Surface Electron Spectroscopies: Principles and Applications

Transcription

1 Surface Electron Spectroscopies: Principles and Applications S. Kaciulis, A. Mezzi CNR - Istituto per lo Studio dei Materiali Nanostrutturati, Area della Ricerca Roma 1 Area della Ricerca di Roma 1 Via Salaria Km 29,300 C.P Monterotondo Stazione, Roma Università di Tor Vergata, dip. Ingegneria Industriale 8 giugno 2015

2 IMPORTANCE of the SURFACE All materials interact with external surrounding through their surface. Chemical reactions (catalysis, corrosion, gas sensing, etc.) - the surface atoms are defining the total reactivity. The surface atoms (either of the material or adsorbed ones) control the friction and wear mechanisms. 2D and 1D microelectronics only the surface is operating. Biocompatible materials the surface is the most important part for interaction with human body. Bulk ~ at. Surface ~ at. Surface / Bulk ~ 10-8

3 ESCA = XPS + AES (Auger) Physical principle: exciting photon excited electron B.E. E f K.E. e - e - hν E 3 E 2 E 1 XPS BE = hn KE WF AES KE 123 = E 1 E 2 E * 3

4 XPS: X-ray Photoelectron Spectroscopy e-gun BE = hn KE WF hn: Al Kα = ev Mg Kα = ev Intensity, arb. unit Au 4f Registered signal: I = f (KE) C 1s Au 4d Ag 3d O 1s SURFACE CHEMICAL COMPOSITION (1-10 nm) Qualitative analysis: elements Quantitative analysis: integral of the peaks Chemical shift: chemical state Chemical imaging ION SPUTTERING Ar Binding Energy, ev Obtained spectrum: I = f (BE)

5 AES: Auger Electron Spectroscopy KE(Auger) = E 1 E 2 E 3 *, where E 1 - energy of the first electron, E 2 - energy of the electron descending to the lower level, E 3* - energy of the level from which is excited the third electron. source electron is interacting with the sample exciting Registered the first electron signal and creating I = the f (KE) hole in the level E 1. the second electron is descending to the hole in the level E 1 (2 1), leaving the hole in the level E 2. the excess of energy is used for the excitation of the third electron from the level E 3. SURFACE CHEMICAL COMPOSITION (1-2 nm) Qualitative analysis: elements Quantitative analysis: not easy Chemical imaging Point A: layer of TiO x Point B: layer of Pt

6 Analysis Depth Mean free path of the electrons λ: I ~ N(z)exp (-z/λ)dz Information depth 3λ Contamination by residual gases: at 10-6 mbar 1 monolayer/sec The pear of SEM EDS N.B. the lateral resolution of EDS is low! UHV

7 Fields of application Chemical-physical characterization of: and any solid state material

8 Ti6Al4V-SIC COMPOSITE XPS CHEMICAL IMAGES Axis Ultra spectrometer (Kratos Analytical) Ti 2p O 1s Lateral resolution < 3 μm THERMAL TREATMENTS T ( C) AS PREP. time (h) C 1s GRAPH. C 1s CARB Si 2p Ti 2p C 1s C 1s Si 2p BE (ev) TiO 2 graphite carbide SiC

9 Ti6Al4V-SIC COMPOSITE Diagonal cross-section by abrasive lapping angle of 2 between the surface and the axis of the fibers SPEM Al 2p chemical image (1x1 mm 2 ) of the lapped sample Peak-fitting of Al 2p spectra in the points A and C of the SPEM image SPEM chemical image (128 μm x 4 μm) of C 1s (a) and photoemission spectra of Al 2p (b), C 1s (c), Ti 3p (d) in the points A and C.

10 Ti6Al4V-SIC COMPOSITE SAMPLE AS PREPARED Ti6Al4V AES INVESTIGATION ESCALAB MkII (VG Scientific) THICKNESS of GRAPHITE LAYER 5 mm Si 80 x 80 mm 2 NON-UNIFORM COMPOSITION OF GRAPHITE LAYER PRESENCE OF IMPURITIES (K, Ca)

11 30 nm Ti6Al4V-SIC COMPOSITE GRAPHITE ON Ti FOIL: XPS investigation GRAPHITE Ti FOIL DEPOSITION BY EVAPORATION DEPOSITION ON Ti6Al4V and Ti ANNEALING IN VACUUM

12 Ti6Al4V-SIC COMPOSITE COMPARISON of covered reference samples (RT and 500 C x 8h) THEORETICAL APPROACH Width of reactive zone - about 10 nm C C s s C C x 0 D erf 2 0 D e Q RT x Dt (2) (1) C diffusion in Ti C diffusion in TiC References Donnini R., Kaciulis S., Mezzi A., Montanari R., Testani C. Surface Interface Analysis 2008, 40: 277, 10 mm 12 nm Deodati P., Donnini R., Kaciulis S., Mezzi A., Montanari R., Testani C., Ucciardello N. Advanced Materials Research Vols (2010) pp 715, Kaciulis S., Mezzi A., Donnini R., Deodati P., Montanari R., Ucciardello N., Gregoratti L., Testani C. Surface Interface Analysis 2010, 42, 707,

13 Ni-BASED SUPERALLOY Determination of diffusion processes affect the coarsening and rafting Distribution of chemical elements in and ' phases of single crystal in as-received condition and after creep 0 Ta 4f A B 20x10 3 Intensity (counts/sec) Re 4f W 4f Ta 4f Hf 4f pt A pt B Kinetic Energy (ev) x10 3 Cuboidal particles with a size of 1 2 mm and channels of about nm between the particles Intensity (counts/sec) Al 2p Ni 3p + Al LMM Co 3p pt A pt B Kinetic Energy (ev)

14 Ni-BASED SUPERALLOY 0 As-cast material SPEM of CM186LC alloy AFM image Re 4f W 4f Images size = 6.4 x 6.4 mm 2 Ta 4f 120

15 As-cast material GRAPHENE OUTLOOK sp 3 - DIAMOND CARBON ALLOTROPES sp 2 GRAPHITE AFM image sp 2 & sp 3 DLC, ac, ac:h 2D sp 2 SWCNT, GRAPHENE Electronic configuration: fourfold sp 3 (diamond), threefold sp 2 (graphite), linear sp 1 ; tetrahedral sp Images size = 6.4 x 6.4 mm 2 configuration - σ bonds; trigonal sp 2 configuration - π bonds. π-type bonds determine the electronic properties and optical gap, σ-type bonds define the mechanical hardness (diamond-likeness). sp 3 sp 2

16 GRAPHENE OUTLOOK Intensity, arb. unit 6- SWNTs 5- DLC 4- carb. wood 3- pellet 2- graphite 1- diamond Binding Energy, ev Electronic spectra: Photoemission only C 1s spectrum. Auger C KLL line a convolution of C KVV transitions 1s-2pπ-2pπ and 1s-2pσ-2pπ; Valence band a convolution of 2pσ and 2pπ states. S. Kaciulis, Surf. Interface Anal ; 44, 1155.

17 GRAPHENE OUTLOOK C KVV spectrum: D parameter - the distance between the most positive maximum and most negative minimum of the first derivative. Assessed peak-to-peak width of C KVV spectrum enables to determine sp 2 /sp 3 ratio in carbon allotropes by using linear calibration from diamond to graphite. J.C. Lascovich et al., Appl. Surf. Sci ; 47, 17. A. Mezzi, S. Kaciulis, Surf. Interface Anal ; 42, 1082.

18 GRAPHENE OUTLOOK Source Sample D, ev hν Graphite ref Diamond ref Graphene/Si 15.0 Graphene/Cu 14.2 Graphene/Cu, T = 400 C sp 2, % Graphene/Cu, cooled LN e Graphite 21.0 Diamond 14.2 Graphene/Si 20.9 Graphene/Cu S. Kaciulis, A. Mezzi, P. Calvani, D.M. Trucchi, Surf. Interface Anal ; DOI 10.2/sia.5382.

19 GRAPHENE OUTLOOK Investigation of different composite materials containing graphene. Very promising results have been already obtained for rubber composites with graphene platelets. Graphene oxide C KVV is different. S. Kaciulis, A. Mezzi, S.K. Balijepalli, M. Lavorgna, H.S. Xia, submitted to Thin Solid Films, 2014.

20 ACKNOWLEDGMENTS Università degli Studi di Roma "Tor Vergata" prof. Montanari R.; prof. Montesperelli, G.; dr. Carbone M. dr. Lavorgna M.: IMCB (CNR) dr. Angella G.; IENI (CNR) dr. Trucchi D.; Suber L.; ISM (CNR) Bianchi M.; Istituto Ortopedico Rizzoli (Bologna) dr. Gregoratti L.; ELETTRA Sincrotrone Trieste prof. Sberveglieri G.; Università degli studi di Brescia dr. Setkus A.; dr. Bondarenka V.; Semiconductor Physics Institute (Vilnius) Wlodarski W.; RMIT University (Melbourne) Prof. V. Ambrogi, University of Perugia, Italy.