The effective dielectric constant of the graded composites was calculated with three different methods, namely, the nonlinear differential effective dipole approximation method (NDEDA), the Maxwell-Garnette method (MGT) and the sum rule method (Sum). In each layer of the graded composites, the distribution of the dielectric constant follows a Drude form. Our numerical results show that when the number of layers N inside the graded composites increases, a gradual transition from sharp peaks to an emerging broad continuous band is clearly obtained. Moreover, the results obtained by the MGT and sum rule methods achieve a good agreement with that by the NDEDA method when N is approaching infinity.
A simplified method with much lower time and energy costs is presented for the rapid synthesis of low thermal expansion materials of CaZr 4 P 6 O 24 , SrZr 4 P 6 O 24 and their solid solution Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 . The coefficients of thermal expansion of CaZr 4 P 6 O 24 , SrZr 4 P 6 O 24 and Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 are measured to be -1.45×10 -6 , 2.1×10 -6 and 0.26×10 -6 , respectively. Raman spectroscopic study confirms the formation of the solid solution of Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 though its symmetric and asymmetric stretching modes are obviously broadened with respect to those of CaZr 4 P 6 O 24 and SrZr 4 P 6 O 24 due to the lattice deformation by incorporation of Ca 2+ and Sr 2+ with different cation size. The shifts of the asymmetric stretching Raman modes and the librational/translational modes with temperature in Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 are between those in CaZr 4 P 6 O 24 and SrZr 4 P 6 O 24 , suggesting a cancelling effect of Ca 2+ and Sr 2+ cations in the thermal expansion of Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 .
Cracking is a serious problem in laser-clad hardfacing layers due to inhomogeneous distribution of coarse brittle phases and stress induced during rapid solidification. Tantalum carbides and borides which can form and precipitate at much higher temperatures are tentatively designed to inhibit the formation of the coarse brittle phases of chromium carbides and borides. It is found by XRD analysis that TaC, Ta4C3, TaB and Ta5B6 were formed in-situ and the coarse brittle phases were largely avoided in laser-clad Ni-based layers. It is also found that the formation sequence of these species is governed by their precipitation temperature instead of the rule determined by the standard free energy of formation. The formation of the chromium carbides and borides is inhibited due to the priority of formation of tantalum carbides and borides during rapid solidification. SEM and penetration visualization examinations show that the microstructure is markedly refined and the cracking susceptibility is significantly reduced by this method. The microhardness of the layers maintains at about 800 Hv.
ZrO2-ZrW2O8 diphasic composites with controllable coefficients of thermal expansion (CTEs) are synthesized by rapid in-situ reactive sintering with ZrO2 and WO3 as reactants. High density of ZrO2-ZrW2O8 composites without decomposition of ZrW2O8 is obtained with Y2O3 sintering additive. The CTEs of specimen with ZrO2 to ZrW2O8 mass ratio 1:1.0, 1:1.3, 1:1.5 and 1:2.0 are measured to be about 1.20×10−6, 0.31×10−6, -0.78×10−6 and -1.13×10−6 K−1, respectively. Raman mappings demonstrate homogenous dispersions of ZrO2 and ZrW2O8 in the ZrO2-ZrW2O8 composites. In addition to the role as sintering additive, some Y3+ cations enter the lattice to substitute Zr4+ in ZrW2O8, leading to an increase in disorder and a decrease in phase transition temperature of ZrW2O8 in the composites.
Abstract The surface-enhanced Raman scattering of fulvic or humic acid adsorbed on copper electrodes demonstrates a unique resolution-enhanced effect. The effect is due to chemical binding of humic substances on copper surfaces. It is deduced that only a few kinds of chemically and geometrically favorable groups or portions such as carboxylic ions and pyridine-substituted rings in the humic aggregates specifically bind onto the copper surfaces while the rest dangles in the solutions. Since the rest are far from the surface and their SERS signals are too weak to be observed, the SERS spectra only characterize the binding groups specifically and therefore they are highly resolved and simple. Such a unique resolution-enhanced effect may be valuable to reveal specific clues regarding the binding groups of humic substances, particularly at low concentrations typically found in aquatic environments. Key Words: Humic acidfulvic acidsurface-enhanced Raman scattering (SERS)copper electrode
nanoimprint was developed quickly in decades because of its ultrahigh resolution, low cost, high throughput. It has demonstrated the ability to pattern 5 nm line-width and 12 inch wafer, and is one of the support technology in NGL. This paper reported a novel nanoimprint to improve the pressure uniformity with air cushion press. The chamber is sealed by a SiO2 window with an elastic ring membrane, on which the mold is fixed . Ultraviolet light solidify resist on the wafer through this window. When air in chamber bleeded the window falled and the mold is pressed into the resist. If air leading into the chamber again, the mold separate from substrate by the elastic ring membrane, then the patterns on mold are translated onto the substrate. Experiments exhibit that this nanoimprint system can replicate features with high fidelity over a large patterning area.
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