graphene nanoribbons: a route to atomically precise
TRANSCRIPT
Graphene Nanoribbons: A Route to Atomically Precise Nanoelectronics
Mike Crommie
Dept. of Physics, UC Berkeley and
Materials Science Division, LBNL Berkeley, CA
Outline
1) Graphene Graphene Nanoribbon (GNR) behavior
2) Potential applications for GNRs.
3) How do we make GNRs?
4) New developments in bottom-up fabrication Molecular bandgap engineering New bottom-up strategies
Graphene Nanoribbon
Electronic Structure of Graphene
zigzag direction
K
M
armchair direction
kx
ky
K
M
Reciprocal Space
kx
ky
Ene
rgy
Conduction band
Valence band Dirac pt.
Graphene Nanoribbon Electronic Structure
∆(e
V)
Armchair
∆(e
V)
Zigzag
Spin-polarized
M. Fujita, et al., J. Phys. Soc. Jpn 65, 1920 (1996); K. Nakada, et al., PRB 54, 17954 (1996); J. Heyd et al, J. Chem. Phys. 118, 8207 (2003); Y.-W. Son, et al, PRL 97, 216803 (2006)
E
k
0
0
Reciprocal Space
No Edge State
Reciprocal Space
Edge StateE
k 0
0
……
Armchairw
… …
Zigzag
Potential GNR Device Advantages
Energy gap, capacitance Bandgap Engineering
GNRs solve the nanotube metallicity problem
ID – VG for nanotubes
H. Park, et al., Nat. Nanotech. 7, 787 (2012)
“on”
“off”
Big gap Small gap
Width
Energy
Length
Uniquely Efficient Tunneling
Fast onset
Length
VSD
VG
k
E
µ
GNR GNR
tube tube
Smaller capacitance Faster
Potential GNR Device Advantages
GNR GNR
tube tube
Smaller capacitance Faster “on”
“off”
Big gap Small gap
Width
Energy
Length
Uniquely Efficient Tunneling
Fast onset
Bandgap Engineering Energy gap, capacitance
GNRs solve the nanotube metallicity problem
ID – VG for nanotubes
H. Park, et al., Nat. Nanotech. 7, 787 (2012)
VSD
VG
k
E
µ
High-current low-dissipation switching: HFET
J. Bokor
New proposed GNR implementation
Requires GNR doping and bandgap/width variation
p n
Large gap
Small gap
Large gap
S D
How Do We Make High Quality GNR Devices?
M. Y. Han et al., PRL 98, 206805 (2007)
Y. Kobayash et al., PRB 71, 193406 (2005) Ritter and Lyding, Nat. Mat. 8, 235 (2009)
Rough Edges are a Problem Graphene platelet on Si(100)
Top-down Lithography
Unzipping Nanotubes: A Better Edge
Au(111)
(8, 1) GNR
0.0 Å
5.5 Å
48 Å × 48 Å
width = 20 nm
C. Tao, et al., Nat. Phys. 7, 616 (2011)
Unzipped GNRs Smooth Edges
X. Wang, et al, Nat. Nanotechnol 6, 563 (2011)
Unzipped GNR FETs High Mobility
Jiao, et al, Nat. Nanotechnol 5, 321 (2010) Kosynkin, et al, Nature 458, 872 (2009)
A problem
Controlling width and chirality
A New Idea
Bottom-up Fabrication: + + + Molecular precursor Final assembled GNR
Bottom-up Fabrication: + + + Molecular precursor Final assembled GNR
+ + + Width
+ + + Chirality
+ + + Edge functionalization
Bottom-up Heterostructures:
n p p ∆1 ∆2 ∆1
p-n junctions bandgap engineering
A New Idea
GNR Bottom-up Synthesis Breakthrough: n=7 AGNRs
.
. 200 °C 400 °C
Metallic surfaces
200 °C n = 7 AGNR
(7 atoms across)
Precursor molecule
STM Image: AGNRs / Au(111)
Fasel, Muellen, & co-workers
J. Cai et al, Nature 466, 470 (2010)
Width = 0.7 nm
STM Allows Measurement of Local Electronic Structure
STM Spectroscopy
EF
EF
Ñwω
tip sample
LDOS(E)
0
V tip
sample EF
M. Koch, et al., Nat. Nanotech. 7, 713 (2012)
P. Ruffieux, et al., ACS Nano 6, 6930 (2012)
∆ = 2.5 eV
GNR Electronic Structure
Au reference
GNR
STM
Using STM to Measure GNR Energy Gap
LUMO dI/dV map
Bandedge Electrons Show Higher Density at GNR Edges
Can We Tune the Energy Gap?
?
N = 7 N > 7
∆(e
V)
Armchair
0
2
4 N=7 Tune?
Must synthesize new precursor molecules
A New Precursor Molecule to Tune GNR Bandgap: N=13
Yen-Chia Chen, et al., ACS Nano 7, 6123 (2013)
.
. 200 °C 400 °C
Metallic surface
200 °C
New Precursor
n = 13
F. Fischer & Crommie
width = 1.4 nm STM image: Polymer stage Fully cyclized (after annealing)
STM Spectroscopy of N=13 AGNR
dI/dV maps
HOMO LUMO
GNR
Au
Y.-C. Chen et al., ACS Nano 7, 6123 (2013)
6.0 7
13 =∆∆
=
=
N
N
2 7
13 ==
=
N
N
widthwidth
+
Molecular Bandgap Engineering (B.E.)
Previous Mesoscale B.E. :
GaAs GaAs AlGaAs
x
E
Sevinçli, et al, PRB 78, 245402 (2008)
Variable-Width Heterostructures
5-9 Junction
New Molecule-scale B.E. : (theory, DFT)
Ec
Ev
Molecular Bandgap Engineering: 7-13 Junctions n=7
n=13
7-13 Junction
Fabricating 7-13 Molecular Junctions on Au(111)
Molecular Bandgap Engineering: 7-13 Junctions n=7
n=13
7-13 Junction
3.8 nm 2 nm
Topograph
++
+
N=7
N=13
3 4
STM Spectroscopy of 7-13 Junction
Topograph
++
++
N=7
N=13
3 4
1 2
STM Spectroscopy of 7-13 Junction: Interface States
Topograph
++
++
N=7
N=13
3 4
1 2
STM Spectroscopy of 7-13 Junction: Interface States
Unit Cell
Assume Periodic Structure: Perform DFT Calculation
Theoretically Modeling the 7-13 Molecular Junction
Theory: Ting Cao, Steven Louie
0 0.5 -1.0-0.5-1.0Energy (eV)
D.O
.S.
Electronic Structure of 7-13 Molecular Junction
n = 130.9 eV
n = 71.7 eV
n=13 LUMO
-1.0
-0.5
0.0
0.5
1.0
S. G. Louie, T. Cao
Calculate LDOS distribution for these states, compare to experiment
1 4 2 3
Theoretical LDOS
Topograph
++
++
34
1 2
Comparing Theoretical Wave-function Maps
to Experiment
Experimental LDOS
How Can Devices be Made From Bottom-up GNRs?
Must transfer GNRs to insulator:
Fischer, Crommie, Bokor
Device Layout for 7-AGNRs
A
26nm gap
PMMA GNRs
Au Mica
Mica
SiO2
Bottom-up GNR Device Results
Schottky barrier behavior: Bottom-up N=7 GNR FET
P. B. Bennett et al., APL 103, 253114 (2013)
n-type
k
E
µe Φ’
metal contact GNR
metal contact
E
x
Challenges: • Improve contacts • Improve transfer to insulator • New GNR heterostructures • Grow directly on insulator?
New Chemistry: New Opportunities
Bergman Cyclization of Enediynes:
Polymerization: . . Q. Sun, et al., JACS 135, 8448 (2013)
A. Riss, et al., Nano Lett. 14, 2251 (2014)
Flexible coupling: + .. Radical step growth
Alkyne coupling
Au(111) SiO2
Difficult
Currently requires metal substrate
Model System for Surface Chemistry
Enediyne Fragment:
Expected Reaction Path:
Felix Fischer (UC Berkeley)
But what really happens?
heat
STM
Imag
es
Imaging Enediyene Cyclization on Ag(100)
heat
STM
Imag
es
Imaging Enediyene Cyclization on Ag(100)
F. J. Giessibl, Appl. Phys. Lett. 76, 1470 (2000)
L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 325, 1110 (2009)
tip
Qplus nc-AFM
G. Meyer & co-workers (2009)
Imaging Enediyene Cyclization on Ag(100)
heat
STM
Imag
es
nc-A
FM Im
ages
D. Oteyza, et al., Science, 10.1126/science.1238187 (2013)
Modifying Enediyne Molecules to Induce Coupling
Enediynes on Ag(100)
Alkyne Coupling
heat
heat
Modifying Enediyne Molecules to Induce Coupling
Radical Polymerization
Enediynes on Au(111)
D. de Oteyza, et al., Science 340, 1434 (2013)
Energy Landscape and Reaction Pathway
Theory: A. Rubio & co-workers
D. de Oteyza, et al., Science 340, 1434 (2013)
Energy Landscape and Reaction Pathway
Theory: A. Rubio & co-workers
Improved Structural Control at the Nanoscale
Conclusions 1) GNRs novel electronic properties.
2) Bottom-up synthesis molecular bandgap engineering.
3) New chemistries new nanostructures.
Future 1) Incorporate bottom-up heterojunctions into devices.
2) New bottom-up GNR structures, improved control.
3) Grow GNRs directly on insulators.
Nano-Bio Spect. Gp., ETSF Sci. Dev. Center, UPV, San Sebastian, Spain: Angel Rubio, Duncan J. Mowbray, Alejandro Perez UC Berkeley / LBL: M. F. Crommie (Physics) Dimas G.de Oteyza (now at Centro de Fisica, San Seb., Spain) Felix Fischer (Chemistry) Alexander Riss (now at Inst. of App. Phys., TU Wien) Steven Louie (Physics) Sebastian Wickenberg Jeff Bokor (EECS) Hsinzon Tsai Marvin Cohen (Physics) Patrick Bennett Alex Zettl (Physics) Miguel Moreno-Ugeda Zahra Pedramrazi Chen Chen Aaron Bradley Danny Haberer Grisha Etkin Patrick Gorman Liang Z. Tan Ivan Pechenezhskiy Yenchia Chen
Collaborators / Funding
THE END