Exploring Size Dependent Brittle-to-Ductile Transition in Single Crystal Silicon Using High Temperature MEMS

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The objectives of this program are to (a) measure brittle-to-ductile (BDT) temperature in Single Crystal Silicon (SCS), widely used in micro/nano scale devices, as a function of size, and (b) unravel the mechanisms of size dependence of BDT. The temperature at which materials become ductile from brittle is known as BDT temperature. At macro scale, BDT is independent of size. There is emerging evidence suggesting that at nano scale, BDT temperature becomes size dependent, although the underlying mechanism is unclear, which this program seeks to explore. The research will be conducted by developing a novel SiC micro mechanical stage that allows testing micro/nanometer scale specimens at room to 1000C while visualizing their microstructure in scanning or transmission electron microscopes.The intellectual merit is that the project explores a fundamental question: how BDT temperature becomes size dependent. Its working hypothesis is, BDT is caused by a sudden increase in density and mobility of crystalline defects such as dislocations. The energy required to activate dislocations from the surface is substantially smaller than that from the bulk. Hence BDT temperature decreases with size. Broader impact: Research will be integrated with education and outreach by developing a hands-on instructional module, and recruiting REU students from diverse backgrounds. Due to collaborations with the Universities of Vienna and of Leoben, Austria, the participants will gain international experience.The study could be transformative if it shows that BDT is size dependent in pure SCS, and its underlying mechanism. The study may offer a new paradigm in the understanding of SCS.