Accurate vibration analysis of thick, cracked rectangular plates

This work applies the Ritz method to accurately determine the frequencies and nodal patterns of thick, cracked rectangular plates analyzed using Mindlin plate theory. Two types of cracked configuration are considered, namely, side crack and internal crack. To enhance the capabilities of the Ritz method in dealing with cracked plates, new sets of admissible functions are proposed to represent the behaviors of true solutions along the crack. The proposed admissible functions appropriately describe the stress singularity behaviors around a crack tip and the discontinuities of transverse displacement and bending rotations across the crack. The present solutions monotonically converge to the exact frequencies as upper bounds when the number of admissible functions increases. The validity and accuracy of the present solutions are confirmed through comprehensive convergence studies and comparison with the published results based on the classical thin plate theory. The proposed approach is further employed to investigate the effects of the length, location, and orientation of crack on frequencies and nodal patterns of simply supported and cantilevered cracked rectangular plates. The results shown are the first ones available in the published literature.     

Study for infrared spectroscopic ellipsometric properties of diamond films

Spectroscopic ellipsometric measurements in infrared region (2.5 - 12.5 μm) are carried out to characterize the structure and quality of diamond films grown by microwave plasma chemical vapor deposition (MPCVD) and hot filament chemical vapor deposition (HFCVD), respectively. It is found that the establishment of appropriate models has the strongest influence on the fit of ellipsometric spectra. The best fit is achieved for MPCVD film with a 77.5-nm middle layer of SiO2, and for HFCVD film with an 879-nm rough surface layer included by Bruggeman effective medium approtimation (EMA). Finally the refractive index and the extinction coefficient are calculated for both films, the results show that the film grown by MPCVD is optically much better than that grown by HFCVD at infrared wavelengths.     

椭偏光谱测量中椭偏参数的灵敏度分析

在对椭圆偏振测量的基本原理进行了简单介绍和推导后,讨论了椭圆偏振测量中椭偏参数关于薄膜参数的灵敏度以及入射角对椭偏参数的影响,并进行了具体的仿真分析,得到如下结论：椭偏参数Delta对薄膜光学常数和薄膜厚度变化的灵敏度明显高于椭偏参数Psi。在椭偏数据处理中,椭偏参数Delta的测量精度直接影响薄膜光学常数和薄膜厚度的拟合精度。为了提高椭偏参数Delta的测量精度,可以选择入射角在膺布儒斯特角附近。所得结论对高精度椭偏测量具有指导意义。     

An ellipsometric method for the characterization of macroscopically heterogeneous films

In conventional compensating ellipsometry one usually measures a polarizer and an analyzer angle and computes from them two optical parameters of a layered structure, provided the individual layers are laterally homogeneous. In order to study a macroscopically heterogeneous thin layer with domains larger in lateral dimension than the wavelength of light, we suggest that furthermore the light intensity be measured at compensation. The additional light intensity, δI, exceeding the value for a homogeneous layer, results from the incoherent superposition of the light reflected from the different domains. From the polarizer and analyzer angles at compensation one obtains the arithmetical average of the optical single domain properties, whereas δI quantifies the heterogeneity, i.e. the relative areas of the domains and the differences in their optical thickness. In special cases this allows for the determination of the optical properties of the domains separately. The model is tested with films composed of two phases, the difference being a fatty acid bilayer of 5.6 nm in thickness. Applications of the model include the study of phase transitions in lipid monolayers.     

椭圆偏振法数据处理软件设计

以C^ Builder 6．0为开发工具,成功设计和编制了一套椭偏法数据处理软件．它具有求解透明膜厚度、折射率和金属复折射率以及绘制(n,d)～(Ψ,△)列线图的功能,求解膜厚和折射率精度分别达到0．01nn、和0001．实验表明该软件的求解结果是准确和可靠的．     

Anomalous scaling for thick electrodeposited films

Anomalous surface roughness scaling, where both the local and the large-scale roughness show a power-law dependence on the film thickness, has been widely observed. Here we show that the value of the local roughness exponent in the early stages of Cu electrodeposition depends on the deposition potential. However, initial anomalous scaling can lead to two qualitatively different types of behavior for large film thickness (t>/ or =4 microm). For Cu films electrodeposited with forced convection at high potential and current density, the anomalous scaling is transient: the local roughness saturates for the thickest films studied. When Cu films are electrodeposited at similar potential and current density but with reduced convection, no saturation of the local roughness is observed. Instead the film forms overhangs such that the surface height becomes a multivalued function of the lateral position.     

Accurate free vibration analysis of thick laminated circular plates with attached rigid core

This paper deals with the free vibration behavior of laminated transversely isotropic circular plates with axisymmetric rigid core attached at the center. The governing equations of motion are obtained based on Mindlin's first-order shear deformation plate theory. Two possible categories of vibration modes related to up-down translation of the core and wobbly rotation of the core about a diameter are studied. Accurate natural frequencies hitherto not reported in the literature are presented for a wide range of thickness-to-radius ratio, inner-to-outer radius ratio, mass and moment of inertia ratios of the core and various boundary conditions at the outer edge of the plate. Numerical results are compared with those of a three-dimensional finite element method (3-D FEM) to demonstrate the high accuracy and reliability of the current analysis.     

Simple method for the complete optical analysis of very thick and weakly absorbing films

In this paper a method for the determination of the thickness and spectral dependences of the optical constants characterizing very thick and weakly absorbing thin films located on nonabsorbing substrate is presented. Within the framework of this method the positions and values of the extrema in the spectral dependences of the reflectance and transmittance are utilized for evaluation the values of the optical parameters mentioned above. The main advantage of the method is that the values of the optical parameters can be determined by means of explicite formulae with relatively high accuracy. The method is utilized for the complete optical analysis of magnetic garnet films.     

基于椭圆偏振显微镜的纳米级磁头润滑膜观测方法

针对磁头飞行导致液体润滑膜的转移研究以及润滑膜在磁头上的动态变化特性观测问题,基于改进的垂直物镜的椭圆偏振显微镜,提出起偏器相移方法的磁头表面润滑膜厚度计算模型,实现了润滑膜厚度的测量。实验以非极性润滑剂Z03覆盖的磁头为样品对椭圆偏振显微镜进行标定,以极性润滑剂Zdol4000作为样品,对其在磁头表面的去湿现象进行观察。该方法测量精度可达0.37 nm,分辨力约0.36 μm,可为其他纳米级薄膜观测提供一定的技术参考。     

In situ ellipsometric study of electrodeposition of manganese films on copper

Electrodeposition of manganese film on copper substrate in a chloride-based solution was investigated by cyclic voltammetry (CV) in combination with in situ spectroscopic ellipsometry (SE). The SE results at different polarization potentials show that the hydrogen evolution has no influence on the SE measurement. The CV results, confirmed by SE data, indicate the starting reduction and oxidation potentials of manganese. The potential for electrodeposition of manganese film with the maximum thickness was determined based on the SE measurements. The SE results show that the manganese film is relatively loose, which is consistent with the observation by scanning electron microscopy (SEM). The growth kinetics of manganese electrodeposition was proposed according to the SE measurements.     

Coupled Ag nanocrystal-based transparent mesh electrodes for transparent and flexible electro-magnetic interference shielding films

In this study, we developed a fabrication method of conductive and transparent Ag mesh electrodes on flexible polymer film at temperatures lower than 100?°C. Random patterned Ag mesh film was fabricated on a flexible PET substrate over 15?×?15?cm² by a self-assembly process. It became conductive by a coupling process at low temperatures. The coupled Ag mesh film showed more than 88% transmittance in visible wavelength and less than 8.2?Ω?sq^?1 in sheet resistance with figure of merit (FoM) value of 350. This transparent flexible EMI shield film fabricated with a coupled Ag mesh pattern showed high EM shielding effectiveness of ?23?dB?at 1.5–10?GHz frequency with a high transparency of 88%.     

Characterization of thick HVPE GaN films

The morphology of the top surface for HVPE GaN layers grown on a MOCVD GaN template with a thin LT-AlN interlayer was investigated. This surface is characterized by the formation of numerous hillocks associated with screw dislocations or nanopipes. Their size is large and may reach more than 1 mm. The rocking curves of the 002 and 102 reflections correspond to a relaxed layer. The HREM images of the as-deposited and annealed interlayers show a perfect atomic structure with a very abrupt AlN/HVPE GaN interface. Thus, the deposition of the LT-AlN layer has promoted the growth of an HVPE layer with an excellent crystalline quality.     

用迈克耳孙干涉仪测量厚透明材料折射率

使用迈克耳孙干涉仪测量了厚透明材料的折射率.在光路中一半视场平行放入待测材料,对应的条纹出现压缩,根据条纹隐入和涨出计算待测材料的折射率,并进行了相关实验和误差分析.应用Zemax软件对实验进行了模拟,验证了其可行性.     

In situ ellipsometric analysis of optically inhomogeneous layers

The problem of analysis and processing of data of in situ ellipsometric measurements obtained in the process of growth of layers on multilayer optically inhomogeneous structures is considered. It is shown that the experimental data allow one to determine, for an arbitrary structure, all its reflective properties described by the complex reflection coefficients R_p and R_s or, alternatively, by a pair of other complex quantities, namely, by the ellipsometric parameter ρ and parameter ϕ characterizing uniformity of the structure. A numerical algorithm is proposed that is applicable to an arbitrary number of experimental points, which allows one to reduce the problem of optimization to a search for a single complex quantity. Numerical simulation performed using this algorithm demonstrates good convergence and stability to both random errors of the measurements and systematic errors.     

Electromechanical properties of graphene transparent conducting films for flexible electronics

We report a systematic study of the electromechanical properties of graphene films for flexible transparent conducting electrodes. The flexibility of graphene films, which were grown using a chemical vapor deposition (CVD) method and transfer process on polyethylene terephthalate (PET) substrates, was investigated using a lab-made inner/outer bending, twisting and stretching test system. The electromechanical properties as a function of the change of bending radius, twisting angle and strain distance were evaluated by measuring the change in resistance. The change in resistance during the inner bending test was less than 8% even when the bending radius was 3 mm. Additionally, the results of the inner bending fatigue test showed a constant resistance throughout 2000 bending cycles. However, in the outer bending test, the resistance increased substantially when the bending radius was smaller than 10 mm. Therefore, we can expect that more cracks form between the grains of graphene during the outer bending test. The twistability and stretchability of the graphene film were also investigated. Both twisting and stretching tests show gradually increasing resistances according to the twisting angle and stretching distance. These results provide useful information regarding the electromechanical properties of graphene transparent conducting films for the development of flexible electronics.     

Spectroscopic ellipsometric characterization of organic films obtained via organic vapor phase deposition

Thin films of Tris(8-hydroxyquinoline)-aluminum(III) (Alq₃) and N,N-Di-[(1-naphthyl)-N,N-diphenyl]-(1,1-biphenyl)-4,4-diamine (-NPD ) were deposited on large-area silicon substrates by means of the recently developed organic vapor phase deposition (OVPD) method. Variable-angle spectroscopic ellipsometry was used to measure the optical constants of OVPD Alq₃ and -NPD layers in the 0.8–5 eV energy range. The absorption onset which defines the lower limit of the optical band gap was found to be at 2.65 eV and 2.9 eV for Alq₃ and -NPD , respectively. Additionally, the thicknesses of the layers as well as the thickness profiles of the organic thin films were determined along the 8 diameter of the wafers. The thickness analysis revealed large-area uniform deposition of the films. PACS 78.20.Ci; 81.70.Fy; 81.15.-z     

The accuracies of photometric, polarimetric and ellipsometric methods for the optical constants of thin films

The inherent accuracies of various techniques for determining the optical constants of thin films have been assessed by computing the errors produced in n and k by known experimental errors in the optical functions being measured. The results are presented as arrays of error parallelograms in the n–k plane covering d/λ from 0.001 to 0.20 and θ from 5° to 85°.The largest regions of accuracy, in the form of annular quadrants, were obtained using the mixed photometric and polarimetric functions at small angles of incidence. Ellipsometry gives similar results at large angles of incidence but for photometry and for polarimetry the accurate regions were in the form of two lobes.The effects of errors in x and θ were also considered.     

Convenient preparation of ITO nanoparticles inks for transparent conductive thin films

We synthesized Pt and Ag nanowires using a mesoporous silica, SBA-15, as templates. The obtained nanowires are a few micrometers (~4???m) long and 7?nm in diameter. The nanowires are free from bundling and, thus, can be separated as single nanowires. The successful synthesis of such nanowires requires a few considerations. In general, SBA-15 has microchannels on the walls through which the mesopores are interconnected when synthesized at 100?°C or higher. We, therefore, synthesized SBA-15 at a low temperature (80?°C) to eliminate the microchannels. Impregnation of the metal precursors and reduction of them into metals forms metal particles outside the pores in addition to the desired metal nanowires inside the pores. Surface alkylation of SBA-15 prohibits the nucleation of metal on the external surface and exclusively forms the nanowires. Finally, the introduction of surface passivating agent, an alkylthiol, during the removal of the template keeps the nanowires from interacting with one another. The Pt and Ag nanowires so-synthesized were characterized by electron microscopy.     

Resistance switching in transparent magnetic MgO films

We have studied the abrupt and hysteretic changes of resistance in MgO-based capacitor devices. The switching behavior is discussed in terms of the formation and rupture of conduction filaments due to the migration of structural defects in the electric field, together with the redox events which affects the mobile carriers. The results presented in this paper suggest that MgO transparent films combining ferromagnetism and multilevel switching characteristics might pave the way for a new method for spintronic multibit data storage.     

Preparation of transparent BN films with superhydrophobic surface

A novel approach was investigated to obtain the superhydrophobicity on surfaces of boron nitride films. In this method boron nitride films were deposited firstly on Si(1 0 0) and quartz substrate using a radio frequency (RF) magnetron sputtering system, and then using CF₄ plasma treatment, the topmost surface area can be modified systematically. The results have shown that the water contact angle on such surfaces can be tuned from 67° to 159°. The films were observed to be uniform. The surfaces of films consist of micro-features, which were confirmed by Atomic Force Micrograph. The chemical bond states of the films were determined by Fourier Transform Infrared (FTIR) Spectroscopy, which indicate the dominance of B-N binding. According to the X-ray Photoelectron Spectroscopy analysis, the surface of film is mainly in BN phase. The micro-feature induced surface roughness is responsible for the observed superhydrophobic nature. The water contact angles measured on these surfaces can be modeled by the Cassie's formulation.