Preparation of CVD diamond coatings on gamma titanium aluminide using MPECVD with various interlayers

CVD diamond coatings were deposited on to γ-TiAl surfaces using a microwave plasma enhanced CVD to improve wear properties and the performance of γ-TiAl. Diamond coatings were directly deposited on to γ-TiAl substrates and deposited on to TiC, Ti₅Si₃, Al₂O₃ + TiO₂, and Si interlayers prepared on γ-TiAl substrates. The diamond coatings deposited directly on γ-TiAl suffered severe delamination and cracked. Those deposited on TiC and Ti₅Si₃ interlayers partially delaminated, whereas those deposited on Al₂O₃ + TiO₂ and Si interlayers adhered well to the underlying surfaces. The diamond films obtained were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that polycrystalline and nanocrystalline diamond films grew on γ-TiAl. Residual internal stresses of the diamond coatings deposited on interlayered-γ-TiAl were estimated experimentally from Raman spectra. The coatings prepared on Al₂O₃ + TiO₂/γ-TiAl and Si/γ-TiAl showed lower residual stresses.     

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.     

Interfacial structure, residual stress and adhesion of diamond coatings deposited on titanium

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH₄ in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength.     

Two-step growth of HFCVD diamond films over large areas

This paper reports the results of a two-step hot filament chemical vapor deposition method to improve the quality of diamond films. Diamond films were deposited on a Si(100) substrate having an area of 45 cm² and a thickness of 60 μm, employing a HFCVD system. The first step is the growth of CVD diamond in the HFCVD reactor. In the second step, the samples were treated in a saturated solution of H₂SO₄:CrO₃ and rinsed in a (1:1) solution of H₂O₂:NH₄OH. After this procedure, a second diamond layer was deposited. The diamond films were analyzed by Raman scattering spectroscopy (RSS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The films showed a high degree of purity with a thickness of 60 μm, presenting uniform characteristics over a large area.     

Synthesis of ultra-smooth and ultra-low friction DLC based nanocomposite films on rough substrates

Rough TiC/a-C films were intentionally grown on smooth surface to simulate a rough finishing of industrial substrates. Surface roughness and growth dynamics of TiC/a-C nanocomposite films deposited on such rough surfaces by non-reactive pulsed-DC (p-DC) sputtering of graphite targets at 350 kHz pulse frequency were studied using atomic force microscopy, cross-sectional scanning electron microscopy. Intensive concurrent ion impingement during the film growth at higher pulse frequency of p-DC sputtering leads to rapid smoothing of such initial rough surfaces. It was shown that rapid smoothing of initially rough surfaces with RMS roughness ~ 6 nm to < 1 nm can be effectively achieved by 350 kHz p-DC sputtering. These films exhibit dense and glassy microstructure. The surface roughness strongly influences the frictional behavior of TiC/a-C nanocomposite films where the rougher surfaces yielded higher steady state friction coefficient (CoF).The observed dynamic smoothing phenomenon was applied to obtain ultra-smooth and ultra-low friction (μ ~ 0.05) TiC/a-C:H nanocomposite films on industrial polished steel substrates by 200 and 350 kHz p-DC sputtering of Ti-targets in an argon/acetylene atmosphere.     

Adhesion Enhancement of Diamond Films on Various Substrates by Carbide Interlayer

Diamond films were prepared on various substrates by a combustion flame technique using an oxyacetylene torch. During the deposition, a carbide interlayer was formed between the surface of the substrate and deposited diamond. The hard interlayers were seen on the molybdenum, tungsten as well as silicon substrates. The adhesion of diamond on the molybdenum substrate was improved with increase in the hardness of the carbide layer. This result strongly supports the premise that the carbide interlayer and/or carbon diffused layer enhances the adhesion of diamond to substrates.     

金刚石薄膜用钢基表面过渡层研究进展

介绍了影响钢基表面金刚石薄膜沉积的不利因素,分析和综述了近10年来在提高金刚石薄膜质量以及薄膜粘结性等方面所采用的各种中间过渡层及其研究进展.过渡层可采用沉积法制备,也可采用表面改性法制备.过渡层可以制备成单层膜结构,也可制备成多层膜结构.对于不同的基底材料应选择不同的过渡层.     

WC-Co硬质合金基体上高附着力金刚石薄膜的制备

采用微波等离子体化学气相沉积(CVD)法在WC-Co硬质合金基体上制备金刚石膜, 研究了TiN_x中间层的引入对金刚石薄膜质量及其附着性能的影响. 结果表明, 在酸浸蚀脱钴处理的基础上, 通过预沉积氮含量呈梯度变化的TiN_x中间过渡层, 可在硬质合金基体上制备出高质量的金刚石薄膜; 压痕法测试其临界载荷达1000N.     

HF-CVD of diamond coatings onto Fluidized Bed (FB) treated CrN interlayers

In the present investigation, Fluidized Bed (FB) treatment is applied to pre-treat CrN interlayers onto WC-Co substrates to promote the growth on them of highly adherent diamond coatings. During FB treatment, the CrN interlayers are submitted to high speed impacts of loose abrasives. The action of their cutting edges is able to deeply change the starting morphology of the as-deposited Physical Vapour Deposition (PVD) CrN interlayers, thus promoting the establishment of a highly corrugated surface on which to grow Hot Filament-Chemical Vapour Deposition (HF-CVD) diamond coatings.Growth, morphology, adhesion and wear resistance of the CVD deposited diamond coatings onto the FB treated and just seeded CrN interlayers were looked into and compared to diamond coated WC-Co substrates with the untreated CrN interlayers or pre-treated with a two-step chemical etching (Murakami's reagent and Caro's acid, MC-treatment) or with FB.FB treatment proved to be an effective technique to tailor the surface morphology and roughness of CrN films deposited by PVD-arc technique, and was found to be very useful in improving the adhesion and wear resistance of CVD diamond onto the CrN interlayers.     

CVD diamond films with hydrophilic micro-patterns for self-organisation of human osteoblasts

Nanocrystalline diamond (NCD) films were prepared by microwave plasma-enhanced chemical vapour deposition (CVD) on Si substrates of different roughness (1 and 500 nm). Diamond nano-crystals are up to 50 nm in size and RMS surface roughness is less than 20 nm. The NCD films were cleaned chemically and terminated by hydrogen using plasma treatment (800 °C, 10 min) to generate a hydrophobic surface. Photolithography mask and oxygen plasma (300 W r.f. power, 3 min) were used to generate O-terminated (hydrophilic) patterns (30-200 μm wide) separated by a H-terminated (hydrophobic) surface. Osteoblast-like human cells were seeded on the patterned flat and rough NCD films in McCoy's 5A medium supplemented with 15% fetal bovine serum (FBS). After two days incubation the cells preferentially adhered on the O-terminated stripes. This phenomenon is not suppressed by the surface roughness and is general for other cell types (fibroblast and cervical carcinoma cells), too. The data are discussed with view to further application of NCD thin films in biotechnology and bio-electronics applications.     

The preparation and properties of Y2O3/AlN anti-reflection films on chemical vapor deposition diamond

Yttrium oxide (Y₂O₃) films have successfully been applied as anti-reflection (AR) and anti-oxidation films for diamond. For significant adhesion improvement between Y₂O₃ coating and diamond, aluminum nitride (AlN) as an interlayer is introduced. Y₂O₃ and AlN films were prepared by RF magnetron sputtering of Y₂O₃ ceramic target in Ar atmosphere and pure Al metal target in Ar + N₂ atmosphere, respectively. The Y₂O₃ and AlN films were studied by X-ray diffraction, X-ray photoelectron spectroscopy, Atomic force microscopy and Spectroscopic ellipsometry. Adherent Y₂O₃/AlN films on high optical quality chemical vapor deposition diamond with optimum thicknesses for infrared transmission enhancement in 8-10 μm were obtained by a Fourier transform infrared spectrometer. More than 28% increase in maximum transmission was observed for Y₂O₃/AlN//Diamond//AlN/Y₂O₃. Comparing between the designed and experimental AR effects for Y₂O₃/AlN film in 8-10 μm wavebands, experimental average AR effects are smaller for the absorption and scattering loss. AR effects for the Y₂O₃/AlN films on CVD diamond are proved to be excellent.     

Simultaneous fabrication of nanocrystalline and {100} textured large-grained diamond films

In this work, we report the simultaneous synthesis of both nanocrystalline and {100} textured large-grained diamond films in one deposition run performed in a 5-kW microwave plasma chemical vapor deposition (MPCVD) reactor. This was achieved by employing the coupled effect of nitrogen addition in the gas phase and substrate temperature on the growth of diamond films. In one deposition run, different substrate surface temperatures were obtained by a novel substrate arrangement, nanocrystalline diamond of high growth rate around 3 μm/h was formed at low temperature, while {100} textured large-grained diamond of much higher growth rate about 11 μm/h was grown at high temperature. This new method opens way for mechanical and tribological applications of both nano-diamond and {100} textured diamond in industrial level. This result indicates that distinct growth modes or growth mechanisms were involved at different substrate temperatures with a certain amount of nitrogen addition. The coupled effect of nitrogen addition and temperature on the growth of CVD diamond films and the involved growth mechanism is briefly discussed from the point of view of gas phase chemistry and surface reactions.     

CVD nanocrystalline diamond coatings on Ti alloy: A synchrotron-assisted interfacial investigation

Diamond coating on Ti-6Al-4V alloy was carried out using microwave plasma enhanced CVD with a super high CH₄ concentration, and at a moderate deposition temperature close to 500 °C. The nucleation, growth, adhesion behaviors of the diamond coating and the interfacial structures were investigated using Raman, XRD, SEM/TEM, synchrotron radiation and indentation test. Nanocrystalline diamond coatings have been produced and the nucleation density, nucleation rate and adhesion strength of diamond coatings on Ti alloy substrate are significantly enhanced. An intermediate layer of TiC is formed between the diamond coating and the alloy substrate, while diamond coating debonding occurs both at the diamond-TiC interface and TiC-substrate interface. The simultaneous hydrogenation and carburization also cause complex micro-structural and microhardness changes on the alloy substrates. The low deposition temperature and extremely high methane concentration demonstrate beneficial to enhance coating adhesion strength and reduce substrate damage.     

Diamond films deposited on WC-Co substrates by use of barrier interlayers and nano-grained diamond seeds

Results on the structure, composition and properties of diamond films deposited onto WC-Co cemented carbides via special multilayer barrier interlayers preliminary seeded by nano-grained diamond particles are presented. The barrier interlayers comprise a layer adjacent to the substrate, which completely prevents substrate decarburization and Co diffusion from the substrate, and a diamond-bonding layer needed to obtain an enhanced adhesion of the PACVD diamond coating. Preliminary seeding the barrier interlayers with nano-grain diamond particles by use of a laser ablation technique allows a fine-grained, uniform and highly adherent diamond coating of high quality to be deposited by use of a conventional PACVD technique. Results on the nature of the interaction between the diamond nano-grained seeds and barrier interlayer are also presented.     

Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment

A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO₂/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO₂ layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity X-rays. It was found that the SiO₂ film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 μm)-layer film and multi thin (0.1 μm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 °C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment.     

Effect of thermal coupling on the electronic properties of hydrogenated amorphous silicon thin films deposited by electron cyclotron resonance

In photovoltaic devices, rather thin intrinsic layers of good quality materials are required and high deposition rates are a key point for a cost-effective mass production. In a previous study we have shown that good quality amorphous silicon (a-Si:H) films can be deposited by matrix distributed electron cyclotron resonance (MDECR) plasma CVD at very high deposition rates (∼ 2.5 nm/s). However, only thick films (> 1 μm) exhibited good transport properties. A very poor thermal coupling between the substrate holder and the substrate is the main reason for such a behaviour. We present here experimental data which support this conclusion as well as the improved transport and defect-related properties of new very thin a-Si:H samples (thickness around 0.3 μm) deposited at a higher temperature than the previous ones.     

UNCD electron emitters using Si nanostructure as a template

The electron field emission (EFE) properties of silicon nanostructures (SiNSs) coated with ultra-nanocrystalline diamond (UNCD) were characterized. The SiNS, comprising cauliflower-like grainy structure and nanorods, was generated by reaction of a Si substrate with an Au film at 1000 °C, and used as templates to grow UNCD. The UNCD films were deposited by microwave plasma-enhanced chemical vapour deposition (MPECVD) using methane and argon as reaction gases. The UNCD films can be grown on the SiNS with or without ultrasonication pretreatment with diamond particles. The EFE properties of the SiNS were improved by adding an UNCD film. The turn-on field (E₀) decreased from 17.6 V/μm for the SiNS to 15.2 V/μm for the UNCD/SiNS, and the emission current density increased from 0.095 to 3.8 mA/cm² at an electric field of 40 V/μm. Ultrasonication pretreatments of SiNS with diamond particles varied the structure and EFE properties of the UNCD/SiNS. It is shown that the ultrasonication pretreatment degraded the field emission properties of the UNCD/SiNS in this study.     

A promising solution using CVD diamond for efficient cooling of power devices

Diamond has several exceptional physical and chemical characteristics. This is the best material for both electrical insulators (10 MV cm⁻¹) and thermal conductors (2000 W m⁻¹ K⁻¹, five times more than copper at room temperature). In this study, we analyzed and quantified the advantages of the insertion of CVD diamond layer in the innovative thermal management assemblies. We also developed a specific model to simulate the working environment of the component. In the simulation, we compared the use of a traditional substrate (AlN) with that of the diamond CVD one in order to confirm that using the diamond substrate reduced thermal resistance.     

Synthesis and characterization of electrolyte-grade 10%Gd-doped ceria thin film/ceramic substrate structures for solid oxide fuel cells

In the present research, spray pyrolysis technique is employed to synthesize 10%Gd-doped ceria (GDC) thin films on ceramic substrates with an intention to use the "film/substrate" structure in solid oxide fuel cells. GDC films deposited on GDC substrate showed enhanced crystallite formation. In case of NiO-GDC composite substrate, the thickness of film was higher (~ 13 μm) as compared to the film thickness on GDC substrate (~ 2 μm). The relative density of the films deposited on both the substrates was of the order of 95%. The impedance measurements revealed that ionic conductivity of GDC/NiO-GDC structure was of the order of 0.10 S/cm at 500 °C, which is a desirable property for its prospective application.     

通过过渡层改善金刚石膜和基底间的结合性能

介绍了在金刚石膜和基底间通过施加过渡层以改善金刚石膜与基底间的结合性能的研究成果。金刚石膜可以通过过渡层沉积于多种基底上,如Ｓｉ、ＳｉＯ２ 、陶瓷（ＳｉＣ,Ａｌ２Ｏ３） 、钢及硬质合金基底等。过渡层有单层（ 如ＤＬＣ、Ｃ６０ 、Ｙ ＺｒＯ２ 、Ｃ Ｎ 膜、ＴｉＣ或ＴｉＮ） 和多层（ 如Ｍｏ／Ｎｉ、Ｍｏ／ＴｉＮ 或Ｂ／ＴｉＢ２／Ｂ 等） 之分,根据金刚石、过渡层及基底的晶格匹配性和热学匹配性,对于不同的基底应选择不同的过渡层。