Figure 5: Optical properties of the material.

(a) Simulated electron energy loss spectrum calculated from the structure model with half of the Cu sites vacant (green) shows a distinct maximum, as compared to the calculated activity based on the structure with all Cu positions occupied (blue). The experimental EEL spectrum after subtraction of the carbon background is shown for comparison in red. As an inset, a visualization of the morphology of the particle used for the simulation is shown. (b) Corresponding calculation of the optical extinction spectra in the Vis–NIR region shows that the structure with vacancies (green) has a significantly improved optical response compared to the model without vacancies (blue). The experimental spectrum is shown in red.