Growth and characterization of carbon nanofibers by a technique of polymer doped catalyst and hot-filament chemical vapor deposition H.J. Ceragioli, A.C. Peterlevitz, J.C.R. Quispe, V. Baranauskas * Departamento de Semicondutores, Instrumentos e Foto ˆnica, Faculdade de Engenharia Ele´trica e Computaça ˜o, Universidade Estadual de Campinas, UNICAMP, Avenida Albert Einstein N 400, CEP 13084-722, Campinas, Brazil article info Article history: Received 25 July 2007 Received in revised form 9 May 2008 Accepted 8 July 2008 Keywords: Carbon nanofibers Nanostructured materials Field emission Nanopolymers abstract Carbon nanostructures have been prepared from the catalytic conversion of polyethylene glycol using a rapid immersion in hot-filament system fed with ethanol, hydrogen and argon. Fiber structures of external diameter about 30 nm have been observed by field emission scanning electron microscopy (FESEM). Raman measurements indicate high degree of C–C sp 2 ordering which suggests that the samples correspond to CNTs of good tube crystallinity. The samples presented remarkable field emission properties. Lowest threshold field achieved for electron emission was 1.0 V/mm. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Intensive research efforts have been focused on the develop- ment of new nanostructured carbon-based materials such as carbon nanotubes (CNTs) [1,2], fullerenes, nanodiamonds [3,4] and conducting polymers [5–7] because of their potential applications as nanowires for active interconnection of nanoelectronic devices, electron sources for field emission displays, and ultra-sensitive bio- chemical sensors and actuators. CNTs may be fabricated by a variety of synthesis and purification methods such as electric discharge, laser ablation, electrolysis, catalytic decomposition of hydrocarbons and so on [1,2]. Each method has its own advantages and constraints, and new methods to produce pure and uniform CNTs at moderate temperatures are of interest. In this work, we report on the fabrication of carbon nanofibers by a combined method of synthesis from bulk polymer (poly- ethylene glycol) using metal catalysts and rapid immersion in a hot-filament system fed with ethanol highly diluted in hydrogen and argon. Polyethylene glycol has been chosen because of its low molecular weight and easy dissolution in ethanol. Field emission scanning electron microscopy (FESEM), Raman spectroscopic analyses, and field emission properties of the samples are pre- sented and discussed. 2. Experimental details Polished copper foils (10 mm  10 mm) of 0.5 mm thickness were used as substrates. The polymer solution was prepared from 1 g of polyethylene glycol diluted in 100 ml of ethanol in ultrasound for 10 min. The substrates were coated by the polymer solution without spinning and dried in a hot plate in air at 373 K for 120 min. Then the samples were wetted by 0.2 ml of acetone doped with nickel nitrate (10 g l 1 ) and immersed for 30 min in the reaction chamber of a hot-filament reactor system fed with hydrogen (34.5% vol), ethyl alcohol vapor, and argon (65% vol). A total pressure of about 20 Torr and a total flow rate of about 100 sccm were maintained throughout. The temperature as measured by a ther- mocouple placed on the underside of the copper substrates was 683 K. Morphological analyses were made by field emission scanning electron microscope (FESEM) using a JEOL JSM-6330F operated at 5 kV, 8 mA. Raman spectra were recorded at the ambient temper- ature using a Renishaw microprobe system, employing an Argon laser for excitation (l ¼ 514.5 nm) at a laser power of about 6 mW. Field emission properties were characterized in a specially designed vacuum system by controlling the distance (d) and the parallelism between anode–cathode (samples) surfaces using a precisely combined XYZ-angular micrometer stage. A Cu rod of 3.3 mm diameter was used as anode in parallel plate configuration with the samples (cathode). Measurement of the current density versus electric field (J–E) was undertaken for a fixed anode–cathode distance of d ¼ 1560 mm. The threshold field (E th ) for electron * Corresponding author. Tel.: þ55 19 3521 3746; fax: þ55 19 3289 1395. E-mail address: vitor.baranauskas@gmail.com (V. Baranauskas). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2008.07.004 Vacuum 83 (2009) 273–275