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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
q rr
exp( . )( ) .
2
LB L
LBN
en u i qzi
A
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
