Scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis. SEM images were collected with a high-resolution scanning electron microscope FEI Nova Nano SEM 450, with an accelerating voltage of 15 kV for images acquisition and 20 kV for EDS collection. All samples were prepared by dispersing the material onto a double sided adhesive conductive carbon tape that was attached to a flat aluminium sample holder and were coated with a platinum layer of 15 nm using an Emtech K575 sputter coater.