Polarity-Driven Polytypic Branching in Cu-Based Quaternary Chalcogenide Nanostructures
Reza R. Zamani,* Maria Ibáñez, Martina Luysberg, Nuria Garcia-Castello, Lothar Houben, Joan Daniel Prades, Vincenzo Grillo, Rafal E. Dunin-Borkowski, Joan Ramon Morante, Andreu Cabot, Jordi Arbiol*
An appropriate way of realizing property nanoengineering in complex quaternary chalcogenide nanocrystals is presented for Cu2CdxSnSey(CCTSe) polypods. The pivotal role of the polarity in determining morphology, growth, and polytypic branching mechanism is demonstrated. Polarity is considered to be responsible for the formation of an initial seed that takes the form of a tetrahedron with four cation-polar facets. Size and shape confinement of the intermediate pentatetrahedral seed is also attributed to polarity as their external facets are anion-polar. The final polypod extensions also branch out as a result of cation-polarity-driven mechanism. Aberration-corrected scanning transmission electron microscopy is used to identify stannite cation ordering, while ab initio studies are used to show the influence of cation ordering/distortion, stoichiometry, and polytypic structural change on the electronic band structure.