Structural and mechanical properties of CNx thin films prepared by magnetron sputtering

In an attempt to define the role of nitrogen in CN chemical bonding and in the formation of CN_x thin films, several coatings with a variable concentration of N₂ were grown onto (100) Si substrates using magnetron sputtering in N₂/Ar discharge. The chemical composition of the as-deposited films was investigated by means of Rutherford backscattering spectroscopy (RBS) and showed an [N]/[C] ratio up to 0.7. Raman and Fourier transform infrared (FTIR) spectroscopy were carried out to measure the optical vibration properties for studying the bonding state of nitrogen.By means of grazing incidence X-ray diffraction (XRD) and transmission electron microscopy (TEM) electron diffraction the structure of the deposited films was proven to be mainly amorphous containing small crystallites of CN_x compounds. Scanning tunneling microscopy (STM) shows the clusterlike surface of the films where the cluster size is characterized by scaling behaviour. The mechanical properties of the CN_x thin films adhering their substrates were investigated using the nanoindentation technique. From the load–displacement curve the hardness H and the Young's modulus E of the films were calculated.The relationships between deposition parameters and properties of CN_x films are shown and discussed. In particular, the influence of the applied r.f. power and the role of the N₂ partial pressure are demonstrated.     

Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

Mechanical properties of DLC films prepared inside of micro-holes by pulse plasma CVD

Diamond-like carbon (DLC) films are metastable amorphous carbon materials with superior tribological characteristics. In order to improve wear resistance of micro-extrusion dies with numerous imperceptible holes, DLC films were deposited on the inner wall surface of model dies with holes of 2 and 0.9 mm in diameter, and 20 mm in depth by using pulse plasma CVD method. This paper will discuss how argon gas, deposition pressure and time affect the characteristics of films deposited on the inner wall surface of dies. This micro-coating method can be applied widely for inner wall surface treatment of components with thin holes.     

Structural and mechanical properties of polystyrene nanocomposites with 1D titanate nanostructures prepared by an extrusion process

Polystyrene (PS) nanocomposites with titanate nanotubes and titanate nanoribbons were prepared by an extrusion process at 180°C. Nanocomposites with 1 wt% of nanofillers and pure PS that had also been exposed to the extrusion process were comparatively examined with scanning electron microscopy (SEM), electron dispersive X‐ray spectrometry (EDS) mapping, solid state proton nuclear magnetic resonance measurements (¹H NMR), tensile tests, and shear creep measurements. SEM images and EDS mapping analysis show that titanate nanoribbons homogeneously distribute at a micrometer length‐scale in the PS matrix during the extrusion process. This is not the case for titanate nanotubes, which show a stronger tendency to form clusters. Solid state ¹H NMR studies, however, proved that the nanocomposites are inhomogeneous at a nanometric scale where structural components with highly mobile PS molecules coexist with domains of rigid PS molecules. Differences in the ¹H spin‐lattice relaxation at and above the glass transition temperature T_g = 373 K suggest that nanofillers affect the thermodynamic properties of nanocomposite domains. Only a slight increase in mechanical tensile properties was observed in the case of the nanocomposite containing 1 wt% of titanate nanoribbons (TiNRs) probably reflecting a weak interaction between the polymer matrix and the nanofiller. Nevertheless, our results prove that the use of functionalized TiNRs may, in combination with the extrusion process, represent a very promising starting point for the preparation of TiNR nanocomposites at the industrial level. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Growth and properties of hydrogen-free DLC films deposited by surface-wave-sustained plasma

Hydrogen-free diamond-like carbon (DLC) films were deposited by a new surface-wave-sustained plasma physical vapor deposition (SWP-PVD) system in various conditions. Electron density was measured by a Langmuir probe; the film thickness and hardness were characterized using a surface profilometer and a nanoindenter, respectively. Surface morphology was investigated using an atomic force microscope (AFM). It is found that the electron density and deposition rate increase following the increase in microwave power, target voltage, or gas pressure. The typical electron density and deposition rate are about 1.87 × 10¹¹–2.04 × 10¹² cm^− 3 and 1.61–14.32 nm/min respectively. AFM images indicate that the grain sizes of the films change as the experimental parameters vary. The optical constants, refractive index n and extinction coefficient k, were obtained using an optical ellipsometry. With the increase in microwave power from 150 to 270 W, the extinction coefficient of DLC films increases from 0.05 to 0.27 while the refractive index decreases from 2.31 to 2.11.     

Structural and mechanical properties of facing-target sputtered amorphous CNx films

Structural and mechanical properties of carbon nitride films, deposited using a DC facing-target reactive sputtering system at various N₂ fractions (P_N) in the gas mixture, were studied systematically. XPS analyses indicate that N concentration is not directly proportional to P_N, and it rises quickly to a saturation value of ∼ 33 at.% at a P_N of 20%. The ratio of N–C(sp²)/N–C(sp³) increases with the rise of P_N from 0% to 20%, and then decreases with further rising P_N. However, the number and size of disordered sp²-hybridized C clusters continue to increase over the whole range of P_N, which is consistent with the Raman and high-resolution transmission electron microscopy measurements. Nanoindenter measurements show that the hardness of the films continuously decreases from ∼ 17.5 to ∼ 5.6 GPa with the increasing P_N from 0% to 100%, due to the conversion from sp³ C to sp² C and the clustering of sp² C structure.     

Structural and mechanical properties of Sr-doped barium niobate thick films

Polycrystalline strontium barium niobates Sr _x Ba_{1 ? x} Nb₂O₆ (SBN, 0.40 ≤ x ≤ 0.75) were prepared by standard solid state ceramic method at relatively at low temperatures. Thick SBN films prepared by simple, low-cost, screen printing route were characterized by XRD. Preliminary structural analysis exhibits the formation of tetragonal tungsten bronze crystal structure at room temperature. Texture coefficient [TC(hkl)], dislocation density (ρ_D), density of crystallites per unit surface area (Ψ), mechanical properties, and microwave behavior of synthesized materials are reported.     

The effect of negative bias pulse on the bonding configurations and properties of DLC films prepared by PBII with acetylene

The effect of negative bias pulse applied to substrate on the bonding configurations and properties of diamond-like carbon (DLC) films prepared by plasma-based ion implantation (PBII) with acetylene were investigated. The research results show that as the plasma density is 10⁹ cm⁻³ and the negative bias pulses applied to substrate decrease from 50 to 10 kV, the Raman spectra of the carbon films all possess the most dominant characterizations of typical a-C:H [J. Robertson, Mater. Sci. Eng., R 37 (2002) 129-281.], the positions and FWHM for G and D peaks vary no distinguished, but the ratio ID/IG decreases monotonically, as the negative bias pulse decreasing to 5 kV, the Raman spectrum possesses rather strong photoluminescence characterized the polymer-like phase. The variation of Raman spectra for plasma density 10⁸ cm⁻³ is analogous to that of the plasma density 10⁹ cm⁻³. The binding energies of XPS C1s peak decrease from the side of diamond peak to the side of graphite peak with the increasing of negative bias pulse from 10 to 50 kV monotonously, the sp³ content in the films increases with the decreasing in the negative bias pulse. With the increasing of negative bias pulse from 0 to 50 kV, the surface electric resistance of the films decreases monotonously, but the surface nanohardness at first increases with the increasing of the negative bias pulse from 0 to 10 kV, then decreases with the increasing of the negative bias pulse from 10 to 50 kV monotonously. These properties of the films are corresponding to the bonding configurations of the films. The reason for the highest sp³ fractions of the a-C:H films formed at higher effective ion energy per C atom in PBII is discussed in this paper.     

Thermal annealing behaviour of alloyed DLC films on steel: Determination and modelling of mechanical properties

A shortcoming of diamond-like carbon (DLC) films is the poor stability of their microstructure and properties at elevated temperatures. In this study, the effect of annealing on the stability of DLC films alloyed with silicon and deposited on steel is investigated. A comprehensive study of the mechanical properties is carried out by a novel method combining normal indentations with micro- and macroindentors assisted by finite element calculations of the indentation. The mechanical properties of the layers are correlated to structural changes in the film and to interface reactions.While it has become a common practice to determine hardness and the Young's modulus of thin films by nanoindentation and to calculate residual stresses from the bending of the film/substrate system, evaluation of the interface toughness, which is a measure of adhesion, and of the film rupture strength is less straightforward. Here, Hertzian-type ring cracks are generated in the film by nanoindentation of the film/substrate system with spherical diamond tips. From the critical load for crack generation the film rupture strength is deduced using finite element calculations. Similarly, Rockwell C hardness tests in combination with calculations are performed to measure the interface toughness.Applying these methods to DLC films on steel, it has been found that the Young's modulus decreases with increasing silicon content and the residual stress drops below 1 GPa. The rupture strength approaches its theoretical limit of E/10. Annealing at 500 °C reduces the adhesion energy significantly. The variation of mechanical properties can be attributed to structural changes in the film as investigated by Raman spectroscopy.     

Polymer diffusion and mechanical properties of films prepared from crosslinked latex particles

Wedescribe energy transfer (ET)measurements to follow polymer diffusion, as well as oscillatory dynamic mechanical measurements and tensile measurements, on films prepared from structured and unstructured latex particles consisting of a copolymer of butyl methacrylate and butyl acrylate with a T_g of 20°C. Structure was introduced in the form of a low level (1 mol%) of crosslinking, using seeded semi-continuous emulsion polymerization to control the locus of the crosslinking agent in the particles. Linear dynamic mechanical measurements showed the G′ and G″ were sensitive to the particle morphology, with particular sensitivity exhibited by the elastic modulus G′. The tensile properties were less sensitive to particle morphology; sufficient polymer diffusion occurs during film formation for the films to acquire strength and toughness. As expected, crosslinking increases strength but decreases elongation to break. Some interesting compromises could be found through control of the location of the crosslinked regions of the film. Dept. of Chemistry, 80 St. George St., Toronto, Ont., Canada M5S 3H6. F-27470 Serquigny, France.     

Static tensile and dynamic mechanical properties of hydroxypropylcellulose films prepared under various conditions

The films of hydroxypropyl cellulose (HPC), which is a lyotropic and thermotropic liquid crystal, were cast under various conditions of temperature and concentration. The effects of the casting conditions on the static tensile and dynamic mechanical properties of the cast films were determined, and the results were compared with those of films prepared by means of hot compression. The tensile properties of the films prepared by both processes (cast and hot compression) were unsatisfactory in comparison with other liquid crystalline polymers, and this was partly due to water absorbed during the test. In dynamic properties, two distinct transitions were detected. The higher one, around 110°C, was associated with the rotation of an unhydroglucose ring and the lower one, around 25°C, was associated with the T_g. There were no marked differences in the properties between cast films and hot-compressed films, except the disappearance of the T_g for hot-compressed film prepared at a relatively higher temperature. The basis for defining the liquid crystalline structure in cast and hot-compressed films are not directly given in this preliminary paper. However, judging from the dynamic mechanical properties and refractive index data for films prepared by both processes, it appears that dimethylacetamide-cast films and films compressed at 180 and 200°C may have some structures related to liquid crystalline phase and that inter- and intramolecular hydrogen bonding play an important role in lyotropic and thermotropic liquid crystalline behavior for HPC.     

Structural,mechanical, and electrical properties of electropolymerized polypyrrole composite films

Electrochemical polymerization of pyrrole in a solution containing dissolved poly(vinyl alcohol) (PVA) produces a homogeneous, free‐standing, flexible, and conductive polymer film. The films were characterized using infrared spectroscopy, wide‐angle X‐ray diffraction analysis, and scanning electron microscopy. The appearance of standard and some new absorption bands for polypyrrole (PPy) and PVA confirms the composite formation. The mechanical properties of conducting PVA + PPy films were studied and found to be improved with respect to the control PPy films. The electrical conductivity of the PVA + PPy films was measured by using standard four‐ and two‐probe methods. The conductivity of the films was found to depend on the pyrrole content. These conducting composites were further used as gas sensors by observing the change in current with respect to ammonia gas. It was observed that the current decreases when these composites were exposed to ammonia gas. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2511–2517, 2001     

Structure, elemental composition, and mechanical properties of films prepared by radio-frequency magnetron sputtering of hydroxyapatite

The phase composition, substructure, and surface morphology of 0.1-to 5.0-μm-thick films grown on different substrates by radio-frequency magnetron sputtering of a hydroxyapatite ceramic target are investigated using transmission electron microscopy (TEM), high-energy electron diffraction, X-ray diffraction, IR spectroscopy, Auger electron spectroscopy, ultrasoft X-ray emission spectroscopy, Rutherford backscattering spectroscopy, scanning electron microscopy (SEM), and atomic-force microscopy (AFM). The hardness and adhesion strength of these films are studied using the nanoindentation and scratching methods. It is revealed that the structure of the films depends on the spatial inhomogeneity of the plasma discharge. Single-phase dense nanocrystalline hydroxyapatite films are formed when the substrate is located above the erosion zone. According to the X-ray diffraction, high-energy electron diffraction, and IR spectroscopic data, the structure of the films corresponds to the hydroxyapatite structure. As follows from the Auger electron, ultrasoft X-ray emission, and Rutherford backscattering spectroscopic data, the elemental composition of the films is similar to the stoichiometric composition of hydroxyapatite. The analysis of the X-ray diffraction and AFM data demonstrates that the films have a dense structure. The results of the mechanical tests show that the hardness of the coatings is higher than 10 GPa and that the maximum adhesion strength (L _C = 12.8 N) is observed for the hydroxyapatite coatings on the titanium substrate modified by the TiC-TaC-Ca₃(PO₄)₂ composite layer.     

The mechanical and biocompatibility properties of DLC-Si films prepared by pulsed DC plasma activated chemical vapor deposition

Films of diamond-like carbon containing up to 22 at.% silicon (DLC-Si) were deposited on to silicon substrates by low-frequency pulsed DC plasma activated chemical vapor deposition (PACVD). The influence of silicon doping on deposition rate, composition, bonding structure, hardness, stress, surface roughness and biocompatibility was investigated and correlated with silicon content. A mixture of methane and tetramethylsilane (TMS) was used for the deposition of DLC-Si films at a pressure of 200 Pa. The deposition rate increased with increasing TMS flow. The addition of silicon into the DLC film leads to an increase of sp³ bonding, as measured by Raman spectroscopy, and also resulted in lower stress and hardness values. The RMS surface roughness of the films was measured by atomic force microscopy and increased from 0.35 nm for DLC to 6.7 nm for DLC-Si (14 at.% Si) due to the surface etching by the H atoms. Biocompatibility tests were performed using MG-63 osteoblast-like cell cultures that were left to grow for 3 days and their proliferations were assessed by scanning electron microscopy. The results indicated a homogeneous and optimal tissue integration for both the DLC and the DLC-Si surfaces. This pulsed PACVD technique has been shown to produce biocompatible DLC and DLC-Si coating with potential for large area applications.     

High-density DLC films prepared using a magnetron sputter type negative ion source

Diamond-like carbon (DLC) films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS). The film characteristics such as density, surface roughness, film structure and thicknesses are obtained and analyzed using X-ray reflectivity (XRR), XPS and AFM methods. XRR results showed that the density of the film varies from 1.9 to 3.0 g/cm³ with respect to the different deposition parameters. At average negative carbon ion energy 700 eV and Cs injector temperature 150 °C, the densest film (3.0 g/cm³) was observed at 1 nm/s deposition rate. The surface roughness of the film was less than 1.0 nm in most cases for the 10-nm thickness film. XPS peak showed no Cs content on the film. The films prepared at different negative ion production yields and negative ion energies were compared. The result suggests that the density is the strong function of negative ion energy and the negative ion production yield.Higher cathode voltage induced denser film, while Cs flow rate had optimum temperature condition around 150 °C.     

Mechanical properties of DLC films prepared in acetylene and methane plasmas using electron cyclotron resonance microwave plasma chemical vapor deposition

Diamond-like carbon (DLC) films were deposited on silicon using methane and acetylene plasma induced by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The mechanical properties of DLC films were characterized by micro-Raman system, atomic force microscope, tribometer, nano-indenter used for both hardness and nano-scratch test measurements. The mechanical properties of both DLC films, prepared in methane and acetylene plasmas, respectively, strongly depended on the kinetic energy of impinging particles. The deposition at −120 V substrate bias gave rise to DLC films with the best mechanical properties for both methane and acetylene plasmas. The hardness measurements with variable indentation depth showed the characteristic changes in hardness values implying elastic deformations of supporting substrates. The maximum hardness value of DLC^M films was 20 GPa while that of DLC^A films was 28 GPa. However, the hardness dropped when DLC films were prepared at substrate biases more negative than −120 V due to the thermal graphitization. The improvement in DLC properties usually provided the films with smaller hydrogen content and higher density of sp³ bondings. These parameters were engineered through controlling the deposition parameters. Particularly, the bombardment of growing DLC films by energetic ions showed to be extremely important to yield films with lower internal stress.     

Structural and mechanical properties of Sr+2-doped bismuth manganite thick films

Bismuth strontium manganites Bi_{1 ? x} Sr _x MnO₃ (0.20 ≤ x ≤ 0.50) belonging to the orthorhombic structural family were prepared in furnace using a solid-state reaction technique. Thick films of Bi_{(1 ? x)}Sr _x MnO₃ were prepared by simple screen printing route. X-ray diffraction data suggest that the synthesized materials have an orthorhombic structure. For synthesized materials, texture coefficient (TC), dislocation density (ρ_D), density of crystallites per unit area (ψ), and mechanical properties are reported along with the influence of x on the structure and mechanical properties of BiMnO₃ thick films.     

Structure and mechanical properties of W incorporated diamond-like carbon films prepared by a hybrid ion beam deposition technique

W incorporated diamond-like carbon films were prepared on silicon(1 0 0) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a tungsten DC magnetron sputter source. The W concentration in the films was controlled by changing the fraction of Ar in the Ar and C₆H₆ reaction gas. The chemical composition, atomic bond structure, and mechanical properties were investigated for W concentrations ranging from 0 to 8.6 at.%. When the W concentration was <2.8 at.%, the W atoms were dissolved in the amorphous carbon matrix without forming a WC_1−x phase. Amorphous and crystalline WC_1−x nano-particles appeared when the W concentration was >2.8 and >3.6 at.%, respectively. It was found that the hardness and elastic modulus were not sensitive to the W concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated W atoms. The change in mechanical properties is discussed in terms of the microstructural changes induced by W incorporation.     

Structural and mechanical properties of YBCO‐polystyrene composites

Microcrystalline powders of yttrium barium copper oxide [YBa₂Cu₃O₇] have been prepared by conventional ceramic preparation technique. The powder belong to orthorhombic symmetry with unit cell dimensions ‘a’=3.8214 Å, ‘b’=3.8877 Å and ‘c’=11.693 Å. XRD and SEM studies revealed that its particle size is in the micrometer range. Micro composites of polystyrene with different loading of yttrium barium copper oxide fillers were prepared by melt mixing in a brabender plasticorder at a rotor speed of 60 rpm. The lattice parameters of the constituent phases are the same in all the composites. Mechanical properties such as stress–strain behavior, Young's modulus, and tensile strength were studied as a function of filler loading. Addition of filler enhances the Young's modulus of the polymer. Because of the poor filler‐matrix adhesion, tensile strength and strain at break decreases with filler loading. To explore more carefully the degree of interfacial adhesion between the two phases, the results were analyzed by using models featuring an adhesion parameter. Finally experimental results were compared with theoretical predictions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation,characterization and properties of Cr-incorporated DLC films on magnesium alloy

Cr-incorporated diamond-like carbon (Cr-DLC) films were deposited on AZ31 magnesium alloy as protective coatings by a hybrid beams deposition system, which consists of a DC magnetron sputtering of Cr target (99.99%) and a linear ion source (LIS) supplied with CH₄ precursor gas. The Cr concentration (from 2.34 to 31.5 at.%) in the films was controlled by varying the flow ratio of Ar/CH₄. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the microstructure and composition of Cr-DLC films systematically. An electrochemical system and a ball-on-disk tribotester were applied to test the corrosion and tribological properties of the film on the AZ31 substrate, respectively. At low Cr doping (2.34 at.%), the film mainly exhibited the feature of amorphous carbon, while at high doping (31.5 at.%), chromium carbide crystalline phase occurred in the amorphous carbon matrix of the film. In this study, all the prepared Cr-DLC films showed higher adhesion to AZ31 than the DLC film. Especially for the film with low Cr doping (2.34 at.%), it owned the lowest internal stress and the highest adhesion to substrate among all the films. Furthermore, this film could also improve the wear resistance of magnesium alloy effectively. But, none of the films could improve the corrosion resistance of the magnesium alloy in 3.5 wt.% NaCl solution due to the existence of through-thickness defects in the films.