Broadband light trapping and photon harvesting induced by self-organised dielectric and plasmonic nanostructures. Francesco Buatier de Mongeot

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1 Broadband light trapping and photon harvesting induced by self-organised dielectric and plasmonic nanostructures Francesco Buatier de Mongeot Dipartimento di Fisica - Università di Genova Via Dodecaneso 33, Genova Italy buatier@fisica.unige.it PLESC Trento

2 Acknowledgements Prof. Davide Comoretto Christian Martella Carlo Mennucci Diego Repetto Valentina Robbiano Daniele Chiappe Andrea Toma Angelica Carrara Emanuele Solari Andrea Voiello CNR, Messina Financial support

3 Photon harvesting with Nanoscale metallic clusters Localised Surface Plasmon Resonances Metal Nanoparticle arrays: Size D<<l (wavelength) Localised Surface Plasmon Resonance A) Light Trapping by Scattering At resonance huge increase of scattering Cross section Collective & resonant oscillation of conduction electrons in metal nanoparticles Polarizability of Nanosphere 3V m h 4 2 h m Resonance wavelength Re( m) 2 h Frohlich conditon H. A. Atwater and A. Polman, Nature Mater 9, (2010) S.A. Mayer Plasmonics: Fundamentals and Applications Springer New York (2007)

4 Tailoring the plasmonic resonance E-field E-field Anisotropic Polarizability of ellipsoids V 4 m h x, y, z L ( ) h m h L geometrical depolarization factor (for sphere L=1/3) Aspect ratio (L γ ) The Localised Surface Plasmon Resonance could be tuned by changing (i) the metal or the host medium (ii) the shape of the nanoparticles Emphasis: Self-organised Nanofabrication methods able to grow arrays of nanoparticles with tailored plasmonic response

5 Plasmon enhanced Photon harvesting (B) Local field enhancement Light concentration using particle plasmons. 25 nm Au NP Plasmon enhanced photon absorption in PV devices Plasmon enhanced bio-sensing e.g. Fluorescence Raman spectroscopy - SEIRA H.A. Atwater, A.Polman Nature Materials 9, (2010)

6 633nm Raman band Plasmon Plasmon Enhanced Raman (SERS) (B) Local field enhancement Extinction spectra TE TM CNR, Messina Transmittance (%) Normalized intensity 3 2x x x Polarised SERS Spectra Au nanocrescents, TM Au nanocrescents, TE Reference Au film Wavelength (nm) Anisotropic SERS amplification (maximum for TM-pol) Disconnected nanoclusters at the border of the crescent are hot spots for SERS Raman Shift (cm -1 ) Giordano et al ACS Appl Mater Interfaces. 2016, 8, 6629

7 Plasmon enhanced Photon harvesting (C) hot electron injection Non Radiative decay of LSPR Hot electron photo-generation Injection across Au-Si Schottky barrier Harvesting of sub bandgap NIR photons r<<l

8 Outline Self-organized physical nanopatterning by defocused Ion Beam Sputtering Self-organized plasmonic nanostructures for light harvesting application Self-organized Au nanowires arrays transparent nanoelectrodes Au nanowire for plasmon mediated hot-electron generation and IR harvesting Tailoring plasmonic arrays from the Visible to NIR and MIR range: Confinement of Au nanowires by glancing angle deposition Self-organized dielectric nanostructures for light harvesting application Au self-organized Nanowires as stencil masks for nanopatterning glass substrates Nanopatterned glass superstrates for light trapping in Amorphous:Si Thin Film Solar cells

9 Ripples & ripples Self-organisation from the macro-scale to the nanoscale Wind Vs. Ion beam Sputtering Desert dunes Glass 500 nm 50 cm

10 Dipartimento di Fisica, Via Dodecaneso 33, Genova, Italy Nanostructuring surfaces by Ion Beam Sputtering Conventional picture Amorphous substrates Ar + Erosive instability Ar + Erosion rate is curvature dependent: Roughening The spatial distribution of the energy transferred from the impinging ions to the substrate causes the faster erosion of the bottom of a trough vs. the crest Relaxation Thermally/ion beam activated relaxation, Viscous flow, Balistic smoothing Down hill mass transport & Smoothing Interplay between erosive instability & diffusive relaxation: Formation of periodic structures

11 Surface Morphology Reorganization h t n x 2 h 2 x n y 2 h 2 y K th 4 h 4 x thermally activated surface diffusion term U. Valbusa et al. J Phys.: Condens. Matter 14, 8153 (2002) coefficients n x n y govern the dependence of the erosion rate on the curvature of the surface Amorphous materials: the ripple orientation is defined by the directionality of the ion beam: For small the ripples are oriented perpendicular to ion direction For large ripples parallel to it Si (001) Ion beam projection Si (001)

12 Au nanowire arrays by defocused Ion Beam Sputtering Ar + ions, E=800 ev, θ= 82 Ar + Au Ar + Ion Dose Glass Au NWs IBS nanopatterning of polycystalline metal film Self-organized Au NWs on glass : transparent electrodes Direct Trasmittance (%) In-Situ transmittance spectra 30min 45min (TM) (TE) 47min (TM) (TE) Wavelength (nm) Ion Dose R T 100 Ω/sq R L 1 5 Ω/sq F. Buatier.et al. Patent US B2 (2014) D.Chiappe et al.small 9, (2013)

13 Z (nm) Self-organized Au Nanowires/Ti/Si Shottky junction NIR broadband plasmonic response: hot electron generation nm Au Si Ti IBS - Adhesion layer - Schottky barrier Au/Ti Nanowires (TM) 1000nm Z[nm] 1000nm Silicon 2.0µm 2.0µm Au 90nm nm 0.00 nm 0nm Au NWs 0.00 nm 20 Si:n 10 0 Silicon Z X[µm] ( m) 6 8 Plasmonic resonance: l R nm Sheet resistance: R T 70 Ω/sq

14 -Broadband response Self-organized Au Nanowires/Ti/Si Shottky junction NIR plasmonic absorption: hot electron generation TE TM Silicon Ag In collaboration with A.Toma - IIT Plasmonic resonance: Max l R nm Preliminary results: - 40% relative photocurrent increase for TM polarization -Possible role of Hot electrons

15 A different approach to plasmonic structures (i) High aspect ratio faceted dielectric templates (Ion Beam sputtering) (ii) A playground for confinement of Plasmonic nanostripes: glancing deposition Goals: -Tailoring plasmonic response from visible to MIR -narrow-band response, -coupled structures increase field enhncement

16 Self-organised Nanopatterning of soda-lime glass templates by Ion Beam Sputtering (IBS) Old scenario: Direct IBS on glass t = 3600 s T < 250 C Θ = 30 Low amplitude disordered pattern Novel IBS conditions: t = s T = 400 C Θ = 30 AFM topography 157nm Faceted ripples

17 Plasmonic Nano-Wires (NW) confinement glancing angle deposition Optical extinction of NWs NW seen by SEM λ LSPR = 620 nm NW width distribution W med = 100 nm RMS 30 nm

18 Tailoring Nano-Wires LSP Resonance role of Au thickness(d) Aspect Ratio e shift LSPR Optical extinction (pol. TM) SEM λ LSPR = 620 nm λ LSPR = 560 nm

19 Tailoring Nano-Wires LSP Resonance role of nanostripe width(w) Optical extinction NW on narrow facet (SEM) λ LSPR = 620 nm λ LSPR = 550 nm

20 Optical response of Nano-Wires finite element simulation Optical trasmittance NW array (d=22 nm, w=100 nm) Experiment Simulations Giuseppe Della Valle Politecnico di Milano Near field enhancement (simulation) Simulation E/E 0 (I/I 0 ) max 50 «Hot spot» lower corners

21 Coupling plasmonic nanowires: Nano-Sandwiches (NS) Local field enhancement Optical exticntion NS ω+ Hybridization of dipolar modes ω- electric dipole ω* magnetic dipole Ref.: A.Dmitriev et al., Small, Vol. 3, 2007

22 Nano-Sandwiches: growth & optical properties Nano-Sandwiches confined by glancing deposition NS Optical transmittance (pol. TM) ω 0 ω* anosandiwiches - SEM cross section ω- dipolar magnetic ω+ dipolar electric Conformal growth

23 Tailoring Nano-Sandwich plasmon response into NIR the role of oxide thickness (h) NS Optical transmittance (pol. TM) ω- Electric dipolar mode: almost unaffected Magnetic dipolar mode resonance shifted tinto NIR ω+

24 Tailoring Nano-Sandwich plasmon response into NIR the role of Au nanostripe thickness (d) NS Optical transmittance (pol. TM) h SiO2 44 nm ω+ ω-

25 Tailoring Nano-Sandwich plasmon response into NIR the role of dielectric constant of spacer layer Simulated spectrum of nanosandwich (w=100nm, d=30nm, h SiO x 44nm) Simulations Giuseppe Della Valle Politecnico di Milano Experiments in progress Preliminary results confirm modeling

26 Near field Nano-Sandwiches (simulation: w=100nm,d=22nm, h SiO x =44nm) Modo elettrico E/E 0 E/E 0 Modo magnetico Simulations Giuseppe Della Valle Politecnico di Milano λ=550nm (I/I 0 ) max 300 λ=820nm Natural candidates for plasmon enhanced spectroscopies - Shifting Au hot spot resonance into NIR

27 Can we shift resonance towards MIR? Parallel polarization

28 Infrared Plasmonics and SEIRA spectroscopy E field parallel to nanoantenna octadecanethiol (ODT) Optical response of nano-antenna nanoantenna ODT vibrations Ref.: F.Neubrech, A.Pucci, Phys.Rev.Lett., Vol. 101, 2008

29 Medium IR transmittance of Nano-Wire array in collaboration with prof. Annemarie Pucci, Università di Heidelberg (Ger) SEM of nanowires Optical trasmission Band of ODT vibrations Nanowire length exceeds many μm Interconnected network No resonance in MIR Similar to continuous Au film

30 Glass template : confinement of selforganised MIR nanoantennas IBS 30 minuti Glass T = 400 C Θ = 30 IBS 5 minuti Glass nm L L 400nm w = 80 nm λ = 225 nm L 3-5 μm w = 40 nm λ = 100 nm L < 1 μm 0.00 nm

31 Self organised nanoantennas for SEIRA: morphology & optical properties SEM NW Au Flux MIR optical transmission Segnale ODT Short nanoantennas L ~ 500 nm in collaboration with prof. Annemarie Pucci, Università di Heidelberg (Ger)

32 SEIRA signal from ODT on Self-organised nanoantennas SEIRA vibrational spectra in collaboration with prof. Annemarie Pucci, Università di Heidelberg (Ger) 5,5% SEIRA Intensity Zona (%) (K=2926 cm -1 ) Top 4,6 Middle 5,0 Bottom 5,5 20 fold enhancement compared to IRRAS (InfraRed Reflection Absorption Spectroscopy) of ODT on Au film 0,3 % SEIRA on best litographic substrates 10 %

33 Conclusions Two Self-organised approaches based on Ion Beam Sputtering : Au nanowire arrays with tailored LSP response in visible NIR (transparent electrodes & hot electron injection) Coupled nanostructures (Nano-Sandwich) allow to reshift response in NIR & strong amplification of near field The self-organised Au nanowire arrays behave as optical nanoantennas resonant in MIR Amplification of SEIRA signal of ODT comparable to state of the art lithographical nanoantennas