| AVS 54th International Symposium | |
| Thin Film | Tuesday Sessions |
| Session TF-TuM |
| Session: | Two-Dimensional Carbon Nanostructures |
| Presenter: | M. Bagge-Hansen, College of William and Mary |
| Authors: | M. Bagge-Hansen, College of William and Mary P. Miraldo, College of William and Mary R.A. Outlaw, College of William and Mary M.Y. Zhu, College of William and Mary M. Hou, College of William and Mary D. Manos, College of William and Mary |
| Correspondent: | Click to Email |
Carbon nanosheets, a new morphology of graphite, have shown remarkable promise as field emission cathodes for applications such as microwave tubes and flat panel displays. The sharp emission edges of the sheets are typically 1-3 graphite sheets thick (~1 nm) and thus provide a superior geometry for field emission enhancement. Fowler-Nordheim theory suggests further field emission enhancement is possible by lowering the work function. The effective work function of carbon nanosheets, previously undetermined, was calculated and found to be analogous to that of graphite, 4.8 eV. By applying a thin film coating of Mo2C (Φ = 3.5 eV), the field enhancement factor from the geometry, ß, was reduced by only a factor of two, yet field emission current substantially increased. A molybdenum coating was deposited on a carbon nanosheets sample by physical vapor deposition in very high vacuum (p ~1x10-8 Torr) and determined to be ~3 monolayers thick by Auger electron spectroscopy. The coated sample was radiatively heated to T~250°C to promote molybdenum reaction with adventitious carbon found in defects of the carbon nanosheets’ emission edges and the underlying graphite structure. Auger electron spectroscopy and scanning electron microscopy were used to verify the composition and conformity of the coating, respectively. Field emission testing in an ultrahigh vacuum (p ~5x10-10 Torr) diode assembly with 250 µm spacing showed lowering of the effective work function after the coating procedure and consequently, increased emission current. At an applied field of 9 V/ µm, the emission current was found to be 100 µA compared ~0.1 µA for the carbon nanosheets. A comparison of linear (R2 = .999) Fowler-Nordheim plots of coated and uncoated samples yielded values for the work function of uncoated CNS and the fractional emitting area of ~2% for carbon nanosheets. The experimental data of Mo2C-coated CNS was significantly more repeatable and stable than the uncoated CNS.