TEM characterization of Rh–Cu2S nano-inorganic cages (a–b) and RuRh–Cu2S nano-inorganic cages (c–d). (a, c) HRTEM images of (a) Rh–Cu2S hybrid cages and (c) RuRh–Cu2S bi-metal hybrid cages. Darker regions are assigned to the metal frame due to higher electron density in those regions. (b, d) HAADF-STEM images of the corresponding cage-structured nanocrystals. Lighter regions have higher scattering in agreement with the Z-contrast imaging principle where higher Z metals are providing stronger signals.