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Surface Vibrational Spectroscopy Prof. Melissa A. Hines Dept. of Chemistry

Surface Vibrational Spectroscopy Prof. Melissa A. Hines Dept. of Chemistry. High-Resolution Electron Energy Loss Spectroscopy (HREELS). Advantages. Disadvantages. • Surface selective • High sensitivity • Sensitive to many vib. modes (dipole + impact scattering). • High vacuum only

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Surface Vibrational Spectroscopy Prof. Melissa A. Hines Dept. of Chemistry

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  1. Surface Vibrational SpectroscopyProf. Melissa A. HinesDept. of Chemistry

  2. High-Resolution Electron Energy Loss Spectroscopy (HREELS) Advantages Disadvantages • Surface selective • High sensitivity • Sensitive to many vib. modes (dipole + impact scattering) • High vacuum only • No polarization information • Moderate resolution (10-20 cm–1)

  3. Single-Molecule Inelastic Electron Tunneling Spectroscopy Measure vib spectrum of single molecules with STM tip B.C. Stipe, M.A. Rezaei, and W. Ho, Science 280, 1732-1735 (1998). 

  4. Single-Molecule Inelastic Electron Tunneling Spectroscopy Advantages • Everything you ever wanted to know about molecule! Disadvantages • Requires very stable low-temperature STM • Not widely applicable Measure vib spectrum of single molecules with STM tip B.C. Stipe, M.A. Rezaei, and W. Ho, Science 280, 1732-1735 (1998). 

  5. Surface Raman Scattering v = 1 v = 0 Advantages Disadvantages • Good resolution (2 cm–1 typ) • Some polarization information • Better low frequency response (≤ 500 cm–1) than FTIR • Surface-enhanced Raman very sensitive • Relatively low S/N • Not inherently surface sensitive

  6. Sum-Frequency Generation Advantages Disadvantages • Inherently surface sensitive! • Excellent temporal resolution(sub-ps) • Limited frequency range • Non-linear response (I  N2) • Requires fast, high-power lasers

  7. Fourier-Transform Infrared (FTIR) Absorption Spectroscopy Advantages • Wide freq. range (500-4000 cm–1) • Outstanding resolution (< 0.01 cm–1) • Polarization analysis • Simple IR source • Inherent wavelength calibration • Designed for industrial use Disadvantages • Not inherently surface sensitive • Monolayer-level sensitivity requires some care • H2O absorbs IR light • Totally unsexy Resolution determined by distance moving mirror scans

  8. CO2 (g) Blackbodyspectrum (IR source) Fingerprints +CH in monolayer Simultiphononabsorption H2O (g) [sharp = gas phase] Example: Silicon surface coated with organic monolayer Challenge for Surface FTIR: No Inherent Surface Sensitivity

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