Polymers are widely used as coating on substrates

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The deposition on substrate or on any metallic part is usually applied to improve surface resistance against friction, fatigue, wear, and corrosion.

Polymers are widely used as coating on substrates because of their use in number of applications, protection against weather conditions, localized corrosion (barrier) by preventing the contact between oil and metallic surface, low friction coefficient, etc. The low friction coefficient of polymers permits their use between two sliding hard surfaces, resulting in cost reduction and contributing to the decrease of environmental impacts from the production of solid residues. [Ref]

The polymer must be selected for its abrasion resistance, friction performance, hardness and adhesion to the substrate. Furthermore, it is important to assess its melting point and structure, which influence the polymer degradation rate and the thin film mechanical properties. Examples of polymers such as polyurethane (excellent abrasion resistance) and epoxidic resins (good hardness), although the use of thermoplastics (PTFE, PE, PP, nylon, ABS, etc) can be inexpensively striking.

Major polymer restrictions include low scratch resistance, poor adhesion to metallic substrates and high gas permeability. The drawbacks of using polymers as coatings have been dealt with by using blends and tailored polymers, high performance polymers() and composites().

The good mechanical, thermal, and chemical stability of polytetrafluoroethylene (PTFF) in connection with its low surface adhesion, frictional resistance, and low dielectric constant, makes this material exceptional for many real and potential applications in mechanics, microelectronics, chemistry, medicine, and bioscience. For certain applications, it is advantageous to formulate PTFE in the form of thin films.

Coatings have been developed by using different techniques, but in this experiment Ni- PTFE (polytetrafluoroethylene) composite films on Silicon and Glass substrates by using Pulsed DC Glow Discharge is carried out. Some of the related research work is given below.

Katharria et al. [1] investigated the systematic studies of thin silicon carbide (SiC) films deposited on Si (100) substrates using pulsed laser deposition technique at room temperature, 370oC and 480oC. X-ray photoelectron spectroscopy showed the formation of SiC bonds in the films at these temperatures along with some graphitic carbon clusters. Fourier transform infrared analysis also confirmed the formation of SiC nanocrystallites in the films. The structural properties of nanocrystallites formed in the films were studied by using electron diffraction and Transmision electron microscopy. Surface morphological analysis using atomic force microscopy revealed the growth of smooth films.

Inoue et al. [2] studied the deposition of crystalline thin films of CdTe-doped PTFE (polytetrafluoroethylene) on silicon (100)/glass substrate by F2 laser (157 nm) ablation in 200 mTorr Ar gas atmosphere. Combining this PTFE thin film process with CdTe microcrystallites synthesis in sizes of 3-7 nm via KrF laser (248 nm) ablation, CdTe microcrystallites-doped PTFE thin films were fabricated. The X-Ray photoemission spectra (XPS) showed that the main architecture of PTFE and CdTe were maintained in the doped films. CdTe microcrystallite doped in PTFE matrix showed an absorption edge shift toward higher energy and a third-order opitical nonlinerity, which were induced by the quantum size effect.

Yamasaki et al. [3] investigated the nickel coating with large surface area formed by a hydrothermal deposition on Teflon (PTFE) substrate. The hydrothermal reduction from nickel sulphate and ammonia solution at 150o C resulted in the formation of uniform nickel layer (20-30 µm) on Teflon surface. Ni-coated Teflon samples were characterized using X-ray diffraction and scanning electron microscopy (SEM). It was found that nickel was homogeneously distributed on Teflon surface.

Deposition of Nickel on Si/Glass:

Deposition of Ni on Glass:

Popovic et al. [4] investigated the deposition of nickel thin film on glass substrate at different N2 gas content using a dc triode sputtering deposition system. Result showed that the deposited film on a substrate at 100oC without N2 in the chamber exhibit a highly preferred (1 1 1) orientation. For nickel films deposited at 9% nitrogen, the preferred orientation changed from(111) to (200), while the deposition at the highest nitrogen content of 23% affected the composition of deposited films by the formation of new, Ni3N phase. Also the electrical resistivity increased with both the content N2 and the substrate temperature. The AFM images showed a grained structure with average particle size of 60 nm, 37 nm and 65 nm, for the deposition of 0%, 9% and 23% N2 in the chamber, respectively. The nickel thin film roughness increased with the increasing nitrogen content. The magnetic force microscopy imaging showed that the local magnetic structure changed from disordered stripe domain of about 200 nm for Ni and Ni (N) to a structure without a magnetic contrast indicating the paramagnetic state of this material, which confirmed the structural transformation from Ni to Ni3N.

Popovic et al. [5] investigated the influence of nitrogen ion bombardment during e-beam triode ion plating of nickel on the microstructure and film orientation. The deposition variables explored were the ion current density and deposition rate while keeping the substrate temperature (ambient), partial pressure of nitrogen (3*10-4 Torr) and substrate bias potential (4.5 KV) were constant. The orientation and growth morphology for films about 1µm thick were determined by, XRD, SEM and STM techniques. The preferred orientation changed from (111) to nearly complete (200) as a function of ion to atom arrival ratio (IAR), and was independent of substrate type (amorphous or monocrystaline). The ion beam bombardment of films after deposition enables the in depth determination of the nickel texture change during growth. For the highest IAR value the complete (200) texture was achieved at the beginning of deposition. The surface morphology (STM) and preferred orientation changes were correlated with ion to atom flux ratio and discussed on the basis of lowering the overall energy of the film.

Lu et al. [6] deposited thin films of nickel oxide (NiO) on glass substrates by RF magnetron sputtering. They discussed the relationship between substrate temperature and resistivity and the microstructural defects of the NiO films. Crystalline NiO film with (111) orientation was obtained in this study. A resistivity of 0.22 Ωcm and a hole concentration of 4.4*10 19 cm-3 were obtained for non-doped NiO films prepared at a substrate temperature of 300 0C in pure oxygen sputtering gas. As the substrate temperature was increased from 300 to 400 0C, the resistivity changed from 0.22 to 0.70 Ω cm. The mechanism of electrical conductivity for the NiO films is discussed from the viewpoint of defect chemistry and was confirmed by X-ray photoelectron (XPS) and energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) data.

Deposition of Nickel on Silicon:

Hotovy et al. [7] studied the deposition of NiO films on silicon substrate by DC reactive magnetron sputtering using a metallic nickel target at different oxygen contents for gas mixture of Ar + O2 ( from 15 to 50%). They observed that by in creasing the oxygen content reduces the deposition rate (from 27 to 17nm/min), changes the amount of oxygen in the film (from 48.9 to 57.8%) and produce a change from amorphous to polycrystalline NiO. They found that good NiO stoichiometric films are obtainable with a polycrystalline (FCC) structure and a resistivity of near 300Ωcm at 25% oxygen content.

Lim et al. [8] investigated the reactivity and morphology of thin sputtered nickel films deposited on SiC in the temperature range 550-1450 °C. The reaction with the formation of silicides and carbon was first observed above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted in to Ni2 Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to1050 °C the relatively higher critical load values of 20-33 N for SiC/Ni couples are formed.

Schmidt et al. [9] deposited nickel manganate thin films of ~700 nm thickness on [100] silicon substrates using RF magnetron sputtering in an argon atmosphere from optimised targets. Targets were sintered at different temperatures and SEM analysis revealed superior surface density for sintering temperatures of at least 1200 0C. The average grain size increased with sintering temperature and fitted a Rayleigh function. For film growth a substrate temperature of 200 0C proved to be optimal. The effect of subsequent annealing in air from 650 0C to 900 0C in steps of 50 0C on the microstructure was investigated. X-ray diffraction studies showed that the films re-crystallized from an amorphous- like structure to a cubic spinel phase. A preferred orientation of the film in the [10 0] out-of plane crystal direction was strongly pronounced in a temperature window around 200 0C substrate temperature. Films were studied by AFM and showed distinct crystallographic grains (sized ~50 nm) after annealing. The lattice constant of thin films was lower than for the bulk target material, but was not correlated with annealing temperature.

Qin et al. [10] reported nickel induced lateral crystallization (NILC) of amorphous silicon at various temperatures in detail. The crystallized film was characterized by micro Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Large leaf-like grains with a length on the order of 10-20 µm and a width on the order of 1-5 µm have been observed by NILC and subsequent heat treatment at 1000 0C. AFM measurements showed that the crystallized film was combined by 'smooth' and 'rough' regions. Further TEM images revealed that the 'smooth' region has larger size and fewer defects, which may be a single grain with preferential (110) orientation. For the 'rough' region, many defects, dislocations and mismatches are found in it. It seems to be mixed by randomly oriented smaller grains. Further high temperature annealing can reduce the defects at the grain boundary and enlarge the grains. It was found that the NILC rate depends strongly on the annealing temperature. A maximum rate occurs at approximately 625 0C, the influences of other factors such as Ni pattern, amount of Ni, annealing time, etc., on the NILC rate were also investigated.

Yoshimura et al. [11] investigated initial stages of Ni reaction on both Si (100) and H-terminated Si (100)-(2 Ã- 1) surfaces by STM. STM images revealed that Ni atoms react with Si atoms on clean surface at the RT and induced disordered sites. While on the other hand, deposited Ni atoms on H-terminated surface did not react with silicon atoms and formed clusters. In the latter case, they found the new adsorption site of Ni atom that stuck in dimerised Si atoms, causing the dimer splitting into both sides. It was also found that, after annealing in the case of the deposition on the clean surface, Si surface surrounding NiSi2 Island had a disordered structure, while the surface with the H-termination showed a homogeneous (2 Ã- n) structure.

Deposition of PTFE on Silicon/Glass:

Deposition of PTFE on Silicon:

Li et al. [12] prepared thin films of crystalline polytetrafluoroethylene (PTFE) on silicon substrate by pulsed-laser deposition using 248 nm UV-excimer-laser radiations. Pressed powder pellets and bulk PTFE were employed as target material. The films were analyzed by means of optical polarization microscopy, stylus profilometry, capacity measurements, XRD and IR spectroscopy. The effect of substrate temperature Ts on the morphology and crystallinity of the films was studied. Films deposited from pressed powder targets at sufficiently high Ts consist mainly of spherulite-like microcrystallites. These films were continuous, pinhole-free, well adherent to the substrate, and have a composition which was similar to that of the target material. It is suggested that film formation is based on laser-assisted material transfer with subsequent melting and crystallization. They were superior to films deposited from PTFF bulk targets, cut from a solid rod, with respect to film morphology, deposition rate, film cohesion, and optical and electrical properties.

Bodas et al. [13] studied the influence of PTFE films deposited on silicon substrate by RF sputtering. FTIR and XPS studies of the deposited and etched film showed that stoichiometric PTFE gets deposited. They showed that the PTFE stayed on the silicon even after etching in 20 wt% KOH solutions at 80 °C temperature for 60 min exposure. Also the contact angle measurement and the interfacial tension was calculated which gave the value of 0.7 dyne cm ‾¹ which confirmed good adhesion of the film and the substrate. An etch rate of 4 A° minˉ¹ was calculated from the masking time data of the films, and the diaphragm etched in silicon proved the better masking characteristics of PTFE. They demonstrated that PTFE could be a good substitute for the conventional masking material, namely SiOâ‚‚ and Si₃Nâ‚„.

Bodas et al. [14] studied the characteristics of the PTFE polymer thin films deposited on mirror polished silicon (100) substrate by RF plasma sputtering in the presence of argon plasma at three different plasma powers of 100, 150 and 200 Watt where as the treatment time was kept constant at 60 min. The structural integrity of the film was assessed by FTIR, XPS and adhesion by contact angle. It was brought into being that sputtering of PTFE target produce thin films with structure quite similar to PTFE target. The FTIR results showed that PTFE film get deposited on the silicon substrate. The XPS results showed the presence of CF₃, CFâ‚‚ groups, etc. indicating the presence of PTFE at higher plasma power. The contact angle measurement showed the lower contact angle value of 50° with water and 44° with diiodomithane, which showed ultra hydrophilicity of the PTFE film, and a lower interfacial tension value of 0.76 dyne/cm indicated good adhesion of the film and substrate. The surface characteristics of the PTFE film showed that at higher plasma levels, stoichiometric PTFE film gets deposited.

Machetta et al. [15] deposited PTFE films on silicon substrate and investigated the electrical and structural properties of PTFE thin films obtained from Algoflons-PTFE nanoemulsions, via spin coating deposition, followed by sintering. Films as thin as 160nm with dielectric strength better than 4MV/cm have been obtained. Breakdown mechanism was also discussed.

Katoh et al. [16] deposited thin films of Teflon-polymers such as PTFE (polytetrafluoroethylene), FEP (polytetrafluoroethylene-co-hexafluoro-pro-pylene) and PFA (polytetrafluoroethylene-co-perluoroalkoxy vinyl ether) on Si (100) substrates by syn- chrotron radiation (the critical wavelength of 1.5 nm) etching of their corresponding starting materials in vacuo. Analysis of the deposited films carried out with X-ray photoelectron spectroscopy (XPS), Fourier transfer infrared (FTIR) spectroscopy as well as X-ray diffraction (XRD) and their surface morphologies were observed under scanning electron microscopy (SEM). For the deposition of the Teflon-polymer films, the processing with the synchrotron radiation photo-etching was compared with that using laser ablation and significant differences between them were discussed.

Deposition of PTFE on Glass:

Stelmashuk et al. [17] studied the fluorocarbon plasma polymer films prepared by magnetron sputtering of PTFE possessed properties that depend on the argon gas pressure. They observed that their wettability decreased with the increase in pressure of argon working gas. The films deposited at 70 Pa were found to be superhydrophobic plasma polymers with a static contact angle 146o for water. Sputtered fluorocarbon plasma polymer films had been characterized by atomic microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy. The paper showed that the surface composition and chemical structure of the films vary with altering the argon gas pressure.

Miller et al. [18] investigated the influence of film roughness on wetting properties of vacuum-deposited polytetrafluroethylene (PTFE) by using Atomic Force Microscopy (AFM) and contact angle goniometery. It has been concluded that nanometer size surface roughness strongly influenced the wetting behavior of water at the surface of PTFE thin film. AFM specially recommended the analysis of such polymer surfaces with nanometer size irregularities. It was found that variation in surface roughness influences the wetting characteristics of the PTFE thin films even at low surface roughness values (Rq ≈ 80 nm). The substrate roughness as characterized by fractal analysis (fractal dimension = 2.2) was found to increase the water contact angle significantly, thereby decreasing the wettability of PTFE thin film. The preparation/production of surfaces with specifically designed surface roughness features should be useful in the development of more efficient water repulsive materials.

Smausz et al. [19] prepared the Polytetrafluoroethylene (PTFE) thin films from pressed powder pellets via pulsed laser deposition by using ArF (193 nm) excimer laser. The applied laser fluences were ranged from 1.6 to 10 Jcm-2 and the substrate temperature was varied between 27 0C and 250oC and post-annealing of the films was carried out in air at temperatures between 320oC and 500oC. Films deposited at 250oC substrate temperature were found to be stoichiometric while those prepared at lower temperatures were fluorine deficient. Morphological analyses proved that the film thickness did not significantly depend on the substrate temperature and post annealing at 500oC resulted in a thickness reduction of approximately 50%. It was demonstrated that the films prepared at 8. Jcm-2fluence and annealed at 500oC followed by cooling at 1oC min-1 rate were compact, pinhole -free layers. The adherence of films to the substrates was determined by tensile strength measurement. Tensile strength values up to 2.4 MPa were obtained. These properties are of great significance when PTFE films were fabricated for the purpose of protecting coatings.

Guo et al. [20] studied the rapid formation of PTFE-like polymer nanocrystals achieved by a novel synthesis method-oriented plasma polymerization (OPP) at atmospheric pressure. The entire process was completed within a short period of time ranging between a few seconds to several minutes through dielectric barrier discharge (DBD) at atmospheric pressure. The surface morphology of the coated organic crystal film was observed through scanning electronic microscope (SEM) and different morphology nanocrystals were found such as nanorods and nanotubes. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the single-crystalline phase of these nanocrystals. The sizes of the nanosingle crystals were from 10 nm to 1 mm. The effects of discharge conditions such as discharge time, ratio of the monomer to carrier gas and power on the nanocrystalline morphology and crystallinity were investigated. As a result, the physical morphology and structures could be controlled through the conditions of the oriented plasma polymerization to some extent. This novel polymerization method opened a new way to nanofabricate polymeric crystallines fast and effectively.


Many workers co-deposited PTFE (polytetrafluoroethylene) and nickel on silicon and glass substrate by using different techniques, such as laser deposition, RF magnetron sputtering, Ion beam sputtering, Plasma polymerization etc. because of their excellent surface properties the use of metal-polymer composites aims to achieve a combination of physical and mechanical properties better than those of a single material, being possible to achieve good barrier and mechanical properties. The previous work of researchers by using above mentioned techniques is given as under:

Lekka et al. [21] studied the method of composite electroplating by allowing co-depositing fine particles of metallic or non metallic compounds into the plated layers in order to improve the surface properties. The aim of this work was to compare the performance of pure nickel and Ni-SiC nano-structured composite coatings as far as corrosion, wear and abrasion resistance were concerned. The characteristics of the coatings were assessed by scanning electron microscopy, micro hardness test, Taber Abrader test, electrochemical impedance spectroscopy and wear corrosion measurements. Additionally accelerated salt spray tests were performed. The results obtained in this study indicated that the co-deposition of nickel and SiC nano-particles led to uniform deposits possessing better abrasion, wear and corrosion properties.

Huang et al. [22] studied the influence of EN (electroless nickel) and EN composite coatings with PTFE and/ or SiC particles were deposited on mild steel substrate by chemical deposition. They conducted the comparison of the properties of EN, EN-SiC, EN-PTFE and EN-SiC-PTFE composite coatings. Results showed that the as-deposited coatings had an amorphous NiP structure incorporated with uniformly distributed PTFE or SiC particles. At 340 °C phase transition from the amorphous NiP to a mixed structure of crystalline Ni and Ni3P alloy was observed. A substantial increase in coating hardness was observed as a result of annealing at 400 °C. The EN-SiC coating showed the highest hardness (¾1365 HV) while the EN-PTFE showed the lowest friction coefficient (¾0.48). The EN-PTFE-SiC showed a moderate hardness and friction coefficient in between, depending on the percentage of the particles included in the coating. The EN-PTFE-SiC composite coating demonstrated a combination of the advantages of the EN-SiC in high hardness and load-bearing capacity and of the EN-PTFE coating in low friction coefficient, low surface energy and high wear resistance. Under the experimental conditions, a sliding wear rate against an alumina pin of approximately 3.6X10-7 mm³ N-1 m-1 was measured for EN-PTFE and EN-PTFE-SiC, which was about a seventh of that recorded for the EN coating. SEM and XRD techniques were employed for the microstructure analysis. For the study of the phase transition of the coating during the heat treatment DSC technique was employed. Hardness indentation, scratch test and pin-on-disc wear test were employed to measure the mechanical and tribological properties. By using water droplet surface contact angle measurement the surface energy was analyzed. The synergistic effects of SiC and PTFE on the wear and anti-sticking properties of the coatings were also discussed.

Liu et al. [23] studied the characteristics of co-deposited PTFE and titanium films on the stainless steel substrate by unbalanced magnetron sputtering technique with the purpose of improving the tribological performance of the substrate and awarded the surface with hydrophobicity. It has been investigated that during RF plasma-sputtering decomposition of PTFE resulted mainly in the growth of fluoropolymer species. The composition of the resulted fluoropolymer films depend on the incident power, high incident power resulted in low F/C ratio in the films and low incident power resulted in high F/C ratio in films. The tribological performance of the coatings depends on the tetrafluoroethylene content in the film bulk and on the film growth process. The films with low tetrafluoroethylene content exhibited dense structure and good wear resistance; on the other hand, such films exhibited a high frictional coefficient. At initial stages of test high tetrafluoroethylene content films with gradient multilayer coatings possessed good tribological performance. During the co-deposition process, the segments were inlaid into the titanium matrix and became strongly mechanically bonded. It has been contemplated that some of the carbon atoms might react with titanium to form titanium carbide in the coatings. Multilayer structure attributed to the decrease in the stress developed between layers. All these factors attributed to the improvement of the tribological performance of the stainless steel substrate.

Pilloud et al. [24] observed the Zr-Si-N films deposited on silicon and steel substrates by DC magnetron sputtering of a Zr-Si composite target in Ar-N2 reactive mixture, with different Si contents. The structural integrity of the films was assessed by FTIR, XPS and XRD. Hardness test have also been carried out. For low Si content, no Si-N bond was detected by FTIR, as Si atoms were inserted in the ZrN lattice, which was confirmed by a strong increase of the compressive stress. For intermediate Si contents, nanocomposite structure (ne-ZrNya-SiNx) was synthesized, where ZrN was detected by XRD and Si-N bonds evidenced by XPS and FTIR. Amorphous films were deposited for silicon content higher than 6 at. %. The film hardness was decreased with increasing silicon content, as a function of the films structure and compressive stress level. Linear relationships were found between hardness and the Young's modulus values.

Lopes et al. [25] studied the low temperature Ti-Si-C films deposited onto silicon and polished stainless steel and high-speed steel substrates by DC magnetron co-sputtered from two Ti targets, one with C pellets and the other with Si pellets. The composition of the films was investigated by Electron Probe Micro-Analysis (EPMA), and structure was characterized by XRD. Where as the hardness and residual stress were studied using depth -sensing indentation and substrate deflection measurement (using Stoney's equation), respectively. Plots of both C/Ti and Si/Ti atomic ratios as a function of the targets current ratio showed the existence of two distinct regions: (i) a silicon rich zone, and (ii) a carbon rich zone. In all scanned properties these two composition regions were found to be of particular influence. In the prepared films Structural analysis revealed the possibility of the coexistence of different phases, namely a sub-sotichiometric fcc NaCl-type TiC structure and a Ti metallic phase (α-Ti or β-Ti). Carbone rich zone exhibited mainly a sub-stoichiometric fcc NaCl TiC-type structure and the films within the silicon rich zone showed a progressive tendency for amorphization. The existence of some C or even Si(C) amorphous tissue could not be excluded. Relatively low values the residual stress states (σr) and the hardness (H) have been observed, which could be as a result of low crystallinity order exhibited by the coatings and/or due to the high amounts of Ti in the coatings.

Wang et al. [26] investigated the Nickel/ultra-dispersed PTFE composite films with various PTFE content which were electrochemically prepared from a Watt's nickel plating bath in which the PTFE particles (mean diameter 0.3 mm) were suspended using a cationic fluorocarbon surfactant. The microstructures of Ni-PTFE composite films were analyzed by means of XRD, SEM and TEM, and their water-repellencies were also measured. The results indicated that the PTFE particles took a homogeneous distribution within all the composite films. The PTFE particle content in the composite films was dependent upon the particle concentration in the plating bath and the plating parameters, and strongly influenced the physical properties of Ni-PTFE composite films such as water-repellency. The contact angle of a water drop on the surface of composite film with maximum PTFE content of about 47.4 vol% reaches 154.9_, showing a superior water-repellency.

Schurmann et al. [27] prepared the polymer-metal nanocomposite films by co-sputtering from two independent magnetron sources. Both gradient films with increasing metal fraction and homogeneous composite films were produced from polytetrafluoroethylene (PTFE) and silver targets using a rotatable sample holder. The structure of the pure sputtered polymer as well as the composite structure was studied. Electrical properties of the composite material near the percolation threshold show the expected, sharp change in the resistivity from 10 7Ω cm at small silver content to 10-3 Ω cm after percolation. The optical absorption in the visible region due to surface plasmon resonances also has a strong dependence on the metal content, showing a red shift of the absorption peak from 405 nm to more than 500 nm at higher silver content.

Eftekhari et al. [28] synthesized LiMn2O4 electrode based on mixed-metals (gold-titanium) codeposition method. By this method, titanium oxideis also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO2 can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn2O4 spinel can be improved by the surface modification with TiO2. This action improved cyclability for lithium battery performance and reduces capacity fades of LiMn2O4 at elevated temperatures.

Berlinder al. [29] deposited Silicon-carbon-nitride (Si-C-N) thin films by reactive magnetron co-sputtering of C and Si targets in a mixed Ar/N2 discharge. Films were grown to a thickness of more than 0.5 µm on graphite and Si (001) substrates held at a negative floating potential of ~-35 V, and substrate temperature between 100 and 700oC. The total pressure was constant at 0.4 Pa (3 mtorr), and the nitrogen fraction in the gas mixture was varied between 0 and 100%. As-deposited films were analyzed with respect to composition, state of chemical bonding, microstructure, mechanical properties, and wetting behavior by Rutherford backscattering spectroscopy (RBS), energy dispersive spectroscopy (EDS), X-ray photoelectron spectrometry (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoindentation and contact angle measurements, respectively. Depending on the deposition condition, ternary SixCyNz films within the composition range 1≤ x≤ 34 at. %, 34≤ y ≤81 at. %, and 16.5 ≤ z ≤ 42 at. % were prepared with a textured, amorphous-to-graphite-like microstructure. For Si-C-N films with low Si content, C-C, C-N and Si-C bonds were present. At higher Si content, N preferentially bonds to Si, while less C-N bonds were observed. Films containing more than ~12 at. % of Si contained widely dispersed crystallites, 2-20 nm in diameter. Incorporation of a few at. % Si resulted in a dramatic reduction of the film surface energy compared to pure CN films. The measured contact angles using distilled water and glycerol liquids were for some films comparable with those on a polytetrafluoroethylene (PTFE), Teflon* surface. The hardness of Si-C-N films could be varied over the range 9-28 GPa.

Zaporojtchenko et al. [30] prepared a method for producing antibacterial metal/polymer nanocomposite coatings by using co-sputtering of noble metals together with polytetrafluorethylene (PTFE), where the precious metals were only incorporated in a thin surface layer. Moreover, they were finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m-2 and Ag: ~0.1 gm-2. The maximum ability for having an antibacterial effect was shown by the Ag-Au/PTFE nanocomposite, followed by the Ag/PTFE


Wang et al. [31] deposited composite films of TiO2-SiO2 on Si (100) wafers and glass (BK7) substrates by helicon plasma sputtering at room temperature. The results of X-ray diffraction and high resolution transmission electron microscopic observation showed that all of the composite films have an amorphous structure. The observation of scanning electron microscopy exhibited that the surfaces of all of the composite films have dense smooth morphology. The refractive index and the transmittance of the composite films varied gradually in the whole composition range of the TiO2-SiO2 binary system. TiO2-SiO2 composite films exhibited a transmittance of more than 90% compared with that of the glass (BK7) substrate. The relationship between refractive index and TiO2 content for the composite films can be described

by using the Lorentz-Lorenz model.

Zhao et al. [32] studied the effects of temperature, pH, substrate materials, cationic surfactant concentration and PTFE concentration in the plating solution on the deposition rate and the compositions of electroless Ni-Cu-P-PTFE coatings on the copper and stainless steel substrate. The coating thickness and compositions were measured using a digital micrometer and an energy dispersive X-ray spectroscopy (EDX) respectively. Scanning electron microscope (SEM) indicated that PTFE particles were uniformly distributed throughout the Ni-Cu-P matrix. The anticorrosion properties of the Ni-Cu-P-PTFE composite coatings in HCl and NaCl solutions were studied. The results showed that the corrosion resistance of the Ni-Cu-P-PTFE composite coatings was superior to that of Ni-P-PTFE composite coating or copper.

Ramesh et al. [33] prepared Nickel composite coatings on mild steel substrates by sediment electro-co-deposition (SECD) technique. Silicon nitride, fly ash and calcium fluoride were used as the reinforcements. Metallographic studies, microhardness, friction and wear tests under various loads and sliding speeds had been carried out on these coatings. Optical and scanning electron microscopy (SEM) studies on the worn surfaces were conducted. A theoretical model was used to predict the wear rates of the composite coatings. All the composite coatings exhibited a lower coefficient of friction and better wear resistance when compared with nickel coatings at all loads and sliding velocities studied. However, nickel-calcium fluoride composite coatings possessed the lowest coefficient of friction and wear rates. Significant effect of load and sliding speed on both the coefficient of friction and wear rates of nickel, nickel-silicon nitride and nickel-fly ash coatings has been observed. SEM studies of the worn surfaces reveal delamination process at higher loads. The predicted wear rates are in reasonable agreement with the experimental values.


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