Materials Science
& Engineering
In situ Microscopy Studies of
CINT/JAIST '09
0D, 1D, and 2D Structures –
Clusters, Nanowires, Graphene
Suneel Kodambaka
Department of Materials Science & Engineering
University of California Los Angeles
In situ Microscopy Labs
Materials Science
& Engineering
3. Growth of Semiconducting Graphene
on Pd(111)
A
B
X
O
X'
Potentially transformative
Can be tailor the
electronic properties of
epitaxial graphene
&
grow "device-ready"
200
layers on Si wafers?
10 nm
40 nm
Pd[110] D 0.20
Gr[2110]
22 Å
height (Å)
C
CINT/JAIST '09
Questions we'd like to address:
1.How does graphene form?
2.What is the role of substrate?
0.15
0.10
0.05
0
50
100 150
X
O
X'
distance (Å)
Graphene/Pd(111):
tunneling bias-dependent image contrast
Materials Science
& Engineering
CINT/JAIST '09
I = 0.24 nA
VT = +1.1 V
I = 0.24 nA
VT = -1.1 V
STS of Graphene/Pd(111)
Materials Science
& Engineering
7
10
0.25 eV STM
LDOS
8
6
6
4
(dI/dV) / (I/V)
5
2
4
0
3
16
-2.0
-1.5
-1.0
-0.5
PDOS
12
10
1
8.3 nm
0
-2
-1
0
V (V)
0.25eV
(dI/dV)/(I/V)
2
1.0
1.5
6
4
2
0
-6
-4
-2
0
2
4
band gap of 0.2-0.3 eV!
1
0
-0.4 -0.2 0.0
0.2
2.0
8
E (eV)
2
CINT/JAIST '09
1
0.5
0.3 eV DFT
14
2
0.0
0.4
Substrate can greatly influence graphene properties
6
Materials Science
& Engineering
2. Nucleation and Growth Kinetics
of Si and Ge nanowires
J. Tersoff, M.C. Reuter, and F.M. Ross
IBM T. J. Watson Research Center, Yorktown Heights
B.-J. Kim, C.-Y. Wen, and E.A. Stach
Dept. Materials Science and Engineering, Purdue University
CINT/JAIST '09
Questions we'd like to address:
1.How do nanowires grow?
2.What is the role of catalyst composition?
Potentially transformative
Can be fabricate nanowire heterostructures with atomically
abrupt interfaces, tunable shapes & structures?
Partially funded by
UC Discovery, UCEI, & Northrop Grumman Space Technology
In situ Microscopy Labs
Materials Science
& Engineering
Si wire nucleation kinetics
T = 525 oC; Si2H6 = 8 10-7 Torr
CINT/JAIST '09
t = 0, vacuum
Crystalline Au + Si2H6 → liquid AuSi droplets → Si nw/AuSi
Materials Science
& Engineering
Si wire nucleation kinetics
t=226 s
r (nm)
6
Si2H6: 410-6 Torr
5 T = 525 oC
4
C
3
CINT/JAIST '09
t=233 s
500
600
t (sec)
700
Rapid initial growth
crossover
to
slow growth
800
3
P
r
dr

 kLS  c1  c0   kVL t  t1    kLS  
R
 R
dt
t=390 s
Critical supersaturation of Si in AuSi droplets
B.J. Kim, J. Tersoff, S. Kodambaka, M.C. Reuter, E.A. Stach, & F.M. Ross,
Science 322, 1070 (2008).
Materials Science
& Engineering
Ge wire growth vs. Ge2H6 flux
CINT/JAIST '09
T = 410 oC
90 nm
tmovie: 30x texpt
wire diameter: 25 nm
Ge nanowire morphology can be
controllably manipulated with
deposition pressures
Materials Science
& Engineering
1. Thermal/Chemical Stability of
Small Clusters
CINT/JAIST '09
Questions we'd like to address:
1.How do hollow core structures
form?
2.What is the role of surface/interface
structure & orientation?
3.What controls their stability?
Potentially transformative
Can be make better &
cheaper catalysts?
Funded by ACS-PRF 48108-G10 & Hitachi Labs
In situ Microscopy Labs
Materials Science
& Engineering
Ostwald ripening of the titania cores
T = 850ºC
CINT/JAIST '09
10 s
236 s
241 s
Larger TiO2 core grows at the expense of
smaller one resulting in hollow graphitic shells
1022 s
1023 s
1024 s
900 s
At longer times, only hollow cores remain.
Materials Science
& Engineering
Ultra-High Vacuum VariableUltraVariable-Pressure
Scanning Electron Microscope
In situ SEM studies of:
* Nanowire nucleation & growth kinetics
* Liquid droplet/solid surface dynamics
* Chemical & thermal stabilities of nanostructures
UHV-CVD in a SEM:
CINT/JAIST '09
Operating pressure: 10-7 – 1 mTorr
Temperatures:
Imaging modes:
300 - 1250 K
SE, BSE, STEM
Funded by Dept. Materials Science & School of Engineering at UCLA