Nanoribbons and Antidot-lattice graphenes Pro 11.pdf · Nanoribbons and Antidot-lattice graphenes...
Transcript of Nanoribbons and Antidot-lattice graphenes Pro 11.pdf · Nanoribbons and Antidot-lattice graphenes...
Large band gaps, ferromagnetism, and
anomalous magnetoresistance oscillations
derived from edge states;
Nanoribbons and Antidot-lattice graphenes
Junji HaruyamaAoyama Gakuin University, Tokyo, Japan
Contents
1. Introduction
2.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
3.Antidot-lattice graphenes fabricated using nano-
porous alumina templates as etching masks
Anomalous magnetoresistance oscillations
Room-temperature Ferromagnetism
Non-lithographic
(10 layers)
(Monolyer)
4.Future plans: (Quantum ) Spin-Hall effect
Nature Nanotech &
Latest Highlights
PRL
Submitted to Nature
Arm Chair
zigzag
zigzag
Edge atomic structures of Graphene (Graphite)
Arm
chair
(超伝導・強磁性)電極
ジグザグ端
(超伝導・強磁性)電極
Graphene nanoribbon
Flat band
Arm chair Zigzag
Tight-binding
Band gap
K.Nakata et al., Phys. Rev. B 54,
17954 (1996)
Strong Electron localization
High EDOS
Spin polarization
Edge states of Graphene (Graphite)
Spin polarization and ferromagnetism at
zigzag edges with hydrogen termination
Kusakabe and Maruyama,
Phys. Rev. B 67, 092406
(2003)
Up spin Down spin
Hydrogen
local-spin-density
approximation
Why graphene edges are important and
interesting??
1. Band gap engineering
3. All carbon magnetism (magnets)
4. Spin Current & (Quantum) Spin Hall Effect
2. Electron correlation with localized edge electrons
So many theoretical reports, but no experimental reports
Large damages by lithographic methods
Non-lithographic methods
Contents
1. Introduction
Non-lithographic
2.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
Nature Nanotech &
Latest Highlights
Advance online publication
Nanoelectronics
Article by Shimizu et al.
Graphene nanoribbons manufactured by
annealing unzipped carbon nanotubes have
been measured to have a large energy
bandgap.
Latest highlights
Current issue
Quantum tunnelling through single bases FREE
RNA nanotechnology: Best of both worlds
Current issue table of contents
Impact Factor 26.309
December 2010 - Vol 5 No 12
Nature Nanotechnology | News and Views
Nanoelectronics: Graphene gets a better gapStephan RocheJournal name: Nature Nanotechnology Volume: 6, Pages: 8–9 Year published: (2011)
DOI:doi:10.1038/nnano.2011.262 Published online 23 December 2010
Introduction of energy band gaps
Absence of energy band gaps
Destruction of symmetry in bilayer graphenes
Voltages, Carrier doping, Substrate
Carrier confinement into 1D space GNRs
Semi metal, Zero- gap
semiconductor
Han, Kim et al., Phys. Rev. Lett., 104,
056801 (2010)
Disordered Graphene Nano-ribbon(Lithographic)
Hopping conductance
Stochastic Coulomb diamond
Large difference between & EaLarge transport gaps
Ec=e2/2C
J.Tour et al.,
Nature 458, 872
(2009)
Rice University, Smalley Institute for Nanoscale Science and Technology
①Formation of GNRs on substrate by air blow
②3stepped annealing(high vacuum, H2)
Our originality
Low-defect GNR formed by unzipping of MWCNTs
1μm
200nm
As-depo
Our originality①Formation of GNRs on substrate by air blow
②by air blowing to droplet①by brushing
AFM
Brush Air blow
Isolated 47 58
Rectangle 14 26
Monolayer 5 15
Formation of GNRs on Si-substrate by air blow
Number of GNRs within 5mm2-substrate
②3-stepped annealing during FET formation process
Our originality for deoxidization and carrier doping
Right after formation of GNRs on substrate High vacuum・ 800 C
Right before formation of EB mark H2 atmosphere・800 C
Right before formation of FET electrode High vacuum ・300 C
For deoxidization & Recovery of defects
For carrier doping
For cleaning
for long time
Nature Nanotech(Dec.19, 2010)
HRTEM
Raman
AFM
As-grown
nanoribbon
FET
Quality of GNRs: low defects
Before
annealing
After
annealing
AIST
Suenaga
Electronic transport for 4 different-type GNRs
W Width (nm)
N Layer number
Nature Nanotech(Dec.19, 2010)
Correlation of ambipolar feature with
annealing time at high vacuum
Deoxidization:p-type Ambipolar
t = 0
t = 24h
Electronic transport:Zero-bias
anomaly & Transport gap
VBG = 1V
Small transport gap
Low defects
W=75nm
N=1
Nature Nanotech(Dec.19, 2010)
Single-electron Spectroscopy
No stochastic diamonds
Disordered GNRsLow-defects GNR
Nature Nanotechnology
Coulomb diamonds
Stochastic diamonds due to
defects (Q-dots connected in
series)Low defects
W=75nm
N=1
Energy band gap in thermal-
activation relationships
7-times larger Ea
No hopping conductance
Transport gap close to Ea values
Nature Nanotech(Dec.19, 2010)
55m
eV
Louie et al., UC Berkeley
Theory for energy band gaps of GNRs
with arm chair edge
GWA
LDA
3 eV for W=1nm
Ea30 meV
for
W100nm
Q1: The large band gaps are relevant for large-width GNRs?
le 300nm
W < 300nm
Remaining
1D
Contents
1. Introduction
2.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
Non-lithographic
Nature Nanotech &
Latest Highlights
3.Antidot-lattice graphenes fabricated using nano-
porous alumina templates as etching masks
Anomalous magnetoresistance oscillations(10 layers)
PRL
Graphene
Antidots
edge
Antidot-lattice graphene
GNR
100nm
Antidot Lattice on Semiconductor 2DEG (1990)
M. Kato,S. Katsumoto, Y. Iye,
PRB 77, 155318 (2008).
D. Weiss, K. von Klitzing et al.,
PRL 70, 4118 (1993)
Rc = (nS)1/2 (h/2)/eBΔBABT = (h/e)/S
Commensurability peak
Aharonov-Bohm-type
Oscillation
Antidots
-
Antidot
Cyclotron orbit
High B
Low B
Under enough antidot spacing
Anomalous FQHEs200nm/Ls600nm = 1/3
Anomalous filling factor
Antidots
No antidots
Composite Fermion
Kang, Stormer, PRL71, 3850 (1993)
In Graphenes: How edge-localized electrons are
interacted with cyclotron-moton electrons?
Antidot Lattice as a scattering center for electrons
on 2DEG
Antidot Lattice Graphene
T. Shen et al., APL 93, 122102 (2008).
S.Russo et al., PRB
77, 085413 (2008).
J. Bai et al., Nature Nanotech. 5,
190 (2010).
Only a few publications No reports for
edges
Graphene
Antidots
Zigzag edge
Formation of low-defect antidot-lattice
graphene by porous alumina templates
GNR
Hydrogen annealing
50nm
Pore spacing 40nm
80nm
Pore spacing 20nm
15nm
Pore spacing 20nm
Porous alumina templates
FESEM images of ADLGs
AFM and STM images of
Hydrogen-terminated ADLGs
500nm
STM
100nm
AFM
T = 80K
Hiroshi Fukuyama
Tokyo University
100nm
M-H@4K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-1.0e-4
-5.0e-5
0.0
5.0e-5
1.0e-4100
0
-100
50
-50
1000-1000 -500 5000
M-H@2K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-6.0e-5
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
6.0e-560
20
40
-60
0
-40
-20
1000-500 5000-1000
M-H@2K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-8.0e-4
-6.0e-4
-4.0e-4
-2.0e-4
0.0
2.0e-4
4.0e-4
6.0e-4
8.0e-4
0
-400
-800
400
800
1000-1000 -500 5000
Magne
tization (e
mu/1
00
m2)
Magnetic field (gauss)
(a) (b) (c)
T = 2K T = 2KT = 2K
Hydrogen Oxygen No antidots
All-carbon Ferromagnetism in ADLG
with Hydrogen-terminated edges
Mono-layer graphene
Evidence for zigzag at antidot edge
Correlation of localized electrons
with MR oscillations??
Sample A
Aharonov-Bohm-type Oscillations
in H2-terminated ADLGs
Commensurability peak = 80 nm
AD Space
80 nm
2Rc = (nS)1/2 (h/2)/eB
= a
nS 4 × 1011 cm-2
le = 2D/vF 800 nm >
2(a/2) = 540 nm
B = 200 mT
ΔBABT = (h/e)/(S)
(b)
52.5 7.51/B (T-1)
FF
T (
arb
. units)
(c)
0 < B < 2.5
2.5 < B < 5
Sample B
Fourier
Spectrum
AB-type oscillation
Low B
High B
Low B B200 mT
Electron trajectories on honey-comb ADL
and magnetoresistance oscillations
ΔBABT=(h/e)/S
S = 6(3-1/2/2)(a/2)2
2Rc = a
a
Runaway orbit
1st Unit cell
2nd Unit cell
SDHO orbit
(Commensurability MR peak orbit)
Graphene
Graphene
nanoribbons
Anti-dots
zigzag edges
Quantized electron orbitals around antidots
in an unit cell
a = 160 nm
En = h2/2mL2(n - Φ/φ0)
AB-type oscillation
2Rc = (nS)1/2 (h/2)/eB
= a
nS 4 × 1011 cm-2
le = 2D/vF 800 nm > 2(a/2) = 540 nm
En = h2/2mL2(n - Φ/φ0)
Aharonov-Bohm-type effect
ΔBABT=(h/e)/S
Sample A
Anomalous MR Oscillations in ADL- multi-layered
Graphenes
Commensurability peak = 80 nm
(b)
52.5 7.51/B (T-1)
FF
T (
arb
. units)
(c)
0 < B < 2.5
2.5 < B < 5
Sample B
Fourier
Spectrum2Rc = (nS)1/2 (h/2)/eB
= a
nS 4 × 1011 cm-2
le = 2D/vF 800 nm >
2(a/2) = 540 nmB260 mT
High B
High B
S: r for pore radius
B260 mT
Electron trajectories on honey-comb ADL
and magnetoresistance oscillations
ΔB=(h/e)/(r2) with r = 40 nm
2Rc = a
a
Runaway orbit
1st Unit cell
2nd Unit cell
SDHO orbit
(Commensurability MR peak orbit)
Graphene
Graphene
nanoribbons
Anti-dots
zigzag edges
Antidot radius
Absent AB effect
Bohr–Sommerfeld quantization
condition =Br2=m(h/e) m: integer
Like flux quanta in superconductor
Edge-
Localized
electrons
Quantization of magnetic flux
-
ΔBAB = (h/e)/(r2)
Aharonov-Bohm effect
2Rc = (nS)1/2 (h/2)/eB
= a
nS 4 × 1011 cm-2
le = 2D/vF 800 nm > 2(a/2) = 540 nm
En = h2/2mL2(n - Φ/φ0)
Aharonov-Bohm-type effect
Vector
potential
A
Ensemble average
Disappearance
ΔBABT=(h/e)/S
12.5 37.525
FF
T (a
rb.
un
its)
1/B (T-1)
(e)
0.6 < B < 1
Sample B
Fourier
Spectrum
△B2 = 70 mT ΔBABT =(h/e)/S =
50 mT
Contribution of larger unit cell (2nd unit cell)
Contents
1. Introduction
2.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
3.Antidot-lattice graphenes fabricated using nano-
porous alumina templates as etching masksAnomalous magnetoresistance oscillations
Non-lithographic
(10 layers)
Nature Nanotech &
Latest Highlights
PRL
Room-temperature Ferromagnetism (Monolyer)Submitted to Nature
All-carbon Ferromagnetism in ADLG
with Hydrogen-terminated edgesM-H@4K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]-1.0e-4
-5.0e-5
0.0
5.0e-5
1.0e-4100
0
-100
50
-50
1000-1000 -500 5000
M-H@2K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-6.0e-5
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
6.0e-560
20
40
-60
0
-40
-20
1000-500 5000-1000
M-H@2K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-8.0e-4
-6.0e-4
-4.0e-4
-2.0e-4
0.0
2.0e-4
4.0e-4
6.0e-4
8.0e-4
0
-400
-800
400
800
1000-1000 -500 5000
Mag
neti
zati
on
(
em
u/1
00
m2)
(a) (b) (c)
T = 2K T = 2KT = 2K
M-H@300K
H[Oe]-1000 -500 0 500 1000
M(T) [emu]
-3.0e-5
-2.0e-5
-1.0e-5
0.0
1.0e-5
2.0e-5
3.0e-5
0
30
20
-10
-20
10
M-H@300K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-3.0e-5
-2.0e-5
-1.0e-5
0.0
1.0e-5
2.0e-5
3.0e-5
-301000500-1000 -500 0
T = 300K
M-H@300K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-6.0e-5
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
6.0e-5
10000-500
60
500-1000
40
20
0
-20
-60
-40
Magnetic Field (gauss)
T = 300K
M-H@40K
H[Oe]-1000 -500 0 500 1000
M(T
) [e
mu
]
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-530
0
15
-15
-30
-500-1000 10005000
T = 300KHydrogen
Hydrogen Oxygen
Oxygen
No antidots
No antidots
(d) (e) (f)
Hydrogen Oxygen No antidots
Estimation of magnetic moment at edge-carbon atoms
Only dangling-bonds at zigzag edges have magnetization
Saturation M/one carbon 100 B 100-times larger than
theory
All carbon atoms within 7nm region from the edges 1.2 B
Weak Ferromagnetism in ADL-Graphite
with Hydrogen-terminated edges
M-H@2K
H [Oe]-1000 -500 0 500 1000
M (
T)[
em
u]
-4.0e-5
-2.0e-5
0.0
2.0e-5
4.0e-5
Hydrogen
T = 2K
Mag
neti
zati
on
(
em
u/1
00
m2)
4
-2
0
2
-4
M-H@300K
H[Oe]-500 0 500
M(T
) [e
mu
]-1.0e-5
-5.0e-6
0.0
5.0e-6
1.0e-5
Hydrogen
T = 300K
-1
-0.5
0
0.5
1
Magnetic Field (gauss)
10005000500-1000 5000-500
2D defects array in Graphite and
Room-temperature Ferromagnetism
Cervenka et al., Nature
Physics 5, 840 (2009)
ZIGZAGArm chair
Ambiguous system and
poor reproducibility
T. Enoki et al., Sol. Stat.
Comm. 149, 1144 (2009)
Zigzag-edge related Ferromagnetism in
Activated carbon Fibers
Spin polarization and ferromagnetism at
zigzag edges with hydrogen termination
Kusakabe and Maruyama,
Phys. Rev. B 67, 092406
(2003)
Up spin
Down spin
Hydrogen
Group-theoretical
consideration
Spin polarization and magnetism of
zigzag-edge nanoribbon
On one edge On both edges
No termination
H. Lee et al.,. Phys. Rev. B 72, 174431 (2005)
first-principles density-
functional calculations
Correlation of Flat band and Spin polarization
with Hydrogen termination FerromagneticMajority Spin Minority Spin
H. Lee et al.,. Phys. Rev. B 72,
174431 (2005)
Antiferromagnetic
1 Hydrogen 2Hydrogen 2 & 1 Hydrogen
Up Spin Down Spin
Elimination of Magnetic moment at zigzag edges
with Oxygen termination
R.G.A. Veiga, et al., J. Chem. Phys.
128, 201101 (2008)
No oxygenOxygen
Edge
Elimination of Magnetic moment by Interlayer coupling in
Zigzag-edge graphite with Hydrogen termination
AB Stack with no termination
No termination
Lee, H. et al. Chem.Phys.Lett. 398 207 (2004)
Advantage of porous alumina template
for formation of low-defect ADLGs
zigzag
Non-lithographic
Hexagonal-shaped ADs placed like honeycomb array
Low damages
Alignment of the same edge structures to each
boundarySix ADs and GNRs/one AD
Large ensemble of GNRs
GNRs
If zigzag structure is the most
stiff, the advantages give a
large volume of zigzag-GNRs
and Ferromagnetism.
Contents
1. Introduction
2.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
3.Antidot-lattice graphenes fabricated using nano-
porous alumina templates as etching masks
Anomalous magnetoresistance oscillations
Room-temperature Ferromagnetism
Non-lithographic
(10 layers)
(Monolyer)
4.Future plans: (Quantum ) Spin-Hall effect
Controlling edge-spins by electric fields
Y-W. Son, S.Louie et al., Nature 444, 347–349 (2006)
0.0
Eext = 0.0 0.05 0.1 VA -1
Spin Current & Filter
Eext
0.05
0.1
Jsy = (h/2e)(J↑
y − J↓y )
Kane, C. L. and Mele, E. J.,.
Phys.Rev. Lett. 95, 226801 (2005)
(Quantum) Spin Hall Effect in Graphene
QSHE regime Insulating
regime
Over estimation of SOI??
M.Schmidt & D.Loss, Phys.
Rev. B 81, 165439 (2010)
Spin Hall Effect in graphen/graphen junction
with hydrogen termination
No SO Interaction
H-CH-C
sp3 SOI
M.Schmidt & D.Loss, Phys.
Rev. B 81, 165439 (2010)
SO Interaction
Spin Hall Effect in graphen/graphen junction
with hydrogen termination
Edge Bulk
Conclusions
1.GNRs fabricated by unzipping of carbon
nanotubes and 3-stepped annealing
Low defects and 7-times larger energy band gaps
2.Antidot-lattice graphenes fabricated using nano-
porous alumina templates as etching masks
Anomalous magnetoresistance oscillations
Room-temperature Ferromagnetism
Non-lithographic
3.Future plans: (Quantum) Spin-Hall effect
Controlling edge-spins by electric fields
MIT: Millie Dresselhaus
Colombia University: Philip Kim
Rice University: James Tour
Tokyo Institute of Technology: T.Ando, T.Enoki
Tokyo University: S.Tarucha, M.Yamamoto,
H.Fukuyama, T.Matsui, H. Aoki
Tokyo University, ISSP: Y.Iye, S.Katsumoto, T.Otsuka
AIST: K. Suenaga
My students and staff
Japan Science and Technology Agency:CREST
Hidetoshi Fukuyama
Jun Akimitsu
So many thanks to