Workshop08 SurfaceAnalysisI XPSAES Handout Final

6/9/2008Advanced Materials Characterization  Workshop X‐ray Photoelectron Spectroscopy (XPS)  and Auger Electron Spectroscopy (AES) Rick Haasch, Ph.D. Supported by the U.S. Department of Energy under grants DEFG02-07-ER46453 and DEFG02-07-ER46471 © 2008 University of Illinois Board of Trustees. All rights reserved. What is Surface Analysis? >1000 nm 100 nm Bulk Analysis <10 nm ThinThin-film Analysis Surface Analysis The Study of the Outer-Most Layers of Materials (~10 nm). © 2008 University of Illinois Board of Trustees. All rights reserved. 2 1 6/9/2008 Particle Surface Interactions Primary beam (source) Ions El t Electrons Photons Secondary beam (spectrometers, detectors) Ions El t Electrons Photons Vacuum © 2008 University of Illinois Board of Trustees. All rights reserved. 3 Spatial resolution versus Detection Limit © 2008 University of Illinois Board of Trustees. All rights reserved. 4 2 6/9/2008 Particle Surface Interactions Photoelectron Spectroscopy Ions Electrons Ions Electrons Photons Photons Joe E. Greene2) Vacuum 5 © 2008 University of Illinois Board of Trustees. All rights reserved. X-ray Photoelectron Spectroscopy (XPS) X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA) is a widely used technique to investigate the chemical composition of surfaces. X-ray1 Photoelectron spectroscopy, based on the photoelectric effect,2,3 was developed in the mid-1960’s as a practical technique by Kai Siegbahn and his research group at the University of Uppsala, Sweden.4 Wilhelm Conrad Röntgen 1. 2. 3. 4. Heinrich Rudolf Hertz Albert Einstein Kai M. Siegbahn W. Röntgen, 1901 Nobel Prize in Physics “in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him.” H. Hertz, Ann. Physik 31,983 (1887). A. Einstein, Ann. Physik 17,132 (1905). 1921 Nobel Prize in Physics “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.” 4. K. Siegbahn, Et. Al.,Nova Acta Regiae Soc.Sci., Ser. IV, Vol. 20 (1967). 1981 Nobel Prize in Physics “for his contribution to the development of high resolution electron spectroscopy.” 6 © 2008 University of Illinois Board of Trustees. All rights reserved. 3 Electrons can be excited in this entire volume.e. i.Φspec BE – binding energy depends on Z.6/9/2008 X-ray Photoelectron Spectroscopy Small Area Detection Electrons are extracted only from a narrow solid angle. X-ray Beam X-ray penetration depth ~1μm. Electrons are emitted from this entire area © 2008 University of Illinois Board of Trustees. 10 nm 10 μm. 7 Photoelectron and Auger Electron Emission KE (measured) = hν (known) .Φspec (calibrated) Eincident X-ray = hν Emitted Auger Electron Free Electron Level Φ Conduction Band Conduction Band Fermi Level Valence Band Valence Band 2p BE L2.1 mm dia. All rights reserved. X-ray excitation area ~1 mm-1 cm diameter. 8 4 .KE .L3 2s L1 1s K Calculate: BE = hν . All rights reserved.BE . characteristic for the element © 2008 University of Illinois Board of Trustees. Φspec (calibrated) Eincident X-ray = hν Emited X-ray Photon Free Electron Level Φ Conduction Band Conduction Band Fermi Level Valence Band Valence Band 2p BE L2.KE .BE .Φspec BE – binding energy depends on Z.e. 9 Photoelectron and Auger Electron Emission © 2008 University of Illinois Board of Trustees. characteristic for the element © 2008 University of Illinois Board of Trustees. All rights reserved.6/9/2008 Photoelectron and Auger Electron Emission KE (measured) = hν (known) . All rights reserved. 10 5 .L3 2s L1 1s K Calculate: BE = hν . i. 6/9/2008 Photoelectron and Auger Electron Emission 11 © 2008 University of Illinois Board of Trustees. All rights reserved. Photoelectron and Auger Electron Emission Energy Scales Conduction Band 0 Fermi Level Valence Band Binding Energy Kinetic Energy Photoelectron Lines Auger Electron Lines © 2008 University of Illinois Board of Trustees. 12 6 . All rights reserved. BE C 1s = 285 eV. 14 7 .6 eV M K Mg Kα = 1253.g. e. Mg 1s =1304 eV.4 eV © 2008 University of Illinois Board of Trustees.6 1253 6 eV V XPS can probe all of the orbitals in only the light elements. 13 Photoelectron and Auger Electron Emission Ultraviolet Photoelectron Spectroscopy Conduction Band Fermi Level Valence Band He II = 40.6/9/2008 Photoelectron and Auger Electron Emission X-ray Photoelectron Spectroscopy Conduction Band Fermi Level Valence Band Al Kα = 1486. All rights reserved. Au 1s ≈ 81000 eV Predominantly. soft X-rays are used.8 eV He I = 22. All rights reserved. © 2008 University of Illinois Board of Trustees. 5 0 0 500 1000 1500 2000 2500 3000 Kinetic Energy (eV) Electrons travel only a few nanometers through solids.5 2 1. R. Powell. *S. R. Powell. 17.5 Auger 4 3. Surface and Interface Analysis. © 2008 University of Illinois Board of Trustees. D. 911-926 (1991). J.5 Carbon Aluminum Copper Silver Gold 3 2. 16 8 . Surface Sensitivity: Electron Spectroscopy Inelastic Mean-Free Path: The mean distance an electron can travel between inelastic scattering events. Inelastic mean-free paths (calculated) based on TPP-2* 5 In nelastic Mean-Free Path(nm) 4. C.5 1 0. D. Surface and Interface Analysis.5 1 0. Penn. Tanuma. All rights reserved.5 0 0 500 1000 1500 2000 2500 3000 Kinetic Energy (eV) Electrons travel only a few nanometers through solids.6/9/2008 Surface Sensitivity: Electron Spectroscopy Inelastic Mean-Free Path: The mean distance an electron can travel between inelastic scattering events.5 2 1. C. 15 © 2008 University of Illinois Board of Trustees. 911-926 (1991).5 Carbon Aluminum Copper Silver Gold 3 2. All rights reserved. 17. *S. Inelastic mean-free paths (calculated) based on TPP-2* 5 In nelastic Mean-Free Path(nm) 4. J.5 XPS 4 3. Penn. Tanuma. 6 I/I0 0. λ ≈ 1.6/9/2008 Surface Sensitivity: Electron Spectroscopy Assuming Inelastic Scattering Only 1 Beer-Lambert relationship: I = I0exp(-d/λcosθ) where d = depth λ = Inelastic mean free path at 3λ.6 nm 0.4 0.8 0.2 0 0 1 2 3 4 d/λ d/ λ 95% of the signal comes from within 5 nm of the surface or less! © 2008 University of Illinois Board of Trustees.05 at 1000 eV. I/I0 = 0. All rights reserved. 18 9 . 17 Surface Sensitivity: Electron Spectroscopy Surface Analysis Advantage Disadvantage Extremely surface sensitive! Extremely surface sensitive! © 2008 University of Illinois Board of Trustees. All rights reserved. X-ray Photoelectron Spectrometer Hemispherical Energy Analyzer X-ray Monochromator Extraction Lenses Detector Sample 54. edited by R. • recoiled target atoms in turn collide with atom at rest generating a collision cascade.5 – 5 keV Ar+ •Ions striking a surface interact with a number of atoms in a series collisions. Sigmund. i.6/9/2008 Ion Sputtering 0. the cascade is “linear”. Springer-Verlag.7 X-ray Source © 2008 University of Illinois Board of Trustees. “Sputtering by ion bombardment: theoretical concepts. approximated by a series of binary collisions in a stationary matrix. • When Ei > 1 keV. All rights reserved. 1981 19 © 2008 University of Illinois Board of Trustees. 20 10 .” in Sputtering by particle bombardment I. All rights reserved. Behrish. Causes physical and chemical damage P. • The initial ion energy and momentum are distributed to among the target recoil atoms.e. 6/9/2008 X-ray Photoelectron Spectrometer Physical Electronics PHI 5400 21 © 2008 University of Illinois Board of Trustees. All rights reserved. 22 11 . All rights reserved. Elemental Shifts Pure Element Fermi Level Electron-electron Electronrepulsion Electron Electron-nucleus Electronattraction Binding Energy Look for changes here by observing electron binding energies ElectronNucleus Separation Nucleus © 2008 University of Illinois Board of Trustees. 6/9/2008 Elemental Shifts 23 © 2008 University of Illinois Board of Trustees. 24 12 . All rights reserved. All rights reserved. Elemental Shifts Core Level Binding Energies 1400 2s 1s 1200 2p Binding Energy (eV) 1000 3s 800 3p 600 3d 400 4s 200 4p 0 0 5 10 15 20 25 30 35 40 45 50 Atomic Number © 2008 University of Illinois Board of Trustees. 2000. 7. units) C ScN Sc3p Sc3s Ti2p Ti2s N1s TiN V2p V2s N1s VN Cr2p Cr2s N1s CrN 1200 1000 800 600 400 200 Ti3p Ti3s V3p V3s Cr3p Cr3s 0 Binding energy (eV) Surface Science Spectra. 26 13 . and CrN Sc2p Metal and N Auger Lines Sc2s N1s Counts (arb. All rights reserved.6/9/2008 Elemental Shifts First-Row Transition Metals Binding Energy (eV) Element 2p3/2 3p Δ Sc 399 29 370 Ti 454 33 421 475 V 512 37 Cr 574 43 531 Mn 639 48 591 Fe 707 53 654 Co 778 60 718 Ni 853 67 786 Cu 933 75 858 Zn 1022 89 933 25 © 2008 University of Illinois Board of Trustees. © 2008 University of Illinois Board of Trustees. Elemental Shifts: An Example First-Row Transition Metal Nitrides: ScN. VN. 167-280. TiN. All rights reserved. C-O-C 286. ether C-O-H.0 © 2008 University of Illinois Board of Trustees.5 Cl bound to C C-Cl 286. 27 Chemical Shifts Functional Group hydrocarbon C-H. 28 14 .8 carbonyl C=O 288.5 F bound to C C-F 287. All rights reserved.0 amine C-N 286. All rights reserved. C-C C 1s Binding Energy (eV) 285.0 alcohol.6/9/2008 Chemical Shifts Electronegativity Effects Carbon-Oxygen Bond Oxygen Atom Valence Level C 2p Core Level C 1s Electron-oxygen atom attraction (Oxygen Electronegativity) Electron-nucleus attraction (Loss of Electronic Screening) C 1s Binding Energy Shift to higher binding energy Carbon Nucleus © 2008 University of Illinois Board of Trustees. Additional information or the use of complimentary methods is essential! © 2008 University of Illinois Board of Trustees.6/9/2008 Chemical Shifts: An Example XPS of polymethylmethacrylate O 1s O 1s 2 C 1s 538 536 1 534 532 530 528 284 282 Binding Energy (eV) C 1s 1000 800 600 400 200 0 Binding Energy (eV) 1 2 4 292 290 3 288 286 Binding Energy (eV) 29 © 2008 University of Illinois Board of Trustees.… Here is what we actually see. 1. All rights reserved. 4. 4 292 290 3 288 2 286 284 282 Binding Energy (eV) Sensitivity to chemical structures with XPS is short-ranged. Chemical Shifts: An Example XPS of polymethylmethacrylate But. All rights reserved. 30 15 . 1 3. C 1s 2. Sundgren.A. 167-280. VN. 31 Ultraviolet Photoelectron Spectroscopy: An Example First-Row Transition Metal Nitrides: ScN. B.1 TiN 1 (1) 397.9 (3) 396. and CrN p-d hybridization 8 MO’s Binding Energy.7 Counts (arb. TiN. 2000. 7. units) Anti-bonding e-/Formula Unit (nominal) N 1s ScN TiN VN CrN 399 398 397 396 395 394 Binding energy (eV) Surface Science Spectra.E. American Institute of Physics Conference Proceedings. Barnett. All rights reserved. 7. TiN. 167-280. 2000. units) C ScN ƒ As the number of electrons per unit cell increases. © 2008 University of Illinois Board of Trustees. S. © 2008 University of Illinois Board of Trustees.17 (0) 396.9 ((2)) 397. the metal 3d bands begin to fill pushing the Fermi level above the minimum in the density-of-states (DOS). A. J.0 CrN 2. from ScN to CrN.O. and CrN Partially hybridized N 2p M 3d anti-bonding and M 3d bonding states states Counts (arb. J. All rights reserved. 149(1).-E. eV ScN -0. Rockett.6/9/2008 Chemical Shifts: An Example N 1s spectra of First-Row Transition Metal Nitrides: ScN. Greene. 95-115 (1986). The Fermi edge then becomes more dominant and the N 2p bands move to higher binding energy. Johansson.3 VN 1. VN. TiN VN CrN 10 8 6 4 2 0 -2 Binding energy (eV) Surface Science Spectra. 32 16 . XPS is considered to be a semi-quantitative technique. Modern acquisition and analysis software can account for the transmission function. © 2008 University of Illinois Board of Trustees. 34 17 . 33 Quantitative surface analysis: XPS By assuming the concentration to be a relative ratio of atoms. cm2 θ = photoelectron emission angle © 2008 University of Illinois Board of Trustees.6/9/2008 Quantitative Surface Analysis: XPS Assuming a Homogeneous sample: Ai = detector count rate detector count rate Ai θ λcos(θ) Sample Dependent Terms where: N = atoms/cm3 σ(γ) = photoelectric (scattering) cross-section. nj Jbeam Ai = ( electrons/volume )( volume ) Ai = ( Niσi(γ)JT(Ei) )( aλi(Εi)cosθ) Instrument Dependent Terms J = X-ray flux flux.j/Si. cm2 λ(Ei) = inelastic electron mean-free path. cm λ γ ni. we can neglect the terms that depend only on the instrument: Ni = Ai/σiT(Ei)λi(Ei) It is difficult to accurately determine λi so it is usually neglected. photon/cm2-sec T(Ei) = analyzer transmission function a = analysis area. Ni = Ai / Si Ci = Ai/Si / Σ Ai. All rights reserved. All rights reserved.j The values of S are determined theoretically or empirically with standards. 00 1.02 1.2 574.13 1.0 396.7 584.02 Bulk value from RBS a.73b After ion bombardment 0.02 1. All rights reserved.03 1.5 575.55b 1. Quantitative surface analysis: An Example First-Row Transition Metal Nitrides: ScN.0 520.3 397.46 0. The satellite is due to a transition into a relaxed final state b. 167-280.4 457.7 As Deposited 1.1 513.5 461.73 0. and CrN XPS Analysis Metal 2p3/2 ScN TiN VN CrN 400.06±0. TiN. Nitrogen/Metal peak ratio decreases after sputtering Surface Science Spectra.1 Satellitea Binding energy (eV) Major peak Metal 2p1/2 Major peak 404.9 Satellitea Composition (N/metal) N 1s 396.11±0.02 0.02±0.4 455.99 0. 36 18 . The composition determination of the CrN layers by peak fitting is less reliable because the commonly used Shirley method for background subtraction does not accurately describe the experimental data.04±0. © 2008 University of Illinois Board of Trustees.8 523. VN. All rights reserved. 2000.0 463.6/9/2008 Quantitative surface analysis: XPS XPS Relative Elemental Sensitivities 12 3d Relative Sensitivity 10 4f 8 2p 6 4 4d 1s 2 0 Li B N F Na Al P Cl K Sc V M Co Cu G As Br Rb Y Nb Tc Rh Ag In Sb I Cs La Pr P Eu Tb Ho T Lu Ta Re Ir Au Tl Bi Be C O Ne M Si S Ar Ca Ti Cr Fe Ni Zn G Se Kr Sr Zr M Ru Pd Cd Sn Te Xe Ba Ce Nd S G Dy Er Yb Hf W Os Pt Hg Pb Elemental Symbol 35 © 2008 University of Illinois Board of Trustees.0 585.9 515. 7.1 397. Angle-resolved XPS: An Example Si with native oxide O 1s Si 2p Si 2s Si 2p Si0 θ = 0º C 1s Si oxide O 1s Si 2p θ = 75º Si0 Si oxide C 1s Si 2s Si 2p © 2008 University of Illinois Board of Trustees. All rights reserved. 38 19 . All rights reserved.6/9/2008 Angle-resolved XPS More Surface Sensitive Less Surface Sensitive θ = 75° θ = 0° θ A film on B IA/IB AB alloy IA/IB θ θ Information depth = dcosθ d = Escape depth ~ 3 λ θ = Emission angle (relative to surface normal) λ = Inelastic Mean Free Path 37 © 2008 University of Illinois Board of Trustees. d=1.2 nm SiO2 Si © 2008 University of Illinois Board of Trustees. © 2008 University of Illinois Board of Trustees.thin overlayer Assuming only inelastic scattering and photoelectrons from layer a will not undergo an inelastic scattering event Beer-Lambert relationship: I = I0exp(-d/λcosθ) d Ia Ib a b Step 1: a=Carbon.e.5 nm 0.3 nm ∫ d/λ = ln(ca/cb +1)cosθ Step 2: a=Carbon+SiO2. All rights reserved. spectrum) is projected onto the detection plane. an energy dispersed image (reciprocal image I. 40 20 . d=0. 39 Imaging X-ray Photoelectron Spectrometer Kratos AXIS Ultra Imaging Mode: Spherical mirror analyzer With the entrance aperture open. a spatially dispersed image (real image) is projected onto the detection plane. b=Si with λ=3 nm.3 nm Carbon 1. b=SiO2+Si with λ=3 nm. All rights reserved.6/9/2008 Angle-resolved XPS: An Example SiO2 Layer thickness calculation: Two-Layer Model. Spectroscopy Mode: Hemispherical energy analyzer With the entrance aperture closed. P. W. © 2008 University of Illinois Board of Trustees. G. Si wafer Y. 123. Harada. Nuzzo. JACS. Li. Bohn. The image confirms the selective deposition of the Pt-complex in the OTS-free areas of the substrate.6/9/2008 XPS Imaging: An Example Pt catalyzed etching of patterned porous silicon 1 O 1s Si wafer Si 2s Si 2p µCP OTS Anneal C 1s OTS 2 Si wafer Spin-coat Pt complex Heat Pt 3 OTS Si wafer Etch PSi 4 Pt 4f Pt 4f Cross-correlated. Bohn. respectively. All rights reserved. X. P. Harada. 123. W. 41 © 2008 University of Illinois Board of Trustees. X. 8709-8717 (2001). Cross-correlated low-magnification XPS image after step 3 for the Pt 4f7/2 (shown in orange) and C 1s (shown in blue) core levels measured at 74 and 285 eV. Li. 42 21 . 8709-8717 (2001). G. XPS Imaging: An Example Pt catalyzed etching of patterned porous silicon 1 O 1s Si 2s Si wafer C 1s Si 2p µCP OTS Anneal OTS Pt 4f 2 Si wafer Spin-coat Pt complex Heat Pt 3 OTS Si wafer Etch PSi 4 Pt 4f Cross-correlated. respectively. All rights reserved. R. R. The image confirms the selective deposition of the Pt-complex in the OTS-free areas of the substrate. Nuzzo. JACS. Si wafer Y. Cross-correlated low-magnification XPS image after step 3 for the Pt 4f7/2 (shown in orange) and C 1s (shown in blue) core levels measured at 74 and 285 eV. © 2008 University of Illinois Board of Trustees. 7. units) C 2p1/2 as-deposited + Ar sputtered 470 465 460 455 450 445 Binding Energy (eV) Surface Science Spectra. 2000. All rights reserved. eV 43 © 2008 University of Illinois Board of Trustees. S h a reduction Such d ti would ld effect ff t the th collector’s efficiency.6/9/2008 Ion Sputtering and Depth Profiling: An Example Analysis of Materials for Solar Cells by XPS Depth Profiling The amorphous-SiC/SnO2 Interface The profile indicates a reduction of the SnO2 occurred at the interface during deposition. Photo--voltaic Collector Photo SnO2 Sn Solar Energy Conductive OxideOxide. 44 22 . All rights reserved. Ion Sputtering and Depth Profiling: An Example TiN 2p3/2 Counts (arb. 167-280.SnO2 p-type aa-SiC 500 496 a-Si 492 488 484 480 Depth Binding Energy. quantitative with standards. not a trace analysis technique. Chemical State Information: Yes. L Lateral l Resolution: R l i S Spectroscopy1 mm to 40 mm. 167-280. Chemical State Information: Yes. © 2008 University of Illinois Board of Trustees.5 – 5 nm. conducting or semiconducting are best best. Sample Types: Solid UHV-compatible. some beam damage g to sensitive materials.5 mm.A Summary XPS UPS Elements: Li and above. Imaging. units) C as-deposited d it d + Ar sputtered 1 0 -1 Binding energy (eV) 10 8 6 4 2 0 -2 Binding energy (eV) Surface Science Spectra. Lateral Resolution: Several mm.. for most elements.6/9/2008 Ion Sputtering and Depth Profiling: An Example Countts (arb. semiconducting and insulating. 46 23 . No some beam damage to sensitive materials. 7. but complicated from valence levels. 45 XPS and UPS.5 – 5 nm. Depth Resolution: 0. All rights reserved. © 2008 University of Illinois Board of Trustees. conducting. Depth Resolution: 0. Elemental Analysis: Yes.1 – 1 atomic % Destructive: No. Sample Types: Solid UHV-compatible. semiquantitative without standards. Sensitivity: 0. All rights reserved. for core levels same as XPS. sometimes from low BE core levels. Destructive: No. units) ScN He I UPS Counts (arb. 2000. Elemental Analysis: Not usually. Lise Meitner Pierre Victor Auger 1. © 2008 University of Illinois Board of Trustees. 205 (1925). 6. All rights reserved. First discovered in 1923 by Lise Meitner and later independently discovered once again in 1925 by Pierre Auger1. 47 Particle-Surface Interactions Auger Electron Spectroscopy Ions Ions Electrons Electrons Photons Photons Joe E. P. 48 24 . is a widely used technique to investigate the composition of surfaces. Auger.6/9/2008 Auger Electron Spectroscopy Auger Electron Spectroscopy (AES). Greene2) Vacuum © 2008 University of Illinois Board of Trustees. J. Radium. All rights reserved. Phys. 50 25 .6/9/2008 Auger Electron Spectroscopy © 2008 University of Illinois Board of Trustees.3) .E(L2. All rights reserved.E(L2. All rights reserved.3) © 2008 University of Illinois Board of Trustees.L3 2s L1 1s K KLL Auger electron EAuger = E(K).3) EX-ray = E(K) – E(L2. 49 Auger Electron Spectroscopy Incident Electron Secondary Electron Emitted Auger Electron Free Electron Level Conduction Band Conduction Band Fermi Level Valence Band Valence Band 2p L2. 3) .3) © 2008 University of Illinois Board of Trustees.6/9/2008 Auger Electron Spectroscopy Incident Electron Secondary Electron Emitted X-ray Photon Free Electron Level Conduction Band Conduction Band Fermi Level Valence Band Valence Band 2p L2. 52 26 .4 0.E(L2.8 Auger Electron Emission 0. 51 Relative Probability of Relaxation of a K Shell Core Hole 1.2 X-ray Photon Emission 0 5 10 15 20 25 30 35 40 Atomic Number B Ne P Ca Mn Zn Br Zr Elemental Symbol The light elements have a higher cross section for Auger electron emission. © 2008 University of Illinois Board of Trustees. All rights reserved.0 Probability 0.6 0.3) EX-ray = E(K) – E(L2. All rights reserved.L3 2s L1 1s K KLL Auger electron EAuger = E(K).E(L2. 54 27 . All rights reserved.6/9/2008 Scanning Auger Electron Spectrometer 53 © 2008 University of Illinois Board of Trustees. Elemental Shifts First-Row Transition Metals Binding Energy (eV) Element 2p3/2 3p Δ Sc 399 29 370 Ti 454 33 421 V 512 37 475 Cr 574 43 531 Mn 639 48 591 Fe 707 53 654 Co 778 60 718 786 Ni 853 67 Cu 933 75 858 Zn 1022 89 933 © 2008 University of Illinois Board of Trustees. All rights reserved. .3 Sc M2.3L2.3 Ti V V Sc L3M2. Paul W. units) C 0 3 k e V s p e c tra . G.3 Sc L3M4.a s d e p o s ite d 3 k e V s p e c t r a . All rights reserved. All rights reserved. MN 1976.5M4.5 Sc L3M2. © 2008 University of Illinois Board of Trustees. N. MacDonald. C.3M4. Eden Prairie. Riach.5 Ti 200 N KL2.3 Ti Ti V V Sc L3M4. 7.3M4M4 Sc M1M4M4 Ti V V Cr Cr O Ti Counts (arb. Physical Electronics Division. 2000. Elemental Shifts: An Example First-Row Transition Metal Nitrides: ScN.5M4.6/9/2008 Elemental Shifts L. R.3 N(E) 600 K in e tic e n e rg y ( e V ) Surface Science Spectra.3L2. 2nd Edition. 167-280.5 Ti Sc L3M2. E.5 Sc M2. units) N KL2.a s d e p o s it e d Ti dN(E) Sc L3M2. Palmberg.3L2. Perkin-Elmer Corp. Weber.3M2.3M2. E. TiN.3M4M4 Sc M1M4M4 Ti Ti V V Cr Cr Cr Cr Cr V Counts (arb.3M4. 55 © 2008 University of Illinois Board of Trustees. Handbook of Auger Electron Spectroscopy. VN. Davis. and CrN 400 600 0 V 400 Cr Cr 200 K in e t ic e n e r g y ( e V ) Cr N KL2. E. 56 28 . All rights reserved. 58 29 .6/9/2008 Quantitative surface analysis: AES Assuming a Homogeneous sample: Ai = detector count rate detector count rate Ai θ λcos(θ) Sample Dependent Terms where: N = atoms/cm3 σ(γ) = ionization (scattering) cross-section. electron/cm2-sec T(Ei) = analyzer transmission function a = analysis area. © 2008 University of Illinois Board of Trustees. Modern acquisition and analysis software can account for the transmission function. Ni = Ai / Si Ci = Ai/Si / Σ Ai. AES is considered to be a semi-quantitative technique.j/Si. cm λ γ ni. cm2 θ = Auger electron emission angle © 2008 University of Illinois Board of Trustees. cm2 χi = Auger transition probability r = secondary ionization coefficient λ(Ei) = inelastic electron mean-free path. nj Jbeam Ai = ( electrons/volume )( volume ) Ai = ( Niσi(γ)χi(1+r)JT(Ei) )( aλi(Ei)cosθ) Instrument Dependent Terms J = Electron flux. All rights reserved.j The values of S are determined theoretically or empirically with standards. so they are usually neglected. 57 Quantitative surface analysis: AES By assuming the concentration to be a relative ratio of atoms. we can neglect the terms that depend only on the instrument: Ni = Ai/σiχi(1+r)T(Ei)λi(Ei) It is difficult to accurately determine λi and r. All rights reserved.1 0.01 0 20 40 60 80 100 Atomic Number © 2008 University of Illinois Board of Trustees.01 0 20 40 60 80 100 Atomic Number 59 © 2008 University of Illinois Board of Trustees.6/9/2008 Quantitative surface analysis: AES 3 kV Primary Beam 10 Sensitivity Factor KLL LMM MNN 1 0. Quantitative surface analysis: AES 10 kV Primary Beam 10 Sensitivity Factor KLL LMM MNN 1 0.1 0. All rights reserved. 60 30 . 02 Bulk composition from RBS a.43 1.02 1.3 and Ti L3M2.82 2.3M2.3 exhibit severe overlap (see spectra).6 Iγ/Iα 1.2 435. All rights reserved.. Nitrogen/Metal peak ratio decreases after sputtering Surface Science Spectra.3L2. 7. the N KL2. VN. 167-280.00 …b 1. 62 31 .3 is omitted in the table and the listed peak intensity ratio corresponds to the sum of N KL2. TiN.5 peak (see spectra).06±0.2 417.0 527.94 1. and CrN ScN AES Analysis Peak energy b. Iα+γ/Iβ).03 1.02±0.2a …b 382.3L2.01 0. © 2008 University of Illinois Board of Trustees.00 2.5 As-deposited Intensity TiN The N KL2. All rights reserved. 2000.30 1.5 (i.4 486.6/9/2008 Quantitative surface analysis: AES 61 © 2008 University of Illinois Board of Trustees.04±0.3M4.02 1.3M2. VN Metal L3M2.10 1.54 1. Therefore.8 (β) 367.3M4. CrN Metal L3M2.5M4.4 472.3 (γ) 382.3 and the Ti L3M2.3 (α) 337.3M2.3L2.95 1.4 381.3L2.3M2.e.69 Iγ/Iβ 2.3L2.14 b After ion Iγ/Iα 1.01 … bombardment Iγ/Iβ 1. Quantitative surface analysis: An Example First-Row Transition Metal Nitrides: ScN.02±0.52b 1.3 in the pure metal spectrum. The latter peak is ~6% of the Sc L3M2.8 N KL2. the peak position of N KL2.3 divided by Ti L3M2.0 384. For the TiN AES spectrum.3 peak overlaps with the weak Sc L3M4. 6/9/2008 AES Depth Profiling: An Example (cross section) © 2008 University of Illinois Board of Trustees. 64 32 . All rights reserved. 63 AES Depth Profiling: An Example © 2008 University of Illinois Board of Trustees. All rights reserved. 100.0 μm In Map of single Au pad From research by D. All rights reserved. Electrical and Computer Engineering Dept. eV © 2008 University of Illinois Board of Trustees.0μm Low magnification SEM image of general sample area 10.6/9/2008 AES Imaging and Mapping: An Example Contamination on patterned semiconductor Survey data was used to identify Indium (In) contamination after the etching step on a patterned semiconductor. semiconductor Then mapping of the In signal showed the position of contamination on the sample. Stillman.0 μm SEM image of a single Au pad 10. 66 33 . 65 © 2008 University of Illinois Board of Trustees. AES Imaging and Spectroscopy: An Example 600 400 dN(E)/E 200 0 -200 C -400 Cr -600 -800 Ni -1000 0 200 400 600 800 1000 1200 Kinetic Energy. Ahmari/G. All rights reserved. eV 400 dN(E))/E 200 10 μm 0 -200 C -400 -600 Cr -800 0 200 400 600 800 1000 1200 Kinetic Energy. 6/9/2008 AES Imaging and Mapping: An Example Cr Map C Map © 2008 University of Illinois Board of Trustees. All rights reserved. All rights reserved. 67 AES Imaging and Mapping: An Example Ni Map C Map © 2008 University of Illinois Board of Trustees. 68 34 . All rights reserved. © 2008 University of Illinois Board of Trustees. 69 AES: A Summary AES Elements: Li and above.6/9/2008 AES Imaging and Depth Profiling: An Example Electron Beam in combination with an SED detector allows for imaging of the sample to select the area for analysis.6 Si -0.2 N PEAK-TO-PEAK c/s Fracture surface of Carbon fibers in BN matrix . sometimes requires highresolution analyzer. some beam damage to sensitive materials. Variations in fracture surface interface for different sample treatments will be reflected in depth profile. 1 COFER73.4 0.5 – 5 nm. for some elements. All rights reserved.6 0. conducting. Sensitivity: 0.2 Ar B -0. From research by C. Elemental Analysis: Yes. Economy.SPE x 10 4 0. semiconducting.8 -1 50 O C 100 150 200 250 300 350 400 Kinetic Energy (eV) 450 500 550 SPUTTER TIME (MIN.8 0. Sample Types: Solid UHV-compatible.4 04 -0.) Survey on Fiber surface at 1 min. Chemical State Information: Yes.analysis area outlined in black 0 -0. © 2008 University of Illinois Board of Trustees. in profile Depth profile on fiber to determine point of fracture. quantitative with standards. Depth Resolution: 0. 70 35 .1 – 1 atomic % Destructive: No. Lateral Resolution: 500 nm. Cofer/J. Yes semi semi-quantitative quantitative without standards standards. not a trace analysis technique. Materials Science Dept. All rights reserved.S. © 2008 University of Illinois Board of Trustees.6/9/2008 Surface Analysis © 2008 University of Illinois Board of Trustees. 72 36 . Department of Energy under grants DEFG02-07-ER46453 and DEFG02-07-ER46471. All rights reserved. 71 Acknowledgements Sponsored by: The Frederick Seitz Materials Research Laboratory is supported by the U.