The behavior of single-crystal silicon to dynamic loading using in-situ X-ray diffraction and phase contrast imaging*

Hydrostatic and uniaxial compression studies have revealed that crystalline silicon undergoes phase transitions from a cubic diamond structure to a variety of phases including orthorhombic Imma phase, body-centered tetragonal phase, and a hexagonal primitive phase [1, 2]. The dynamic response of silicon at high pressure, however, is not well understood. Phase contrast imaging has proven to be a powerful tool for probing density changes caused by the shock propagation into a material [3]. In order to characterize the elastic and phase transitions, we image shock waves in Si with high spatial resolution using the LCLS X-ray free electron laser and Matter in Extreme Conditions instrument. In this study, the long pulse optical laser with pseudo-flat top shape creates high pressures up to 60 GPa. We measure the crystal structure by observing X-ray diffraction orthogonal to the shock propagation direction over a range of pressures. We describe the capability of simultaneously performing phase contrast imaging and in situ X-ray diffraction during shock loading and discuss the dynamic response of Si in high-pressure phases. [1] Jamieson, Science, 139, 762 (1963); Hu et al. Phys. Rev.B 34, 4679 (1986) [2] McMahon and Nelmes, Phys. Rev. B 47, 8337 (1993); Mogni et al. Phys. Rev. B 89, 064104 (2014) [3] Nagler et al. J. Synchrotron Rad. 22 (2015); Schropp et al. Scientific Reports 5, 11089 (2015)