Flexible CNT-array cathodes: Effect of bending on field electron emission

In this work, we report results showing a correlation between the curvature of PDMS-supported CNT-tip arrays and their emission properties. CNTs were produced by using a hot-filament chemical-vapor-deposition (HFCVD) setup. VA-CNTs were synthesized using 28-Torr mixtures of methane (20 SCCM) and hydrogen (30 SCCM) as feedstock. Temperatures of filaments and substrates were 2050 and 750 degC, respectively. In order to make flexible emitters, pre-polymer PDMS was initially coated on the extremely clean, flat, and smooth surfaces of rigid supports, such as silicon and glass slide. The flatness and smoothness were necessary to form a thin and uniform pre-polymer layer, and the cleanness was important for easy detachment of PDMS films from the supports after curing. Next, we put a silicon substrate with a patterned VACNT-column array upside down on a support covered with an uncured thin pre-polymer layer so that uncured pre-polymer could infiltrate a VACNT-column array evenly from the contact side. We were able to control the PDMS-infiltration height by changing curing temperature of PDMS. A chemical etching process was required to expose CNTs in the back side. A solution of TBAF (tetrabutylammonium fluoride) inNMP (N-Methelpyrrolidone) (3:1; v/v; NMP/75% TBAF in water) was used to etch PDMS sufficiently without degrading the mechanical and elastic characteristics of the PDMS platform.