Abstract
Carbon nanotubes (CNTs) were firstly discovered by Iijima, S in 1991. Conductivity polymer was discovered by Heeger, MacDiarmid and Shirakawa in 1970’s. Polyaniline (PANI) possesses physicochemical characteristics similar to CNTs. Their conductive and optical properties could be modulated. PANI has widely been regarded as quasi-one-dimensional semiconductor; whereas CNT can be considered as quantum wires. The novel electronic, photonic and optical properties obtained by coupling these two components are potentially attractive. In this thesis, in-situ polymerization was applied to produce PANI/MWNTs composites and various functional groups were used as template for aniline polymerization. To study the thermoelectric properties of multi-walled carbon nanotubes-polyaniline (MWNTs/PANI), we applied “PGEC” model of thermoelectric materials to an organic hybrid system, which was consisted of an aromatic amine functionalized MWNTs (AA-MWNTs) and PANI. The obtained TEP was up to 31 □V/K, which was 1.5~3.5 times to that of neat PANI. The voltage generated by PANI/AA-MWNTs was in the 32 oC temperature gradient, indicating PANI/AA-MWNTs possessing wider operating temperature than PANI (□T<12 oC). The improvement was attributed to the aromatic amine on MWNTs surface and enhanced interface adhesion between PANI and MWNT. To study the optical properties of MWNTs/PANI composite, two functional MWNTs, AA-MWNTs and AC-MWNTs (aniline contacted MWNTs), were prepared by chemical bonding and physical absorption with aniline, respectively. For AA-MWNTs, decreasing band gap for π-π* transition is obtained. The electrons generated in MWNTs could transfer directly to aromatic amine group when MWNTs absorb UV or visible light. The aromatic amine was suggested to trap quickly excitation energy and to enhance luminescence behavior. For AC-MWNTs, the interaction between MWNTs acceptor and aniline donor or acid-base/electrostatic reactions between carboxyl group and aniline anion quenched the luminescence. The PANI/AC-MWNTs made of short-chain PANI led band gap increase and red shift luminescence behavior was observed. Directly charge transfer from CNT to modifier on CNT surface and modifier trapped excitation energy from CNT was proposed as two key factors responsible for optical behavior of CNT-base material. To study the morphology and dopant effect on conductivity of MWNTs/PANI composite, MWNTs wrapped with polyanaline (MWPs) and aligned with polyanaline (MAPs) composites were prepared by using different addition sequence of oxidant. Systematic study demonstrated the orientation of polyanaline (PANI) long chains and the direction of electron transport in MWNTs and PANI played an important role in conductivity. At RT, the conductivity of MWPs was higher as PANI and MWNTs aligning parallel. However, at higher temperature de-doping resulted in decreasing conductivity. For MAPs, the perpendicular alignment between PANI and MWNTs resulted in lower conductivity at RT. At higher temperature, PANI short chains would switchover and got adsorbed on MWNTs to form a near parallel orientation. More aromatic amine of PANI would directly graft to MWNTs, resulting in increasing conductivity of MAPs. Similar morphology and dopant caused MWPs and MAPs to possess similar conductivity. The results indicate that morphology and dopant are critical for governing the conductivity of MWNTs/PANI composites at RT. At temperature above 150 oC, morphology becomes the dominant influencing factor. To study the photoluminescence tuning and stabilization of CdS nanoparticles by surface modification of tetra-aniline, 11-Mercaptoundecanoic acid (11-MUA) capped CdS and 11-MUA/ tetra-aniline capped CdS were prepared. The modification of the CdS surface with 11-MUA and tetra-aniline organic compounds increases the solubility and stability of CdS/11-MUA/TA particles. Decreasing band gap and enhancing spectroscopic properties by efficient charge-transfer between CdS and tetra-aniline was observed. To study atomic distribution in CdS nanoparticles by ToF-SIMS, the atomic distribution in the monolayer of two different Mn-doped CdS quantum dots (QDs) was studied for the first time with ToF-SIMS. The model Cd:Mn QDs were immobilized on Au substrate by use of a self-assembly-monolayer via 1,10-decanedithiol. Morphological analysis by SPM and TEM indicate larger particle size of in-situ synthesizing CdS:Mn. ToF-SIMS depth profile and 3D-images revel that Mn atoms reside on the surface of in-situ synthesizing CdS:Mn and are uniformly embedded in capped CdS:Mn. Comparable results obtained by SPM, TEM, XPS and ToF-SIMS are obtained, indicating that ToF-SIMS might find potential applications in surface and interface study of semiconductor nanocrystals.