Development of scanning field emission current microscopy

Spatial uniformity and durability of field emission are main issues in carbon nanotube (CNT) field emission devices fabricated by a screen-printing process. In this paper, we propose a novel method to visualize field emission sites of CNT films two-dimensionally by adopting scanning probe microscopy. While an anode probe with a small tip diameter of <100 nm was scanned over a CNT emitter surface whose dimension is 200 μm × 200 μm, the field emission current was recorded by a Keithley 6517A, SR570 (low-noise current preamplifier) and NI USB-6009 (data acquisition board), converted into 256 grayscale level, and displayed on a monitor through the LabView™ program. The anode probe was made by electrochemically etching tungsten wire and the CNT emitter sample was fabricated by screen-printing multiwall CNTs whose diameter is 4–6 nm and length 1–2 μm on indium-tin-oxide (ITO) glass. During scanning, the gap between W anode and ITO glass surface was maintained to be a few tens of μm. For large-scale imaging, we used an inertial nano-positioner whose model number is ANPxyz100, made by Attocube Systems, as a long-range scanner. With this system, we could obtain an electron emission current map over large surface areas under constant anode voltage.