Hard-hydrogenated tetrahedral amorphous carbon films by distributed electron cyclotron resonance plasma F. Piazza * Department of Physics, Faculty of Natural Sciences-Phase II, University of Puerto Rico, Office c-302, P.O. Box 23343, San Juan, PR 00931, USA Received 11 November 2004; accepted 12 July 2005 Abstract Hard-hydrogenated tetrahedral amorphous carbon films (ta-C:H) are deposited from acetylene-fed distributed electron cyclotron resonance (DECR) plasma over large area (300 mm diameter disk) at near room temperature (below 140 °C). The effects of the ion flux and energy on the structure and physical properties are investigated. For a constant substrate bias V 0 of 150 V, the mass–den- sity, YoungÕs modulus and hardness reach a maximum value of 2.5 g/cm 3 , 280 GPa, and 45 GPa, respectively, and the hydro- gen content reaches a minimum of 26 at.% at the maximum ion flux / + of 6.3 · 10 15 ions cm 2 s 1 . For a constant ion flux and pressure, the mass–density and YoungÕs modulus reach a maximum at a substrate bias of 300 V, and the hydrogen content is mini- mised. Electron diffraction, and Raman spectra show that the films grown at the maximum ion flux and a negative substrate bias ranging between 150 and 500 V are ta-C:H. The films contain sp 2 -carbon clusters and chains. sp 2 -carbon clustering increases with the increase of the substrate bias and decreases with the increase of the ion flux. The disorder increases with the ion flux and decreases with the bias. The optical band-gap decreases with disorder and with sp 2 -carbon clustering. It depends primarily on dis- order rather than on clustering. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Tetrahedral amorphous carbon; Diamond-like carbon; DECR; Hardness; Raman spectroscopy; Band-gap 1. Introduction There is great interest in amorphous carbon films, hydrogenated (a-C:H) or not (a-C) containing a high fraction of sp 3 -bonds between carbon atoms [1]. The sp 3 -bonding between carbon atoms of a-C (and of a- C:H) confers on it many of the beneficial properties of diamond, such as its high hardness and large YoungÕs modulus, low coefficient of friction, high wear resis- tance, smoothness, optical transparency in a wide range of wavelengths, chemical and biological inertness, low electron affinity, high electrical resistance, lack of mag- netic response [1]. The films can be grown at near room temperature, and are much cheaper to produce than dia- mond. Therefore they have widespread applications, mainly as protective coatings in areas such as magnetic storage disks [2], optical windows, micro-electromechan- ical devices [1], optical storage discs [3,4], tools [5] and engines [6,7]. There are many forms of a-C (and a-C:H) films. The key parameters in such materials are: (1) the sp 3 -content; (2) the clustering of the sp 2 -phase; (3) the orientation of the sp 2 -phase; (4) the cross-sectional nano-structure; (5) eventually, the hydrogen content, and C–H bonding. The sp 3 -content alone mainly controls the elastic con- stants, but films with the same sp 3 - and hydrogen con- tents but different sp 2 -clustering, sp 2 -orientation or cross-sectional nano-structure can have different optical and electronic properties [1]. The bonding and properties of a-C:H fall into four regimes defined primarily by the energy of the ion 0263-4368/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2005.07.004 * Tel.: +1 787 7640000x2602; fax: +1 787 7567717. E-mail address: fabrice@adam.uprr.pr International Journal of Refractory Metals & Hard Materials 24 (2006) 39–48 www.elsevier.com/locate/ijrmhm