Plasma properties of CrO x films synthesized by a cathodic arc evaporation process Yin-Yu Chang ⁎ , Shun-Jan Yang, Yu-Hsien Liu, Da-Yung Wang Institute of Materials and System Engineering, MingDao University, Pitou Shiang, Changhua County 52345, Taiwan Available online 13 July 2007 Abstract The plasma in a cathodic arc evaporation process used for the deposition of Cr 1-x O x films was studied by an optical emission spectroscopy (OES). With the introduction of Ar and oxygen into the chamber at deposition pressures from 0.7 Pa to 2.7 Pa, high density of evaporated chromium catalyzes the decomposition of oxygen reactive gas, and induces the formation of Cr 1-x O x films. Optical emission spectra including atomic and ionized Cr, excited and ionized oxygen revealed that excitation, ionization and charge transfer reactions of the Cr–O plasma occurred during the Cr 1-x O x deposition process. A simplified empirical model which incorporates the relevant atomic processes in the gas phase with the chemical composition and deposition rate of the deposited Cr 1-x O x coating was developed. Rhombohedral Cr 2 O 3 and tetragonal CrO 2 were observed in the Cr 1-x O x coatings deposited at higher pressure than 1.3 Pa. The Cr 1-x O x coating depicted a dense and compact microstructure with well-attached interface. © 2007 Elsevier B.V. All rights reserved. Keywords: Hard coating; Cathodic-arc evaporation; Hardness; Carbon 1. Introduction Chromium oxide (Cr 1-x O x ) coatings, such as Cr 2 O 3 and CrO 2 , synthesized by physical vapor deposition (PVD) have been increasingly applied in mechanical and magnetic recording industries due to their superior tribological, corrosion and magnetoelectronic properties [1–3]. Such coatings can be produced by different PVD techniques, such as magnetron sputtering and cathodic arc evaporation [3–5]. In the cathodic- arc ion plating deposition process, high-energy metal plasma with ion kinetic energies in the range of 20–100 eV [6,7], depending on the cathode material and on the charge state of the ions, assists the decomposition of reactive gases. As a result, a metal oxide film can be deposited on the substrate. For the main atomic process between the metallic Ti plasma and neutral gases, either N 2 or O 2 , previous studies by Demidenko and Martin et al. [8,9] showed that the main atomic reaction responsible for the generation of molecular ions was charge-exchange process between metallic ion and reactive gas molecules. In the present study, a cathodic arc ion plating process with chromium cathode was used for the deposition of Cr 1-x O x coatings. An optical emission spectrometer (OES) was used for the plasma diagnostics of the deposition process. It is usually used during a sputtering process to determine informa- tion on the active species and the dominating plasma reactions in the discharge. However, OES studies on the Cr 1-x O x cathodic arc evaporation are still limited. The mechanism of the arc discharge differs significantly from glow discharges used for conventional sputtering. In this study, the effect of the gas pressure and oxygen flow on the plasma condition during the cathodic arc evaporation and microstructure of Cr 1-x O x coatings were discussed. 2. Experimental details Cr 1-x O x coatings were deposited on polished silicon samples by using a cathodic arc evaporation system. A circular chromium target was arranged on the chamber wall to deposit the Cr 1-x O x coatings. A dc arc current of 80 A was applied between the anode and the cathode. Ar and reactive gas (O 2 ) were introduced through a conducting duct around the target to enhance the reaction of the plasma and reduce the macroparticles produced during the deposition process. The deposition parameters are Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 5536 – 5540 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: yinyu@mail2000.com.tw (Y.-Y. Chang). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.07.023