Characterization of diamond-like carbon thin films produced by pulsed-DC low pressure plasma monitored by a Langmuir probe in time-resolved mode C. Corbella, E. Pascual, M.A. Go ´ mez, M.C. Polo, J. Garcı ´a-Ce ´spedes 1 , J.L. Andu ´jar, E. Bertran T FEMAN, Departament Fı ´sica Aplicada i O ` ptica, Universitat de Barcelona, Av. Diagonal 647, E08028 Barcelona, Spain Available online 19 February 2005 Abstract The deposition process and physical properties (mechanical and surface) of diamond-like carbon (DLC) films prepared at room temperature by asymmetric bipolar pulsed-DC methane plasma-enhanced CVD (PECVD) are described in this study. The pulse frequency ranged from 100 to 200 kHz and voltage peaks ran between 600 and 1400 V. Plasma parameters within the pulse cycle were measured by a Langmuir probe with a time resolution of 1 As. The results show a splitting of two electron populations at high positive bias voltage of the I –V plasma characteristics, the hotter one reaching a temperature of 10 eV. Plasma potential varied smoothly around 30 V and ion density increased promptly in the low-voltage region of the pulsed-DC cycle. Indentation and surface profilometry provided the results of hardness and stress, respectively. The behavior of the friction coefficient was analyzed by the scratch test method, using a 200 Am-diameter diamond spherical tip. Film characteristics are discussed as a function of technological parameters and compared to the characteristics of films grown using methane-glow discharge excited by rf power. For industrial purposes, pulsed-DC PECVD is a promising alternative to the more commonly used rf PECVD, because of the lower cost of its technology, lower film stress and higher deposition rate. DLC films grown by pulsed-DC PECVD with improved mechanical properties (high adherence and wear resistance, low stress, low roughness and low friction coefficient) are a real alternative for use as protective coatings on magnetic storage devices and sliding surfaces. D 2005 Published by Elsevier B.V. Keywords: Diamond-like carbon; Langmuir probe; Mechanical properties; Pulsed-DC glow discharge 1. Introduction Diamond-like carbon (DLC) films are among the most useful protective coatings for magnetic storage support surfaces, mainly due to their excellent mechanical and tribological properties, and also because they are extremely smooth, continuous and chemically inert, with roughness below 1 nm. In the near future, increased magnetic storage density will require thinner carbon films to reduce the distance between the head and the magnetic layer to 2 nm. Other characteristics of DLC films such as low stress and low friction are desirable because they increase adherence to substrate and avoid the need for further treatments of the DLC surface with molecular lubricants. One of the methods proposed for producing thinner films with suitable characteristics for these applications, with sputtering, is plasma-enhanced chemical vapor deposition (PECVD) [1] as one of the most common technologies in DLC deposition industry. This paper reports the improvement in stress and tribological properties due to the lower surface roughness of DLC coatings deposited by pulsed- DC PECVD. Along with these mechanical and tribological character- istics, DLC films are also biocompatible and chemical inert. These are, in principle, suitable properties for medical applications in artificial hip joints. However, these days the most common systems are based on metallic or ceramic heads sliding against an ultra-high molecular weight poly- ethylene (UHMWPE) cup or on metal–metal sliding pairs. 0925-9635/$ - see front matter D 2005 Published by Elsevier B.V. doi:10.1016/j.diamond.2004.12.059 T Corresponding author. Tel.: +34 93 402 1135; fax: +34 93 402 1138. E-mail address: ebertran@ub.edu (E. Bertran). 1 Presenting author. Diamond & Related Materials 14 (2005) 1062 – 1066 www.elsevier.com/locate/diamond