Surface Chemistry XPS X-Ray Photoelectron Spectroscopy SIMS Secondary Ion Mass Spectrometry MALDI Matrix Assisted Laser Desorption Ionization Surface and Surface Analysis Analytical Resolution vs. Detection Limit X-Ray Photoelectron Spectroscopy, XPS History of XPS Scattering of Photoelectrons 0.00E+00 1.00E+05 2.00E+05 3.00E+05 020040060080010001200 Counts/s Binding Energy (eV) Survey C1s N1s O1s O2s S2s S2p XPS X-Ray Photoelectron Spectroscopy ESCA Electron Spectroscopy for Chemical Analysis Introduction to XPS Ek(e-) = hν - Eb Ek (e-) Kinetoc Energy of ejected photoelectron hν characteristic energy of X-ray photon Eb Binding Energy of the atomic orbital from which the electron originates The average distance an electron travels through a solid before losing energy through inelastic collisions. Elecron Inelastic Mean Free Path, IMFP XPS Peak Notation Analysis of XPS Data, Surface Spectroscopy Polyamide 6 Chemical Shifts - change in binding energy of a core electron of an element due to a change in the chemical bonding of that element - very powerful tool for functional group and oxidation state Chemical Shifts ý Mapping & Imaging XPS Depth Profile Angle Resolved XPS Instrumentation Thermo Scientific Escalab250Xi Thermo Scientific Escalab250Xi • Identification of all elements (except H & He) • Quantitative • Chemical state identification • Chemical state distributions → Photoelectron Spectroscopy - Energy Resolution FWHM ≤ 0.45 eV of the Ag 3d5/2 peak - Spatial Resolution ≤ 20 µm → Lateral (x,y) - Mapping with < 25 µm resolution - Imaging with < 3 µm resolution → Depth (z) - Sputter depth profiling - Angle dependent depth profiling Thermo Scientific Escalab250Xi, Analysis Capabilities • Catalysis • Polymers • Coatings • Surface functionalization • Corrosion • Semiconductors • Thin films • Adhesions Secondary Ion Mass Spectrometry, SIMS • SIMS is a surface analysis technique used to characterize the surface and sub-surface region of materials. • It effectively employs the mass spectrometry of ionised particles – secondary ions which are emitted when a solid surface is bombarded by energetic primary ions. Sputtering process, Collision Cascade Excitation - Bombardment with primary ions - (Ga+, Bi1-3+, C60+...) - energy ~ 10-60 keV - collision cascade in solid Results -Desorption of neutrals, secondaty ions (+/-) - depth of origin 1-2 monolayers - implantation of primary ions -Atoms mixing - damaging of organic molecules Secondary Ion Yields • Sputtering Yield • Ion Sputtering Yield SIMS Matrix Effect Effect of Primary Ions Secondary Ion Mass Spectrometry, SIMS Time of Flight TOF Modes of Operation Surface Spectrometry, PET Fingerprint of polymers Surface Imaging, Rat Brain CrossSection A. Brunelle et. al. ICSN, CNRS, France Field of View: 18 x 18 mm2 255 Carboxylate 283 C18 Fatty acid 771 Phospholipid 892 Triclyceride Depth Profiling, SIMS, Analysis Capabilities • composition of organic, inorganic solids at the outer 5 nm of sample • detection of all elements and izotopes • composition of sample at varying spatial and depth resolution → spatial or depth profile of elemental or molecular concentrations • detection of impurities and trace elements • detection limit ppm-ppb • spatial resolution ~ 100 nm Matrix Assisted Laser Desorption Ionization MALDI • Soft ionization - analyze intact biomolecules and synthetic polymers • Broad mass range - analyze a wide variety of biomolecules • Simple mixtures are okay • Relatively tolerant of buffers and salts • Fast data acquisition • Easy to use and maintain, no water or gas hook ups required • High sensitivity, superior mass resolution and accuracy hn Laser AH+ +20 kV Variable Ground Grid Grid Sample plate MALDI, Sample preparation MALDI/LDI mechamism Laser matrix & analyte Sample support a m m m m m m m m a a a a + + + + m a m + 1. Sample (A) is mixed with excess matrix (M) and dried on a MALDI plate. 2. Laser flash ionizes matrix molecules. 3. Sample molecules are ionized by proton transfer from matrix: MH+ + A à M + AH+. LDI mechamism Matrix Assisted Laser Desorption Ionization MALDI MALDI Matrix matrix properties and requirements: • Be able to embed and isolate analytes (e.g. by co- crystallization) • Be soluble in solvents compatible with analyte • Be vacuum stable • Absorb the laser wavelength • Cause co-desorption of the analyte upon laser irradiation • Promote analyte ionization MALDI Matrix MALDI Matrix Matrix Assisted Laser Desorption Ionization MALDI MALDI, Analysis capabilities