LASER MEDIATED NANOPARTICLE

SYNTHESIS AND

SELF-ASSEMBLING PAOLO M. OSSI

Dipartimento di Energia Centre for NanoEngineered Materials and Surfaces – NEMAS

Politecnico di Milano, Italy

3rd International School “Lasers in Materials Science – SLIMS”, San Servolo (VE), July 8-15, 2012

OBJECTIVE

l. synthes. NPs contr.

size morph. stoich.

+ arrange NPs “suitably” (film)

f (appl.)

3 paths • ns p. amb. g. • PLAL {ns/(fs) p.} • fs p. vacuum

abl. pl. fluid ρ

Plasma expansion film str. + morph. tailor film pr.

ambient gas Δ pl. energetics expansion: pl. – gas inter.

≠ target – gas – exp. cond. = seq., ≠ thr.

synthesis of NPs: complex phenomen. scatt. sl. down th. diff. recomb. s.w. cluster.

abl. sp. vis. fluor. sh. fr. edge conf.

pl.

low – p: f. – dir. flow; ↓ scatt. abl. part. 3 propag. reg. trans.: ↑ Δp (abl. – gas); s. w.; pl. diff. abl. part. H. p.

pl. beh. i. Δ free exp. if at pl. frontier: mg ≈ Mp hemisph. pl. : (2/3)πρgrp

3 ≈ Mp

Briefings on PLUME EXPANSION MODELS

S W front E0 gas, ρ0

x(t) = ξ (E0/ρ0)1/5 t2/5 : SW

ξ = [(75/16π) (γ-1)(γ+1)2/(3γ-1)]1/5 [Y.A. Zeldovich, Y.P.Raizer, 1966]

O.K.: Mp < mg (No PLD) ; O.K. at xt, pg ;

at pp ̴ pg SW ≤ xSW ≤

TSW ̴ 104 K O.E. exc. sp. pl.

phenomen. (C, Al, YBCO): drag

[D.B. Geohegan et al., 1992]

a: stop. dist.

β: sl. coeff. fit. par.

pl. ≡ ens. v ∝ Fv

low pg

in. pl. exp.

O.K. ; if

pg > 102 Pa

t > 4 µs xdrag < xexp ; pl. stops at x ̴ 4-5 λ

diffus. transport

pg low

hyp.

x(t) = (Dt)1/2 ; D = <v>(ngσ)/3 : diffusion

<v> = (v0 +vg)/2 : <coll. vel.>

low pg

early exp

at x(t) < xexp

λ

[Rode et al., 2000]

MIXED PROPAGATION (m.p.)

pl. exp. quasi – expl. KN vf

ng ng,eff << ng : modif. diff. coeff.: D’ = kv0(ngσ)-1

v0 : in. pl. vel.

from drag model, 1D exp.: modified drag (m.d.)

, )1(')( '0

tD eRtR β−= DRR 0'<

in. cond.: R(0) = 0 ; v0 = dR(0)/dt

diff. + visc.

fl. class. part.

st. dist.: v0, in. pl. vel. ; µ, diff. coeff. x t-1

st. coeff.:

when DRR 0'< (m.d.)

pg

mg < ma

v0 O.K.

in. KE visc. exp. / SW v0D at << v0

DR 0'

)1(')( '0

tD eRtR β−=DRR 0'<

)("')( 00DD ttDRtR −+= DRR 0'>

,

, (1)

10 )(" −= σκν gD nD

DR 0' : unphys. disc. 2 exp. reg. D0ν

pl. res. v mod. visc. st.

pl. in. v mod. diff. st.

EXPERIMENTS

• PLA+D of Ag (99.999%) & Au (99.999%)

• RT; KrF (248 nm; 25 ns; 10 Hz; 45°; E: 600 mJ; f: 2.0 Jcm-2)

• p0 : 10-4 Pa

• pAr : 10; 40; 70; 100 Pa

• # pulses : 500 – 30000

• dt-S : 35 mm

• substr. : (100) Si ; a-C/Cu grids; Corning 5049

ANALYSIS

Plasma imaging : iCCD Andor iStar (DH – 734) (delays) : 80 ns – 60 µs ; 10 ns < tint < 500 ns ;

gain 1- 60)

SEM : Zeiss Supra 40 f.i. (5 kV)

TEM : Zeiss Leo 912 AB (80 kV)

UV-vis : Perkin Elmer Lambda 2 spectroph.

Raman : JY-HR460 monochr. , CCD , notch filter (100 µW at 100x); He-Ne 632.8 nm; JY-HR800, Diode 785 nm

Ag plasma exp. in Ar 40 Pa m. drag

m. diff.

IF pg , + ma >> mg SW

ex. Au pl. in Ar at 40 100 Pa

5/25/1

0

0 )()( tEtRρ

ξ= DRR 0'<

)("')( 00DD ttDRtR −+= DRR 0'>

,

,

SW

m. diff.

Au

m. drag + m. diff.

SW + m. diff.

PROCESS PICTURE

• NP synthesis : in plume during expansion • film growth : NP aggregation on the substrate

plasma anal. (fast phot.) [1]

model NP synth. (isol. NPs) mixed-propag. model [2]

<Nat> NP-1 in expanding plasma

<d>NP,th. <d>NPs,TEM

[1] F. Neri, P. M. Ossi and S. Trusso, Laser Part. Beams, 28 (2010) 53. [2] A. Bailini, P.M. Ossi, Europhys. Lett., 79 (2007) 35002.

N = <Nat> NP-1 in expanding plasma

( ) ( )fgagfaaa tvntvnN −− ∗= σσ

vn aaa −σ

vn gag −σ

ft

NP growth

pl. scatt. + conf.

NP formation t

gn

aa−σ

ga−σ

an

v

ft

# dens. gas at

coll. cross sect. abl. part. coll. cross sect. abl. part. – gas at. < plasma # dens. > <v> plasma part. t to fly xaggr

known

Fast Imaging techniques

( ) ( )fgagfaaa tvntvnN −− ∗= σσAg

pAr (Pa)

<na> (cm-3)

<v> (cm/µs)

tf (µs)

xaggr (cm)

d (nm)

N

10 7.15 x 1014 0.48 0.79 0.66 0.7 15

40 1.36 x 1015 0.28 3.32 0.49 1.7 158

70 2.24 x 1015 0.22 5.17 0.40 2.8 716

100 2.78 x 1015 0.21 7.37 0.39 4.1 2344

Ar 70 Pa; 10000 pulses

Ar 100 Pa; 10000 pulses

dth.: 2.8 nm dexp: 2.85 ± 1. nm

dth.: 4.1 nm dexp: 3.7 ± 2 nm

Δ Ar p + Δ laser pulse # tail. <d>, n : isol. NPs

SELF-ASSEMBLING of Ag & Au NPs on a SUBSTRATE

• Ar p + laser pulse #: isolated clustered NPs

• Ar p + laser pulse #: islands (smooth edges) percolated structures[1, 2]

[1] E. Fazio, F. Neri, P. M. Ossi and S. Trusso, Appl. Surf. Sci, 255 (2009) 9676. [2] P.M. Ossi, F. Neri, N. Santo, S.Trusso, Appl. Phys. A, 104 (2011) 829.

10000 pulses; 100 Pa Ar Ag

isolated , sph. – like NPs; NO coalesc.

70 Pa ̴ 100 Pa

black : drop. + small sph.-like NPs;

Δ spher. size; inc. coal.

30000 pulses; 70 Pa Ar Au left: isl. size ext. inter-isl. ch.; <width>ch: 2̴0 nm at ch. bottom : NPs (below)

right: dense, un. cov. Au isl.: 1̴0÷20 nm thin interconn. ch. few NPs at ch. bottom

NPs at ch. bottom; ≠ sh.; 4÷7 nm; larger, non-sph. ̴ 2nm: smaller, sph.

STAGES of GROWTH PROCESS

1. NP synthesis : in flight plume confinement 2. NP coalescence large isolated NPs 3. island formation (irr. sh. size); substr. den. 4. percolation : channel filling, substr. coverage

Δ Ar p + Δ laser pulse # tail. f. morph. + nanostr.

PULSED LASER ABLATION in LIQUID (PLAL)

transp. l. ; ̴ mm thick t. vapor. – exp. - conf. – form. exc. plasma

HT( 1̴03 K)

Hp ( ̴GPa) NP synth.

NPs ͻ t. at. + l. at.

stoich., str., morph. exotic

NPs suspension coll. sol.

PLAL features:

1. no remnants prec., interm. react. prod., reagents NO purification

2. extreme conf. cond. VHT,Hp fav. unusual met. ph.

3. sol. t. + liq. vapor. coll. can ͻ at. from both

4. exp. set- up simple

spec. t. – l. comb. nanostr. comp. with ad hoc props.

YET

• NP product. for long t gen. proc. • proc. par. must be optim.

Prod. of NM (Au) NPs via PLAL : proc. par. vs. NP props. ns l. pulses (KrF, 248 nm; Ep = 20mJ)

Δ liq. layer th. re-focus + focal plane det.

liq. lay. th. + lens pos. l. spot ɸ oper. F. critical

than in

vac. gas

[E. Fazio et al., Appl. Surf. Sci. (2012), in press.]

vacuum: ɸmin ≡ lens – t.d.= Lp = focal d. = L0 water : ΔLp = -10 mm ÷ +3 mm: Δɸ ̴ 0; ΔLp , ɸ

Au c. from I520nm (SPR) in UV-Vis coll. sol. [S. Link et al., J. Phys. Chem., 103 (1999), 3529.]

Au cMax: ΔLp = 2.5 mm; liq. lay. th.: 18 mm

ɸ not minimum (≠ vac.; gas BUT pl. scatt. + abs. puls. abl. eff. )

Ep: 20 mJ t: 20 min

liq. lay. thick.?

ΔLp ? Au NP c.

Fixed abl. par. at MAX Au NPs prod. yield: ΔEp 6 mJ 150 mJ

With Ep: • SPR (520 nm): red-shift • absorbance • feat. ~750 nm: clust.

Au NP c up to Ep= 20 mJ, then : fragment.

[U. Kreibig et al., Optical Props. of Metal Clusters, Springer, Berlin, (1996), 265.]

OBSERVATION of Au NPs

a. Ep, 10mJ

b. Ep, 20mJ

c. Ep, 50mJ

d. Ep, 100mJ

: unif. distr. ~ sph. NPs, size < ~ 10 nm + a few > 30 nm : Hρ NPs, <d>: 3 ÷ 5 nm

: chain-like aggl. NPs ~ 50 nm : col. – sh. nanostr.

Δ abl. par. Δ morph. Au NPs (nanostr.) Δ opt. resp. NP arrays (f.)

Compr. scenario PLAL ͻ ∀ const. (ph., liq. mol., sol. t., l. prod. part. + inter. among them

SW + l. ind. bubbles NP form. [Z. Yan, D.B.Chrisey, J. Photoch. & Photobiol. C: Photoch., (2012) in press.]

s. S abs. l.E and emits SWs to relax excess E

2 compr. W. ͻ s. fast exp. imm. after SW l., S. front Δ refr. index: SW front observable

SURFACE ENHANCED RAMAN SCATTERING (SERS) from ARTIFICIAL,

ROUGH NM ARCHITECTURES powerful

non-destr. rapid

fingerprint mol. sp. Raman spectr.

σR ~ 10-30 cm2 mol-1

SERS from M rough S R Int. up to 1012 – 1014 4

00

0

)(),(

wEwrEQSERS =

[M. Moskovitz, Rev. Mod. Phys., 77 (2000) , 783.]

Q: EM enh.; E(r, w0), local f. at mol. pos.; E(w0), incid. f. NO polariz.; NO sel. rul.

art. corr. surf. SERS substrates no prec.

Ag, Au: Δ morph. (NP <d>, shape, aggr.) Δ SPR

SERS measurements

He-Ne (632.8 nm); diode l. (785 nm)

dyes: Rh6G: Raman (NO fluor.); Apomorphine; Garanza lake

1h soaking w. sol. ≠ M conc.

LOCALISED SURFACE PLASMON RESONANCE

LSPR : enhancements when Plasmon freq. ≅ incident EM wave freq. UV – Visible Spectroscopy choice of excitation frequency

Ag NPs in Ar: a) 15000 pulses. b) 70 Pa

Ag NPs UV - Vis

10 Pa 15K p

40 Pa 15K p

70 Pa 15K p

70 Pa 30K p

SERS: Rh6G Ag NPs in Ar a) 15000 pulses, 1 x 10-4 M, #p b) 30000 pulses, 70 Pa, #M

Ar p, %S. cov. NP. % cluster. NPs than at 15K Pa, # hot spots

5x10-8 M

5x10-7 M

2x10-6 M

1x10-4 M

Au NPs UV - Vis

10, 40, 70, 100 Pa in Ar with 30000 pulses

Red-shift coal. single, isol. NPs + EM at junctions

100 Pa 30000 l. pulses: SPR ~ 850 nm

785 nm exc.

SERS – Apomorphine Au NPs in Ar

Apomorphine – dopamine agonist (Parkinson) pharm. drug: blood conc.: critical

Apo ≠ M in water + SERS (785 nm exc.)

• spectra reproducible • M conc. R spectrum

Au 100 Pa 30000 pulses

SERS of ORGANIC DYES

Artwork : select. identif. ≠ chromophores in org. dyes dating

restoration

problem: a) X-ray fluor. NO elem. sign. b) FT-IR ᴐ features from binders / extenders superimp. dyes c) UV-Vis often non-selective

SERS: possible solution ex.: SERS of Garanza lake ᴐ

alizarin

purpurin [dye from Zecchi, Florence]

glass / Ag NPs (70 Pa, 30000 l. pulses)

GARANZA LAKE (UV-Vis)

5 x 10-3 M

weak absorption NO sel. ident. chromoph.

SERS of GARANZA LAKE Ag NPs in Ar

water sol.; exc.: 632.8 nm Raman (5 x 10-3 M): fluoresc. SERS at #M Alizarin : Purpurin:

[I.T. Shadi et al., J. Raman Spectrosc., 37 (2004), 800.]

CONCLUSIONS • NM NPs synth. in laser-gen. plasmas → Ar ≠ p small, isol., sph. NPs • Ag & Au th. f. morph. isl., irr. sh., ↑ size + aggr. ~ cont. film • isol. NPs : <d>NP, TEM ~ <d>NP, model fast phot. plasma exp. par. mixed-prop. model par. PLAL: principles, colloid feat. Au coll.: str./opt. props. vs procs. par. • tail. art. corr. surf. SERS substr. : Rh6G, Apo., Garanza lake ↓ conc.

ACKNOWLEDGEMENTS

N. R. AGARWAL, A. LUCOTTI N. SANTO

M.C. SPADARO, E. FAZIO, F. NERI

R. PONTERIO, S. TRUSSO

Dip. Fisica della Materia & Ingegneria Elettronica, Università di Messina

CNR – Ist. per i Processi Chimico-Fisici, Messina

Centro Interdipartimentale Microscopia Avanzata, Università degli Studi di Milano

Dip. Chimica, Materiali, Ing. Chimica, Politecnico di Milano