F7360 Characterization of thin films and surfaces Katarína Bernátová Brno, 30.5.2016 Outline • Paper introduction • Experimental details and coatings • Characterization methods • Appropriateness of the methods • Achieved results Introduction • Tribological behaviour of titanium carbide/amorphous carbon nanocomposite coatings: From macro to the micro-scale • J.C. Sánchez-López , D. Martínez-Martínez 1, C. López-Cartes, A. Fernández [1] • Motivation of the study – quality nanocomposite coatings (low friction and wear resistance, good toughness) Experimental details and coatings • DC (graphite target) and RF (Ti target) magnetron sputtering • SPR (Sputtering power ratio) ~ P(C)/P(Ti) • Argon gas, total pressure = 0.75 Pa • TiC/a-C nanocomposite coatings Characterization methods 1. X-ray diffraction • Atomic and molecular structure of crystal • Diffraction of X-ray beam on crystal lattice • Bragg´s law: • Structure factor [2] fn - an atom´s structure factor h, k, l - Millers index u, v, w – coordinates of an atom d – spacing between diffracting planes Θ – the incident angle (X-ray and planes) n – integer λ – wavelenght of the beam (0,01-10keV) Characterization methods 2.Transmission electron microscopy (TEM) • Crystal structure, dislocations and grain boundaries in structure • High energy beam of electrons (keV) • Thin sample (nm) • Absorption of el. in material [3] Characterization methods 3. Electron energy-loss spectroscopy (EELS) • Elemental compositions, chemical bonds • The study of the vibrational motion of atoms and molecules • On or near the surface • Interaction between the electron beam (0.1-10keV) and the specimen [4] Characterization methods 4. Micro-Raman spectroscopy • The study of the interaction between light (inelastic scattered) and matter • Photons of a single wavelength • Stokes Raman scattering • Functional group, the structure of the molecules • Micro-Raman spectroscopy – microscopic samples [5] Appropriateness of the methods • XRD – crystal structure of the films • EELS, Raman, XRD – a-C/TiC rates, chemical composition, phases proportion inside the film • Combination ofTEM with EELS spectrometer • Pin-on-disk tribometer – tribological tests for friction coefficients, wear rates Achieved results Tribological properties Film microstructure Phase composition Achieved results 1)TEM • Fig.1: a) SPR = 1,TiC crystal (5-10nm) with random orientation • Fig.1: b) SPR = 4, 1 nm sparticles, amorphous matrix Achieved results 2) EELS • EELS spectra on the C K-edge core loss • Shape and position of the spectra changed gradually (fromTiC to a-C phases) • The best tribological performance (low friction, low instabilities) – for the highest a-C contents Table 1: Summary of samples, phase contents and tribomechanical properties Achieved results 3) XRD • TiC phase – crystal size is strongly reduced as the carbon content increases (5% to 85%) • Sample J – non-stochiometricTi-enrichedTiC phases Achieved results 4) Raman spectroscopy • a) sample A: a-C content 85% - two bands: 1370 cm-1 and 1565 cm-1 (sp2 content) • b) sample I: a-C content 5% - understochiometricTiC (active due to carbon vacancies) • c) sample J: a-C content 0% - Iron oxides formation by tribochemical reaction of the steel ball with the atmosphere Conclusion a-C content > 60-65% Surface prevention from Mechanical wear and oxidation References [1] J.C. Sánchez-López ⁎, D. Martínez-Martínez 1, C. López-Cartes, A. Fernández, Surface & Coatings Technology 202 (2008) 4011–4018 [2] Rentgenová spektroskopie a difrakce [online]. Univerzita Karlova v Praze, [cit. 2012-5-5]. Dostupné na . [3] http://www.britannica.com/technology/transmission-electron-microscope https://www2.warwick.ac.uk/fac/sci/physics/current/postgraduate/regs/mpags/ex5/techniques/structural/tem/ [4] http://iopscience.iop.org/article/10.1088/0034-4885/72/1/016502/pdf http://tpm.amc.anl.gov/Lectures/EELSAEMShortCourse.pdf [5] http://www.microspectra.com/support/technical-support/raman-science/35-technical-support/126- science-of-micro-raman-spectroscopy Thank you for your attention!