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

2. The Reading MONET Team Tugce Andrey

3. 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 There is Plenty of Room at the Bottom of the Nano-Scale!

4. Low Energy Electron Diffraction (LEED) Nobel prize 1937 for 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 pattern Information about the long-range structure. LEED-IV analysis Information about the local surface geometry. H2OH2O D2OD2O

6. LEED-IV Analysis

7. CLEED Program Package

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

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

10. Water on Ru{0001}: Feibelman’s Model 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 H 2 O, 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 & Madey Surf. Sci. 123 (1982) Partially dissociated bilayer Feibelman, Science 295 (2002). Michaelides et al. JACS 125 (2003).

11. X-ray Photoelectron Spectroscopy 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 E kin. Synchrotron XPS: Photon energy tunable for high cross section. XPS: E kin = hv – BE – Φ XPS

12. H 2 O on Ru{0001}: Temperature Programmed XPS 1 ML H 2 O adsorbed at 110 K Heating rate 0.1K/s (1.5K / spectrum) Sharp transition from low T phase to partially dissociated bilayer around 150K. H2OH2OOH O 170K 130K OH H2OH2O H2OH2O Beam damage

13. Experiments at MAX-lab (Lund), beamline 311: Relatively large X-ray spot on surface (0.3 x 2 mm 2 ). Photon flux ~ 1.2 x 10 13 ph s -1 cm -2 electron flux ~ 1.5 x 10 12 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. Andersson et al. PRL 93 (2004) Faradzhev et al. CPL 415 (2005)

14. Beam damage Experiments at MAX-lab (Sweden), beamline 311: Relatively large X-ray spot on surface (0.3 x 2 mm 2 ). Photon flux ~ 1.2 x 10 13 ph s -1 cm -2 electron flux ~ 1.5 x 10 12 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. Andersson et al. PRL 93 (2004) Faradzhev et al. CPL 415 (2005) 155K 100K

15. H 2 O 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) H2OH2O DFT: Desorption H 2 O+OH Intact H 2 O Energy (eV/mol) ~0.5 H2OH2O ~0.3 0.53 Dissociation Break O-H bond Break H 2 O-surface bond and hydrogen bonds

16. H 2 O coadsorbed with oxygen H 2 O adsorption on O-precovered surface: H 2 O + O ad  2 OH ad (disproportionation) Clay et al. CPL 388 (2004) H 2 O + O ad  HOH—O ad (H-bonding) Doering & Madey Surf. Sci. 123 (1982) O ad O HH Ru n O ad O HH Ru n O ad H O H

17. H 2 O coadsorbed with oxygen: TP-XPS 0.5 ML O (> 0.25ML): High BE O1s peak 180-220K No OH formation 0.1 ML O (< 0.20ML): O at peak converts to OH H 2 O + OH disappear at 200K O at H2OH2O H2OH2O OH 200K 220K 180K Low O coverage High O coverage Gladys, GH, et al. Chem. Phys. Lett. 414 (2005) 311

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

19. H 2 O coadsorbed with oxygen 0.1ML O0.5ML O Plot XPS intensity (~ coverage) of each adsorbate species vs temperature. H 2 O+OH

20. H 2 O coadsorbed with oxygen 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. 220K 180K (Doering & Madey Surf. Sci. 123, 1982) 0.1ML O 0.5ML O H 2 O+OH

21. H 2 O 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 (H 2 O + OH). Hydrogen bonds parallel to surface. N.I. and 70º spectra more similar for H 2 O on 0.5ML O. Hydrogen bonds tilted.

22. Is Ru the exception or the rule? Ru (4d) hcp lattice, a(0001) = 2.71Å Pd (4d) fcc lattice, a(111) = 2.75Å Ir (5d) fcc lattice, a(111) = 2.71Å RuRhPd OsIrPt hcp fcchcp fcc 2.71Å fcc 2.69Å2.75Å 2.77Å2.71Å fcc 2.74Å Water adsorption on hexagonal surfaces of Pt group metals with similar lattice constants, using the same method (XPS)

23. H 2 O + O on Pd{111} O coverage up to 0.25 ML (p(2x2)-O overlayer). 100K: No reaction between H 2 O and O. 160K: Reaction between H 2 O and O: mixed H 2 O+OH layer (O coverages up to 0.25 ML) p( √ 3 x √ 3) LEED pattern. [H 2 O] : [OH] not stoichiometric. Desorption between 175-180K. H 2 O ads. at 160 K H 2 O ads. at 100 K H2OH2O OH O Pd 3p 3/2

24. H 2 O on Pd{111} surface oxide Higher O coverage (~ 0.67ML O): p(√6 x√6) surface oxide. No dissociation of H 2 O (170K). No stabilisation: desorption ~ 180K. 67.5 eV STM: Lundgren et al. PRL 88 (2002) 246103 O1s

25. H 2 O + O on Ir{111} O coverage up to 0.25 ML (p(2x2)-O overlayer). 100K: No reaction between H 2 O and O. 170K: O-induced partial dissociation of H 2 O: mixed O + OH + H 2 O layer. Amount of atomic O unchanged. [OH] : [H 2 O] = 0.4ML : 0.5ML H 2 O ads. at 170 K H 2 O ads. at 100 K H2OH2OOH O

26. Reactivity of Water on O-covered Ru{0001} Low O coverage (< 0.25 ML): Low O coverage (< 0.25 ML): Mixed (H 2 O + OH) layer Mixed (H 2 O + OH) layer Temperatures around 140K. Temperatures around 140K. Ru, Pd, Pt. Ru, Pd, Pt. Ir{111}: atomic O not part of the reaction. Ir{111}: atomic O not part of the reaction. High O coverage (> 0.25 ML): High O coverage (> 0.25 ML): No dissociation of H 2 O. No dissociation of H 2 O. Stabilisation of H 2 O through hydrogen bonds. Stabilisation of H 2 O through hydrogen bonds. Pd{111}: no stabilisation on oxidised surface. Pd{111}: no stabilisation on oxidised surface. Desorption temperatures similar for dissociative and intact adsorption. 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 Modified Metal / Oxide Surfaces Effect of oxygen on water dissociation Effect of oxygen on water dissociation Growth of ‘thick’ ice layers: Growth of ‘thick’ ice layers: Adsorption on ice Adsorption on ice Mesoscopic structure (nanostructures, porous ice). Mesoscopic structure (nanostructures, porous ice). Metal interface with aqueous solutions Metal interface with aqueous solutions Alcohols (fuel cells) Alcohols (fuel cells) Fatty acids, Amino acids (biological systems). Fatty acids, Amino acids (biological systems). Experimental Methods: Experimental Methods: Low-energy Electron Diffraction Low-energy Electron Diffraction Photoelectron Spectroscopy Photoelectron Spectroscopy NEXAFS NEXAFS

29. Chiral Systems

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

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. (STM: Driver et al. in preparation) Pt{531} – thermal instability Pt{531} 200 Å 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)

35. 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). Pt{531} – LEED IV curves 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

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

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 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} R {531} S 23 eV S-Alanine R-Alanine {531} S {531} R

39. XPS: R/S-Alanine on Cu{531} R 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. hv = 630 eV 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   * C O forbidden allowed Near Edge X-ray Absorption Fine Structure XPS: E kin = hv – BE – Φ NEXAFS: hv = BE occ - BE unocc NEXAFS 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. XPS NEXAFS

41. (3x2) Alanine on Cu{110} Molecular orientation from NEXAFS using 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 ~ cos 2  (  = angle between E and normal of O-C-O) E Jones et al. Surf. Sci. 600 (2006) 1924 O1s(C1s)   * not allowed if E parallel to O-C-O triangle.

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

43. ñ1ñ1 ñ2ñ2 Alanine on Cu{531} R : single or multiple adsorption sites? Single adsorption site ñ Multiple adsorption sites I = I o cos 2 (  ) I = I 1 cos 2 (   ) + I 2 cos 2 (   )  Large oscillations   - intensity goes to zero  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, I 311 : I 110 = 0.5. All kink-sites can be involved in adsorbate bond in p(1x4) superstructure.

45. R/S-Alanine on Cu{531}: Local geometries {110} {311} S-Alaninate: distorted molecules on {110} facetts. Θ 110 = Θ 311 R-Alaninate (model 1): distorted molecules on {110} and {311} facets; Θ 110 = Θ 311 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. R-Alaninate (model 2): distortion on {110} facets relaxed; Θ 110 > Θ 311

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

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

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