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Optical (a) and SEM images (b) and (c) of the SWNT strands used for the field emission measurements. Centimeters long SWNT strands are shown in (a); SEM observations show that these SWNT strands are made up of well-aligned SWNT bundles (b), scale-bar ; numerous upward SWNT bundles can be seen in the top view of the tip of a SWNT strand, and the diameter of the SWNT bundles is approximately (c), scale-bar .
Characteristic plots of the electron emission current as a function of the applied electric field for a SWNT strand with different heights , inset is the corresponding FN plots.
The emission stability of a SWNT strand under a vacuum of at room temperature with an initial emission current of (corresponding to a current density of ) in .
The height , threshold electric field , and enhancement factors of a SWNT strand. is defined as the applied electric field to obtain a emission current density of ; is the total enhancement factor calculated from the FN plot; is the enhancement factor related to the aspect ratio of the macroscopically long SWNT strand and is calculated from (Ref. 14); and is related to the diameter; length, and packing density of the SWNT bundles composing the SWNT strand, and is calculated from .
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