Creating semiconductor nanocages

The surface area of nanomaterials can be increased by creating open cage structures. Now it seems that the shape of nanocrystals can be used as a tool to manipulate crystal structure in nanocrystals. Wu et al. show how single nanocrystals of copper oxide are converted through anion exchange reactions to multiply twinned open cages of a copper sulfide in a process that changes the crystal lattice symmetries. These structures were then converted into cadmium sulfide nanocages through cation exchange.

Abstract

The crystal structure of ionic nanocrystals (NCs) is usually controlled through reaction temperature, according to their phase diagram. We show that when ionic NCs with different shapes, but identical crystal structures, were subjected to anion exchange reactions under ambient conditions, pseudomorphic products with different crystal systems were obtained. The shape-dependent anionic framework (surface anion sublattice and stacking pattern) of Cu₂O NCs determined the crystal system of anion-exchanged products of Cu_xS nanocages. This method enabled us to convert a body-centered cubic lattice into either a face-centered cubic or a hexagonally close-packed lattice to form crystallographically unusual, multiply twinned structures. Subsequent cation exchange reactions produced CdS nanocages while preserving the multiply-twinned structures. A high-temperature stable phase such as wurtzite ZnS was also obtained with this method at ambient conditions.

Science 18 Mar 2016:
Vol. 351, Issue 6279, pp. 1306-1310
DOI: 10.1126/science.aad5520
 
http://science.sciencemag.org/content/351/6279/1306