Silver nanowires underneath the protective layer are not visible in AFM topography and phase images. However, they are clearly visible in the PiFM image since the near-field from the tip is coupled effectively to the conductive nanowire, creating a strong attractive force even through a rather thick protective layer (> 100 nm). The same principle allows PiFM to image metal layers underneath a dielectric layer (not shown).
These transparent conductors are composed of silver nanowires embedded in clear plastic. AFM topography (left) displays those nanowires that contribute to surface morphology. However, buried nanowires do not appear in topographic images.
PiFM imaging (right) does reveal the placement of embedded nanowires by taking advantage of the enhancement of the overlying acrylate polymer signal (1745cm-1) in the presence of a metallic nanowire.
Careful inspection of the PiFM image reveals buried silver nanowires not detected in the topography image. The effect of the buried silver metal wires on the strength of the recorded 1745cm-1 signal can be felt through nanometers of insulating acrylate.
Mapping Silver Nanowires in Transparent Conductors
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