Mechanical properties and friction-wear characteristics of VN/Ag multilayer coatings with heterogeneous and transition interfaces

The heterogeneous multilayer interface of VN/Ag coatings and transition multilayer interface of VN/Ag coatings were prepared on Inconel 781 and Si(100),and the microstructures,mechanical and tribological properties were investigated from 25 to 700℃.The results showed that the surface roughness and average grain size of VN/Ag coatings with transition multilayer interface are obviously larger than those of VN/Ag coatings with heterogeneous multilayer interface.The coatings with transition multilayer interface have higher adhesion force and hardness than the coatings with heterogeneous multilayer interface,and both coatings can effectively restrict the initiation and propagation of microcracks.Both coatings have excellent self-adaptive lubricating properties with a decrease of friction coefficient as the temperature increases,but their wear rates reveal a drastic increase.The phase composition of the worn area of both coatings was investigated,which indicates that a smooth Ag,Magnéli phase(V2O5)and bimetallic oxides(Ag3VO4 and AgVO3)can be responsible to the excellent lubricity of both coatings.To sum up,the coatings with transition multilayer interface have excellent adaptive lubricating properties and can properly control the diffusion rate and release rate of the lubricating phase,indicating that they have great potential in solving the problem of friction and wear of mechanical parts.

Atom Diffusion Behavior and Bonding Strength of Ag/Cu Composite Interface

The atom (Ag,Cu) diffusion behavior and the effect of technology on the interface of rolled Ag/Cu composite contact were investigated. The concentration of Ag and Cu atoms near the interface was determined with electron probe. The bonding strength of composite interface was tested and the fracture in tensile sample was observed by SEM. The results show that there was inter diffusion of Ag and Cu atoms on the interface, which formed compact layer with high bonding strength of 98 MPa. The practical application proved that the Ag/Cu composite interface is reliable.

Mg、Si含量对Al-Cu-Mg-Ag-Si合金析出相的影响

研究了Mg、Si元素含量对Al-Cu-Mg-Ag-Si合金实际析出相种类及性能的影响。结果表明,Al-Cu-Mg-Ag-Si合金中高Mg含Si合金析出了大量S相和粗大的第二相;低Mg低Si合金中析出了常见的θ相和Ω相;低Mg含Si合金中出现了6系铝合金中常见的σ相和β″相等多种析出相,且具有非常细小弥散的θ相,为合金提供了良好的强化效果。Si和Mg的存在均极大地改变了合金的析出序列,无法通过增加Mg含量抵消Si的作用。Si的加入显著抑制了Ω相的析出,而大幅增加Mg含量则会促进S相的析出。

Interfacial enhancement of Ag and Cu particles sintering using(111)-oriented nanotwinned Cu as substrate for die-attachment

The electroplated(111)-oriented nanotwinned-Cu(nt-Cu) film was utilized as substrate for Ag and Cu sinter joining to improve the weak interface connection between the metal paste and the substrate.It was found that both Cu and Ag sinter joints using(111)-oriented nt-Cu film exhibited a higher bonding strength than that using traditional random-oriented Cu film.Especially,the joints sintered with Cu paste on(111)-oriented nt-Cu film possessed a higher bonding strength of 53.7 MPa at the sintering condition of 300 °C,0.4 MPa in N2 atmosphere,compared to that on random-oriented Cu film with a value of 31.3 MPa.The results show that as metal substrate layer,the(111)-oriented nt-Cu film can improve the connection performance of Ag and Cu sinter joints,which could further promote their application in dieattachment technology for the next-generation power semiconductors.

Theoretical Studies on the Si(001)-SiO_2 Interface Structure

Novel models （2× 1） of Si（001）-SiO2 interface structure have been established. The method of the first-principle General Gradient Approximation （GGA） is employed to structurally optimize the established theoretical models under the K-point space of periodic boundary condition. The structures after optimization have been analyzed, and the results show that the interfaces present in disordered state and both Si-O-Si and Si=O structures exist. Meanwhile, the bonding of surface structure is analyzed via the graphics of electron localization function（ELF）.

Effect of surface finish metallization on interfacial bonding behavior of sintered Ag joints

In this work,the sandwich joints were joined by low temperature pressureless sintering Ag paste.The morphology and thermal behavior of Ag nanoparticle paste was characterized and analyzed.The sintered Ag joints with different metallization were prepared and tested.The joints with Ag metallization exhibited superior shear strength and interface bonding ratio.However,the joints with Cu metallization showed lowest shear strength and interface delamination.The interfacial microstructures were observed and the diffusion kinetics between Ag and Au atoms were both calculated.The excessive diffusion of Ag atoms towards the Au layer deteriorated the interface bonding ratio and shear strength.This work will help understand the bonding mechanism between sintered Ag and other metallization.

Primary Mg_(2)Si phase and Mg_(2)Si/α-Mg interface modified by Sn and Sb elements in a Mg-5Sn-2Si-1.5Al-1Zn-0.8Sb alloy

The microstructure of primary Mg_(2)Si and the interface of Mg_(2)Si/α-Mg modified by Sn and Sb elements in an as-cast Mg-5Sn-2Si-1.5Al-1Zn-0.8Sb(wt.%) alloy were investigated.In the primary Mg_(2)Si phase not only the Si atoms but also the Mg atoms could be substituted by Sn and Sb atoms,resulting in the slightly reduced lattice constant a of 0.627 nm.An OR of Mg_(2)Si phase and α-Mg in the form of[001]Mg_(2)Si‖[01■1]α,(220)Mg_(2)Si‖(0■12)αwas discovered.Between primary Mg_(2)Si phase and α-Mg matrix two transitional nano-particle layers were formed.In the rim region of primary Mg_(2)Si particle,Mg_(2)Sn precipitates sizing from 5 nm to 50 nm were observed.Adjacent to the boundary of primary Mg_(2)Si particle,luxuriant columnar crystals of primary Mg_(2)Sn phase with width of about 25 nm and length of about100 nm were distributed on the α-Mg matrix.The lattice constant of the Mg_(2)Sn precipitate in primary Mg_(2)Si particle was about 0.756 nm.Three ORs between Mg_(2)Sn and Mg_(2)Si were found,in which the Mg_(2)Sn precipitates had strong bonding interfaces with Mg_(2)Si phase.Three new minor ORs between Mg_(2)Sn phase and α-Mg were found.The lattice constant of primary Mg_(2)Sn phase was enlarged to 0.813 nm owing to the solution of Sn and Sb atoms.Primary Mg_(2)Sn had edge-to-edge interfaces with α-Mg.Therefore,the primary Mg_(2)Si particle and α-Mg were united and the interfacial adhesion was improved by the two nano-particles layers of Mg_(2)Sn phase.

Forward and reverse electron transport properties across a CdS/Si multi-interface nanoheterojunction

The electron transport behavior across the interface plays an important role in determining the performance of op- toelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole-Frenkel regime respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of inter- facial trap states and the existence of localized electric field respectively. These results might be helpful for optimizing the preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.

STUDY OF INTERFACES AND SURFACES OF YBa_2Cu_3O_(7-x)-Ag

Interfaces and surfaces of YBa_2Cu_3O_(7-x)(YBCO)-Ag have been studied by SEM-EDX and AES.No effect of Ag on 123 structure in X-ray diffraction pattern was observed for 0.4 mol Ag doped YBCO.AES analysis indicated that Ag segregated on surface of YBCO and resulted in decrease of YBCO-metal lead resistance.In addition,solution and segregation of Ag as elemental state were often appeared on interfaces and surfaces of high temperature annealed YBCO,whether elemental Ag or compound Ag_2O and AgNO_3 adopted as doping material.

The vitreomacular interface in different types of agerelated macular degeneration

AIM： To evaluate the vitreomacular interface in cases with wet age-related macular degeneration（AMD） and to compare them to eyes with dry AMD and normal eyes.METHODS： This was a cross-sectional comparative study that included 87 eyes with wet AMD,42 eyes with dry AMD and 40 eyes without AMD as a control group.Optical coherence tomography（OCT） examination was performed for all patients to assess the vitreomacular interface.RESULTS： In the wet AMD group,34.5% of cases had vitreomacular adhesion（VMA）.Only 14.3% of dry AMD cases and 10% of control cases had VMA.There was a significant difference between the control group and the wet AMD group（P=0.004） as well as the dry and wet AMD group（P=0.017）.There was also a significant difference between the incidence of VMA in patients with subretinal choroidal neovascularization（CNV,type 1） and intraretinal CNV（type 2 or type 3）（P=0.020）.CONCLUSION： There is an association between posterior vitreous attachment and AMD.There is also an increased incidence of VMA with intra-retinal CNV.

First-principles calculations of the hole-induced depassivation of SiO2/Si interface defects

The holes induced by ionizing radiation or carrier injection can depassivate saturated interface defects.The depassivation of these defects suggests that the deep levels associated with the defects are reactivated,affecting the performance of devices.This work simulates the depassivation reactions between holes and passivated amorphous-SiO_(2)/Si interface defects(HP_(b)+h→P_(b)+H^(+)).The climbing image nudged elastic band method is used to calculate the reaction curves and the barriers.In addition,the atomic charges of the initial and final structures are analyzed by the Bader charge method.It is shown that more than one hole is trapped by the defects,which is implied by the reduction in the total number of valence electrons on the active atoms.The results indicate that the depassivation of the defects by the holes actually occurs in three steps.In the first step,a hole is captured by the passivated defect,resulting in the stretching of the Si-H bond.In the second step,the defect captures one more hole,which may contribute to the breaking of the Si-H bond.The H atom is released as a proton and the Si atom is three-coordinated and positively charged.In the third step,an electron is captured by the Si atom,and the Si atom becomes neutral.In this step,a Pb-type defect is reactivated.

Passivation and dissociation of P_(b)-type defects at a-SiO_(2)/Si interface

It is well known that in the process of thermal oxidation of silicon,there are P_(b)-type defects at amorphous silicon dioxide/silicon(a-SiO_(2)/Si)interface due to strain.These defects have a very important impact on the performance and reliability of semiconductor devices.In the process of passivation,hydrogen is usually used to inactivate P_(b)-type defects by the reaction P_(b)+H_(2)→P_(b)H+H.At the same time,P_(b)H centers dissociate according to the chemical reaction P_(b)H→P_(b)+H.Therefore,it is of great significance to study the balance of the passivation and dissociation.In this work,the reaction mechanisms of passivation and dissociation of the P_(b)-type defects are investigated by first-principles calculations.The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band(CI-NEB)method and harmonic transition state theory(HTST).By coupling the rate equations of the passivation and dissociation reactions,the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects(P_(b),P_(b)0,and P_(b)1)at different temperatures is calculated.

Synthesis of Silver Sulf ide Quantum Dots Via the Liquid–Liquid Interface Reaction in a Rotating Packed Bed Reactor

We developed the high-gravity coupled liquid-liquid interface reaction technique on the basis of the rotating packed bed(RPB)reactor for the continuous and ultrafast synthesis of silver sulfide(Ag2S)quantum dots(QDs)with near-infrared(NIR)luminescence.The formation of Ag2S QDs occurs at the interface of microdroplets,and the average size of Ag2S QDs was 4.5 nm with a narrow size distribution.Ag2S QDs can disperse well in various organic solvents and exhibit NIR luminescence with a peak wavelength at 1270 nm under 980-nm laser excitation.The mechanism of the process intensification was revealed by both the computational fluid dynamics simulation and fluorescence imaging,and the mechanism is attributed to the small and uniform droplet formation in the RPB reactor.This study provides a novel approach for the continuous and ultrafast synthesis of NIR Ag2S QDs for potential scale-up.

Effect of Metallurgical Behaviour at the Interface between Ceramic and Interlayer on the Si_3N_4/1.25Cr-0.5Mo Steel Joint Strength

By using newly developed CuNi5~25Ti16~28 B rapldly solidifled brazing filler the joining of Si3 N4/1.25Cr-0.5Mo steel has been carried out with interlayer method. If employing the interlayer structure of steel (0.2 mm)/W (2.0 mm)/Ni(0.2 mm), the joint strength can be increased greatly compared with employing that of Ni/W/Ni, and the three point bend strength of the Joint shows the value of 261 MPa. The metallurgical behaviour at the interface between Si3N4 and the interlayer has been studied. It is found that Fe participated in the interfacial reactions between Si3N4 and the brazing filler at the Si3N4/steel (0.2 mm) interface and the compound Fe5Si3 was produced. However, since the reactions of Fe with the active Ti are weaker than those of Ni with Ti, the normal inter facial reactions were still assured at the interface of Si3N4/steel (0.2 mm) instead of Si3N4/Ni (0.2 mm), resulting in the improvement of the joint strength. The mechanism of the formation of Fe5Si3 is also discussed. Finally, some ideas to further ameliorate and simplify the interlayer structure are put forward.

Microstructure of interaction interface between Al-Si,Zn-Al alloys and Al_2O_(3p)/6061Al composite

Interaction behaviors between Al-Si, Zn-Al alloys and Al2O)3p)/6061Al composite at different heating temperatures were investigated. It is found that Al2O)3p)/6061Al composite can be wetted well by AlSi-1, AlSi-4 and Zn-Al alloys and an interaction layer forms between the alloy and composite during interaction. Little Al-Si alloys remain on the surface when they fully wet the composite and Si element in Al-Si alloy diffuses into composite entirely and assembles in the composite near the interface of Al-Si alloy/composite to form a Si-rich zone. The microstructure in interaction layer with Si penetration is still dense. Much more residual Zn-Al alloy exists on the surface of composite when it wets the composite, and porosities appear at the interface of Zn-Al alloy/composite. The penetration of elements Zn, Cu of Zn-Al alloy into composite leads to the generation of shrinkage cavities in the interaction layer and makes the microstructure of Al2O)3p)/6061Al composite loose.

Aging impairs the neurovascular interface in the heart

Aging is a major risk factor for impaired cardiovascular health.Because the aging myocardium is characterized by microcirculatory dysfunction,and because nerves align with vessels,we assessed the impact of aging on the cardiac neurovascular interface.We report that aging reduces nerve density in the ventricle and dysregulates vascular-derived neuroregulatory genes.Aging down-regulates microRNA 145(miR-145)and derepresses the neurorepulsive factor semaphorin-3A.miR-145 deletion,which increased Sema3a expression or endothelial Sema3a overexpression,reduced axon density,mimicking the aged-heart phenotype.Removal of senescent cells,which accumulated with chronological age in parallel to the decline in nerve density,rescued age-induced denervation,reversed Sema3a expression,preserved heart rate patterns,and reduced electrical instability.These data suggest that senescence-mediated regulation of nerve density contributes to age-associated cardiac dysfunction.

微量Si和Ag对低Cu/Mg比Al-Cu-Mg合金时效行为及微观组织结构演化的影响

采用计算机模拟与透射电镜相结合研究微量Si和Ag对低Cu/Mg比Al-Cu-Mg合金时效行为和微观组织结构演变的影响。结果表明:微量Si和Ag的添加改变了该合金的时效析出过程,显著增强了合金的时效硬化效应。微量Si的存在导致了合金时效早期Mg原子团簇、Cu-Mg原子团簇弥散化,而微量Ag的添加导致形成大量Mg-Ag原子团簇。微量Si和Ag极大地改变了合金时效早期的原子团簇化过程从而导致了时效过程中微观组织结构的不同演化过程。

Ag／Si-NPA基底上共吸附R6G和CV的表面增强拉曼散射

以硅纳米孔柱阵列(Si-NPA)为基底,采用浸渍沉积技术制备了具有较高表面增强拉曼散射(SERS)活性的Ag/Si-NPA衬底,并采用扫描电子显微镜和透射电子显微镜对其表面形貌和结构进行了表征.在此基础上,选择罗丹明6G(R6G)和结晶紫(CV)2种生物染料分子并采用不同的混合吸附程序对其共吸附状态下的SERS光谱进行了探测.结果表明,当2种分子的溶液浓度均为10-7 mol/L时,无论采用何种浸渍吸附程序,其SERS谱中CV的特征拉曼峰都被R6G完全掩盖.对溶液采用错级配置(R6G和CV的浓度分别为10-9和10-7 mol/L)后,所测SERS谱上获得了分别对应于R6G和CV的分离良好、相对强度匹配、分辨率高的2个SERS特征峰组,从而有利于简化现实混合探测过程中对SERS特征峰的指认和判断.

Ag 在 Si 表面吸附的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法计算优化了Ag原子在硅惯习面Si(111)和Si(220)晶面的最佳吸附位置,并计算了Ag/Si(111)和Ag/Si(220)体系的表面吸附能和表面态电子结构.研究表明:Si基表面Ag原子的最稳定吸附居于Si(220)晶面的穴位,此时的吸附能最低,其值为5.256 9 eV,属于强化学吸附;同时由于在Ag/Si(220)体系中,Ag-4d轨道和表面态Si-3s、3p轨道电子的强相互作用,以及Ag-4p轨道的电子云强偏向于Si-3s、3p轨道使得体系的能隙宽度变窄,导电性急剧增大.

Interfacial characteristics and microstructural evolution of Sn-6.5Zn solder/Cu substrate joints during aging

The influence of isothermal aging at 150 °C on the microstructural characteristics and microhardness of the Sn-6.5Zn solder/Cu joint was studied. The mechanisms for the formation and evolution of intermetallic compound （IMC） at the interface of the Sn-6.5Zn/Cu joint were also analyzed. The results indicate that a continuous layer consisting of CuZn and Cu5Zn8 IMCs is formed in the interface zone. As the aging time prolongs, the thickness of the IMC layer first increases and then decreases, and the continuous and compactable layer is destroyed due to the decomposition of the Cu-Zn IMC layer. A discontinuous layer of Cu6Sn5 IMC is present within the Cu substrate near the decomposed region. The interface becomes rough and evident voids form after aging. The microhardness of the interface increases owing to the application of aging.