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We report on the investigation of the surface morphology and DC conductivity of nanostructured layer-by-layer (LbL) films from nickel tetrasulfonated phthalocyanine (NiTsPc) alternated with either multi-walled carbon nanotubes (MWNTs/NiTsPc) or multi-walled carbon nanotubes dispersed in chitosan (MWNTs+Ch/NiTsPc). We have explored the surface morphology of the films by using fractal concepts and dynamic scale laws. The MWNTs/NiTsPc LbL films were found to have a fractal dimension of ca. 2, indicating a quasi Euclidean surface. MWNTs+Ch/NiTsPc LbL films are described by the Lai-Das Sarma-Villain (LDV) model, which predicts the deposition of particles and their subsequent relaxation. An increase in the wetting contact angle of MWNTs+Ch/NiTsPc LbL films was observed, as compared with MWNTs/NiTsPc LbL films, which presented an increase in the fractal dimension of the first system. Room temperature conductivities were found be ca. 0.45 S/cm for MWNTs/NiTsPc and 1.35 S/cm for MWNTs+Ch/NiTsPc.

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There is great interest on the study of the semiconductor/dielectric interface of organic field-effect transistors (OFETs), where a conducting channel is formed. Here, we use the interface selectivity, chemical sensitivity, and field-induced enhancement of sum-frequency generation (SFG) vibrational spectroscopy to probe interfacial molecular ordering and degradation processes in poly-3-hexylthiophene (P3HT) OFETs and also the electric field within their dielectric layer (poly(methyl methacrylate), PMMA). P3HT active layers fabricated by the Langmuir−Schaefer method are more orientationally ordered than spin-coated films. Upon electrical degradation of the device in ambient conditions, no noticeable changes were detected in the SFG spectra of the semiconductor/dielectric interface because the sensitivity of our experiment was not enough to detect degraded polymer chains due to loss of SFG electronic resonance enhancement. Perhaps for the same reason, we were also not able to detect any significant changes in the SFG spectra of the P3HT/dielectric interface upon charge accumulation induced by the gate bias. However, we found that upon polarizing the device, PMMA vibrational bands appeared due to field-induced reorientation of its polar groups. Therefore, SFG spectroscopy can be used to probe the electric field within the organic dielectric, including its sign, bringing the possibility of a complete device characterization by nonlinear spectroscopy/microscopy, mapping out the electric field both within the semiconductor and dielectric layers of the OFETs.