The Studies of Low Dimensional Carbon and Germanium Nanostructures: Synthesis and Their Applications via Surface Functionalizations

Abstract

A lot of efforts have been conducted for finding the new materials to replace or to complement silicon, since its technology will be reached the theoretical limits. Among them, carbon and germanium, carbon families in periodic table, have been attractive for their unique physical, chemical and electrical properties. Carbon has several low dimensional structures, fullerene, carbon nanotubes and graphene, which show unique properties depending on their structures. Carbon nanotubes have been attracted due to their electronic, thermal properties and chemical reactivity. Graphene, the first developed two dimensional structure, which shows not only high optoelectronic and mechanical properties but also fundamental physicochemical studies. Germanium, the first generation material for transistor, has shown interestingly high carrier mobility, low band gap and facile integration process. Also, germanium nanowire is a good candidate for high performance electronic devices and optical devices using direct band gaps.In part I, the development of alcohol sensor using surface chemistry of carbon nanotubes and the synthesis of graphitic structures on dielectric substrates were discussed. Glycine molecules were easily adsorbed on the surface of carbon nanotubes and then alcohol molecules were selectively immobilized on the surface of carbon nanotubes with the help of probe molecules, glycine. Alcohol adsorptions were investigated with electrical signal measurement and their sensing mechanisms were theoretically proposed (PART I, Section 3). The formation of graphitic platelets was also investigated with simple chemical vapor deposition process without metal catalyst. The platelets were nucleated at the step edges of sapphire substrates and large size platelets were uniquely observed on (0001) sapphire substrate. The structural characterizations were conducted with AFM and Raman spectroscopy method and the growth mechanisms were also discussed (PART I, Section 5).In part II, the facile growth methods and their growth mechanisms of germanium nanowires and germanium selenide combs were discussed. To replace (the) toxic gas precursors such as germane or digermane, the liquid precursor, GeCl4, was used. Germanium nanowires were successfully synthesized with liquid precursor via vapor-liquid-solid (VLS) process. However it needed additional impurities, silicon, besides the gold nanoparticles. By investigating the existence of impurities in nanowire, the roles of impurities were discussed (PART II, Section 8). Finally, germanium selenide (GeSe) combs were simply formed via physical vapor deposition process. It showed hyper branched comb structure, which occurred by the V-shaped defect driven dislocations (PART II, Section 9).