Biomedical Engineering Reference
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Fig. 7 Imaging topography and conductance of polymer blends. Top panels show 3D overlay of
conductance and topography ( left panel ), corresponding phase image ( second panel from left ) for
conductive and insulating ( right panels ) regions of a thin PEDOT-PSS fi lm. Highly conductive
regions are colocalized with high roughness and high phase variability. Bottom right shows high-
resolution images of selected regions showing detailed lamellar structure of conducting region
( bottom middle ) and nonlamellar structure of nonconducting region ( bottom right ). Schematic
drawing of setup shown in bottom left . For details, see Ionescu-Zanetti et al. ( 2004 )
light-emitting diodes (Carter et al. 1997 ). Although macroscopic structural studies
are available and performed mainly by X-ray diffraction (Aasmundtveit et al. 1999 ) ,
information about the effect of local morphology of polymer blends on the charge
injection at the surface has been lacking. AFM can combine imaging with spectro-
scopic capabilities and can be used to map the local charge transfer properties in
correlation to the molecular superstructure of the polymer blend (Ionescu-Zanetti
et al. 2004 ) .
Structure-function analysis of poly(3,4-ethylenedioxythiophene) doped with
poly(styrene sulfonate) (PEDOT-PSS) was performed: current between the tip and
the sample was measured by biasing the AFM tip while simultaneously imaging
the 3D structure (Fig. 7 ). This multimodal AFM experiment shows that the
PEDOT-PSS consists of molecular lamellae of PEDOT and PSS, with ~3-nm
interlamellar distance. In places where the edges of the PEDOT lamellae are
exposed to the surface and can be contacted by the AFM tip, increased current is
observed and a more effi cient charge injection occurs mainly along these lamellae.
Phase imaging simultaneously reveals a larger variation along the regions with
higher conductivity.
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