TiO2 coatings

This paper presents the influence of coating thickness on the photocatalytic activity of TiO2 coatings. Methylene blue decomposition under UV light was tested. Transparent anatase TiO2 thin films were prepared by the sol-gel method using alcoholic solutions. Thin films were deposited on a borosilicate glass substrate by the multiple dip-coating technique across a much wider range than is typically described in literature, specifically, from 1 to 12 dip-coating cycles. The degradation of MB dissolvent in water was measured by UV-Vis spectroscopy. The structure, morphology and optical properties of thin film coatings were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The crystalline structure of TiO2 films was identified as the anatase phase, consisting of uniform spherical particles from 25 to 32 nm depending on the number of dip-coatings cycles. Decreasing roughness and optical band gaps were also observed in the produced oxide films with increasing numbers of dip-coating cycles. The reaction rate of discoloration of the dye solution by photocatalytic degradation is strongly related to the thickness of the layer, the number of layers and its morphology. The thicker the oxide layer, the faster the reaction; however, this relationship is not linear. In addition, in this article, a methylene blue discoloration reaction model was proposed which takes into account stoichiometry, reagent electric charge balance and the REDOX type of reaction.

Characteristics and Plasmochemical Deposition of Coatings Based on Amorphous Hydrogenated Silicon Carbide

The effects of major technological parameters in plasmochemical deposition have been examined as regards the properties of thin-film coatings based on amorphous hydrogenated silicon carbide (a-SiC : H) formed by the use of methyltrichlorosilane. Effects have been established from the substrate temperature, discharge power, and pressure of the reagent gases in the reaction chamber on the plasma performance. The films have been examined by secondary mass spectroscopy, and by infrared and optical spectroscopy, as well as by hardness testing by nanoindentation. Films based on amorphous hydrogenated silicon carbide can be used as wear-resistant coatings for metal-cutting tools and as active layers in semiconductor devices.

Atomistic simulation of surface evolution during PVD coating processes

To a great extent, the properties of thin film coatings are determined by their surface structure. PVD coating processes are simulated with an atomistic simulation to investigate the development of the surface structure at early stages of the film deposition. For this simulation, atoms are added to the surface of a single crystal fcc substrate with (100) and (111) surfaces and with a size of approximately 5000 atoms. These added atoms form a film on the substrate material. Periodic boundary conditions in two dimensions were used to reduce unwanted surface effects. During the simulation, the following parameters were varied: substrate temperature, substrate orientation, angular distribution and kinetic energy of the added atoms. The surface structure was evaluated after a deposition of approximately 10 atomic layers and cooling of the substrate. We found the number of neighbouring surface atoms to be a useful way to describe surface roughness and orientation. Obviously, the substrate temperature is the dominating parameter for the smoothening of the surface, but at temperatures below 0.6 · T m , the angular distribution and the kinetic energies of the film atoms have great influence as well. In addition, we investigated the resputtering and evaporation of film material during the deposition and its dependence on the process parameters.

Non-destructive evaluation of TiN films with interface defects by surface acoustic waves

Surface acoustic wave (SAW) measurements are a fast and reliable way to obtain information about the elastic properties of thin film coatings. Measuring the surface wave phase velocity which is dependent on frequency and performing the inverse solution of dispersion relation for surface wave propagation in coated materials enable us to determine the elastic parameters of the film and substrate material. Measuring equipment is used where wide-band surface wave impulses are generated by short laser pulses and received with a piezoelectric transducer. The surface wave phase velocity is obtained by Fourier transforming the impulse form. In this work we are interested in Young's modulus of the film material and its relation to the defects in the interface region of the substrate. Young's modulus is a characteristic material parameter, depending on atomic composition and on the microscopic structure of the material. It is theoretically and experimentally established that, if defects such as flaws are incorporated, Young's modulus is reduced in comparison with that of bulk material. The examined samples were steel pieces (42CrMo4) coated with TiN by ion plating. During the deposition process we have only varied the duration of the ion etching process, while keeping all other technological parameters constant. The ion etching is responsible for the adhesion of the coating by removing residual contamination from the substrate surface. In this way a more or less non-defective interface zone is built up. The procedure of varying only the etching time allows us to obtain different interface properties while leaving film properties constant. Film properties were characterized by means of Auger, X-ray texture and dynamic hardness measurements. It was shown that there is a correlation between Young's modulus and conventional scratch test results. The acoustic emission was used to evaluate the coated material behaviour in the scratch test. From a Weibull diagram of the acoustic emission signals an initial crack load L i was determined. It could be proved that the initial crack load and the Young's modulus correlate with a coefficient R = −0.78.

Monte-Carlo simulation of the deposition process in PVD-technology

AbstractThe Magnetron Sputter Ion Plating (MSIP) technology has been applied in a wide range of modern technological fields, due to the virtually unlimited potential of coating and substrate materials. However, up to now, the development of optimization has been depending mainly on empiricism and experiments.Energies and the directions of the particles sputtered with various ejection angles and initial energies from the target surface are changed due to collisions with gas atoms during their movement within the sputtering chamber. Therefore the particles have a distribution of incident energies and angles which have a great influence on structure and properties of thin film coatings. This paper describes computer investigations to simulate the motions of the particles from target to substrate using a Monte-Carlo method and a binary collision approximation. The applied model takes into account non-uniform sputtering effects of the target in the MSIP process due to the magnetic field and the erosion zone.

Monte-Carlo simulation of the deposition process in PVD-technoIogy

ABSTRACTThe Magnetron Sputter Ion Plating (MSIP) technology has been applied in a wide range of modem technological fields, due to the virtually unlimited potential of coating and substrate materials. However, up to now, the development of optimization has been depending mainly on empiricism and experiments.Energies and the directions of the particles sputtered with various ejection angles and initial energies from the target surface are changed due to collisions with gas atoms during their movement within the sputtering chamber. Therefore the particles have a distribution of incident energies and angles which have a great influence on structure and properties of thin film coatings. This paper describes computer investigations to simulate the motions of the particles from target to substrate using a Monte-Carlo method and a binary collision approximation. The applied model takes into account non-uniform sputtering effects of the target in the MSIP process due to the magnetic field and the erosion zone.

Microstructures and tribological characteristics of electron-beam co-deposited Ag/Mo thin film coatings

The tribological characteristics of surface coatings on a metal substrate are affected by several factors including the microstructure of the coatings, the interactions between the coating and metal substrate, and the mechanical properties of the substrate. Techniques are available to fabricate different types of metastable film structure to aid in unraveling their influences on tribological behavior. In this study, we investigated the friction and wear properties of thin film coatings consisting of Ag and Mo which were co-deposited by electron-beam evaporation in an ultra high vacuum. Ag and Mo were chosen because the metastable structures, such as extended solid solutions or nano-crystalline microstructures, can be formed by co-deposition, although alloys of the two metals cannot exist in thermodynamic equilibrium. Using a Cameron-Plint high frequency pin-on-plate friction machine, test results show that a co-deposited film having an optimum composition ratio of Ag: Mo = 69:31 (denoted by Ag 69Mo 31), and having a thickness of 150 nm, has the lowest friction (20%–25% reduction) and improved antiwear properties compared with coatings of other compositions. A bare steel plate after dry sliding of 30 h against a steel sphere shows substantial wear and plastic deformation. In contrast, the same plate with a thin film coating of Ag 69Mo 31 shows a much smoother surface. The improved tribological characteristics may be attributed to the greater wear-resistant and shearing capabilities of nano-crystalline binary mixtures on iron surfaces.