On the stress distribution at scratching of thin film structures

Scratching of thin film/substrate structures is studied theoretically and numerically. In most cases, the material behavior of the film as well as the substrate is described by classical elastoplasticity accounting for large deformations; further, pressure-sensitive flow models are considered. The main efforts are devoted toward an understanding of the influence from the film/substrate boundary on the stress distribution at scratching but for comparative reasons, scratching of homogeneous materials are also studied and pertinent results presented. Among other things, the results are discussed in relation to delamination initiation and growth at scratching. The numerical investigation is performed using the finite element method, and the numerical strategy is discussed in some detail. The most important finding given by the present study is that high shear stresses are the main driving force for delamination initiation and growth along the film/substrate interface. It was also noted that the influence from pressure-sensitive flow on the stress fields related to delamination initiation is small, both quantitatively and qualitatively.     

Theory of combustion of thin film structures

The problem of combustion of thin film compositions is considered in view of the finite reaction rate at the interfaces. Formulas defining the combustion rate in the diffusion mode and the mode limited by the boundary kinetics are obtained. On the basis of these formulas, techniques for estimating the parameters of the diffusion and boundary kinetics are proposed. Unsteady combustion modes are studied, and features of the transition from the kinetic to the diffusion mode are revealed.     

Patterned Si thin film electrodes for enhancing structural stability

A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.     

电沉积Co-Mo合金薄膜的结构和热稳定性

通过电沉积,在铜基体上制备了Co-Mo合金薄膜.讨论了薄膜组成与结构以及非晶合金的晶体结构与热处理温度的关系.测定了薄膜磁性能(饱和磁化强度和矫顽力)随热处理温度变化的关系曲线.结果表明,薄膜中钼含量(质量分数)为6.05%～30.03%时,镀态Co-Mo合金薄膜具有非晶态结构;经连续升温到400℃并热处理1.5 h后,Co-Mo非晶态合金发生晶化,且随着薄膜中钼含量的增加,薄膜的晶化温度提高,热稳定性增强;在较高温度(高于500 ℃)下热处理后,Co-Mo非晶态合金晶化,并析出单一的hcp-Co相;热处理后,Co-Mo合金薄膜的软磁性变差.     

Production of thin graphite sheets for a high electrical conductivity film by the mechanical delamination of ternary graphite intercalation compounds

Herein we propose a production scheme for conductive films composed of thin graphite sheets with high crystallinity and polymeric resin. The crystalline graphite sheets were successfully produced from natural graphite powder by solution-phase synthesis of graphite intercalation compounds (GICs), following a wet planetary-ball milling under mild conditions. The shear forces in the milling pot lead to a peeling of graphite flakes. Taking into consideration the interlayer bonding force, the delamination should be preferentially done from the expanded GICs interlayer rather than intrinsic graphite one. Some composite films derived from the phenolic resin and flaky graphite sheets displayed much higher electrical conductivities compared to the film from the feed graphite particles. We also demonstrate the stage structure of synthetic GICs affected the film conductivity. The composite films made from exfoliated products of ground (around stage IV) GICs exhibited high electrical conductivity with a small amount of the graphite sheets.     

On the application of liquid‐crystal thermography for the nondestructive detection of delamination in composite structures

To prevent the catastrophic failure of composite structures, several nondestructive testing methods have been developed. In this study, a new technique to evaluate these structures by using thermochromic liquid crystal (TLC) thermography is presented. Temperature gradients produced by sensitive liquid‐crystals are used to detect delamination in composite specimens. The effects of constituent materials and delamination size/location are investigated. The results from TLC thermography are compared to those from infrared thermography. Finally, advantages/disadvantages of the new method are discussed. On the basis of the results from this study, it could be concluded that the TLC thermography can be used as an inexpensive nondestructive testing method in inspection of composite structures. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Regulation of film thickness, surface roughness and porosity in thin film growth using deposition rate

This work focuses on distributed control of film thickness, surface roughness and porosity in a porous thin film deposition process using the deposition rate as the manipulated input. The deposition process includes adsorption and migration processes and it is modeled via kinetic Monte Carlo simulation on a triangular lattice with vacancies and overhangs allowed to develop inside the film. A distributed parameter (partial differential equation) dynamic model is derived to describe the evolution of the surface height profile of the thin film accounting for the effect of deposition rate. The dynamics of film porosity, evaluated as film site occupancy ratio, are described by an ordinary differential equation. The developed dynamic models are then used as the basis for the design of a model predictive control algorithm that includes penalty on the deviation of film thickness, surface roughness and film porosity from their respective set-point values. Simulation results demonstrate the applicability and effectiveness of the proposed modeling and control approach in the context of the deposition process under consideration.     

低温制备二氧化钛光催化剂薄膜的研究进展

详细介绍了化学浴、连续离子层吸附反应、液相沉积法、溶胶-凝胶法、粘结剂法和溅射法等低温制备TiO2薄膜的常用方法,概述了其制膜原理和薄膜性能,指出低温制备TiO2晶态薄膜技术目前存在的问题及未来的发展方向。     

The structures and positive magnetoresistance of metallic Sr2CrWO6 epitaxial thin film

Double perovskite Sr₂CrWO₆ films have been prepared on SrTiO₃ (111) substrates by pulsed laser deposition in high vacuum (10^?5 Pa). X-ray diffraction patterns indicate that the films are (111)-oriented. Both atomic force microscopy (AFM) and cross-section transmission electron microscopy (TEM) images prove that the films have very smooth surfaces. Detailed microstructures given by high resolution transmission electron microscopy (HRTEM) further confirm that the films are epitaxial with sharp and coherent substrate/film interface. Well saturated magnetization–magnetic field hysteresis loop is observed with the saturation magnetization of 1.2 μ_B/formula unit at 10 K. The films show metallic transport behavior and large positive magnetoresistance (～180% at 10 K). The structure–property relationship is discussed in detail.     

The influence of oxygen partial pressure on the performance and stability of Ge-doped InGaO thin film transistors

The device performance and bias stability of radio frequency (RF) sputtered Ge-doped InGaO (GIGO) thin film transistors (TFTs) were investigated as a function of oxygen partial pressure during the deposition step. At low oxygen partial pressure, the electrical performance and stability of GIGO TFTs were significantly improved with a decrease of oxygen deficient bonding states, suggesting strong oxygen bonding ability of Ge atoms. We demonstrate that these changes can be corroborated with the evolution of the electronic structure, such as band alignment and band edge states below the conduction band, as measured by X-ray photoelectron spectroscopy and spectroscopic ellipsometry analysis. As the oxygen partial pressure decreased, the energy difference between the conduction band minimum and Fermi level and the deep band edge states was decreased. In particular, it was revealed that, with an increase of oxygen partial pressure, the relative energy level of the band edge states was shifted to a deeper level within the bandgap.     

MOCVD growth of epitaxial pyrochlore Bi2Ti2O7 thin film

Growth of Bi₂Ti₂O₇ films on the substrates having cubic-structure was investigated by metal organic chemical vapor deposition (MOCVD). (1 0 0), (1 1 0) and (1 1 1)SrTiO₃ single crystals, (1 1 1)-oriented Pt- and SrRuO₃-coated (1 1 1)SrTiO₃ were used as substrates together with (1 1 1)Pt/TiO₂/SiO₂/Si. Peaks originated to Bi₂Ti₂O₇ phase were not detected on (1 0 0), (1 1 0) and (1 1 1)SrTiO₃ substrates. On the other hand, (1 1 1)-oriented Bi₂Ti₂O₇ phase was ascertained to be prepared on (1 1 1)Pt//(1 1 1)SrTiO₃ and (1 1 1)Pt/TiO₂/SiO₂/Si substrates in spite of the almost the same lattice parameters of SrRuO₃ and SrTiO₃ with Pt. From the pole figure measurement, Bi₂Ti₂O₇ films prepared on the (1 1 1)Pt//(1 1 1)SrTiO₃ substrates were ascertained epitaxial grown, (1 1 1)Bi₂Ti₂O₇//(1 1 1)Pt//(1 1 1)SrTiO₃, while that on the (1 1 1)Pt/TiO₂/SiO₂/Si were (1 1 1)-one-axis-oriented Bi₂Ti₂O₇ with in-plain random. The easy growth of (1 1 1)-oriented Bi₂Ti₂O₇ film on (1 1 1)Pt layer can be explain by the existence of the sub-unit in (1 1 1)Pt plane consist of three Pt atoms.     

Correlation of film structure and molecular oxygen reduction at nitrogen doped amorphous carbon thin film electrochemical electrodes

Nitrogen doped amorphous carbon (a-C:N) thin film electrodes with a range of film structures have been deposited using a filtered cathodic vacuum arc system. The correlation between film structure and electro-reduction of molecular oxygen in aqueous media at the electrodes has been explored. In aqueous 0.1 M NaOH, dioxygen reduction is inhibited at all the a-C:N electrodes compared with that at glassy carbon electrodes. The potential of the dioxygen reduction current peak shifts negatively at a-C:N electrodes as the sp³ C fraction in the a-C:N materials increases, while the current peak height decreases simultaneously. The a-C:N electrodes possess high sensitivity for investigating the mechanism of dioxygen reduction. It was found that the catalytic H₂O₂ reduction to H₂O on carbon materials is attributed to oxygen species at sp² C sites.     

High quality homoepitaxial diamond thin film synthesis with high growth rate by a two-step growth method

Homoepitaxial diamond films grown in the condition of CH₄/H₂ ratio lower than 0.15% in a microwave-assisted plasma chemical vapor deposition system had excellent electrical and optical properties without any unepitaxial crystallites (UCs). Under such a low CH₄ concentration condition, however, the growth rate becomes too slow to obtain a useful thickness. In order to overcome this problem, we attempted a two-step growth method. In the first step the substrate surface was treated by homoepitaxial growth of diamond in the presence of 0.05% CH₄ in H₂; in the second step the CH₄ concentration was increased. By considering the origin of UCs with cross-sectional transmission electron microscope studies, it was found that this method is based on surface improvement of the initial substrate by means of ultra-low CH₄ concentration growth. This method was quite useful for obtaining high quality films, with high growth rate and reproducibility.     

Evidence for the rate determining step at the solution—oxide film interface in the anodic growth of thin oxide films at platinum and nickel electrodes in aqueous solutions

The rates of growth of anodic oxide films at Pt in acid and alkaline solutions and Ni in alkaline solutions are compared. In acid solutions, the rates are pH independent. In alkaline solutions, they are affected by pH. The exchange current densities, i₀, in alkaline solutions increase one decade as pH increases one unit. The dependence of i₀ on pH is not expected for the model of high field assisted formation of films with either the step at the metal—oxide film interface or a step within the film as rate determining. It is suggested that a process at the oxide film—solution interface is rate determining with OH^? as reaction species. In acid solutions, too, this step is rate determining but with H₂O as reacting species. The possibility that this step can be rate determining is usually overlooked in analyses of growth of anodic films.     

Hierarchical microstructure growth in a precursor-derived SiOC thin film prepared on silicon substrate

Silicon oxycarbide film deposited on a silicon substrate has shown superior electrical conductivity relative to its monolithic counterpart. In this work, the evolution of different microstructures detected on the SiOC film reveals its hierarchical microstructure. The existence of sp²-hybridized carbon domains has been unambiguously confirmed by means of Raman spectroscopy and transmission electron microscopy corroborated with electron energy loss spectroscopy. The diffusion coefficient of carbon in silica and its dependence on temperature were studied by assessing energy-dispersive X-ray spectroscopy profiles taken from the cross-sections of samples annealed at temperatures in the range from 1100°C to 1400°C. The activation energy for diffusion of carbon in silica was determined to be approximately 3.05 eV, which is significantly lower than the values related to the self-diffusion of silicon and oxygen. The microstructural evolution of precursor to SiC_nO_4-n and SiC serves as migration path of sp²-hybridized carbon to the SiO_x layer. With increasing temperature, the formation of microscale carbon-rich segregation is promoted while the SiOC film becomes thinner.     

Macroscopic investigation of hydrate film growth at the hydrocarbon/water interface

Clathrate hydrate film growth has been investigated at the hydrocarbon/water interface for cyclopentane and methane hydrate, using video microscopy combined with gas consumption measurements. Hydrate formation was characterized by the film thickness, propagation rate across the hydrocarbon/water interface, and gas consumption. The film formation processes of cyclopentane and methane hydrate were measured over the temperature range of 260-273 K and pressure range of atmospheric to 8.3 MPa. Hydrate formation was initiated by the propagation of a thin, porous film across the hydrocarbon/water interface. This thickening rate was strongly dependent on the hydrate former solubility in the aqueous phase, in the absence and presence of hydrate. The methane hydrate film thickness began at about and grew to a final thickness (20-) which increased with subcooling. The cyclopentane hydrate film thickness began at about and grew to a final thickness (15-) which again increased with subcooling. The hydrate film grew into the water phase. Gas consumption indicated that the aqueous phase supplied hydrate former during the initial hydrate growth, and the free gas supplied the hydrate former for film thickening.     

Investigating the stability of falling films at round vertical film carriers under high pressure

The instability of a falling film under high pressure (droplet formation) was characterized by the dimensionless Reynolds, Weber, and fluid-film numbers and could be predicted in a characteristic diagram. Incipient droplet formation was achieved with the given material properties of the system, i.e., at a constant K_F number, by increasing the volumetric flowrate of the liquid phase. The investigations were performed with the material systems α-tocopherol/CO₂ and squalane/CO₂ in the pressure ranges between 8 and 35 MPa and 6 and 12 MPa, respectively, at four different temperatures between 313 and 353 K. The volumetric flowrate of the liquid phase was varied between 10 and 300 ml/min, whereas the speed of the supercritical gas phase in counter-current flow to the falling film in the falling-film cell was kept constant at 7 mm/s. The high-pressure falling-film cell used for this purpose had an external diameter of 104 mm, an internal diameter of 34 mm, and a total length of 710 mm. The diameter and length of the cylindrical falling-film carrier were 10 and 500 mm, respectively.     

Deposition and characteristics of iron–silicon thin film catalyst for CNT growth

Fe–Si catalyst thin films for the growth of carbon nanotubes were prepared using co-sputter deposition. As-deposited Fe–Si films consist of different amounts of α-Fe and amorphous Si. The amount depends on the Si concentration in the film. Hydrogen plasma etched Fe–Si films become particles having different sizes. The particle size is also dependent on the Si concentration. Correlation among the Si concentration, the particle size, and the growth rate of carbon nanotube was made. Optimal growth of carbon nanotubes at 370 °C was obtained at an average particle size of 45 nm or a Si concentration of 21%.     

Effect of potential on bismuth telluride thin film growth by electrochemical atomic layer epitaxy

In the present study, bismuth telluride compound thin film was grown by means of electrochemical atomic layer epitaxy (ECALE) with an automated thin layer flow cell deposition system. The dependence of the Bi and Te deposition potentials on Pt electrode was studied. Because developing a contact potential between the substrate and the growing semiconductor, the deposition potential adjustment is necessary for the first 30 or more cycles of each component. The dependence of the deposit as a function of the deposition potential adjustment slope has been investigated. The results show that an excess elemental Bi existed at a slope of −2 mV/p (p indicates per cycle), indicating that this is a lack of deposition at the potential. Single-phase Bi₂Te₃ compound could be obtained between −4 and −6 mV/p. Bi₂Te₃ and Bi₄Te₃ coexistence is observed at a slope of −10 mV/p. The EDS data indicates that the stoichiometry of compound is consistent with XRD result. SEM studies show that the deposits are inhomogeneous and have an micron sized particles morphology.