Relationship between Surface-enhanced Raman scattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) analyzed with single Ag nanoaggregates

Relationship between Surface-enhanced Raman scattering (SERS) and surface enhanced hyper Raman

scattering (SEHRS) analyzed with single Ag nanoaggregates adsorbed by dye molecules

AIST1, Kwansei Gakuin Univ.2 Osaka Univ.3

Tamitake Itoh1, Vasudevanpillai Biju1, Mitsuru Ishikawa1, Yukihiro Ozaki2, Hiroyuki Yoshikawa3, Takuji Adachi3, Hiroshi Masuhara3

[email protected]

Outline

Electromagnetic (EM) mechanism of SERS

Relationship between SERS and SEHRS

EM mechanism of SERS

M

sc （D （I (sc)

R12

1 （M (i ）SERS intensity: E(i) { }

2

Two-fold dipole-dipole coupling

lh

f ig g

Two-fold EM enhancement in SERS process

B. Pettinger, JCP. 85, 7442 (1986).

ħ(I-

ħI

Adsorbed molecule

Plasmon resonance Plasmon resonance molecular resonance

1

2

3

45 6

7

8

1

2

34 5 6

7

8

2 3 4

7

1

6 85

50 nm

Particle-by-particle variations in Plasmon resonance maxima

700650600550500450Wavelength / nm

Inte

nsit

y / a

.u.

Increment and red-shift of plasmon resonance bands induced by increment of particle size

100×120 ｍ 100×120 ｍ

Raman shift/cm-1

16001200 800

Nor

mal

ized

Int

ensi

ty (

a.u.

)

Plasmon resonance Rayleigh scattering image

SERRS image

SERS spectrumPlasmon resonance spectrum

700650600550500450Wavelength / nm

Experimental set-up

HM

White light

M4L2 L1

O2

O1

P2N

Pinhole

L3Polychromator

+ CCD2

CCD1

P1W

M5

Dark-field

sample laser

M1 M3

laser

M2プラズモン共鳴散乱像

SERS像

暗視野コンデンサー

Fig. 3. 単一ナノ粒子のプラズモン共鳴、SERS測定装置、M: ミラー, P: 偏光板, L: レンズ, W: ¼波長板, N: ノッチフィルター, O: 対物レンズ

Nor

mal

ized

Int

ensi

ty (

a.u.

)

Wavelength/nm700650600550500450

Raman shift/cm-116001200 800N

orm

aliz

ed I

nten

sity

(a.

u.)

プラズモン共鳴スペクトル

SERSスペクトル

HM

White light

M4L2 L1

O2

O1

P2N

Pinhole

L3Polychromator

+ CCD2

CCD1

P1W

M5

Dark-field

sample laser

M1 M3

laser


SERS像



HM

White light

M4L2 L1

O2

O1

P2N

Pinhole

L3Polychromator

+ CCD2

CCD1

P1W

M5

Dark-field

sample laser

M1 M3

laser


SERS像


HM

White light

M4L2 L1

O2

O1

P2N

Pinhole

L3Polychromator

+ CCD2

CCD1

P1W

M5

Dark-field

sample laser

M1 M3

laser


SERS像



Nor

mal

ized

Int

ensi

ty (

a.u.

)

Wavelength/nm700650600550500450

Nor

mal

ized

Int

ensi

ty (

a.u.

)

Wavelength/nm700650600550500450


orm

aliz

ed I

nten

sity

(a.

u.)


orm

aliz

ed I

nten

sity

(a.

u.)

プラズモン共鳴スペクトル

SERSスペクトルKr laser568 nm

Plasmon resonance spectrum

SERS spectrum

Dark-field condenser

Wavelength /nm

Cro

ss s

ecti

on /

m2 ×

10-4

300400500600700800

1

2

3

20 nm

2.5×1080.0 2.6×1060.0

0°

30°

60°

90°

120°

150°

2.0 2.5 3.0Photon energy /eV

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

Nor

mal

ized

inte

nsit

y [a

rb.u

.]

Polarization angle / degree0 50 100 150

0

1

Comparison of experimental and FDTD calculation results

2.0×1070.0

Polarization dependence of SERS spectra

0°

30°

60°

90°

120°

150°

0500

1000 0°

30°

60°

90°

120°

150°

1.75 2.00 2.25

Inte

nsit

y [c

ount

]

Photon energy / eV

0500

1000

0500

1000

0500

1000

0500

1000

0500

1000

Nor

mal

ized

inte

nsit

y [a

rb.u

.]

0 50 100 150

Polarization angle /degree

0

1

2.0 2.5 3.0Photon energy /eV

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

Nor

mal

ized

inte

nsit

y [a

rb.u

.]

Polarization angle / degree

0 50 100 1500

1

Nor

mal

ized

inte

nsit

y [a

rb.u

.]

2.5×1080.0

)()()(

)(

)(

)()(

22

mLscaLinmL

ImL

L

LI

LL

mL MME

E

E

EM

SERS enhancement factor: M

1st enhancement 2nd enhancement

M

Adsorbed molecule

Ag nanoaggregate

ħ(I-ħI

Inoue and Ohtaka. J. Phys. Soc. Jpn. 52, 3853 (1983)

Practical calculation of SERS spectra using Two-fold SERRS EM enhancement model

)())()()(( scaFLRRSininSERRS MqM SERS cross section: SERS (cm-2)

Resonance Raman cross section: RRS (cm-2)Fluorescence cross section: FL (cm-2), q: quenching factor


Reproduction of SERS spectra

×X 1

0-27 c

m2

2520151050

700650600550500Wavelength (nm) Wavelength (nm)

＝

700650600550500

2520151050

X 1

09

568 nm

Wavelength (nm)

250200150100500

640620600580560540

X 1

0-18 c

m2

MinM

sca

σ SER

RS

σ RR

S +

q σ

FL

568 nm

300

200

100

0

x10-

18

640620600580560540

experimentcalculation 　

Wavelength (nm)σ SE

RR

S (

cm2 )

)( RRS )( FL2520151050

X 1

0-27 (

cm2 )

700650600550500 700650600550500

X 1

0-24 (

cm2 )

80400

120

Wavelength (nm) Wavelength (nm)

× q 　

+

)())()()(( scaFLRRSininSERRS MqM

568 nm

568 nm q=5X10-6

q=5X10-6

q=5X10-6

R1231.8×1010

1.7×1010

5.6×109

Reproduced nanoaggregate-by-nanoaggregate variations in SERS spectra of R123

Wavelength (nm) Wavelength (nm)

Min M

scaM

in Msca

Min M

sca

σ Ray

leis

h (cm

2 )σ R

ayle

ish (

cm2 )

σ Ray

leis

h (cm

2 )

σ SER

RS (

cm2 )

σ SER

RS (

cm2 )

σ SER

RS (

cm2 )

blue ：experimentred ： calculation 　

30

20

10

0

x10

-12

700650600550500

20

15

10

5

0

x109

8

6

4

2

0

x10

-12

700650600550500

6

4

2

0

x109

300

200

100

0

x10-

18

640620600580560540

600

400

200

0

x10-

18

640620600580560540

120

80

40

0

x10-

18

640620600580560540

30

20

10

0

x10-

12

700650600550500

2520151050

x10 9 568 nm

514 nm

Wavelength (nm)

568 nm

647 nm

q=1X10-8

q=1X10-8

q=1X10-8

σ SER

RS (

cm2 )

σ SER

RS (

cm2 )

σ SER

RS (

cm2 )

blue ： experimentred ： calculation 　

Reproduced variations in SERS spectra of R6G of the same nanoaggregate for three excitation wavelength

R6G

σ Ray

leis

h (cm

2 )σ R

ayle

ish (

cm2 )

σ Ray

leis

h (cm

2 )

Min M

sca

R6G

2.9×1010

7.5×109

Wavelength (nm)

Min M

scaM

in Msca

60

40

20

0

x10

-12

700650600550500

6

4

2

0

x10 9

5040302010

0

x10

-12

700650600550500

30

20

10

0

x109

MinMsca=6.3×109

8

6

4

2

0

x109

700650600550500

60

40

20

0

x10-

12

12

8

4

0

x10-

18

700650600550500

400

300

200

100

0

x10-

18

640600560

60

40

20

0

x10-

18

720700680660640620600

拡大表示

拡大表示

Results

(1) We developed quantitative SERS model including excitation wavelength, molecular absorption bands, molecular fluorescence bands, plasmon resonance bands according to 2-fold enhancement theory.

(2) The SERS model quantitatively reproduced and explained variations in SERRS spectra.

Result (1)-(2) revealed that SERS spectra are simply described as follows;

Conclusion

).())()()(( scaFLRRSinin MqM

Peak values of MinMsca are around 109 – 1010.Values of q are around 10-6 – 10-8.

Relationship between SERS and SEHRS,

T. Itoh et al, APL 88, 084102, 2006

Background Light-Emission (BLE) of Surface-enhanced hyper Raman scattering (SEHRS)

This is a typical SEHRS, BLE, and SEHRlS spectrum of R6G adsorbed on an Ag nanoaggregate. Such spectrum can be measured even using cw NIR laser.

532 nm

Inte

nsit

y [c

ount

/2s]

0

2 0

4 0

6 0

5 0 0 6 0 0 7 0 0 8 0 0

Wavelength / nm

SEHRSWeek SEHRlS

BLE

G. Brehm, et al, J. Mol. Struct. 735, 85 (2005).

1. BLE is always overlapped with SEHRS using cw NIR laser excitation.

We focus on the BLE to elucidate a detailed mechanism of SEHRS.

Enhancement factors; MSERRS, MBLE

Ein : incident electric fieldELoc : local electric field

： frequency of the incident laser lightmol: vibrational frequency


Adsorbed molecule

h(I-hI

Ag nanoaggregate

22

)(

)(

)(

)(

molin

molLoc

in

Loc

SERRS E

E

E

EM

22

)(

)(

)(

)(

Lin

LLoc

in

Loc

BLE E

E

E

EM


L: fluorescence frequency

24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRS E

E

E

EM

24

)2(

)2(

)(

)(

in

Loc

in

Loc

SEHRlS E

E

E

EM

24

)(

)(

)(

)(

Lin

LLoc

in

Loc

BLE E

E

E

EM

Consideration of enhancement mechanism of SEHRS, BLE, SEHRlS

deduced from SERRS two-fold EM enhancement thory

1st enhancement

2nd enhancement

Inoue, JPSJ. 52, 3853 (1983)

Enhancement factors; MSEHRS, MBLE, MSEHRlS

H. Xu. PRL. 93, 243002 (2004).

M. Moskovits, Rev. Mod. Phys. 57, 783 (1985). B. Pettinger, J. Chem. Phys. 85, 7442 (1986).

O1

P

L

White light

C

Ag nanoaggregates

Optical Fiber

Polychromator

+ CCD

O1

P

L

Laser beam

(1064 nm)DM

O1

P

L

N

Laser beam

(532 nm)

O2

Experiment setup

Plasmon resonance band

Wavelength/nm700650600550500450

0

50

100

150

SERRS and BLE

0

50

100

SEHRS, BLE and SEHRlS

Laser power densityMax 6 MW/cm2

Laser power density Max 30 W/cm2

500 600 700 800Wavelength/nm 500 600 700 800

Wavelength/nm

pinhole

lens

200 m

objective

Inte

nsit

y (c

ount

s)

500 600 700 800

0

1 0 0

2 0 0

0

1 0 0

2 0 0

0

1 0 0

2 0 0

0

1 0 0

2 0 0

0

1 0 0

2 0 0

0

1 0 0

2 0 0

0

1 0 0

2 0 0

Wavelength / nm

0

1 0 0

2 0 0

0-2 s

2-4 s

4-6 s

6-8 s

8-10 s

10-12 s

12-14 s

14-16 s

Temporal fluctuation of SEHRS and BLE spectra from a single Ag nanoaggregate

SEHRS, BLE, and SEHRlS

SEHRS spectra often show intermittence of intensity on the time scale of several seconds. Intermittence on this time scale is too slow considering diffusion of free molecules crossing a SEHRS-active site because the time scale due to Brownian motion is within a millisecond. However, chemical affinity between R6G and Ag surfaces decreases the intermittence rate and such slow intermittence can be one proof of single molecule detections [A. Weiss, JPCB 105, 12348 (2001)]. Following the previous work on SERRS, we consider that the SEHRS signals in the present experiment is also a proof of single molecule detections.

Comparison between BLE spectrum of SEHRS and that of SERRS from large number of Ag nanoaggregates

0.8

0.6

0.4

0.2

0.0800700600500

Wavelength / nm

Residual spectrum after subtracting ISEHRS() from ISERRS() is similar to fluorescence spectrum of monomer R6G

SEHRS with BLEFluorescence of monomer R6G

Nor

mal

ized

inte

nsit

y 0.8

0.6

0.4

0.2

0.0800750700650600550500

Wavelength / nm

ISEHRS()

SERRS and BLEFluorescence of monomer R6G

Wavelength / nm

Nor

mal

ized

inte

nsit

y) 1.0

0.8

0.6

0.4

0.2

0.0800750700650600550500

ISERRS()

ISERRS() - ISEHRS() =

500×500 ｍ

The residual spectrum indicates that R6G monomers cannot have SEHRS activity.

Spectral variations in BLE of SEHRS from single Ag nanoaggregates(not from larger number of Ag nanoaggregtes)

2-photon fluorescence spectrum of monomer R6G0

200

400

SEHRlS spectra from single Ag nanoaggregate

0204060

0

20

40

500 600 700 8000

200

4000

50

100

Wavelength / nm

Inte

nsit

y (c

ount

s)

500 600 700 800

SEHRS with BLE

BLE spectra of SEHRS are different from nanoaggregate to nanoaggregate.These various spectra are composed of three bands indicated by red-lines whose positions are red-shifted from fluorescence maxima of monomer R6G.

SEHRS, BLE, and SEHRlS spectra from three single Ag nanoaggregates

Comparison of BLE of SEHRS with that of SERRS for identical single Ag nanoaggregates

BLE spectra of SEHRS are similar to those of SERRS for the identical nanoaggregates except fluorescence of monomer R6G.

Wavelength / nm

Identical four Ag nanoaggregates

SEHRS with BLE

0

200

400

02040600

2040

500 600 700 8000

200

4000

50100

2 photon fluorescence spectrum of monomerR6G

Inte

nsit

y (c

ount

s)

SERRS with BLE

0

500

1000

01000

20000

100

200

500 600 700 8000100

2000

50100150

Inte

nsit

y (c

ount

s)

Wavelength / nm

1 photon fluorescence spectrum of monomer R6G

200×200 ｍ

1.Why is monomer fluorescence of R6G not observed ?

2. Why is fluorescence of aggregates selectively observed ?

1. BLE spectra of SEHRS are composed of three bands whose maxima are red-shifted from fluorescence maxima of monomer R6G.

2. BLE spectra of SEHRS are similar to those of SERRS for the identical nanoaggregates except monomer fluorescence.

Based on the red-shifts and the similarity, we attributed the three BLE bands of SEHRS to two-photon fluorescence of J-like aggregates of R6G molecules. Indeed, several papers concluded such red-shifts arise from linear aggregation of R6G. (e.g. C. T. Lin, et al, CPL 193, 8 (1992), J. Bujdak 2006, 110, 2180 (2006) JPCB)

Conclusion 1

Questions

3. Why is SEHRS intensity comparable to SEHRlS intensity ?

BLE1 of J-like aggregates of dye molecules is ~8-10 times larger than that of monomers because of increase in transition dipole moment (C. T. Lin, et al, Chem. Phys. Lett. 193, 8 (1992)) . Thus, BLE2 of J-like aggregates is expected to be ~60-100 times larger than BLE1. This increasing can compensate the smaller BLE2. Thus, this compensation may be the reason for selective observation of fluorescence from J-like agrgegates.

1. Why is monomer fluorescence not observed ?

2. Why fluorescence of J-like aggregates is selectively observed ?

BLE1 (1.9 x 10-16 cm2, J. Opt. Soc. Am. B 13, 481 (1996). ) is 3.0 x 107 times larger than the effective two-photon cross-section BLE2 (6.4 ± 0.6 x 10-23 cm2 at (6x105) MW/cm2). (here, 105 is conventional EM field enhancement factor for single molecule detection) However, excitation power for two-photon fluorescence (6 MW/cm2) is only ~ 5.0 x 105 times larger than that of one-photon fluorescence (30 W/cm2). Thus, the small BLE1 of monomer may be the reason for lack of observation of monomer fluorescence.

Our answers

3. Why is SEHRS intensity comparable to SEHRlS intensity ?It will be discussed later.

Too small one-photon cross-section of monomer R6G: BLE1

Larger BLE2of R6G J-aggregetes than that of monomers

Intensity variations of SEHRS, BLE, and SEHRlS intensity

Scattering of data points of single nanoaggregate measuremets is much larger than that of large aggregate measurements.

BL

E in

ten

sity

(co

un

ts)

SEHRS intensity (counts)100 500

10

50

100

200

100 500

400

20004000

SEHRS intensity (counts)

SE

HR

lS in

ten

sity

(co

un

ts)

500 600 700 800

0

50

100

Wavelength / nm

Single Ag nanoaggregate400

300

200

100

0

800750700650600550500

Large number of Ag nanoaggregates

500×500 ｍ


SE

HR

lS in

ten

sity

(co

un

ts)

100

567

10

2

34567

2x101 3 4 5 6 BL

E in

ten

sity

(co

un

ts)


456789

100

2

3

6 7 8 9100 2 3

Wavelength / nm

Origin of Ag nanoaggregate by nanoaggregate variations

SEHRS, BLE, and SEHRlS spectra are modulated by plasmon resonance due to 2nd enhancement.In other words, the scattering of data points is indirect evidence of 2nd enhancement.

24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRS E

E

E

EM

24

)2(

)2(

)(

)(

in

Loc

in

Loc

SEHRlS E

E

E

EM

24

)(

)(

)(

)(

Lin

LLoc

in

Loc

BLE E

E

E

EM

2st enhancement(plasmon resonance)

Wavelength / nm

Inte

nsit

y (a

.u.)

Wavelength / nm

Single Ag nanoaggregate Large number of Ag nanoaggregates

Spectral blue-shifts in plasmon resonance Rayleigh scattering and BLE spectra

Wavelength / nm Wavelength / nm Wavelength / nm

00 .0 20 .0 40 .0 60 .0 8

00.020.040.060.08

0.1

500 600 700 8000

0.020.040.060.080.1

0.12

Rel

ativ

e in

tens

ity

(cou

nts)

Inte

nsit

y (c

ount

s)

0

0.02

0.04

0

0.04

0.08

500 600 700 8000

0.05

0.1

0

100

200

0

200

400

500 600 700 8000

100

200

300

Rel

ativ

e in

tens

ity

(cou

nts)

Inte

nsit

y (c

ount

s)

0

200

400

0

50

100

500 600 700 800

0

20

0

20

40

60

0

50

100

500 600 700 8000

50100150200

0

100

200

300

400

0

200

400

0100200300400

500 600 700 800

BLE of SEHRSBLE of SERRSPlasmon resonance

Blue-shifts in BLE spectra of SEHRS, BLE spectra of SEHRlS, plasmon resonance spectra coincidentally happened.

Origin of the spectral blue-shifts of BLE

Wavelength / nm

Inte

nsit

y (a

.u.)

2st enhancement(plasmon resonance)

24

)(

)(

)(

)(

Lin

LLoc

in

Loc

BLE E

E

E

EM

SEHRS, BLE, and SEHRlS spectra has modulated by plasmon resonance due to 2nd enhancement.In other words, the blue-shift is direct evidence of 2nd enhancement.

Conclusion

24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRS E

E

E

EM

24

)2(

)2(

)(

)(

in

Loc

in

Loc

SEHRlS E

E

E

EM

24

)(

)(

)(

)(

Lin

LLoc

in

Loc

BLE E

E

E

EM

(2) Ag nanoaggregate by nanoaggregte variations in SEHRS, BLE, and SEHRlS spectra support that their signals are enhanced through two-fold EM interactions described as following;

(1) Spectral analysis of BLE revealed that J-like aggregates of R6G molecules selectively show SEHRS and BLE because of their larger dipole moment than that of monomers.

Unclosed questionWhy is SEHRS intensity comparable to SEHRlS? (SEHRlS intensity should be several hundred times larger than SEHRS intensity.)

Laser power dependence of SEHRS, BLE, and SEHRlS from large number of Ag nanoaggregates

SEHRlS shows nonlinear response, but SEHRS and BLE does show nonlinear responses.

BL

E in

ten

sity

(co

un

ts)

SE

HR

S in

ten

sity

(co

un

ts) 400

300

200

100

0403020100

300

200

100

0403020100

Incident laser power (kWcm2) Incident laser power (kW/cm2)

SE

HR

lS in

ten

sity

(co

un

ts)

600

400

200

0

403020100

Incident laser power (kW/cm2)

Wavelength / nm

400

300

200

100

0700650600550

Inte

nsit

y (c

ount

s/2s

)

500×500 ｍ

1. Why does only SEHRlS show nonlinear response?

2. Why does SEHRS and BLE not show nonlinear response?

Why does SEHRS and BLE show linear dependence even SEHRlS shows nonlinear dependence?

Destruction of R6G molecules by laser excitationWe checked SEHRS intensity several times for the same Ag nanoaggregates, but they showed almost same intensity.Thus, we think that destruction of Ag nanoaggregates may not be a reason for lack of nonlinear dependence of SEHRS and BLE.

Saturation of nonlinear resonance of R6G by high power excitationWe think this is an important candidate to explain the lack of nonlinear dependence.

SEHRlS from mainly Ag nanoaggregatesAg nanoaggregates which do not show SEHRS show SEHRlS.Thus, a part of SEHRlS photons is independently generated from directly Ag nanoagregtas.Thus, defines the nonlinear dependence of SEHRlS arises from nonlinear polarization of Ag nanoaggregates

300

200

100

0

750700650600550500

300

200

100

0

750700650600550500

Inte

nsit

y (c

ount

s/2s

)

Wavelength / nm Wavelength / nm

1. Why does only SEHRlS show nonlinear response?

2. Why does SEHRS and BLE not show nonlinear response?

BLE2 of R6G monomer = 2.0 x 10-50 cm4 sec/photon.

Effective BLE2 of R6G 6.4 x 10-21 cm2

Incident photon density 6 MW/cm2 = 3.2 x 1025 photon/sec cm2

Expected enhanced local photon density 6 x 105 MW/cm2 = 3.2 x 1030 photon/sec cm2

3.2 x 1030 photon/sec cm2 X 6.4 x 10-21 cm2 = 2.05 x 109 photon/sec

Absorption 8.2 photon/molecule

Life time of R6G = 4 x 10-9 sec (R. F.Kubin,. J. Lumin. 1982, 27, 455.)

Almost R6G molecules is always photo-excited. Thus, saturation effect may be reasonable from the estimation.

Disappearance of two-photon absorption (optical resonance) due to saturation effect.

Simple estimation of saturation of nonlinear optical resonance

Estimated BLE2 of R6G monomer = 2.0 x 10-48 cm4 sec/photon.

100

200 10002000

500

SERRS intensity (counts)

SE

HR

S in

tens

ity

(cou

nts)

Relationship between intensity of SERRS and that of SEHRS

Intensity of SERRS and SEHRS does not have any correlation even both of them are from identical Ag nanoaggregates. The lack of correlation indicates that intensity of SEHRS depends on enhanced EM fields at both 532 nm and 1064 nm, but intensity of SERRS depends on enhanced EM fields at 532 nm only.

500 600 700 800

0

50

100

Wavelength / nm

500 600 700 8000

50

100

150

Wavelength / nm

SERRS SEHRS1st enhancement

22

)2(

)2(

)2(

)2(

molin

molLoc

in

Loc

SERRS E

E

E

EM

532 nm24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRS E

E

E

EM

1064 nm

Common 1st enhancement

500 600 700 8000

50

100

Wavelength / nmWavelength / nm500 600 700 8000

20

40

60C3 C4

SERRS SEHRS

Second enhancement in SERS

Stokes Anti-Stokes

Laser line

Wavelength / nm

Intensity (a.u.)Band shape of plasmon resonance

Wavelength / nm

)(M

)(M

=

The correlation between plasmon resonance and SERRS spectra shows that SERRS bands overlapping with a vicinity of plasmon resonance maximum are selectively enhanced. For example, anomalous anti-Stokes bands are result of coupling SERRS and plasmon having maximum in the anti-Stokes region.

)()()(

)(

)(

)()(

22

mLscaLinmL

ImL

L

LI

LL

mL MME

E

E

EM

400

300

200

100

0

700650600550500

Comparison between background light-emission spectrum of SEHRS and that of SERRS from large number of Ag nanoaggregates

Residual spectrum after subtracting ISEHRS() from ISERRS() is similar to fluorescence spectrum of monomer R6G

SERRS with background light-emissionand Fluorescence of R6G

Wavelength / nm

Nor

mal

ized

inte

nsit

y)

500×500 ｍ

R6G monomers cannot have SEHRS activity?

250

200

150

100

50

0

2.52.01.51.00.50.0

800

600

400

200

0

2.52.01.51.00.50.0

(1) Lack of intensity correlation between SERRS and SEHRS indicates that 1st enhancement is not common for them.

(2) Linear intensity correlation among SEHRS, background light-emission, and hyper-Rayleigh scattering indicates that those kinds of light are generated through common 1st enhancement.

Conclusion 2

24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRS E

E

E

EM

24

)2(

)2(

)(

)(

in

Loc

in

Loc

HR E

E

E

EM

24

2 )(

)(

)(

)(

Lin

LLoc

in

Loc

PL E

E

E

EM

Results (1) and (2) support the comprehensive mechanism of SEHRS, background light-emission, hyper-Rayleigh scattering provided as follows;

A. K. Sarychev, et al, PRB 60, 16389(1999).

Polarization

02 04 06 08 0

500 600 700 8000

40

800

200400600800

500 600 700 8000

40

80

Inte

nsit

y (c

ount

s)

01 0 02 0 03 0 04 0 0

500 600 700 8000

40

80

500 600 700 8000

50

1000

40

80

Inte

nsit

y (c

ount

s)

050 0

1 0 001 5 002 0 00

0200400600800

Inte

nsit

y (c

ount

s)

A1 A2

A3 A4

B1 B2

B3 B4

C1 C2

500 600 700 8000

50

100

Wavelength / nmWavelength / nm500 600 700 8000

20

40

60C3 C4

Manners of disappearance of SEHRRS with background light-emission

Nanoaggregate A

Nanoaggregate B

Nanoaggregate C

SERRS SEHRS

0

50

100

150

600 700

Bac

kgr

oun

d li

ght

emis

sion

in

ten

sity

(co

un

ts)

F

Peak wavelength / nm

600 700

0

200

400

600

SE

HR

RS

inte

nsi

ty (

cou

nts

)

E

Peak wavelength / nm

Relationship between SEHRRS intensity and peak wavelength of plasmon resonance bands

Above Eqs. imply that efficient coupling between incident NIR light and plasmons contributes to stronger first enhancement. This means that Ag nanoaggregates whose plasmon resonance maxima in longer wavelength region are advantageous to get larger first enhancement. Indeed, Figs. 3E and F approximately indicate that Ag nanoaggregates whose plasmon resonance maximum wavelength is longer than 650 nm show larger intensity of SEHRRS and background-light emission than those shorter than 650 nm.

0

1 00

2 00

3 00

4 00

500 600 700 800Wavelength / nm

500 600 700 800

0

0.02

0.04

0.06

0.08

0.1

0.12

Wavelength / nm

SEHRRS and background light-emission

Plasmon resonance maxima

24

)2(

)2(

)(

)(

molin

molLoc

in

Loc

SEHRRS E

E

E

EM

24

2 )(

)(

)(

)(

Lin

LLoc

in

Loc

PL E

E

E

EM

1064 nm

SERRS intensity (counts)

02

200

20 0 2000

Bac

kgr

oun

d li

ght

emis

sion

in

ten

sity

(co

un

ts)

A

Relationship between SERRS and background light-emission

The positive correlation indicates that SERRS and background light-emission are generated from common enhanced EM local fields.

This indication agrees with the SERRS-EM model which describes that incident EM fields which are coupled with plasmons induce both SERRS and its background light-emission.

22

1 )(

)(

)(

)(

Lin

LLoc

in

Loc

PL E

E

E

EM

22

)(

)(

)(

)(

molin

molLoc

in

Loc

SERRS E

E

E

EM

532 nm

532 nm 500 600 700 800

0

50

100

150

Wavelength / nm

SERRS with background light-emission

Common 1st enhancement

0

Wavelength (nm)700650600550

Nor

mal

ized

inte

nsit

y (a

.u.)

0

1

0

10

1

0

10

1

1

Norm

alized intensity (a.u.)

0

1

0

1

0

1

0

1

0

1

0

1

A

B

C

D

E

F

Lum

ines

cenc

e m

axim

um (

nm)

Plasmon resonance maximum (nm)

660

640

620

600

580

560680660640620600

Inte

nsit

y (c

ount

s)

0

2 0

4 0

6 0

0

20

40

60

0

2 0

4 0

6 0

0

2 0

4 0

6 0

0

2 0

4 0

6 0

0

2 0

4 0

6 0

0

2 0

4 0

6 0

0

2 0

4 0

6 0

Wavelength / nm

0-2 s

2-4 s

4-6 s

6-8 s

8-10 s

10-12 s

12-14 s

14-16 s

500 600 700 800

Origin of SERRS background light-emission

(a)

E

metal surface adsorbed molecule

electron

EP

S1 state

S0 state

CT state

EF

hi

hl

(b)

hi

EF

E

metal surface adsorbed molecule

electron

EP

hl

S1 state

S0 state

ECT

T. Itoh et al, JPC B, 110, 21536, 2006

Nor

mal

ized

inte

nsit

y (a

.u.)

10

10

10

10

10

10

1

700650600550Wavelength (nm)

Fluorescence spectrum of R6G in an aqueous solution

We attributed the three background light-emission to fluorescence 　 coupled with plasmon and emitted from monomer, dimer, and two kinds of higher-order aggregates of R6G molecules on an Ag surface.

0 50 100 150

Polarization angle /degree

Nor

mal

ized

inte

nsit

y [a

rb.u

.]

0

1

SERRS image

+++ +

- - - -Incident light

Electric field

Polarization

①

②

③

時間領域差分法による電場計算

SERS 発現メカニズム－電磁場増強モデル－SERS 発現メカニズム－電磁場増強モデル－

表面プラズモン共鳴（ SPR ）102 ～ 103 　程度の電場増強

108 ～ 1010 程度の電場増強

SPR によって生じる局所増強電場が SERS を引き起こしている

Documents

Relationship between Surface-enhanced Raman scattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) analyzed with single Ag nanoaggregates