| dc.description.abstract | Abstract
Scanning probe microscopies (SPMs) are important technologies providing the variety properties of material surfaces with nanometer-scale spatial resolution. Atomic Force Microscopy (AFM) was one of the most widely used techniques of the SPM. The surface morphology and the physical properties of the materials can be measured simultaneously by recording the various interactions as well as the atomic force between the sample and the tip. By applying a voltage between sample and a conductive AFM tip, a so-called Conducting Atomic Force Microscopy (C-AFM), topographic and current images were obtained simultaneously. Furthermore, a current-voltage trace can be recorded on a selected spot of the image, where one can study the electrical characteristics of the surface. The topographical images of emeraldine base (EB) are similar to emeraldine salt (ES). The globular-shaped structure was observed in polyaniline (PANI) films prepared from HCl and HClO4 aqueous solutions, whereas the entangled fiber-shaped structure is detected when PANI films were prepared in H2SO4(aq). The topographical images also depend on the doping level, film thickness and dopant. The conductivity images, which provide information on the distribution of conducting (insulating) islands surrounded by insulating (conducting) areas, demonstrate that electron conduction across the PANI film is heterogeneous and the conducting homogeneity also depends on doping level, thickness, and dopant. As the doping level of PANI film increased, the size of conducting islands also increased and the I-V curves showed semiconducting and metallic conducting characteristics. As the thickness of PANI film increased, the number and area of conducting domains increased, and the I-V curves showed semiconducting and semi-metal conducting behavior. PANI films prepared from HClO4(aq) (thickness <120 nm) have the smallest degree of conjugation and their I-V curves show semiconducting characteristic no matter they were doped with HCl, H2SO4, or HClO4. The degree of conjugation in PANI films prepared from H2SO4(aq) is the same as those prepared from HCl(aq). These PANI films have the highest conductivity when doping with HClO4(aq), and the I-V curves of all surface show metallic conducting behavior. | en_US |