(Color online) (a) Sketch of the process used to fabricate a freestanding flexible cathode based on a VACNT-column array. First, synthesize a VACNT-column array on a silicon substrate by combining HFCVD and photolithographic patterning processes: see the SEM image in (b). Second, lay down the VACNT-column array upside down on a metal sheet covered with an uncured spin-coated PDMS prepolymer, then cure PDMS at for 2 min by using a hot plate [see the photograph in (c)]. Third, detach the VACNT-PDMS emitter from both the Si substrate and metal sheet: see the photograph in (d). Finally, etch the back side of the freestanding VACNT-PDMS emitter by the mixture of TBAF and NMP.
(Color online) (a) SEM image of the PDMS-free top surface of a VACNT column; inset: illustration of a freestanding PDMS-CNT film; (b) high magnification SEM image of nanotubes top surface showing no trace of PDMS.
(Color online) Schematic sketch of field-emission test on bending cathode; a photograph illustrates bendable PDMS-CNT film (upper inset); a plan-view image of the undeformed SWCNT-PDMS emitter (lower inset).
(a) curves and corresponding FN plots (inset) of the flexible CNT-emitter cathode under different bending angle and anode-cathode distance; at 0° and , at 0° and , at 36.5° and , at 50° and , at 66.5° and , at 66.5° and , and at 66.5° and . (b) curves measured at the bending angle of 66.5° and anode-cathode gap of ; the first bending (open circles) and after going through a few hundred times of bending (solid circles).
Electric field distributions at the surfaces of bent cathodes from a series of COMSOL simulation: (a) equipotential lines corresponding to the bias voltage of 2000 V at the bending angle of 66.5° and (b) electric field at the position of column at the bending angles of 0°, 36.5°, 50°, and 66.5° and the anode-cathode distances of 570, 870, 1070, and .
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