Phase Transition in Silicon Nanowires

Phase Transition and Compressibility in Silicon Nanowires
Wang, Y., J. Zhang, J. Wu, J.L. Coffer, Z. Lin, S.V. Sinogeikin, W. Yang, and Y. Zhao. Nano Letters, 8, 2891, (2008)

Silicon nanowires (Si NWs), one-dimensional single crystalline, have robust applications in electrical and optical devices as well as in the strengthening of diamond/SiC superhard composites. HPCAT experiments revealed that the onset pressure for the Si I-II transformation in Si NWs is approximately 2.0 GPa lower than previously determined values for bulk Si, a trend that is consistent with the analysis of misfit in strain energy. The bulk modulus of Si-I NWs derived from the pressure-volume measurements is 123 GPa, which is comparable to that of Si-V NWs but 25% larger than the reported values for bulk silicon. The reduced compressibility in Si NWs indicates that the unique wire-like structure in nanoscale plays vital roles in the elastic behavior of condensed matter. High resolution x-ray diffraction data clearly display peak splittings that result from symmetry-lowering transitions, proving strong evidence against the nanotwin theory for the monoclinic phases at morphotropic phase boundaries, which asserts that observed monoclinic phases are actually nanotwinned rhombohedral and tetragonal nanodomains.

Pressure-volume data measured at room temperature for Si NWs.

Microstructural characterization of fabricated Si NWs.