| AVS 55th International Symposium & Exhibition | |
| Graphene Topical Conference | Monday Sessions |
| Session GR+TF+NC-MoM |
| Session: | Graphene and 2-D Carbon Nanostructures |
| Presenter: | M.Y. Zhu, College of William and Mary |
| Authors: | M.Y. Zhu, College of William and Mary R.A. Outlaw, College of William and Mary H. Chen, College of William and Mary M. Bagge-Hansen, College of William and Mary D.M. Manos, College of William and Mary |
| Correspondent: | Click to Email |
Field emissions from two-dimensional free-standing carbon nanosheets with ultra-thin edges synthesized in radio frequency (RF) plasma enhanced chemical vapor deposition from CH4/H2 gas mixture have been previously reported. When C2H2/H2 gas mixture was used, the growth temperature was lowered by 100-150 °C and well aligned vertical sheets with uniform height distribution were obtained. Typical C2H2 nanosheets were deposited on Si substrates using 80% C2H2 diluted in H2 gas (5 sccm total gas flow rate) at 600 ºC substrate temperature and 35 mTorr total pressure with 1000 W RF power for 10 min. The growth rate of the nanosheets measured from cross-sectional scanning electron microscopic images was 10.8 µm/hr. In this report, field emission measurements were taken from nanosheet samples 1.8 µm in height. Custom LabView software controlled automatic diode I-V measurements of C2H2 nanosheets yielded a threshold field, for an emission current density of 10 μA/cm2, of ~3 V/µm, which was ~2 V/µm lower than CH4 nanosheets. At an applied field of 5.3 V/µm, the current density was 1.1 mA/cm2 compared to the CH4 nanosheets of ~0.007 mA/cm2. Calculations from the Fowler-Nordheim plots and their linear fits indicated that the effective emission area of C2H2 nanosheets was ~15 times that of CH4 nanosheets and the β factor of C2H2 nanosheets was ~26% higher than CH4 nanosheets. The results are consistent with the morphology differences between the two kinds of nanosheets. The lifetime tests of C2H2 nanosheets conducted in a DC mode with a base pressure lower than 5×10-9 Torr showed a conditioning from an emission current of ~1.1 mA to a current level of 0.65 mA after 200 hour operation without any drop-outs or arcing failure. These tests were conducted with minimal anode cooling, which may account for the decay of the current on this timescale. The vacuum pressure of the testing system was recorded along with the emission current, and found to be closely correlated to the emission current.