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PhD thesis defense: Vapor Phase Infiltration (VPI) and Doping of Conducting Polymers

Thursday, October 26, 2017 - 11:00
CFM Auditorium
Weike Wang, Nanomaterials Group, nanoGUNE
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In this thesis, the ¨ Vapor Phase infiltration ¨ (VPI), a vacuum based process derived from the atomic layer deposition (ALD), is used for the top-down infiltration and doping of various conducting polymers. In the first part of this thesis, a single precursor vapor phase infiltration (VPI) process to dope polyaniline (PANI) is presented. As dopants, the vaporized Lewis acidic precursors SnCl4 and MoCl5 were used at a process temperature of 150 °C. After 100 cycles, the MoCl5-infiltrated PANI showed the highest conductivity, 2.93 × 10-4 S/cm, which is a significant enhancement of up to 6 orders of magnitude in comparison to undoped PANI. SnCl4-infiltrated PANI showed highest conductivity after 60 cycles with a value of 1.03 × 10-5 S/cm. The doping process with MoCl5 and SnCl4 results in an oxidation of PANI backbone. As a result, the electron mobility along the polymer chains is significantly enhanced and the structure is stabilized even at an elevated temperature in a vacuum environment. The second part of this thesis describes the single precursor VPI and doping of poly(3-hexyl)thiophene (P3HT). During the infiltration processes, the Lewis acid MoCl5 was used as precursor at a process temperature of 70 °C. The highest values show an increase of 5 orders of magnitude for the conductivity, namely from 1.44 × 10-5 S/cm in the as prepared P3HT to 3.01 S/cm after infiltration 100 cycles. In the last part of this thesis, the multiple pulsed vapor phase infiltration (MPI) process was applied to dope polyaniline (PANI). For the process, the two typical ALD precursors diethylzinc (DEZ) and deionized water (H2O) were used at a process temperature of 155 °C. The room temperature I-V plots show the conductivity of Zn-infiltrated PANI increasing to 18.42 S/cm, up to three orders of magnitude higher than obtained upon conventional doping with 1 M HCl in wet-chemical ways. Infiltration of PANI with Zn from the vapor phase results in a hybrid or composite material consisting of ZnO and PANI in the subsurface area of the polymer. Being chemically bound to each other, the inorganic and organic components mutually dope each other for the benefit of the resulting conductivity.

Supervisor: Mato Knez

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