Electronic structure, morphology and magnetic properties of Pt3Co and Au/Pt3Co dumbbell nanoparticles

GIOVANETTI, L.; MARTÍN DANIEL MIZRAHI; JOSE MARTIN RAMALLO LOPEZ; CECILIA DOS SANTOS CLARO; SHEVCHENKO, ELENA; REQUEJO, F. G.

Beijing

Conferencia; 15th International Conference on X-Ray Absorption Fine Structure; 2012

Multicomponent nanocrystals (MNCs) became an important class of materials due to their abilities to carry multiple functions that can be utilized simultaneously.1-3 In addition to additive properties, multicomponent nanostructures can reveal new collective phenomena originating from interactions of their constituents or enhancement of the properties of certain constituents4. Recent progress in synthesis of MNCs allows obtaining different types of nanoparticles such as core-shells,1 dumbbells, or other geometries.5 Synthesis of such structures is often based on the nucleation of the second component on the seed material. However, the synthesis of such materials is often empirical. Recently we have described a systematic study of synthesis of metallic dumbbell-like structures and propose the mechanism of the nucleation and growth of metallic dumbbells.5 In particular, we report here our characterization studies on MNCs of Pt3Co and Pt3Co/Au suspended in different solvents. The characterization was performed using electron microscopy (TEM), X-ray absorption (XAS), X-ray scattering at low angle (SAXS), global magnetic measurements (MM) and magnetic circular dichroism measurements (XMCD). Combination of TEM and SAXS results show spherical particles with a size dispersion of about 5% for Pt3Co system, while it was possible to observe the regular formation of dumbbell-like structures with the addition of Au. SAXS reveals that the addition of Au modify the stability of MNCs in solution producing the appearance of different types of oligomer. From MM is observed that all samples exhibit superparamagnetic behavior at RT with a blocking temperature which decreases in smaller Pt3Co MNCs. XMCD at the Pt-L2,3 edges measurements show that there is a transfer of magnetic moment from Co atoms to Pt for both systems and also reveals that addition of Au does not affect the magnetic behavior for the Pt atoms. Combination of XAFS measurements at the Pt L2,3 edges and Co K allows to reveal changes in the electronic configuration of Pt and Co atoms in the MCNs for example Co K edge reveals changes in the oxidation state of Co after Au deposition. XANES at the Pt L2,3 edges reveals a charge transfer from Pt 5d level after Au deposition respect to the Pt configuration in the MNCs used as seed. This work was supported by LNLS (projects DXAS – 10964, SAXS1 - 10969 and XAFS1-10889), ANPCyT (PICT-2008-00038 and PICT-2010- 0423) CONICET (PIP314112-200801-03079) and CIAM collaborative project (CONICET/CNPq). 1 Lee, J.-S.; Bodnarchuk, M. I.; Shevchenko, E. V.; Talapin, D. V. J Am Chem Soc. 2010, 132, 6382-91. 2 Xu, C. J.; Wang, B. D.; Sun, S. H. J. Am. Chem. Soc. 2009, 131, 4216. 3 Nam, S. H.; Shim, H. S.; Kim, Y. S.; Dar, M. A.; Kim, J. G.; Kim, W. B. Acs Appl. Mater. Interfaces 2010, 2, 2046-2052. 4 Rodriguez-Gonzalez, B.; Burrows, A.; Watanabe, M.; Kiely, C. J.; Liz-Marzan, L. M. J. Mater.Chem. 2005, 15, 1755-1759. 5 Galyna Krylova, Lisandro J. Giovanetti, Felix G. Requejo, Nada M. Dimitrijevic, Alesia Prakapenka, and Elena V. Shevchenko. J. Am. Chem.l Soc. 2012, 134 (9), 4384-4392.