Tribological properties of metal doped a-C film by RF magnetron sputtering method

We deposited various metal doped amorphous carbon (a-C:Me) films by radio frequency (RF) magnetron co-sputtering method. Tungsten (W), molybdenum (Mo), and chromium (Cr) were used as the doping metals in a-C film. The applied power on carbon and metal (W, Mo, and Cr) target were 150 W and 40 W, respectively. a-C:Me films exhibited smooth and uniform surface roughness and the hardness over 15 GPa. Specially, a-C:W film showed the maximum hardness of 18.5 GPa. The coefficient of friction of a-C:W film is relatively lower than that of other films and the critical load value of a-C:W film is higher. These results are related to the concentration of metal in the carbon matrix by the difference of sputtering yield and the change of the structure by the metal bonding. Consequently, W metal is good candidate as the doping metal for the improvement of tribological characteristics.     

The effects of pulse frequency and substrate bias to the mechanical properties of CrN coatings deposited by pulsed DC magnetron sputtering

The chromium nitride coatings have been prepared by the bipolar symmetric pulsed DC magnetron reactive sputtering process at 2 kHz and 20 kHz pulse frequencies, respectively. Different substrate bias was applied with a pulsed DC bias unit with 50 kHz pulse frequency. Oscilloscope traces of the I–V waveforms indicate high power and high current density outputs during the symmetric bipolar pulsed mode. It is concluded that the (200) orientation of CrN films is observed. The grain size decreases with increasing pulse frequency and substrate bias. The substrate bias has a strong influence on the mechanical properties of CrN films. The scratch tests of the CrN coatings show that almost only tiny chipping failure is occurred. Sufficient adhesion strength quality of the coating is also observed. The substrate bias for the deposition of CrN films with sufficient hardness and adhesion properties combination is − 290 V at 20 kHz and − 408 V at 2 kHz pulse frequency, respectively.     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Structural and optical properties of chlorinated plasma polymers

Amorphous hydrogenated chlorinated carbon (a-C:H:Cl) films were produced by the plasma polymerization of chloroform–acetylene–argon mixtures in a radiofrequency plasma enhanced chemical vapor deposition system. The main parameter of interest was the proportion of chloroform in the feed, R_C, which was varied from 0 to 80%. Deposition rates of 80 nm min^? 1 were typical for the chlorinated films. Infrared reflection–absorption spectroscopy revealed the presence of C–Cl groups in all the films produced with chloroform in the feed. X-ray photoelectron spectroscopy confirmed this finding, and revealed a saturation of the chlorine content at ~ 47 at.% for R_C ≥ 40%. The refractive index and optical gap, E₀₄, of the films were roughly in the 1.6 to 1.7, and the 2.8 to 3.7 eV range. These values were calculated from transmission ultraviolet–visible-near infrared spectra. Chlorination leads to an increase in the water surface contact angle from ~ 40° to ~ 77°.     

Titanium oxide thin films synthesis by pulsed – DC magnetron sputtering

Titanium oxide thin films (1–4 μm) were deposited on the porous Hastelloy-X substrates using the pulsed – DC magnetron sputtering technique and characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Firstly, the films were deposited at different distances between the magnetron and the substrate, as magnetron current and pressure in the deposition chamber were constant. The distance between the magnetron and the substrate was changed from 3 cm to 7 cm, and the deposition rate varied between 10.1 nm/min to 6.0 nm/min. Secondly, pressure influence for the deposition rate was investigated. The deposition rate decreased nearly 15% with the decrease of oxygen pressure from 1.3 to 6.0 Pa. Finally, the influence of the bias (applied to the substrate for the increase of deposition rate) on thin films phase and microstructure was investigated.The experimental results showed that formation of pure titanium oxide thin films was observed in all experimental cases. Only crystallite sizes and orientation were changed. The results showed that there is a possibility to change porosity and uniformity of the growing film by changing oxygen partial pressure during deposition or bias application to the substrate. The existence of columnar boundaries and nanocrystalline structure in the films was observed.     

Deposition of TiB2 onto X40 CrMoV 5-1-1 steel substrates by DC magnetron sputtering

Titanium diboride (TiB₂) films are being investigated due to their promising uses not only in electronic devices but also for mechanical purposes. Its excellent corrosion resistance and chemical stability, as well as high hardness and wear resistance, makes TiB₂ particularly suitable for aluminium processing (e.g. extrusion, die-casting and machining). In the present work, TiB₂ coatings were produced by non-reactive DC magnetron sputtering from a TiB₂ target on a tool steel substrate (AISI H13 premium/EN X40 CrMoV 5-1-1). Substrates similar to those frequently found on the aluminium injection industry were produced by vacuum quenching and tempering. The deposition parameters, namely the target/substrate distance, discharge current and substrate bias, were varied in order to obtain crystalline and well-structured films, suiting the substrate composition and microstructure. The coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy/EDS.A deposition rate of 23 nm/min was obtained for 0.85 A cathode current intensity and 70 mm substrate–magnetron distance. For positively biased substrates, all films are dense, without a columnar structure and show a (0 0 1) texture. For negatively biased substrates, there are less surface heating effects due to a much lower electron current through the substrate, and an ordered structure appears only at −150 V.     

Structural and biocompatible characterization of TiC/a:C nanocomposite thin films

In this work, sputtered TiC/amorphous C thin films have been developed in order to be applied as potential barrier coating for interfering of Ti ions from pure Ti or Ti alloy implants. Our experiments were based on magnetron sputtering method, because the vacuum deposition provides great flexibility for manipulating material chemistry and structure, leading to films and coatings with special properties. The films have been deposited on silicon (001) substrates with 300 nm thick oxidized silicon sublayer at 200 °C deposition temperature as model substrate. Transmission electron microscopy has been used for structural investigations. Thin films consisted of ~ 20 nm TiC columnar crystals embedded by 5 nm thin amorphous carbon matrix. MG63 osteoblast cells have been applied for in vitro study of TiC nanocomposites. The cell culture tests give strong evidence of thin films biocompatibility.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Synthesis and characterization of thermally evaporated Cu2SnSe3 ternary semiconductor

Copper Tin Selenide (CuSnSe) powder was mechanically alloyed by high energy planetary ball milling, starting from elemental powders. Synthesis time and velocity have been optimized to produce Cu₂SnSe₃ materials. Thin films were prepared by thermal evaporation on Corning glass substrate at T_s = 300 °C. The structural, compositional, morphological and optical properties of the synthesized semiconductor have been analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and transmission electron microscopy. The analyzed powder exhibited a cubic crystal structure, with the presence of Cu₂Se as a secondary phase. On the other hand, the deposited films showed a cubic Cu₂SnSe₃ ternary phase and extra peaks belonging to some binary compounds. Furthermore, optical measurements showed that the deposited layers have a relatively high absorption coefficient of 10⁵ cm⁻¹ and present a band gap of 0.94 eV.     

High rate deposition of a-Si:H and a-SiNx:H by VHF PECVD

Very High Frequency (VHF) plasma enhanced chemical vapour deposition (PECVD) has been applied to hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiN_x:H) films for thin film transistors (TFTs) fabrication. The effect of the excitation frequency on the deposition rate and the film quality of both films has been investigated. The films were prepared by VHF (30 MHz∼50 MHz) and HF (13.56 MHz) plasma enhanced CVD.High deposition rates were achieved in the low pressure region for both a-Si:H and a-SiN_x:H depositions by the use of VHF plasma. The maximum deposition rates were 180 nm/min for a-Si:H at 50 MHz and 340 nm/min for a-SiN_x:H at 40 MHz. For a-SiN_x:H films deposited in VHF plasma, the optical bandgap, the hydrogen content and the [Si–H]/[N–H] ratio remain almost constant regardless of an increase in deposition rate. The increase of film stress could be limited to a lower value even at a high deposition rate. The TFTs fabricated with VHF PECVD a-Si:H and a-SiN_x:H films showed applicable field effect mobility. It is concluded that VHF plasma is useful for high rate deposition of a-Si:H and a-SiN_x:H films for TFT LCD application.     

Crystallographic behavior of FeS2 films formed on different substrates

FeS₂ polycrystalline films were prepared on amorphous glass, monocrystalline Si (1 0 0), polycrystalline Al and microcrystalline TiO₂ film substrates by sulfuration annealing of magnetron sputtered iron films. The crystal microstructure and orientation distribution of the films were investigated. The FeS₂ films formed on Si (1 0 0) and glass substrates have relatively fine and uniform grains and small lattice distortion at the interface between the film and substrate but insignificant preferred orientation. The FeS₂ films formed on Al or TiO₂ substrates have relatively inhomogeneous microstructure, large lattice distortion at the interface and a (2 0 0) or (2 2 0) preferred orientation. High strain energy at the interface should be responsible for the preferred orientation and inhomogeneous microstructure in the films.     

Reflectance spectra and refractive index of a Nd:YAG laser-oxidized Si surface

The reflectance spectra and refractive index of Nd:YAG laser-oxidized SiO₂ layers with thicknesses from 15 to 75 nm have been investigated with respect to the laser beam energy density and substrate temperature. Thickness and refractive index of films have been determined from reflectance measurements at normal light incidence in the spectral range 300–800 nm. It was found that the oxide-growth conditions at higher substrate temperatures and laser powers greater than 3.36 J cm⁻² provides a better film quality in terms of both optical thickness and refractive index. However, the refractive indices of the films are smaller in the whole spectral range studied as compared to that of conventional thermally grown SiO₂. This might be due to the porous structure formed during the laser-assisted oxidation. The results suggest the need of post-oxidation annealing to improve the refractive indices of the films, suitable for Si-device applications.     

Formation of F-doped ZnO transparent conductive films by sputtering of ZnF2

Fluorine-doped ZnO transparent conductive thin films were successfully deposited on glass substrate by radio frequency magnetron sputtering of ZnF₂. The effects of rapid thermal annealing in vacuum on the optical and electrical properties of fluorine-doped ZnO thin films have been investigated. X-ray diffraction spectra indicate that no fluorine compounds, such as ZnF₂, except ZnO were observed. The specimen annealed at 500 °C has the lowest resistivity of 6.65 × 10^? 4 Ω cm, the highest carrier concentration of 1.95 × 10²¹ cm^? 3, and the highest energy band gap of 3.46 eV. The average transmittance in the visible region of the F-doped ZnO thin films as-deposited and annealed is over 90%.     

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (1 0 0)

In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni_82.5Fe_17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0).     

Structural and optical properties of BaTi2O5 thin films prepared by pulsed laser deposition at different substrate temperatures

BaTi₂O₅ thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (T_sub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on T_sub, and the b-axis oriented BaTi₂O₅ thin film could be obtained at T_sub = 973–1023 K. The surface morphology of the films was different with changing T_sub, which showed a dense surface with an elongated granular texture at T_sub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi₂O₅ thin films were highly transparent with an optical transmittance of ～70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for T_sub = 923 K to 3.56 eV for T_sub = 1023 K.     

Wide bandgap Mg-doped ZnAlO thin films for optoelectronic applications

Magnesium-doped ZnAlO thin films were grown on quartz substrate by ablating the sintered target with a KrF excimer laser. The effect of growth temperature from 30 °C to 700 °C on structural, optical, and electrical properties has been studied. These films are highly transparent in visible spectrum with average transmittance of 82%. The films grown at low temperature are amorphous while films grown at high temperature are crystalline in nature. These films are highly oriented along (0 0 2) direction. The electrical conductivity, carrier concentration, and electron mobility is found to increase with increase in temperature and then decreases with further increase in temperature. The bandgap is found to vary from 3.86 eV to 4.00 eV for various films.     

Laser-induced transformation of a-C:H thin films

In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp³/sp² ratio, and sp² clustering) is studied. The results show that a loss of hydrogen and an increase of the sp² phase are the main processes in the laser power range between 1.8 and 5 MW/cm². Only these processes are stronger for “more polymer-like” and “graphite-like” films than for “more diamond-like” films.     

Growth technology,X-ray and optical properties of CdSe thin films

An ammonia-free chemical-bath deposition was used to obtain CdSe thin films on glass substrate. The materials used in the chemical bath were cadmium chloride complexed with sodium citrate and sodium selenosulphate. The preparation conditions, especially the starting solution characteristics, such as concentration of dissolved materials, temperature, pH value as well as deposition time and immersion cycles were optimized to obtain homogeneous stoichiometric films with good adherence to the glass substrate. The films thickness was in the range of 400–500 nm with a growing time of 4 h. The material obtained was characterized by optical absorption, SEM with the energy dispersive X-ray analysis (EDS) and X-ray diffraction. The films obtained at bath temperatures of 70 and 80 °C had the hexagonal structure (of wurtzite type), with crystallite size of about 20 nm. Room temperature deposition results in films with the cubic structure and crystallite size of about 4 nm. From optical transmission data, an energy gap equal to 1.88 eV was found. The material is interesting for applications in hybrid systems for solar energy conversion.     

Microstructural characterisation of nanocomposite nc-MeC/a-C coatings on oxygen hardened Ti-6Al-4V alloy

Nanocomposite coatings are novel, important systems composed of two or more nanocrystalline, or nanocrystalline and amorphous, phases. Such coatings offer a possibility of tailoring the coating microstructure and achieving new improved properties of coated materials. In this work a duplex surface treatment, consisting of an oxygen diffusion treatment and deposition of low friction nanocomposite nc-MeC/a-C (Me = transition metal, Ti, W or Cr) coatings, was applied for improvement of the Ti-6Al-4V alloy properties. The coatings composed of nanocrystallites of transition metal carbides (TiC or Cr_xC_y or WC) embedded in hydrogen-free amorphous carbon (a-C) matrix were deposited onto the surface of an oxygen hardened Ti-6Al-4 V alloy substrate by means of a simple DC magnetron sputtering. A nano/microstructure of the substrate material and coatings has been examined by scanning- and transmission electron microscopy complemented with the results of X-ray diffraction analyses.It was found that the nanocomposite coatings are composed of different carbide nanocrystals (with sizes of a few nanometres) embedded in an amorphous carbon matrix. The results of qualitative and quantitative analyses of the nanocrystalline phase in the coatings with use of high-resolution transmission electron microscopy combined with image analysis are given in the paper.An effect of the nano/microstructure parameters of the coated alloy onto its micro-mechanical (nanohardness and Young's modulus) and tribological properties (wear resistance and friction coefficient) is discussed in the paper.     

NiCo films with perpendicular magnetization anisotropy deposited on dielectric substrate by using polyol process

In this paper, the polyol process, a catalyst free, non-aqueous, and electroless process, is developed to deposit the nanostructured Ni_xCo_100 ? x magnetic films on aluminum nitride (AlN) substrate. Nickel (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate were reduced by ethylene glycol (EG) at 180 °C, and the reduced Ni and Co nanostructures were deposited on the AlN substrate merged in boiling EG for 60 min. The elongated nanostructures in the films are detected through the scanning electron microscopy (SEM). Interestingly, some of the elongated nanostructures are pointing out of the substrate. It indicates that the component ratio of Ni and Co in the films is different with the starting precursor molar ratio. The film thickness increases from 1 to 1.8 μm when the atomic ratio of Co (at.%) in the film increased from 44.6% to 70.8%. Furthermore, it is found that the crystallite size decreases from 44 to 25 nm with increasing Ni (at.%). In addition, the magnetic properties have been analyzed through vibrating sample magnetometer (VSM) at room temperature. The results show that the films have the perpendicular preferred anisotropy. The anisotropy field (H_K) for the Ni₅₀Co₅₀ is about 4.75 kOe, which is possibly caused by the assembled direction of the elongated nanostructures.