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Relationship between S urface - enhanced R aman scattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) analyzed with single A g nanoaggregates adsorbed by dye molecules AIST 1 , Kwansei Gakuin Univ. 2 Osaka Univ. 3

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  1. Relationship between Surface-enhanced Ramanscattering (SERS) and surface enhanced hyper Raman scattering (SEHRS) analyzed with single Agnanoaggregatesadsorbedbydye molecules AIST1, Kwansei Gakuin Univ.2 Osaka Univ.3 Tamitake Itoh1, Vasudevanpillai Biju1, Mitsuru Ishikawa1, Yukihiro Ozaki2, Hiroyuki Yoshikawa3, Takuji Adachi3, Hiroshi Masuhara3 tamitake-itou@aist.go.jp

  2. Outline Electromagnetic (EM) mechanism of SERS Relationship between SERS and SEHRS

  3. EM mechanism of SERS

  4. Two-fold EM enhancement in SERS process ħwI M M ħ(wI-wn) |l> |h> |e> |f> |i> |g> |g> Adsorbed molecule B. Pettinger, JCP. 85, 7442 (1986). Two-fold dipole-dipole coupling 2 1 } { (a0M(wsc)) SERS intensity: I (wsc) E(wi) （a0M(wi） （a0D） R12 Plasmon resonance molecular resonance Plasmon resonance

  5. Particle-by-particle variations in Plasmon resonance maxima 4 5 6 3 7 8 2 1 700 650 600 550 500 450 Wavelength / nm 4 5 6 3 7 Intensity / a.u. 8 2 1 Increment and red-shift of plasmon resonancebands induced by increment of particle size 50 nm 1 4 2 3 7 8 5 6

  6. 700 650 600 550 500 450 Wavelength / nm Normalized Intensity (a.u.) 800 1200 1600 100×120 mｍ 100×120 mｍ Plasmon resonance Rayleigh scattering image SERRSimage Raman shift/cm-1 SERS spectrum Plasmon resonance spectrum

  7. Experimental set-up Plasmon resonance spectrum Dark-field condenser SERS spectrum Kr laser 568 nm

  8. Comparison of experimental and FDTD calculation results 0° 0.4 0.2 30° 0 0.4 0.2 60° 0 0.4 0.2 90° 0 Normalized intensity [arb.u.] 0.4 0.2 120° 0 0.4 0.2 150° 0 0.4 0.2 0 2.0 2.5 3.0 Photon energy /eV 1 0 150 0 50 100 Polarization angle q / degree 20 nm 3 2 Cross section / mm2 ×10-4 1 800 700 600 500 400 300 Wavelength /nm 2.5×108 0.0 0.0 2.0×107 2.6×106 0.0

  9. Polarization dependence of SERS spectra 0.4 0.2 0 0.4 0.2 0 0.4 0.2 0 Normalized intensity [arb.u.] 0.4 0.2 0 0.4 0.2 0 0.4 0.2 0 2.0 2.5 3.0 Photon energy /eV 2.5×108 0.0 0° 1000 0° 500 0 30° 1000 30° 500 0 60° 1000 60° 500 0 Intensity [count] 90° 1000 90° 500 0 120° 1000 120° 500 0 150° 1000 150° 500 0 1.75 2.00 2.25 Photon energy / eV 1 1 Normalized intensity [arb.u.] Normalized intensity [arb.u.] 0 0 150 0 50 100 0 50 100 150 Polarization angle q / degree Polarization angle q/degree

  10. Practical calculation of SERS spectra using Two-fold SERRS EM enhancement model ħwI ħ(wI-wn) Adsorbed molecule SERS enhancement factor: M Ag nanoaggregate 1st enhancement 2nd enhancement Inoue and Ohtaka. J. Phys. Soc. Jpn.52, 3853 (1983) SERS cross section: sSERS (cm-2) 1st enhancement 2nd enhancement Resonance Raman cross section: sRRS (cm-2) Fluorescence cross section: sFL (cm-2), q: quenching factor

  11. Reproduction of SERS spectra 25 20 15 10 568 nm 25 5 X 10-27 cm2 σRRS + q σFL 20 MinMsca × 0 X 109 15 500 550 600 650 700 10 Wavelength (nm) 5 0 500 550 600 650 700 Wavelength (nm) 568 nm experiment 300 calculation 250 200 σSERRS (cm2) ＝ X 10-18 cm2 -18 200 σSERRS 150 x10 100 100 50 0 0 540 560 580 600 620 640 560 580 600 620 640 540 Wavelength (nm) Wavelength (nm) × q 25 + 120 20 X 10-27 (cm2) X 10-24 (cm2) 15 80 10 40 5 0 0 500 550 600 650 700 500 550 600 650 700 Wavelength (nm) Wavelength (nm)

  12. Reproduced nanoaggregate-by-nanoaggregate variations in SERS spectra of R123 blue：experiment R123 red：calculation 1.8×1010 568 nm 25 30 q=5X10-6 300 20 -12 20 -18 x10 σRayleish (cm2) 15 200 MinMsca σSERRS (cm2) x10 9 x10 10 10 100 5 0 0 0 500 550 600 650 700 540 560 580 600 620 640 20 1.7×1010 600 q=5X10-6 568 nm 30 15 -12 x10 σRayleish (cm2) 20 400 MinMsca -18 10 σSERRS (cm2) x10 9 x10 10 5 200 0 0 500 550 600 650 700 0 540 560 580 600 620 640 8 q=5X10-6 5.6×109 568 nm 6 120 6 σRayleish (cm2) -12 -18 x10 σSERRS (cm2) 4 80 4 x10 MinMsca 9 x10 2 40 2 0 0 0 540 560 580 600 620 640 500 550 600 650 700 Wavelength (nm) Wavelength (nm)

  13. Reproduced variations in SERS spectra of R6G of the same nanoaggregate for three excitation wavelength blue：experiment R6G red：calculation 514 nm R6G MinMsca=6.3×109 60 q=1X10-8 12 6 -12 -18 40 σSERRS (cm2) 8 σRayleish (cm2) x10 4 x10 x10 MinMsca 9 20 4 2 0 0 0 500 550 600 650 700 500 550 600 650 700 568 nm 拡大表示 2.9×1010 30 400 50 q=1X10-8 40 300 -18 -12 20 σRayleish (cm2) x10 σSERRS (cm2) MinMsca 30 200 x10 x10 9 20 10 100 10 0 0 0 560 600 640 500 550 600 650 700 647 nm 拡大表示 60 60 7.5×109 8 q=1X10-8 40 -18 40 6 -12 σRayleish (cm2) σSERRS (cm2) x10 x10 MinMsca 4 x10 20 9 20 2 0 0 0 600 620 640 660 680 700 720 500 550 600 650 700 Wavelength (nm) Wavelength (nm)

  14. Conclusion 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; Peak values of MinMscaare around 109 – 1010. Values of q are around 10-6 – 10-8.

  15. Relationship between SERS and SEHRS,

  16. Background Light-Emission (BLE) ofSurface-enhanced hyper Raman scattering (SEHRS) 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 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. SEHRS G. Brehm, et al, J. Mol. Struct. 735, 85 (2005). Week SEHRlS 6 0 532 nm 4 0 Intensity [count/2s] BLE 2 0 0 T. Itoh et al, APL 88, 084102, 2006 1. BLE is always overlapped with SEHRS using cw NIR laser excitation. We focus on the BLE to elucidatea detailed mechanism of SEHRS.

  17. Consideration of enhancement mechanism of SEHRS, BLE, SEHRlS deduced from SERRS two-fold EM enhancement thory Enhancement factors; MSERRS, MBLE Enhancement factors; MSEHRS, MBLE,MSEHRlS 1st enhancement 2nd enhancement 1st enhancement 2nd enhancement Inoue,JPSJ. 52, 3853 (1983) M. Moskovits,Rev. Mod. Phys.57, 783 (1985). B. Pettinger, J. Chem. Phys. 85, 7442 (1986). 1st enhancement 2nd enhancement hnI H. Xu.PRL. 93, 243002 (2004). h(nI-nn) n：frequency of the incident laser light nmol: vibrational frequency nL: fluorescence frequency Adsorbed molecule Ein : incident electric field Ag nanoaggregate ELoc: local electric field

  18. Experiment setup 450 500 550 600 650 700 Wavelength/nm 1 5 0 1 0 0 1 0 0 5 0 5 0 0 0 5 5 0 0 0 0 6 6 0 0 0 0 7 7 0 0 0 0 8 8 0 0 0 0 Laser power density Max 30 W/cm2 Laser power density Max 6 MW/cm2 White light C O2 Laser beam (1064 nm) objective Laser beam (532 nm) O1 O1 Ag nanoaggregates O1 DM pinhole N P P P Polychromator + CCD lens L L L Optical Fiber Plasmon resonance band SEHRS, BLE and SEHRlS SERRS and BLE 200 mm Wavelength/nm Wavelength/nm

  19. Temporal fluctuationof SEHRS and BLE spectra from a single Ag nanoaggregate 2 0 0 1 0 0 0 0-2 s 2 0 0 1 0 0 0 2-4 s 2 0 0 1 0 0 0 4-6 s 2 0 0 1 0 0 0 6-8 s 2 0 0 1 0 0 0 8-10 s 2 0 0 1 0 0 0 10-12 s 2 0 0 1 0 0 0 12-14 s 2 0 0 1 0 0 0 14-16 s 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 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. Intensity (counts)

  20. Comparison between BLE spectrum of SEHRS and that of SERRS from large number of Ag nanoaggregates SEHRS with BLE Fluorescence of monomer R6G SERRS and BLE Fluorescence of monomer R6G 1.0 ISERRS(l) 0.8 ISEHRS(l) 0.8 Normalized intensity) 0.6 0.6 Normalized intensity 500×500 mｍ 0.4 0.4 0.2 0.2 0.0 500 550 600 650 700 750 800 0.0 500 550 600 650 700 750 800 Wavelength / nm Wavelength / nm 0.8 0.6 0.4 0.2 0.0 500 600 700 800 Wavelength / nm ISERRS(l) -ISEHRS(l) = Residual spectrum after subtracting ISEHRS(l) from ISERRS(l) is similar to fluorescence spectrum of monomer R6G The residual spectrum indicates that R6G monomers cannot have SEHRS activity.

  21. Spectral variations in BLE of SEHRS from single Ag nanoaggregates (not from larger number of Ag nanoaggregtes) 4 0 2 0 0 6 0 4 0 2 0 0 1 0 0 5 0 0 5 0 0 6 0 0 7 0 0 8 0 0 SEHRS with BLE 4 0 0 2-photon fluorescence spectrum of monomer R6G 2 0 0 0 5 0 0 6 0 0 7 0 0 8 0 0 SEHRlS spectra from single Ag nanoaggregate Intensity (counts) SEHRS, BLE, and SEHRlS spectra from three single Ag nanoaggregates 4 0 0 2 0 0 0 Wavelength / nm 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.

  22. Comparison of BLE of SEHRS with that of SERRS for identical single Ag nanoaggregates 4 0 0 1 0 0 0 2 0 0 5 0 0 0 0 4 0 2 0 0 2 0 1 0 0 0 0 6 0 2 0 0 0 4 0 1 0 0 0 2 0 0 0 1 5 0 1 0 0 1 0 0 5 0 5 0 0 0 200×200 mｍ SERRS with BLE SEHRS with BLE 1 photon fluorescence spectrum of monomer R6G 2 photon fluorescence spectrum of monomerR6G Identical four Ag nanoaggregates Intensity (counts) Intensity (counts) 4 0 0 2 0 0 2 0 0 1 0 0 0 0 5 0 0 6 0 0 7 0 0 8 0 0 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm Wavelength / nm BLE spectra of SEHRS are similar to those of SERRS for the identical nanoaggregates except fluorescence of monomer R6G.

  23. Conclusion 1 1. BLE spectra of SEHRSare 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 identicalnanoaggregates exceptmonomer 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) Questions 1.Why is monomer fluorescence of R6G not observed ? 2. Why is fluorescence of aggregates selectively observed ? 3. Why is SEHRS intensity comparable to SEHRlS intensity ?

  24. Our answers 1. Why is monomer fluorescence not observed ? Too small one-photon cross-section of monomer R6G: sBLE1 sBLE1 (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 sBLE2(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 sBLE1of monomer may be the reason for lack of observation of monomer fluorescence. 2. Why fluorescence of J-like aggregates is selectively observed ? Larger sBLE2of R6G J-aggregetes than that of monomers sBLE1 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, sBLE2 of J-like aggregates is expected to be ~60-100 times larger than sBLE1. This increasing can compensate the smaller sBLE2. Thus, this compensation may be the reason for selective observation of fluorescence from J-like agrgegates. 3. Why is SEHRS intensity comparable to SEHRlS intensity ? It will be discussed later.

  25. Intensity variations of SEHRS, BLE, and SEHRlS intensity 400 300 200 100 2 0 0 0 500 550 600 650 700 750 800 1 0 0 4000 2000 7 3 6 5 5 0 4 400 2 3 2 100 10 9 8 7 6 7 5 6 500 100 1 3 4 5 6 2x10 5 4 2 3 6 7 8 9 100 1 0 1 0 0 5 0 0 Large number of Ag nanoaggregates Single Ag nanoaggregate 500×500 mｍ 1 0 0 5 0 0 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm Wavelength / nm 100 SEHRlS intensity (counts) BLE intensity (counts) SEHRlS intensity (counts) BLE intensity (counts) SEHRS intensity (counts) SEHRS intensity (counts) SEHRS intensity (counts) SEHRS intensity (counts) Scattering of data points of single nanoaggregate measuremets is much larger than that of large aggregate measurements.

  26. Origin of Ag nanoaggregate by nanoaggregate variations Single Ag nanoaggregate Large number of Ag nanoaggregates Intensity (a.u.) 2st enhancement (plasmon resonance) Wavelength / nm Wavelength / nm 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.

  27. Spectral blue-shifts in plasmon resonance Rayleigh scattering and BLE spectra 4 0 0 0 . 0 8 6 0 3 0 0 0 . 0 6 4 0 2 0 0 0 . 0 4 2 0 1 0 0 0 . 0 2 0 0 0 1 0 0 0 . 1 0 . 0 8 5 0 0 . 0 6 0 . 0 4 0 . 0 2 0 2 0 0 0 4 0 0 0 . 1 2 1 5 0 0 . 1 3 0 0 0 . 0 8 1 0 0 2 0 0 0 . 0 6 5 0 0 . 0 4 1 0 0 0 0 . 0 2 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 2 0 0 0 . 0 4 0 . 1 1 0 0 2 0 0 0 . 0 2 0 . 0 5 0 0 . 0 8 4 0 0 1 0 0 0 3 0 0 0 0 0 . 0 4 2 0 0 2 0 0 5 0 0 2 0 1 0 0 0 0 0 0 5 0 0 6 0 0 7 0 0 8 0 0 5 0 0 6 0 0 7 0 0 8 0 0 Plasmon resonance BLE of SERRS BLE of SEHRS Relative intensity (counts) Intensity (counts) 4 0 0 2 0 0 0 5 0 0 6 0 0 7 0 0 8 0 0 5 0 0 6 0 0 7 0 0 8 0 0 Relative intensity (counts) Intensity (counts) 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm Wavelength / nm Wavelength / nm Blue-shifts in BLE spectra of SEHRS, BLE spectra of SEHRlS, plasmon resonance spectra coincidentally happened.

  28. Origin of the spectral blue-shifts of BLE Intensity (a.u.) 2st enhancement (plasmon resonance) Wavelength / nm 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.

  29. Conclusion (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. (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; Unclosed question Why is SEHRS intensity comparable to SEHRlS? (SEHRlS intensity should be several hundred times larger than SEHRS intensity.)

  30. Laser power dependence of SEHRS, BLE, and SEHRlS from large number of Ag nanoaggregates 500×500 mｍ 600 400 SEHRlS intensity (counts) 200 0 0 10 20 30 40 400 Incident laser power (kW/cm2) 400 300 300 300 200 Intensity (counts/2s) 200 BLE intensity (counts) 200 SEHRS intensity (counts) 100 100 100 0 0 0 0 10 20 30 40 0 10 20 30 40 550 600 650 700 Incident laser power (kWcm2) Incident laser power (kW/cm2) Wavelength / nm SEHRlS shows nonlinear response, but SEHRS and BLE does show nonlinear responses. 1. Why does only SEHRlS show nonlinear response? 2. Why does SEHRS and BLE not show nonlinear response?

  31. Why does SEHRS and BLEshow linear dependence even SEHRlS shows nonlinear dependence? 300 300 200 200 100 100 0 0 500 550 600 650 700 750 500 550 600 650 700 750 1. Why does only SEHRlS show nonlinear response? SEHRlS from mainly Ag nanoaggregates Ag 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 Intensity (counts/2s) Wavelength / nm Wavelength / nm 2. Why does SEHRS and BLE not show nonlinear response? Destruction of R6G molecules by laser excitation We 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 excitation We think this is an important candidate to explain the lack of nonlinear dependence.

  32. Simple estimation of saturation of nonlinear optical resonance sBLE2of R6G monomer = 2.0 x 10-50 cm4 sec/photon. EstimatedsBLE2of R6G monomer = 2.0 x 10-48 cm4 sec/photon. Incident photon density 6 MW/cm2 = 3.2 x 1025 photon/sec cm2 Expected enhanced local photon density 6 x 105MW/cm2 = 3.2 x 1030 photon/sec cm2 EffectivesBLE2of R6G 6.4 x 10-21 cm2 3.2 x 1030 photon/sec cm2 X 6.4 x 10-21 cm2 = 2.05 x 109 photon/sec Life time of R6G = 4 x 10-9 sec (R. F.Kubin,. J. Lumin. 1982, 27, 455.) Absorption 8.2 photon/molecule 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.

  33. Relationship between intensity of SERRS and that of SEHRS 500 100 1 0 0 5 0 0 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 200 1000 2000 Common 1st enhancement 1 5 0 1 0 0 5 0 0 SEHRS intensity (counts) C3 C4 1 0 0 6 0 5 0 4 0 0 SERRS intensity (counts) 5 0 0 6 0 0 7 0 0 8 0 0 2 0 Wavelength / nm Wavelength / nm 0 5 0 0 6 0 0 7 0 0 8 0 0 SEHRS SERRS 1st enhancement 532 nm 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 1064 nm 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. SERRS SEHRS

  34. Second enhancement in SERS Laser line Anti-Stokes Stokes Intensity (a.u.) Wavelength / nm 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. Wavelength / nm = Band shape of plasmon resonance

  35. Comparison between background light-emission spectrum of SEHRS and that of SERRS from large number of Ag nanoaggregates 500×500 mｍ SERRS with background light-emission and Fluorescence of R6G Normalized intensity) Wavelength / nm Residual spectrum after subtracting ISEHRS(l) from ISERRS(l) is similar to fluorescence spectrum of monomer R6G R6G monomers cannot have SEHRS activity?

  36. Conclusion 2 Polarization (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. 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).

  37. Manners of disappearance of SEHRRS with background light-emission 8 0 8 0 0 6 0 6 0 0 4 0 0 4 0 2 0 0 2 0 0 0 8 8 8 0 0 0 4 4 4 0 0 0 0 0 0 4 0 0 5 5 5 0 0 0 0 0 0 6 6 6 0 0 0 0 0 0 7 7 7 0 0 0 0 0 0 8 8 8 0 0 0 0 0 0 8 0 3 0 0 4 0 2 0 0 1 0 0 0 1 0 0 0 5 0 0 5 0 0 6 0 0 7 0 0 8 0 0 8 0 0 2 0 0 0 6 0 0 1 5 0 0 4 0 0 1 0 0 0 2 0 0 C3 C4 0 5 0 0 1 0 0 0 6 0 5 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 2 0 Wavelength / nm Wavelength / nm 0 5 0 0 6 0 0 7 0 0 8 0 0 SERRS SEHRS A1 A2 Nanoaggregate A Intensity (counts) A3 A4 B1 B2 Nanoaggregate B Intensity (counts) B3 B4 C1 C2 Nanoaggregate C Intensity (counts)

  38. Relationship between SEHRRS intensity and peak wavelength of plasmon resonance bands 6 0 0 1 5 0 4 0 0 4 0 0 1 0 0 0 . 1 2 0 . 1 3 0 0 0 . 0 8 2 0 0 5 0 2 0 0 0 . 0 6 0 . 0 4 1 0 0 0 . 0 2 0 0 0 0 6 6 0 0 0 0 7 7 0 0 0 0 5 0 0 6 0 0 7 0 0 8 0 0 E F Background light emission intensity (counts) SEHRRS intensity (counts) Peak wavelength / nm Peak wavelength / nm Plasmon resonance maxima 1064 nm Wavelength / nm SEHRRS and background light-emission 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 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.

  39. Relationship between SERRS and background light-emission 0 A Background light emission intensity (counts) 0 2 0 2 SERRS intensity (counts) 2000 Common 1st enhancement 1 5 0 1 0 0 5 0 0 2 0 0 SERRS with background light-emission 532 nm 532 nm 5 0 0 6 0 0 7 0 0 8 0 0 Wavelength / nm 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.

  40. 1 A 1 0 6 6 6 6 6 6 6 6 0 0 0 0 0 0 0 0 0 1 B 4 4 4 4 4 4 4 4 0 0 0 0 0 0 0 0 1 2 2 2 2 2 2 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 C 1 Normalized intensity (a.u.) 660 0 0 1 D Normalized intensity (a.u.) 640 1 Luminescence maximum (nm) 620 0 0 1 1 E 600 0 0 1 580 F 1 560 0 0 600 620 640 660 680 Wavelength (nm) Plasmon resonance maximum (nm) 5 0 0 6 0 0 7 0 0 8 0 0 600 700 650 550 0-2 s 2-4 s 4-6 s 6-8 s Intensity (counts) 8-10 s 10-12 s 12-14 s 14-16 s Wavelength / nm

  41. Origin of SERRS background light-emission 1 0 1 0 1 0 1 Normalized intensity (a.u.) 0 1 0 1 0 1 1 Normalized intensity [arb.u.] 0 0 50 100 150 Polarization angle q/degree Fluorescence spectrum of R6G in an aqueous solution SERRS image (a) adsorbed molecule metal surface S1 state EP ECT CT state hwi hwl EF electron S0 state E (b) adsorbed molecule metal surface S1 state EP hwi 550 600 650 700 Wavelength (nm) hwl We attributed the three background light-emission to fluorescencecoupled with plasmon and emitted from monomer, dimer, and two kinds of higher-order aggregates of R6G molecules on an Ag surface. EF S0 state electron E T. Itoh et al, JPC B, 110, 21536, 2006

  42. Polarization SERS発現メカニズム－電磁場増強モデル－ + + Electric field + + ① 表面プラズモン共鳴 （SPR） Incident light 102～103程度の電場増強 - - - - ② ③ 108～1010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 時間領域差分法による電場計算

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