Ludo Juurlink , Ph.D. L eiden Institute of Chemistry Leiden University, Leiden, the Netherlands

1. Spectroscopic and related techniques in surface science for unravelling heterogeneously catalyzed reaction mechanisms • Ludo Juurlink, Ph.D. • Leiden Institute of Chemistry • Leiden University, Leiden, the Netherlands • Office:Gorlaeus Laboratories DE0.01 • Email: l.juurlink@chem.leidenuniv.nl • phone +31 71 527 4221 • Course objectives:  • At the this short course students • can explain how surface science attempts to understand heterogeneous catalysis • can outline how common experimental (spectroscopic) techniques reveal information on surfaces, adsorbates, and chemical reactions • Understand why and how (supersonic) molecular beams are useful herein • are informed on some recent examples in the field of gas-surface dynamics

2. Surface Science and Gas-Surface Reaction Dynamics Schedule

3. Surface Science and Gas-Surface Reaction Dynamics Schedule

4. Surface Science to help understand Heterogeneous Catalysis

5. CH4 + H2O 3H2 + CO Heterogeneous Catalysis: example MSR ~1000 °C 30 bar CH4 + H2O  3H2 + CO

6. Al2O3 pellets Heterogeneous Catalysis: example MSR Also promotors and other chemical to stabilize particles!

7. Heterogeneous Catalysis: example MSR CH4 + H2O  3H2 + CO Ni Ni Ni

8. Heterogeneous Catalysis: example MSR CH4 + H2O  3H2 + CO Too much energy required -- reactants don’t react. Intermediate blocks surface – no product formation G. Jones et al. Journal of Catalysis 259, 147 (2008)

9. Heterogeneous Catalysis: Fischer-Tropsch https://www.youtube.com/watch?v=44OU4JxEK4k

10. Surface Science approach using single crystals 1970’s onward: Single crystal surfaces: Macroscopic pieces of pure metals, alloys, semiconductors, oxides, …. with a polished surface exposing a single type of ordering of atoms. 2000’s onward: Well-defined particles grown on crystal surfaces: Microscopic single crystalline particles of pure metals, alloys, oxides, …. grown by vapor deposition onto a well-ordered oxide support.

11. Single crystals Ta single crystal polishing Re single crystal cutting by spark erosion

12. Single crystals Ag single crystal with a curved surface

13. Basics of two-dimensional crystallography

14. Bulk crystal structures • 1. triclinic • 2. monoclinic • 3. orthorhombic • 4. rhombohedral • 5. tetragonal • 6. hexagonal 7 lattice systems 14 Bravais lattices base-centered simple simple base-centered body-centered face-centered 7. cubic simple body-centered face-centered simple body-centered

15. Bulk crystal structures

16. Bulk crystal structures • examples • Body centered cubic (bcc) Fe, W • Face centered cubic (fcc) Ni, Cu, Pt • Hexagonal close packed (hcp) Ru, Co • Diamond lattice Cdiamond, Si, Ge • Zinc blende structure ZnS, GaAs, InP • Rock salt NaCl, NiO

17. [111] [001] surfacelayernormalto [111] [010] [100] Atomically flat surfaces as bulk truncations surfacelayernormalto [100] Example: fcc

18. A real single crystal surface on a manipulator Ru(0001) 10 mm 2 mm LN2 LN2

19. [111] [110] 54.7° [001] Vicinal surfaces (001) Families of planes e.g. {100}, {111}, {110} (1-11) (001) [110] (1-11) (1-10) [110] (1-10) 54.7° 35.3°

20. Vicinal surfaces stepped stepped and kinked

21. Do these surfaces represent the surface of particles? Helveget al., Nature427, 426 (2004) Behrens et al., Science336, 893 (2012)

22. Do these surfaces represent the surface of particles? R.A. Olsen and L.B.F. Juurlink, Hydrogen dissociation on stepped Pt surfaces, in Dynamics of Gas-Surface Interactions: Atomic-level Understanding of scatttering processes at surfaces, Ed. Busnengo and Diez-Muiño, Springer Series in Surface Science, Springer (Berlin, 2013) Honkalaet al., Science307, 555 (2005)

23. Referring to surfaces: Miller indices • Plane with Miller indices h, k and l is (hkl). It is orthogonal to reciprocal lattice vector [hkl]. • Determine intercept plane on axes a1, a2, and a3 • Take reciprocal of obtained numbers: 1/a1, …. • Reduce to smallest integers with same ratio (321) a3 a3 h = 1 / (1/3) k = 1 / (1/2) l = 1 / 1 1/2 of a2 a2 a1 1/3 of a1

24. Miller indices • Plane with Miller indices h, k and l is (hkl). It is orthogonal to reciprocal lattice vector [hkl]. • Determine intercept plane on axes a1, a2, and a3 • Take reciprocal of obtained numbers: 1/a1, …. • Reduce to smallest integers with same ratio

25. Some important crystal structures

26. Some important crystal structures

27. Imaging surface in reciprocal space Low Energy Electron Diffraction

28. Reciprocal lattice • Reciprocal lattice: where h and k are integers and …. • Reciprocal lattice vectors: reciprocal space lattice real space lattice

29. Bragg’s law and the Ewald sphere 3-D crystals: conservation of 3D momentum and (3D) energy

30. Low Energy Electron Diffraction (LEED) • Wavelength, , must be close to interatomic distance, “a” For example: Ekin = 20 eV,  = 2.7 Å Ekin = 200 eV,  = 0.87 Å  Inverse relation between the ‘position’ of the diffraction spot and the distance between atoms = n  for diffraction ‘hot spot’

31. Low Energy Electron Diffraction (LEED)

32. Interpretation of a LEED pattern • Sharpness: well-ordered surface shows bright, sharp spots • Geometry: gives information on crystallographic structure • Spot profile: intensity distribution across width of spot -> surface imperfections cause weakening of spot • I-V analysis: evaluation of atom positions

33. Surface and overlayer structures (superstructure) a2 a1

34. Notation for surface and overlayer structures • Matrix notation: • Wood’s notation: • Primitive and centered: ‘p’ and ‘c’

35. Low Energy Electron Diffraction (LEED) Ogletree et al, Surf. Sci. 173, 351 (1986)

36. Diffraction techniques • Electron-based techniques • Low energy electron diffraction (LEED: typically 50 eV) • Reflection high-energy electron diffraction (RHEED: typically 20 keV) • Transmission electron diffraction (TED: typically 200 keV) • Auger electron diffraction (AED) • X-ray based techniques • Grazing-incidence X-ray diffraction (GIXRD; typically 15 keV) • Surface X-ray diffraction (SXRD; typically 15 keV) • Grazing-incidence small-angle X-ray scattering (GISAXS) • Other techniques • Photo-electron diffraction (PED) • Thermal-energy atom diffraction (typically 15 meV He atoms)

37. Imaging surface in real space Scanning Tunneling Microscopy

38. Evac E EF EF + eV sample tip vacuum Scanning Tunneling Microscopy d F

39. tip trajectory piezo element specimen A V tip specimen Scanning Tunneling Microscopy

40. Scanning Tunneling Microscopy Forschungszentrum Jülich, Germany

41. Scanning Tunneling Microscopy Au(111) Leiden Probe Microscopy BV

42. STM images of adsorbates H2O ‘double strands’ along a Pt(553) edge Diffusion of In atoms in a Cu(100) surface Kolb et al., Phys. Rev. Lett. 116, 136101, (2016) Gastel et al, Phys. Rev. Lett. 86, 1562 (2001)

43. STM images of adsorbates