David Herbert Roach

Degradation of carbon nanotube field emitters driven by anode adsorbed water

The field degradation of carbon nanotube field emitters in diode emission at constant current was demonstrated to be highly dependent upon the presence of water at partial pressures as low as 10−9Torr. The anode surface was also seen to significantly impact the degradation rate, with metallic Al films yielding the worst degradation rates. Coating the anode surface with a carbon or polymer film lowered the degradation rate. It is suggested that a majority of the degradation seen in nanotube field emission devices is due to ionization of water adsorbed at the anode surface.

Enhancing lifetime of carbon nanotube field emitters through hydrocarbon exposure

The effect of carbon containing gasses on the field emission degradation rate of carbon nanotube field emission devices has been measured. Long chain hydrocarbons were seen to form a carbonaceous deposit on the anode surface which effectively lowered the degradation rate. Simple hydrocarbons such as methane, ethylene, and acetylene reversed degradation by continually enhancing emission. This continuous enhancement was repeatable and continued over 500h. Carbon dioxide exposure at low partial pressures resulted in an increased field emission degradation rate similar to oxygen and water exposure as reported earlier.

13.2: Electrochemical Deposition of Carbon Nanotube Films and Applications in Field Emission Display Devices

An electrochemical deposition (ECD) process for the formation of carbon nanotube (CNT) thin films on ITO coated glass is described. This simple and scalable process takes advantage of a highly stable aqueous dispersion of ribonucleic acids (RNA) wrapped CNTs reported previously. Thin films showing dense coverage of nanotubes can be prepared in a few minutes by the application of a few volts between a conductive substrate and a stainless steel counter electrode with both immersed in the RNA-CNT aqueous dispersion. Patterned deposit with feature size of microns can be readily obtained by masking the conductive layer on the substrate. Since ECD is an additive process with efficient use of CNTs, it provides a cost effective alternative to photoimagable deposition. Unlike electrophoretic deposition, the ECD process is an aqueous, low voltage, and field independent process. Fringing field issues which can affect deposition uniformity on patterned surfaces are therefore avoided. for electron field emission applications such as display or backlight, ECD films can be sintered and surface treated to obtain highly emissive surfaces with low threshold voltage and high uniformity emission. The field emission performance of diode and triode devices prepared with ECD is discussed.