Sample size effect in Ni-TiO2 composites fabricated by supercritical CO2 emulsified CO-electroplating for miniaturized device

Abstract

This study reports the micro-mechanical property and sample size effect in Ni-TiO 2 composites (NTO) fabricated by supercritical CO 2 emulsified co-electroplating (SCNTO). NTO by conventional co-electroplating (CVNTO) is also prepared as a comparison. The micro-mechanical property is evaluated by micro-compression test of micro-pillars prepared from the NTO by focus ion beam system. Cross-sections of the micro-pillars are 5 μm × 5 μm, 7.5 μm × 7.5 μm and 10 μm × 10 μm, and the height is kept twice of one side of the cross-section. The yield strength of a SCNTO micro-pillar with the dimensions of 7.5 μm × 7.5 μm × 15 μm is 3.37 GPa, which is three times higher than that of the CVNTO. The sample size effect is not observed in the SCNTO micro-pillars, while a smaller-is-weaker effect is observed in the CVNTO micro-pillars. The ultrafine (<10 nm) average grain size of the Ni in the SCNTO is suggested to cause the weakening in the sample size effect. The average grain size of the CVNTO is 23.6 nm, which is in the region of grain boundary-mediated mechanism that leads to the smaller-is-weaker effect. • Sample size effect in Ni-TiO 2 composites is investigated by micro-compression tests • Co-electroplating with supercritical CO 2 is used in preparation of the composite • Square-top pillars of 5 μm ~ 10 μm sample size are fabricated by FIB milling • 3-fold enhancement in the mechanical strength of the composite is observed • Mechanical strength of the composite is independent of the sample size