NANO EXPRESS Field Emission and Radial Distribution Function Studies of Fractal-like Amorphous Carbon Nanotips F. Sola ´ Æ A. Biaggi-Labiosa Æ L. F. Fonseca Æ O. Resto Æ M. Lebro ´n-Colo ´n Æ M. A. Meador Received: 30 September 2008 / Accepted: 28 January 2009 / Published online: 13 February 2009 Ó to the authors 2009 Abstract The short-range order of individual fractal-like amorphous carbon nanotips was investigated by means of energy-filtered electron diffraction in a transmission elec- tron microscope (TEM). The nanostructures were grown in porous silicon substrates in situ within the TEM by the electron beam-induced deposition method. The structure factor S(k) and the reduced radial distribution function G(r) were calculated. From these calculations a bond angle of 124° was obtained which suggests a distorted graphitic structure. Field emission was obtained from individual nanostructures using two micromanipulators with sub- nanometer positioning resolution. A theoretical three-stage model that accounts for the geometry of the nanostructures provides a value for the field enhancement factor close to the one obtained experimentally from the Fowler-Nord- heim law. Keywords Carbon nanotips  Graphite-like a-C  EELS  EFED  Field emission Introduction Nanotips made of carbon can have many different applications such as scanning microscope probes [1] and field emission (FE) sources [2]. For instance, recently carbon nanofibers were used as the electron source in order to test and build an FE display device prototype where a new nanocrystalline silicon—polymer film—was used as the phosphor material [3]. Carbon nanotubes, from single to film dispersed cases, have been exten- sively studied due to their tensile strength, electrical properties, chemical inertness, and high aspect ratio [4–10]. However, an advantage that amorphous carbon (a-C) nanotips have over carbon nanotubes is that when a-C nanotips are synthesized using the electron beam- induced deposition method with a transmission electron microscope (TEM-EBID) their growth process can be followed in real-time and the nanostructures can be grown at preferred positions by controlling the electron beam [11]. Recently, FE studies were done on an indi- vidual one-dimensional a-C nanotip grown by the TEM- EBID method, where a field enhancement factor of the order of 10 was found [12]. In this study, a field enhancement factor of the order of 10 3 was obtained for fractal-like a-C nanotips consisting of several branches, each branch similar in shape to the previously mentioned one-dimensional nanotips. A theoretical three-stage model that accounts for those findings is presented and discussed. Multistage models have been used for other types of nanostructures such as carbon nanotubes and tungsten oxide nanowires [7, 13–15]. In addition, we also present information of the short-range order of our nanostructures, using the radial distribution function (RDF) obtained by electron diffraction patterns. With this information average nearest-neighbor distances and their bond angle were obtained. The results are consistent with distorted graphitic-like structure that can account for the moderate conductivity of the tips observed in the FE results. F. Sola ´  A. Biaggi-Labiosa  L. F. Fonseca (&)  O. Resto Department of Physics, Institute for Functional Nanomaterials, University of Puerto Rico, Rio Piedras, P.O. Box 23343, San Juan, PR 00931, USA e-mail: luis.upr@gmail.com M. Lebro ´n-Colo ´n  M. A. Meador Polymeric Materials Branch, Materials and Structures Division, National Aeronautics and Space Administration Glenn Research Center, 21000 Brookpark Road, Cleveland, OH 44135, USA 123 Nanoscale Res Lett (2009) 4:431–436 DOI 10.1007/s11671-009-9270-5