Optical Absorption Spectra of deposited Gold-Clusters from Cavity Ring-Down Spectroscopy

Transcription

1 Optical Absorption Spectra of deposited Gold-Clusters from Cavity Ring-Down Spectroscopy Stefan Gilb, TU München Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 1

2 Outline Motivation The CO-Combustion on Au-Cluster Experimental Setup Results small Gold Clusters Gold-Nanoparticles Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 2

3 Non-Scalable Scalable Size Regime ( ) ( ) GN = G +bn β Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 3

4 The Non-Scalable Size Regime de Heer Rev. Mod. Phys. 65 (1993) 611 E. Schumacher et al. Chimia 42 (1988) Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 4

5 The 3 rd dimension of the Periodic Table Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 5

6 CO-Combustion.17 % ML CO +O2 CO 2+O Au Film C 16 O 18 O + Signal [a.u.] 13 Each Atom Au 2 Counts 2 Au 18 Au 12 Au 9 Number of CO b) Au 8 Au 7 Au 6 Au Temperature [K] n / Number of atoms per cluster A. Sanchez, S. Abbet, U. Heiz, W.-D. Schneider, H. Hakkinen, R. N. Barnett, Uzi Landman J. Phys. Chem. A 1999, 13, 9573 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 6

7 Oxidation of CO on Au Langmuir-Hinshelwood-Periphery Mechanism O 3 O 1 C Adsorption by reverse spillover O 2 Initial State Transition State ~.5 ev [~.8 ev] A. Sanchez, S. Abbet, U. Heiz, W.-D. Schneider, H. Ha1kkinen, R. N. Barnett, Uzi Landman J. Phys. Chem. A 1999, 13, Å 2. Å Reaction Coordinate d(c-o 1 ) Final State Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 7

8 The role of the support CO Au 8 /MgO(1) defect-rich 33 K O 2 13 C 16 O 18 O + Ion Signal [a.u.] 14 K 28 K 28 K 22 K 16 K 1 K Transmittance [%] 13 CO F-center Oxygen vacancy Temperature [K] Wavenumbers [cm -1 ] B. Yoon, H. Häkkinen, U. Landman, A. Wörz, J.-M. Antonietti, S. Abbet, K. Judai, U. Heiz, Science 37 (25) 43 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 8

9 The role of the support II 13 C 16 O 18 O + Ion Signal [a.u.] Au 8 /MgO(1) defect-poor Transmittance [%] 33 K 28 K 22 K 16 K 1 K CO 213 Redshift induced by F-center: Δν = 3-5 cm Temperature [K] Wavenumbers [cm -1 ] B. Yoon, H. Häkkinen, U. Landman, A. Wörz, J.-M. Antonietti, S. Abbet, K. Judai, U. Heiz, Science 37 (25) 43 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 9 212

10 Cavity Ring-Down Setup Dye-Laser High Reflectivity Mirrors Photomultiplier Oscilloscope L Λ = s L 1 1 c τ s τ Ideally, absorption losses of about 1 ppm are detectable A typical dipole-allowed transition in small noble metal clusters (~.1 Å 2 ) can be detected with a coverage of 1 9 / cm2 Engels et al., JCP 11 (1999), 2732 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 1

11 Sample Preparation by Softlanding Gilb, Arenz, Heiz Materials Today 9 (26) Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 11

12 Experimental Setup YAG Laser Q-mass for size-separation separation Cluster source Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 12

13 Gold Nanocrystals: Preparation Dip-coating 1 x 1 μm 2 Substrate Oxygen Plasma nm HAuCl 4 Ø 1-2 nm H.-G. Boyen et al., PRB 65 (22), Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 13

14 Au-Particles on SiO 2 Au n -density: cm 2 Loss [ppm] Au 1 Au 2 Au x13 5 Au 8 Au nm Photon Energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 14

15 Softlanding 8 6 Au 1 Loss [ppm] Au Photon Energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 15

16 Adsorption Sites on α SiO 2 With alkaline impurities 2.3 Å 2.25 Å 2.2 Å [ Si-Au] Non-satured Si D e (Au) = 3.16 ev [ Si-O-Au] Non-satured O D e (Au) = 2.16 ev [ Si-O-Au] - center Charged center D e (Au) =.89 ev Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 16

17 XPS Characterization of the Substrate Element Atomic % O Si 24.3 K 2.6 Na 2.5 Al 1.7 Ti 1. Zn.7 Ar.6 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 17

18 Interpretation for Au 1 /SiO 2 loss [ppm] 5 Au/SiO 2 Si-Au calc. int. [arb units] x 2 Si-O-Au 5d Au 6s Au [ Si-O-Au] - 5d Au σ*(6s Au -2p O ) 5d Au σ*(6s Au -2p O ) 6s Au sp Si photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 18

19 Interpretation for Au 1 /SiO 2 loss [ppm] 5 Au/SiO 2 Si-Au calc. int. [arb units] x 2 Si-O-Au [ Si-O-Au] photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 19

20 Interpretation for Au 2 /SiO 2 loss [ppm] 4 2 Au 2 /SiO 2 Si-Au 2 calc. int. [arb units] x 1 Si-O-Au 2 x 1 [ Si-O-Au 2 ] - (2p) Au(5d6s) photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 2

21 Interpretation for Au 4 /SiO 2 loss [ppm] 2 Au 4 /SiO 2 Si-Au 4 calc. int. [arb units] x 2 Si-O-Au 4 x 2 [ Si-O-Au 4 ] photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 21

22 Interpretation for Au 8 /SiO 2 loss [ppm] 4 2 loss [ppm] 4 2 Si-Au 8 Si-Au 8 calc. int. [arb units] Si-O-Au 8 x 5 [ Si-O-Au 8 ] - calc. int. [arb units] x 4 Si-O-Au 8 x 4 [ Si-O-Au 8 ] - x photon energy [ev] photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 22

23 Interpretation for Au 8 /SiO 2 loss [ppm] 4 2 loss [ppm] 4 2 Si-Au 8 Si-Au 8 calc. int. [arb units] Si-O-Au 8 x 5 [ Si-O-Au 8 ] - calc. int. [arb units] x 4 Si-O-Au 8 x 4 [ Si-O-Au 8 ] - x photon energy [ev] photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 23

24 Optical Spectrum of Au 2 / SiO 2 loss [ppm] 4 2 Au 2 /SiO 2 TD-LDA calculations with jellium model photon energy [ev] Theory: J. Lermé et al., Eur. Phys. J. D 4 (1998) 95 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 24

25 Mie-Drude-Model d d = 1nm d = 2nm d = 4nm d = 6nm d = 8nm d = 1nm d = 2nm Bulk photon energy [ev] Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 25

26 Mie-Drude-Model 15x1 3 d=2.9 nm d loss [ppm] 1 d = 1nm d = 2nm d = 4nm d = 6nm 5 d = 8nm d = 1nm d = 2nm Bulk photon energy [ev] photon energy 2.8 Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 26

27 Thank You Aras Kartouzian Judith Peter Katrin Hartl Dr. Jean-Marie Antonietti Dr. Marcin Michalski Prof. Ulrich Heiz Dr. Annalisa Del Vitto Dr. Livia Giordano Prof. Gianfranco Pacchioni Dr. Kok Hwa Lim Prof. Notker Rösch Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 27

28 Oxidation of CO on Au 8 Bound to Defect-Poor and Defect- Rich MgO(1) Surfaces Langmuir-Hinshelwood-Top Mechanism O 1 O 2 O 3 C Direct Adsorption Initial State Transition State ~.1 ev Final State 3.1 Å 2. Å Reaction Coordinate d(c-o 1 ) Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 28

29 Applications of Clustermaterials: Optical Materials Absorption losses of about.5 ppm are detectable A typical dipole-allowed transition in small noble metal clusters (~.1 Å 2 ) can be detected with a coverage of.5% ML Cavity Ring-Down User Meeting 26 Cork, 18 th /19 th September 29