The Bottom-Up Approach to Materials by Design

This chapter reveals that the bottom-up approach implies understanding the building blocks and then assembling them into a useful structure. For nanoparticle and multilayer composites used in aggressive loading environments, this requires an understanding of the length scales controlling the strength and toughness of the blocks. This chapter examines both nanospheres of silicon and thin films of Au in the 30 nm to 300 nm regime. With mechanical probing by nanoindentation thee chapter explores that length scales can be defined by volume to surface ratio with connectivity to dislocation evolution. These can predict to first order the variations in hardness that may be initially high due to an indentation size effect but then later dislocation harden due to a back stress mechanism. The importance of length scales, their measurement, and their inclusion in design rules for materials performance have been demonstrated. This chapter emphasizes two important aspects of volume/surface and dislocation slip-band morphology in length scale interpretations. These are shown to be important in understanding the hardening mechanisms in both silicon nanospheres and thin gold films in the 30-300 nm regime.