Thesises of the PhD dissertation. György János Kovács. Eötvös Loránd University, Budapest Faculty of Science Physics doctoral school

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1 Structure and Properties of CN x -Ni nanocomposite thin films Thesises of the PhD dissertation György János Kovács Doctoral school: Head of doctoral school: Doctoral program: Doktori program vezetıje: Supervisor: Eötvös Loránd University, Budapest Faculty of Science Physics doctoral school Professor Zalán Horváth, academician Materials science and solid-state physics Professor János Lendvai Professor György Radnóczi, DSc, head of department (MTA MFA) MTA MFA Research Institute for Technical Physics and Materials Science Budapest, 2007

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3 The aim of work The research of thin films and thin film growth is one of the major activities in the Research Institute for Technical Physics and Materials Science (MFA), with traditions through the decades. By the end of the 1990s fullerene-like structures in thin films came into focus in the institute. My PhD work, dealing with magnetron sputtered carbon and carbon nitride based films, has been started in I aimed the modification of such films by the parallel deposition of carbon (nitride) and metal, creating a composite structure that is composed of a continuous carbon (nitride) matrix and a metallic dispersed phase. I hoped that the metallic dispersed phase would have significant effects on the growth and atomic structure of the matrix, resulting in new, interesting properties and phenomena.the major aim has been the observation and the understanding of these effects. The aquired knowledge may be very useful in the fundamental understanding of the growth and properties of carbon (nitride)-metal composite systems, and may give the industry important know-how in the fabrication of carbon based composite protective and decorative coatings, or carbon (nitride)-metal magnetic data storage films. The aim of this dissertation is the examination of the morphology, the microstructure, and the atomic structure of carbon (nitride)-nickel nanocomposite thin films, the investigation of the mechanical properties, and, based on the aquired informations, the creation of the structure growth model. The primary method of investigation was transmission electron microscopy. Beyond that, nanoindentation and many other spectroscopic methods were applied to examine the microstructure and the atomic structure of the films. 3

4 Methods of investigation The C-Ni és CN x -Ni films were deposited by d.c. magnetron sputtering in a high vacuum system equipped with a turbomolecular pump. The sputtering gas was pure Ar for C-Ni films and pure nitrogen for CN x -Ni films. The methods of investigation were: Transmission electron microscopy (TEM) and High Resolution TEM (HRTEM), by a Philips CM20 and a JEOL3010 microscope in the MFA. Energy dispersive x-ray spectroscopy on a Philips CM20 microscope in the MFA. Electron energy loss spectroscopy (EELS), the measurements were done by Giovanni Bertoni and Virginie Serin in CEMES-CNRS, Toulouse, by a Philips CM20 and a Vacuum Generators HB501 transmission electron microscope. Scanning tunneling microscopy (STM) and spectroscopy (STS), the measurements were done by Antal Koós in the MFA, by a Digital Instruments Nanoscope E device. X-ray photoelectron spectroscopy (XPS/ESCA), the measurements were done by Imre Bertóti and Tamás Ujvári in the KKKI, by a Kratos XSAM 800 device. Raman spectroscopy, the measurements were done by Miklós Veres in the SZFKI, by a Renishaw 1000 B spectrometer equipped on a Leica Dm/LM optical microscope. Nanoindentation, the measurements were done by Tamás Ujvári in the KKKI, by a Micro Materials Nanotest 600 nanoindentor. 4

5 Scientific results (thesises) 1. Between 25 and 800 o C growth temperatures, by parallel magnetron sputtering of carbon and nickel with argon or nitrogen sputtering gas, nanocomposite thin films were deposited. The nanocomposite consists of a crystalline dispersed phase and a continuous amorphous matrix. The dispersed phase is hexagonal nickel carbide (Ni 3 C) below 400±50 o C growth temperature, and above is fcc nickel. The matrix is amorphous carbon or carbon nitride. By HRTEM I evinced the layered ordering of the matrix around the surface of the disperse phase [1]. 2. I created a consistent structure growth model to describe the morphological development of the films through the o C growth temperature range. I pointed to the dominant morphology-determining nature of liquid-like coalescence in the case of CN x -Ni films at and above 600 o C growth temperature, while in the case of C-Ni films the liquid-like coalescence does not play an important role up to 800 o C. 3. By nanoindentation I investigated the hardness of the films as a function of the growth temperature between 25 and 800 o C. I revealed that the hardness is maximal at 200 o C (~14 Gpa). The maximum can be explained by the disappearence of the ballistic growth of the matrix (hardening up to 200 o C), and by the appearance of the dislocation deformation mechanism in the dispersed phase (softening above 200 o C) [1, 4]. 4. I found a new component in the carbon 1s XPS band of the C-Ni films at 282,9 ev, in the region of metal-carbid components. I revealed that the new component can be related to the carbon atoms bonded in the interfaces between the dispersed phase (Ni 3 C or Ni) and the matrix [2]. 5

6 5. By local EELS investigations I revealed that the density of the matrix π states are increased along the interfaces between the dispersed phase (Ni 3 C or Ni) and the matrix. This effect can be explained by a charge transfer between the carbon and nickel atoms at the interfaces [3]. 6. By STM and STS investigations I revealed that the hills on the surface of the films have metallic electronic behaviour, and these points can be indentified as the tops of the dispersed phase s crystalline grains. I concluded that above 200 o C growth temperature the surface roughness is determined by the morphology of the dispersed phase [3]. 7. By Raman and TEM investigations I evinced that the dispersed phase enhances the layered ordering (i.e. the growth of two dimensional, sp 2 -bonded clusters) of the matrix in the C-Ni és CN x -Ni nanocomposite films. The atomic structure of the clusters is different for C-Ni and for CN x -Ni films. The clusters - in the C-Ni films are graphene-like, i.e. are built up from condensed sixfold rings, - in the CN x -Ni films are fullerene-like, i.e. consist of non-sixfold rings as well. 6

7 Conclusions The magnetron sputtered carbon nickel and carbon nitride-nickel films have a nanocomposite structure. In this particle strengthened structure the grain size of the dispersed phase can be varied between 3 and 100 nm with the variation of the growth temperature. Due to the nanometer scale grain size, the matrix-dispersed phase interfaces contain a significant amount of atoms, compared to the total amount of atoms in the film (10%), so the interface interactions (electron orbit overlaps between the atoms of the dispersed phase and the matrix) start to play an important role. At and above 600 o C growth temperature the dominant growth mechanism is different for the carbon nickel and for the carbon nitride-nickel films. The carbon-nickel films have Zone III morphology from 25 to 800 o C, while the nickel in the carbon nitridenickel films shows a so-called bimodal grain growth at and above 600 o C. In this latter case, grains with diameter of 100 nm or more are on the top of the film, while near to the substrate only a small amount of rarely distributed, small diameter (up to 10 nm) grains are present. This morphology is created by liquid-like coalescence. The presence of nickel in the films modifies the structure and the properties of the matrix. In the carbon-nickel films the nickel enhances the graphene-like ordering of the matrix, so the films can have, with the percolation of nickel carbide grains, good conduction, high (~130 GPa) elastic modulus, low coefficient of friction (~0,3) and highly elastic behaviour (H/E ~ 0,1). Such films may be good coatings in applications where the optimal balance between the values of these parameters is more important than the extremely high value of only one or two parameters. Beyond that, the disperse phase can be removed (dissolved) from the thin films, resulting in a porous, highly sp 2 -ordered carbon or carbon-nitride foam. The results in the dissertation apply to films with 17 at% nickel content. With the variation of the nickel content some of the physical properties can be tuned in an even wider range than in this work. Investigating the properties of films with different composition can be an interesting research topic, especially in the case of films with gradient composition. 7

8 Publications with impact factor related to the thesises 1. Gy. J. Kovács, G. Sáfrán, O. Geszti, T. Ujvári, I. Bertóti, G. Radnóczi Structure and mechanical properties of carbon-nickel and CN x -Ni nanocomposite films Surface and Coatings Technology, , (2004) 2. Ujvári T., A. Tóth, Gy. J. Kovács, G. Sáfrán, O. Geszti, G. Radnóczi, I. Bertóti Composition, Structure and Mechanical Property Analysis of DC Sputtered C Ni and CN x Ni Nanocomposite Layers Surface and Interface Analysis, 36, (2004) 3. Gy. J. Kovács, A. Koós, G. Bertoni, G. Sáfrán, O. Geszti, V. Serin, C. Colliex, G. Radnóczi Structure and spectroscopic properties of C-Ni and CN x -Ni nanocomposite films Journal of Applied Physics 98, (2005) 4. G. Radnóczi, Zs. Czigány, K. Sedlácková, Gy. J. Kovács, F. Misják Structure and Physical Properties of Nanocomposite Coatings Nanopages 1 (2), (2006) Publications without impact factor related to the thesises 5. T. Ujvári, A. Tóth, Gy. J. Kovács, G. Sáfrán, O. Geszti, G. Radnóczi, I. Bertóti Composition, Structure and Mechanical Property Analysis of DC Sputtered C-Ni and CN x -Ni Nanocomposite Layers ECASIA 2003 conference (Berlin, Germany), poster 6. G. Radnóczi, Gy. J. Kovács, G. Sáfrán, K. Sedlácková, O. Geszti, T. Ujvári, I.Bertóti: Structure and properties of carbon based nanocomposite films Metallic Materials with High Structural Efficiency (Eds: O.N.Senkov, D.B.Miracle, S.A.Firstov) , Kluwer Acad.Publ. (2004) 8

9 7. G. Radnóczi, Gy. J. Kovács, G. Sáfrán, K. Sedlácková, O. Geszti,T. Ujvári, I. Bertóti Structure and properties of carbon/ni and CNx/Ni nanocomposite films Proc. Nanotechnology in Research and Application, ed. by I. Horváth, Bratislava, March G. Radnóczi, Gy. J. Kovács, G. Sáfrán, K. Sedlácková, O. Geszti, T. Ujvári, I. Bertóti Structure and properties of carbon based nanocomposite films Poster at the seminar of Bay and Fraunhofer Institute, Budapest 9. Gy. J. Kovács, G. Sáfrán, O. Geszti, A. Koós, K. Sedlackova, G. Radnóczi, V. Serin, G. Bertoni, L. Calmels Structure, formation and electric properties of C-Ni and CNx-Ni nanocomposite films Strasbourg (France), E-MRS 2004 Spring Meeting, talk 10. Gy. J. Kovács, M. Veres, A. Koós, G. Sáfrán, G. Radnóczi Spectroscopic properties of CN x -Ni nanocomposite thin films Strasbourg (France), E-MRS 2005 Spring Meeting, poster 11. G. Radnóczi, Gy. J. Kovács, K. Sedlácková, Zs. Czigány, T. Ujvári, I. Bertóti Structure and physical properties of Ni-C nanocomposite thin films Hungarian Nanotechnology Symposium, NENAMAT, Budapest, March 21-22, talk 12. G. Radnóczi, Zs. Czigány, K. Sedlácková, Gy. J. Kovács Structure and physical properties of nanocomposite thin films MCEM, Portoroz, 2005, invited talk 9

10 13. G. Radnóczi G, Zs. Czigány, K. Sedlácková, Gy. J. Kovács Structure and Physical Properties of Nanocomposite Thin Films Proc. 7th Multinational Congr. On Microscopy, Portoroz, Slovenia,, ed. by M. Ceh, G. Drazic, S. Fidler, Slovene Soc. for Microscopy, 2005, p Invited talk 14. G. Radnóczi, R. Grasin, Gy. J. Kovács, K. Sedlácková, G. Sáfrán, O. Geszti, Zs. Czigány, J. Lábár Nem kristályos szénszerkezetek elektrondiffrakciós vizsgálata ELFT, Anyagtudományi Öszi Iskola, Visegrád (Hungary), 2005, invited talk 15. Gy. J. Kovács Szén+nikkel és szén-nitrid+nikkel nanokompozitok szerkezete és spektroszkópiai tulajdonságai ELFT seminar, ELFT Székház, Budapest, May 9, 2006, invited talk 16. Gy. J. Kovács Szén+nikkel és szén-nitrid+nikkel nanokompozitok spektroszkópiai tulajdonságai 2006 Congress of the Hungarian Microscopic Society (May 20, 2006) 10