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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. 10 - 00015 Monterotondo Stazione, Roma Università di “Tor Vergata”, dip. Ingegneria Industriale 8 giugno 2015

Surface Electron Spectroscopies: Principles and Applications · AES: Auger Electron Spectroscopy KE(Auger) = E 1 –E 2 –E 3 *, where E 1 - energy of the first electron, E 2 - energy

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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. 10 - 00015 Monterotondo Stazione, Roma

Università di “Tor Vergata”, dip. Ingegneria Industriale – 8 giugno 2015

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 ~ 1023 at.

Surface ~ 1015 at.

Surface / Bulk ~ 10-8

B.E. Ef K.E.

E3

E2

E1

e-

Physical principle: exciting photon → excited electron

BE = hn – KE – WF

e-

AESXPS

KE123 = E1 – E2 – E*3

ESCA = XPS + AES (Auger)

XPS:X-ray Photoelectron Spectroscopy

BE = hn – KE – WF

hn:Al Kα = 1486.6 eV

Mg Kα = 1253.6 eV

Registered signal: I = f (KE)

Obtained spectrum: I = f (BE)

e-gun

0 200 400 600

Inte

nsity,

arb

. u

nit

Binding Energy, eV

Au 4f

C 1s

O 1s

Ag 3dAu 4d

SURFACE CHEMICAL COMPOSITION (1-10 nm)

Qualitative analysis: elements Quantitative analysis: integral of the peaks Chemical shift: chemical state Chemical imaging

Ar+

ION SPUTTERING

AES: Auger Electron Spectroscopy

KE(Auger) = E1 – E2 – E3*,

where E1 - energy of the first electron, E2 - energy of

the electron descending to the lower level, E3* - energy

of the level from which is excited the third electron.

source electron is interacting with the sample exciting the first electron and creating the hole in the level E1.

the second electron is descending to the hole in the level E1 (2→1), leaving the hole in the level E2.

the excess of energy is used for the excitation of the third electron from the level E3.

Registered signal I = f (KE)

SURFACE CHEMICAL COMPOSITION (1-2 nm)

Qualitative analysis: elements Quantitative analysis: not easy Chemical imaging

Point A: layer of TiOx

Point B: layer of Pt

Analysis Depth

The “pear” of SEM – EDS

N.B. – the lateral resolution of EDS is low!

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

UHV

Fields of application

… and any solid state material

Chemical-physicalcharacterization of:

Ti 2p O 1s

C 1s

GRAPH.C 1s

CARB.

Si 2p

Ti 2p C 1s C 1s Si 2p

BE (eV) 458.8 284.7 283.0 99.9

TiO2 graphite carbide SiC

Lateral resolution < 3 μmXPS CHEMICAL IMAGESAxis Ultra spectrometer (Kratos Analytical)

T (°C)time(h)

AS PREP.

400 100

400 500

400 1000

600 100

600 500

600 1000

THERMAL TREATMENTS

Ti6Al4V-SIC COMPOSITE

SPEM Al 2p chemical image (1x1 mm2) of the lapped sample

Diagonal cross-section by abrasive lapping

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.

angle of 2° between the surface and the axis of the fibers

Ti6Al4V-SIC COMPOSITE

NON-UNIFORM COMPOSITION OF GRAPHITE LAYER

PRESENCE OF IMPURITIES (K, Ca)

SAMPLE AS PREPARED

80 x 80 mm2

Ti6Al4V

Si

12

3THICKNESS of GRAPHITE LAYER

≈ 5 mm

AES INVESTIGATION

ESCALAB MkII (VG Scientific)

Ti6Al4V-SIC COMPOSITE

GRAPHITE ON Ti FOIL:XPS investigation

Ti FOIL

GRAPHITE

DEPOSITION BY EVAPORATION

DEPOSITION ON Ti6Al4V and Ti 99.99+

30

nm

ANNEALING IN VACUUM

Ti6Al4V-SIC COMPOSITE

COMPARISON of covered reference samples(RT and 500°C x 8h)

Width of reactivezone - about 10 nm

Dt

xerf

CC

CC

s

xs

20

RT

Q

eDD

0

THEORETICAL APPROACH

C diffusion in Ti C diffusion in TiC

10 mm12 nm

(1)

(2)

Ti6Al4V-SIC COMPOSITE

References

Donnini R., Kaciulis S., Mezzi A., Montanari R., Testani C.Surface Interface Analysis 2008, 40: 277,

Deodati P., Donnini R., Kaciulis S., Mezzi A., Montanari R., Testani C., Ucciardello N.Advanced Materials Research Vols. 89-91 (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,

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

Cuboidal ’ particles with a size of 1 ÷ 2 mm and

channels of about 100 nm between the particles

Ni-BASED SUPERALLOY

120

100

80

60

40

20

0

120100806040200

A

B

Ta 4f

20x103

15

10

5Inte

nsi

ty (

cou

nts

/sec)

490480470460450

Kinetic Energy (eV)

pt A pt B

12x103

10

8

6

4

Inte

nsi

ty (

cou

nts

/sec)

450445440435430425420

Kinetic Energy (eV)

pt A pt B

Re 4f W 4f

Ta 4f

Hf 4f

Al 2p

Ni 3p + Al LMM

Co 3p

SPEM of CM186LC alloy

120

100

80

60

40

20

0

120100806040200

Re 4f

120

100

80

60

40

20

0

120100806040200

W 4f

120

100

80

60

40

20

0

120100806040200

Ta 4f

As-cast material

AFM image

Images size = 6.4 x 6.4 mm2

Ni-BASED SUPERALLOY

sp3 - DIAMONDsp2 – GRAPHITE

2D sp2 – SWCNT, GRAPHENEsp2 & sp3 – DLC, aC, aC:H

CARBON ALLOTROPES

As-cast material

AFM image

Images size = 6.4 x 6.4 mm2

Electronic configuration:fourfold sp3 (diamond), threefold sp2 (graphite), linear sp1;tetrahedral sp3 configuration - σ bonds;trigonal sp2 configuration - π bonds.π-type bonds determine the electronic properties and optical gap,σ-type bonds define the mechanical hardness (diamond-likeness). sp3 sp2

GRAPHENE OUTLOOK

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. 2012 ; 44 , 1155.

280 285 290 295

2- graphite

1- diamond

6- SWNTs

3- pellet

5- DLC

Inte

nsity,

arb

. u

nit

Binding Energy, eV

4- carb. wood

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 sp2/sp3 ratio in

carbon allotropes by using linear calibration from diamond to graphite.

A. Mezzi, S. Kaciulis, Surf. Interface Anal. 2010 ; 42 , 1082.

J.C. Lascovich et al., Appl. Surf. Sci. 1991 ; 47 , 17.

GRAPHENE OUTLOOK

Source Sample D, eV sp2, %

Graphite ref. 21.2 100

Diamond ref. 13.7 0

Graphene/Si 15.0 100

Graphene/Cu 14.2 100

Graphene/Cu,

T = 400 °C15.2 100

Graphene/Cu,

cooled LN2

13.5 100

e–

Graphite 21.0 100

Diamond 14.2 0

Graphene/Si 20.9 100

Graphene/Cu 21.0 100

S. Kaciulis, A. Mezzi, P. Calvani, D.M. Trucchi, Surf. Interface Anal. 2014 ; DOI 10.1002/sia.5382.

GRAPHENE OUTLOOK

GRAPHENE OUTLOOK

Investigation of different composite materials containing graphene.

Very promising results have been already obtained for rubber compositeswith 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.

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.