Formation of 1D and 2D gold nanoparticle arrays by divalent DNA-gold nanoparticle conjugates

Divalent DNA-AuNP (gold nanoparticle) conjugates comprising two DNA strands at diametrically opposed positions are prepared. Highly linear 1D and tetragonal lattice-like 2D AuNP arrays are constructed using the conjugates and DNA assemblies based on T- and double-crossover motifs and the Holliday junction.     

Shock compaction of NiTi alloy powder

The shock recovery experiment for the equiatomic NiTi alloy powder was performed by the flyer impact technique. The powder samples with the initial density of 70% of full density were shock-treated in the dyer velocity range 0.65 to 1.7 km sec^?1. At the optimum flyer velocity of 1.3 km sec^?1, the powder sample is compacted up to 99.5% of the full density. With increasing flyer velocity, new pores are formed in the melted layer instead of the disappearance of initial interstices. Effects of the mechanical deformation and the annealing brought by the shock treatment evidently appear in the temperature dependence of electrical resistivity accompanied with the martensitic transformation. The shock state and the relaxation of the heterogeneous temperature by the shock treatment are estimated, which indicate the annealing condition caused by shock-loading and the formation of new pores.     

Cu2ZnSnS4 thin films and nanowires prepared by different single-step electrodeposition method in quaternary electrolyte

We investigated the effect of single-step electrodeposition methods for the fabrication of CZTS thin films as solar cell absorber layer. For deposition of CZTS thin films, a potentiostatic method and a pulsed potential electrodeposition method were examined. Near stoichiometric CZTS thin films were prepared by potentiostatic deposition method. On the other hands, the samples deposited by pulsed potential method showed wire-like CZTS nanostructures. The nanowires were composed of the Cu and S element mainly and included Zn and Sn microelements. From these results, we realized that the electrodeposition methods strongly affect the structural and compositional characteristics of as-deposited CZTS thin films.     

Formation of electroless barrier and seed layers in a high aspect ratio through-Si vias using Au nanoparticle catalyst for all-wet Cu filling technology

An all-wet process was achieved using electroless deposition of barrier and Cu seed layers for fabrication of a high aspect ratio through-Si via (TSV). Formation of a thin barrier metal layer of Ni–B, Co–B and Co–W–B is possible using a Au nanoparticle (AuNP) catalyst, which is densely adsorbed on the SiO₂ of the TSV sidewall. A silane coupling agent of 3-aminopropyl-triethoxysilane is effective for enhancement of the density of adsorption for AuNP. A conformal electroless Cu layer is deposited on the barrier layer by displacement plating without a catalyst. The adhesion strength between the electroless barrier layer and the SiO₂ substrate is increased by annealing at 300 °C. These results strongly suggest that an all-wet process for the formation of Cu-filled TSV with a high aspect ratio is practically possible.     

Characterization of sputtered tungsten nitride film and its application to Cu electroless plating

In this study, W and tungsten nitride films were fabricated by reactive sputtering in a N₂/Ar atmosphere, the native oxide growth on the surface of the tungsten nitride films was investigated by X-ray photoelectron spectroscopy (XPS). It was found that tungsten nitride films were the mixture of W and W₂N sputtered in atmospheres of 3 mTorr argon and at the N₂ partial pressure from 0.1 to 2.0 mTorr. The ratio of W and W₂N in films was changed with the nitrogen partial pressure in sputtered chamber. Surface oxidations of the W film and tungsten nitride films advanced with time. Electrochemical measurement shows that all reduction-oxidation (redox) potentials of tungsten and tungsten nitrides were lower than that of copper film in electroless copper solution. And so, electroless-plated copper could be deposited on the surface of tungsten nitride films when the substrates were immersed into electroless copper plating solution without any pretreatment. Tungsten nitride films are appropriate for ULSI Cu interconnections using electroless Cu deposition.     

Surface morphologies of sputter-deposited aluminum films studied using a high-resolution phase-measuring laser interferometric microscope

Sputter-deposited aluminum (Al) film surface morphologies were studied with a new nondestructive method that incorporates a high-resolution phase-measuring laser interferometric microscope. Good correlation is obtained between rms roughness and reflectivity for various conditions of temperature and argon gas pressure. It should be noted that the rms roughness is much more sensitive than reflectivity when reflectivity exceeds 90%. A drastic change is observed in the temperature dependence of the rms roughness and the skewness at 200 °C. As a result there are changes in Al grain sizes and surface morphologies based on concomitant scanning electron microscope observations. We found that the rms roughness value depends on the resolution of the objective especially when the Al grain sizes are comparable to the resolution.