Alloy Formation at the Tetrapod Core/Arm Interface

Abstract

The nature of the interfacial structure between the core and the arms of a tetrapod quantum dot (QD) formed during the heteroepitaxial growth of a ZnS arm onto a CdSe core is not well understood but can be analyzed through the use of high-frequency electron paramagnetic resonance (HF-EPR) spectroscopy. The spectroscopic resolution at high frequency allows the presence of unique crystal fields reflecting interfacial alloying to be analyzed by incorporating Mn­(II) ions as a dopant into the QD to act as an intentional EPR active spectroscopic probe. In addition, the HF-EPR can spectroscopically observe the presence of ion vacancies that are anticipated to form at the heteroepitaxial interface to accommodate structural mismatch. The HF-EPR spectra for Mn­(II) are extremely sensitive to perturbations of the microenvironment due to changes in the crystal field. The HF-EPR spectra of Mn­(II) in a CdSe (core)/ZnS (arm) tetrapod exhibiting wurtzite symmetry for both core and interface of the tetrapod provide clear evidence of heteroalloying at the core–arm interface and formation of intrinsic dislocations at grain boundaries. The formation of the interfacial alloy and grain boundaries reflects short-range ion migration at the heteroepitaxial layer to reduce strain energy due to the 12% lattice mismatch between the wurtzite lattices of CdSe and ZnS