Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.
The field-emission sites’ distribution was measured to monitor the emission uniformity from randomly oriented carbon-nanotube (CNT) emitters using electron-beam resists (ER). The dot-patterned CNT emitters were fabricated by screen-printing a photoimageable CNT paste on an indium doped tin oxide (ITO) coated glass plate. An ER-coated Si substrate used as an anode provides the detection of the location and amount of the electron emission from the partial number of active emission sites among many existing CNTs. The measurements were carried out with the variation of electrical fields through continuous- or pulsed-voltage applications on a diode-type configuration. Developed ER images after a similar dosage of field-emission current flow indicate that emission uniformity is improved as the electrical field is increased. This method suggests that the emission uniformity could be estimated for various conditions of emitter preparation, such as CNT type, paste composition, and dispersion process, as well as the variation of the electrical field, the existence of a resistive layer, and so on.
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