Field emission property of arrayed nanocrystalline diamond ☆ Bohr-Ran Huang a,b , Shyankay Jou c, ⁎, Tzu-Ching Lin b , Ying-Kan Yang b , Chia-Hui Chou b , Yao-Ming Wu b a Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, ROC b Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, ROC c Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, ROC abstract article info Available online 18 January 2011 Keywords: Nanocrystalline diamond Field emission Arrays Edge effect Arrays of nanocrystalline diamond (NCD) stripes were fabricated by plasma etching of a NCD film. Electron field emission (EFE) of NCD arrays with 100-μm-wide stripes separated by different spacings was analyzed. The NCD arrays had higher EFE efficacy than the non-patterned blanket NCD film. The turn-on electric field (E on ) decreased from 5.4 V/μm -1 for the blanket NCD film to 4.2, 4.4 and 4.7 V/μm -1 for the NCD arrays with 100, 500 and 1000 μm of spacing, respectively. Both the effective emitting area and the field enhancement factor for the NCD emitters were increased by patterning. The enhanced EFE from arrayed NCD stripes was possibly attributed to the edge effect and reduction of electrostatic screening. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nanocrystalline diamond (NCD) films have a variety of excellent properties such as high breakdown field strength, chemical inertness, high thermal conductivity, and high electron field emission (EFE) efficacy [1–3]. Due to its high EFE efficacy, NCD films have been utilized as electron emitters for vacuum microelectronics, pressure sensors and gas sensors [4–6]. EFE from diamond films at low applied electric fields of 3–5 V/μm has been intensely studied [7,8]. Morphology and bonding structure of NCD films significantly influenced EFE. Protrusion of crystallites and grain boundary defects such as mixed sp 2 and sp 3 carbon in NCD have been correlated to EFE enhancement [5,9,10]. On the other hand, patterning diamond into tips or sharp edge-shaped geometry, giving rise to the enhancement of electric field, could significantly improve EFE efficacy [11,12]. Carbon nanotubes (CNTs) have been known as a promising material for electron emitter. Yet the EFE efficacy of densely packed CNTs was affected by field-screening effect among neighboring nanotubes [13]. Patterning aligned CNTs into arrays of pillars or squares with proper spacing has been found to increase EFE efficacy [14–21]. Enhanced EFE of patterned CNTs arrays has been attributed to the enhancement of electric field and the reduction of screening effect near the edge of CNTs patterns [14,15]. NCD films have been known to emit electrons from discrete sites [22].A field-screening effect among proximate emitting sites on NCD surface might also affect EFE. An emission site density of about 5 × 10 4 /cm 2 , equivalent to an inter-site distance of about 45 μm, has been observed in a NCD film at a high current density [23]. In this study, we patterned NCD films into array of stripes with spacings larger than 50 μm to reduce the field-screening effect. The EFE properties of arrays of NCD stripes and a blanket NCD film were compared. 2. Experimental details A NCD film was deposited on p-type silicon (100) substrates using a microwave plasma-enhanced chemical vapor deposition system. Before the NCD film was deposited, silicon substrates were first polished using diamond powders (0.5 μm) and then ultrasonically cleaned in acetone and in ethanol in that order for 10 min each. NCD films were deposited in a mixture of methane/hydrogen/oxygen (30/169/0.2 sccm), at a pressure of 2.66 × 10 3 Pa, at a substrate temperature of 600 °C for 6 hours. Arrays of NCD stripes were fabricated by utilizing oxygen (O 2 ) plasma etching of the NCD film with an etch mask consisting aluminum (Al) stripes of 314 nm in thickness and 100 μm in width. The patterned Al masks were generated on the NCD surface by using photolithographic and lift-off processes. The unmasked region of the NCD film was etched back to the surface of Si substrate in an O 2 plasma with a microwave power of 250 W, an O 2 flow rate of 20 sccm, at a pressure of 1.33 × 10 3 Pa for 30 min. Then the oxidized Al mask was removed by wet chemical etching in H 3 PO 4 solution to obtain arrays of bare NCD stripes on Si substrate. A H 3 PO 4 -treated blanket NCD film was also prepared as reference, following the above process sequence including coating a continuous Al film, exposure to the O 2 plasma, and etched in H 3 PO 4 solution. The surface morphology and cross-section of the as-deposited NCD film and the patterned NCD stripes were inspected by a field-emission scanning electron microscope (FESEM, JSM-6700F). The surface rough- ness of the NCD films and NCD stripes were measured using an atomic force microscope (AFM, Veeco CP-R). The bonding structure of the NCD Diamond & Related Materials 20 (2011) 314–317 ☆ Presented at NDNC 2010, the 4th International Conference on New Diamond and Nano Carbons, Suzhou, China. ⁎ Corresponding author. Tel.: +886 2 27376665; fax: +886 2 27301265. E-mail address: sjou@mail.ntust.edu.tw (S. Jou). 0925-9635/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2011.01.018 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond