Alloy Formation at theTetrapod Core/Arm Interface.

The nature of the interfacial structure between the coreand thearms of a tetrapod quantum dot (QD) formed during the heteroepitaxialgrowth of a ZnS arm onto a CdSe core is not well understood but canbe analyzed through the use of high-frequency electron paramagneticresonance (HF-EPR) spectroscopy. The spectroscopic resolution at highfrequency allows the presence of unique crystal fields reflectinginterfacial alloying to be analyzed by incorporating Mn(II) ions asa dopant into the QD to act as an intentional EPR active spectroscopicprobe. In addition, the HF-EPR can spectroscopically observe the presenceof ion vacancies that are anticipated to form at the heteroepitaxialinterface to accommodate structural mismatch. The HF-EPR spectra forMn(II) are extremely sensitive to perturbations of the microenvironmentdue to changes in the crystal field. The HF-EPR spectra of Mn(II)in a CdSe (core)/ZnS (arm) tetrapod exhibiting wurtzite symmetry forboth core and interface of the tetrapod provide clear evidence ofheteroalloying at the core–arm interface and formation of intrinsicdislocations at grain boundaries. The formation of the interfacialalloy and grain boundaries reflects short-range ion migration at theheteroepitaxial layer to reduce strain energy due to the 12% latticemismatch between the wurtzite lattices of CdSe and ZnS. [ABSTRACT FROM AUTHOR]