Understanding the thermal evolution mechanisms of metal nanoparticles (NPs) at the quantum-dot-scale is arrestive and meaningful for utilization of nanomaterials. Herein, an interesting fusion evolution phenomenon of Ag-Cu NPs induced by in-situ TEM high-energy electron beam illumination has been observed and investigated. It turned out that a rapid fusion process was in progress as reflected by the significant morphological change as the electron beam illumination time increased. The Ag-Cu NPs clusters tended to shrink their overall surface area along with the increase of sintering neck radii and decrease of neck curvature which was dominated by lattice diffusion mechanism. In addition, the necks among three Ag-Cu NPs continuously grew until the three particles became a short nanorod with a relatively uniform lateral diameter of about 20 nm after 300 sʹ illumination. It was also worthy of note that the smaller particles disappeared faster than bigger ones due to their highest surface energy.

Three-dimensional (3D) nanohierarchical Ni nanomace (Ni NM) array was fabricated on copper substrate by only one step with electroplating method, the unique structure was covered with Au film (Ni/Au NM) without changing its morphology, and in the following step, it was sintered with silver nanoparticle (Ag NP) paste. The structure of the Ni NM array and its surface morphology were characterized by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. The sintered interface was investigated by SEM, transmission electron microscopy, and energy-dispersive X-ray spectroscopy to analyze the sintering mechanism. The results showed that a metallurgical bond was successfully achieved at 250 °C without any gas or vacuum shield and extra pressure. The Cu substrate with Ni/Au NM array was able to join with the Ag NP paste without obvious voids. Due to the compatible chemical potential between Ag NPs and Ni/Au NM array, the Au element was able to diffuse into the Ag layer with about 800 nm distance. Based on the excellent 3D nanohierarchical structure, the shear strength of Ni/Au NM array was 6 times stronger than the flat Ni/Au coated substrate. It turned out that the substrate surface played a crucial role in improving the shear strength and sintering efficiency. The 3D Ni NM array had achieved an excellent bonding interface and had great potential application in the microelectronics packaging field.Keywords: interface analysis; interface connection; nanojoining; nanomace array; shear strength; silver nanoparticles; sintering;

Low temperature nanojoining has been identified as a challenging nanotechnology in the construction of nanoscale structures as well as microelectronic devices. Herein, three kinds of Ag–Cu nanopastes have been designed by mixing different organics with the Ag–Cu nanocrystalline particles synthesized in our previous work. The mechanical properties of sintered Ag–Cu nanopaste including hardness, Young’s modulus and shear strength were investigated and analyzed. It turned out that the sintered Ag–Cu nanopaste-B with 20 wt% addition of polyethylene glycol (PEG) has lower hardness and Young’s modulus, but a much higher shear strength than Ag–Cu nanopaste-A (1,2-propanediol) and -C (terpineol), which is superior to be considered as die-attach material for high temperature packaging material for wide band gap semiconductors. The uniform and dense sintered nanopaste-B layer presents a feature of eutectic microstructure comprised of Ag-rich and Cu-rich phases. It was also interesting to find that remarkable nanostructural solid solubility arose in Ag-rich phase (36 At% Cu) and Cu-rich phase (44 At% Ag). Moreover, the atomic inter-diffusion at interface could eventually interlock between the sintered nanopaste and substrate, which allows the Cu chip firmly attaching onto the Cu substrate. This work not only breaks through the synthesis bottleneck of Ag–Cu alloy NPs and a new bonding material, but also has the potential to affect a broad fields range.

The explosion of high density and high temperature electronic devices is intensifying the desire for high temperature Pb-free solders. Alloying high melting point elements with conventional solders is one of the most potential solutions drawing attention. In this paper, the relationship between cracking and microstructure evolution of SnAgCu and Ni, Sb, Bi alloyed SnAgCu solders during thermal cycling was systematically studied and compared by ultrasonic C-scanning, SEM, EDX, EBSD, etc. It turned out that alloying Ni, Sb, Bi with SnAgCu solder offered better crack resistance by strengthening and recrystallization energy consumption before ~600 cycles. However, its failure dramatically accelerated after those cycles because of the large amount of grain boundaries caused by severe early recrystallization, the coarsened IMCs, and the decrease of Schmid Factor as SnAgCu were softened, while SnAgCuNiSbBi can be excessively hardened by thermal cycles.

Ultrafine Ag–Cu nanoparticles (NPs) have been synthesized by a rapid one-step reduction within only 10 min. Effects of temperature and dispersants on the phases and morphology of Ag–Cu NPs were investigated. Results showed that citric acid exhibited an advantageous nature to avoid the formation of Cu2O and form uniform morphology over PVP. The average particle size of the Ag–Cu NPs synthesized simply in ice-cubes bath could be controlled in 8.6 nm about a quarter of that synthesized at room temperature. The synthesized Ag–Cu NPs presented alloy states near the eutectic composition of 72:28. Due to the lower Ostwald ripening rate and citric acid protection, smaller Ag–Cu NPs were achieved in ice-cube bath. Results also showed that the ultrafine Ag–Cu NPs could be expected to sinter at about 330 °C which was much lower than the eutectic temperature (779 °C) of bulk Ag–Cu alloy. The ultrafine Ag–Cu NPs could be applied as potential die attach materials for SiC power devices.

In this study, Ag–Cu nano-particles (NPs) with face-centered cubic crystal structure have been synthesized through a facile one-step approach. The statistical design of experiment has been employed to optimize the process parameters and find significant factors that affect the particle size of Ag–Cu NPs. Results showed that the reaction temperature, reaction time, and binary interaction of them have played a significant role in affecting the particle size. The increase in reaction time drove the particle size to increase heavily under the high level of reaction temperature. Furthermore, a mathematical model of particle size corresponding to factors was obtained by analysis of variance and regression fitting. Repetitive experimental verification showed that the average size of Ag–Cu NPs could be controlled within 10–15 nm under the optimal combination of 0 °C of reaction temperature, 5 min of reaction time, 2 of the molar ratio of Ag+/Cu2+, 4 of the molar ratio of reductant/precursors, and 1000 rpm of stirring speed. Lower temperature can result in high nucleation rate and prevent the further growth of Ag–Cu NPs as well. This study provides a new thought and guidance for the synthesis of bimetallic NPs.

•CrO crystal slices were firstly grown on chromium substrate.•The firing under water vapor atmosphere was used to synthesis the new structure.•The CrO crystal slices were single crystal face-centered cubic structure.•The thickness direction of CrO single crystal slices is 〈111〉 orientation.In this letter, CrO single crystal slices were successfully synthesized on chromium substrate under water vapor atmosphere by firing. XRD pattern indicated that relatively weak diffraction peaks belonged to CrO slices while the intensive ones belonged to Cr2O3 under the layer of CrO, which was further proved by HR-TEM image. The as-synthesized CrO single crystal slices were uniform with a thickness of about 100 nm when obtained at 1080 °C for 4 h. And the SAED result showed that the thickness direction of CrO single crystal slices is 〈111〉 orientation. Moreover, the formation mechanism of the CrO single crystal slices was given.

Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys with long period stacking ordered (LPSO) structure phases were prepared by conventional solidification process. By OM, SEM, EDS, XRD and TEM analysis the phases and 14H-LPSO structures of the two alloys were characterized. The results show that as-cast Mg-alloy with the atomic ratio of Zn/RE = 1 will lead to LPSO phase; adding of Gd element to Mg92Zn4Y4 alloy can facilitate the formation of LPSO phase, and its volume fraction increases from 12.1% to 30.4%; Mg dendrites are split and refined during the precipitation of LPSO phase formed at high temperature, resulting in that the average grain size of α-Mg decreases from 50 µm to 10 µm; the solidification microstructure of as-cast Mg92Zn4Y4 alloy is α-Mg solid solution + Mg12ZnY + Mg3Zn3Y2 + Mg-Y; In Mg92Zn4Y3Gd1 alloy, the as-cast microstructure is confirmed to be composed mainly of α-Mg solid solution, Mg12Zn(Y, Gd) and Mg3Zn3(Y, Gd)2; at room temperature, the compression ratio and the thermal conductivity of Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys are 12.4% and 15.5%, and 99.233 W·(m·K)−1 and 88.639 W·(m·K)−1, respectively.

An AlN composite ceramic layer was designed and fabricated on WCu substrates by hydrolysis-assisted solidification and firing. First, the surface of WCu substrates were pre-coated with polycarbosilane/AlN ceramic layers by spinning; the layers were then fabricated by firing. The phase composition, microstructure, and element distribution of the ceramic layer and interfacial reaction layer were investigated by use of scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction. The results showed that the ceramic layers were composed of AlN, mullite, and Al2O3. There were many nanocrystalline rods on the surface of the ceramic layers. The Cr layer prevented the WCu substrate from reacting with water vapor during firing, and the Ni layer prevented diffusion of tungsten into the Cr layer. Study of the cross section of the ceramic layer fired on the Cr/Ni/WCu substrate revealed a perfect interfacial reaction layer.

•Homogeneous high-melting-point Cu6Sn5 and Cu3Sn intermetallic compound joints were fabricated.•The ultrasonic joining method was utilized to fabricate intermetallic compound joints at room temperature in air.•The processing time was dramatically reduced to only several seconds.•The sonochemical effects of acoustic cavitation were investigated.Homogeneous intermetallic compound joints are demanded by the semiconductor industry because of their high melting point. In the present work, ultrasonic vibration was applied to Cu/Sn foil/Cu interconnection system at room temperature to form homogeneous Cu6Sn5 and Cu3Sn joints. Compared with other studies based on transient-liquid-phase soldering, the processing time of our method was dramatically reduced from several hours to several seconds. This ultrarapid intermetallic phase formation process resulted from accelerated interdiffusion kinetics, which can be attributed to the sonochemical effects of acoustic cavitation at the interface between the liquid Sn and the solid Cu during the ultrasonic bonding process.

The multiferroic Ba0.7Sr0.3TiO3 (BSTO)–Ni0.8Zn0.2Fe2O4 (NZFO) nanofibers with different molar ratios were prepared by electrospinning method. After annealing at 700 °C, the composite nanofibers showed highly crystalline structure with no impurity phase. The fibers before and after heat treatment had high aspect ratios, and the fibrous morphology could be observed obviously. The maximum value of magnetic coercivity was obtained corresponding to the BSTO–NZFO nanofibers with molar ratio of 80/20. The values of coercivity, saturation magnetization and retentivity for the BSTO–NZFO (molar ratio=80/20) nanofibers were 44.873 Oe, 2.479 emu/g and 0.189 emu/g, respectively. Moreover, the magnetodielectric, dielectric and ferroelectric properties were measured at room temperature.Highlights·► Multiferroic Ba0.7Sr0.3TiO3–Ni0.8Zn0.2Fe2O4 nanofibers were synthesized. ► Nanofibers showed highly crystalline structure with no impurity phase.·► The fibers before and after heat treatment had high aspect ratios.·► The maximum value of magnetic coercivity was 44.873 Oe.·► The magnetodielectric, dielectric and ferroelectric properties were displayed.

We report a Cu-to-Cu interconnects fabrication process based on the pressureless low temperature sintering of Ag nanoparticles for electronic packaging. The organic shells of citrates covering the nanoparticles stabilize the Ag nanoparticles. It is not necessary for organic shells to be completely decomposed for sintering to take place. Instead, it is sufficient that the chemical bonds that connect the organic shells with Ag nanoparticles are broken. This new point of view leads to a way to lower bonding temperature. A novel pinecone-like recrystallization morphology of sintered Ag nanoparticles is obtained, which results from the residuals of organic shells by the sintering process. The effect of recrystallization morphology on the thermal conductivity of sintered Ag nanoparticles is discussed. The shear strength of joints reaches 17–25 MPa at temperatures ranging from 423 K to 473 K.Highlights► Pressureless sintered joints are achieved at low bonding temperatures of 423–473 K. ► Sintering can take place so long as the chemical bonds on nanoparticles are broken. ► We find a novel pinecone-like recrystallization morphology of Ag nanoparticles. ► Thermal conductivity of sintered Ag layers is reduced due to the scattering effect.

Multiferroic materials possess at least two ferroic properties which make them particularly suitable for multifunctional device applications. The purpose of this work was to get one-dimensional multiferroics by doping of Co into ferroelectrics. Multiferroic Ba0.7Sr0.3Ti0.95Co0.05O3 nanofibers were prepared via a sol–gel and electrospinning technique. The nanofibers annealed at 700 °C exhibited highly crystalline structure with no detectable impurity phase. The nanofibers before and after heat treatment were both well-distributed, and the fibrous morphology could be observed obviously. After the annealing process, the nanofibers showed a rough surface and relatively tight structure. The magnetic hysteresis loop confirmed the expected ferromagnetic properties with a saturation magnetization of 398.99 memu/g, a retentivity of 20.233 memu/g, and a coercivity of 112.54 Oe measured at room temperature.Highlights► Multiferroic Co-doped barium strontium titanate nanofibers were synthesized. ► The nanofibers were well-distributed with highly crystalline structure. ► The nanofibers showed a relatively tight structure after the annealing process. ► The success of Co doping was confirmed by XPS and EDS analysis. ► The ferromagnetic behavior was displayed by magnetic hysteresis loop.

Cemented carbide (WC-15 wt.%Co)/beryllium bronze (BeCu) brazed with Ag-based filler was conducted by using a hybrid ultrasonic resistance brazing method. Based on microstructural analysis (nondestructive and cross-sectional observation) and mechanical evaluation (shear and hardness test), when hybrid ultrasonic vibrations with a frequency of about 30 kHz, it was shown that, not only the well-brazed area of the brazing joint interface increases more than 35% (up to 85%), resulting in that the shear strength increases 40% (about 241 MPa), but also the softened region of the BeCu foil is preserved within the contact area with the WC-Co bar, resulting from restraining the grain growth in the BeCu foil through deceasing the heat input and the high temperature residence time. Due to the acoustic cavitation and the acoustic streaming effects, robust brazed joints of dissimilar alloys or materials could be realized successfully even with no flux, and the properties of the base materials can be sustained as much as possible.

The growth behaviors of the intermetallic compounds (IMCs) formed at the eutectic Sn3.5Ag/polycrystalline Cu and pure Sn/polycrystalline Cu interfaces are comparatively studied based on an experiment in which the liquid solder is removed before the end of soldering. This removal of the solder allows for the capture and visualization of the interfacial IMCs formed during liquid-state soldering and avoids the influence of Cu6Sn5 precipitated from the solder matrix during cooling. The results show that round, scallop-type Cu6Sn5 grains with a strong texture form at the molten solder/Cu interface and that their growth is controlled more by grain boundary (GB) diffusion at the beginning of the reaction followed by volume diffusion, whereas the growth of Cu3Sn is only volume-diffusion-controlled. In addition, in contrast to the predictions of some studies, Ag does not inhibit interfacial IMC growth. Instead, by changing the interfacial energy between the molten solder and the interfacial IMC, the addition of Ag affects the growth orientation and coarsening behavior of interfacial Cu6Sn5 grains. These changes lead to more Cu6Sn5 GBs at the interface and therefore greater IMC formation and Cu consumption in the Sn3.5Ag/Cu reaction than in the Sn/Cu reaction under the same reflow conditions.Highlights► We design an experiment to obtain IMCs formed at molten solder/Cu interface. ► Round Cu6Sn5 grains with strong texture form at molten solder/Cu interface. ► Growth orientations of Cu6Sn5 grains affect their coarsening behaviors. ► Coarsening behaviors of Cu6Sn5 grains affect their growth thickness. ► Ag does not inhibit the interfacial IMC growth.

This study investigates the influence of aging treatment on deformation behavior of 96.5Sn3.5Ag eutectic solder alloys with lower strain rate (<10−3 s−1) during tensile tests under the scanning electron microscope. Results showed that because of the existence of Ag3Sn intermetallic particles and the special microstructure of β-Sn phases in Sn3.5Ag solder, grain boundary sliding was not the dominant mechanism any longer for this Pb-free solder. While the interaction of dislocations with the relatively rigid Ag3Sn particles began to dominate. For the as-cast specimen, accompanied by partial intragranular cracks, intergranular fracture along the grain boundaries in Sn–Ag eutectic structure or the interphase boundaries between Sn-rich dendrites and Sn–Ag eutectic phases occurred primarily in early tensile stage. However, the boundary behavior was limited by the large Ag3Sn particles presented along the Sn-rich dendrites boundaries after aging. Plastic flow was observed in large area, and cracks propagated in a transgranular manner across the Sn-dendrites and Sn–Ag eutectic structure.

•Crystallized BLFMO/BSTCO films were obtained with no impurity phase detected.•The BSTCO layer could effectively enhance the magnetic properties of BLFMO film.•The leakage current density of BLFMO/BSTCO film was lower than that of BLFMO film.We report the synthesis of Bi0.9La0.1Fe0.95Mn0.05O3 (BLFMO) films with enhanced multiferroic properties and without second phase using Ba0.7Sr0.3Ti0.95Co0.05O3 (BSTCO) film as a buffer layer. Sol–gel processes were used to prepare the crystallized BLFMO/BSTCO films, in which magnetic domains were observed and no impurity phase was detected. We found that the buffer layer could effectively enhance the saturation magnetization and retentivity values of the BLFMO films, and especially the magnetic coercive field of these bilayer films was significantly stronger than that of the BLFMO films without buffer layers.