Ceramic TiC/a:C protective nanocomposite coatings: Structure and composition versus mechanical properties and tribology

The relationship between the structure, elemental composition, mechanical and tribological properties of TiC/amorphous carbon (TiC/a:C) nanocomposite thin films was investigated. TiC/a:C thin film of different compositions were sputtered by DC magnetron sputtering at room temperature. In order to prepare the thin films with various morphology only the sputtering power of Ti source was modified besides constant power of C source. The elemental composition of the deposited films and structural investigations confirmed the inverse changes of the a:C and titanium carbide (TiC) phases. The thickness of the amorphous carbon matrix decreased from 10 nm to 1–2 nm simultaneously with the increasing Ti content from 6 at% to 47 at%. The highest hardness (H) of ~26 GPa and modulus of elasticity (E) of ~220 GPa with friction coefficient of 0.268 was observed in case of the film prepared at ~38 at% Ti content which consisted of 4–10 nm width TiC columns separated by 2–3 nm thin a:C layers. The H3/E2 ratio was ~0.4 GPa that predicts high resistance to plastic deformation of the TiC based nanocomposites beside excellent wear-resistant properties (H/E=0.12).     

Structural,mechanical and biological comparison of TiC and TiCN nanocomposites films

The vacuum deposition provides great flexibility for manipulating material's chemistry and structure. A combination of metallic (Ti) and carbon phase can enhance certain physical properties of nanocomposite thin films.In this work, the comparison of nanocomposite films composed of TiC or TiCN grains embedded in amorphous carbon matrix is reported. The films were prepared by dc magnetron sputtering at 200 °C in argon and nitrogen. In the case of argon deposition, 4–5 nm TiC grains in carbon matrix were observed. The nitrogen deposition combined with low content of Ti (～1.2 at%) proved to be insufficient for the development of larger crystals. The carbon had carbide character in TiC film, whereas in TiCN film all the carbon had graphite type environment. TiC film deposited in argon exhibited better mechanical properties than TiCN films deposited in nitrogen. In both cases, the good biocompatibility was observed after 7 days osteoblast cells seeding.     

Examination of nanocrystalline TiC/amorphous C deposited thin films

The relationship between structural, chemical and mechanical properties of nanocrystalline TiC/amorphous C (TiC/a:C) thin films was studied. Thin films were deposited by DC magnetron sputtering on oxidized silicon (Si/SiO₂) substrates in argon at 25 °C and 0.25 Pa. The input power of the carbon target was kept at constant value of 150 W while the input power of the titanium target was varied between 15 and 50 W.It was found that all thin films consist of a few nanosized columnar TiC crystallites embedded in carbon matrix. The average size of TiC crystallites and the thickness of the carbon matrix have been found to correlate with Ti content in the films. The mechanical properties of the films have been strictly dependent on their structure. The highest values of the nanohardness (∼66 GPa) and Young's modulus (∼401 GPa) were observed for the film with the highest TiC content which was prepared at the largest input power of Ti target.     

Sputtered nanocrystalline ceramic TiC/amorphous C thin films as potential materials for medical applications

The relationship between structural behaviour of sputtered TiC/amorphous C (TiC/a:C) thin films and corrosion properties was measured in three various pH solutions (0.5 M NaCl (pH=6); 0.1 M HCl (pH=1); and 0.1 M NaOH (pH=13)). The ~400 nm thick nanocomposites were deposited by DC magnetron sputtering on different substrates (Ti6Al4V alloy and CoCrMo alloy) in argon at 25 °C and 0.25 Pa with 150 W input power of carbon target and 50 W input power of titanium target. The structure and composition of nanocomposites were investigated by Transmission and Scanning Electron Microscopy. In both samples the structural investigations confirmed columnar structure of TiC/a:C films with 25–50 nm sized cubic TiC. These columns were separated by 2–3 nm thin amorphous carbon layers. TiC/a:C /Ti6Al4V alloy implant material showed better corrosion resistance than the TiC/a:C/CoCrMo alloy in 0.5 M NaCl solution based on results of the Electrochemical Impedance Spectroscopy. For both samples, the 0.1 M NaOH solution was the most corrosive media.     

Temperature influence on the interlayer and surface morphology of diamond coating on 3D porous titanium substrates

Nanocrystalline (NCD) and/or microcrystalline (MCD) diamond films grown on three-dimensional porous titanium (Ti) substrate were obtained by hot filament chemical vapor deposition (HFCVD) technique. The morphology variation of diamond films grown on porous three-dimensional titanium substrate was studied at four different deposition temperatures to investigate their influence on nucleation density. Scanning electron microscopy images depicted the continuous change from microcrystalline diamond grains with a random crystallographic orientation, at 500 °C and 600 °C, to a cauliflower-like structure for deposits at 700 °C and 800 °C. Visible Raman spectroscopy confirmed the good quality of diamond films and revealed that the amount of amorphous carbon increased associated to the film morphology changes from MCD to NCD. X-ray diffraction analyses, performed both through θ–2θ scans and at grazing incidence angle, allowed the investigation of the crystallographic properties and structural evolution of the different film/substrate interface phases, such as TiC(111), TiC(200) and TiH₂. The results revealed that the temperature enhanced the nucleation sites for diamond growth.     

Vapor deposition of stable copolymer thin films in a batch iCVD reactor

This study demonstrates the deposition of poly(ethylhexyl acrylate-co-ethylene glycol dimethacrylate) (P(EHA-co-EGDMA)) copolymer thin films in a batch type initiated chemical vapor deposition (iCVD) reactor. Crosslinked copolymers are desired for many applications because of their high stable properties. iCVD polymers derived by monomers bearing only one vinyl bond are usually linearly structured polymers and hence they are not durable, which is unfavorable for many real-world applications. Robust crosslinked iCVD films can be produced with the help of crosslinkers. In a typical iCVD process, copolymer thin film is produced by constantly feeding monomer vapor and crosslinker into the reactor. The monomer/crosslinker ratio should be precisely controlled for fabrication of reproducible thin films. In order to eliminate problems caused by adjusting the flowrates of precursors, a closed-batch type iCVD reactor was used for the first time in this study to produce copolymer thin films. The variation of precursors' partial pressures allowed control over the copolymer thin film structures. As compared with homopolymer, copolymers showed the better chemical and thermal stable properties. Almost 40% of the copolymer thin film remained on the substrate surface at an annealing temperature of 300°C, whereas the homopolymer film was completely removed at an annealing temperature of 280°C.     

Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy

ABSTRACT: Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films.PACS: 81; 81.05.Dz; 81.15.Hi.     

Pulsed-Laser Deposition of Barium Titanate Thin Films

Barium titanate (BaTiO₃) thin films have been deposited on single-crystal magnesia (MgO) substrates by pulsed-laser ablation. Temperature dependence of capacitance measurements show a peak of 110°C, indicative that a ferroelectric phase transition has occurred at this temperature. This value is lower than that determined for single-crystal BaTiO₃, but consistent with that found for BaTiO₃ thin films produced by other methods. It has been demonstrated that the microstructure of the films can be varied by changes in the deposition parameters. Optimizing these variations permits the formation of thin films with controlled microstructures and properties.     

Coating of DLC film by pulsed discharge plasma CVD

Diamond-like carbon (DLC) films were deposited onto Ti plate substrate by means of pulsed discharge (PD) plasma chemical vapor deposition (CVD) from gas mixture of methane and hydrogen, and their structures were investigated with transmission electron microscope (TEM). When the polarity of the substrate was negative, the DLC film was grown on the substrate. The transmission electron diffraction (TED) pattern of the deposited film, which was shaved with knife from the surface of the substrate, showed that both TiC and diamond structures were formed, showing that the DLC film can be coated with good adhesion by means of the formation of TiC interlayer. The coatings of DLC films onto a stainless steel plate and a drill of WC, on which Ti film were deposited previously, was also succeeded by the PD plasma CVD method with good adhesion.     

Electrostatic Spray Deposition of Doped Ceria Films

Dense and thin electrolyte films are desirable for solid oxide fuel cells (SOFCs) because of their low gas leakage and low ohmic resistances. This work aims at the preparation of thin dense Gd‐doped ceria (CGO) electrolyte films using a cost‐effective deposition method in ambient atmosphere–electrostatic spray deposition (ESD). The deposition parameters such as deposition temperature, concentration and flow rate of precursor solution were changed systematically to examine their effects on film morphology and hence electrochemical performance. While the film morphology was examined by a scanning electron microscope, the electrochemical performance was revealed by measuring open circuit voltages (OCVs) of NiO‐CGO/CGO/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ (BSCF) cells in 500–700 °C with humidified hydrogen as fuel and air as oxidant. The results show that a CGO film of 25 μm thick obtained at a deposition temperature of 400 °C, a precursor solution flow rate of 6 ml h^–1 and a precursor concentration of 0.3 M was dense with very few isolated pores and the OCV of the associated cell was 0.915 V at 500 °C. This implies that the CGO film has negligible gas leakage and ESD is a promising method for preparing thin dense electrolyte films for SOFCs.     

Aluminum Nitride Thin Films on an LTCC Substrate

Aluminum nitride thin films deposited on a low-temperature co-fired ceramics substrate by reactive magnetron sputtering were investigated with regard to their crystal orientation and microstructural characteristics. Strong c -axis orientations of AlN thin films were observed when either a higher deposition temperature or an RF bias was adopted. This orientation was believed to be responsible for the high thermal conductivity of 26 W/mK for the AlN films deposited at 700°C under 25-W bias. Photoluminescence spectrum in the wavelength range of 350–650 nm was analyzed to prove the involvement of potential oxygen-related defects in the thin films.     

Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y₂O₃ (Y_{1– x} Eu _x )₂O₃ thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y_{1– x} Eu _x )₂O₃ thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 10³ Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y₂O₃, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y_{1– x} Eu _x )₂O₃ was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.     

Improved biocompatibility of parylene‐C films prepared by chemical vapor deposition and the subsequent plasma treatment

The purpose of this study is to prepare the thin film of C‐type parylene (C‐type polyxylylene, parylene‐C) with improved biocompatibility for the biomedical applications, since in spite of the popularity, the parylene‐C has been known to have the less biocompatibility than the N‐type or D‐type parylene. To prepare the well‐designed parylene films through the chemical vapor deposition (CVD) process and the subsequent plasma surface treatment, the parameters of deposition and surface modification were controlled to obtain optimized physical and surface properties. Using CVD, the thin films of parylene‐C as thick as 5 μm were prepared under different deposition pressures. When increasing the deposition rate of parylene film or the deposition pressure, the tensile strength of film increased, whereas the properties such as the surface contact angle and permeability, and the elongation decreased. The deposition rate could be controlled to optimize the physical and physiochemical properties of films. The hydrophilicity of the parylene‐C film increased after plasma surface treatment by showing the larger water contact angle than untreated one. When the radio frequency power was above 100 W in the plasma process, the thin film obtained reveals an excellent cytotropism. It shows the improved biocompatibility with living cells. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pb-Diffusion Barrier Layers for PbTiO3 Thin Films Deposited on Si Substrates by Metal Organic Chemical Vapor Deposition

The interfaces between metal organic chemical vapor deposited PbTiO₃ thin films and various diffusion barrier layers deposited on Si substrates were investigated by transmission electron microscopy. Several diffusion barrier thin films such as polycrystalline TiO₂, amorphous TiO₂, ZrO₂, and TiN were deposited between the PbTiO₃ thin film and Si substrate, because the deposition of PbTiO₃ thin films on bare Si substrates produced Pb silicate layers at the interface irrespective of the deposition conditions. The TiO₂ films were converted to PbTiO₃ by their reaction with diffused Pb and O ions during PbTiO₃ deposition at a gubstrate temperature of 410°C. Further diffusion of Pb and O induces formation of a Pb silicate layer at the interface. ZrO₂ did not seem to react with Pb and O during PbTiO₃ deposition at the same temperature, but the Pb and O ions that diffused through the ZrO₂ layer formed a Pb silicate layer between the ZrO₂ and Si substrate. The TiN films did not seem to react with Pb and O ions during the deposition of PbTiO₃ at 410°C, but reacted with PbTiO₃ to form a lead-deficient pyrochlore during postdeposition rapid thermal annealing at 700°C. However, TiN could effectively block the diffusion of Pb and O ions into the Si substrate and the formation of Pb silicate at the interface.     

The structural and mechanical characterization of TiC and TiC/Ti thin films grown by DC magnetron sputtering

The formation of TiC and Ti phases and their influence on their mechanical properties was studied in this work. Thin layers were deposited by DC magnetron sputtering at room temperature in ultrahigh vacuum from Ti and C targets.Cubic TiC phase (c-TiC) was formed from 58 to 86?at.% Ti content. First formation of hexagonal Ti (h-Ti) occurred from 86?at.% Ti content. The c-TiC disappears from 90?at.% Ti content. Films with 86?at.% Ti content the c-TiC structure can transform to h-Ti by sequential stacking faults. Dominance of c-TiC(111) texture with increasing Ti content was observed.The hardness of thin films agree with structural observations. The highest hardness value (～26?GPa) showed the c-TiC thin film with 67?at% Ti content. The nanohardness values showed decreasing character with increasing Ti content over 70?at.%. The lowest values of nanohardness (～10?GPa) was observed for thin films with only h-Ti phase.     

Mechanical and tribological properties of diamond-like carbon films prepared on steel by ECR-CVD process

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10⁻¹⁷ m³/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.     

Temperature effect on bonding structures of amorphous carbon containing more than 30at.% silicon

Bonding evolution of amorphous carbon incorporated with Si or a-C(Si) in a thermal process has not been studied. Unhydrogenated a-C(Si) films were deposited by magnetron sputtering to undergo two different thermal processes: i) sputter deposition at substrate temperatures from 100 to 500 °C; ii) room temperature deposition followed by annealing at 200 to 1000 °C. The hardness of the films deposited at high temperature exhibits a monotonic decrease whereas the films deposited at room temperature maintained their hardness until 600 °C. X-ray photoelectron spectroscopy and Raman spectroscopy were used to analyze the composition and bonding structures. It was established that the change in the mechanical property is closely related to the atomic bonding structures, their relative fractions and the evolution (conversion from C–C sp³ → CC sp² or CC sp² → C–Si sp³) as well as clustering of sp² structures.     

Deposition of Pb(Zr,Ti)O3 Thin Films by Metal-Organic Chemical Vapor Deposition Using β-diketonate Precursors at Low Temperatures

Lead zirconate titanate (PZT) thin films were deposited by metal-organic chemical vapor deposition (MOCVD) using β-diketonate precursors and 0₂ at temperatures below 500°C on variously passivated Si substrates. PZT thin films could not be deposited on bare Si substrates, owing to a serious diffusion of Pb into the Si substrate during deposition. Pt/SiO₂/Si substrates could partially block the diffusion of Pb, but a direct deposition of PZT thin films on the Pt/SiO₂/Si substrates resulted in a very inhomogeneous deposition. A TiO₂ buffer layer deposited on Pt/SiO₂/Si substrates could partially suppress the diffusion of Pb and produce homogeneous thin films. However, the crystallinity of PZT thin films deposited on the TiO₂-buffered Pt/SiO₂/Si substrate was not good enough, and the films showed random growth direction. PZT thin films deposited on the PbTiO₃-buffered Pt/SiO₂/Si substrates had good crystallinity and a- and c-axis oriented growth direction. However, the PZT thin film deposited at 350°C showed fine amorphous phases at the grain boundaries, owing to the low chemical reactivities of the constituent elements at that temperature, but they could be crystallized by rapid thermal anneaiing (RTA) at 700°C. PZT thin film deposited on a 1000-å PbTiO₃,-thin-film-buffered Pt/SiO₂/Si substrate at 350°C and rapid thermally annealed at 700°C for 6 min showed a single-phase perovskite structure with a composition near the morphotropic boundary composition.     

碳纤维增强碳复合材料表面多层复合涂层中SiC和TiC内层的比较(英文)

采用包埋法制备了碳纤维增强碳(carbon fiber reinforced carb on composites,C/C)复合材料表面多层涂层,包括SiC,TiC内层,SiC,TiC中间层以及SiC+TiC复合外层。利用场发射扫描电镜和X射线衍射对其表面和断面的结构进行研究。结果显示:和TiC内层相比较,SiC内层较厚而且致密,具多孔结构且和C/C复合材料结合紧密;TiC内层较薄且和C/C复合材料结合松散。制备的SiC+TiC复合外层由SiC,TiC和Ti3SiC2组成。     

氮化硅薄膜生长随时间演化过程及其特性研究

氮化硅SiN_x薄膜凭借介电常数高和稳定性好的特点而被广泛应用于光电器件中,但薄膜的厚度对器件的性能有重要影响。针对此问题采用等离子体化学气相沉积技术,以高纯NH₃、N₂和SiH₄为反应气体,优化其他沉积参数,通过改变沉积时间来生长SiN_x薄膜。用X射线衍射谱(XRD),紫外-可见光光谱(UV-VIS)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对薄膜结构进行表征,详细研究了沉积时间与薄膜厚度的关系以及沉积时间对薄膜性能的影响。试验结果表明:所制备的样品为非晶SiN_x薄膜结构,薄膜厚度随沉积时间均匀增加;薄膜折射率随沉积时间的增加而增大,光学带隙基本不随时间变化。SEM测试结果表明,随着沉积时间增加,薄膜致密性与均匀性越来越好,氧含量也越来越少,说明薄膜致密性提高可以有效阻挡O原子进入薄膜,阻止后氧化现象的发生。