By immersion of silicon into a solution containing metal-salt and hydrofluoric acid, fine metal particles are deposited onto the silicon surface by electroless displacement reaction. The particle density of deposited metal varies widely depending on the kind of metal and the surface condition of silicon substrates. The platinum particle density changes to an especially large degree according to silicon surface conditions. This study revealed the relation of deposition time to platinum particle density deposited by electroless displacement deposition on argonplasma-etched Si surfaces. Single-crystalline n-Si（100）wafers were chemically pretreated and were then etched with argon plasma using a radiofrequency glow discharge spectrometer. The electroless displacement deposition of platinum particles onto the silicon surface proceeds by immersion of silicon wafers into a hexachloroplatinic（IV）acid solution containing hydrofluoric acid. Platinum particles were deposited in the progressive mode until 450 s, and reached 1011 cm－2. The particle density was decreased by immersion longer than 450 s, and was maintained at 1010 cm－2 after 900 s. Dimples appeared on the silicon surface by immersion for 600 s and longer. Dimples were formed by local anodic dissolution of silicon under the platinum particles. The initial increase and posterior decrease in the particle density are explained, respectively, as the influence of argon-plasma etching and the dissolution of the influenced region of a silicon wafer.
The preparation of cobalt-antimony thermoelectric film using pulse electrolysis was investigated in ethylene glycol (EG)-CoCl2-SbCl3 non-aqueous solutions at 393 K. The layered structures consisting of Co rich Co-Sb alloy layers and Sb rich Co-Sb alloy layers were obtained by applying alternately the potentials for electrodepositing the former, ECo, and the latter, ESb, in the 90.0 mol%EG-9.09 mol%CoCl2-0.91 mol%SbCl3 bath, and were heat-treated at 673 K for 24 h in Ar gas atmosphere to prepare the Co-Sb alloy films with uniform composition. The composition of Co-Sb alloy film was found to be controlled by adjusting the ratio of applied duration at ECo, tCo, to one at ESb, tSb, in the potential rectangular wave used in the pulse electrolysis. At the (tSb / tCo) ratio of 7.0, the Co-Sb alloy film with the composition of 26.1 mol%Co-73.9 mol%Sb was obtained after heat treatment. This alloy film was not the CoSb3 single phase, but included it as constituent and exhibited a p-type thermoelectric conversion by the given temperature difference.
For this study, we applied a specific type of plasma in liquid phase named “solution plasma process（SPP）” for high-speed synthesis of gold nanoparticles（AuNPs）using an ethanol-water mixture as a liquid medium. Sputtering was conducted for the AuNP production. By applying high voltage across a pair of gold electrodes（∅＝1.0 mm）immersed in the liquid medium, ions formed in the plasma collided with the gold electrode surface and caused sputtering of the gold atoms. Subsequently, these atoms formed AuNPs immediately before dispersal into the medium. We inferred that the medium properties greatly influenced the SPP system sputtering mechanism. Accordingly, the influence of the ethanol-water mixture composition on the formation mechanism was studied in addition to the yield of the synthesized AuNPs. Results indicate that composition of the ethanol-water mixtures strongly influenced the breakdown conditions for the plasma formation and that the largest current observed at the ethanol mole fraction was 0.089-0.14. It is particularly interesting that this composition of the ethanol-water mixture led to the highest AuNPs formation yield. Our findings suggest that high-speed synthesis of metal nanoparticles in the SPP system is achievable by altering the type and/or composition of the liquid medium.