Journal of Nanomedicine & Nanotechnology

Understanding the surface properties of metallic nanoparticles by combining aberrationcorrected TEM studies with molecular dynamics simulations

2^nd International Conference on Nanotek and Expo

December 3-5, 2012 DoubleTree by Hilton Philadelphia Center City, USA

Bernd Rellinghaus

Scientific Tracks Abstracts: J Nanomed Nanotechol

Abstract:

Nanoparticles owe their peculiar properties to their nanoscopic dimensions or their enhanced surface-to-volume ratio and the fact that chemical and physical properties strongly depend on the atomic coordination and on symmetries. Accordingly, a thorough understanding of the surface properties is mandatory in order to tailor the particles? properties. In the case of metallic alloys the question arises, if the miscibility of their constituents known from bulk ?survives? the introduction of surfaces to an extent which affects a non-negligible fraction of atoms. E.g., FePt nanoparticles in the intermetallic L10 phase which are of interest for data storage applications due to their excellent magnetic hardness are often found to be magnetically softer than expected. This behavior is (partially) attributed to a surface segregation of Pt. The structural signature of such segregation is a surface-near lattice expansion. We present systematic studies on the structural characterization of FePt nanoparticles by means of state-of-the- art aberration-corrected HR-TEM investigations. Molecular dynamics simulations are conducted to relax the structure of FePt model particles which then serve as input for HR-TEM contrast simulations. From a comparison of the experimental HR-TEM studies with the simulated HR-TEM images it is shown that the typical surface-near lattice expansion is indeed due to a partial segregation of Pt toward the particle surface. Comparative studies on CuAu and Au nanoparticles reveal (i) that segregation is not bound for FePt, but is rather a general phenomenon in alloy particles and (ii) that its impact on the surface-near lattice structure depends strongly on the particle morphology.

Biography :

Bernd Rellinghaus has earned his PhD in physics from the University of Duisburg, Germany. Awarded with a Research Stipend of the German Science Foundation he then joined the IBM Almaden Research Center in San Jose, CA, USA. In 1997 he returned to Duisburg and moved to Dresden, Germany, in 2004, where he since then heads the Department for Metastable and Nanostructured Materials at the Leibniz Institute for Solid State and Materials Research (IFW Dresden). Bernd Rellinghaus is an expert in metallic materials, nanoparticles and high resolution transmission electron microscopy. He has published about 100 papers in reputed journals.