Electron field emission from diamond-like carbon, a correlation with surface modifications Peter Grant and Christophe Py a) Institute for Microstructural Sciences, National Research Council of Canada, Montreal Road, Ottawa Ontario K1AOR6, Canada Claudia Mo ¨ ßner SI Software Innovation, 67346 Neustadt, Germany Alexandre Blais De´partement de Physique et Centre de Recherche en Physique du Solide, Universite´ de Sherbrooke, Sherbrooke, Que´bec J1K 2R1, Canada Hue Tran and Mae Gao Institute for Microstructural Sciences, National Research Council of Canada, Montreal Road, Ottawa Ontario K1AOR6, Canada ~Received 14 July 1999; accepted for publication 25 October 1999! We report a series of experiments characterizing the emission obtained from near-amorphous carbon deposited by excimer laser ablation. We found that vacuum arc discharge and material transfer are responsible for morphology modifications that greatly enhance emission. When the morphology of the materials are well controlled, we find that our carbon has a work function one half that of silicon. @S0021-8979~00!06803-1# INTRODUCTION Great effort has been invested in the past years for the development of reliable field emitters for field emission dis- plays ~FED!. Several approaches have been investigated, the most common being the Spindt type emitters. 1 It has been shown that impressive and stable current could be drawn from an array of these tips. However, their fabrication into arrays, which are necessary for commercialization, is still a technical challenge. More recently, a lot of interest has been focused on diamond-like carbon ~DLC! because of its FED compatible chemical and physical properties. DLC films were reported to emit at relatively low fields, as low as a few tens of V/mm. 2,3 Hence, DLC could resolve the necessity for arrays of tips as was shown by SIDT. 4 It could also be ap- plied as a coating for arrays of Spindt-type tips providing protection against deterioration in a static vacuum, and pos- sibly enhance emission. 5,6 However, the mechanism of emis- sion was not well understood and very low values of work function were erroneously attributed to DLC. Several ap- proaches have been developed to explain low field emission: negative electron affinity ~NEA!, and emission from impuri- ties, among others. It was pointed out by Gro ¨ ening et al. 7 and Talin et al. 8 that the high currents at low field often seen in the literature could be due to enhancement of the field magnification factor, b , due to localized surface modifica- tions. They reported formation of craters in the diamond film due to field emission ~FE! initiated discharges. This article supports those observations and demonstrates that other types of surface modification occur during FE. EXPERIMENTAL SETUP The DLC films used in these experiments were deposited using excimer pulsed laser deposition ~PLD!. High purity graphite targets were used and the films were deposited on silicon substrates. In this article we refer to our films as DLC, but amorphous carbon may be a more accurate de- scription. The films are very smooth, hard, and free of grain structure visible by scanning electron microscopy ~SEM! or optical means. The bonding is mainly sp 2 with some sp 3 as determined by Raman spectrometry. A detailed description of those films has been made elsewhere. 9 All field emission measurements where conducted in a turbo pumped vacuum chamber at pressure less than 4 310 26 Torr. To form a reference, measurements were also conducted on n –type, low resistivity, 0.01–0.02 V cm, silicon wafers. The substrates carrying the carbon films were cleaved in 1 cm squares that were then washed in ethyl alcohol and water with ultrasonics for 10 min. They were then washed for 10 more minutes in ethyl alcohol with ultrasonics. Finally, they were blown dry with ultrahigh purity nitrogen. In order to avoid surface contamination, the silicon wafers were cleaved in a clean room environment and only exposed to ambient atmosphere just before measurement. A simple test cell made with a DLC film, a conducting anode and two glass spacers was constructed for measuring the surface emission. Glass spacers of various thickness could be used to adjust the spacing between the cathode and anode. The cathode and anode were offset so that leads could be conveniently connected away from the area of high elec- tric field, which was typically 5 mm35 mm. A drawing showing test cell construction is shown in Fig. 1. The cath- ode was usually a DLC coating on a silicon substrate. The anode was stainless steel or sometimes a ZnO phosphor a! Electronic mail: christophe.py@nrc.ca JOURNAL OF APPLIED PHYSICS VOLUME 87, NUMBER 3 1 FEBRUARY 2000 1356 0021-8979/2000/87(3)/1356/5/$17.00 Downloaded 09 May 2003 to 130.132.248.36. Redistribution subject to AIP license or copyright, see http://ojps.aip.org/japo/japcr.jsp