Surface Analysis by XPS & ToF-SIMS Basics, Strengths, and Limitations

Transcription

1 Surface Analysis by XPS & ToF-SIMS Basics, Strengths, and Limitations Michael Bruns KIT University of the State of Baden-Württemberg and National Laboratory of the Helmholtz Association

2 The Merger of Forschungszentrum Karlsruhe and Universität Karlsruhe 1956 Karlsruhe Nuclear Research Center 10/ 2009 KIT Campus North 2 Michael Bruns

3 Thermo Fisher Scientific: K-Alpha & Glovebox ESCA5/Alpha110 XPS Quant. Chemical Information Depth Profiles FE-SEM Topography EDS Elemental Images Surface Analysis ToF-SIMS Chemical & Molecular Information 3D Elemental Information Zeiss GmbH: Merlin inert transfer IN-TF GmbH: TF.SIMS 5 6 Michael Bruns

4 Textbooks X-ray Photoelectron Spectroscopy XPS Auger Electron Spectroscopy AES Time-of-Flight Secondary Ion Mass Spectrometry ToF-SIMS ~ 60 ~ 200 ~ Michael Bruns

5 8 Michael Bruns

6 Surface Analysis Bulk Analysis Thin Film Analysis Surface Analysis 3 nm 10 nm Top Surface Near Surface Top Surface Near Surface Top Surface Near Surface nm Thin Film Thin Film nm Coating Coating Bulk 9 Michael Bruns

7 Surface Analysis Analytical Resolution Versus Detection Limit 10 Michael Bruns

8 X-Ray Photoelectron Spectroscopy (XPS) Relationship to Electronic Structure Au E B = hν - E K - ω (mono) Al Kα ev Mg Kα ev s singlet p doublet (3/2 & 1/2) d doublet (5/2 & 3/2) f doublet (7/2 & 5/2) John F. Watts, John Wolstenholme, An Introduction to Surface Analysis by XPS and AES, Wiley & Sons, Chichester, UK, Michael Bruns

9 XPS Characteristics Depth of analysis 5nm All elements except hydrogen Readily quantified All materials (ultra high vacuum compatible) Depth profiling by angle resolved XPS or sputtering Analysis area mm 2 to 30 micrometres Chemical images Complementary Theta Methods Probe ToF-SIMS LEIS RBS FE-SEM &EDS TEM VG ESCA5 & Thermo Fisher Alpha 110 Analyzer Thermo Fisher K-Alpha Application Lab, UK 12 Michael Bruns

10 XPS Instrumentation: X-Rays Mg 13 Michael Bruns

11 XPS Instrumentation: Concentric Hemispherical Analyzer Channeltron Mu-Metal: Ni 81/Fe19 - Alloy 14 Michael Bruns

12 Speziation / Chemical Shift 15 Michael Bruns

13 Speziation Chemical Shift 16 Michael Bruns

14 XPS: Depth of Analysis 0.5 λ ~ E Intensity as a function of depth 65% of the signal from < 1λ 85% from < 2λ 95% from < 3λ 17 Michael Bruns

15 X-Ray Induced Auger Emission E KL2,3L2,3 (Z) = E K (Z) [E L2,3 (Z) + E L2,3 (Z + 1)] 18 Michael Bruns

16 MgKα vs. AlKα X-Rays ev ev XPS and Auger peaks 19 Michael Bruns

17 Electron Spectroscopy (AES) Electron Solid Interactions Primary Electron Beam Auger-Electrons Secondary Electrons Backscattered Electrons X-rays Surface All elements Z>2 Conducting and semiconducting surfaces Spatial resolution <10nm Detection limit >0.1at.% Quantitative elemental information 3µm Exitation Volume 20 Michael Bruns

18 MgKα vs. AlKα X-Rays ev ev XPS and Auger peaks Shake-up/off satellites X-ray satellites Background Surface charging 22 Michael Bruns

19 Shirley Type Background ( ) * I E = I I b b b a b ( ) I E 0 a ( ) I E 0 de x x x de x x x 23 Michael Bruns

20 Monochromatic AlKα X-Rays FWHM ev 180 spherical sector analyser multi-channel detector photoelectrons focused by high-transmission lens toroidal crystal anode electron gun Bragg: nλ = 2d sinθ θ = 78.5, AlKα Quartz Michael Bruns

21 Speciation: SAMs for Biological Applications X-Ray Induced Damage intensity [arbitrary units] C H 3 C 1s C- C-H S Au microfocused X-rays 1. Multi-point analysis with short acquisition time 2. Collapse data set to one single spectrum binding energy [ev] SAM alteration dependant on the X-ray exposure time (-- as received, -- 9 min., -- 21min., min.). 25 Michael Bruns

22 Thiol-SAMs Benzylguanine disulfide (BGT) H 2 N N N H N N S S CH 3 6 NH EG3Me thiol HS CH 3 3 Methoxy-capped tri(ethylene glycol) undecanthiol 1. S. Engin, V. Trouillet, C. M. Franz, A. Welle, M. Bruns, and D. Wedlich, Langmuir 26 (2010) M. Bruns, C. Barth, P. Brüner, S. Engin, T. Grehl, C. Howell, P. Koelsch, P. Mack, P. Nagel, V. Trouillet, D. Wedlich, R. G. White, Surf. Interface Anal. 44 (2012) Michael Bruns

23 SNAP-tag system for covalent immobilization of proteins Protein of interest SNAP S Applications cell culture: cell adhesion, migration, differentiation biosensors in diagnosis, lab-on-chip technology, NH N H 2 N N CH NH N.. Au S CH 3 CH 3 3 CH 3 Au S 3 Au S SNAP-tag system: genetically modified 6 -alkylguanin-dna alkyltransferase Au Au S S 27 Michael Bruns

24 Thiol SAMs for Biological Applications BGT H 2 N N N H N N Au-S-C -CH- C S 1s -C--C- -NH- -N= N 1s 2p -C--C- pure BGT Au S S EG3Me CH 3 6 NH intensity [arbitrary units] -C= -C= EG3Me S CH 3 Au 3 -C= binding energy [ev] Michael Bruns

25 XPS Information Depth Depends on Electron Emission Angle 29 Michael Bruns

26 Parallel ARXPS: non-destructive Depth Profile 30 Michael Bruns

27 Parallel ARXPS: EG3Me SAM non-destructive Depth Profile 120 C H 3 S Au atomic concentration [%] C 1s 1s -C 2 H 4 - -CH 2 - -S- Au depth [nm] 31 Michael Bruns

28 High-sensitive Low Energy Ion Scattering SAM Thickness CH 3 27 Projectile: 3 kev 3 He + Au peak onset energy shift: EG3Me = 200 ev 2.2 nm SAM thickness well-ordered SAM Au S Au Reliable estimation of the SAM thickness is prerequisite for the reconstruction of non-destructive elemental depth profiles from parallel ARXPS data. Qtac Michael Bruns

29 ER PES: EG3Me SAM non-destructive Depth Information CH ev 1100 ev -C 2 H 4 - -CH 2 - -S- Au S Au 33 Michael Bruns

30 Sputtering Ion Solid Interaction Implantation 34 Michael Bruns

31 Depth Information via Sputter Depth Profiles Analyzer X-rays Ar + ion source 35 Michael Bruns

32 500.0µm XPS Sputter Depth Profiles DP Point BST right 2 Collaboration: Tascon GmbH, Heisenbergstr. 15, D Münster, Germany 36 Michael Bruns

33 XPS Sputter Depth Profiles Time-to-Depth Conversion j P = Ion beam density z( t) = j P N Y A i e M 0 i ρ t i N A e 0 t Y i M = Avogadro constant = Elementary charge = Sputter time = Sputter yield = Molecular weight ρ i = Density 37 Michael Bruns

34 XPS Sputter Depth Profiles Loss of Chemical Information Ti 4+ Ti 2 intensity [arbitrary units] Ti 2p Level 0 Level 1 Level 2 Level 3 Level 4 1 kev Ar + ions 20 s / level binding energy [ev] 38 Michael Bruns

35 ToF-SIMS Time-of-Flight SIMS Principle A short-pulsed ion beam defines the starting point of the time-of-flight measurement. All secondary ions are accelerated to the same kinetic energy: the time-of-flight for a given drift path varies as the square root of mass. Time focusing devices (i.e. electrostatic fields) for good mass resolution. 39 Michael Bruns

36 ToF-SIMS Ion Solid Interaction Excitation Bombardment with primary ions, energy: 5-25 kev (Ga +, Au n+, Bi n+, 2+, Cs +, Ar +, Xe +,...) Collision cascade in solid Results Desorption of neutrals (95%), electrons, and secondary ions (+/-). area 5-10 nm diameter depth of origin 1-2 monolayers Implantation of primary ions Atoms relocation (mixing) Damaging of organic molecules 40 Michael Bruns

37 ToF-SIMS Characteristics + detection of all elements + isotope sensitivity + chemical information molecules, clusters + low detection limit ppm - ppb + small information depth first 1-3 monolayers + high depth resolution <1 nm + high lateral resolution <100 nm + high mass resolution > high mass range up to u + parallel mass detection - quantification limited typical ion yield (requires standards) strong influence of chemical environment -/+ destructive 41 Michael Bruns

38 ToFSIMS Modes of peration Surface Spectroscopy Surface Imaging Depth Profiling 3D Analysis Quasi non-destructive surface analysis of the outer monolayers Features: - elemental and molecular information - ppm/ppb sensitivity - suited for insulators 42 Michael Bruns

39 Surface Spectroscopy High Mass Resolution in Positive and Negative Polarity SiH + x10 2 Si-Wafer F - R = 13, H Si Mass Calibration Mass Resolution 43 Michael Bruns

40 ToF-SIMS Detection Limits Element detection limits detection limits (atoms / cm 2 ) (atoms / cm 2 ) 7 Li 1E7 11 B 5E7 = 0.4 ppt 52 Cr 1E8 55 Mn 1E9 Na 1E7 24 Mg 2E7 56 Fe 2E8 58 Ni 1E9 Al 2E7 Co 2E8 39 K 1E7 63 Cu 3E8 40 Ca 3E7 48 Ti 2E8 51 V 2E8 69 Ga 1E9 * As 3E9 98 Mo 6E9 1 Monolayer = 1.5E 15 atoms/cm²), the error is estimated to be within a factor of Michael Bruns

41 ToFSIMS Modes of peration Surface Spectroscopy Surface Imaging Chemical Mapping of the surface Depth Profiling 3D Analysis Features: lateral distribution of elements and molecules lateral resolution down to 60 nm parallel acquisition of all images 45 Michael Bruns

42 (Bio)Molecular Surface Patterning by Phototriggered xime Ligation via shadow-mask techniques XPS ToF-SIMS T. Pauloehrl, G. Delaittre, M. Bruns, M. Meiβler, H. G. Börner, M Bastmeyer, and C. Barner-Kowollik, Angew. Chem. Int. Ed., 51 (2012) Michael Bruns

43 ToFSIMS vs. XPS Chemical Image ToFSIMS (1 min acquisition time) XPS (> 3000 min acquisition time) Sn 1s Si 1s Sn Snap 2 Si 2 1s Snap 500x500 µm 2! Different positions! XPS chemical images are very time consuming Parallel imaging using Thermo Scientific ESCALAB 250 Xi 47 Michael Bruns

44 ToFSIMS Modes of peration Surface Spectroscopy Surface Imaging Depth Profiling 3D Analysis Analysis of the in-depth distribution of elements and molecules Features: elemental and cluster information depth resolution < 1 nm thin layers from 1 nm to > 10 µm 48 Michael Bruns

45 ToFSIMS Sputter Depth Profiling Dual Beam Mode 49 Michael Bruns

46 ToF-SIMS Sputter Depth Profile of a R.F. Magnetron Sputtered Li-Mn- Thin Film calibrated by XPS ECASIA 2013, Cagliari, Italy 50 Michael Bruns

47 Thank you! Florian Vanessa Volker Vanessa Udo Stemme Trouillet Winkler berst Geckle 51 Michael Bruns