SiC在异质衬底生长金刚石膜的作用分析

利用扫描电子显微镜 (SEM)、Raman光谱分析了Si衬底上金刚石膜核化和生长的过程 ,并着重分析了核化过程产生的SiC的性能。利用划痕法测量了在WC衬底上沉积SiC和未沉积SiC时生长金刚石膜的粘附力 ,同时还分析了WC衬底上有和没有SiC沉积层时表面附近金刚石膜的内应力。结果表明 ,SiC层大大地增强了含碳粒子的聚集和金刚石膜与衬底之间的粘附性 ,降低了金刚石膜与衬底之间的内应力     

微波等离子体刻蚀处理对金刚石薄膜涂层刀具附着力和切削性能的影响

用HFCVD法在硬质合金（YG6）刀具衬底上沉积金刚石薄膜,用氢微波等离子体刻蚀的方法对衬底进行表面预处理,研究了该预处理技术对WC硬质合金衬底表面成分的影响,进一步探讨了所沉积金刚石薄膜的表面形貌和附着力,并通过难加工材料实际切削试验。研究了所制备的金刚石薄膜涂层刀具的切削性能。试验结果表明,Ar-H2微波等离子体刻蚀脱碳处理是提高金刚石薄膜附着力和改善涂层刀具切削性能的有效预处理方法。     

火焰法在硬质合金上合成金刚石薄膜

用Ｏ２／Ｃ２Ｈ２燃烧火焰法在各种不同性质的衬底材料上直接合成金刚石薄膜，研究了硬质合金刀头的不同的冷却方式下，对合成金刚石膜的影响。结果表明：ＹＧ６硬质合金由于Ｃｏ的存在影响了金刚石膜的质量；当冷却方法不当时，硬质合金头刃部易过热；采和分段沉积法可改善金刚石膜与硬质合金的附着性。     

Elasto-plastic properties of gold thin films deposited onto polymeric substrates

This work examines mechanical properties of 50–300 nm gold thin films deposited onto micrometer-thick flexible polymer substrates by means of tensile testing of the film–substrate system and modeling. The film properties are extracted from mechanical testing of the film–substrate system and modeling of the bimaterial. Unlike materials in bulk geometry, the film elastic modulus and yield strength present an important dependence with film thickness, with modulus and yield strength of about 520 and 30 GPa, respectively, for the thinner films and decreasing toward the bulk value as the film thickness increases. The relation between grain size, film thickness, and yield strength is examined. Finite element analysis provides further insight into the stress distribution in the film–substrate system. L. Llanes—MS student at ITM, Merida, Mexico.     

Growth of diamond films on SiC, WC and cubic BN substrates

The growth morphology of diamond films grown on single crystals of SiC and on sintered WC and cubic BN (CBN) substrates by hot filament assisted chemical vapour deposition was examined using transmission electron microscopy and scanning electron microscopy. Diamond was found to have the form of particles on the substrates of SiC and WC in the initial stage of film growth. Both an amorphous layer and a directly bonded area were seen at the interface. Several orientation relationships, different from the cube/cube relation, were observed in these systems. On the other hand, in the case of diamond films on CBN substrates, the growth morphology of diamond was affected by the surface condition of the substrates. When CBN substrates were polished with a diamond paste before deposition, diamond grew in the form of particles. The growth morphology was changed by ion sputtering of the surface of the substrate from particle growth to uniform film growth. These results are discussed on the basis of lattice mismatch at the interface. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of Ti- and Zr-based interlayer coatings on the hot filament chemical vapour deposition of diamond on high speed steel

The prospect of obtaining good adhesion of diamond films onto steel substrates is highly exciting because the achievement of this objective will open up applications in the cutting and drilling industry. However, a major problem with depositing diamond onto steel is high diffusion of carbon into steel at chemical vapour deposition (CVD) temperatures leading to very low nucleation density and cementite (Fe₃C) formation. Therefore, the study of the nucleation and growth processes is timely and will yield data that can be utilised to get a better understanding of how adhesion can be improved. This work focuses on investigating the adhesion of thin diamond films on high speed steel previously coated with various interlayers such as ZrN, ZrC, TiC and TiC/Ti(C,N)/TiN. The role of seeding on nucleation density and the effect of diamond film thickness on stress development and adhesion has been investigated using SEM, XRD and Raman spectroscopy.The main emphasis in this study is the TiC interlayer which for the first time proved to be a suitable layer for diamond CVD on high speed steel (HSS). In contrast from other interlayer materials investigated here, no delamination was observed even after 3 h of CVD at 650 °C only when TiC was employed. Nevertheless, the increase of diamond film thickness on TiC coated HSS substrates led to the delamination of small areas in various regions of the substrate. This occurrence suggests that there was a distribution of adhesive toughness values at the diamond/TiC interface with stress development being dependent on film thickness.     

The effects of film thickness variations on the residual stress distributions in coated Cr thin films

Generally, the residual stress of thin film coatings is calculated using Stoney's equation. However, variables in the manufacturing of the coated film, such as crystalline particle size and the unevenness of the thickness of the film, cause the radius of curvature of the beam to vary all over the beam. The cantilever beam curves not only in the axial direction but also in the transverse direction. Therefore, the residual stress in a film coating comprises not only axial residual stress but also transverse residual stress, and its distribution is also not uniform. Under such conditions, Stoney's equation must be modified. In this study, Si was used as a substrate in the production of cantilever beam specimens. Chromium thin films of various thicknesses were coated onto the Si substrates. The 3D digital image correlation technique was used to measure the out‐of‐plane displacement of the specimens at various positions. Then the modified Stoney's equation was used to obtain the axial and transverse residual stress at each measurement point to study the effect of variations in the thickness of the thin film on the magnitude and uniformity of the distribution of the residual stresses. Three thin film thicknesses 1, 2, and 3 μm were studied, and three specimens for each thickness were used. For each specimen, axial and transverse residual stresses were obtained at nine test points, and the equivalent residual stress was calculated. The results of this study reveal that as the difference between the thicknesses of the coating increased, average equivalent residual stress decreased and the distribution of stresses became more uniform. By comparing the corresponding results for the 1‐ and 3‐μm‐thick films revealed that the confidence levels in the average value and uniformity of the equivalent residual stress distribution, which increased with thickness, were 92.81% and 80.57%, respectively.     

Diamond deposition on copper: studies on nucleation, growth, and adhesion behaviours

This paper presents a systematic study on diamond growth on copper by microwave plasma chemical vapour deposition (MPCVD). It includes the following four main parts. 1. Effect of substrate pre-treatment on diamond nucleation. 2. Effect of deposition conditions on diamond nucleation and growth. 3.Preparation of free-standing diamond films using copper substrate. 4. Adherent diamond coating on copper using an interlayer. In the first part we show that diamond nucleation on copper is strongly affected by the substrate pre-treatment. The residues of abrasives left in the surface of the copper substrate play an important role in the diamond nucleation. In the second part we show that the diamond growth rate increases with microwave power and gas pressure. The effect of the microwave power is mainly an effect of substrate temperature. Increasing methane concentration results in a higher nucleation density and higher growth rate, but at the cost of a lower film quality. Gas flow rate has little influence on the diamond nucleation density and growth rate. In the third part we demonstrate the possibility of preparing large area free-standing diamond films using copper substrate, which has nearly no carbon affinity and usually leads to weak adhesion of the diamond films. The normally observed film cracking phenomenon is discussed and a two-step growth method is proposed for stress release. In the fourth part we show that adherent diamond coating on copper can be obtained using a titanium interlayer. Residual stress in the films is evaluated by Raman spectroscopy. It is found that with increase in the film thickness, the diamond Raman line shifts from higher wave numbers to lower, approaching 1332 cm–1. The stress variation along the depth of the film is also analysed using Airy stress theory.     

DEPOSITION OF DIAMOND FOR CUTTING TOOL APPLICATIONS

The poor adhesion of diamond film to substrates is one of the major problems for practical use in a cutting tool (1-4). in this study, sintered tungsten carbide (WC) body without Co metal, not cemented carbide, was used as the substrate (5), and the effects of surface decarburization of the substrate for improvement in the adhesion of diamond films were investigated. The surface decarburization and diamond coating were carried out in a microwave plasma CVD system. From the results of several adhesion tests, including the cutting tests, it is concluded that the good adhesion is obtained by surface decarburization of the substrate before diamond coating. The reasons for improvement in adhesion are considered by observing the interface structure between the film and the substrate. The damage mechanism of diamond coating on cutting an AI-18%Si alloy with increasing cutting speed is also discussed.     

Microstructure and superconducting properties of Y-Ba-Cu-O films prepared by chemical spray pyrolysis

Y-Ba-Cu oxide superconducting films were prepared by spray pyrolysis on (100) MgO substrates and alumina coated with a silver buffer layer. Acetate, nitrate, and oxide precursors were used as starting materials. The optimum starting compounds have been assessed and the effectiveness of rapid thermal processing as a fabrication tool for annealing of highT _c superconducting films has been established. The superconducting behavior was found to be strongly dependent on the type of the precursor used, on the method of heat treatment, and on the substrate material. The films show preferred orientation and good adherence to the substrate. Transport measurements indicated that the films exhibited a superconducting transition with an onset temperature between 83–93 K and ending between 52–74 K. The critical current density was found to be strongly dependent on film processing.     

Microstructural control of boundary region between CVD diamond film and cemented carbide substrate

Effects of the composition, texture and pretreatment of cemented carbide substrates on the microstructure of the boundary region between CVD diamond film and the substrate were investigated using a microwave plasma CVD in the CO-H₂ system. Optimum CVD conditions for a uniform coating on to the edge part of cutting insert were: microwave power, 550 W; total pressure, 30 Torr; total flow rate, 200 ml/min; CO concentration, 5–20 vol%; treatment time, 3–5 h. An adherent and tough diamond coating was prepared by initial coating at lower CO concentrations and by subsequent coating at higher CO concentrations. A cemented carbide substrate in the binary WC-Co system which comprised fine-grained tungsten carbide and low content of cobalt was suited for preparation of adherent diamond coating. De-cobaltization pretreatment of the substrate surface in acid solution followed by an ultrasonic microflawing treatment enhanced the nucleation density and adherence of diamond film to the substrate. The rotation of substrate was found to be effective for increasing the uniformity and decreasing the grain size of diamond film.     

Raman spectroscopy characterization of diamond films on steel substrates with titanium carbide arc-plated interlayer

Diamond chemical vapour deposition (CVD) on steel represents a difficult task. The major problem is represented by large diffusion of carbon into steel at CVD temperatures. This leads to very low diamond nucleation and degradation of steel microstructure and properties. Recent work [R. Polini, F. Pighetti Mantini, M. Braic, M. Amar, W. Ahmed, H. Taylor, Thin Solid Films 494 (2006) 116] demonstrated that well-adherent diamond films can be grown on high-speed steels by using a TiC interlayer deposited by the PVD-arc technique. The resulting multilayer (TiC/diamond) coating had a rough surface morphology due to the presence of droplets formed at the substrate surface during the reactive evaporation of TiC. In this work, we first present an extensive Raman investigation of 2 μm, 4 μm and 6 μm thick diamond films deposited by hot filament CVD on TiC interlayers obtained by the PVD-arc technique. The stress state of the diamond was dependent on both the films thickness and the spatial position of the coating on the substrate. In fact, on the top of TiC droplets, the stress state of the diamond was much lower than that of diamond in flatter substrate areas. These results showed that diamond films deposited on rough TiC interlayers exhibited a wide distribution of stress values and that very large compressive stress exists in the diamond film grown on flat regions of steel substrates with a TiC interlayer. Diamond films could accommodate stresses as large as 10 GPa without delamination.     

Effect of thermal annealing on transparent conductive LaNiO3 thin film prepared by an aqueous method

Dense, crack-free and uniform lanthanum nickel oxide (LNO) thin films were prepared by an aqueous method on various substrates, such as single crystal silicon, microcrystalline glass ceramic (GC) and amorphous glass. The effects of various thermal annealing temperatures on the microstructure, interface and electrical properties of the LNO films were investigated by XRD and SEM with the EDX and a four-probe method, respectively. It was found that with the increase in thermal annealing temperature, the LNO film on Si substrates displayed a structure change from pseudocubic to rhombohedral and was accompanied by the appearance of a NiO impure phase, while the LNO film on a GC substrate diffused into the substrate. In these cases, the film resistivity was increased. As a result, a LNO thin film with a resistivity of 2–3 × 10^–5 · m was achieved by thermally annealing at 750–800°C for 1 hour in air. The measurement of the surface resistance under different temperatures shows that the LNO film possesses better high temperature stability. Its transmittance spectrum was also observed.     

Nanocrystalline diamond growth on different substrates

Nanocomposite films consisting of diamond nanoparticles of 3-5 nm diameter embedded in an amorphous carbon matrix have been deposited by means of microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ gas mixtures. Si wafers, Si coated with TiN, polycrystalline diamond (PCD) and cubic boron nitride films, and Ti-6Al-4V alloy have been used as substrates. Some of the substrates have been pretreated ultrasonically with diamond powder in order to enhance the nucleation density n_nuc. It turned out that n_nuc depends critically on the chemical nature of the substrate, its smoothness and the pretreatment applied. No differences to the nucleation behaviour of CVD PCD films were observed. On the other hand, the growth process seems to be not affected by the substrate material. The crystallinity (studied by X-ray diffraction) and the bonding environment (investigated by Raman spectroscopy) show no significant differences for the various substrates. The mechanical and tribological properties, finally, reflect again the influence of the substrate material: on TiN, a lower hardness was measured as compared to Si, PCD and c-BN, whereas the adhesion of c-BN/nanocrystalline diamond (NCD) system was determined by that of the c-BN film on the underlying Si substrate.     

Numerical simulation of residual stresses in diamond coating on Ti-6Al-4V substrate

In this paper, we present numerical simulations of the residual stresses developed between diamond coatings and Ti-6Al-4V substrates when using chemical vapour deposition technique. The large difference in thermal expansion coefficients of diamond and titanium alloys results in high residual stresses in the diamond film. This could lead to interfacial cracking and material failure. The finite element method was used to simulate the cooling process of diamond films at various thicknesses and deposited at temperatures ranging from 600 °C to 900 °C. The influence of different parameters such as temperature, film thickness, material characteristics, geometry and edge effects are investigated for different case geometries. The film debonding and cracking is discussed and numerical results are compared with existing experimental and numerical results. Finally, some propositions are made to enhance the experimental process in order to reduce the residual stress intensities and the possible material degradation.     

Ellipsometry study of InN thin films prepared by magnetron sputtering

Indium nitride (InN) thin films have been deposited on Si(1 0 0) substrates at temperature of 100–400 °C by reactive radio frequency (RF) magnetron sputtering. We measured the ellipsometric spectra of the InN film samples, and obtained the optical constants for the wavelength range of 410–1100 nm. The absorption edge of the InN films is 1.85–1.90 eV. The thicknesses of various InN films are found to be dependent on the substrate temperature.     

Effects of low temperatures, low pressures and seeding over the crystalline quality, yield and stress of diamond films grown by ECR-assisted chemical vapor deposition

We have studied diamond films grown by electron cyclotron resonance (ECR)-assisted chemical vapor deposition (CVD) on Si (100) substrates seeded with diamond, boron nitride and unseeded. Relatively low temperatures (550–710°C) and low pressures (1–2 Torr) were employed. Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the crystalline quality, diamond yield, and stresses developed in these films. Most of the diamond films exhibit a Raman blue-shift with respect to natural diamond, indicating that the net stress is compressive. However, this net stress is significantly more compressive than the one estimated by taking into account the thermal interfacial stress and the stress developed at the grain boundaries. In addition, this net stress exhibits an inverse correlation with diamond yield, and a direct correlation with crystalline quality. These results were interpreted in terms of the critical interplay between the supply of precursor species to the growing surface and the surface mobility of adsorbed species. The excess (or intrinsic) compressive stress shows an inverse correlation with diamond crystalline quality, indicating that the creation of point defects serves as a stress-relieving mechanism. Seeding effects, in general, are deleterious to diamond quality, in this temperature and pressure regime studied. Seeding with boron nitride had the effect of reversing the net stress from compressive into tensile, but this effect was rapidly lost as the diamond yield increased.     

Stress formation and relaxation in amorphous Ta–Cr films

In the present paper, measurements of the intrinsic stress of thin amorphous Ta–Cr alloy films made by magnetron sputtering have been carried out. From the curvature of the substrates and by use of the Stoney formula, the stresses were determined. The bombardment of the growing film with energetic particles is shown to control the magnitude and sign of the intrinsic stress. When changing the deposition parameters, compressive or tensile stresses can be generated in the films in a range from about −2 GPa to +1 GPa. Also the stress relaxation, the change in the stress with time, has been studied for various temperatures. The stress relaxation was measured with a cantilever beam technique using a three-terminal capacitance method to detect the beam (substrate) deflection. The stress-relaxation data have been fitted to a mathematical model for stress relaxation related to inhomogeneous flow in amorphous films. This behaviour is expected to occur in the low-temperature, high-stress regime with deformation taking place along localized shear bands.     

Deposition and modification of titanium dioxide thin films by filtered arc deposition

Thin films of titanium dioxide have been deposited on glass substrates and conducting (100) silicon wafers by filtered arc deposition (FAD). The influence of the depositing Ti⁻ energy, substrate types and substrate temperature on the structure, density, mechanical and optical properties have been investigated. The results of X-ray diffraction (XRD) showed that with increasing substrate bias, the film structure on silicon substrates changes from anatase to amorphous and then to rutile phase without auxiliary heating, the transition to rutile occurring at a depositing particle energy of about 100 eV. However, in the case of the glass substrate, no changes in the structure and optical properties were observed with increasing substrate bias. The optical properties over the range of 300–800 nm were measured using spectroscopic elliosometery, and found to be strongly dependent on the substrate bias, film density and substrate type. The refractive index values of the amorphous, anatase and rutile films on Si were found to be 2.56, 2.62 and 2.72 at a wavelength of 550 nm, respectively. The hardness and elastic modulus of the films were found to be strongly dependent on the film density. Measurements of the mechanical properties and stress also confirmed the structural transitions. The hardness and elastic modulus range of TiO₂ films were found to be between 10–18 and 140–225 GPa, respectively. The compressive stress was found to vary from 0.7 to 2.6 GPa over the substrate bias range studied. The composition of the film was measured to be stoichiometric and no change was observed with increasing substrate bias. The density of the film varied with change in the substrate bias, and the density ranged between 3.62 and 4.09 g/cm³.     

Influence of WC-Co substrate pretreatment on diamond film deposition by laser-assisted combustion synthesis

The quality of diamond films deposited on cemented tungsten carbide substrates (WC-Co) is limited by the presence of the cobalt binder. The cobalt in the WC-Co substrates enhances the formation of nondiamond carbon on the substrate surface, resulting in a poor film adhesion and a low diamond quality. In this study, we investigated pretreatments of WC-Co substrates in three different approaches, namely, chemical etching, laser etching, and laser etching followed by acid treatment. The laser produces a periodic surface pattern, thus increasing the roughness and releasing the stress at the interfaces between the substrate and the grown diamond film. Effects of these pretreatments have been analyzed in terms of microstructure and cobalt content. Raman spectroscopy was conducted to characterize both the diamond quality and compressive residual stress in the films.