A novel method for improving the adhesion strength of the electrodeposited Ni films in MEMS

Adhesion performance of MEMS materials is increasingly important with the widely use of miniaturized devices. This paper proposed a novel method for improving adhesion performance between electrodeposited Ni multi-layers. The new method is to treat the Ni substrate in nickel chloride plating solution by pulse reverse current technique before electrodeposition. The dense oxide film of Ni substrate can be removed effectively by this electrochemical method, meanwhile, the proper roughness of Ni substrate is in favor of epitaxial growth during electrodeposition. Moreover, the Ni film is electrodeposited by the new method with low stress and coarse crystal grain. Consequently, the adhesion performance of Ni films is improved dramatically. The experimental results show that the adhesion performance of Ni film electrodeposited by the new method is about 3 times that of by traditional method.     

Seed bubbles stabilize flow and heat transfer in parallel microchannels

Seed bubbles are generated on microheaters located at the microchannel upstream and driven by a pulse voltage signal, to improve flow and heat transfer performance in microchannels. The present study investigates how seed bubbles stabilize flow and heat transfer in micro-boiling systems. For the forced convection flow, when heat flux at the wall surface is continuously increased, flow instability is self-sustained in microchannels with large oscillation amplitudes and long periods. Introduction of seed bubbles in time sequence improves flow and heat transfer performance significantly. Low frequency (∼10 Hz) seed bubbles not only decrease oscillation amplitudes of pressure drops, fluid inlet and outlet temperatures and heating surface temperatures, but also shorten oscillation cycle periods. High frequency (∼100 Hz or high) seed bubbles completely suppress the flow instability and the heat transfer system displays stable parameters of pressure drops, fluid inlet and outlet temperatures and heating surface temperatures. Flow visualizations show that a quasi-stable boundary interface from spheric bubble to elongated bubble is maintained in a very narrow distance range at any time. The seed bubble technique almost does not increase the pressure drop across microsystems, which is thoroughly different from those reported in the literature. The higher the seed bubble frequency, the more decreased heating surface temperatures are. A saturation seed bubble frequency of 1000–2000 Hz can be reached, at which heat transfer enhancement attains the maximum degree, inferring a complete thermal equilibrium of vapor and liquid phases in microchannels. Benefits of the seed bubble technique are the stabilization of flow and heat transfer, decreasing heating surface temperatures and improving temperature uniformity of the heating surface.     

Investigation on microstructure and properties of CrAlN/AlON nanomultilayers

Artificially modulated CrAlN/AlON nanomultilayers were synthesized by direct current reactive magnetron sputtering. The microstructure and mechanical properties were evaluated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The crystallization of AlON layer and its influence on the mechanical property of the nanomultilayers were studied. The results revealed that, under the template effect of NaCl structural CrAlN layer, amorphous AlON was forced to crystallize and grew epitaxially with CrAlN layer when AlON layer thickness was below 0.9 nm, leading to an increase of hardness up to 32.8 GPa. With the further increase of the AlON layer thickness, AlON layer gradually transformed into amorphous structure and blocked epitaxial growth of the multilayers, resulting in the decrease of hardness. The effect of CrAlN layer thickness on hardness of CrAlN/AlON nanomultilayers was also investigated. With the decrease of CrAlN layer thickness, the hardness increased gradually. The maximum hardness was 34.7 GPa when CrAlN layer thickness of was 3.0 nm. The strengthen mechanism of CrAlN/AlON nanomultilayers was finally discussed.     

Ligand acceleration in ZnI2-catalyzed intramolecular hydroamination of unfunctionalized olefins

Zinc halide-promoted hydroamination of 4-penten-1-amine compounds was studied. Preliminary results indicated that both steric and electronic factors are crucial for this Lewis acid-promoted reaction. ZnI₂ gave the most promising results and the reactivity could be further increased upon addition of a suitable ligand. Up to 95% isolated yields were obtained when the reactions were carried out in 1,4-dioxane in the presence of 10 mol % of ZnI₂ and 8-hydroxyquinoline.     

异硫氰酸铬(Ⅲ)二(18-冠-6)铵配合物的合成、特征和光化学

本文报道了标题中所指的配合物固体和单晶的制备,测定了IR,UV-Vis光谱以及该配合物在CH₃CN和DMF中的光化学性质。采用单晶X射线衍射测定了该配合物的结构,它属于单斜晶系,空间群P2₁/n,测定了固体配合物在CH₃CN和DMF中的量子产率Φ_NCS,并讨论了光反应机制。     

Direct observation of dendritic domain growth in perpendicular magnetic anisotropy CoFe/Pt multilayers

We present the experimental results on thermally activated magnetization reversal for [Co_0.9Fe_0.1(5.0 Å)/Pt(20 Å)]₄ multilayer. Direct domain observations show that magnetization reversal is initiated with rare nucleation and followed by dendritic growth of domain walls. Based on macroscopic magnetic parameters from experimental data, the dendritic domain growth mode is qualitatively interpreted by Monte Carlo simulations in terms of a simple uniaxial magnetic anisotropy model. Moreover, both time evolution of domain growth observation and magnetic relaxation measurements reveal that CoFe/Pt multilayer has a relatively large activation volume compared with Co/Pt multilayers.