Film surface morphology and field-emission characteristics of a carbon-nanotube array pattern fabricated under a magnetic field I.-S. Tsai C.-W. Huang H.-K. Huang J.-M. Jehng T.-C. Pan Abstract — This study focuses on the influence of sodium metasilicate binder on CNT paste and the arrangment of Mg–Ni alloy multi-walled carbon nanotubes on the surface of CNT film under the influence of a magnetic field. The CNT paste was prepared by mixing CNTs with silver epoxy resin and sodium metasilicate solution and coating them onto the surface of indium tin oxide (ITO) glass. The impact of sodium metasilicate solution and magnetic strength on the morphology of the paste film’s surface and on the field-emission (FE) characterics of the cathode was examined. The experi- mental results showed that the CNT paste provided good adhesion between the CNT array and silver epoxy resin when sodium metasilicate solution was presented. CNT paste containing sodium meta- silicate showed a better dispersion with silver epoxy resin and a better CNT-array pattern, and better vertical alignment of the CNT was obtained when the magnetic field and grid were both appied. An optimal condition for a better CNT-array pattern for both the morphology and FE characteristics had a magnetic strength of 189 mT, magnetization time of 30 min, and a grid above the cathode. Keywords — CNT-array pattern, Mg–Ni alloy multiwalled CNT, FE characteristics, magnetic field, sodium metasilicate. 1 Introduction Carbon nanotubes (CNTs) exhibit excellent field-emission (FE) characteristics and are one of the most actively studied materials for cold-cathode field emitters due to the CNT’s high aspect ratio, small-tip radii of curvature, mechanical strength, and good chemical and thermal stability. 1 Several researches have used a magnetized CNT to improve the alignment of the CNT. B. W. Smith and Z. Benes reported that thick films of aligned SWNTs and ropes have been pro- duced by filtration and deposition from suspension in a strong magnetic field. 2 G. Korneva and H.Ye reported on a simple and versatile technique to produce magnetic tubes by filling a CNT with paramagnetic iron oxide particles (10 nm in diameter). 3 T. Kimura reported that polymerizing MWNT-monomer dispersion under a magnetic field freezes the alignment of a MWNT in the polyester matrix. 4 J-H. Par and J-W. Nam reported that CNT paste with an inorganic binder (SOG) demonstrated improved uniformity, disper- sion, adhesion, and FE characteristics. 5 S. Y. Sheng and C.- C. Zhu reported a new composite of CNT with silicon dioxide (SiO 2 ) nanoparticles for the FED cathodes, improv- ing their emission-current-density properties and stable- emission characteristics. 6 For fabrication of cathodes using screen-printing techniques, a common problem is the alignment of the CNT in the CNT paste. The screen-printing causes a resultant force on the CNT paste during the processing. The resultant force is divided into two components: one is a vertical pres- sure force caused by the screen, the other is a transverse force. This resultant force causes the CNTs to align horizon- tally, parallel to the ITO glass, as indicated in Fig. 1. Most of the CNTs are covered by the CNT paste, which results in poor FE characteristics because there are too few CNT emitters. In this study, we tried to solve the problem of covering CNTs with CNT paste by using two approaches. One approach was to add an inorganic binder as filler and to dilute the viscosity of the CNT paste so as to let the CNTs protrude out of the film’s surface without being covered by silver epoxy resin. Theoretically, phase separation occurs in the blending of organic and inorganic binder and is layered according to specific weight. The top layer of the CNT paste on ITO glass is the CNT array; the next layers are sodium Extended revised version of a paper presented at Asia Display 2007 (AD ‘07) held March 12–15, 2007 in Shanghai, China. The authors are with Feng Chia University, Nanotechnology Research Center, No. 100 Wenhwa Rd., Seatwen, Taichung, Taiwan 40724, R.O.C.; telephone +886-04-245-17250-6850, fax +886-04-245-23485, e-mail: istsai@fcu.edu.tw. © Copyright 2008 Society for Information Display 1071-0922/08/1605-0639$1.00 FIGURE 1 — Schematic diagram of the alignment of CNT in CNT paste on ITO glass during the screen-printing process. Journal of the SID 16/5, 2008 639