Cu_2O Nanocrystal-Templated Growth of Cu_2S Nanocages with Encapsulated Au Nanoparticles and In-Situ Transmission X-ray Microscopy Study

摘要

Cubic and octahedral Cu_2O nanocrystals and Au-Cu_2O core-shell het-erostructures are used as sacrificial templates for the growth of Cu_2S nanocages and Au-Cu_2S core-cage structures. A rapid sulfidation process involving a surface reaction of Cu_2O nanocrystals with Na_2S, followed by etching of the Cu_2O cores with HCI solution for =5 sec, results in the fabrication of Cu_2S cages with a wall thickness of 10-20 nm. Transmission electron microscopy characterization reveals the formation of crystalline walls and the presence of ultrasmall pores with sizes of! nm or less. Formation of Cu_2O-Cu_2S core-shell structures and their conversion into Cu_2S cages is verified by UV-vis absorption spectroscopy. X-ray photoelectron spectra further confirm the composition of the cages as Cu_2S. The entire hollowing process via the Kirkendall effect is recorded using in-situ transmission X-ray microscopy. After shell formation, continuous ionic diffusion removes the interior Cu_2O. Intermediate structures with remaining central Cu_2O portions and bridging arms to the surrounding cages are observed. The nanocages are also shown to allow molecular transport: anthracene and pyrene penetration into the cages leads to enhanced fluorescence quenching immediately upon adsorption onto the surfaces of the encapsulated gold nanocrystals.