the design of dielectric environment for ultra long lifetime of graphene plasmon dr. qing dai...

The design of dielectric environment for ultra long lifetime of graphene plasmon

Dr. Qing Dai

22/10/2015

Surface Plasmons (SPs)

Surface free charges oscillations

-

E(t)

+

Manipulation of light at nanoscale

Spatial confinement Local field enhancement

Science, 2010, 328, 440

Metamaterials map

Ultra-high mobility

Low carrier density

Low interband losses

Graphene is an ideal material for plasmon!

Atwater, Science, 2011

Plasmon lifetime

Graphene

Calculated lifetime :~10 ps in mid-IR~10 ns in THz

A. Principi, et al. PRB, 2013, 88, 195405

Properties of graphene plasmon： Electrical tunability Low intrinsic losses Broad band operation Suitability of on-chip integration High field enhancement for

strong light-matter interaction

T. Low, et al. ACS Nano, 2014, 8, 1086

J.N. Chen, et al. Nature, 2012, 487, 77

Graphene Plasmons

Motivation & Objectives

SubstrateSubstrate

All atoms are exposed to the substrate

A small portion of atoms are exposed to substrate

Au Graphene

Substrate design for high performance GP

？ Surface phonon mode hybridization

？ Electron Scattering (dangling bond, impurities)

？ Radiation loss (surface roughness)

Near-field(s-SNOM)

Far-field extinction spectrum（ FTIR）

Nanoribbon arrays to excite local plasmon;Extinction spectra obtained (675-4000 cm-1);Multi-modes characterization.

Experimental measurement of graphene plasmon

Metal-coated AFM tips to excite propagating plasmon (~15 nm);High-order demodulated harmonics of the near-field signals to obtain weak signals;

Hybridization of GP and surface phonons

Free standing --- one peak; On silica substrate --- three peaks

Graphene Plasmon coplanar coupling

Decrease of inter-ribbon spacing caused red shifts of plasmonic resonances

f is ribbon to period ratio

Coplanar coupling of GPs is verified by resonance red shift

Plasmon resonance varied as inter-ribbon spacing

Ribbon to period ratio

Plasmon coupling strength on various Substrates

Ribbon to period ratio

Non-polar substrate results in stronger coplanar couplingX. Yang, et al. Small, 201400515

Van der Waals heterostructures: for long lifetime

Plasmon-phonon hybrid modes: Long lifetime of phonons in monolayer

crystals; High field enhancement.Design of ultra-thin functional device: Combine functions of varied 2D

crystals; Excellent electrical properties.

G/BN heterostructure

Geim, et al. Nature, 2014

Graphene/h-BN heterostructure

Graphene/monolayer h-BN/SiO2 Graphene/SiO2

1、 Peak 4 origins from the coupling with LO phonon of h-BN（ 1370 cm-1）；2、 the positions of Peaks 1 and 2 move slightly. (806, 820 cm-1)。 The linewidths become narrower.

Wavenumber (cm-1)800 1200 1600 2000

-0.21 eV

-0.25 eV

-0.29 eV

-0.33 eV

EF=-0.35 eV

-0.15 eV

-0.1 eV

Ext

inct

ion (

%)

0.2

0.4

0.6

0.8

1.0

0

W=160 nmPeak1Peak2

Peak3 Peak4

1.2

Peak a

c

Peak4Peak3

Peak2

Peak1

d

Ext

inct

ion (

%)

a

Wavenumber (cm-1)800 1000 1200 1400

0.2

0.4

0.6

0.8

0

Peak gPeak b

Peak a

EF=-0.35 eV W=100 nm

Wavenumber (cm-1)700 800 900

b

Ext

inct

ion (

%)

0.2

0.4

0

0.6o-TO (h-BN)

(820 cm-1)SO1(SiO2)806 cm-1

Peak b

Peak1

Peak2

1600 1000

EF=-0.35 eV

55 nm75 nm

100 nm

110 nm

120 nm

130 nm

140 nm

160 nm

W=220 nm

Wavenumber (cm-1)

Ext

inct

ion (

%)

800 1200 1600 2000

0.4

0.8

1.2

1.6

2.0

2.4

2.8

0

Peak4Peak3Peak2

Peak1Out-of-plane TO phonon（ 820 cm-1） of BN interact with graphene plasmon.

Graphene/h-BN heterostructure

Graphene/h-BN heterostructure

For monolayer h-BN: 3 optical phonons

( ) 0qiT r

exp(i . )( ) ,

2

oTB oT

oTBN

en u qz

A

qq

q rr

exp( . )( ) .

2

LB L

LBN

en u i qzi

A

qq

q rr

Remote phonon scattering mechanism： effective electrical potential

1, in-plane LO phonon (1370 cm-1)

2, in-plane TO phonon (820 cm-1)

3, out-of-plane TO phonon (820 cm-1)

A new coupling mode: the o-TO phonon interact with plasmon.

Fano resonanceEIT

Graphene/h-BN heterostructure

Lifetime of the hybrid modes

lifetime of Fano peaks: t =2h/G

Lifetimes:Near BN phonon: ~1.6 ps; Far from phonons: ~100 fs;Near SiO2 phonon: ~180 fs;Without coupling: ~40 fs;For Ag LSP: ~10 fs.

1370 cm-1

Peak1 Peak2 Peak3 Peak4

Eres (cm-1)800 1200 1400 16001000

Life

time

(fs)

200

400

600

800

1000

1200

1400

0

1600

1800

GNR/SiO2

GNR/BNR

800 cm-1

900 cm-1 980 cm-1960 cm-1940 cm-1920 cm-1 1000 cm-1

900 cm-1 940 cm-1 980 cm-1

G/BN heterostructure

G/SiO2 device

Near-field images

900 cm-1

950 cm-1

1000 cm-1 0 50 100 150 200 250 300 350 400 450

0.2

0.4

0.6

0.8

1

1.2

1.4 1

2

3

4

5

6

7

89

101112

Amplitude A=26.8742

Propagating wave vector q1=0.077792

Decaying wave vector q2=0.002939

q2/q1=0.037781

Constant part=0.51909

sse=0.078434

x (nm)

Vo

ltag

e (

10-5

V)

0 100 200 300 400 500 600

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1

2

3

4

5

6

78

910

Amplitude A=28.1792

Propagating wave vector q1=0.062555

Decaying wave vector q2=0.0024063

q2/q1=0.038467

Constant part=0.46674

sse=0.048575

x (nm)

Vo

ltag

e (

10-5

V)

0 100 200 300 400 500 600 700

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.81

2

3

4

5

6

7

8 910

Amplitude A=86.3336

Propagating wave vector q1=0.049104

Decaying wave vector q2=0.0021745

q2/q1=0.044283

Constant part=0.74817

sse=0.21005

x (nm)

Vo

ltag

e (

10-5

V)

Plasmon wavelength: 260 nmIncident wavelength: 900 cm-1

Confinement: 43Lifetime: 73 fs

Plasmon wavelength: 180 nmIncident wavelength: 950 cm-1

Confinement: 59Lifetime: 66 fs

Plasmon wavelength: 140 nmIncident wavelength:1000 cm-1

Confinement: 72Lifetime: 54 fs

Near-field images

Dispersion

Peak2

GNR/BNR

0.1 10

400

800

1200

1600

Life

time

(fs)

Group velocity (x0.01c)

Graphene plasmon: electrical tunability & dielectric environment effect;

Substrate surface phonon effects on GP: Tradeoff between modulation bandwidth\coupling efficiency ;

Long lifetime hybrid modes of plasmon and phonon:Van der Waals heterostructures can improve plasmon lifetime significantly by combine the low loss and highly field enhancement.

Summary

Acknowledgements

Thank you for your attention!

National Natural Science Foundation of China (NSFC)The Recruitment Program of Global Experts