Gradient Films Research Articles

Fabrication and Characterization of Functionally Gradient Diamond-Like Carbon Coatings

ABSTRACTPure diamondlike carbon thin films largely bonded by four-fold coordination suffer from a large internal compressive stress that gives rise to a serious adhesion problem. In this work, functionally gradient (FG) diamondlike carbon thin coatings were prepared by pulsed laser deposition in a high vacuum chamber as an alternative approach to address the adhesion problem of diamondlike films. Copper, silver and titanium were incorporated into the growing films with their concentration as a function of the distance from the substrate surface. The top of the thin coating is pure DLC of about 400 nm in thickness. The total thickness of the functionally graded superhard DLC coatings can exceed 1.0 μm without buckling. Visible micro-Raman spectroscopy was used to characterize the bonding structure of the layers which contain alloy atoms. High resolution transmission electron microscopy was employed to study the microstructure of the coatings. Nanoscale mechanical characterizations using Nanoindenter XPTM were carried out to study the mechanical behavior of the functionally gradient DLC films.

Fabrication and Characterization of Functionally Gradient Diamondlike Carbon Coatings

AbstractPure diamondlike carbon thin films largely bonded by four-fold coordination suffer from a large internal compressive stress that gives rise to a serious adhesion problem. In this work, functionally gradient (FG) diamondlike carbon thin coatings were prepared by pulsed laser deposition in a high vacuum chamber as an alternative approach to address the adhesion problem of diamondlike films. Copper, silver and titanium were incorporated into the growing films with their concentration as a function of the distance from the substrate surface. The top of the thin coating is pure DLC of about 400 nm in thickness. The total thickness of the functionally graded superhard DLC coatings can exceed 1.0 μm without buckling. Visible micro-Raman spectroscopy was used to characterize the bonding structure of the layers which contain alloy atoms. High resolution transmission electron microscopy was employed to study the microstructure of the coatings. Nanoscale mechanical characterizations using Nanoindenter XP™ were carried out to study the mechanical behavior of the functionally gradient DLC films.

Formation of Ti/O compositional gradient film on Ti–6Al–4V alloy by reactive DC sputtering

Coating of Ti–6Al–4V alloy substrates with Ti/O compositional gradient films was carried out by reactive DC sputtering not only to improve the biocompatibility and the surface hardness of the alloy but also to relax the stress concentrated at the interface between the film and the alloy. The compositional gradient was realized by varying continuously the oxygen content in Ar–O 2 sputter gas during depositing. Under AES, it was confirmed that a Ti/O compositional gradient film had formed on the alloy, and it was concluded that the oxygen atoms which had concentrated at the surface of the alloy substrate diffused into the titanium layer in the compositional gradient film. Based on the results of XRD, it was found that α-titanium phase was formed in the compositional gradient film with (002) orientation dominant during the film growth. Furthermore, based on indentation–fracture test, it was concluded that this depositing method improved the adhesion of the deposited film to the alloy substrate and the toughness of the film.

Fe–N gradient films and epitaxial Fe16N2 single-crystal films

Fe–N gradient films and epitaxial Fe16N2 single-crystal films were prepared with a facing-target sputtering system. The Rutherford backscattering spectrum, x-ray diffraction, and selected area electron diffraction indicate that the gradient films possess some composition and structure gradient. The α′′-Fe16N2, γ-Fe4N, ε-FexN(2<x⩽3), and ζ−Fe2N phases are present in the gradient films at different depths. The α′′-Fe16N2 single-crystal films correspond to a deformed body-centered tetragonal structure with parameters of a=b=5.72 Å and c=6.29 Å. They grew epitaxially on a NaCl(100) substrate with an orientation relationship of α′′-Fe16N2(001)∥NaCl(001) and α′′-Fe16N2[100]∥NaCl[100]. Perfect electron diffraction patterns with perfect symmetry in the [1̄11], [011], and [001] directions can be observed distinctly by a rotational double tilting sample stand. By controlling N2 partial pressure, substrate temperature, and crystal orientation, α′′-Fe16N2 single-crystal films can be successfully grown epitaxially.

COATING OF Ti-6Al-4V ALLOY SUBSTRATE WITH Ti/N COMPOSITIONAL GRADIENT FILM BY REACTIVE DC SPUTTERING

Coating of Ti-6Al-4V alloy substrates with Ti/N compositional gradient films was carried out by reactive DC sputtering, to improve the blood compatibility of the alloy and to relax the stress concentrated at the interface. The compositional gradient was realized by varying continuously the nitrogen content in Ar-N 2 sputter gas during depositing. The deposited film appeared to be uniform and adhesive. TiN formation at the surface of the film was assumed, because of its yellow gold color and high hardness. Under SEM, it was found that the surface had fine particles dispersed on a smooth, accumulated deposit and that this depositing method improved not only the structural property of the film surface but also the adherence of the film with the substrate. Under AES, it was confirmed that nitrogen concentration in the film decreased gradually from the surface toward the substrate. © 1997 Elsevier Science Ltd

Formation of Aluminum Gradient Films on Stainless Steel by Ion Implantation

Formation of Aluminum Gradient Films on Stainless Steel by Ion Implantation

Study on the effect of the interlayer on the adhesion of 400 μm thick film

We have studied on the effect of the interlayers on the adhesion of 400 μm thick NiTiN gradient films. In order to improve the adhesion of the NiTiN films, the interlayer films are formed at the interfaces between the thick films and tungsten carbide substrates (WC-Co). The interlayers have the SiNi multilayer structures and are prepared by ion beam and vapor deposition (IVD) method. The Si interlayers are prepared at various internal stresses on tungsten carbide substrates and the Ni interlayers also are prepared at various internal stresses on the Si interlayers. The 400 μm thick films are formed by cathodic are ion-plating method on the SiNi interlayers. As a result, it seems that it is possible to improve the adhesion of the thick films by decreasing internal stress mismatch among the lower layers of the thick films, upper layers of interlayers and lower layers of interlayers.

Surface Microstructures of Ferroelectric SrBi2Ta2O9, BaTiO3 and Metallic SrRuO3 Epitaxial Thin Films

ABSTRACTWe have made a comparative invetigation of the surface microstructures of epitaxially grown ferroelectric SrBi2Ta2O9, BaTiO3 films, and metallic SrRuO3 films, using scanning probe microscopy. Though their lattices (or pseudotetrogonal lattices) match closely with SrTiO3 (001) substrates, SPM results show very different surface microstructures. The surfaces of SrRuO3 films display atomically flat terraces of 90° oriented step edges. The size of steps is about 6 Å. The surface of BaTiO3 films deposited at various temperatures displays uniform rectangular islands. Different stages of SrBi2Ta2O9 epitaxial growth have been studied on thickness gradient films, which show clearly 2D nucleation and layer-by-layer growth, following a transition from 2D to 3D island growth. It finally develops into a surface exhibiting round hills consisting of curved terraces with size of steps ranging from 6 Å to 12.5 Å.

イオンプレーティングによるＡｌＮのメタライジング 表面改質による窒化アルミニウムと金属の接合 （第２報）

Metallization method of AlN substrate by ion plating technique has been developed. Dual coating films of 5-10 μm thick nitrides (TiN, ZrN and CrN) and 10 μm thick copper were formed on the AlN substrate by ion plating. The functionally gradient films of TiN Ti were also deposited on the AlN substrate. The adherent strength of metallized films against AlN substrate was evaluated by the tensile test at room temperature. The morphologies of nitride films were quite sound and they were stuck AlN together well. Element analyses by EPMA and ESCA revealed that nitrides such as TiN, ZrN and CrN were hardly reacted with AlN substrate or Cu film. The adherent strength of TiN, ZrN, CrN coating film and the functionally gradient films indicated the average values of 50-60 MPa in any cases. The joint strength of TIN+Cu dual metallized AlN to copper soldered by Sn-38 mass%Pb solder was about 33 MPa.

Local optical emission spectroscopy of excited species effused from an evaporation cell and a sputter source into dense plasmas - Basic studies for the deposition of thin gradient films.

Space resolved optical emission spectroscopy has been applied to determine the distribution of excited species in dense plasmas which are used for the deposition of thin coatings. Typical electron densities and electron temperatures in the plasma facility PETRA ( Plasma Engineering and Technology Research Assembly) are in the range of n(e) = 10(12) cm(-3) and T(e) = 10 eV. During the deposition process material (Al) is evaporated from a vapour cell under controlled conditions. The vapour stream is guided into a dense plasma which is composed of inert gas, Ar or He, and hydrocarbon species produced from the dissociation of C(2)H(2). The evaporated Al-stream which travels with thermal velocity into a plasma of high electron density, is nearly completely ionized due to the short mean free path for electron impact ionization in the above mentioned parameter range. Optical emission spectroscopy has been applied to investigate the interaction processes between the vapour stream and the plasma as well as the transport of the ionized Al along the applied magnetic field. For the measurements space resolved optical emission spectroscopy with an in-situ translation mechanism of the optical fibre has been used to measure the local concentrations of excited Al neutrals and ions as well as the concentration of the background plasma species.

Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3 and propylene

Fluorocarbon polymer films were prepared by plasma polymerization using nitrogen trifluoride (NF3) and propylene as starting materials. To improve their adhesiveness to substrates, a novel functionally gradient film in which the content of fluorine decreased continuously from the surface to the interior was prepared by changing source gas composition during deposition. This film had a smooth and pinhole-free surface, and had a high contact angle (110°) for water drop. In addition, it showed good adhesion to a glass substrate. © 1996 John Wiley & Sons, Inc.

Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3 and propylene

Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3 and propylene

Ａｌ‐Ｎ膜の電気および光学特性の制御方法および傾斜機能膜の形成

The optical and electrical properties of RF-sputtered Al-N films have been controlled by changing the content of nitrogen gas and total sputtering pressure. For Al-rich Al-N films, post-N+-implantation and post-heat-treatment in a nitrogen atmosphere effectively change optical and electrical properties. A new, colorful, wear-resistant, anticorrosion AlN/Al/AlN film has been made by adding a very thin layer of Al between two stoichiometric AlN layers, based on the phenomenon that the coloration of Al-N films is mainly caused by the extra Al in the film and the interference of light. A compositionally and structurally gradient Al-AlN film was fabricated. The structure, morphology, and Al element distribution across the cross section of the gradient film was investigated using X-ray diffraction, SEM, and EMPA

Functionally Gradient NiTi Films Fabricated by Sputtering

The processing of homogeneous NiTi film has already been reported, but not that of heterogeneous NiTi film. The deposition and processing of functionally gradient films (FGF) of NiTi are discussed and demonstrated. NiTi-FGF were fabricated by RF magnetron sputtering with control of the input power to a titanium target. Films were heat-treated to induce crystallization and memorization. The characteristics have been investigated using a differential scanning calorimeter (DSC) and an electric resistance meter, respectively. The films that were solution-treated at 700° C had a gradient composition, and they showed two types of crystal structure, namely, a nickel-rich layer and a titanium-rich layer in the film. The entire NiTi-FGF transformed gradually and the temperature range between the start and finish of transformation was twice that of homogeneous film. It was verified that motion of FGF could be controlled easily by current intensity.

Al / Al-N / Ain Compositional Gradient Film Synthesized by Ion-Beam Assisted Deposition Method

AbstractAl / AI-N / AIN compositional gradient thin film was deposited on a Si(100) substrate at room temperature by ion-beam assisted deposition method, with a diminishing ion beam current from 1.4 to 0 mA at increments of 0.3 mA in order to gradually decrease the nitrogen to aluminum ratio at the substrate. The gradual Al and AIN variation in composition was shown by the change of the Al / N atomic ratio analysed by the energy dispersive X-ray spectroscopy(EDX) and the X-ray photoelectron spectroscopy (XPS) in the cross section of the film. The formation of crystalline Al metal and AIN ceramic layer on the Si substrate was revealed by X-ray diffraction(XRD). The cross sectional image taken by high resolution transmission electron microscope (HRTEM) showed a nano-sized crystalline AI-N ceramic material and the flat interface between the Si substrate and the AIN film.

Facing targets sputtered Fe-N gradient films

Fe-N gradient films were prepared with a facing targets sputtering system. During deposition, the nitrogen pressure increased linearly up to a value, which is called the ‘‘ultimate pressure.’’ Composition profiles, microstructure, magnetic properties, and corrosion resistance of the films were investigated by various methods. The experimental results indicate that the Fe-N films possess some composition and structural gradients. The Fe concentration decreases from the substrate to the film surface from 100 to 66 at. %. The phases α″-Fe16N2, γ′-Fe4N, ε-FexN(2<x≤3) and ζ-Fe2N are present in the gradient films at different depths. Ms under the ultimate nitrogen pressure of 0.05 Pa has a value of 1803 emu/cc which is higher than that of bulk iron, this is attributed to the presence of Fe16N2. Increasing further the ultimate nitrogen pressure, Ms decreases monotonically. The corrosion resistance of the gradient film with higher nitrogen concentration near the surface is good enough for magnetic recording heads.

Preparation of compositionally gradient Ti-TiN films by r.f. reactive sputtering

The r.f. reactive sputtering of a Ti target in a mixed gas of Ar and N2 was used to fabricate compositionally gradient films consisting of Ti and TiN phases. In this paper, two methods are described to form the compositionally gradient Ti-TiN films. The first uses the N2 flow-to-total flow ratio (FN2Ftotal) control method, and the other is the r.f. power control method. The compositionally gradient Ti-TiN films were deposited onto microscope glass slides. The substrate was at room temperature. The crystallographic structure, the composition and the morphology of the deposited films were characterized by X-ray diffractometry, Auger electron spectroscopy and scanning electron microscopy, respectively.Both the FN2Ftotal and r.f. power control method can be used to grow compositionally gradient films. It was demonstrated that the deposited film has a structure with a non-oriented TiN layer on a c-axis perpendicular Ti layer. The morphology of the films is independent of the deposition method. It is also shown that optical emission spectroscopy and mass spectroscopy are useful tools to monitor the growth of these films.

Preparation of compositionally gradient Ti-TiN films by r.f. reactive sputtering

The r.f. reactive sputtering of a Ti target in a mixed gas of Ar and N 2 was used to fabricate compositionally gradient films consisting of Ti and TiN phases. In this paper, two methods are described to form the compositionally gradient Ti-TiN films. The first uses the N 2 flow-to-total flow ratio ( F N 2 F total ) control method, and the other is the r.f. power control method. The compositionally gradient Ti-TiN films were deposited onto microscope glass slides. The substrate was at room temperature. The crystallographic structure, the composition and the morphology of the deposited films were characterized by X-ray diffractometry, Auger electron spectroscopy and scanning electron microscopy, respectively. Both the F N 2 F total and r.f. power control method can be used to grow compositionally gradient films. It was demonstrated that the deposited film has a structure with a non-oriented TiN layer on a c -axis perpendicular Ti layer. The morphology of the films is independent of the deposition method. It is also shown that optical emission spectroscopy and mass spectroscopy are useful tools to monitor the growth of these films.

Multiphase iron nitride gradient films

Fe-N gradient films were prepared by facing target sputtering. The nitrogen pressure increased linearly during deposition. X-ray photoelectron spectroscopy was employed to investigate the Fe and N atom profiles and the results show that the concentrations of the Fe and N atoms vary gradually from the substrate side to the surface side through the whole thickness of the film, ranging from 90 to 65.5 at.%. There are α-Fe, α″-Fe 16N 2, ε- Fe x N (2 < x ⩽ 3) and ζ-Fe 2N phases characterised by X-ray diffraction in the films. The Fe-N films are of similar composition and structural gradient.

Multiphase FeN gradient films prepared by facing target sputtering

FeN gradient films are fabricated by facing target sputtering. During deposition, the nitrogen pressure increases linearly from a small initial value to an ultimate one at a rate of 0.025 Pa/min. The composition gradient determined by XPS shows the Fe concentration to decrease from the substrate to the surface, ranging from 100 to 66 at%. XRD and TEM indicate that there exist α″-Fe16N2. γ′-Fe4N, ε-FexN (2 < x ≦ 3), and ζ-Fe2N in proper order in the film. The saturation magnetic moment σs decreases monotonously with the increase of the ultimate nitrogen pressure. The value of σs obtained under an ultimate nitrogen pressure of 0.05 Pa is 237 emu/g, which is higher than that of bulk iron due to the contribution of Fe16N2.