Shear modulation force microscopy study of near surface glass transition temperatures

We report results of glass transition (T(g)) measurements for polymer thin films using atomic force microscopy (AFM). The AFM mode, shear modulation force microscopy (SMFM), involves measuring the temperature-dependent shear force on a tip modulated parallel to the sample surface. Using this method we have measured the surface T(g) of thin (17-500 nm) polymer films and found that T(g) is independent of film thickness (t>17 nm), strength of substrate interactions, or even presence of substrate.     

氧化钛薄膜调控金属铜的表面等离子体共振特性研究

提出了一种利用氧化钛薄膜对金属铜薄膜表面等离子体共振特性调制的想法。实验中首先使用电子束蒸发制备一批同等厚度的氧化钛薄膜,再利用磁控溅射方法在氧化钛薄膜上沉积厚度为5～80 nm不等的金属铜薄膜。测试结果表明,氧化钛膜层对不同厚度的金属铜薄膜表面等离子体共振增强具有不同调制效果,金属铜薄膜厚度小于20 nm时,底层的氧化钛薄膜对Cu薄膜表面等离子体共振增强效果显著,且随着金属Cu膜层厚度增加表面等离子体共振峰发生蓝移,而当金属铜膜层的厚度超过20 nm时,共振增强效果因金属Cu薄膜消光能力的上升而开始减弱。     

Experiments on the reflection of cold atoms from magnetic thin films

We report the results from a series of experiments in which ferromagnetic thin films were used as atom mirrors for laser-cooled rubidium atoms released from a magneto-optical trap. The thin films were made of cobalt and lanthanum calcium manganite (LCMO) with thicknesses between 20 and 300 nm. The magnetic domains in these thin films have a periodic structure where the spatial period is of the order of the thickness of the film, and the field decays exponentially above the film over a length scale comparable to the domain size. Thus, the neutral atoms reflect off these films from distances comparable to the thickness of the film, resulting in modification of the reflectivity due to the competition between the repulsive magnetic force and the attractive short-range forces such as van der Waals and Casimir forces. The smoothness of the atom mirror is also modified due to the proximity of the magnetic domains. The reflectivity is sensitive to the domain structure and size, which can be modified in LCMO by applying a modest external magnetic field. In this paper, we discuss the evaluation of the thin films as magnetic mirrors for atom optics, and the measurement of the van der Waals force with an accuracy of about 15%, using cobalt thin films. We also discuss some preliminary results on the temperature-dependent reflectivity for atoms near the ferromagnetic transition at 250 K in the LCMO film, and on the domain dynamics and relaxation.     

Effects of metal doping on the physical properties of ZnTe thin films

Zinc telluride (ZnTe) thin films were sublimated on a glass substrate using closed space sublimation (CSS) technique. ZnTe thin films of same thickness were tailored with copper (Cu) & silver (Ag) doping, considered for comparative study. X-ray diffraction (XRD) patterns of as-deposited ZnTe thin film and doped ZnTe samples exhibited polycrystalline behavior. The preferred orientation of (111) having cubic phase was observed. XRD patterns indicated that the crystallite size had increased after silver and copper immersion in as-deposited ZnTe thin films. Scanning electron microscopy (SEM) was used to observe the change of as-deposited and doped sample's grains sizes. EDX confirmed the presence of Cu and Ag in the ZnTe thin films after doping respectively. The optical studies showed the decreasing trend in energy band gap after Cu and Ag-doping. Transmission also decreased after doping. Resistivity of as-deposited ZnTe thin film was about 10⁶ Ω cm. The resistivity was reduced to 68.97 Ω cm after Cu immersion, and 10⁴ Ω cm after Ag immersion. Raman spectra were used to check the crystallinity of as-deposited, Cu and Ag-doped ZnTe thin film samples.     

Resonance ultrasound spectroscopy with laser-Doppler interferometry for studying elastic properties of thin films

We propose an advanced method to determine the elastic-stiffness coefficients Cij of thin films using resonance ultrasound spectroscopy (RUS). It uses free-vibration resonance frequencies of a film/substrate layered solid and derives inversely the film's Cij from the resonance frequencies. We develop a piezoelectric tripod consisting of two pinducers and one support to place the specimen on it and measure the resonance frequencies with high enough accuracy. Furthermore, we achieve mode identification by measuring deformation distributions on the vibrating specimen surface using laser-Doppler interferometry. Accurate measurements of frequencies and correct mode identification are the keys for deducing reliable Cij of the film. We applied this technique to copper thin films deposited of Si substrates. The resulting film's Cij are considerably smaller than the bulk's Cij and show anisotropy between the out-of-plane direction and in-plane direction.     

方块电阻法原位表征Cu薄膜氧化反应动力学规律

提出并建立了一种基于方块电阻测量的原位表征Cu薄膜氧化反应动力学规律的方法.利用Cu薄膜方块电阻随氧化时间的变化情况，得到氧化产物厚度与氧化时间的关系，反应动力学表征结果符合抛物线规律.还利用不同的氧化反应温度条件和对应的抛物线常数之间的关系得到体系的扩散激活能.结果表明，提出的表征方法适用于Cu薄膜氧化反应体系.     

Selective electroplating of copper lines on pre-patterned tantalum oxide thin films

Direct selective metal deposition on semiconductors is of interest to electronic device technology, in particular for interconnects and Schottky devices. In this study, we investigate selective copper electrodeposition on patterned tantalum oxide thin films. Cyclic voltammetry studies show that thick tantalum oxide thin films have insulating properties while oxide films thinner than a critical value are semiconductors. Copper films electrodeposited on tantalum oxide thin films are known to form Schottky contacts. We demonstrate the formation of copper patterns on pre-patterned tantalum oxide films by a simple process: an insulating tantalum oxide film was grown electrochemically, the film was then mechanically scratched followed by mild oxidation to produce a thin tantalum oxide film inside the scratch. Based on the differential behavior of thin and thick tantalum oxide films, metal lines were electrodeposited selectively under formation of Schottky junctions. The process demonstrated in this paper is compatible to standard processes for semiconductor device fabrication while permitting flexible prototyping for research at small scales.     

Effect of annealing conditions on structural and magnetic properties of laser ablated copper ferrite thin films

The effect of annealing conditions on structural and magnetic properties of copper ferrite thin films on (100) Si substrates was examined in detail. After deposition, the ferrite thin films were post-annealed in vacuum and in oxygen atmosphere for several hours. It is found that the crystal structure of CuFe₂O₄ thin films changed drastically depending on different heating process. A maximum magnetization was achieved in the film that was vacuum annealed and it decreased remarkably after oxygen annealing.     

Fracture force analysis at the interface of Pd and SrTiO3

The objective of this work is to develop an experimental indentation based method to determine the fracture force at the interface of Pd thin films and SrTiO₃ perovskite substrate. This paper reports on the results obtained for indentation into Pd thin films which were deposited in various thicknesses from 20 nm to 200 nm under vacuum and 300 °C substrate temperature by an electron beam physical vapor deposition. Initially, the relation between grain size, elastic module and hardness was considered as a function of film thickness. Thereafter, in developing new method, oscillating indentation was performed with different applied forces and oscillating times in order to measure the critical fracture force in each thickness. The effect of oscillating time on plastically deformed regions surrounding an indentation was schematically explained in conjunction with variation of oscillating time to determine the interfacial properties of the Pd thin film. Furthermore, the accuracy of the critical fracture force was ensured by applied force versus piling up height plot. The method is validated experimentally for the soft thin films over the hard substrate. However, further study would be essential to measure the film adhesion by means of fracture force at the interface.     

Combining Brillouin spectroscopy and laser-SAW technique for elastic property characterization of thick DLC films

Surface Brillouin spectroscopy (SBS) has been widely used for elastic property characterization of thin films. For films thicker than 500 nm, however, the wavelength of surface acoustic wave in the frequency range available for SBS is smaller than film thickness, and the SBS measures only the Rayleigh wave of the film. The laser-SAW technique, on the other hand, measures only the low-frequency portion of the surface acoustic wave dispersion and can estimate only one elastic modulus of the film (typically Young's modulus). In this work, we have combined the two methods to determine both Young's modulus and Poisson's ratio of a diamond-like carbon (DLC) film. It was found that reasonable estimates can be obtained for the longitudinal wave velocity, shear wave velocity, and Young's modulus of the film. The Poisson's ratio, however, still has a relatively large measurement error.     

温度对超薄铜膜疲劳性能影响的分子动力学模拟

用嵌入原子势的分子动力学方法模拟了温度对超薄铜膜疲劳性能的影响. 通过模拟, 首先给出了超薄铜膜的总能及应力随循环周次的变化曲线; 根据叠加经验式得出的叠加量随循环周次变化曲线, 判断出各种恒定温度下超薄铜膜的疲劳寿命. 由 200–400 K温度范围内超薄铜膜的疲劳寿命-温度变化曲线, 可以发现存在两个温度区域: 在约370 K以下, 超薄铜膜的疲劳寿命随温度升高缓慢增加, 而在约370 K以上增加较快. 建立了模型并用位错演化机制解释了超薄铜膜疲劳寿命的温度依赖关系. 关键词： 分子动力学 疲劳 温度效应 位错     

Evaluation of repeated single-point diamond turning on the deformation behavior of monocrystalline silicon via molecular dynamic simulations

A three-dimensional molecular dynamics simulation study is conducted to investigate repeated single-point turnings of a monocrystalline silicon specimen with diamond tools at nanometric scale. Morse potential energy function and Tersoff potential energy function are applied to model the silicon/diamond and silicon/silicon interactions, respectively. As repeated nano-cutting process on surfaces often involve the interactions between the consequent machining processes, repeated single-point diamond turnings are employed to investigate the phase transformation in the successive nano-cutting processes. The simulation results show that a layer of the damaged residual amorphous silicon remained beneath the surface after the first-time nano-cutting process. The amorphous phase silicon deforms and removes differently in the second nano-cutting process. By considering the coordination number (CN) of silicon atoms in the specimen, it is observed that there is an increase of atoms with six nearest neighbors during the second nano-cutting process. It suggests that the recovery of the crystalline phase from the amorphous phase occurred. Moreover, the instantaneous temperature distributions in the specimen are analyzed. Although the tangential force (F _X ) and the thrust force (F _Y ) become much smaller in the second cutting process, the material resistance rate is larger than the first cutting process. The larger resistance also induces the increase of local temperature between the cutting tool and the amorphous layer in the second cutting process.     

Combining Brillouin spectroscopy and laser-SAW technique for elastic property characterization of thick DLC films

Surface Brillouin spectroscopy (SBS) has been widely used for elastic property characterization of thin films. For films thicker than 500 nm, however, the wavelength of surface acoustic wave in the frequency range available for SBS is smaller than film thickness, and the SBS measures only the Rayleigh wave of the film. The laser-SAW technique, on the other hand, measures only the low-frequency portion of the surface acoustic wave dispersion and can estimate only one elastic modulus of the film (typically Young's modulus). In this work, we have combined the two methods to determine both Young's modulus and Poisson's ratio of a diamond-like carbon (DLC) film. It was found that reasonable estimates can be obtained for the longitudinal wave velocity, shear wave velocity, and Young's modulus of the film. The Poisson's ratio, however, still has a relatively large measurement error.     

Microstructure and electrical properties of Ba0.5Sr0.5TiO3 thin films prepared on copper foils with La2O3 buffer layers

Ba_0.5Sr_0.5TiO₃ (BST) thin films were deposited on copper foils via sol-gel method with La₂O₃ as a buffer layer. The films were processed in almost inert atmosphere so that the substrate oxidation was avoided while allowing the perovskite film phase to crystallize. The existence of a La₂O₃ buffer layer between the BST thin film and Cu foil improved the dielectric constant and reduced the leakage current density of the BST thin film. Meanwhile, the BST thin film exhibited ferroelectric character at room temperature, which was contrast to the para-electric behavior of the film without the buffer layer. Effects of La₂O₃ buffer layer on the crystallizability and microstructure of BST thin films were also investigated.     

Analysis of protective oxide films on copper—nickel alloys by photoelectron spectroscopy

Photoelectron spectroscopy was used to determine the elemental composition of thin films formed on 70:30 cupronickel exposed to sodium chloride solutions at different impressed electrochemical potentials. At anodic potentials below the passivation potential, ?0.350 V versus SCE under the experimental conditions, either no film or a film containing copper and nickel in the same ratio as the alloy existed on the alloy. At the passivation potential the spectrum of the passive film indicated primarily nickel oxide and was very similar to the spectrum obtained from a pure nickel specimen passivated in the same environment.     

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

In this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.     

Crystallization Kinetics of Lamellar Crystals Confined in Polymer Thin Films

We used dynamic Monte Carlo simulations to investigate the crystallization kinetics of flat-on lamellar polymer crystals in variable thickness films. We found that the growth rates linearly reduced with decreasing film thickness for the films thinner than a transition thickness d_t , while they were constant for the films thicker than d_t . Moreover, the mean stem lengths (crystal thickness) we calculated decreased with film thickness in a similar way to the growth rates, and the intramolecular crystallinities we calculated confirmed the film thickness dependence of the crytsal thickness. Besides, the crystal melting rates in thin films were calculated and increased with decreasing film thickness. We proposed a new interpretation on the film thickness dependence of the crystal growth rate in thin films, suggesting that it is dominated by the crystal thickness in terms of the driving force term (l–l _min) expressed by Sadler, rather than the chain mobility based on experiments. The crystal thickness can determine whether a crystal grows or melts in a thin film at a fixed temperature, indicating the reversibility between the crystal growth and melting.     

On the connection between the strength and conditions of preparation of copper and aluminum vacuum condensates

A method of measuring the microhardness and tensile strength of thin films has been devised, and this has been used to investigate copper and aluminum films obtained by condensation in vacuum. The connection between the strength of the films and the condensation conditions has been studied.     

Surface roughness modulated resistivity in copper thin films

The surfaces of metallic thin films are never flat. The resistivity in thin films is very different from that in bulk because of the unavoidable rough surfaces. In this study, we apply a quantum-mechanical method to study the resistivity in metallic thin films. The resulting resistivity formula for metallic thin films merely involves two parameters: bulk relaxation time and surface roughness. We use the formula to fit a large number of experimental data sets for copper thin films obtained using different growing methods. With an additional tuning parameter for calibrating the film thickness, the quantum formula can provide a universal fitting to most data with a satisfactory precision, regardless of their growing methods or data source.     

基于微波透射法的金属薄膜方块电阻测量理论及其应用

依据矩形波导基模的场分布表达式和电磁边界条件,解析推导了插入金属薄膜后的矩形波导透射系数,建立了考虑介质衬底影响的金属纳米薄膜微波透射系数仿真计算方法及其方块电阻的微波测量方法.运用全波电磁仿真方法对金属纳米薄膜方块电阻的微波测量装置进行了仿真验证,结果表明透射系数幅度与方块电阻的对数之间呈线性关系.采用磁控溅射工艺分别在高阻硅和玻璃两种介质衬底表面制备了不同方块电阻值的银薄膜,并测量其微波透射系数.实测结果表明,提出的方法适用于方块电阻阻值为0.05—0.5?/square的金属薄膜.研究结果对于微纳制造领域的导电薄膜方块电阻表征具有参考价值.