Key Engineering Materials Vols. 645-646

Abstract: In this paper, silver nanostructures were synthesized via a solvothermal method by reducing silver nitrate with ethylene glycol in the presence of poly (vinylpyrrolidone) and using NaCl, MgCl₂, AlCl₃, FeCl₃, Fe₂(SO₄)₃ , NaOH, NaBr and Na₂S as reaction inhibitor, respectively. Characteristics of the as-prepared silver nanostructures were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible (UV-vis) absorption spectrum. It is found that the mixture of nanoparticles and nanorods and nanowires can be observed in the AlCl₃ and NaOH systems, the nanorods as main products can be obtained in the MgCl₂ and NaCl and Fe₂(SO₄)₃ systems, the large scale silver nanowires as main products can be obtained in the FeCl₃ and Na₂S systems, especially in the Na₂S system, silver nanowires are very long and curved. The results indicated the reasons of the effect of the reaction inhibitors on the morphologies of silver nanostructures depend on the solubility product constant of silver salt which formed with silver ion and inhibitor anion ion in the initial stage and the properties of metal cationic ion of inhibitor. The smaller solubility product constant of silver salt or the presence of Fe³⁺ or low valence metal ion greatly facilitate the formation of one-dimensional silver nanostructures, especially to nanowires.

Abstract: The section structure and growth mechanism of oxide films on titanium alloys Ti-6Al-4V (TC4) in the oxalate, silicate and phosphate hybrid electrolyte system by anodic oxidation method were investigated. Using TC4 as anodic, stainless steel as cathode, oxide films on the surface of TC4 titanium alloy were prepared by anodic oxidation process. X-ray diffract meter, spiral-micrometer, eddy current thickness meter and scanning electron microscope were used to measure the crystal structure, thickness, microstructure and chemical composition of the film . The experimental results indicate that NaOH concentration has almost no effects on the crystal structure of oxide films which are amorphous state. The oxide films on TC4 grow through three stages. At anodic oxidation primary stage, a thicker TiO₂ films on TC4 are able to form due to an abundant oxygen atmosphere. At anodic oxidation middle stage, a middle TiO_1.5 films form due to a not enough oxygen atmosphere. At anodic oxidation latest stage, a thin TiO_1.5 films form due to a heavily insufficient oxygen atmosphere. With NaOH concentration increasing, the ingrowth velocity (V_OA) of the interface between TC4 and oxide film is faster than dissolution rate (V_AD) of the surface oxide film resulting in a slight oxide film growth. The thickness of oxide film no longer varies when V_OA is equal to V_AD.

Abstract: A new analytical potential energy functions is presented, the potential energy function is examined by 13 examples of different diatomic molecules or ions——homonuclear ground-state for neutral diatomic molecules, heternuclear ground-state for charged diatomic molecular ion, heternuclear excitation-state neutral diatomic molecules ,heternuclear excited-state for charged diatomic molecular ion, homonuclear excited-state for neutral diatomic molecule , homonuclear excited-state for charged diatomic moleculeetc.. as a consequence, the theoretical values of the vibrational energy level of molecules calculated by the potential energy function are in high-precision consistent with RKR data (Rydberg-Klein-Rees) or experimental data.

Abstract: Electro-migration has become a critical reliability issue for high density solder joints in flip chip technology, especially for current crowding and joule heat. Electro-migration force and mean time to failure of flip chip are introduced in this paper. This study employs two-dimensional simulation to investigate the distribution of current density and Joule heating in the flip chip joint. It is found that current crowding and Joule heat effect are very serious in the solder bump. The Joule heat may play important role in the void formation and thermo-migration in solder bump. And the factors that impact the distribution of current density and Joule heat are studied. The results show that the thickness of Al and UBM has great influence on the distribution of current density and Joule heat.

Abstract: Based on first-principles calculations, we have investigated atomic and electronic structures of 4H-SiC crystal doped by N, P and As elements as n-type dopants. We have obtained the bond lengths of the optimization system, as well as the impurity levels, the band structure and the density of states. The results show that the higher impurity level above the Fermi level is observed when 4H-SiC doped by N with concentration as 6.25% in these dopants, and the band gap of 4H-SiC decreases while the doping concentration or the atomic number of dopant increases.

Abstract: In order to obtain ultrasmooth polymer films, in combination with sacrificial layer a variety of impending structures in MEMS devices can be easily prepared. Two methods using polymer concentration control and spin speed adjustment to planarize polymer surface are presented. The influence of polymer concentration and spin speed on the effect of photoresist planarization is studied on. Through a large number of experiments, optimized process parameters are collected. It is found that the roughness was reduced effectively when the spin high speed was 5000rpm for 50 seconds under the condition of volume dilution ratio of 1:5. This process is able to produce a smooth surface structure.

Abstract: Based on capillary tension, surface free energy and elasticity theory, a collapse model of nanopore in C-S-H gel was created in hardened cement pastes. The stability of pore was analyzed by Gibbs free energy theory. The results show that, the capillary is more stable while the capillary is grater and rounder in the case of the aperture changing in the nanometer scope. When the aperture is changing in the scope of micrometer, the collapse possibility of the capillary is tiny. If the capillary size is fixed, the capillary is more stable while the elastic modulus of hydrated products is higher.

Abstract: In MEMS device, heavily boron doped layers are widely used as structural layers. For the manufacture of the thick heavily boron doped layer (boron concentration ≥ 5×10¹⁹ cm^-3), conventional two-step method exposes disadvantages of low efficiency and high energy consumption. Hence, multi-step method is introduced to improve the energy efficiency. In our study, simulation of diffusion in silicon is carried out to compare multi-step method with conventional method. The simulation reveals that multi-step method obtains more quantity of boron dopants and shows better potential to fabricate thick heavily boron doped layers, compared to conventional method within the same total diffusion time. As a typical application of the multi-step method, a butterfly-shape resonant is fabricated.

Abstract: Controlled composite materials arrays have been widely applied for their unique physical and chemical properties, with the aim of developing nanodevices functionality. Nanosphere lithography is a successful technique for fabricating highly ordered arrays of various materials. In this work, the polystyrene colloidal crystal template in large area on Si substrate was obtained via dipping method. The thickness of the single layer template fabricated can be precisely controlling the particle concentration and the film formation speed. The ordered arrays of Fe₂O₃ nanowires were obtained via convenient spin method on this template and heat treatment subsequently. Finally, the uniform Al/Fe₂O₃ arrays were produced by magnetron sputtering method. These periodic composite arrays cover large area substrates (of dimensions > 1 cm × 1 cm) and are uniform in terms of nanowire height and density. The arrays thickness and gaps between nanowires are easily controlled by either the diameter of colloidal crystal or the parameters of magnetron sputtering.

Abstract: At present, the chemical mechanical polishing is the only means for global planarization of an integrated circuit. After the node of the integrated circuit processing comes into 45nm, the diameter of wafer is 300mm, and the copper interconnect layer is above the 10 layer. In the same time the new low dielectric constant materials are used to the integrated circuit processing. That requires the property of the slurry used in the chemical mechanical polishing stricter. So the domestic and international companies carry out a series research works. Based on investigation and research for many years, the new alkaline copper rough slurry has been developed by the teachers and students in the Hebei University of Technology. The slurry has advantages as disadvantages. The composition of cost-effective slurry is simple and the effect of chemical mechanical polishing is good. But its stability is poor. In order to improve the stability, the compositions of the slurry need to adjust.The new alkaline copper rough slurry composed by abrasive, surface, chelating agent, oxidizing agent and deionized water. Experiments investigate the influence rule of copper polishing rate by the concentration of abrasive, the content of surface, the content of oxidizing agent and the content of chelating agent. The conclusion is arrived. When the concentration of abrasive is 4%, the content of surfactant is 10ml/l, the content of chelating agent is 10ml/l and the content of oxidizing agent is 5ml/l, the copper polishing rate keep 5000 Å /min.