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The Reading Group

The Reading Group. Water-Metal Interface Chiral Surface Systems. Georg Held. The Reading MONET Team. Andrey. Tugce. There is Plenty of Room at the Bottom of the Nano-Scale!. Chemical interaction takes place at a length scale < 1nm → chemical composition → molecular orientation

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The Reading Group

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  1. The Reading Group • Water-Metal Interface • Chiral Surface Systems Georg Held

  2. The Reading MONET Team Andrey Tugce

  3. There is Plenty of Room at the Bottom of the Nano-Scale! Chemical interaction takes place at a length scale < 1nm→ chemical composition→ molecular orientation Surface relaxations / reconstructions: < 0.1 nm→ electronic structure Internal structure, crystallinity of ‘nano-objects’: < 0.1 nm→ electronic, magnetic properties

  4. Low Energy Electron Diffraction (LEED) • Nobel prize 1937for C.J. Davisson: Proof that electrons behave like waves (together with Germer). • Electron energy 30-300 eV (wavelength around 1 Å). • Electrons penetrate about 10 Å into the surface. • Elastically scattered electrons are detected at the fluorescent screen.

  5. Low Energy Electron Diffraction LEED-IV analysis LEED pattern H2O D2O Information about the local surface geometry. Information about the long-range structure.

  6. LEED-IV Analysis

  7. CLEED Program Package

  8. Water – Ru Interface • Heterogeneous catalysis: • reactant, product, intermediate. • Electrochemistry: • Fuel Cells. • Water-water hydrogen bonding competes with water-metal bond. • Small energy difference between intact and partially dissociated water.

  9. Water molecules in ice Ice Ih • Every water molecule is involved in 4 hydrogen bonds. • Hexagonal bilayer structure.

  10. Partially dissociated bilayer Water on Ru{0001}:Feibelman’s Model Feibelman, Science 295 (2002). Michaelides et al. JACS 125 (2003). • Problem: • No geometry found by DFT with intact coplanar water molecules as found by LEED. (Held & Menzel Surf. Sci. 316 (1995)) • Ice-like bilayer would not wet Ru{0001} surface. • Ice clusters are more stable. • Solution: Partially dissociated bilayer. • Overlayer consists of H2O, OH, and H. • Positions of O and Ru atoms agree with those from LEED. • All hydrogen bonds parallel to surface. • Dissociation barrier ~0.5eV. Bilayer model Doering & MadeySurf. Sci. 123 (1982)

  11. X-ray Photoelectron Spectroscopy XPS XPS • Core levels: • element specific binding energies (BE). • chemical shifts in BE depending on chemical environment (molecular species, adsorption site). • Surface sensitive (electron energy < 1000 eV) • Quantitative for high Ekin. • Synchrotron XPS:Photon energy tunablefor high cross section. XPS: Ekin = hv – BE – Φ

  12. H2O on Ru{0001}:Temperature Programmed XPS O • 1 ML H2O adsorbed at 110 K • Heating rate 0.1K/s(1.5K / spectrum) • Sharp transition from low T phase to partially dissociated bilayer around 150K. H2O OH H2O OH H2O 170K Beam damage 130K

  13. Beam damage Andersson et al. PRL 93 (2004) Faradzhev et al. CPL 415 (2005) • Experiments at MAX-lab (Lund), beamline 311: • Relatively large X-ray spot on surface (0.3 x 2 mm2). • Photon flux ~ 1.2 x 1013 ph s-1 cm-2electron flux ~ 1.5 x 1012 e s-1 cm-2. • Shortest spectra correspond to0.01 e per molecule. • Low T phase very beam sensitive:spectrum changes after irradiation with ~0.1 e / molecule • Partially diss. bilayer less sensitive:no changes up to several e / molecule.

  14. 155K 100K Beam damage Andersson et al. PRL 93 (2004) Faradzhev et al. CPL 415 (2005) • Experiments at MAX-lab (Sweden), beamline 311: • Relatively large X-ray spot on surface (0.3 x 2 mm2). • Photon flux ~ 1.2 x 1013 ph s-1 cm-2electron flux ~ 1.5 x 1012 e s-1 cm-2. • Shortest spectra correspond to 0.01 e per molecule. • Low T phase very beam sensitive:spectrum changes after irradiation with ~0.1 e / molecule • Partially diss. bilayer less sensitive:no changes up to several e / molecule.

  15. Desorption Dissociation Energy (eV/mol) H2O 0.53 ~0.5 ~0.3 Intact H2O H2O+OH H2O on Ru{0001}: Thermodynamic Considerations • Two configurations of water • Metastable intact water layer • Adsorption energy similar to sublimation energy of ice. • Clusters or 2D-layer. • Partially dissociated layer • Most stable configuration. • Barriers for desorption and dissociation are similar. • Surface composition determined by kinetics rather than equilibrium thermodynamics. Michaelides et al. JACS 125 (2003)Meng et al. CPL 402 (2005) DFT: Break H2O-surface bond and hydrogen bonds H2O Break O-H bond

  16. H2O coadsorbed with oxygen • H2O adsorption on O-precovered surface: • H2O + Oad 2 OHad (disproportionation)Clay et al. CPL 388 (2004) • H2O + Oad HOH—Oad (H-bonding)Doering & Madey Surf. Sci. 123 (1982) H O O H H H H O H Run Oad Run Oad Oad Oad

  17. H2O coadsorbed with oxygen: TP-XPS Gladys, GH, et al. Chem. Phys. Lett. 414 (2005) 311 High O coverage Low O coverage H2O Oat Oat • 0.5 ML O (> 0.25ML): • High BE O1s peak 180-220K • No OH formation OH H2O 220K 200K 180K • 0.1 ML O (< 0.20ML): • Oat peak converts to OH • H2O + OH disappear at 200K

  18. H2O coadsorbed with oxygen Gladys, GH, et al. Chem. Phys. Lett. 414 (2005) 311 • 0.5 ML O (> 0.25ML): • High BE O1s peak 180-220K • Stronger bond than H2O-Ru. • Non-recombinative desorption • 0.1 ML O (< 0.20ML): • Oat + H2O  2OH below 140K • Recombinative desorption: 2OH Oat + H2O at 200K

  19. H2O coadsorbed with oxygen H2O+OH 0.1ML O 0.5ML O • Plot XPS intensity (~ coverage) of each adsorbate species vs temperature.

  20. (Doering & Madey Surf. Sci. 123, 1982) H2O coadsorbed with oxygen 220K 0.1ML O 0.5ML O H2O+OH 180K • Differentiate = Desorption Rate: • Approx. TPD spectra. • Good agreement with published TPD spectra (Doering & Madey Surf. Sci. 123, 1982) • Non-recombinative and recombinative desorption at similar temperatures.

  21. H2O coadsorbed with 0.5ML oxygen: NEXAFS • Big difference in angle dependence of NEXAFS spectra: • Large differences between normal (N.I.) and grazing incidence (70º) spectra for PDB (H2O + OH).Hydrogen bonds parallel to surface. • N.I. and 70º spectra more similar for H2O on 0.5ML O.Hydrogen bonds tilted.

  22. Is Ru the exception or the rule? Water adsorption on hexagonal surfaces of Pt group metals with similar lattice constants, using the same method (XPS) • Ru (4d) hcp lattice, a(0001) = 2.71Å • Pd (4d)fcc lattice, a(111) = 2.75Å • Ir (5d) fcc lattice, a(111) = 2.71Å Ru Rh Pd 2.71Å 2.69Å 2.75Å fcc hcp fcc Os Ir Pt 2.74Å 2.71Å 2.77Å hcp fcc fcc

  23. H2O + O on Pd{111} H2O ads. at 100 K • O coverage up to 0.25 ML (p(2x2)-O overlayer). • 100K:No reaction between H2O and O. • 160K:Reaction between H2O and O: mixed H2O+OH layer(O coverages up to 0.25 ML) • p(√3 x√3) LEED pattern. • [H2O] : [OH] not stoichiometric. • Desorption between 175-180K. H2O OH O H2O ads. at 160 K Pd 3p3/2

  24. H2O on Pd{111} surface oxide 67.5 eV O1s • Higher O coverage (~ 0.67ML O): p(√6 x√6) surface oxide. • No dissociation of H2O (170K). • No stabilisation: desorption ~ 180K. STM: Lundgren et al. PRL 88 (2002) 246103

  25. H2O + O on Ir{111} H2O ads. at 100 K • O coverage up to 0.25 ML (p(2x2)-O overlayer). • 100K:No reaction between H2O and O. • 170K: O-induced partial dissociation of H2O:mixed O + OH + H2O layer. • Amount of atomic O unchanged. • [OH] : [H2O] = 0.4ML : 0.5ML H2O OH O H2O ads. at 170 K

  26. Reactivity of Water on O-covered Ru{0001} • Low O coverage (< 0.25 ML): • Mixed (H2O + OH) layer • Temperatures around 140K. • Ru, Pd, Pt. • Ir{111}: atomic O not part of the reaction. • High O coverage (> 0.25 ML): • No dissociation of H2O. • Stabilisation of H2O through hydrogen bonds. • Pd{111}: no stabilisation on oxidised surface. • Desorption temperatures similar for dissociative and intact adsorption.

  27. Acknowledgement • Cambridge: Mick Gladys, Ali El Zein • Lund: Jesper Andersen, Anders Mikkelsen. • Sandia Albuquerque: Peter Feibelman

  28. Andrey’s Project • Modified Metal / Oxide Surfaces • Effect of oxygen on water dissociation • Growth of ‘thick’ ice layers: • Adsorption on ice • Mesoscopic structure (nanostructures, porous ice). • Metal interface with aqueous solutions • Alcohols (fuel cells) • Fatty acids, Amino acids (biological systems). • Experimental Methods: • Low-energy Electron Diffraction • Photoelectron Spectroscopy • NEXAFS

  29. Chiral Systems

  30. Molecular Recognition at Surfaces Geometry of the adsorption complex: LEED, STM NEXAFS XPS, RAIRS DFT • Enantioselectivity / Enantiospecificity requires multiple adsorbate-surface bonds/interaction. • Lock and key effects. • Depends on geometry of the adsorption complex • Chiral Adsorbates / Reactants • Amino acids (Alanine) • Chiral Substrates • Non-symmetric surface planes: {531}

  31. Intrinsically Chiral Surfaces: fcc{531} • No mirror plane. • High Miller indices, h  k  l  0. • Templates for enantio-selective adsorption or heterogeneous catalysis.(e.g. G. Attard J. Phys. Chem. B 103, 1381) • {531} has smallest unit cell of all chiral fcc surfaces.Highest density of low (6-fold) coordinated kink atoms. • R(D) surface if {111}–{100}–{110} facets clockwise.(McFadden, Gellman, et al. Langmuir 12, 2483).

  32. Cu{531}R and Cu{531}S Cu{531}R Cu{531}S

  33. Intrinsically Chiral Surfaces: fcc{531} • No mirror plane. • High Miller indices, h  k  l  0. • Templates for enantio-selective adsorption or heterogeneous catalysis.(e.g. G. Attard J. Phys. Chem. B 103, 1381) • {531} has smallest unit cell of all chiral fcc surfaces.Highest density of low (6-fold) coordinated kink atoms. • R(D) surface if {111}–{100}–{110} facets clockwise.(McFadden, Gellman, et al. Langmuir 12, 2483).

  34. Pt{531} 200 Å Pt{531} – thermal instability Almost no energy cost involved in the creation of adatom-vacancy pairs, but gain in entropy. Kinked surfaces are unstable. (Power et al. Langmuir 18, 3737) (STM: Driver et al. in preparation)

  35. Puisto et al. Phys. Rev. Lett.95 (2005) 036102.Puisto et al. J. Phys. Chem. B 109 (2005) 22456. Experiment Theory flat surface Theory rough surface Pt{531} – LEED IV curves • Zero spot intensities over large energy ranges (~100 eV). (Different from close packed surfaces.) • Can only be explained by high degree of surface roughness (interference between atoms from different layers).

  36. 0.44 Å (-) (0.53 Å) top view 0.70 Å (+) (0.54 Å) 0.50 Å (-) (0.73 Å) 0.94 Å (+) (0.78 Å) 0.56 Å (-) (0.66 Å) side view Surface Structure of Pt{531} Puisto et al. J. Phys. Chem. B 109 (2005) 22456. • Alternating contraction and expansion of inter-layer spacings. • Large gap between 4th and 5th layer • Lateral shifts of surface atoms between 0.06 and 0.10 Å . (DFT) bulk : 0.66 Å

  37. Alanine on chiral Cu{531} surfaces • Cu{531} more stable than Pt{531}. • Two ways of matching alaninate ‘footprint’: {110} and {311} facets. • Asymmetric C not involved in bonding. • Enantioselective adsorption?

  38. LEED: R/S-Alanine on Cu{531}R/S S-Alanine R-Alanine • Alanine adsorbed at 300K, annealed to 390K. • Sharp (1x4) LEED pattern (good long-range order) for S/{531}R and R/{531}S. • Diffuse superstructure but still (1x4) for R/{531}R and S/{531}S {531}S {531}S S-Alanine R-Alanine 23 eV {531}R {531}R

  39. XPS: R/S-Alanine on Cu{531}R hv = 630 eV • C 1s and N 1s spectra identical (intensity and peak positions/shape) for both enantiomers. • Identical peak position for O 1s but intensity difference of about 15%. • Low kinetic energy: different photoelectron diffraction effects due to different local geometries. • C 1s, N 1s and O 1s peak positions identical (within 0.1 eV) to alaninate on Cu{110}: • Adsorbed as alaninate • Surbstrate bond through two O and N. Williams et al. Surf Sci. 368 (1996) 303 (RAIRS) Barlow et al. Surf. Sci. 590 (2005) 243 (RAIRS, XPS, STM) Rankin & Scholl Surf. Sci. 548 (2004) 301 (DFT) Jones et al. Surf. Sci. 600 (2006) 1924 (NEXAFS, XPS, DFT)

  40. 1s  * forbidden O allowed C Near Edge X-ray Absorption Fine Structure NEXAFS XPS • Excitation into unoccupied molecular orbitals near the Fermi level. • Needs tunable light source(Synchrotron). • Cross section depends on: • Polarisation of X-rays. • Symmetry of orbitals. •  Molecular Orientation. NEXAFS XPS: Ekin = hv – BE – ΦNEXAFS: hv = BEocc - BEunocc

  41. E (3x2) Alanine on Cu{110} O1s(C1s)  *not allowed if E parallel to O-C-O triangle. • Molecular orientation from NEXAFSusing dipole selection rules: • O-C-O in-plane tilt angle. • E.g -resonance for Alanine on Cu{110} disappears almost completely when E parallel to [1-10] (close packed rows). • Intensity of -resonance ~ cos2( = angle between E and normal of O-C-O) Jones et al. Surf. Sci. 600 (2006) 1924

  42. In-plane NEXAFS of R/S-Alanine on Cu{531}R Rotate Ewithin the surface plane Ē 90º 0º • Large difference between R and S-alanine (ca. factor 2). • -intensity does not go to zero.

  43. ñ ñ1 ñ2 Alanine on Cu{531}R: single or multiple adsorption sites? I = Iocos2() Single adsorption site • Large oscillations • - intensity goes to zero Multiple adsorption sites I = I1cos2(1) + I2cos2(2) • Small oscillations • -intensity does not go to zero

  44. R/S-Alanine on Cu{531}: Fit to Data • Fit results compatible with adsorption on {311} (1~ 25º) and {110} (2~ - 45º) facets: • S-Alanine: 1= 23º,2= - 57º, equal amounts. distorted molecules on {110} facetts. • Ambiguous result for R-Alanine: 1= 5º,2= - 55º, equal amounts;1= 29º,2= - 39º, I311 : I110 = 0.5. All kink-sites can be involved in adsorbate bond in p(1x4) superstructure.

  45. R/S-Alanine on Cu{531}: Local geometries S-Alaninate: distorted molecules on {110} facetts.Θ110 = Θ311 {110} • Hydrogen bonds between molecules(O-N, O-O ~ 2.5 Å). • Distortion of molecules induced by interaction with metal atoms (?). • Surplus of molecules on {110} facets would be compatible with diffuse LEED pattern. {311} R-Alaninate (model 2): distortion on {110} facets relaxed;Θ110 > Θ311 R-Alaninate (model 1): distorted molecules on {110} and {311} facets;Θ110 = Θ311

  46. Enantiospecific Adsorption ofAlanine (Alaninate) on Cu{531} • Different degrees of long-range order (LEED):better order for S-Ala/Cu{531}R (sharper LEED spots). • Two adsorption sites occupied by R and S-Ala (NEXAFS):triangular footprints on {311} and {110} facets. • Possibly differentoccupation numbers of{311} and {110} sites:R-Ala Θ110 > Θ311S-Ala Θ110 = Θ311 • Different moleculardistortions:induced by intermolecular hydrogen bonding and/or interaction with substrate.

  47. Acknowledgement Amy V. Stevens Nicola Scott Mick J. Gladys Amy V. Stevens, Nicola Scott Jaspreet S. Ottal Glenn Jones University of Cambridge Mick J. Gladys David Batchelor , Berlin

  48. Tugce’s Project • Lock and key effects / Enantioselectivityon Catalyst Surfaces • Enantioselective heterogeneous Catalysis. • Chiral Adsorbates / Reactants • Amino acids • Chiral Substrates • Non-symmetric surface planes • Enantioselective adsorption/reactions

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