Engineering of the structures of carbon nanotubes and graphene-based materials for electronic applications

Abstract

Carbon nanotubes and graphene have been studied extensively for transparent conductors as replacement of ITO, high performance transistors as replacement of silicon and other electronic applications. The current graphene-based transparent conductors face three main problems: 1) high cost and limited size for the epitaxial grown graphene films; 2) low conductivity for chemically exfoliated graphene films due to the defects on graphene sheets and sheet-sheet junction resistance; 3) instability of doping. The junction resistance and instability of doping causes troubles for the SWNT based transparent conductors as well. To address the above problems, several types of solution-based flexible transparent conductors have been developed in this thesis, including reduced graphene oxide films, hybrid films of self-assembled silver network with unsorted SWNTs, sorted metallic SWNTs, and CVD-grown graphene. While all the hybrid films show similarly excellent performance in terms of sheet resistance, transmittance, stability in ambient conditions and bendability, unsorted SWNT-Ag hybrid films (R;-5.8 n sq" at T-83.7%) are more suitable for industrial applications due to the all solution-based scalable process and low cost. The application of the hybrid films as photovoltaic electrodes is also demonstrated. In addition, reduced graphene oxide (RGO) thin films were applied as platforms for gold nanostructure synthesis. By different reduction methods, viz. hydrazine vapor reduction, H 2 annealing, and ethanol/He reduction, the RGO reduction degree was controlled from low, to moderate, and to high, respectively. By simply immersing the RGO thin films into Au 3 + solution, Au nanoparticles, long Au nanowires and semicircularshaped Au nanoplates were produced on slightly-, moderately-, and highly-reduced III