Hannu Häkkinen Physics / Chemistry University of Jyväskylä Finland Hannu.J.Hakkinen@jyu.fi

Golden superatoms and quantum dots

DEISA – PRACE 12.5.2009 Amsterdam

Thiolate protected Gold nanoparticles •  Huge current interdisciplinary interest •  Chemical protection (passivation of the Au core surface) •  Control of size & Functionalization of the ligand layer Improved biolabels,

nanocatalysts, sensors, components for molecular electronics, therapeutics…

•  The precise atomic structure of the most stable particles has not been known until… •  Breakthrough in 2007 when the structure of a so-called Au102 particle was

resolved via X-ray diffraction from a single crystal sample by R. Kornberg group, Stanford (Noble Prize in chemisty 2006)

•  Researchers at NSC in Jyväskylä explained the electronic structure & stability of the Au102 particle and developed a theoretical model to understand the stability of chemically protected Au clusters (Walter et al PNAS 105, 9157 (2008))

Gold-in-Cages Group-meeting seminar

BIT-Karlsruhe 11.08.06

Source:Tsukuda,2006ISSPICGöteborg

4

HAu(III)Cl4

NaBH4

excess

~0 ℃

GS ligands

+

–

Au102(SR)44 R=p-MBA = C6H4COOH

19 October 2007

Large-scale parallel calculations for solving the electronic structure problem via density-functional theory

CP2K •  localized basis •  pseudopotentials (scalar-relativistic for Au, 5d- 6s- shells in valence) •  PBE xc functional •  http://cp2k.berlios.de

GPAW •  projector-augmented wave (all-electron density, frozen core, Au scalar-relativistic) •  real-space grids (coarse uniform grid for valence region & spherical grid for atom cores) •  PBE xc functional •  https://wiki.fysik.dtu.dk/gpaw

The heaviest computations for Au102(p-MBA)44 (about 3400 valence electrons, crystal structure coordinates further relaxed with CP2K, the electronic structure analyzed & optical spectra calculated with GPAW)

GPAW CAN USE THOUSANDS OF CORES EFFECTIVELY

development project 2005-2008 funded by the Finnish Funding Agency for Technology and Innovation (TEKES) DTU (K.W. Jacobsen), JY (Hannu Häkkinen), HUT (Risto Nieminen), TUT (Tapio Rantala), CSC (Jussi Enkovaara) Project coordinated by CSC (J. Ignatius)

Speed-up vs # cores in solving for the electronic structure of Au102(SCH3)44 w/ about 1800 valence electron states (Cray XT /CSC)

GPAW HAS BEEN SELECTED AS ONE OF THE BENCHMARK CODES FOR PETASCALE COMPUTING

Au102: Analysis of the electron structure around Fermi level (at zero energy)

2P+1G 3S+2D+1H

•  In the Au102(SR)44 particle, the core consists of only 79 atoms arranged in a decahedral symmetry •  The protecting shell has 23 Au atoms and 44 thiolates (realization of a ”Divide and Protect” structural motif, Hakkinen et al JPCB 2006) •  clear angular-momentum symmetries seen for electron shells in the Au79 core the particle is a giant ”superatom”

2P+1G Walter et al, PNAS 2008

Sterically protected and electronically stable “superatoms”

Au11(PH3)7Cl3 n* = 8 (1S21P6) Au11(PH3)7(SCH3)3 8 Au13(PH3)10Cl23+ 8 Au25(SR)18

- 8 Au39(PH3)14Cl6- 34 (8e- 1D102S21F14) Au102(SR)44 58 (34e- 2P61G18)

( Ls • AuN XM ) with charge z, is stable IF: N (Au,6s) – M – z = n*, n* = shell closing number

Here L = PH3 and X = Cl, SR

L ”weak ligand” X electron withdrawing (localizing) ligand

Walter et al, PNAS 105, 9157 (2008)

OUR DEISA HIGHLIGHT #1

Prediction for a structure of a massive (29 kDa) Au144(SR)60 particle

Cover of JPCC-C April 2 2009

Powder X-ray diffr. function

Experiment: Schaaff et al, JPCB 2001

•  12-atom hollow shell, 30+12 shell = 54 atom Mackay Icosahedron •  60 – atom rhombicosi-dodecahedron 114-atom core, I-symmetry •  Arrangement of RS-Au-SR units chiral ( like in Au102(SR)44 )

Au144(SR)60 = Au114 core+ 30 protecting SR-Au-SR units

O. Lopez-Acevedo et al, J. Phys. Chem. C 113, 5035 (2009)

FROM “SUPERATOMS” (DEISA HIGHLIGHT 1) TO “GOLDEN QUANTUM DOTS” (HIGHLIGHT 2)

(FLAT GOLD CLUSTERS GROWN ON THIN OXIDE FILMS)

Lin, Nilius, Freund, Walter, Frondelius, Honkala, Häkkinen, Phys. Rev. Lett 2009 in print

Flat Au clusters on MgO(2L)/Ag STM topography

Flat Au clusters on MgO(2L)/Ag Comparison of theory and experiment precise atomic structure known

Lin, Nilius, Freund, Walter, Frondelius, Honkala, Häkkinen, Phys. Rev. Lett 2009 in print

SHAPES OF FRONTIER ORBITALS EXPLAINED BY A PLANAR HARMONIC QUANTUM DOT MODEL ELECTRON COUNTING POSSIBLE

Lin, Nilius, Freund, Walter, Frondelius, Honkala, Häkkinen, Phys. Rev. Lett 2009 in print

SUMMARY

•  large-scale DFT computations can explain the stability and electronic properties of chemically protected and passivated gold nanoparticles •  the “superatom model” has been developed as a useful concept to explain the stability •  the degree of “metallicity” can be characterized by the number of delocalized valence electrons in the core •  this gives a solid theoretical background for understanding & functionalizing the optical and chemical properties

•  a combined STM/DFT study was able, for the first time, to precisely determine the atomic structures and the electronic properties of small gold clusters grown on a few-monolayer oxide film •  important for further understanding of e.g. catalytic properties of these systems

PUBLICATIONS FROM THE WORK USING DEISA RESOURCES

O. Lopez-Acevedo, J. Akola, R.L. Whetten, H. Grönbeck, H. Häkkinen Structure and Bonding in the Ubiquitous Icosahedral Metallic Gold Cluster Au144(SR)60 J. Phys. Chem. C (Letter) 113, 5035 (2009) (cover article of issue 13/113, 2 April 2009).

X. Lin, N. Nilius, H.-J. Freund, M. Walter, P. Frondelius, K. Honkala, H. Häkkinen Quantum well states in two-dimensional gold clusters on MgO thin films Phys. Rev. Lett. 2009 in print; preprint available (arXiv:0811.3812)

ACKNOWLEDGEMENTS

J. Akola, P. Frondelius, K. Honkala, O. Lopez-Acevedo, M. Walter R.D. Kornberg group (Stanford) R.L. Whetten (Atlanta) H. Grönbeck (Göteborg)

Academy of Finland CSC – Espoo (J. Enkovaara, J. Fagerholm, P. Nikunen, J. Ignatius) NIC – Juelich DEISA