Optimizing light harvesting for high magnetooptical performance in metal-dielectric magnetoplasmonic nanodiscs

Transcription

1 Optimizing light harvesting for high magnetooptical performance in metal-dielectric magnetoplasmonic nanodiscs Alfonso Cebollada, Juan Carlos Banthí, David Meneses, Fernando García, María Ujué González, Antonio García-Martín, and Gaspar Armelles IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, E Tres Cantos, Madrid, Spain

2 Magneto-Plasmonic structures Systems where constituents with Plasmonic and Ferromagnetic (Magneto-Optical) properties coexist Magneto Plasmonics

3 Group Members A.Garcia-Martin J.C.Banthí A.Kaidatzis G.Armelles Staff scientists J.M. Garcia-Martin N. Sousa J.Fernandez R.Fermento PhD Students + Post docs A.Vitrey M.U.Gonzalez B. Caballero A.Cebollada D.Meneses D.Martin Prof. E.Muñoz (visiting scientist) A. Calle J.V.Anguita P.Prieto Technician Staff (Collaboration) E.Ferreiro

4 Surface Plasmons Electromagnetic waves associated to a collective oscillation of conduction electrons localized at the interface between a media ε r <0 (metal) and a media ε r >0 (dielectric material) k sp Propagating or Surface Plasmon Polaritons (SPP): continuous layers Localized Surface Plasmons (LSP): Nanoparticles/Nanoentities

5 Propagating surface plasmons (SPP) ε d > 0 ε r m < 0 k s -In plane propagating excitation but localized at the interface: surface localized waves. -Can be excited only if both frequency and wavevector of the exciting light match those of the SPP. k s > k light k s = k light + k ω/ω k light = ω k s * n d = k light c ε m ε + ε d m Grating Prism Defect Light k// = k sp k = nsin // c ω θ θ K (nm -1 ) (Kretchsmann)

6 Localized Surface Plasmons (LSP) -Occur when the incident photon frequency is resonant with the collective excitation of the conduction electrons of the particle. -Can be excited with light of appropriate frequency irrespective of the wavevector of the exciting light. -Localized excitation.

7 The Lycurgus cup (British Museum. 4th Century) When illuminated from outside cup appears green, but turns into red when illuminated from inside. Labors of the Months (Norwich, England, ca. 1480) The ruby color is probably due to embedded gold nanoparticles. 1,0 I A R Absorption 0,8 0,6 0,4 0,2 0,0 spheres T 2,0 2,2 2,4 2,6 2,8 3,0 Energy (ev)

8 Messages: Both LSP and SPP are characterized by: -Strong localization of the electromagnetic field in subwavelength volumes Enhanced electromagnetic field due to its localization. -Very sensitive to the metal dielectric interface. k s = k light ε d ε m + ε m Application in Optical nanodevices + Sensors Absorb (emit) light: (nano)antennas.

9 Signature of plasmon excitation Reflectivity (%) Propagating plasmons in continuous films (Kretchsmann) nm Co 50 nm Au Incident angle Extinction (arb. units) Typical plasmonic material: noble metal Localized plasmons in nanodiscs Energy (ev) D = 60 nm Au Co h = 32 nm

10 Magneto-Plasmonic systems Noble metals: Exhibit intense plasmon resonances Low optical absorption: Long propagation length Narrow Resonances (Optical constants) No MO activity (MO constants) Reflectivity (%) nm Co 50 nm Au Incident angle Ferromagnetic metals: Weak plasmon resonances High optical absorption: Shorter propagation length Boarder resonances MO at low magnetic fields Reflectivity (%) nm Au / 6 nm Co / 6nm Au 50 nm Au Incident angle

11 Magnetoplasmonics: Materials explored Noble metals: Au, Ag. Low optical absorption. No MO activity Ferromagnets: Metals: Fe, Co. High MO activity. High optical absorption. Ferromagnet Take the best of each counterpart: ε εxx ε = εxy ε 0 0 xy xx ε 0 0 zz Noble metal

12 MO effects Polar Longitudinal Transverse (ΔR/R) E ε k E ε k E z θ k θ 0 θ k θ 0 y M M M x 0,30 θ; ε; ΔR/R -0,02 0,00 0,02 Magnetic field (Ts) Kerr Ellip. (º) 0,15 0,00-0,15 1,8 2,4 3,0 Energy (ev) εxx ε ε = εxy ε 0 0 xy xx ε 0 0 zz

13 Magnetic Modulation of Plasmon properties: ACTIVE PLASMONICS Magneto Plasmonics Plasmonic properties depend on the constituents dielectric tensor (which in the case of the MO component can be activated by an external magnetic field). k s = k light ε m ε + ε d m ε εxx ε = εxy ε 0 0 xy xx ε 0 0 zz

14 Plasmon effects in MO properties: ENHANCED MO ACTIVITY Magneto Plasmonics MO activity basically proportional to the EM field intensity at the MO active componet*. Φ ( z) ε ( xy, ) E ( zxy,, ) E ( zxydxdy,, ) S ( ε 0) MO MO s p GOAL: Exploit light harvesting properties of plasmonic systems to maximize the EM field at the MO layer!!! * thin film approximation

15 J.Fernández R.Fermento E. Ferreiro MO active dielectrics Magnetoplasmonic Activity in Systems with Localized and Extended Surface Plasmons MO and SPP k modulation in continuous layers EM field distribution in nanodiscs N. Sousa B. Caballero (Col. MoLE (Col. Cuevas UAM) UAM) D.Martin Magnetoplasmon interferometry and sensing applications Theoretical developments NS. Coupled diplole method BC. Scattering Matrix Techniques D.Meneses Colloidal lithography A.Vitrey Near field studies of magnetoplasmonic structures A.Kaidatzis PLasmon ASsisted MAgnetic Recording Metal-dielectric magnetoplasmonic nanoresonators J.C.Banthí

16 Magnetoplasmonic effects in systems with propagating plasmons Enhanced MO activity upon SPP excitation Ag vs Au Epitaxial vs polycrystalline Magnetic field wavevector modulation J.B. González-Díaz et al., Physical Review B, 76 (2007) E. Ferreiro Vila et al. IEEE Transactions on Magnetics, 44 (2008) E.Ferreiro-Vila et al., Physical Review B, 80 (2009) E. Ferreiro-Vila, et al., Physical Review B, 83 (2011)

17 Magnetoplasmonic effects in systems with propagating plasmons Magnetic field modulation of the SPP wavevector: Active Plasmonics Probing the EM field within a continuous gold layer V.V. Temnov et al; Nature Photonics 4 (2010) 107 D. Martín-Becerra et al., Appl. Phys. Lett. 97, (2010)

18 Magnetoplasmonic effects in systems with propagating and localized plasmons G.Armelles, et al., Optics Express, 16 (2008) G Armelles et al., Journal of Optics A: Pure and Applied Optics, 11 (2009)

19 Magnetoplasmonic effects in systems with propagating plasmons SENSING B.Sepúlveda et al., Opt. Lett. 31 (2006) D. Regatos et al., Journal of Applied Physics, 108 (2010) M.G.Manera et al., Journal of Materials Chemistry, 21 (2011)

20 Magnetoplasmonic effects in systems with localized plasmons Peak in the LSPR spectral region 16 nm Au 10 nm Co 6 nm Au 85nm (ϑ 2 +ϕ 2 ) NP /(f*(ϑ 2 +ϕ 2 ) CF ) ,5 2,0 2,5 3,0 Energy (ev) nm LSPR excitation: strong concentration of the EM field in the nanodisc. Enhancement of the MO activity in the LSPR spectral region with respect to continuous layer (with only 20% the amount of Co) (J.B. González-Díaz, et al.; SMALL 4 (2008) 202)

21 Magnetoplasmonic effects in systems with localized plasmons MO activity of PURE Au nanodisks B. Sepúlveda et al., Phys. Rev. Lett. 104 (2010)

22 Magnetoplasmonic effects in systems with localized plasmons EM field distribution within the nanodisc LSPR off LSPR on Vertical EM field distribution: - U shaped -varies in the nanometer scale -asymmetric due to the presence of a substrate (FDTD simulations: Au disc, h = 55 nm, φ = 150 nm ) D.Meneses et al. SMALL (in press) DOI /smll

23 Experimental mapping of the EM field distribution outside the nanostructure (SNOM) or extract its integrated vertical distribution (TEM-EELS)... but not straightforward to experimentally probe the EM field inside the nanostructure

24 Effect of the insertion of a 6 nm Co layer in the EM field distribution Co bottom LSPR on LSPR on Co center Co top Co insertion does not vary: - U shape -Variation in the vertical direction in the nm scale -Substrate induced asymmetry Non perturbative probe LSPR on D.Meneses et al. SMALL (in press) DOI /smll

25 MO activity as a function of Co position: Continuous layers vs discs D= 130 nm 0,20 0,08 h= 54 nm d2 d1 Au Co Au Z Co Φ (deg) 0,15 0,10 Φ (deg) 0,06 Cr 0,05 0, Z Co (nm) z Co (nm) D.Meneses et al. SMALL (in press) DOI /smll

26 Can we tailor/control this EM field distribution?? Can we maximize the EM field at the MO active component and minimize it in the others?? Our first approach: insertion of a dielectric layer

27 Metal-dielectric nanodiscs A.Dmitriev, et al. Small 3 (2007) 294

28 A.Dmitriev, et al. Small 3 (2007) 294

29 Metal-dielectric nanodiscs Our approach: insertion of Co layer in the Metal-dielectric nanodisc 20 nm SiO 2 15 nm Au 10 nm Co 10 nm Co 15 nm Au J.C.Banthí et al. Advanced Materials (accepted)

30 Colloidal-hole lithography process Deposition of a Au/Co/Au trilayer PMMA A4/BK7 O 2 Plasma O 2 Plasma (RIE) After deposition trilayer, Lift- off procedure with aceton PDDA Tape striping º Au Coat Polystyrene colloidal particles

31 Metal-dielectric nanodiscs Ø 110 nm, h 68 nm 15 nm Au 10 nm SiO 2 10 nm Co 10 nm SiO 2 15 nm Au J.C.Banthí et al. Advanced Materials (accepted)

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35 0,2 (a) Experimental (b) Theoretical 0,4 Extinction, log(i ref /I) 0,1 0,0 0,3 (c) LWP HWP HWP (d) LWP HWP 0,3 0,2 0,1 0,0 0,3 - Log(T) I Φ (deg) 0,2 LWP LWP HWP 0,2 I Φ (deg) 0,1 0,1 0, ,0 Wavelength (nm) Wavelength (nm) J.C.Banthí et al. Advanced Materials (accepted)

36 0,2 (a) Experimental (b) Theoretical 0,4 Extinction, log(i ref /I) 0,1 0,0 0,3 (c) LWP HWP (d) LWP HWP 0,3 0,2 0,1 0,0 0,3 - Log(T) I Φ (deg) 0,2 0,1 LWP HWP HWP 0,2 0,1 I Φ (deg) LWP 0, Wavelength (nm) 0, Wavelength (nm) J.C.Banthí et al. Advanced Materials (accepted)

37 EM field redistribution J.C.Banthí et al. Advanced Materials (accepted)

38 Figure of Merit: MO activity vs optical losses J.C.Banthí et al. Advanced Materials (accepted)

39 Summary: Key issue: EM field distribution. EM field engineering by insertion of a dielectric layer + adequate stacking of all different layers Maximize the EM field at the MO active layer Reduce the EM field at the non-mo layers. Large MO activity + low optical losses magnetoplasmonic system