Internal Stress Of Films Research Articles

Reducing the Internal Stress of Fe-Ni Magnetic Film Using the Electrochemical Method

Soft magnetic materials are important functional materials in the electrical engineering, radio, and high-tech fields, but thin and brittle flakes present challenges to the manufacturing industry. In this study, the effect and mechanism of saccharin sodium in reducing the internal stress of Fe-Ni magnetic films were analyzed. The effects of the pH value, temperature, and the concentration of saccharin sodium on the deposition process of Fe-Ni alloys were investigated. The polarization curve of the Fe-Ni alloy deposition process was measured by using a multifunctional electrochemical workstation, and the morphology and crystal structure were measured by a scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that saccharin sodium significantly reduced the stress of the iron-nickel magnetic film; the mechanism through which the internal stress was reduced is analyzed in this paper. Briefly, the Fe2+ and the amino group of saccharin sodium synthesized a metal complex with positive charge on the surface of the electrode, which prevented the hydrogen ions from approaching the cathode and increased the discharge activation energy of the hydrogen ion, which reduced the hydrogen evolution and improved the internal stress of the coating. This research will help to solve the challenges of producing magnetic film, and promotes the application of new stress-reducing agents.

Effect of plastic deformation on mechanical properties and corrosion resistance of nickel-aluminum bronze

PurposeNickel-aluminum bronze (NAB) has been widely used in ship propellers. It is always subjected to local micro-plastic deformation in service environments. This paper aims to study the influence of plastic deformation on the mechanical strength and corrosion resistance of NAB in 3.5 Wt.% NaCl solution.Design/methodology/approachScanning electron microscope and X-ray diffraction were used to analyze the microstructure of NAB alloy with different plastic deformations. Mechanical properties of the sample were measured by tensile experiment, and corrosion behavior was studied by electrochemical measurements and the long-term immersion corrosion test.FindingsResults showed that the plastic deformation caused lattice distortion but did not change the microstructure of NAB alloy. Microhardness and yield strength of NAB were significantly improved with the increase of deformation. The lattice distortion accelerated the formation of corrosion product film, which made the deformed alloy show a more positive open-circuit potential and an increased Rp. However, during the long-term immersion corrosion, the corrosion resistance of NAB alloys deteriorated with the increase of plastic deformation. This is because larger plastic deformation brought about higher internal stress in corrosion product film, which resulted in the premature peeling of the film and the loss of its protective effect on the alloy substrate.Originality/valueTensile plastic deformations were found to cause a decline in the corrosion resistance of NAB. And the mechanism was clarified from the evolution of corrosion products during the corrosion process.

Calculation of Internal Stress in Oxide Films of Zirconium Alloy

The internal stress in the oxide film of zirconium alloy is an important factor in the corrosion kinetics of zirconium alloy. At present, there is no unified method to obtain the internal stress in the oxide film, and the data is quite different. Based on the traditional experimental and theoretical methods, the double layer oxidation bending model of ZrO2/Zr is established, the internal stress in the oxide film under different corrosion conditions is calculated, the change rule of the internal stress is obtained and the influencing factors is analyzed, which provides a more reliable way for the research of the internal stress in the oxide film of zirconium alloy.

Influence of ion implantation on the charge storage mechanism of vanadium nitride pseudocapacitive thin films

The influence of microstructural or structural defects is seldom investigated in pseudocapacitive electrodes. Indeed, most of the synthesized materials do present defects at every scales which contribute to the improvement of the charge storage. In this study VN thin films were deposited by reactive magnetron sputtering. The as-deposited VN films were compared with similar films implanted with arsenide cations (As+) with energies ranging from 20 keV up to 150 keV. The influence of the ionic implantation on the structure and microstructure of the pristine films was characterized by several techniques. The initial curing of the internal stress of as-deposited VN films observed for low implantation energies was lost with increasing implantation energy. Concomitantly, the electrochemical behaviors of the VN films were investigated. All the VN films show a pseudocapacitive behavior at 2 mV.s−1. At low scan rates, the as-deposited film exhibits the highest areal capacitance (45 mF.cm−2) which drastically decreases upon increasing the scan rate. Only 30% of the initial capacitance is maintained at 100 mV.s−1. Despite lower capacitances at 2 mV.s−1, As+ implanted VN films exhibit better capacitance retention in the same conditions, i.e. up to 65% of the initial capacitance is maintained at 100 mV.s−1. The contributions coming from surface and subsurface reactions have been determined which enable to propose possible origins for the changes occurring in charge storage mechanisms upon ion implantation.

Measurement of internal stress in thin films using MEMS structures

Measurement of internal stress in thin films using MEMS structures

Anisotropic in-situ stretching-strain engineering of flexible multilayer thin-film nanogenerators with Cu interlayers

Strain engineering has been extensively recognized as an influencing methodology in finely modulating properties of materials. However, there has been no report of proposing the stretching-strain-dependent piezoelectricity in flexible thin-film nanogenerators processed with deliberate lattice strain. Herein, we propose two combined ways of enhancing piezoelectricity and thus electromechanical energy harvesting performance, i.e., imposing a considerable level of internal stress in ZnO thin films by an in-situ deposition method using a substrate-stretching mode and incorporating a metallic interlayer between the ZnO thin films to form a multi-layered structure. The intentional strain results primarily in an elongation of unit cell along the vertical axis and a larger contribution to spontaneous polarization. As a highlight, the highest stretching strain of ~ 4.87% induced a ~ 212% enhancement of output voltage and a ~89% increase of output current in the final optimized thin-film nanogenerators consisting of Cu-interlayered ZnO multilayer thin films.

Mechanisms of Stress Generation in Thin Films and Coatings

Analysis of the literature data on the reasons for the development of mechanical stresses in epitaxial, polycrystalline, and amorphous films during their formation and under various external influences is carried out. The mechanism of the appearance of internal stresses during heteroepitaxial growth of films caused by the mismatch of the crystal lattice constants of the film and substrate is described. The relationship between the development of mismatch stresses in heteroepitaxial films and changes in the nature of their growth is shown. Models of the occurrence of compressive and tensile stresses in polycrystalline films due to the formation and coalescence of islands at the initial stage of their growth are considered. The regularities of the evolution of internal stresses in continuous films are discussed depending on the conditions of their deposition, as well as their chemical composition, structure, and mechanical properties. The mechanisms of development of internal stresses in thin films associated with the formation of point defects in them, the incorporation of impurities, and phase transformations occurring in the deposition process are reviewed. External factors that lead to the appearance of stresses in thin films during their storage and operation are considered in detail.

Effects of substrate bias voltage on structure and internal stress of amorphous carbon films on γ-Fe substrate: Molecular dynamics simulation

In this paper, the deposition process of amorphous carbon (a-C) films on γ-Fe substrate was simulated by molecular dynamics (MD). The effects of substrate bias voltage (abbreviated as bias) on structure and internal stress of a-C films was investigated. The results showed that the growth process of a-C films on γ-Fe substrate can be divided into five stages, namely, the diffusion stage of C atoms, island-like nucleation stage of a-C films, formation stage of the pseudo diffusion zone, diffusion stage of Fe atoms and stable growth stage of a-C films. The structure of a-C films after deposition can be divided into four zones, namely, the substrate zone, pseudo diffusion zone, intrinsic zone and surface zone. The intrinsic zone is the main part of a-C films, and its structure is mainly composed of sp3-C and sp2-C atoms. The percentage of sp3-C atoms is fluctuated with the increase of bias. When bias is 25 V, the percentage of sp3-C atoms is the largest, which is 26.19%. When bias is 75 V, the percentage of sp3-C atoms is the smallest, which is 23.92%. The percentage of sp2-C atoms is increased with the increase of bias. When bias is 75 V, the percentage of sp2-C atoms is the largest, which is 73.69%. With the increase of bias, the internal stress of the intrinsic zone is firstly increased. When bias is 25 V, the internal stress is the highest, which is 6.94GPa and then is decreased gradually. The pseudo diffusion zone is a transition zone between a-C films and γ-Fe substrate, and is a mixed zone composed of C and Fe atoms. With the increase of bias, the internal stress in the pseudo diffusion zone is decreased gradually. When bias is 75 V, the internal stress is the lowest, which is 0.40GPa.

Ultrasound-assisted electrodeposition of Fe-Ni film for OLED mask

Fe-Ni alloy is considered as the most suitable metal for OLED mask making due to its excellent properties. However, electrodeposited Fe-Ni film is often companied with poor surface quality and thermal expansion. To get proper film for masks making, experiments of electroforming Fe–Ni were performed with different ultrasonic powers and current densities. Results show that Fe-Ni film with smooth surface could be electrodeposited at high current density due to the reducing of internal stress of film by ultrasonic power. The iron content, grain size, micro-hardness and Young’s modulus of film all present an upward trend with ultrasonic power increases from 13 W to 93 W, and then a downward trend due to the intensively transient cavitation caused by higher ultrasonic power 120 W. With the ultrasonic power of 93 W and current density of 1 A/dm2, a good surface quality of Fe-Ni films with 60.07 wt.% iron content, microhardness 351 HV, Young's modulus 167.5 GPa and CTE 3.38 × 10−6/℃ can be electrodeposited.

Simple Non-Destructive Method of Ultrathin Film Material Properties and Generated Internal Stress Determination Using Microcantilevers Immersed in Air

Recent progress in nanotechnology has enabled to design the advanced functional micro-/nanostructures utilizing the unique properties of ultrathin films. To ensure these structures can reach the expected functionality, it is necessary to know the density, generated internal stress and the material properties of prepared films. Since these films have thicknesses of several tens of nm, their material properties, including density, significantly deviate from the known bulk values. As such, determination of ultrathin film material properties requires usage of highly sophisticated devices that are often expensive, difficult to operate, and time consuming. Here, we demonstrate the extraordinary capability of a microcantilever commonly used in a conventional atomic force microscope to simultaneously measure multiple material properties and internal stress of ultrathin films. This procedure is based on detecting changes in the static deflection, flexural and torsional resonant frequencies, and the corresponding quality factors of the microcantilever vibrating in air before and after film deposition. In contrast to a microcantilever in vacuum, where the quality factor depends on the combination of multiple different mechanical energy losses, in air the quality factor is dominated just by known air damping, which can be precisely controlled by changing the air pressure. Easily accessible expressions required to calculate the ultrathin film density, the Poisson’s ratio, and the Young’s and shear moduli from measured changes in the microcantilever resonant frequencies, and quality factors are derived. We also show that the impact of uncertainties on determined material properties is only minor. The validity and potential of the present procedure in material testing is demonstrated by (i) extracting the Young’s modulus of atomic-layer-deposited TiO2 films coated on a SU-8 microcantilever from observed changes in frequency response and without requirement of knowing the film density, and (ii) comparing the shear modulus and density of Si3N4 films coated on the silicon microcantilever obtained numerically and by present method.

Determining intrinsic stress and strain state of fibre-textured thin films by X-ray diffraction measurements using combined asymmetrical and Bragg-Brentano configurations

Measuring intrinsic macro stresses in fibre-textured thin films have always been challenging. Due to the nature of preferential orientation in these films, only d-spacings aligned with the film surface are observable in Bragg-Brentano X-ray diffraction scans, and to collect sufficient diffraction data needed for the stress calculation, a sample stage with tilt capabilities is essentially required. In this article, a new method is developed to lift this requirement. Based on the thin film crystal structure, an incident angle for asymmetrical XRD configuration is calculated to reveal tilted planes belonging to the same group of crystallites which are the textured majority. Measurement of d-spacing for this angle of incidence in combination with the Bragg-Brentano configuration is shown to successfully extract stress-free lattice parameter and the internal stress of the cubic metallic thin film. This method can also be adapted to determine stress and strain in polycrystalline thin films.

Intrinsic stress-induced bending as a platform technology for controlled self-assembly of high-Q on-chip RF inductors

This work reports on the modelling and process technology development for the design and fabrication of vertical, 3D, monolithic RF-MEMS inductors based on self-assembly via intrinsic stresses otherwise referred to as residual or internal stresses in thin films. Stress-induced bending in different cantilever designs were modelled at various film thicknesses using finite element analysis method and bending conditions were optimized. Intrinsic stress-induced bending mechanism is verified by fabrication of bi-layer metallic micro cantilever structures with varying stress conditions which reach bending angles of up to 137° and possibly more upon release. By modulating the loading mode (tensile or compressive) along the beam length, complex out-of-plane wavy cantilevers with multiple upward and/or downward bends were realized. The fabrication and modelling results display large overlap which further demonstrates the applicability of intrinsic stress-induced bending as a controllable technology towards fabrication of out-of-plane 3D micro components. Additionally, as a potential application to RF-MEMS inductors, stress-induced self-assembly of patterned thin film stacks into out-of-plane inductor topologies of varying geometries was investigated. Electromagnetic modelling tools were used to study the effect of bending on inductor performance (primarily the Q factor and self-resonance frequency—f SR), and results were evaluated by comparison to planar inductors of the same number of turns and dimensions, which revealed Q factor and f SR improvement of more than 100% upon bending away from substrate surface.

Internal Stresses in Plasma Deposited Polymer Film Coatings

A technique for measuring the internal stresses in polymer films deposited on a glass substrate in gas discharge plasma is developed. Using this technique, the dependence of internal stress in thin films of polymethylmethacrylate and polystyrene on the deposition time and the current density of the barrier discharge at atmospheric pressure is studied. It is found that, when forming thin polymer coatings from monomers with high polymerization efficiency, the average value of internal stresses is higher than that for coatings obtained from monomers having low polymerization efficiency in barrier discharge plasma at atmospheric pressure. This can be explained by an increase in the specific number of cross-links in the first type of films under the action of ultraviolet radiation from the plasma. The quasi-optimal deposition time of the polymer film coating from styrene is found in which the value of the internal stress is minimal at a film thickness acceptable for a number of practical applications.

Molecular dynamics simulation of temperature effects on deposition of Cu film on Si by magnetron sputtering

The temperature effects on the growth of Cu thin film on Si (0 0 1) in the context of magnetron sputtering deposition were systematically studied using molecular dynamics (MD) method. To improve the comparability of simulation results at varying temperatures, the initial status data of incident Cu atoms used in all simulations were read from an identical file via LAMMPS-Python interface. In particular, crystalline microstructure, interface mixing and internal stress of Cu thin film deposited at different temperatures were investigated in detail. With raising the substrate temperature, the interspecies mixed volume and the proportion of face-centered cubic (fcc) structure in the deposited film both increased, while the internal compressive stress decreased. It was found that the fcc structure in the deposited Cu thin films was 〈1 1 1〉 oriented, which was reasonably explained by surface energy minimization and the selectivity of bombardment energy to the crystalline planes. The quantified analysis of interface mixing revealed that the diffusion of Cu atoms dominated the interface mixing, and the injection of incident Cu atoms resulted in the densification of phase near the film-substrate interface. More important, the distribution of atomic stress indicated that the compressive stress was mainly originated from the film-substrate interface, which might be attributed to the densification of interfacial phase at the initial stage of film deposition.

GaN epitaxial layers grown on multilayer graphene by MOCVD

In this study, GaN epitaxial layers were successfully deposited on a multilayer graphene (MLG) by using metal-organic chemical vapor deposition (MOCVD). Highly crystalline orientations of the GaN films were confirmed through electron backscatter diffraction (EBSD). An epitaxial relationship between GaN films and MLG is unambiguously established by transmission electron microscope (TEM) analysis. The Raman spectra was used to analyze the internal stress of GaN films, and the spectrum shows residual tensile stress in the GaN films. Moreover, the results of the TEM analysis and Raman spectra indicate that the high quality of the MLG substrate is maintained even after the growth of the GaN film. This high-quality MLG makes it possible to easily remove epitaxial layers from the supporting substrate by micro-mechanical exfoliation technology. This work can aid in the development of transferable devices using GaN films.

Tunable shape recovery progress of thermoplastic polyurethane by solvents

PurposeThis study aims to present that the chemo-responsive shape recovery of thermoplastic polyurethane (TPU) is tunable by solvents with different solubility parameters, and it is generic for chemo-responsive shape-memory polymer and its composites.Design/methodology/approachTwo kinds of commercial TPU samples with different thicknesses were prepared by panel vulcanizer and injection molding (an industrial manner) to investigate their chemo-responsive shape memory properties in acetic ether and acetone.FindingsResults showed that all of TPU films with different thicknesses can fully recover their original shapes weather they recover in acetic ether or acetone. But the recovery time of TPU films in acetone is greatly reduced, especially for the twisting samples. The residual strains of recovery TPU samples after extension reduce obviously.Research limitations/implicationsThe great decrement of recovery time is related to two factors. One is due to the bigger solubility parameter of acetone with higher dipole moment compared with those of acetic ether, and the other is the remained internal stress of TPU films after preparation. The internal stress is identified to have an effect on the shape-memory properties by comparing the recovery process of samples with/without annealing. The reduced residual strains of recovery TPU samples after extension is due to the increasing mobility of polymer segments after molecules of acetic ether penetrates into the polymeric chains.Originality/valueThis is a universal strategy to control the recovery process of shape-memory materials or composites. The underlying mechanism is generic and should be applicable to chemo-responsive shape-memory polymers or their composites.

Interface defects and stress relief of super hard Ti+C/a-CNx gradient multilayer films

Ti + C/a-CNx gradient multilayer film (GMF) are prepared using ion-beam assisted magnetron sputtering. The hardness of as-deposited Ti + C/a-CNx-GMF reach 29 GPa, which is obviously higher that of pure CNx film. Transmission electron microscopy (TEM) and optical microscope (OM) were used to examine the structure and morphologies of Ti + C/a-CNx-GMF films. Investigation results indicated that there was a Ti + C gradient layer zone with gradual Ti lattice parameter existed in this super hard Ti + C/a-CNx-GMF, and interface zones are mainly composed of nanocrystallie TiC and Ti grains and amorphous matrix, the growth of interlayer depends on compressive stress. As deposited GMFs voluntarily buckling and peeling along the interfacial defect zone (Ti-Si-O), due to the existence of high internal stress in films, lead to adhesion failure. After undergoing thermal treatment, Ti + C gradient multilayer (GM) zone present a semi-coherent type with some misfit, which could relax the internal stress of GMFs.

Internal stress and opto-electronic properties of ZnO thin films deposited by reactive sputtering in various oxygen partial pressures

In this article, we propose ZnO thin films as a suitable material for piezoresistors in transparent and flexible electronics. ZnO thin films have been deposited by DC reactive magnetron sputtering at room temperature at various oxygen partial pressures. All the films have a wurtzite structure with a strong (0002) texture measured by XRD and are almost stoichiometric as measured by inductively coupled plasma optical emission spectroscopy. The effect of oxygen concentration on grain growth has been studied by in-situ multi-beam optical stress sensor, showing internal stress going from 350 MPa to −1.1 GPa. The transition between tensile and compressive stress corresponds to the transition between metallic and oxidized mode of reactive sputtering. This transition also induces a large variation in optical properties—from absorbent to transparent, and in the resistivity—from 4×10−2Ω.cm to insulating. Finally, the piezoresistance of the thin film has been studied and showed a gauge factor (ΔR/R)/ε comprised between −5.8 and −8.5.

Influence of internal stress in optical thin films on their failure modes assessed by in situ real-time scratch analysis

In this study we present a new in situ real-time approach to perform and analyze scratch tests of transparent coating/substrates systems. This method allows for the observation of the contact region during the scratching process. As an example, thin TiO2 layers exhibiting stress levels ranging from tensile to compressive were deposited by ion beam assisted evaporation onto plastic substrates. Failure processes obtained using an increasing and a novel decreasing load scratch sequences were then linked to the internal stress in the coatings allowing one to draw a stress management diagram and to evaluate the yield stress of the TiO2 layers. This work enhances the understanding of the optical films’ failure mechanisms, and outlines a new pathway to increase measurement reproducibility.

Long-term time dependence of internal stress in lanthanum titanium oxide (H4) optical thin films.

The time variation in the internal stress of optical thin films composed of lanthanum titanium oxide (H4) deposited by ion-beam assisted deposition (IAD) and electron beam deposition was observed over a period of 10 years after deposition, and it was found that the internal stresses in the optical thin films can be controlled by optimizing the IAD conditions. Both tensile stress and compressive stress could be created by IAD, and the chemical bonding state of Ti may affect the stress behavior. The network size of the chemical bonds may affect the stress direction.