AVS 56th International Symposium & Exhibition
    Thin Film Thursday Sessions
       Session TF-ThM

Paper TF-ThM6
Tailoring Local Conductivity by the Formation of Ag Nanoparticles in SiO2 Xerogel Films

Thursday, November 12, 2009, 9:40 am, Room B4

Session: Nanostructuring Thin Films II
Presenter: M.F. Bertino, Virginia Commonwealth University
Authors: M.F. Bertino, Virginia Commonwealth University
R.J. Caperton, Virginia Commonwealth University
A.A. Baski, Virginia Commonwealth University
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Thin SiO2 xerogel films (~200 nm) were fabricated by dip coating and were doped with Ag+ by adding AgNO3 to the parent solution. Nanoparticles were then fabricated inside the pores of these films by either exposing them to ultraviolet (UV) illumination or by locally injecting charge using a conducting atomic force microscope (CAFM). In both cases, reduction of the Ag+ ions to the metallic state and the subsequent formation of Ag nanoparticles was observed by optical absorption spectroscopy and X-ray diffraction. Surprisingly, the formation of these Ag nanoparticles was accompanied by a decrease in the electrical conductivity of the films. For exposed regions with nanoparticle formation, CAFM measurements demonstrated no measurable current (< 1 pA) at sample bias voltages above 10 V. We attribute this decreased conductivity to a change in the morphology of the conducting Ag species in the film. Before reduction, Ag+ ions are attached to negatively charged pore walls in a comparatively dense packing and produce a conducting film. After reduction with UV exposure or CAFM charge injection, the silver metal agglomerates into conducting nanoparticles that no longer form a percolated network, leading to insulating behavior. Local modification of the conductivity on the nanometer-scale is possible by operating the CAFM with an applied voltage above 6 V and scanning a defined pattern. Subsequent imaging of the area at lower voltage then shows insulating behavior in the previously patterned regions. Larger-scale patterning on the micron-to-mm scale is possible by utilizing a mask when exposing the film to UV illumination. Extensions of this method to the fabrication of photonic and plasmonic devices is being explored.