This report describes methods to produce large-area films of graphene oxide from aqueous suspensions using electrophoretic deposition. By selecting the appropriate suspension pH and deposition voltage, films of the negatively charged graphene oxide sheets can be produced with either a smooth "rug" microstructure on the anode or a porous "brick" microstructure on the cathode. Cathodic deposition occurs in the low pH suspension with the application of a relatively high voltage, which facilitates a gradual change in the colloids' charge from negative to positive as they adsorb protons released by the electrolysis of water. The shift in the colloids' charge also gives rise to the brick microstructure, as the concurrent decrease in electrostatic repulsion between graphene oxide sheets results in the formation of multilayered aggregates (the "bricks"). Measurements of water contact angle revealed the brick films (79°) to be more hydrophobic than the rug films (41°), a difference we attribute primarily to the distinct microstructures. Finally, we describe a sacrificial layer technique to make these graphene oxide films free-standing, which would enable them to be placed on arbitrary substrates.
Carbon nanotubes (CNTs) grown on SiC are metal-free, well-aligned, and with low
structural defects. In this study, CNT formation on SiC is examined in high vacuum (10-5torr) and
ultra-high vacuum (10-8torr). Multi-wall carbon nanotubes and graphitic structures are the main
products on the SiC surface at 1400-1800°C in 10-5torr. Under ultra-high vacuum, the
decomposition rate of SiC is much lower than in high vacuum, indicating that SiC is decomposed
by oxidation reaction. Using X-ray photoelectron spectroscopy (XPS), the intensity of the O1s peak
at 530.3 eV decreases with increasing take-off angle, indicating that this oxygen species exists on
the walls of CNTs. The results show that oxygen with a low pressure not only oxidizes SiC, but
also forms a highly thermally stable carbon-oxygen compound, and interacts with the CNTs at high
temperatures.
Aligned carbon nanotubes (CNT’s) are formed on the surface of silicon carbide (SiC)
wafers during high temperature anneals. The exposed 4H SiC surface transforms into CNT’s for
temperatures in the range of 1400-1700°C and under moderate vacuum conditions (10-2
– 10-5
torr).
The rate of formation on the C-face (0001,‾) is about three times the rate on the Si-face (0001), but
both rates increase with anneal temperature. SEM, TEM and Raman scattering measurements have
confirmed the presence of both single-wall and multi-wall CNT’s. The carbon source is believed to
be residual carbon from the SiC left on the surface after preferential evaporation of Si. CNT
formation is believed to be catalyzed by low concentrations of residual oxygen in the chamber.
Subsequent I-V measurements provide insight into the electrical characteristics of the CNT’s and
the SiC/CNT interface.
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