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Polythiophene-Gold Nanoparticle Hybrid Systems: Langmuir-Blodgett Assembly of Nano-Structured Films

Sundaramurthy Jayaraman1, Ting Yu Liew2, Prashun Gorai2, and MP Srinivasan2. (1) Chem and Biomol Engg, NUS, 4 Engg Drive 4, Singapore, Singapore, (2) ChBE, NUS, 4 Engg Drive 4, Singapore, Singapore

Langmuir-Blodgett (LB) assembly technique is one of the most powerful tools to control molecular orientation, organization and for building uniform multilayer assemblies, and is a logical method to construct nano-structured thin films for micro- and nano-scale devices. Conducting polymers such as polythiophenes with excellent electronic and fluorescent properties can be deposited using the LB technique. Polythiophenes are one of the important classes of conducting polymers and the thin films of polythiophene finds application in field effect transistors, biosensors, organic photovoltaic cells and many more. Attempts have been made to increase the conductivity of ultra thin films of polythiophene either by doping, functionalization or incorporation of conducting nanoparticles.

In this work, we have fabricated nano-scale hybrid systems from polythiophene LB ultra thin film assembly with incorporated Au nanoparticles (AuNP). Investigation of electronic properties such as oxidation potential, conductivity and the electron mobility showed increase in measured parameters with increase in number of layers. Blends of an amphiphilic regioregular, ether-terminated polythiophene with a poly alkyl thiophene were also employed. Interaction studies showed that a net repulsive force exists between the two thiophene species making the film assemblies potential candidates for patterned incorporation of AuNP. A number of interesting phenomena in terms of affinity of AuNP for thiophenes were observed by the various microscopic and spectroscopic characterization techniques. Electronic properties were investigated using Hall and surface resistivity measurements. A significant enhancement was observed in the conducting properties upon incorporation of AuNP.