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  • Instituto de Ciencia de Materiales de Sevilla

    MICROSTRUCTURE AND MAGNETIC MICROSTRUCTURE AND MAGNETIC

    BEHAVIOUR OF ALKANETHIOLBEHAVIOUR OF ALKANETHIOL--CAPPED CAPPED

    GOLD NANOPARTICLESGOLD NANOPARTICLES

    Nanostructured Materials - A. Fernndez- T.C. Rojas- E. Guerrero- M. A. Muoz-Mrquez

    Instituto de Magnetismo aplicado(RENFE-UCM-CSIC)

    - A. Hernando- P. Crespo- M. Multigner- M.A.Garca

  • Gold and Pd-Nanoparticles GoldGold andand PdPd--Nanoparticles Nanoparticles

    electronicoptical

    magneticMetallic NPs NOVEL

    The Magnetism in Pd and Au cluster is not completely understood.Further experiments are needed. Applications in Nanobiotechnology, Nanomaterials design, Nanoelectronic are foreseen

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    Ferromagnetic hysteresis at room temperature in 1.7nm gold NPs cappedby alkanethiol molecules (PRL 93, 087204 (2004))

    Ferromagnetic order in alkylammonium and alkanethiol protected Pd NPs(PRL 91, 237203 (2003); PRB 73, 054404 (2006); Nanotechn. 17, 1449 (2006)

    Theory: Orbital ferromagnetism and giant anisotropy (PRL 96. 057206 (2006)

  • Synthesis Gold-NPSSynthesisSynthesis GoldGold--NPSNPS

    AuCl4-(toluene) + RSH (-AuISR-)n(polymer)

    Method of Brust et al. Two-step process:

    1-

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    In the first step Au(III) isreduced to Au(I) by oxidizingthe thiols to disulfides. In non polar solvents the AuI(SR) species aggregate forming a polymeric phase.We have isolated thisintermediate polymeric phase

  • Synthesis Gold-NPSSynthesisSynthesis GoldGold--NPSNPS

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    Polym-aged Polymer e-irradiated

    The polymeric phase evolves by aging at room temperature (even in dark) or by e-beam irradaition in the TEM microscope

    This sample can also be isolated

  • Au/Thiol1:2 1:1

    Synthesis Gold-NPSSynthesisSynthesis GoldGold--NPSNPS

    (-AuISR-)n + BH4- Aux(SR)yS

    S

    S

    S

    S

    S

    S S

    S

    S

    S S

    S

    S

    S

    S

    1 nm.

    S

    S

    S

    S

    S

    S

    S S

    S

    S

    S S

    S

    S

    S

    SSS S S S

    SSSS

    SSS SS

    SS

    Second step: reduction of the polymeric phase by borohydride. Formationof typical gold NPs functionalised by alkanethiol molecules.

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    2-

  • HREMHREM

    CharacterizationCharacterizationCharacterization

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    2.4

  • Sample AuWt%

    FeWt%

    Swt%

    CWt%

    HWt%

    Au/S(at. Ratio)

    Dm(nm)

    TotalNr

    % Nr

    Au-SR1 70.5 0.018 3.7 23.6 4.1 3.0 2.2 249 162

    Au-SR2 50.3 0.007 4.1 24.3 4.4 1.7 2.0 177 122

    Au(I)-SR2-Polym

    49.5 0.012 7.8 36.4 6.2 1.0 ?

    CharacterizationCharacterizationCharacterization

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    SizeSize andand chemicalchemical compositioncomposition

    The polymeric phase is minimising the Au:S atomic ratio

  • CharacterizationCharacterizationCharacterizationXANESXANES

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    White line

    Unoccupieddensities of d

    states

    -10 0 10 20 30 40

    -10 0 10 20 30 40

    Inte

    nsity

    (a.u

    .)

    E - E0

    Au Foil Au(I)-SR2- Polym Au(I) Sulfide

    Au Foil Au-SR1 Au-SR2

    E - E0

    Au LII- edge

    Charge transferfrom Au to S

  • CharacterizationCharacterizationCharacterizationEXAFS EXAFS Modulus of the Fourier Transform of EXAFS oscillations

    at the Au L3-edge

    1 2 3 4 5

    IT.F

    I

    R()

    Au-SR1 Au-SR2 Au Foil

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    1 2 3 4 5

    IT.F

    I

    R()

    Au(I)-SR2- Polym Au(I) Sulfide Au Foil

    Au-S

    Au-Au

    Au-Au

    Au-S

  • CharacterizationCharacterizationCharacterizationEXAFSEXAFS Best fitting of the Au L3 edge EXAFS oscillations

    0 1 2 3 4

    IF.T

    I

    R ()

    Au(I)-SR2-Polym

    0 1 2 3 4

    Au-SR1

    0 1 2 3 4

    Au-SR2Au-SR1 Au-SR2

    Au(I)-SR2-polym

    2 4 6 8 10 12 14

    Au-SR2

    Au-SR1

    X2xK

    K (-1)

    Au(I)-SR2-PolymAu(I)-SR2-polym

    Au-SR1

    Au-SR2

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

  • SampleCoordination number

    R: bondlength.

    : Debye-Waller factors.

    2x10-3(2)

    E0(eV)

    Au Foil (Au-Au)m 12 2.850 0.073

    Au-SR1 (Au-S)(Au-Au)m

    0.458.8

    2.3002.802

    0.090.094

    3.5 4.3

    Au-SR2 (Au-S)(Au-Au)m

    0.716.8

    2.2892.772

    0.0910.099

    4.5 6.5

    Au(I)-SR2-

    Polym

    (Au-S) 1.3 2.280 0.036

    Au(I) Sulfide

    (Au-S) 1.7 2.307 0.063

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    CharacterizationCharacterizationCharacterization

    EXAFSEXAFS Best fitting parameters of the Au L3 edge EXAFS oscillations

  • CharacterizationCharacterizationCharacterization

    XPSXPS

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    80 82 84 86 88 90 920,0

    0,2

    0,4

    0,6

    0,8

    1,0 Energy shift (eV)Au 4f

    norm

    alis

    ed in

    tens

    ity (a

    rb. u

    nits

    )

    binding energy (eV)

    Au-SR1 Au-SR2 Au2S Polymer

    0.00- 0.03+0.51+0.57

    80 82 84 86 88 90 920,0

    0,2

    0,4

    0,6

    0,8

    1,0

    norm

    alis

    ed in

    tens

    ity (a

    rb. u

    nits

    )shifted binding energy (eV)

    Au Foil Au-SR1 Au-SR2 Au2S Polymer

    Au 4f Peak width (eV)1.141.261.361.461.84

    The Au(I)-SR polymeric sample is the one maximazing the chargetransfer from Au to S and the number of gold atoms bonded to sulfur

  • 400 500 600 700 800

    Abs

    orba

    nce

    Wavelength (nm)

    Au-SR1 Au-SR2 Au(I)-SR2-Polym Au(I)-SR2-Polym-aged

    CharacterizationCharacterizationCharacterization

    UVUV--VISVIS

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    Three samples have been obtained withdifferent microstructures at the nanoscale:

    Gold nanoparticles (NPs) of 2.2 nm average diameter capped through Au-S bonds by alkanethiol molecules

    Gold nanoparticles (NPs) of 2.0 nm average diameter capped through Au-S bonds by alkanethiol molecules

    A polymeric Au(I)-SR phase containingAu atoms fully dispersed in an alkane-thiol matrix with 100% of the gold atomsbonded to sulfur

  • 5 K 300 KSample Ms (emu/gr Au) Hc(Oe) Ms (emu/gr Au) Hc (Oe) Au-SR1 0.0045 (3050 Oe) 115 0,0034 (2023 Oe) 55 Au-SR2 0,094 (10000 Oe) 180 0,049 (10000 Oe) 20

    Magnetic behaviourMagneticMagnetic behaviourbehaviour

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    -10000 -5000 0 5000 10000-0,010

    -0,005

    0,000

    0,005

    0,010

    -10000 -5000 0 5000 10000

    -0,10

    -0,05

    0,00

    0,05

    0,10a)Au-SR1 T = 5K T = 300K

    M (e

    mu/

    g Au

    )

    H (Oe)

    b)Au-SR2 T = 5 K T = 300K

    M (e

    mu/

    g Au

    )

    H (Oe)

    -200 -100 0 100 200-0,010

    -0,005

    0,000

    0,005

    0,010

    M (e

    mu/

    g A

    u)

    H (Oe)

    Au-SR2Au-SR1

    Factors improving the ferromagnetic order:Smaller particle size, smaller Au:S atomic ratios, charge transfer from Au to S

  • Magnetic behaviourMagneticMagnetic behaviourbehaviour

    -10000 -5000 0 5000 10000-0,010

    -0,005

    0,000

    0,005

    0,010

    -10000 -5000 0 5000 10000-0,010

    -0,005

    0,000

    0,005

    0,010 T = 5K T = 300K

    M (e

    mu/

    g Au

    )

    H (Oe)

    T = 5K T = 300K

    M (e

    mu/

    g Au

    )

    H (Oe)

    Au(I)-SR2-Poym Au(I)-SR2-Poym-Aged

    MICROSTRUCTURE AND MAGNETIC BEHAVIOUR OF ALKANETHIOL-CAPED GOLD NANOPARTICLES

    The polymeric phase is the one maximizing charge transfer from gold to sulfur andmaximizing the number of Au atoms bonded to S.However the simultaneous presence of Au-S and Au-Au bonds is necessary to detectthe ferromagnetic like behaviour.Orbital ferromagnetism: Orbital states associated to a certain cluster of gold atoms

  • ConclusionsConclusionsConclusionsThree samples have been studied containing gold atoms functionalised with alkane-thiol molecules (-SR), having three different microstructures at the nanoscale:

    Gold NPs of 2.2 nm average particle size. Capped through Au-S bonds by alkanethiol molecules. Au:S at. ratio=3.0

    Gold NPs of 2.0 nm average particle size. Capped through Au-S bonds by alkane-thiol molecules. Au:S at. ratio=1.7

    Polymeric Au(I)-SR phase containing 100% of Au atoms bonded to S in the alkanethiol molecules. Total dispersion of gold. Au:S at.ratio=1.0

    It has been experimentally demonstrated that the presence of a ferromagnetic likebehaviour is associated with the simultaneous presence of Au-Au and Au-S bonds.

    The presence of metallic or condunting clusters or surfaces are necessary to produce orbital moments induced in atomic like localized states.

    These crucial