Outline. Raman Scattering Spectroscopy Resonant Raman Scattering: Surface Enhaced Raman Scattering Applications. RRS in crystals RRS in molecules

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1 Outline Raman Scattering Spectroscopy Resonant Raman Scattering: RRS in crystals RRS in molecules Surface Enhaced Raman Scattering Applications Charging and discharging of single molecules probed by SERS Ultrasensitive Detection of Molecules on Surfaces The ferroelectric phase transition in nanostructures Pump & probe spectroscopies and the search of phonon lasing

2 Raman scattering and the phase transition in ferroelectric BaTiO 3 /SrTiO 3 Superlattices A. Bruchhausen, A. Fainstein, and S. Tinte, A. Soukiassian, X. X. Xi, and D. Schlom IB-CAB-CNEA, Bariloche, Argentina Universities at Penn and Cornell, USA

3 Multifunctional oxides: Thin films

4 Multifunctional oxides: Critical thickness?

5 Multifunctional oxides: The nanoscale

6 Experimental challenge: MBE growth Reactive Cornell University (Darrell Shlom s Group) Int. RHEED (arb. u.) (BaTiO 3 ) 8 (SrTiO 3 ) 4 Ti shutter open Ba shutter open Sr shutter open (BaTiO 3 ) 8 (BaTiO 3 ) 8 (a) (b) (SrTiO 3 ) 4 Tiempo (sec.) (SrTiO 3 ) 4

7 Experimental challenge: Epitaxial quality TEM (BTO 5 / STO 4 ) x 25

8 Vibrational spectroscopy: Raman BaTiO 3 Tenne et al., J. Am. Ceram. Soc. 91,1820 (2008)

9 Experimental challenge: gaps in the UV Tenne, Bruchhausen et al., Science 313, 1614 (2006)

10 Experimental challenge: gaps in the UV High-resolution UV-Raman UV-enhanced CCD gr/mm gratings Tenne, Bruchhausen et al., Science 313, 1614 (2006) HeCd 325nm laser (50mW) All optics UV-back-reflection coated

11 Experimental challenge: gaps in the UV (BTO 5 /STO 4 )x25 (BTO 5 /STO 4 )x25 UV excitation λ L =351.1nm SrTiO 3 substrate Visible excitation λ L =514.5nm

12 MBE and UV-Raman in ferroelectric nanostructures Ferroelectric superlattices of excellent quality can be grown by state-of-the-art molecular beam epitaxy (MBE) UV-Raman allows the observation of phonons in ultrathin oxide multilayers

13 Optical phonon modes

14 Experimental challenge: gaps in the UV (BTO 5 /STO 4 )x25 (BTO 5 /STO 4 )x25 UV excitation λ L =351.1nm SrTiO 3 substrate Visible excitation λ L =514.5nm Tenne, Bruchhausen et al., Science 313, 1614 (2006)

15 SLs: temperature dependence of Raman modes Tenne, Bruchhausen et al., Science 313, 1614 (2006)

16 Determination of T c TO 4 mode (~540 cm -1 ) σ Raman P 2 Intesity [arb. units] 5K 400K Raman shift [cm -1 ] SL: (BTO 2 / STO 13 ) x 20 TO 4 - Raman Int. [arb. units] Ferroelectric mean field theory: P = P ( T T ) 1/ / c T c Temperature [K]

17 Tuning of T c : strain, size, coupling Tc decreases with n due to dipole-dipole interaction BTO strained 2%

18 Tuning of T c : strain, size, coupling Tc decreases with n due to dipole-dipole interaction m=4 BTO-BTO coupling BTO strained 2% m=13

19 Ferroelectric transition in SrTiO 3 /BaTiO 3 superlattices The selection rules that apply to the Raman scattering of optical phonons in titanates allow the determination of T c The ferroelectric T c can be tailored to vary more than 500K by the appropriate tuning of SrTiO 3 and BaTiO 3 layer thickness (size reduction, coupling, strain)

20 QUESTION # 3 From what you have learnt of Raman scattering, how would you expect that a phase transition be reflected in a Raman experiment? Consider different types of transitions.

21 Outline Raman Scattering Spectroscopy Resonant Raman Scattering: RRS in crystals RRS in molecules Surface Enhaced Raman Scattering Applications Charging and discharging of single molecules probed by SERS Ultrasensitive Detection of Molecules on Surfaces The ferroelectric phase transition in nanostructures Pump & probe spectroscopies and the search of phonon lasing

22 Control of phonon emission in cavities N. D. Lanzillotti-Kimura, M. F. Pascual Winter, G. Rozas, A. Fainstein, A. Huynh, B. Perrin, B. Jusserand, A. Lemaitre, A Soukiassian, X. X. Xi, and D. G. Schlom INSP & LPN, Paris LPO (CAB)-CNEA, Bariloche Cornell U., USA

23 Background A. Kent, M. Henini et al., PRL 96, (2006) A. Huyhn et al., PRL 97, (2006).

24 Background A. Kent, M. Henini et al., PRL 96, (2006) Next time, Mr. Bond, I ll use a SASER

25 SLs as acoustic phonon mirrors 1,0 l l a b = λ / 4 = 3λ / 4 Acoustic reflectivity 0,8 0,6 0,4 0,2 stop-band 0, Energy [cm -1 ] 4 10 Energía [cm -1 ] K [π nm -1 ] u(z) 2 [u. arb.] Position [nm] N R = 1 4Z + O( Z 2 4N v2ρ2 v ρ Z GaAs / AlAs = 1 1 R ) ρ [kg/m 3 ]

26 Acoustic phonon nanocavity l l a b = λ / 4 = 3λ / 4 l c = nλ / 2 F L = π d eff R (1 R) 3000 τ c = L eff vln( R) L eff v 500 M. Trigo et al., PRL 89, (2002) A. Fainstein and B. Jusserand, Light Scattering in Solids IX

27 Ultrafast optics facility Facilidad de Optica Ultrarrápida Lab. Espectroscopía Raman

28 Coherent phonon generation with ultrafast laser pulses Probe Pump FT Tenne, Bruchhausen et al., Science 313, 1614 (2006) A. Huyhn, D. N. Lanzillotti-Kimura et al., PRL 97, (2006).

29 Coherent acoustic phonon generation Probe Pump FT A. Bruchaussen et al., PRL 101, (2008) N. D. Lanzillotti-Kimura et al., PRL 104, (2010) A. Huyhn, D. N. Lanzillotti-Kimura et al., PRL 97, (2006).

30 Coherent control: Turning on and off confined phonons Probe Pump2 Pump1 Amplitude (arb. units) Pump1 + Pump2 in phase Pump1 Pump 1 + Pump2 in counterphase 0 0,25 0,30 0,35 0,40 0,45 0,50 0,55 0,60 0,65 0,70 Energy (THz) * Cavity mode amplitude (arb. units) Fixed Pump Variable Pump ,50 0,75 1,00 1,25 1,50 1,75 2,00 2,25 Relative phase (λ) Lanzillotti-Kimura et al., PRB Rapid Comm., in press

31 Acoustic cavities and coherent phonon generation Nanocavities can be grown by epitaxial techniques that confined hypersound in the GHz-THz range (nm wavelength) These vibrations can be coherently generated and their dynamics studied with pump&probe techniques based on ultrafast lasers

32 The Raman-SASER SASER: Sound Amplification by Stimulated Emission of Radiation laser Raman Phonon P f N laser ( N + 1)( N + 1) Raman Phonon N. D. Lanzillotti-Kimura et al., PRL 104, (2010)

33 GaAs/AlAs optical+acoustic microcavities Optical spacer n n optic 2 Z GaAs / AlAs = 1 v2ρ2 v ρ 0.84 acoustic Z GaAs / AlAs = A. Fainstein et al.,prl 75, 3764 (95) A. Fainstein et al.,prl 78, 1576 (97) A. Fainstein et al.,prl 86, 3411 (01)

34 Confined acoustic phonons FT 1 st 3 rd 5 th Q phonon > 1000

35 Time dependence of phonon population: WFTs 1. Standard GaAs bulk substrate 2. GaAs microcavity

36 Non-exponential coherent phonon time evolution Bulk GaAs GaAs Microcavity

37 Non-exponential coherent phonon time evolution Bulk GaAs GaAs Microcavity

38 Pump laser power dependence

39 Pump laser power dependence

40 Complex coupled mode dynamics

41 Cavities of light and sound Cavities can be designed that confine acoustic phonons and photons of the same wavelength (nm-thz optomechanics) Complex phonon dynamics has been observed, with possible evidence of phonon stimulation

42 Acknowledgements Aristide Lemaitre Daniel Lanzillotti-Kimura Axel Bruchhausen Florencia Pascual-Winter Guillermo Rozas Bernard Jusserand Darrel G. Schlom Bernard Perrin

43 Theory of coherent phonon generation in heterostructures In a SL: M. F. Pascual Winter. PHd Thesis IB (2009)

44 Theory of coherent phonon detection in heterostructures In a SL: M. F. Pascual Winter. PHd Thesis IB (2009)