Ultrafast spectroscopy of a single metal nanoparticle. Fabrice Vallée FemtoNanoOptics group

Transcription

1 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE Ultrafast spectroscopy of a single metal nanoparticle Fabrice Vallée FemtoNanoOptics group LASIM, CNRS - Université Lyon 1, France

2 Metal Nanoparticles: from IV...to XXI century Metallic particles in glasses: jewelry, ornament Ag Au Ancient cup (Central Europe) Lycurgus Cup: a Roman Nanotechnology Roman Era (4th Century A.D). It appears green in scattered light...and red in transmitted light.

3 Optical response of metal nanoparticles Metal nanosphere (ε = ε 1 + iε 2 ) in a matrix (ε m ): Mie theory for sphere R << λ (dipolar): σ abs 18πVε = λ 3/ 2 m ( λ) 2 2 [ ε ( λ) + 2ε ] + ε ( λ) 1 ε 2 m 2 E O ε(ω) E int R ε m resonance for ε 1 (λ) + 2ε m Surface Plasmon Resonance Ensemble of identical nanoparticles: α = N part σ abs Ag particles in glass Resonance depends on: - environment - shape + light polarization (ellipsoids, rods,...) manipulation of light at subwavelength plasmonics

4 Optical response of metal nanoparticles Metal dielectric function ε( ω) = ε bound electrons (interband) b ( ω) ω 2 p ( i τ) ω ω + free electrons (intraband) interband transitions E F CB intraband transitions d - bands SPR Frequency: ε ib 1 ΩR ) + 2εm ΩR ωp ε1 + 2 ( ε m 5 4 Ag - D = 13 nm - p = 2x1-4 Surface Plasmon Resonance 1 Au - colloids - D = 1 nm 3 Interband Transitions Threshold Ω R αl 2 1 Ω ib Ω R Wavelength (nm) Wavelength (nm)

5 Ultrafast spectroscopy of metal nanoparticles

6 Femtosecond investigation: pump-probe hν Matrix τ p-m e e τ th τ e-ph Lattice τ p-m Matrix Electron excitation (hν) + Femtosecond probing (nonlinear optical response) Coherent response Nonequilibrium electron kinetics Intrinsic electron scattering processes - Internal thermalization ( T e ) electron-electron : τ th ~ 3 fs - External thermalization (T e T L ) electron-lattice : τ e-ph ~ 1 ps Confined vibrational modes Extrinsic processes: nanoparticle - environment coupling Nonlinear optical response

7 Pump Femtosecond excitation and probing Probe I S T x I S ΔT/T Sample Femtosecond excitation: intraband absorption f T e = T f() f(t) T e > T hω P +hω P Femtosecond probing: E F t < t = t > Athermal electron distribution Thermalization + Cooling Transmission change ΔT/T dielectric function change Δε(t D ) Probe wavelength different electron interactions C.K.Sun, et al., Phys. Rev. B 5, (1994) T.Tokizaki, et al., Appl. Phys. Lett. 65, 941 (1994) ; J.Y.Bigot, et al., Phys. Rev. Lett. 75, 472 (1995) C.Voisin et al., J. Phys. Chem B 15, 2264 (21). E F E F

8 Experimental setup: femtosecond pump-probe Verdi Argon Laser Laser Ti:sapphire laser nmnm 11W W - 25fs fs BBO ω 2ω 3ω Reference Chopper ((f) ω) Variable Delay prism pair fω Pump: red pulse (25 fs) (or 2ω) Probe: red pulse (ω ; 25 fs) Sample blue (2ω ; 3 fs) or UV (3ω ; 55 fs) Perturbation : ΔT e ~ 1 K - 2 K Sensitivity : depends on mean power on detector maximum: ΔT/T ~ 1-7 (f = 1 khz) Signal Computer Signal Lock-in Amplifier + - Reference

9 Electron energy losses: electron-phonon coupling Ag - D = 3 nm in Al 2 O B.C..8 ΔT/T.1 E F ΔT/T Probe Delay (ps) Blue probe UV probe bandes d d-bands Probe Delay (ps) pump: IR (93nm) probe: Blue (465nm) or UV (31 nm) UV probe : Risetime: electron thermalization electron-electron interactions Decay: energy transfer to the lattice electron-lattice coupling Blue probe: Energy in the electron gas electron-lattice coupling Size effect?

10 Electron interactions: Size dependences.9.8 Ag film 3 Ag film τ e-ph (ps) Ag nanoparticles polymer BaO-P 2 O 5 Al 2 O 3 MgF 2 deposited Nanoparticle diameter (nm) τ th (fs) 2 Ag nanoparticles BaO-P 2 O 5 matrix Al 2 O 3 matrix Deposited on glass Nanoparticle diameter (nm) Electron lattice interaction: τ e-ph (A. Arbouet, PRL 9, (23)) Tin and Gallium: τ e-ph D (M. Nisoli et al., PRL 78, 3575 (1997)) Electron electron scattering: τ th (C. Voisin, et al., PRL 85, 22 (2)) Screening reduction close to the surface Many studies on large ensembles (1 4 to 1 6 particles) Single nanoparticle Size and shape fluctuations

11 Femtosecond spectroscopy of a single nanoparticle 1) Optical detection and characterization: linear absorption spectroscopy 2) femtosecond pump - probe: nonlinear response Pump P t Probe I S T x I S ΔT/T Sample Sample

12 Optical detection and spectroscopy of a single metal nanoparticle

13 Optical study of a single metal nanoparticle Non luminescent object: Detection of light scattering or absorption Near field: local environment perturbation T. Klar et al. Phys. Rev. Lett. 8, 4249 (1998) Far field: focused beam 3-5 nm diluted sample ( < 1 particle / µm 2 ) - Scattering ( V 2 ; size 2 nm): Dark field microscopy C. Sönnichsen et al., Appl. Phys. Lett. 77, 2949 (2) K. Lindfords et al. Phys. Rev. Lett. 93, 3741 (24) - Absorption ( V ; small particle): Focused laser beam: 3-5 nm Gold nanosphere D = 2 nm - 5 nm: absorption of of the incident light Photothermal technique D. Boyer et al., Science 297, 116 (22) Spatial modulation technique (quantitative) A. Arbouet et al., Phys. Rev. Lett. 93, (24)

14 Optical detection of a single metal nanoparticle (A. Arbouet et al., Phys. Rev. Lett. 24) Absorption by a single nanoparticle: - Focused laser beam: 3-5 nm - Gold nanosphere D = 2 nm - 5 nm: absorption of of the incident light Spatial Modulation Technique: Modulation of the nanoparticule position f Modulation of transmitted light f or 2f microscope objective 1x sample f f, 2f lock-in amplifier Light piezo f Transmitted power P XY scanner

15 Gold nanoparticles - <D> = 1 nm Transmitted power: t i ext (I: intensity profile at the focal spot) ( ) P = P σ I x, y δ y Modulation of the particle position at f : y P P σ t i ext I( x, y ) σ ext I y y δ y σ sin(2 πft) 2 y + δ y sin(2πft) ext 2 y I 2 y δ 2 y sin 2 (2πft) y I(x,y ) Sample image: X/Y scan - λ = 532 nm Diluted sample (< 1 particle/μm 2 ): 1 nm gold nanoparticle spin-coated on a substrate y ΔP/P ΔP/P X (µm) X (µm) f Y (µm) 2f Y (µm)

16 Absorption spectroscopy of a single nanoparticle Ti- sapphire femtosecond oscillator 1 mw - 78 nm - 2fs grating Non-linear photonic crystal fiber Supercontinuum λ > 45 nm SMS microscope Optical absorption signature

17 Single nanoparticles: optical characterization λ = 532 nm; modulation along Y at f = 1 khz ΔT/T nm Tunable source 3 Spectroscopy σ abs (nm 2 ) 2 X (µm) Y (µm) 1 18 nm Wavelength (nm) Counts Nanoscope <D> = 16.6 nm Counts <η > =.9 Nanoscope Absolute value of the absorption cross-section + polarization dependence Counts TEM15 16 <D> 17 18= nm21 6 Diameter (nm) Diameter (nm) Counts TEM Aspect ratio c/a <η > = Aspect ratio c/a Optical identification of a nanoobject: size and shape and orientation O.L.Muskens et al., Appl. Phys. Lett. 88, 6319 (26)

18 Femtosecond optical nonlinearity of a single nanoparticle femtosecond pump - probe study : Pump Probe I S T x I S ΔT/T Sample

19 Femtosecond spectroscopy of a single nanoparticle t D CF tunable Ti:Al 2 3 fs oscillator Chameleon BBO Ch x y f PC DVM Lock-in PD CF

20 Femtosecond spectroscopy of a single Ag nanosphere Optical characterisation of a single nanoparticle (linear absorption spectrum) Microscope Objective 1x & femtosecond pump - probe study : Transmitted Power ΔT T 1nanoparticle Δσ = σ ext ext pump σ S ext probe IR excitation / SPR probing (425 nm) σ ext (x 1-15 m 2 ) 1 5 Ag - D = 3 nm D = 21 nm ΔT/T (x 1-4 ) ΔT/T max (x 1-4 ) P P (µw) Longueur d'onde (nm) Probe delay (ps)

21 Electron-phonon energy exchange in single Ag nanospheres Mechanism ΔT/T electron excess energy Decay: electron-lattice energy exchange τ e-ph 1.5 τ e-ph (ps) τ e ph Strong excitation regime excitation dependent decay: τ e (T e ) Weak excitation regime ΔT decay with τ e-ph = c T / G Pump power (mw) Thermal distributions: Two temperature model T e ; T L ; G = e-lattice coupling constant C e (T e ) = c T e ; C L : heat capacities C C e L dte ( Te ) = G( Te T dt dtl = G( Te TL ) dt L )

22 Electron-phonon coupling in single Ag nanospheres 1.5 max Known nanoparticle known excitation T e -T τ e-ph (ps) Pump power (mw) Comparison wih two temperature model: pump power T e max Same electron-phonon coupling as in ensemble measurements (in glass) comparison with the two-temperature model τ e-ph / τ e-ph No environment dependence (large excitation).1 1 No e-ph coupling dependence (T max -T e ) / T on excitation regime O.Muskens, N. Del Fatti and F. Vallee, Nano Letters ΔT e max : K (3nm) ΔT e max : K (21nm)

23 Acoustic vibration of a single nano-object: pair of nanoprisms Vibrational acoustic modes: Frequency: size and shape dependent Damping: environment / size and shape distribution Single nanoparticle

24 Gold nanoprisms: detection TEM image M. El-Sayed Georgia Inst. Tech., Atlanta Nanosphere lithography: Organized nanoprisms: size 12 nm thickness 3 nm (W. Huang et al., Nano Lett. 4, 1741 (24)) Optical image (at 41 nm) AFM image Optical observation of prism pairs 5 x 5 µm 2

25 Gold nanoprism pair: acoustic vibrations J. Burgin et al., J. Phys. Chem. C 112, (28) - Breathing mode: single T 3 = 12 ps ; ensemble: T 3 = 14 ps. Prism pair Ensemble ΔT/T (x1-3 ) Probe delay (ps) ΔT/T (a.u.) Probe delay ( ps ) -Twomodes: pair: T 1 = 64 ps, T 2 = 49 ps ; ensemble: T 1 = 67 ps, T 2 = 4 ps - Pair: period fluctuations + slower relaxation (reduced inhomogeneous damping) First isotropic modes of a triangle:

26 Gold nanoprisms: acoustic vibrations Gold nanoprisms: acoustic vibrations.2 6 ΔT/T (x1-3 ) Probe delay (ps) Main mode periods: T 1 and T 2 T 2 (ps) τ 1 (ps) T 1 (ps) T 1 (ps) Period fluctuations: Correlated fluctuations shape/size effect Damping: Energy tranfer to the substrate - 1 ps τ 1 6 ps <τ 1 > 26 ps - ensemble measurement: τ 1 7 ps (inhomogeneous damping) - No τ 1 - T 1 correlation fluctuation of the prism-substrate contact

27 Optical investigation and electron microscopy of a single nanoparticle

28 Single nanoparticle spectroscopy: Correlation with electron microscopy - Au particles on Si 3 N 4 substrate Optical TEM Silica sphere markers Pair of interacting Au nanospheres: 9 1 nm σ ext (λ) (1 4 nm 2 ) μm 9 D = 12 nm Agreement with Mie theory 6 Light polarization 9 Wavelength (nm) σ ext (λ) (1 4 nm 2 ) σ ext (λ) (1 4 nm 2 ) Light polarization Wavelength (nm)

29 Conclusion Single nanoparticle optical absorption detection spatial modulation technique: direct absorption measurement absorption cross section down to 5 nm (gold) - 3nm (silver) far-field technique dilute sample (< 1 particle per μm 2 ) spectroscopy: optical identification of a single nanoobject Femtosecond time-resolved spectroscopy electron-phonon coupling in a single metal nano-object acoustic vibration: acoustic properties at a nanoscale nonlinear optics with a single nanoobject combination with electron microscopy Extension to hybrid nanoparticles: semiconductor-metal

30 Acknowledgements Université Bordeaux 1 D. Christofilos A. Arbouet O. Muskens J. Burgin P. Langot Université Lyon 1 FemtoNanoOptics Group V. Juvé (Ph.D) H. Baida (Ph.D) P. Maioli A. Crut N. Del Fatti Université Lyon 1 - France J.R. Huntzinger P. Billaud E. Cottancin M. Pellarin J. Lermé M. Broyer G. Bachelier A. Brioude Universidad Vigo - Spain L. Liz-Marzan Université Paris VI - France M.P. Pileni Georgia Institute of Technology - USA M. El-Sayed