ProduÃÃo de heterojunÃÃes de polianilina/silÃcio e nanofibras de polianilina para aplicaÃÃes em dispositivos hÃbridos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

In this work we develop the methodology for the synthesis and fabrication of Polyaniline (PANI) â Silicon (Si) heterojunctions, with great potential for technological applications as sensors in different areas such as optics, ionizing radiation and gas detection. Besides, we were able to implement the electrospinnin technique with the goal of producing polyaniline fibers with diameters in the sub-micron range. Thin films of polyaniline with thickness around 100 nm, deposited on silicon substrates by the spin coating technique, are the active interface of the heterojunctions. To be able to perform current â voltage (I x V) measurements, metal contacts were deposited by resistive thermal evaporation on the front and backside of the heterojunctions. The contact with silicon uses aluminum and the contact with polyaniline uses gold. Our devices show electrical properties with good reproducibility and a clear dependence of the I x V characteristics on the level of protonation of the polymer. Optical absorption measurements done on polyaniline (natural, doped, undoped) films fabricated on common glass substrates let us compare between the different levels of protonation and the state of protonation of the heterojunctions previously fabricated. With the help of the I x V and optical absorption characterizations it was possible to determine a more realistic model for the energy band diagram of the eterojunction PANI/Si. PANI fibers were produced with the implemented electrospinning technique, in which a polymeric jet, initially placed inside a capillary spinneret, is formed due to application of an intense electric field. While the polyaniline jet is traveling across the air, the solvent of the solution (formic acid) evaporates and consequently solid fibers of the polymer are formed. The fibers are finally collected on silicon or silicon dioxide substrates. To achieve the production of fibers with sub-micron dimensions, it was required to set up the whole experimental equipment involved in the electrospinning technique and to determine the conditions of applicability of this method to polyaniline. Scanning electron microscope (SEM) images were taken in order to study the morphological characteristics of the fibers and the effects of the different fabrication parameters. A preliminary study on the charge carrier transport properties of the fibers was done by current â voltage (I x V) measurements. The possibility to fabricate pure polyaniline nanofibers allied to precise selective control of conductivity in the polymer, brings new perspectives in the area of semiconducting hybrid devices, in particular, the possibility to fabricate rectifiers and field effect transistors (FETs) based only in polymers.

ASSUNTO(S)

semiconductor interfaces condensed matter physics sensores fisica conducting polymers sensors fÃsica da matÃria condensada efeitos de radiaÃÃo radiation effects interfases semicondutoras polÃmeros condutores

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