Arto V. Nurmikko* Brown University - Home | Quantum … · Arto V. Nurmikko* Brown University Jeon...

Nanoscale Energy Conversion Workshop – Sept 2006, Nice

Nanophotonics – so what, and for what?

Arto V. Nurmikko* Brown University

Jeon et al (1993)

ZnSe green-bluecw QW diode laser

my own lesson in life: new technologies are unpredictable vs. long term impact


Major Photonics Application/Technologies

Focus on “active devices” (vs. passive ‘optical wires’):

Displays

λ(µm)0.2 0.6 1

Optical storage

IC LithographyEtc.

Optical telecom

Photovoltaics

• mostly single crystal epitaxy• e.g. highest diode laser efficiency >70% (VCSEL)• e.g. multijunction tandem PV cell ~40% (Spectrolab), and poly-Si• e.g. white light inorganic and organic LEDs


Nanophotonic Devices – Is smaller better ?

FP/DFB lasers/VCSELs/RCLEDs

• smaller is better only if it is a lot better (performance, cost, application)• otherwise (and additionally) need and explore novel application spaces

Photonic Crystal LEDsand diode lasers

Nanophotonic regime

1) Require creative fabrication strategies for:

(i) Nanomaterial/composite assembly(ii) Electrical access/junctions(iii) nano-macroscale bridge for process

flow (compatibility issues)

2) Look for enhanced light-matter coupling

‘few photon’ (single photon)coherent sources

Dec

reas

ing

sour

ce s

ize

~λ

<λ

at least 2-dimensions of (individual) elements are <<λ


Top-Down or/and Bottom-Up Fabrication

1 nm 10 nm 100nm 1000nm

Direct nanomaterialssynthesis

1x1 µm2

GaN QDs

High resolutionlithography (ebeam)

InGaN QWs

Challenge: assembly, contacts Challenge: size limit/expensive

epitaxyvs.colloidalQDs


Possible Elements of a New Toolkit

e.g. for a “few photon” or single photon source

1) Enhanced Light Matter Interaction

- semiconductor microcavities vs. atom microcavity physics- near field (dipole-dipole) collective interaction

2) Efficient internal energy transfer on ‘nanoscale’ (Forster = dipole/dipole)e.g. from pump or for multiple-element chromophores

3) For coherent sources (including single photon emitter), need stronglocal feedback on sub-λ scale

Nanocomposite active optical material


Possible Elements of a New Toolkit

Strong Light-MatterCoupling

EfficientInternalE-transfer

“LocalFeedback”(resonatorless)

Electrical Injection

“Piecewise Material Examples”:

J-aggregate/microcavity

InGaN nanopostArrays

Plasmonic particlesin gain medium

QD/J-aggregate

InGaN/organicjunction

• Interfaces and interactions: excitation vs. charge transfer• Inorganic, organic, and noble metal nanomaterials


Cartoon Approach to Design

What is this ?

Contact layer

Flexible substrate

Contact layer

Nano composite layer

Nano-opticalantenna

Photoelectronicconversion; chargeand excitation transport

Nano AND macroscale contacts

Need a spatially organized, optically high density, electronically “flexible”, and low loss electrically accessible nanomedium (for emitters and possibly PV)


1) Basic Semiconductor Microcavity Physics

ca. 1994-2005

e.g. organicsemiconductormicrocavity(~4 monolayers)

e.g. ZnCdSe QW microcavity


Strong Light-Matter Coupling Regime in Semiconductors:Single Exciton (atom) regime and QED

Reality Check:

ΩR = µEvac/ħ = (πe2f)1/2 / (4πεmoVm)1/2

g2 > (γc- γx)2 /16

Strong coupling criteria:

Light-matter coupling strength:

Cavity modal volume:

n2εo|Evac|2 Vm = hν/2

Possible to achieve ħΩR > kT near temperature for a nanostructuredSemiconductor-based structure for single-photon regime


Device Example : Single Photon Emitter

(a) Single organic moleculein single mode 3D microcavity

(b) Single InAs quantum dotin 3D microcavity (2004)

e.g. J-aggregateLcoh ~ 100 nm (RT)

Reichtmaier et al (2004)Yoshie et al (2004)Arakawa et al

• a special “zero-threshold” laser• single exciton “molecule” (“two-level atom) within 3D confined optical field:analog to single-atom-in-microcavity (!)

• fJ-aggr ~ 10 – 100 fQD room temp operation in strong coupling regime• QED and ‘special’ photon statistics for quantum information processing

“random”


Prelude: J-aggregate Organic in a Microcavity

• Organic semiconductors and organic/inorganic hybrids/nanocomposites• Microcavity effects to enhance light-matter interaction: Exciton-Polariton

400 450 500 550 600 650 700 750 8000.00

0.05

0.10

0.15

0.20

0.25

FWHM= 20nm

Cyanine dye/PVA-J aggregate

J-Aggregate Monomer

Abs

orba

nce

(αL)

Wavelength (nm)Room Temperature absorbance

694nm

monomer(solution)

J-band

e.g. J-aggregate (vs.monomer):

• giant exciton oscillator strength

• fast relaxation time

• imbed in inorganic microcavity• recently: layer-by-layer depositionα > 106 cm-1 (Bradley et al 2006)

Extraordinarily densePotential opticalGain medium

“extended Frenkel”


An Organic Exciton-Polariton Microcavity

optical pumping: e.g. Lidzay et al

• λ/2 microcavity

• Normal mode (Rabi) splitting~ 200 meV >> kT

J. Tischler at al, PRL (2005)


400 500 600 700

10

20

30

40

50

60

70

80

90

100

3 2.7 2.4 2.1 1.8

400 500 600 7000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3 2.7 2.4 2.1 1.8

Wavelength (nm)400 500 600 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3 2.7 2.4 2.1 1.8

(A) (B) (C)

UB

Abs

LB UB LB

UB LB

PL

(%) R

efle

ctiv

ity

Abs

orba

nce,

PL

Inte

nsity

(a.u

.)

EL

Inte

nsity

(a.u

.)

Wavelength (nm) Wavelength (nm)

Energy (eV) Energy (eV) Energy (eV)

400 500 600 700

10

20

30

40

50

60

70

80

90

100

3 2.7 2.4 2.1 1.8

400 500 600 7000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3 2.7 2.4 2.1 1.8

Wavelength (nm)400 500 600 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3 2.7 2.4 2.1 1.8

(A) (B) (C)

UB

Abs

LB UB LB

UB LB

PL

(%) R

efle

ctiv

ity

Abs

orba

nce,

PL

Inte

nsity

(a.u

.)

EL

Inte

nsity

(a.u

.)

Wavelength (nm) Wavelength (nm)

Energy (eV) Energy (eV) Energy (eV)

Exciton-Polariton Organic Microcavity LED

• implementation with metallic reflectors• emission from lower polariton band• possibilities for a polariton laser ?

J. Tischler PRL (2005)


Current efforts: J-aggregates as superhigh gain medium

• employ layer-by-layer synthesis • measure coherence area by fsec 4-wave mixing spe’cy• aim at a 2D “crystal” of 100 nm coherence area: giant dipole

for a single photon emitter


2) Examples of Interactions and Interfaces

Organic/inorganic semiconductors and metal nanoparticles:

Energy transfer:

• InGaN nanopost arrays

• J-aggregate-QD transfer

• Plasmon focusing

Charge transfer:

• InGaN/organic heterojunction


B800nm

B850nm

e.g. variableD-A length

Eg. Rhodopsoremnas acidophilia:• a truly multichromophore system: beyond Förster theory• very high local chromophore density


(a) Multichromophore, High Density Nanoparticle“Artificial” Composite Material Systems ?

i) Simple Forster (inelastic photon tunneling):

ii) Multichromophore enhancements:

• multiple length scales over which D-A centers interact• degenerate multiexciton systems (‘vanishing Stoke shifts’)• quantum mechanical coherence and collective effects

Silbey, PRL 2004,

PhotonsP P

~10-50 nm

InGaN nanoposts/ODs

organicmedium

Dicke: superradiance

KR ~ (n-4)(Ro/R)6


InGaN Nanorod Mesoscopic Active (Optical Gain) Media

Yiping He (2004-2005)

360 380 400 420 440Wavelength (nm)

e.g. 10 InGaN QWs

~ 40-60nm pillar diameter~ <50 nm edged-to-edge separation

• high resolution ebeam litho, etching• high spontaneous emission efficiency:

low surface state recombination• stimulated emission at very low threshold• physics: photon localization vs. dipole-

dipole interaction (nanoscale resonators)sapphire substrate

GaN bufferlayer ~2µm

InGaN MQWActive medium

AlGaN200nm


Enhanced Photon-Exciton Coupling in HighDensity Nanorod Arrays

(1) Evidence for enhanced photon-electron interaction on ~1 um scale:

• Photon scattering (localization/effective mean free path)• Near-field electrodynamics (dipole-dipole interaction: multichromophore)

(2) Nonideality factors from surface roughness and fabrication imperfections: a form of inhomogeneous broadening

very strong coupling/short photon mean free path in a high fosc medium

Prior work in “random lasers”:

a) Molecular dyes in “ground glass”(e.g. Lawandy et al, 1995)

b) Random ZnO nanocystallites in dielectric host (Cao et al, 2000)

Photon diffusion length < 100 nm


(b) Energy Transfer from Colloidal QDs to J-aggregate

500 550 600 650

0

20

40

60

80

100

TTBC J-agg

QD & TTBC

QD565div by 5

Inte

nsity

(a.u

.)

Wavelength (nm)

PL SpectrumEx@380nm

400 450 500 550 600 650 7000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Abs

Wavelength (nm)

TTBC J-agg

QD & TTBC

QD565

Absorbance Spectrum

CdSe/ZnS QD emission: 565nmJ-aggregate emission: 580nm

• QD emission was significantly quenched

• TTBC J-agg emission was red-shifted and greatly enhanced

• The presence of QDs may interfere with formation of J-aggregates

Colloidal QD as the “pump”QD in silica spheres,Organic ‘cladding’

Optical pumping:

(Zhang 2006)


Forster Energy Transfer from QDs to J-aggregate

400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

1.2Absorbance Spectrum

Abs

Wavelength (nm)

TTBC J-aggQD & TTBC

QD655

550 600 650 700

0

50

100

150

200

250

300

TTBC J-agg

QD & TTBC

QD655

Inte

nsity

(a.u

.)

Wavelength (nm)

PL SpectrumEx@530nm

400 450 500 550 600

0

100

200

300

400

500

0.2

0.4

0.6

0.8

1.0

1-T

PLE SpectrumEm@653nm

QD & TTBC

QD655

Inte

nsity

(a.u

.)

Wavelength (nm)

QD emission: 655nmJ-aggregate emission: 580nm

• QD emission was greatly enhanced when the excitation wavelength is in the neighborhood of TTBC absorption.

• Monomers and dimers seems to couple better to QDs than J-aggregate

• J-aggregate emission was still red-shifted


(c) Metal Nanoparticles (resonant plasmons) to enhance efficiency local field/feedback on sub-λ scale?

• “Plasmonics”: giant optical antenna effects on sub-λ size scale– means to couple, guide, and concentrate optical field– also for providing interconnects to nanorods/nanocrystals

• Metal nanoparticle-enhanced semiconductor quantum dot emission ?– Plasmon Extinction = Absorption + Scattering

Quenching Enhancement

photons-in

“absorptive”

QD M

photons-in

QD M

“scattering”

photons-out

“cast a giantShadow”


Concentration/Scattering of Light on Nanoscale (<<λ)

“cast a giantshadow” 80nm

20nm

0nmE

80nm

20nm

0nm

80nm

20nm

0nmEE

NSOM image

after ultrashort pulselaser irradiation (at ωp)

100 nm

SEM image

100 nm

(Atay et al,Nanolett 2005)

• tailoring the surface plasmon resonance by adjacent nanoparticle interaction• optical field local concentration 10-100 fold at touching point(estimate)• colloidal QDs added (so far) for resonant energy transfer/interaction• immerse in optical gain medium: giant scattering cross section (low loss) (Lawandy)


(c) Nanocomposite II-VI QD-Ag Structures Colloidal II-VI and InGaN nanocrystals

200~400nm

50nm

30nm

Patterned area (100 μm × 100 μm )

PMMA

QDs

Excitation PL

• Samples: Diameter – lattice constant #1: 100nm – 200nm#2: 100nm – 260nm#3: 140nm – 300nm#4: 160nm – 300nm

• SEM image after developing(pattern #4)

• Most QDs within SPP field• Localized + propagating

SPP

J.H. Song, Nanolett (2005)


(d) Hexagonal Dense Array of Colloidal II-VI QDs

Before J-aggregate cladding: closely packed

Silicasphere

Q. Zhang (2006)

CenteredCdSe/ZnSQD


Spatial control of QD or nanorod placement

Single (coated) QDs in nanofabricated 100 nm “wells”

CdSe/ZnS QD/silica captured in wellConductiveback electrode

Colloidal particles

• Self-assembling of colloidal QDs onto electron-beam lithography patterned PMMA template (by capillary and other driving force).• aim at single photon statistics (photon antibunching) under optical pumping


Summary: Can we really make something like this?

Contact layer

Flexible substrate

Contact layer

Nano composite layer

Nano-opticalantenna

Photoelectronicconversion; chargeand excitation transport

Nano AND macroscale contacts

Acknowledgements:V. Bulovic, J. Tischler, S. Bradley (MIT)Jung Han (Yale)T. Atay, Q. Zhang, Y. He, Y.-K. Song, R. Zia (Brown)

Arto V. Nurmikko* Brown University - Home | Quantum … · Arto V. Nurmikko* Brown University Jeon...

Documents

Transcript of Arto V. Nurmikko* Brown University - Home | Quantum … · Arto V. Nurmikko* Brown University Jeon...