Nitrogen incorporation into titanium diboride films deposited by dc magnetron sputtering: Structural modifications C.M.T.Sanchez 1 , H.D.Fonseca-Filho, M.E.H.Maia da Costa, F.L.Freire Jr. ⁎ Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, RJ,22451-900, Brazil a b s t r a c t a r t i c l e i n f o Article history: Received 11 February 2008 Received in revised form 9 February 2009 Accepted 13 February 2009 Available online 1 March 2009 Keywords: Borides Atomic force microscopy X-ray photoelectron spectroscopy (XPS) X-ray diffraction Sputtering Surface roughness Stress This work reports a study of titanium boron nitride (Ti–B–N) films deposited at room temperature by dc magnetron sputtering using a TiB 2 target in different Ar–N 2 gas mixture atmospheres. The influence of the nitrogen partial pressure on the structural, mechanicaland tribologicalproperties of these films has been studied.The films were analyzed by Rutherford backscattering spectrometry in order to determine their chemical composition and atomic density. X-ray diffraction (XRD) was used to probe the film microstructure and X-ray photoelectron spectroscopy (XPS) for the chemical characterization of the film surface. An atomic force microscope (AFM) was used to analyze the surface topography and, when operating in the lateral forc mode,for the friction characterization of the films.The XPS results showed that the surface of the films deposited in pure argon atmosphere was composed essentially by Ti and B oxides, while TiB 2 , TiB, TiN and BN phases were present in the sputtered Ti–B–N films. Characterization by XRD determined the nanocrystalline nature of the films structure. While internalstress and friction increase upon the nitrogen incorporation, AFM measurements reveal a strong reduction of the surface roughness. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Titanium diboride (TiB 2 ) has many interesting properties, e.g. high hardness (30 GPa), good corrosion resistance, high melting point and low density [1]. TiB 2 in thin film form can be produced by using CVD (chemical vapor deposition) or PVD (physical vapor deposition) deposition techniques[2–5]. The use of TiB 2 films as protective coatings has been extensively studied due to their mechanical and tribological properties [6–8]. However, it is too brittle to be used as a wear resistant coating. TiB 2 films are characterized by a strong [001] texture of the columnar grains and the grain boundaries perpendi- cular to the surface represents short cracks path that can also impair the toughness [9]. To improve the properties of TiB 2 films, a solution can be the incorporation ofnitrogen into this materialobtaining a ternary compound, titanium boron nitride (Ti–B–N). Many investiga- tions were motivated by the presumption that the incorporation of nitrogen to TiB 2 coatings might have an influence to optimize their mechanicaland tribologicalproperties.Ti–B–N films are composite materials that have potential applications as coating in machine tools for cutting, forming and stamping [10]. They have interesting proper- ties, such as high hardness, high toughness and good thermodynamic stability at high temperatures [9,11–13], which are important for the reliable operation of machining tools. In order to obtain Ti–B–N films, different CVD and PVD deposition techniques were employed. Depending on the deposition conditions, these materials can present hardness as high as 40 GPa and a superior wear resistance [14–15]. Magnetron sputtering is the mostcommonly used PVD technique since sputtering offers advantages over many other techniques, like deposition at low substrate temperatures, high deposition rate and the absence of toxic or explosive gases [16–18].However,a detailed investigation on the role of the nitrogen content on the microstructure evolution and its influence on the film properties is still necessary. In this work, Ti–B–N films were deposited by dc magnetron sputtering from a TiB 2 target in argon–nitrogen atmospheres. The atomic concentration of the elements and their chemical environment were characterized by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS), respectively.The film microstructure was revealed by X-ray diffraction (XRD). An atomic force microscope (AFM) operating in the lateral force mode was used for the friction characterization of the films. The internal stress was also investigated. 2. Experimental procedures Ti–B–N films were deposited by dc magnetron sputtering using a high-purity TiB 2 target (purity: 99.5%, diameter: 75 mm) in various Ar–N 2 mixtures at different nitrogen partial pressures. Thin films with a typical thickness of 200 nm were deposited onto silicon (100) substratesmounted on a water-cooled 3-inch grounded copper cathode.Prior to deposition,the substrates were ex-situ cleaned in acetone,hydrofluoric acid and distilled water. The target–substrate Thin Solid Films 517 (2009) 5683–5688 ⁎ Corresponding author. E-mail address: lazaro@vdg.fis.puc-rio.br (F.L. Freire). 1 Present address: Instituto de Física, Universidade Federal Fluminense, Niterói, RJ, Brazil. 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.02.122 Contents lists available at ScienceDirect Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f