Neutral and negatively charged bismuth clusters, Bi n and Bi(-)n (n=2-13), are investigated by first-principles simulations with the scalar-relativistic projector-augmented wave potential and the spin-polarized generalized gradient approximation. Both types of clusters show size-dependent odd-even oscillations in stability, density of states, and vertical and adiabatic electron affinities, in close agreement with experiment. The negative charge thoroughly reverses the oscillations and considerably influences the geometric structures, particularly of the odd-sized clusters. We note that most atoms in the ground states and the low-lying isomers are three coordinated with a quasilayerlike growth mode based on pentagon units, due to a weak s-p hybridization. The Bi12 cluster is found to prefer a small elongated tubelike structure with the surface consists of six curved-pentagon rings and two triangular facets, which may be the basis for the formation of bismuth nanotubes experimentally reported.
Fast copper electroplating with void free via filling is required in though-silicon-via (TSV) manufacture. Copper electrodeposition in methanesulfonic acid (MSA) bath with additives is considered to be more effective and efficient than that in sulfuric acid used in Damascene. In this paper, a novel evaluation method is proposed for specific additives (sodium 3,3 -dithiodipropane sulfonate and polyethylene glycol) used in Cu electroplating of TSV in MSA bath based on their acceleration and inhibition at different potential region of liner sweep voltammetry (LSV) curve. The peak and valley of the LSV curve are closely related to the thickness of the deposited copper inside the via. Relatively lower potential region of the LSV curve corresponds to deeper positions inside the via during electroplating. Combined with the analysis of the LSV curve, the mechanism of void formation is proposed, which is further confirmed by the wafer-segment plating of TSV with three particular potentials.
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