Formation of an r8-Dominant Si Material

The rhombohedral phase of Si (r8-Si), a promising semiconducting material, is formed by indentation together with the body-centered cubic phase (bc8-Si). Using a novel sample preparation method, x-ray diffraction is used to determine the relative volume of these phases in indented Si and allow observation of a distorted unit cell along the direction of indentation loading. Theoretical calculations together with these observations suggest the indent contains an intrinsic compression of ∼4  GPa that stabilizes the r8 phase.We would like to acknowledge and thank Beamline Scientist Ruqing Xu for his help in obtaining the X-ray data. J. E. B. would like to acknowledge the Australian Research Council (ARC) (FT130101355). B. H. gratefully acknowledges funding through a Weinberg Fellowship sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy and ORNL’s Neutron Facilities, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. A. M. acknowledges support from MINECO Project No. MAT2016-75586-C4-3-P (Spain)

Thermal evolution of the indentation-induced phases of silicon

Novel phases of Si that are predicted to have industrially desirable properties can be recovered after indentation-induced pressure. However, the thermal stability of these phases is not well understood. Furthermore, in the past, different methods of annealing have resulted in conflicting reports on annealing stability and transformation pathways. This study investigates the thermal stability of several metastable Si phases called r8-Si, bc8-Si, hd-Si, and Si-XIII under furnace annealing, incremental annealing, and laser annealing using Raman microspectroscopy and electron diffraction. The temperature range of stability for these metastable phases is thus determined. Of particular interest, hd-Si is stable to a much higher temperature than previously reported, being the predominant phase observed in this study after annealing at 450 °C. This finding was enabled through a new method for confirming the presence of hd-Si by detailed electron diffraction. This high thermal stability generates renewed interest in exploiting this phase for industrial applications, such as strain-tailored solar absorption.J.E.B. would like to acknowledge the Australian Research Council (ARC) (No. FT130101355). A.M. acknowledges support from MINECO (Spain). B.H. gratefully acknowledges funding through a Weinberg Fellowship sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy (DOE) and ORNL’s Neutron Facilities, a DOE Office of Science User Facility operated by the Oak Ridge National Laborator