IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 41 (2008) 055309 (7pp) doi:10.1088/0022-3727/41/5/055309 Synthesis of DLC films with different sp 2 /sp 3 ratios and their hydrophobic behaviour R Paul, S N Das, S Dalui, R N Gayen, R K Roy, R Bhar and A K Pal 1 Department of Instrumentation Science, USIC Building, Jadavpur University, Calcutta-700 032, India E-mail: msakp2002@yahoo.co.in Received 29 December 2007, in final form 22 January 2008 Published 14 February 2008 Online at stacks.iop.org/JPhysD/41/055309 Abstract Diamond-like carbon (DLC) films were deposited on glass substrate by sputtering of a vitreous carbon target in Ar + H 2 plasma. The sp 2 /sp 3 content in the films depended on the relative amount of hydrogen in the Ar + H 2 plasma. The films were characterized by Fourier transformed infrared studies, Raman studies, scanning electron microscopy, atomic force microscopy and optical measurements. Hydrophobicity in these films was studied by measuring the contact angles of the water droplets and it was found that the films were extremely hydrophobic. The results are interpreted in terms of hybridization of carbon in these DLC films. (Some figures in this article are in colour only in the electronic version) 1. Introduction In general, diamond-like carbon (DLC) films consist of graphitic clusters linked by sp 2 (π bonding) or sp 3 bonding (σ bonding) forming an extended carbon network and the relative amounts of the sp 2 and sp 3 bonded carbon present in the network dictate the physical properties. The above property would permit the production of tailored DLC films for device applications. There are a large number of publications [1–5] on the dependence of the properties of the DLC films on the sp 2 /sp 3 bonding ratio indicating the dependence of the electrical properties on the sp 2 bonding and optical band gap on the lowest π –π ∗ transition while the sp 3 bonding determines the mechanical properties. Studies of the microstructural, mechanical, electrical, optical and thermal properties of hydrogenated amorphous carbon films deposited by various techniques were reported by many workers [6–11]. Depending on the bias voltage, hydrogen may go to the bonded or non-bonded state. It is known that the amount of hydrogen in the bonding configuration determines the hardness, optical band gap and the electrical resistivity [1–3], whereas the amount of non- bonded hydrogen plays a dominant role in determining the stress and adhesion of the film on the substrate. Earlier studies indicated that the partial pressure of hydrogen in the 1 Author to whom any correspondence should be addressed. working gas mixture affected not only the bonding hydrogen concentration but also the bonding configuration ratio among CH, CH 2 and CH 3 present in the film [8]. Recently, DLC films have come to the centre stage of developing coatings for moisture resistant lubricant, water repellant and cathode for lithium batteries [12–15]. Fluorination was found to improve the hydrophobic properties of the DLC films. The addition of fluorine in DLC matrix was found to modulate the D- and G-peaks regarding their position and intensity. In this paper, we present our studies on the DLC films prepared by sputtering of vitreous carbon in argon plasma containing different amounts of hydrogen in it. The films were characterized by Fourier transformed infrared (FTIR) studies, Raman studies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical measurements. Hydrophobicity in these films was studied by measuring the contact angles of the water droplets. 2. Experimental details The deposition system for sputtering a vitreous carbon target consisted of a stainless steel vacuum chamber (12 inch diameter) with appropriate stainless steel vacuum couplings through which requisite vacuum gauges, gas inlets, thermocouples, etc could be attached. The sputtering target 0022-3727/08/055309+07$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK