Anmin Hu

High-performance Si-based 3D Cu nanostructured electrode assembly for rechargeable lithium batteries

In this work, we report the synthesis of a Si/Cu nanocone-array (NCA) electrode via a facile ambient electrodeposition method with subsequent magnetron sputtering deposition. The close connection between the Cu NCA and the silicon layer facilitates the charge transfer in the system and supports a binder-free technique of preparing lithium ion battery (LIB) anodes. The void spaces between Si cylinders allow not only greater alleviation of the strain caused by the Si expansion during lithiation but also a significantly enhanced rate performance due to the increasing electrode/electrolyte contact area, and shortening path lengths for electronic and Li+ transport. Such engineered electrodes exhibit a long cycle life up to 2000 cycles and can be very promising for high-performance anode applications.

Structural control of a cobalt nanocone array grown by directional electrodeposition

A metallic nanocone array by means of a directional electrodeposition method without any template is reported. With the crystallization modifier in the nickel electroplating solution, the cobalt conical structure can be deposited onto different metal substrates. The morphology of the nanocones can be controlled by changing the electroplating condition. The as-prepared Co nanocones grow preferentially along directions with very sharp tips. The conical structures are single crystalline without any disruption of the lattice planes. The growth mechanism is also briefly discussed.

Microstructure and mechanical properties of Sn–Zn–Bi–Cr lead-free solder

In this paper, Traces of Cr were added into Sn-8Zn-3Bi solder alloys to study the influences of Cr on mechanical properties and high temperature reliability of solder alloys by room temperature tensile test and high-temperature aging treatment. With observation of microstructure and fracture surface analysis, the strengthening mechanisms of Cr in solder alloys were discussed. Experiments show that: the microstructure was refined after traces of Cr added and two kinds of intermetallic compound (IMC) formed. Therefore the addition of Cr improved the plasticity of Sn-8Zn-3Bi alloy. The elongation reached up to 50.96% after 0.1% Cr added; and the fracture mechanism converted from quasi-cleavage fracture into ductile fracture. But after more than 0.3% Cr added, the brittleness of the alloy increased. During 0, 4, 9, 16 days aging, the mechanical properties of Sn-8Zn-3Bi-0.3Cr alloy were improving slightly with aging time. Through the microstructure analysis it was found that the Sn-Zn-Cr phase was transited after aging and Zn in alloy was consumed, so that primary Zn phase was reduced and microstructure was improved.

Effect of Ag on oxidation of Cu-base leadframe

It was found that trace Ag on surface has great effect on the oxidation failure of Cu-base lead frame. Trace Ag on the surface increases its peeling resistance in dry condition, while decreases that under hygrothermal aging treatment. The oxide thickness, morphology and compositions were examined to understand the key factor of peeling of oxide film. It becomes evident that Ag has ability to block the diffusion of copper atoms, and so hold back the oxidation of copper. But adhesive strength between copper and oxide layer has little relation with oxide thickness but more important influence comes from internal compressive stress which has great relations with initial structure of the copper lead frame.

Oxidation of the copper alloy with pure copper plating

The oxidation failure of a copper alloy lead frame with/without a copper plating layer was investigated. The oxidation rate and adhesion strength of oxide films on copper alloy substrates were studied by measuring the thickness and by carrying out peel tests. The adhesion strength of the oxide film was mainly influenced by the composition but not the thickness of the oxide film. The highest adhesion strength was obtained when the oxide film was composed mainly of Cu2O. When the thickness of the copper preplated layer was over 0.165 μm, the Cu atoms of the preplated copper were available for oxidation. Thus the oxidation process was within the copper preplated layer, and the main product of the oxidation was Cu2O. It was found that the large column grain of the oxide film on the copper alloy with a copper plated layer, favored the diffusion of copper or oxygen atoms that led to the formation of Cu2O, and lead to higher adhesion strength. This indicated that the oxidation resistance of a copper alloy lead frame can be effectively improved by electroplating copper.

Superhydrophobic and anti-corrosion Cu microcones/Ni–W alloy coating fabricated by electrochemical approaches

In this work, we present a simple method for fabricating a microstructured Cu/Ni–W alloy coating by combining electroless and electro deposition. Field emission scanning electron microscopy (FESEM) results show that a layer of Ni–W alloy has covered uniformly the conical surface of Cu microcone arrays, forming a multilayer coating. The Tafel curve shows the prominent anti-corrosion property of the as-deposited Ni–W film. Wettability results reveal that the water contact angles can be increased from 106° to 153.2° by adjusting the electrodeposition time of the Ni–W layer. The liquid–solid–air contact mode between the superhydrophobic Ni–W hemisphere decorated Cu microcone array and the water drop is briefly discussed. This work also showed potential for use in a wide range of applications, such as the commercial production of anti-wetting and anti-corrosion devices.

Synthesis of hierarchical mushroom-like cobalt nanostructures based on one-step galvanostatic electrochemical deposition

Hierarchical mushroom-like cobalt materials were synthesized by galvanostatic electroplating. The morphology of the product, which can evolve from cone-like to mushroom-like nanostructures, is controllable by changing the deposition parameters. The nanostructure is a single hexagonal close-packed crystal with a preferential growth direction. The proposed growth mechanism is based on the metal ion deficient layer (MIDL) theory which explains both the time-dependent morphology evolution and the effects of the crystalline modifier C2H4(NH2)2. Depositions using several organic crystalline modifiers were compared; only C2H4(NH2)2 yielded the mushroom-like structure.

An investigation into copper oxidation behavior

Copper electrodeposited on nickel and copper alloys substrates is easy to be oxidized, and the adhesion between the oxides and substrates can be so poor that delamination happens at these interfaces, which may lead to an overall failure to the electronic device. In this work, three different substrates were prepared by applying direct current; of all these substrates the amorphous nickel-phosphorous substrate was barely discussed in previous literature. The surface morphology, the orientation of electrodeposited copper film, the composition of oxide and the oxidation kinetics were investigated. The result showed that the nickel-phosphorous substrate electrodeposited with copper was superior to the other two specimens in oxidation resistance property. It is mainly attributed to the nickel-phosphorous substrate has an even surface and it owns a higher activation energy when oxided.

Oxidation Behavior and Intermetallic Compounds Growth of Sn-Ag-Bi-Cr Lead-free Solder

Concentrations of 0.1. 0.3. and 0.5 wt.% of Cr were added to Sn-3Ag-3Bi alloy to produce Sn-Ag-Bi-Cr alloys. The microstmcture is refined with Cr additions, while significantly improves the oxidation resistance. There is no change in the wettability and liquidus temperature after Cr additions. In addition, the effect of Cr addition on the intermetallic compounds was discussed.

Formation and growth of interfacial intermetallic layers of Sn-8Zn-3Bi-0.3Cr on Cu, Ni and Ni-W substrates

In this paper, the formation and growth of intermetallic compounds (IMCs) of Sn-8Zn-3Bi-0.3Cr solder on Cu, Ni and Ni-W substrates have been investigated. For the Cu substrate, only Cu₅Zn₈ intermetallic compound was observed. For the Ni substrate, a Ni₅Zn₂₁ film formed at the interface due to the fast reaction between Ni and Zn. For the Ni-W substrate, a thin Ni₅Zn₂₁ film appeared between the solder and Ni-W layer, whose thickness decreases with the increase of W content. An amorphous bright layer was also found to form below the Ni₅Zn₂₁ layer as aging time extended, which is caused by the diffusion of Zn into Ni-W layer.