Fabrication of high-quality graphene by hot-filament thermal chemical vapor deposition Syed Muhammad Hafiz, Su Kong Chong, Nay Ming Huang * , Saadah Abdul Rahman * Low Dimensional Materials Research Centre, Physics Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia ARTICLE INFO Article history: Received 25 July 2014 Accepted 10 January 2015 Available online 16 January 2015 ABSTRACT To the best of our knowledge, the previously reported graphene fabricated using catalytic chemical vapor deposition techniques contained a high defect density, which will hinder its opto-electronic properties. In this work, the effects of two crucial parameters, namely deposition time and hydrogen flow rate on the growth of graphene using a hot-filament thermal chemical vapor deposition technique were systematically studied. Fabrications were conducted at substrate and filament temperatures of 1000 °C and 1750 °C, respec- tively. Very low I D /I G ratios (0.1) were obtained for all the samples, which reflected the for- mation of high-quality graphene deposited on Cu foils. A quasi-static equilibrium copper vapor inside an alumina tube was found to be an important factor to obtain a low defect density graphene. A growth mechanism was then proposed, where the cuprous oxide (Cu 2 O) acted as a nucleation site for graphene growth. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Graphene is a two-dimensional (2D) carbon material of hex- agonally packed carbon atoms bonded by sp 2 bonds. It is highly transparent, up to 97.4%, with a relatively low resis- tance (125 X/sq) [1]. It is also reported that graphene has high electron mobility at room temperature (250,000 cm 2 /Vs) and an elastic stiffness of 340 N/m, which may allow it to replace state-of-the-art indium tin oxide (ITO) in transparent conduc- tor technology [1]. It also has a very large surface area of 2630 m 2 /g, which is double that of single-walled carbon nano- tubes (CNT) [1]. These unique properties have given graphene a potential role in many applications such as electrical trans- parent conducting films and electrochemical sensors, which are necessary in the field of electronic devices. Many efforts have been devoted to developing diverse approaches to fabricate graphene, aiming for the large and uniform area synthesis of high-quality graphene. Thermal chemical vapor deposition (T-CVD) technique is widely used nowadays to fabricate graphene [2]. Nickel (Ni), copper (Cu), ruthenium (Ru), iridium (Ir), platinum (Pt), cobalt (Co), palla- dium (Pl), and gold (Au) have all been used as metal sub- strates, though the most common are Ni and Cu [3]. The versatility of this technique has been proven because it is nor- mally used to deposit diamond and other carbon-containing layers. Thus, it is also feasible to fabricate graphene. A depo- sition process was carried out by introducing carbon sources such as methane (CH 4 ) diluted with hydrogen H 2 [4–6]. The carbon sources will then thermally decompose to produce active carbon species to form graphene, which can be con- trolled by many factors such as the substrate temperature, deposition time, pressure, type of substrate, and gas composition. Among these factors, controlling the hydrogen in the hydrocarbon precursors has recently been recognized to play a critical role in controlling the size and morphology. In http://dx.doi.org/10.1016/j.carbon.2015.01.018 0008-6223/Ó 2015 Elsevier Ltd. All rights reserved. * Corresponding authors. E-mail addresses: huangnayming@gmail.com (N.M. Huang), saadah@um.edu.my (S. Abdul Rahman). CARBON 86 (2015) 1 – 11 Available at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/carbon