Raman imaging on high-quality graphene grown by hot-filament chemical vapor deposition S. Kataria, a * Avinash Patsha, b S. Dhara, b A. K. Tyagi b and Harish C. Barshilia a * We report the synthesis of high-quality graphene on Cu foils using hot-filament chemical vapor deposition technique and demonstrate that by suitably varying the CH 4 and H 2 flow rates, one can also obtain hydrogenated graphene. Micro-Raman spectroscopy studies confirm the growth of monolayer graphene as inferred from the intensity ratio of 2D to G peak which is nearly four in unhydrogenated samples. Detailed Raman area mapping confirms the uniform coverage of monolayer graphene. The grown layer is also transferred onto a Si substrate over ~10  10 mm sq. area. The present results provide a leap in synthesis technology of high-quality graphene and pave way for scaling up the process. Copyright © 2012 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article. Keywords: hot-filament CVD; graphene; hydrogenation; Raman spectroscopy Graphene, the fascinating strongest two-dimensional single layer of sp 2 bonded carbon atoms, has stimulated an escalating research interest since its discovery in 2004. It is considered as a strong candidate for post silicon technology owing to its proven unique electronic, mechanical and thermal properties. [1,2] Its electronic properties are well demonstrated by ballistic transport of electrons at room temperature which behave like massless Dirac particles, exhibition of room temperature quantum Hall effect and tunable band gap. [1–3] Graphene encompasses an interdisciplinary research area of materials, chemistry, physics and biology that has attracted ever increasing attention of scientific community. Owing to such astonishing physical proper- ties of graphene, it has numerous applications which include optoelectronics, high-performance devices, flash memory devices and bio-sensors. [4–7] There is a great stride to grow graphene on sufficiently large scale so that it can be applied to make useful devices. High-quality graphene samples can be produced by mechanical exfoliation method through which it was discovered, but the size of graphene flakes obtained by this method is limited to few micrometers. [1] Therefore, for the last few years, a lot of research is dedicated to large-scale production of graphene leading to its commercial applications. Among these, chemical vapor deposition (CVD) of graphene on a catalyst surface using hydrogen and a carbon source has become the centre of attraction. [3,8] CVD method has been successfully used for synthesis of graphene. [9–11] Generally, metals as catalysts are used to obtain graphene by CVD method, and its further transfer to another useful substrate is followed. [8] Raman spectroscopy is the indispensable non-destructive tool to characterize the carbon-based materials with graphene being no exception. [12] Raman spectrum of sp 2 bonded carbon materials is dominated by G and D peaks at around 1580 and 1360 cm 1 , respectively. [13] The G peak corresponds to the E 2g phonon at Brillouin zone centre (Γ point) and is due to bond stretching of all pairs of sp 2 carbon atoms in rings and chains. However, D peak is due to the breathing mode of sp 2 atoms in rings and its intensity is strongly related to the presence of six fold aromatic rings. It is activated by an inter-valley scattering process and comes from the transverse optical phonon at K point of Brillouin zone. [13] The activation of D peak requires the presence of defects, and, therefore, its presence in the Raman spectrum is generally used to determine the quality of graphene sample in a qualitative man- ner by determining intensity ratio of D and G bands i.e. I D /I G . [12] Raman spectroscopy has also been used to determine the num- ber of graphene layers. [12,13] Here, we report the synthesis of graphene using hot-filament CVD (HF-CVD) technique which has been extensively used for growing other carbon nanostructures like nanotubes, nanowalls and diamond thin films. [14–16] The choice of HFCVD is enacted due to the following reasons. The most significant advantage of HF-CVD technique over conventional tube furnace CVD is that the former is already being used for industrial production of other carbon nanostructures. Therefore, synthesis of graphene can be readily scaled up to mass production using HF-CVD tech- nique. Other advantages include option of substrate biasing and plasma generation during graphene synthesis which are not pos- sible in commonly used tube furnace CVD. To the best of our knowledge, reports on graphene growth by HF-CVD technique * Correspondence to: S. Kataria, Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore-560017, India. E-mail: skataria2k2@ gmail.com Harish C. Barshilia, Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore-560017, India. E-mail: harish@nal.res.in a Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India b Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India J. Raman Spectrosc. (2012) Copyright © 2012 John Wiley & Sons, Ltd. Rapid Communication Received: 9 March 2012 Revised: 20 April 2012 Accepted: 22 April 2012 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/jrs.4113