Advanced Materials Research Vol. 629

Abstract: SiC_P/Cu composite was prepared by metal injection molding process. Microstructure, mechanical properties, fracture surface, and wear resistance of SiC_P/Cu composite were investigated in this study. The research results show that SiC_P/Cu were sintered sucessfully by the sintering process with hydrogen protection and high temperature of 1050°C. The tensile strength of the composites depends on the fraction and distribution of SiC particles which is resulted from microcracks nucleate in the matrix between SiC particles because of SiC particle aggregation. The tensile strengths of 5vol.%, 10vol.%, and15vol.%SiC_P/Cu are 254MPa, 291MPa and 278MPa separately. SiC particles are contribute to enhance the abrasive resitance of the composite when particle volume fraction increase from 10% to 15%.

Abstract: In this paper, a novel Z-direction flowing RTM technology using an in-mold resin distributor has been applied to the “Ex-situ” composites and the process feasibility was evaluated. The effect of injection type on distribution of fiber volume fraction and thermoplastic toughener in the composite were investigated. The results showed that perfect internal quality composite panels could be fabricated via the novel RTM technology and the injection type has some effects on distribution of fiber volume fraction along the thickness direction of the panels. After the injection and curing cycle, the typical bicontinuous phase structures were mainly observed at the interlaminar and also slightly spreading into the fibre beam.

Abstract: A top-down silicon nanowire fabrication using a combination of optical lithography and orientation dependent etching has been developed using Silicon-on Insulator (SOI) as the starting substrate. The design of experiments for the optimization of the process flow especially on the orientation dependent etching using potassium hydroxide (KOH) and Tetra-Methyl Ammonium Hydroxide (TMAH) are presented in this paper. Based on the etching experiments using silicon substrates, KOH with added isopropyl alcohol (IPA) had shown to have a consistent etch rate with acceptable silicon surface roughness as compared with its other counterparts. The concern regarding the effect of line edge roughness (LER) as a result of optical lithography was highlighted and, therefore, the optimization of the patterning procedure was also discussed and presented.

Abstract: The cast iron melting process can be based on metallic charge with pig iron or on steel scrap exclusively (i.e. synthetic cast iron). The analysis of the synthetic cast iron microstructure was presented and compared to micros of the cast iron produced on the base of pig iron. The analysis consisted of size and shape of the graphite precipitations and the metal matrix structure, too. The results of examinations and calculations were presented in form of figures and graphite distribution histograms. Based on researches conducted the authors confirmed opinions of heredity of the alloys microstructure cited in the literature.

Abstract: In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH4)2S concentrations in the passivation of n-type GaAs. Samples were degreased and immersed in aqueous (NH4)2S solutions of concentrations 22% and 10%for 10 min at 295 K, immediately prior to plasma enhanced atomic layer deposition of LaAlO3. The chemical bonding state of (NH4)2S treated GaAs surface were investigated by X-ray photoelectron spectroscopy (XPS), which indicate that Sulfur passivation can reduce intrerfacial GaAs-oxide formation. Transmission electron microscopy (TEM) was implemented to characterize the interface morphology. Finally, capacitance-voltage (C-V) and leakage current density-voltage (J-V) measurement were used to characterize the electrical properties of LaAlO3 films.

Abstract: In order to save fuel consumption by reducing the weight of automobile body, the use of aluminum alloys has a great advantage. However, how to join aluminum alloys with steels becomes a big problem in the assembly lines. Cold metal transfer (CMT) is a promising joining process for steel/Al dissimilar materials. To evaluate the shear strength and to investigate the failure modes of CMT brazed lap joints of dissimilar materials, both experimental observation and numerical simulation are performed. A numerical model for the failure criteria of the interface layer failure between steel and aluminum is developed. The interface layer of CMT brazed lap joint can be modeled by the interface element. The failure stress and failure energy at the interface element are proposed as the failure criteria for the prediction of shear strength of CMT lap joints. If steel sheet thickness becomes thicker, stress distribution and concentration at interface layer elements have some change and shear strength at the interface layer can be improved. Then the failure occurring at the interface element may transfer to the fusion line at the side of the aluminum alloy sheet.

Abstract: Fermi level pinning (FLP) and dipole formation in TiN/HfO₂/SiO₂/Si stacks are investigated. The magnitude of FLP at TiN/HfO₂ interface is estimated to be ~0 V based on dipole theory using concepts of interfacial gap states and charge neutrality level (CNL). The dipole amount at HfO₂/SiO₂ interface is experimentally extracted to be +0.33 V. These results show that dipole formation at HfO₂/SiO₂ interface is important for tuning flatband voltage of the TiN/HfO₂/SiO₂/Si stacks. Possible origin of dipole formation is demonstrated and attributed to be lower CNL of HfO₂ compared with that of SiO₂/Si stacks.

Abstract: The energy levels of polaron in a wurtzite InxGa1-xN/GaN parabolic quantum well are investigated by adopting a modified Lee-Low-Pines variational method. The ground state energy, the transition energy and the contributions of different branches of optical phonon modes to the ground state energy as functions of the well width are given. The effects of the anisotropy of optical phonon modes and the spatial dependence effective mass, dielectric constant, phonon frequency on energy levels are considered in calculation. In order to compare, the corresponding results in zinc-blende parabolic quantum well are given. The results indicate that the contributions of the electron-optical phonon interaction to ground state energy of polaron in InxGa1-xN/GaN is very large, and make the energy of polaron reduces. For a narrower quantum well，the contributions of half-space optical phonon modes is large , while for a wider one, the contributions of the confined optical phonon modes are larger. The ground state energy and the transition energy of polaron in wurtzite InxGa1-xN/GaN are smaller than that of zinc-blende InxGa1-xN/GaN, and the contributions of the electron-optical phonon interaction to ground state energy of polaron in wurtzite InxGa1-xN/GaN are greater than that of zinc-blende InxGa1-xN/GaN. The contributions of the electron-optical phonon interaction to ground state energy of polaron in wurtzite InxGa1-xN/GaN (about from 22 to 32 meV) are greater than that of GaAs/AlxGa1-xAs parabolic quantum well (about from 1.8 to 3.2 meV). Therefore, the electron-optical phonon interaction should be considered for studying electron state in InxGa1-xN/GaN parabolic quantum well.

Abstract: The objective of the work is to propose a dual visco-hypoelasticity model and a numerical procedure for the analysis of Polymeric materials subjected to large displacements and rotations. In the proposed dual approach, the Hencky’s logarithm strain measure is a function of the rotated Kirchhoff stress history in terms of a convolution equation. The material is assumed to be isotropic and the kernel functions, associated with the shear and bulk compliance moduli, are represented in Prony series. The problem is formulated within a Total Lagrangian framework and employs the Galerkin finite element method in the discretization process. Finally some numerical examples are presented in order to attest the proposed model and to verify the robustness and performance of the proposed numerical scheme.

Abstract: The second-order two-scale asymptotic expansions of the increment of temperature and the displacement for the quasi-periodic structure of composite materials under coupled thermo-elasticity condition are derived formally in this paper. The characteristic of the asymptotic model is the coupling between macroscopic scale and microscopic scale. Numerical examples including different coefficients are presented illustrating the efficiency and stability of the computational strategy. They show that the expansions to the second terms are necessary to obtain the thermal and mechanical behavior precisely, and the local and global oscillation of the increment of temperature and displacement are dependent on the microscopic and macroscopic part of the coefficients respectively.