失晶粗化金属界面提高金—塑界面结合强度

金—塑界面存在于多种金—塑结构的修复体和各类金属、金—瓷修复体的粘固面,该界面的结合强度关系到修复体的持久性。因此,在提高树脂材料性能的同时,金属界面的处理是重要课题。

金属表面失晶粗化法在义齿制作过程中的应用

失晶粗化金属表面是一种增强金属—塑料结合强度的新方法,由马轩祥等提出应用长方形晶体制作预成含晶蜡片粗化金属界面,利用可溶性晶体盐在蜡型表面陷入,溶去晶体盐后,蜡型表面形成一定粒度的凹陷面,通过包埋铸造,形成一定形状的粗糙面。这一粗糙面和塑料或粘结剂结合后,靠增加结合界面面积和机械结合提高界面结合强度。

失晶粗化金属界面提高金—塑结合强度的研究(Ⅱ)

在蜡型表面陷入晶体盐并溶出晶体,经包埋、铸造后,金属表面形成一定形状的凹陷表面,是提高金—塑结合强度的新方法。本研究以测试抗张、剪切结合强度为手段,证明了粗化处理后的效果,并与目前临床常用的方法作了比较,显示了该处理方法的优点。文中还介绍了失晶粗化金属表面的方法。作者倡议在义齿制作中对铸件的结合面或粘固面进行常规粗化处理,提高金、塑结合的强度和持久性。

失晶法粗化金属表面提高金属—塑料结合强度的研究

金属—塑料的界面结合强度关系到修复体的远期效果。失晶粗化法是利用廉价的可溶性晶体盐陷入蜡铸型表面内,失晶后再铸出有粗化表面的金属修复体,用以增加其与塑料结合强度。结果经统计学分析具有科学性。

Effect of Lattice Mismatch on Luminescence of ZnO/Si Hetero-Structure

The photoluminescence （PL） and Raman spectra of undoped ZnO films deposited directly on Si substrate （sample A）,on Si substrate through a SiC buffer layer （sample B）,and on a ZnO crystal wafer （sample C） are investigated. There are emission peaks centered at 3.18eV （ultraviolet,UV） and 2.38eV （green） in these sampies. Comparing the Raman spectra and the variation of the PL peak intensities with annealing atmosphere, we conclude that the luminescence of the samples is related to the tensile strain in the ZnO film due to the lattice mismatch between the film and the substrate. In particular, the tensile strain reduces the formation energy of OZn antisite oxygen defects,which generate the green emission center. After annealing in oxygen-rich atmosphere, many OZn defects are generated. Thus, the intensity of green emission in ZnO/Si hetero-structure materials increases due to tensile strain in ZnO films.

Studies on Crystalline Growth of MoFe Protein from a nifZ Deleted Strain of Azotobacter vinelandii

Under a given condition of crystallization, dark brown short rhombohedron crystals could be obtained from Δ nifZ MoFe protein purified from a nifZ deleted mutant strain of Azotobacter vinelandii Lipmann. Systematic studies on the effect of concentrations of PEG 8000,MgCl 2, NaCl,Tris and buffer pH on the crystallization and crystal growth of the protein showed that the protein could not be crystallized in lower concentrations of the chemicals and lower buffer pH. A large amount of smaller crystals of the protein appeared in a week with gradual increasing in the chemical concentrations and pH≥8.0. When the chemical concentrations were further increased, the time for crystallization was increased and a few high grade crystals of larger size were formed. If the concentrations of the chemicals were continuously increased, many crystals with smaller size, and, sometimes of poor quality appeared again and eventually ceased to produce any crystals. The optimal concentration for each of the above mentioned chemicals varies with other variable factors. Only one bigger crystal (both of the longest two sides: 0.16 mm) could be obtained in a hanging drop of protein sample when the concentrations of PEG 8000, MgCl 2, NaCl,Tris and protein were kept at 1.86%, 300 mmol/L, 400 mmol/L, 53 mmol/L and 4.64 g/L , respectively, with Tris buffer pH 8.2.

Processing map and microstructure evaluation of AA6061/Al_2O_3 nanocomposite at different temperatures

Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workability of nanocomposite.Theactivation energy of285kJ/mol for the hot compression test is obtained by using hyperbolic sine function.By means of dynamicmaterial model(DMM)and the corresponding processing map,safe zone for the hot workability of AA6061/Al2O3is recognized attemperature of450°C and strain rate of0.0005s-1and at temperature of500°C and the strain rate range of0.0005-0.5s-1,with themaximum power dissipation efficiency of38%.Elongated and kinked grains are observed at400°C and strain rate of0.5s-1due tothe severe deformation.

Failure analysis of polycrystalline diamond compact cutters for breaking rock by bending waves theory

The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.

Lattice Mismatch Induced Tunable Dimensionality of Transition Metal Dichalcogenides

Low-dimensional materials have excellent properties which are closely related to their dimensionality.However,the growth mechanism underlying tunable dimensionality from 2D triangles to 1D ribbons of such materials is still unrevealed.Here,we establish a general kinetic Monte Carlo model for transition metal dichalcogenides(TMDs) growth to address such an issue.Our model is able to reproduce several key findings in experiments,and reveals that the dimensionality is determined by the lattice mismatch and the interaction strength between TMDs and the substrate.We predict that the dimensionality can be well tuned by the interaction strength and the geometry of the substrate.Our work deepens the understanding of tunable dimensionality of low-dimensional materials and may inspire new concepts for the design of such materials with expected dimensionality.

Towards Cheaper Solar Cells： A New Path to Grow Silicon Ribbons

The silicon wafer accounts nearly half of the photovoltaic module cost, and hence on this issue an important opportunity remains for further decreasing the cost of photovoltaics. It is well known that ribbon technology has a large potential for costs reduction by avoiding kerr losses since no saw processes are used, preventing material losses up to 50% of the initial feedstock. On the other hand we ought to ask ourselves why we should use solid silicon feedstock, which has already undergone a crystallization process with high energy content to recrystallize it again in a crucible, spending even more energy, when we can go directly from the gaseous feedstock source to the final ribbon. The cost cutting strategy that supports the Silicon over Dust Substrate （SDS） technology, here presented, is based on the belief that ribbon technology and the silicon feedstock issue will play an important role on ＂wafer＂ cost reduction.

Interface-induced warping in hybrid two-dimensional materials

Two-dimensional hybrid materials consisting of heterogeneous domains have been of great interest. Using empirical molecular dynamical simulation, we show that the morphology of such hybrid 2D materials can extend into the third dimension via strong warping intrinsic to the interfaces between the domains. The interface warping stems from the compressive stress in the domain with a larger lattice constant and even penetrates into the stretched domain. Based on classic plate theory, we analytically quantify the amplitude, wave length and penetration depth of the interface warping as functions of the lattice mismatch, achieving good agreement with the simulations. Moreover, we propose that periodically placing pentagon-heptagon dislocations along the interface can eliminate the warping in the 2D material and such defective interface can be more favorable than the warped one over a critical domain size, which is consistent with recent experimental observations. Our results suggest that the interface warping in 2D hybrid materials should be considered in further exploring their promising properties.

A systematic analysis of good matching sites between two lattices

The geometrical matching/mismatching of lattices overlapped in 1, 2 and 3 dimensions have been analyzed systematically by variation of lattice misfit in a large range, far beyond the limits for semicoherent interfaces. In order to evaluate the degree of matching, the density of good matching site （GMS） between two lattices is calculated. The analysis shows that the GMS density remains approximately constant, irrespectively to the degree of lattice misfit. This constant, defined as the average GMS density, decreases exponentially with the increasing dimension of misfit. Typically, for 6 = 15%, the average GMS densities are approximately 30%, 7%, and 1.4% for 1D, 2D, and 3D lattice misfits, respectively. The GMS density deviates significantly if a CSL of small X can be defined. The relationship between the GMS distribution and O-lattice is investigated. It indicates that an abrupt increase in the GMS density in an interface parallel to a principal O-lattice plane is equivalent to a reduction of dimension of misfit. This shows the agreement between the selections of principal O-lattice planes as candidates of the preferred interfaces and the condition that interfaces with high GMS density are preferred.

Blue LED growth from 2 inch to 8 inch

Growth of blue InGaN based LED structures on sapphire wafers from 2 inch to 8 inch in diameter was investigated using the Veeco K465 MOCVD platform. Our results indicate that the same pressure,rotation rate and hydride flows can be used for all wafer sizes. AFM and X-ray studies reveal that all wafer sizes have comparable high-quality crystallinity and defect levels for GaN and InGaN/GaN MQW growth. Although the larger diameter wafers exhibit larger wafer bow due to lattice and thermal mismatch,with proper wafer pocket design,good wavelength and thickness uniformity can be obtained for all wafer sizes.

DFT Investigation of Structural,Electronic,Elastic and Optical Properties of SrMO_4(M=Mo and W)

A planes waves pseudo-potential calculations are performed for the SrMO4 （M=Mo and W） compound in order to investigate the structural, electronic, elastic and optical properties. The calculated lattice constants are in good agreement with experiment ones. The electronic structures show that SrMO4 has a direct band gap situated at F point. The calculated elastic constants indicate that both structures are mechanically stable. The bulk modulus, shear modulus, Young＇s modulus and Poisson ratio are investigated from the elastic constants, in the same time the anisotropy of the elastic properties is discussed. The imaginary part of the dielectric functions is calculated and the contributions of various transitions peaks are analyzed. Furthermore, the other optical properties such as absorption coefficient I（w）, optical reflectivity R（w）, energy-loss spectrum L（w）, and the refractive index n（w） have been investigated.

Elastic wave propagation and localization in band gap materials:a review

Band gap materials(i.e.phononic crystals) are the artificially periodic structures,which have the stop band characteristic for elastic waves.The elastic waves will be localized in phononic crystals with defects,which results in the energy being accumulated around the defects.As a result,it is important to analyze the wave propagation and localization in band gap materials,especially for the structures consisting of smart materials.For example,with the mechanical-electro and mechanical-electro-magneto coupling,the phononic crystals consisting of piezoelectric and magnetoelectroelastic materials can be applied widely.This sets the theoretical basis for the design of band gap materials with multi fields coupling.This paper reviews the recent development of the elastic wave propagation and localization in both ordered and disordered band gap materials.The discussion focuses on the stop band and localization characteristics of elastic waves.Analytical methods and important results are also presented.Finally,some problems for further studies are discussed.This work aims to present the basic properties of wave band gaps in phononic crystals and wave localization in disordered periodic structures(e.g.phononic crystals with definite and random defects and phononic quasicrystals).

Reversible enhanced upconversion luminescence by thermal and electric fields in lanthanide ions doped ferroelectric nanocomposites

Luminescence modification of lanthanide ions has attracted great attention due to its applications in sensing,colorful display, information transmission and anti-counterfeiting. Traditional methods of tuning fluorescence typically employ tuning compositions that are not conducive to the development of multi-environment detection and anti-counterfeiting. In this study, lanthanide ions doped ferroelectric nanocomposite was exploited with external stimuli. The upconversion luminescence modification was preformed via both the thermal and electric fields. The anti-thermal quenching phenomenon was observed in the prepared nanocomposite, which could effectively enhance the upconversion luminescence of lanthanide ions. Based on the electromechanical softness of the ferroelectric lattice, exceptional luminescence modification was realized through electric polarization. The luminescence modifications by thermal and electric fields exhibited excellent reversibility and non-volatility. These results provide unique insights into the development of integrated stimulus responsive smart devices, colorful display and advanced multi-mode sensing materials.