Shell or dots - precursor controlled morphology of Au-Se deposits on CdSe nanoparticles

The most prevalent image of the morphology of Au-CdSe hybrid nanoparticles (HNPs) is that of dumbbells or matchsticks with CdSe nanoparticles (NPs) acting as seed material onto which spherical Au dots are deposited. On the basis of a system with only three reaction components, CdSe seeds, n-dodecyltrimethylammonium bromide-complexed AuCl, and dodecanethiol, we demonstrate how the morphology of the Au deposits on the semiconductor NPs, either in the form of dots on the vertices or in the form of a shell around the NP surface, can be determined by controlling the oxidation state of the metal precursor. Furthermore, we apply X-ray photoelectron spectroscopy to show that the resultant deposits are composed of partially oxidized Au, corresponding to a Au-Se compound regardless the deposit morphology. To obtain a detailed characterization of the HNPs with different morphologies and to gain mechanistic insights into the deposition process, (cryogenic) high-resolution transmission electron microscopy, mass spectrometry, cyclic voltammetry, and computational simulations have been performed. Our results emphasize that the knowledge of the surface chemistry of the seed particles as well as a defined picture of the metal precursors is necessary to understand heterodeposition processes.C.K. and M.M. acknowledge the European Union for the ERC Starting Grant 2D-SYNETRA (304980, Seventh Framework Program FP7) and the Deutsche Forschungsgemeinschaft for granting the project KL 1453/9-1. B.H.J. is thankful for funding in the frame of the following projects: S2013/MIT2740 from Comunidad de Madrid and FIS2012-33011 and MAT2013-47395-C4-3-R and FIS2015-67367-C2-1-P from the Spanish Ministry of Economy and Competitiveness. R.O. is thankful for FIS2012-33011. Furthermore, the authors thank the Helmholtz Zentrum Berlin to have benn granted access to the BESSY-II facility, in particular the SurICat UHV XPS station. N.G.B. acknowledges financial support by MINECO through the Ramon y Cajal program (RYC-2012- 10991) and by the European Commission Seventh Framework Programme (FP7) through the Marie Curie Career Integration Grant (322153-MINE).Peer Reviewe