Effect Of Surfaces On Strength Evolution Of Silicon Nanostructures
Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Through a mix of atomic force microscope based fracture strength experiments, molecular dynamics modeling, and comparisons to past experiments we have show that the previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient. In a fully developed native oxide the Si-SiO2 interface flattens. As a result the strength recovers with some indication that it becomes slightly stronger than in its initially hydrogen terminated state. Experimental results are corroborated by Brad Boyce at Sandia National Laboratories using a completely separate line of testing involving micro-scale, polysilicon devices and the slack chain method. In addition, we demonstrate improvements to the calibration of the strength testing procedure, justify constitutive assumptions, and reduce overall uncertainty. Finally, we make an effort to extend the previous study of the effect of methyl monolayers on strength evolution of Si nanostructures by looking at more coating materials and longer time scales.
Silicon; Oxide; Strength
Warner,Derek H.; Phoenix,Stuart Leigh; Hines,Melissa A
Theoretical and Applied Mechanics
Ph. D., Theoretical and Applied Mechanics
Doctor of Philosophy
dissertation or thesis