Stable Electron Field Emission from PMMACNT Matrices Archana Pandey, Abhishek Prasad, Jason P. Moscatello, and Yoke Khin Yap* Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States F or more than a decade, electron field emission has been recognized as a promising application of carbon nanotubes (CNTs). 15 This is due to the high aspect ratios, good thermal and electri- cal conductivity, and robust chemical and mechanical stability of CNTs. However, reli- able commercial electron field emitters based on CNTs are still not available. Appar- ently, device lifetime, long-term emission stability, and low emission density are the major issues for practical field emission de- vices. Many techniques have been studied to enhance the performance of multiwalled carbon nanotubes (MWCNTs) for electron field emission. 68 Some attempted to modify the properties of CNTs by coating with metal oxide (In 2 O 3 ), wide band gap ma- terials, polymer, MgO, and barium stron- tium oxide. 913 Most of these works fo- cused on reducing the threshold electric field for emission. However, device lifetime, long-term emission stability, and emission density are scarcely discussed. Poor device lifetime due to resistive heating and me- chanical failure at the interface of CNTs/sub- strate has been reported. 14 On the other hand, recent work starts to evaluate the fun- damental factors behind stable field emis- sion and high emission density. We found that the graphitic order of CNTs is one of the key factors for stable field emission. 15 Re- cently, we show that both emission stabil- ity and density can be enhanced by self- organized opened-tip CNT bundles. 16 We report here that PMMACNT matri- ces are excellent electron field emitters with all the desired properties, such as low emis- sion threshold field, prolonged emission stability, and high emission density. We re- fer to PMMACNT matrices as arrays of opened-tip vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) embed- ded with poly(methyl methacrylate) (PMMA). We found that the emission thresholds (E th , electric field required for an emission current density of 1 A/cm 2 ) of PMMACNT matrices can be more than 2-fold lower than that of the as-grown VA-MWCNTs. Furthermore, PMMACNT matrices can continue to emit electrons for 40 h with negligible degradation. These PMMACNT matrices also have very uni- form and dense emission sites. Descriptions on sample preparation and field emission characterization are given in the Methods (Figure 1). RESULTS AND DISCUSSION Figure 2 shows the scanning electron microscope (SEM) images and the related Raman spectroscopy for our samples. All of these samples have VA-MWCNTs of 4 m length and 40 nm diameter (Figure 2a). Figure 2b shows that the as-grown VA- MWCNTs can be fully embedded in PMMA after the dip coating and curing processes. Magnified SEM view on the embedded sample was obtained after coating the sample with a thin layer (1 nm) of Au *Address correspondence to ykyap@mtu.edu. Received for review April 28, 2010 and accepted October 04, 2010. Published online October 18, 2010. 10.1021/nn100925g © 2010 American Chemical Society ABSTRACT We have created PMMACNT matrices by embedding opened-tip vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) with poly(methyl methacrylate) (PMMA). These PMMACNT matrices are excellent electron field emitters with an emission threshold field of 1.675 V/m, more than 2-fold lower that that of the as-grown sample. In addition, the emission site density from these matrices is high, merely filling up the entire sample surface. Emission stability test at 1.35 mA/cm 2 was performed continuously for 40 h with no significant degradation. On the basis of our theoretical simulation and hypothetical modeling, we attribute these performances to the reduced screening effect and fewer Joule heatings due to the shorter effective transport distance of the electrons in MWCNTs. KEYWORDS: carbon nanotubes · field emission · stability · Joule heating · screening effect ARTICLE VOL. 4 ▪ NO. 11 ▪ PANDEY ET AL. www.acsnano.org 6760