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MSE Seminar - Prof. Jonathan E. Spanier, Drexel University
Friday, May 1, 2009
1:00 p.m.
Room 2108, Chemical and Nuclear Engineering Bldg.
For More Information:
Annette Mateus
301 405 5207

"When Beauty Is Only Skin Deep: Molecular Adsorbate and Inorganic Nanowire-Interactions"

Extreme reduction in nano-structured particle size is often accompanied by finite-size dependence of many properties. Additional materials functionality is also enabled by the unique physical and/or chemical environment on nanoparticle surfaces. Two sets of examples from our recent work involving interactions between molecular adsorbates and inorganic nanowires (NWs) at and near these surfaces highlight the additional significant role of and new opportunities involving, inorganic nanocrystal surfaces. First, I will discuss the unusual growth dynamics and structure of tapered semiconductor NWs that enable investigation of size-dependent electromagnetic (EM) properties. Aided by molecular adsorbates, probing the local EM field at and near the surface of the NWs reveals distinct diameter- and excitation-wavelength dependence in the inelastic optical scattering by these NWs and by molecules. In the second part of my talk I will also discuss our recent experimental proximal probe-based, and spectroscopic investigations and model calculation results involving the existence and switching of ferroelectric polarizations oriented along the smallest dimension in individual ferroelectric oxide perovskite NWs and ultra-thin nano-shells. Despite more than five decades’ worth of experimental and theoretical investigations of the scaling of ferroelectricity with particle size or film thickness, elucidation of this evolution of the ferroelectric phase transition temperature Tc as seen in individual nanostructures is only beginning to emerge. Significantly, we propose and discuss two mechanisms that act to stabilize ferroelectricity in nanostructures and ultra-thin films. One involves passivation of surface polarization charge by molecular adsorbates, and second, particularly in ultra-thin ferroelectric nano-shells, also involves the effects of strain and strain gradients owing to extreme curvature. A combination of density functional theory simulations, modified phenomenological Landau theory, and thermodynamic analysis demonstrates that the experimental behavior is well described by these mechanisms.

Jonathan E Spanier received the BA degree in physics from Drew University in Madison, NJ, and the PhD with Distinction from Columbia University in 2001 in applied physics with Professor Irving P. Herman. He completed a postdoctoral fellowship in physical chemistry at Harvard University with Professor Hongkun Park prior to joining the Drexel faculty in 2003. He is presently an associate professor in the Department of Materials Science & Engineering, he has an affiliated appointment in Electrical and Computer Engineering, and he currently also serves as the University Provost Fellow, working on the implementation of selected aspects of Drexel’s strategic plans. Prior to completing the PhD Professor Spanier held research and technical staff positions at NRL in physical acoustics and in the semiconductor device industry. Professor Spanier’s current research interests include the synthesis of, and collective electronic, optical and functional properties in, single- and multi-component inorganic nanostructures, particularly semiconductor and functional oxide nanowires. His research is supported by the NSF, the US Army Research Office, the Air Force Office of Scientific Research, and private industry. Professor Spanier received the PECASE in 2007 and the US Army Research Office Young Investigator Award in 2004.

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