DFT investigation of surface Magnetism on CdSe Quantum Dot due to Dangling Bonds and Ligands*

Surface magnetism of CdSe quantum dots (QD) is not well understood. Neeleashwar et al.  [1] claim that surface dangling bonds are responsible for the observed magnetism and determined a dangling bond concentration of 2000 ppm for a 1.5 nm QD, that decreases as the size of QD increases. On the other hand, Meulenberg et al. [2] attribute the magnetism to ligands rather than dangling bonds. According to [2], the concentration of dangling bonds is higher [3], which should result in a larger Currie constant than that observed experimentally, therefore, cannot be the cause of the magnetism. We performed density function theory (DFT) calculations on CdSe QD to resolve the controversy over the experimentally observed results. Our results indicate that every surface atom with a coordination number less than four does not possess unpaired electrons. Only atoms with coordination numbers less than three possess unpaired electrons and, therefore, contribute to the observed magnetism. Our calculation of Cd₁₄Se₁₄ QD capped with OP(CH₃)₃ and N(CH₃)₃ indicates that the choice of ligands influences the density of states of the surface Cd atoms.

 

1. [1] Neeleshwar, S.; Chen, C. L.; Tsai, C. B.; Chen, Y. Y.; Chen, C. C.; Shyi, S. G.; Seehra, M. S. Phys. ReV. B 2005, 71, 201307.
   
   [2] Meulenberg, R. W.; Lee, J. R. I.; McCall, S. K.; Hanif, K. M.; Haskel, D.; Lang, J. C.; Terminello, L. J.; van Buuren, T. J. Am. Chem. Soc. 2009, 131, 6888.
   
   [3] Katari, J. E. B.; Colvin, V. L.; Alivisatos, A. P. J. Phys. Chem. 1994, 98, 4109.