Growth of Branched Carbon Nanostructures in Nanopatterned Surfaces Created by Focused Ion Beam
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Growth of Branched Carbon Nanostructures in Nanopatterned Surfaces Created by Focused Ion Beam Francisco Solá, Oscar Resto, Azlin Biaggi-Labiosa, and Luis F Fonseca Physics, University of Puerto Rico, Ponce de Leon Av., Rio Piedras, 00931, Puerto Rico ABSTRACT A method to grow arrays of multibranched carbon nanostructures is demonstrated. We use the electron-beam-induced deposition method using a transmission electron microscope with ~10-6 Torr vacuum where hydrocarbons are present in the chamber. Saw-tooth nano-patterns were made with a focused ion beam in porous silicon substrates as a template of the array. We found that the adequate ion dose to create well defined saw-tooth nano-patterns was between 8 and 10 nC/µm2 at 30kV. Due to the dielectric properties of the films the patterns provide the corresponding sites in which high local electric fields appear during irradiation thus allowing the hydrocarbons to become preferentially attracted to those active sites.. Electron energy-loss spectroscopy on the branched carbon nanostructures show a high concentration of sp2 sites suggesting that they are made of graphite-like amorphous carbon. INTRODUCTION One promising technique to synthesize nanostructures in a well controllable manner is the electron beam induced deposition (EBID) method. This method, when performed on the vacuum chamber of a transmission electron microscope, allows to follow the process in real time and to grow the nanostructures at preferred positions by controlling the electron beam. This technique uses the e-beam to induce surface local charging on insulating substrates to promote the deposition of charged chemical species from the gas existing in the vacuum chamber. The chemical species can be injected on purpose into the chamber in a controllable manner [1] or can exist in the vacuum chamber if its pressure is of the order of 10-6 Torr [2]. In the latter case hydrocarbons existing in the TEM have been reported to deposit at the position where the ebeam is irradiating the surface. In both cases the local fields can promote a multibranched dendritic growth when irradiated areas are in the order of a few microns (controlled area of growth), although other types of nanostructures such as nanodots can be obtained with this method when the irradiated areas are in the order of nanometers [3]. Recently we have used this method to fabricate silica/carbon heterostructures in which silica nanorods were decorated with carbon producing a nanopalm like structure [4]. Although the synthesis of branched nanodendritic like amorphous carbon (a-C) by EBID is already known, methods to form nanoarrays of such nanostructures in a controlled way have not been proposed yet. Nanoarrays of such materials could be useful for sensing applications. Here we discuss how to form such arrays by preparing saw-tooth nano-patterns with a focused ion beam microscope. When using the EBID method the saw-tooth nano-patterns become preferential sites for the growth of the above mentioned multibranched a-C structures becau
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