Applications of XPS, AES and ToF-SIMS for Solving Problems in
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The Surface Analysis Laboratory Applications of XPS, AES and ToF-SIMS for Solving Problems in Materials Research John F Watts Surrey Materials Institute & Faculty of Engineering and Physical Sciences SI-Ontario University of Toronto 20 March 2008 University of Surrey The Surface Analysis Laboratory Surface Analysis X-Ray Photoelectron Spectroscopy (XPS) The Surface Analysis Laboratory Auger Electron Spectroscopy (AES) Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Handling Contamination The Surface Analysis Laboratory C O Al Si C O Al Si 17.0 58.2 24.8 0.0 40000 37.4 40.2 16.1 6.3 80000 60000 30000 Counts / s Counts / s 40000 20000 20000 10000 0 0 1200 1000 800 600 400 200 0 1200 1000 800 600 400 200 0 Binding Energy (eV) Binding Energy (eV) Clean aluminium foil (LHS) low adventitious carbon concentration, following handling by operative (hand cream user) concentration of carbon increases and significant concentration of silicon from silicone oils in hand cream (confirmed by ToF-SIMS). Forensic Analysis The Surface Analysis Laboratory Canned beer is provided with a dense head by carbon dioxide contained in plastic “widget” Early version were three part precision mouldings, but there was a desire to replace this with a single part “top hat” component heat sealed to the bottom of the container XPS Survey Spectra The Surface Analysis Laboratory C1s O1s 400 μm XPS Epoxy Lacquer Epoxy Lacquer Internal can surface Widget bonding surface 2 mm N1s Nylon Nylon Photocured Adhesive The Surface Analysis Laboratory • LuxtrakTM photocured resin based on methacrylate type monomers •Planned use in microelectronics industry •Surface mounting of components on alumina •Fails “pressure cooker” test i.e. adhesion in hot water •Investigate failure surfaces by XPS after aqueous exposure Resin Component O O O Reactive Diluent C1s Spectra of Failure Surfaces The Surface Analysis Laboratory d = 1nm A M Taylor, C H McLean, M Charlton, J F Watts, Surf Interf Anal, 23, 342, (1995) Molecular Dynamics The Surface Analysis Laboratory Computer chemistry visualisation of reactive diluent at interface XPS shows the overlayer on substrate side of failure to be about 1 nm of reactive diluent Reformulated Resin The Surface Analysis Laboratory Reformulated resin without reactive diluent has better durability Note π → π* on both interfacial failure surfaces The Problem Faced by the Analyst The Surface Analysis Laboratory 10’s μm - mm d Adhesive or Coating Interface Region 100’s μm - mm Substrate ARXPS d ~10nm X-ray spectroscopies d ~200nm RBS d ~1μm The Buried Interface The Surface Analysis Laboratory Obtaining analytical information from intact interfaces is very difficult. Carrying out in-situ experiments within the spectrometer can be useful but only rarely is the interphase chemistry exposed in this manner J F Watts, Surf Interf Anal, 12, 497-503, (1988) TEM/PEELS Cross-Sections The Surface Analysis Laboratory PAA treated joint PAA + primer joint abrupt interface diffuse interphase A J Kinloch, M Little, J F Watts, Acta Materialia, 48, 4543, (2000) Oxide Stripping + Depth Profiling The Surface Analysis Laboratory Chemical removal of metal substrate, depth profiling of oxide in situ by ion sputtering. Interphase can then be analysed directly J F Watts, J E Castle, J Mat Sci, 18, 2987, (1983) Interface Chemistry The Surface Analysis Laboratory Iron 2p3/2 spectrum Fe(II) showing Fe(II) Fe(II) satellite component at interface. Bulk oxide is entirely Fe(III). Ultra Low Angle Microtomy The Surface Analysis Laboratory Microtome Knife Angled Sectioning Block Polypropylene Block Angle Sectioning Block 12 x 12 x 7 mm3 + 25 μm = 0.03O + 50 μm = 0.07O + 100 μm = 0.15O + 200 μm = 0.33O ULAM Geometry The Surface Analysis Laboratory Depth resolution attainable depends on the taper angle and the size of the analytical probe. In small area XPS in the range 15 -500 μm, for ToF-SIMS < 1 μm Small area XPS analysis mode (100 μm) XPS ULAM taper angle/o spot 0.03 0.33 2.0 size/μm 100 60 600 3500 15 13 100 500 Coating θ Substrate Depth Resolution ULAM/nm S J Hinder, C Lowe, J T Maxted, J F Watts, J Mater Sci, 40, 285, (2005) XPS Line Scan Along Taper The Surface Analysis Laboratory PVdF Topcoat on Polyurethane Primer 20 X-ray Spot = 15μm 4 18 3.5 16 Step Size = 18 μm 3 N: ΔZ = 27 nm 14 2.5 12 Atomic % Fluorine 10 2 Nitrogen 8 1.5 13nm 6 F: ΔZ = 50 nm 1 4 0.5 2 0 0 0 0.013 0.026 0.039 0.052 0.065 0.078 0.091 0.104 0.117 0.13 0.143 0.156 0.169 Depth / um PVdF Polyurethane ToF-SIMS of ULAM Section The Surface Analysis Laboratory a) +ve SIMS b) -ve SIMS FoV is 500 μm Polyurethane ions (a) m/z = 149: C8H5O3+ (b) m./z = 26: CN- (c) m/z = 59: C3H4F+ (d) m/z = 19: F- c) d) 2 250 nm 500 μm 3 1 PVdF ions S J Hinder, C Lowe, J T Maxted, J F Watts, Surf Interf Anal, 36, 1575, (2005) ToF-SIMS Anions from Images The Surface Analysis Laboratory a) 3500 25 3000 Point 2: Bulk Polyurethane 2500 2000 66 c) Counts 1500 41-42 49 121 2 1000 100 500 0 3 c) 15000 0 20 19 40 60 80 100 m /z 120 140 160 180 200 1 13500 12000 10500 9000 Point 1: Bulk PVdF Counts 7500 6000 39 4500 3000 49 85 1500 0 0 20 40 60 80 100 120 140 160 180 200 m /z ToF-SIMS at Interface The Surface Analysis Laboratory Negative ToF-SIMS b) 1400 19 1200 Point 3: PU and PVdF at Interface 1000 85 c) 800 Counts 2 600 31 400 55 71 200 87 121 3 141 185 0 1 0 20 40 60 80 100 120 140 160 180 200 m /z PCA on Positive Spectra from Interfacial Region to Identify Those that are not Characteristic of PVdF or PU Minor Additive The Surface Analysis Laboratory 3000 31 2700 2400 71 2100 41 1800 85 Counts 1500 1200 900 55 x10 600 185 300 0 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 m/z A negative ion ToF-SIMS mass spectra of the pure acrylic co-resin component of the PVdF topcoat formulation in the mass range 30-200m/z. ToF-SIMS Images of Acrylic Ions The Surface Analysis Laboratory a) b) Negative Ion Mass Selected Images (a) m/z = 31: CH3O- c) d) (b) m/z = 55: C3H3O- (c) m/z = 71: C3H3O2- (d) m/z = 85: C4H5O2- (e) m/z = 87: C4H7O2- e) f) (f) m/z = 141: C9H13O4- The Thin Film Approach The Surface Analysis Laboratory 10’s μm - mm d Adhesive or Coating Interface Region 100’s μm - mm Substrate thin (< 2 nm film on substrate) select sample from the plateau region of the adsorption isotherm Organosilane Adhesion Promoters The Surface Analysis Laboratory Molecular Dynamics Models of: (a) Epoxy (b) Amino (c) Vinyl Aluminium Pretreatment for Structural Adhesive Bonding The Surface Analysis Laboratory 2.5 1 hr hydration + silane Optimised silane pre-treatment Grit-blasted only 2.0 CAA pre-treatment Fracture energy (kJm -2) PAA pre-treatment 1.5 1.0 0.5 0.0 0 20 40 60 80 100 120 140 160 180 Exposure time (hrs) High Resolution ToF-SIMS The Surface Analysis Laboratory The intense SiOAl+ peak is indicative of a covalent bond between the aluminium oxide and the organosilane adhesion promoter Specific Interactions The Surface Analysis Laboratory OH HO Si (CH2)3 O CH2 CH CH2 O H O O H Al OH HO Si (CH2)3 O CH2 CH CH2 O O Al Wedge Test Failure Surfaces The Surface Analysis Laboratory Epoxy Adhesive + 1% GPS: XPS Images Optical C1s Al2p Si2p mirror images Single Fibre Pull-Out Test: Cradle to Grave ToF-SIMS The Surface Analysis Laboratory • Single fibre mounted in carrier syringe needle • Specially designed cradle used to hold sample • Fibre observed using optical microscope • Fibre presented to spectrometer for ToF-SIMS analysis pre- embedding into resin system • Fibre embedded and SFPO test conducted • ToF-SIMS analysis of pulled-out fibre • Optical and SEM images of pulled-out fibre Mounting cradle ION-TOF sample platen ION-TOF TOF.SIMS 5 A R Wood, P A Smith, J F Watts, Comp Interf, 14, 287, (2007) Mechanical Testing The Surface Analysis Laboratory 0.18 0.16 Load cell 0.14 Swivel links 0.12 Fibre carrier needle Force (N) 0.10 0.08 Mould cap 0.06 0.04 0.02 Mounting bolt 0.00 0.60 0.80 1.00 1.20 1.40 1.60 1.80 Crosshead adapter Extension (mm) Material df (μm) L (μm) Fmax (N) τ (MPa) Glass/Polyester 12.2 849 0.157 4.8 Positive ToF-SIMS Spectra The Surface Analysis Laboratory 4 x10 Si C3H9 1. 5 Pre-embedded fibre tip I nt ensi y Si C2H6 t 1. 0 Si 2C5H1 5O C8O3H5 •Bi3+ Ca C7H5O 0. 5 Si K C7H7 C9H7 C9H1 1O •Bunched mode x10 3 Si C3H9 Pulled-out fibre tip •128 μm x 128 μm 5. 0 Pulled-out fibre tip 4. 0 •128x128 I nt ensi y resolution t 3. 0 Si 2C5H1 5O C8O3H5 2. 0 Ca C7H7 C7H5O Si C2H6 C9H7 1. 0 Si K C9H1 1O 20 40 60 80 100 120 140 160 180 m ass / u Mass (u) Formula Characteristic Structure Mass (u) Formula Characteristic Structure PDMS/Silane/N 58 [SiC2H6]+ [SiC2H6]+ 91 [C7H7]+ Polyester resin + species CH3 + 73 [SiC3H9]+ PDMS/Silane H3C Si CH3 105 [C7H5O]+ Polyester resin O CH3 Glass fibre size + 115 [C9H7]+ Polyester resin 135 [C9H11O]+ HO C (epoxy) CH3 O + 149 [C8H5O3]+ Polyester resin H O O In-Situ Controlled Strain Rate Fracture The Surface Analysis Laboratory Controlled strain rate + load cell + PC control = Load: Extension curve in situ Correlation of XPS with Electrochemical History The Surface Analysis Laboratory Corrosion Beneath Organic Coating The Surface Analysis Laboratory Anodic Region Cathodic Region 25 μm SAM Identifies Cathodic Regions The Surface Analysis Laboratory SEM Ca LMM CKLL OKLL FeLMM NaKLL NIST SRM Multilayer The Surface Analysis Laboratory • Superb Depth Resolution from metal multilayer structure (layer thickness only 5nm), achieved by: – Low ion beam energy – Azimuthal rotation of specimen during sputtering cycle – Almost grazing incidence analysis by use of specimen tilt Chemical State Mapping The Surface Analysis Laboratory High energy resolution (0.1%) Cu maps allow separation of Cu and CuO AES/EDX of Inclusions in Steel The Surface Analysis Laboratory Field of View ca. 5 μm SAM Provides Superior Spatial Resolution to EDX Grain Boundary Embrittlement This phenomenon renders engineering steels brittle in nature as a result of the presence of sub-monolayer quantities of impurities at grain boundaries and phase boundaries. This can be studied by examining such fracture surfaces by AES but if fracture in air the steel will oxidise and obscure the analytical signal of the segregant. In Situ Fracture Studies by AES For the study of grain boundary segregation phenomena in metals the sample must be fractured, in an intergranular manner, within the UHV of the Auger microscope In Situ Fracture of Steels Although predominantly intergranular failure this micrograph shows a region of transgranular failure in the centre of the field of view. This provides a convenient “standard” spectrum of the bulk steel In Situ Fracture 3Cr-0.5Mo Steel Hot Cracking of Austenitic Steel Weldment: AES and EDX AES: S, EDX: Cr Hot Cracking of Austenitic Steel Weldment: AES and EDX EDX alone would indicate that the enhanced Cr was a result of the present of Cr2O3 in crack. AES data alone would indicate that sulphur segregation is the cause of ductility-dip cracking. AES and EDX together indicates a second Cr-rich phase has formed at grain boundaries: Liquation Cracking Conclusions The Surface Analysis Laboratory • All three techniques have various hierarchies of use ranging from simple elemental analysis to in-depth chemical characterisation at high spatial resolution • XPS, AES and SIMS are powerful analytical methods for the chemical and elemental characterisation of surfaces • For metallurgical studies AES/SAM is perhaps the most useful • For polymers a combination of XPS and ToF-SIMS is hard to beat • Surface analysis is expensive! • So start with a service lab such as SI-O or University of Surrey!