Secondary electron images were captured using a Hitachi S-4300 scanning electron microscope (SEM). An accelerating voltage of 5 kV was used to collect the images.
Transmission electron microscopy (TEM) images were captured using a JEOL 2100 with an accelerating voltage of 5kV. All acquisition has been performed along the [10-10] zone axis.
Cathodoluminescence hyperspectral imaging measurements were carried out at room temperature in a modified FEI Quanta 250 field emission SEM using electron energies of 15.0 keV and beam currents of approximately 7 nA. Light was collected using an NA 0.28 reflecting objective with its axis perpendicular to the electron beam and focused directly on the entrance of the spectrograph using an off-axis paraboloidal mirror. We used a 125 mm focal length spectrograph with a 600 lines/mm grating and 50 μm entrance slit, coupled to a cooled electron multiplying charge-coupled device (EMCCD) detector.