Frontiers in Materials Science and Technology

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Authors: Zhi Hua Chen, Zheng Wu, Jian Jun Bao, Gao Qing Max Lu, Qi Qing Zhang, Lian Zhou Wang, Xian Fang Zhu
Abstract: An improved technique to fabricate PMMA/Ag core-shell nanocomposite via a two-step procedure is reported. The procedure includes an improved particle surface treatment and an improved, subsequent Ag reduction reaction strategy. Well-dispersed PMMA/Ag core-shell nanoparticles with uniform particle size distribution were successfully fabricated using this improved technique. Different functional group treatment on the PMMA particle surface led to an electronically graded transition from the covalent bond of PMMA core to the metallic bond of silver shell. The improved fabrication technique thus allows a highly tailorable size of PMMA core and controllable thickness of Ag shell, which is crucial to producing a tunable plasmon resonance signal to different bio-/chem-environments.
Authors: Xin Yi Chen, Qiang Li, Zheng Wu, Xian Fang Zhu
Abstract: Fabrication, optical property of nano coreshells and their potential applications in chemical and biological sensors have attracted much research interest. In this paper, we simulated the effect of size, structure, and dielectric properties as well embedding medium on the optical properties of gold or silver coated coreshell nanoparticle and the corresponding effects both of phase-retardation and of electron interface scattering as well as the nansize effect were discussed. Intriguing transition of the optical properties was simulated when a two-phase core-shell nanoparticle changes gradually into the single phase nanoparticle. We also obtained a good correlation of the simulation to the experimental results. Thus, the simulation has many implications and can guide further core-shell nanostructure fabrication with optimization of its optical properties.
Authors: Koay Mei Hyie, Iskandar Idris Yaacob
Abstract: Fe/Pt bimetallic nanoparticles at various molar ratios have been prepared by simultaneous reduction of FeCl2 and H2PtCl6 with hydrazine hydrate in water/Triton X- 100/cyclohexane/pentanol microemulsions at room temperature. The size, structure, composition and the magnetic properties of the resultant nanoparticles were characterized by XRD, EDX, TEM and AGM. XRD patterns indicated the formation of face centered cubic FePt nanoparticles with crystallite size in the range of 4 nm to 8 nm. Higher content of iron resulted in larger FePt nanoparticles. EDX analyses on the samples confirmed the presence of Fe and Pt elements in the particle. The composition for each particle was roughly consistent with the Fe2+ to Pt 4+ ratio of initial solution. TEM micrograph showed homogeneous fine spherical particles. The physical sizes were similar to the crystallite sizes of FePt nanoparticles calculated from XRD. The Fe/Pt molar ratio of 1 to 1 showed optimum magnetic properties with coercivity (Hc) of 68.67 Oe .
Authors: Chun Chih Lai, John M. Bell, Nunzio Motta
Abstract: A new, direct method has been developed to measure the adhesion forces of bovine serum albumin (BSA) on surfaces by using Atomic Force Microscopy (AFM) in liquid environment. We were able to measure interactions between proteins and substrate surface in PBS solution directly without any modification to the substrate or the AFM tip. Two different surfaces have been used in the experiments: mica (hydrophilic surface) and polystyrene (hydrophobic surface). The results show that a polystyrene surface is more adhesive to BSA than a mica surface. This is consistent with previous research, which assessed that hydrophobic surfaces enhance protein adhesion but hydrophilic surfaces do not, demonstrating the effectiveness of the technique.
Authors: Z. Zhang, L. Lu, P. Wu, C. Shu
Abstract: This paper reviews our systematic and exhaustive studies on the lead zirconate titanate doped with dopants using ab initio density functional theory calculations in order to understand the mechanisms behind the dopings. Different candidates of dopants were selected by screening the periodical table of elements. In our studies, group VA, VIA elements (B-site donors), group IIA elements (A-site donors), group IIIB elements (B-site acceptors), and group VB elements (A-site donor, B-site acceptor/donors) are investigated as dopants in PZT. We found that there exist different mechanisms behind the improved ferroelectric properties, especially the fatigue behaviors. For donors doping, diluted oxygen vacancy concentration and reduced electronic suppression of polarization contribute to the fatigue-free behaviors of donor doped PZT. On the other hand, for acceptor doping, acceptor-oxygen-vacancy-acceptor clusters are energetically preferred, which greatly reduce the oxygen vacancy mobility and the domain pinning effects. We expect that this study could provide important information for the experiments on PZT-based materials.
Authors: Rui Xiang Bai, H. Jiang, Cheng Yan
Abstract: In this study, the stress-strain distributions and interface failure in a BGA (Ball Grid Array) package subjected to thermal cycling were investigated using 2D and 3D finite element analyses. The viscous behavior of the adhesive material and thermal mismatch between the dissimilar materials in the package were considered. The potential failure sites in the solider and adhesive joints were analyzed.
Authors: Ling Chen, De Chang Zeng, Wan Qi Qiu, Xin Wei Shi, Zheng Yi Liu
Abstract: Arc ion plating(AIP) has higher deposition rates, whereas macro-particles (MPs) make the film properties decreasing. In this paper, AIP with or without magnetic filter (MF or AIP) and composition of AIP followed with magnetic filter (MFAIP) were designed to deposit TiN films on silicon (Si) and high-speed steel(HSS), respectively. Scanning electron microscope (SEM), nanoindentation and microscratch tests were investigated. SEM showed that both the MF and the MFAIP films had a superfine layer among the columnar crystals grown vertically against substrate surface. However, the columnar crystals of MF films were leptosomatic and well-orientational, while MFAIP ones were coarse and short, and even ragged in size and orientation. Nanoindentation test results showed the highest hardness for MF films and the lowest one for AIP films. A new parameter Scratch Crack Propagation Resistance (CPRs) was introduced to evaluate the film adhesion properties in a scratch test. MF films had the highest adhesion. AIP films were most susceptible to failure as the CPRs was the lowest, although the Lc1 was higher than MFAIP ones. It was proposed that the MPs were effectively removed with the MF, and the MF layers were superfine to improve the properties of the films.
Authors: Zaki Ahmad, M. Ahsan
Abstract: Erosion corrosion and environmental chamber corrosion studies conducted on plasma sprayed samples from three different spray dried and densified nanopowders showed good resistance to corrosion. A dense, uniform and even distribution of splats and small number of microvoids and pores offered a high resistance to erosion-corrosion in sodium chloride polystyrene slurry. The coatings offer a high resistance in salt spray chamber environment.
Authors: Jiang Ting Wang, Peter D. Hodgson, Jing De Zhang, Chun Hui Yang
Abstract: To combine the merits of both metals and ceramics into one material, many researchers have been studying the deposition of alumina coating using plasma spray on metal substrates. However, as the coatings are deposited at a high temperature, residual thermal stresses develop due to the mismatch of thermal expansion coefficients of the coating and substrate and these are responsible for the initiation and expansion of cracks, which induce the possible failure of the entire material. In this paper, the residual thermal-structural analysis of a Fe3Al/Al2O3 gradient coating on carbon steel substrate is performed using finite element modelling to simulate the plasma spray. The residual thermal stress fields are obtained and analyzed on the basis of temperature fields in gradient coatings during fabrication. The distribution of residual thermal stresses including radial, axial and shear stresses shows stress concentration at the interface between the coatings and substrate. The mismatch between steel substrate and composite coating is still the dominant factor for the residual stresses.
Authors: Chao Chang Arthur Chen, Wei En Fu, Meng Ke Chen
Abstract: Subsurface residual stresses of tungsten films induced by Chemical Mechanical Polishing (CMP) processes were investigated by the Grazing Incident X-Ray Diffraction (GIXRD). Basis of the GIXRD measurement was introduced and the experiments were conducted for residual stress of tungsten film measurements. Experimental procedures of the GIXRD measurements were presented. The obtained residual stresses value of tungsten films from 800 nm to 400 nm varies from 1086.1 ± 105.2 MPa to 1670.6±103.4 MPa prior and after CMP process.

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