AVS 61st International Symposium & Exhibition
    Nanometer-scale Science and Technology Wednesday Sessions
       Session NS+AS-WeA

Paper NS+AS-WeA4
Shape and support interaction of size-selected Pd and Pt NPs on TiO2(110)

Wednesday, November 12, 2014, 3:20 pm, Room 304

Session: Nanoscale Imaging and Materials Characterization 
Presenter: Mahdi Ahmadi, University of Central Florida
Authors: M. Ahmadi, University of Central Florida
F. Behafarid, University of Central Florida
B. Roldan Cuenya, Ruhr-University Bochum, Germany
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The shape and the support interaction of 3D palladium and platinum nanoparticles (NPs) deposited on TiO2(110) was investigated using scanning tunneling microscopy (STM). The NPs were synthesized using inverse micelle encapsulation. In spite of the initial random location of the micelle-prepared NPs on the support, step edge decoration was observed after annealing at high temperature (>1000°C). In general, resolving the shape of 3D NPs using STM is very challenging due to the tip-convolution effects. However, a combination of ultra-sharp STM tips and samples containing structurally well-defined NPs allowed us to resolve the NP shape, with the highest features on the NPs being unaffected by tip artifacts. It was found that all NPs had a truncated octahedron shape, with {111} top and interfacial facets. Furthermore, the alignment of the NP edges (or symmetry axes) with the TiO2(110)-[001] atomic rows evidenced the epitaxial relationship with support achieved after annealing. The STM data were analyzed following the Wulff-Kaischew theorem, and a MATLAB code was used to reconstruct the NP shape, eliminating overestimations in the lateral size inherent to the STM technique due to tip effects. The surface energy ratio γ100/γ111 was calculated for each Pd NP with an average value of 1.12±0.07, which is in good agreement with theoretical values. Moreover, the adhesion energy was found to display a size-dependence, with larger NPs having smaller adhesion energy. This phenomenon can be explained based on the minimization of the interfacial strain by reducing the contact area. Following similar analysis of Pt NPs on TiO2(110), a higher γ100/γ111 ratio of 1.18±0.1 was obtained as compared to Pd. Also, the rate of decrease in the adhesion energy with increasing NP height was lower for Pt as compared to Pd.