Study of novel materials for nanoelectronics: A scanning probe microscope study of graphene and graphite oxide
Approaching the miniaturization limit of silicon based microelectronics has presented ample research and development opportunities to grow and characterize materials for next generation electronic devices. Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS) and Atomic Force Microscopy (AFM) techniques offer unique capabilities to investigate the structural and electronic properties of these materials. Novel materials like hybrid organomolecular silicon, graphene and graphite oxide were examined during this study. STM/STS were performed on two organic molecules 4-trifluoromethylbenzenediazonium tetrafluoroborate and 4-methylbenzenediazonium tetrafluoroborate, covalently bonded to hydrogen passivated Si(111) substrate. It was established that STS can provide reproducible Current-Voltage response, I(V), on organic films of these molecules covalently bonded to the Si(111) substrate. With the help of STS we were able to demonstrate that conductance is strongly dependent on the terminal molecular end-group of the molecule attached to the substrate. STM studies were performed on epitaxial graphene films grown on the carbon face of 4H-SiC (0001) substrate by thermal annealing. The hexagonal arrangement of carbon atoms on few layer graphene (FLG) were identified, confirming the good quality of graphene prepared. STM/AFM studies were also performed on graphene films grown by chemical vapor deposition (CVD) methods on thin metal film of nickel/copper and transferred on to silicon dioxide (SiO2) substrate. Large area STM/AFM scans (5 μm × 5 μm) demonstrated the presence of ridges and wrinkles arising due to thermal mismatch of the carbon and the metal underneath. High resolution STM images demonstrated the hexagonal lattice of carbon atoms confirming the growth of FLG. STM/STS and AFM studies were performed on atomically thin graphite oxide flakes deposited on highly oriented pyrolytic graphite (HOPG) substrate. AFM topography and phase images indicated the presence of graphite oxide flakes of mean area 5 μm2 on HOPG. AFM images also showed varied topography including wrinkles, folds and cracks in graphite oxide flakes possibly arising during deposition process. Low resolution STM images supported the topography obtained by AFM study. High resolution STM images revealed the surface decorated with the rectangular lattice of oxygen atoms with lattice constants 0.273±0.008 nm and 0.406±0.013 nm. STS measurement indicated the presence of finite band gap of 0.25 eV when graphite oxide is deposited on HOPG.
Reifenberger, Purdue University.
Nanoscience|Condensed matter physics|Nanotechnology
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