Uniformity in length of carbon nanotwists by filament discharge treatment for stable field electron emission

We have shown that a helical carbon nanofiber, carbon nanotwists (CNTws) on substrate are made to stand up by dielectric barrier discharge (DBD) treatment and this enhances their field emission property [1]. In this study, we present that the height of CNTws on substrate became uniform by the DBD treatment. CNTws with ethyl cellulose and silicone binders were printed on indium-tin-oxide-coated glass substrate [2]. The CNTws-coated substrate was treated by DBD in nitrogen atmosphere for 30 sec. The gap length of the DBD apparatus and nitrogen gas flow rate were 1 mm and 2 L/min, respectively. The CNTw amount in the binders ($A_{CNTw})$ was varied between 2.5 and 20 phr. Stand up of CNTws were seen when $A_{CNTw}$ was $\ge $ 5 phr. The length of CNTws on substrate ($L_{CNTw})$ at $A_{CNTw}$ = 10 phr was $\sim $4.5 $\mu $m, and the tip heights were not uniform. This unevenness was improved at $A_{CNTw} \quad \ge $ 15 phr. The field emission property of the CNTws at $A_{CNTw}$ = 20 phr was measured to be threshold electric field of 3.9 V/$\mu $m and highest emission current density of 630 $\mu $A/cm$^{2}$. [1] Yuji Hosokawa, et al, J Phys. D, 41 (2008) 205418 [2] Yuki Sugioka, et al, Jpn. J. Appl. Phys., submitted