US-Korea Nano Workshop, April 5, 2010
Dislocation-Driven Nanomaterial Growth: Nanowire
Trees, Nanotubes, and Their Potential Applications
in Solar Energy Conversion
Song Jin
Department of Chemistry
University of Wisconsin – Madison, Madison, WI 53706, USA
The Jin Research Group March 2010
back: Chad Dooley (PD), Jeremy Higgins, Steve Morin, Matt Faber,
Middle: Mark Lukowski, Jeannine Szczcech, Miguel Caban, Ruihua Ding, (undergrad), Song Jin,
front: Penny Carmichael (visiting), Chris Sichmeller, Jack DeGrave, Fei Meng, Rachel Selinsky,
e-mail: [email protected]
Group webpage: jin.chem.wisc.edu/
Overview of Research Interests:
Chemistry and Physics of Nanoscale Materials
Energy
Silicide
Nanowires
J. Mater. Chem. 2010, 20, 223.
Nano Lett., 2007, 7, 965.
APL 2007, 90, 173122.
Chalcogenide
Nanomaterials
Thermoelectrics
CrSi2, MnSi1.8 nanowires;
Chem. Mater. 2007, 19, 3238.
Nano Lett. 2007, 7, 1649.
JACS 2008, 130, 16086.
J. Solid State Chem. 2008, 181, 1565.
Solar Energy
PbSe, PbS nanowires
Energy Environ. Sci., 2009, 1050. (Perspective)
Nano Lett. 2007, 7, 2907.
J. Mater. Chem. 2009, 19, 934.
Science 2008, 320, 1060.
JACS 2009, 131, 16461.
Dislocation-Driven Growth
mechanism of 1-D nanomaterials
Spintronics
magnetic semicond.
nanomaterials
Magnetic Fe1-xCoxSi and
silicon-based spintronics
Nano Lett. 2006, 6, 1617.
J. Phys. Chem. B. 2006, 110, 18142.
Chem. Mater. 2007, 19, 126.
Nano Lett., 2008, 8, 810.
J. Mater. Chem. 2010, 20, 1375.
Nano Lett. 2008, 8, 2356.
EuS, EuO nanocrystals
and nanowires
Adv. Mater. 2007, 19, 2677. (EuO)
APL 2009, 95, 20251. (EuS XMCD)
Biomimetic Assembly
of nanomaterials
JACS 2007, 129, 14296.
JACS 2007, 129, 13776.
J. Mater. Chem. 2008,18, 3865.
Angew. Chemie. 2009, 48, 2135.
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Nanowires for Solar Energy Conversion
Caltech
Harvard Nature 2007
PV
PEC
Caltech JACS 2007
Science 2010
Berkeley JACS 2008
PSU JACS 2007
photovoltaics, photoelectrolysis,
Other applications in energy: thermoelectrics, battery electrodes
Vapor-Liquid-Solid Nanowire Growth
reactant
1-d growth nucleation
gold nanocatalyst
reactant
SiH4
SEM image
ΔTEM image
Si + 2 H
Gold
Nanoparticle
HRTEM image
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AuSi nano-alloy
10 μm
Vapor-Liquid-Solid growth
AuSi nano-alloy
Supersaturation
SiNW
Nucleation
5 nm
Using Silicon nanowires as examples
Using Silicon nanowires as examples
Morales & Lieber, Science 279, 208 (1998)
Cui et al., Appl. Phys. Lett. 78, 2214 (2001)
Wagner & Ellis Appl. Phys. Lett. (1964).
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A New Twist on Nanowire Formation
See Science 2008, 320, 1060 for details.
Jin Research Group
jin.chem.wisc.edu
Forest of PbS Nanowire “X-mas Trees”
These nanowire tree structures demonstrate an
entirely different nanowire growth mechanism
that is driven by screw dislocations.
100 μm
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A Primer on Dislocations
Edge dislocation
Burgers vector (b): The displacement vector to close a lattice circuit
Edge dislocation: Burgers vector ⊥ line of cut
Screw Dislocation: Burgers vector // line of cut
Dislocation&Crystal Growth: Frank’s Mechanism
Idealized layer-by-layer crystal growth on perfect
crystals
1930s Kossel, Stranski, Becker & Doring, Gibbs
1949 & 1951, Sir F. Charles Frank (1911-1998),
a self-perpetual step for adding new layers in crystal growth – screw dislocations
cause “growth spirals”
Growth Spirals observed
on crystal faces
Burton, Cabrera & Frank, Philos. Trans. R. Soc. London A, 1951, 243, 299.
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Dislocation & 1-D Anisotropic Crystal Growth
a self-perpetual step for adding new layers for crystal growth at low
supersaturation!
√
×
×
Tree Nanowires – combination of fast
dislocation-driven trunk NW growth and
slower VLS growth of branch NWs
1-D anisotropic crystal growth! -whiskers, nanowires…
DCTEM Observation of Screw Dislocations in
PbS X-mas Tree NWs
A
B
C
D
E
F
Bierman, Lau, … & Jin Science 2008, 320, 1060.
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“Eshelby Twist”
Strain associated with screw dislocation
Bierman, Lau & Jin Science 2008, 320, 1060.
Screw dislocation, if no opposite torque
is applied at its ends
α=
b
πR 2
J.D. Eshelby. Screw dislocations in thin rods. J. Appl. Phys. 24, 1953, 176-179.
II. Screw dislocation driven growth of 1D
nanomaterials is general to both vapor
phase and solution
phase growth
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Aqueous Solution Growth of ZnO Nanowires/tubes
High density, high aspect ratio, thin ZnO nanowires
ƒMost popular route:
Aqueous hydrolysis of zinc
nitrate with
hexamethylenetetramine
(HMT)
ƒGenerates low aspect ratio
nanowires/rods.
1 μm
ƒWe overcome this problem
by targeting low
supersaturation growth
conditions that promote
dislocation driven
growth.
2 μm
10 μm
Morphology Change with Supersaturation
c Axis Growth
Morin, Bierman, Tong & Jin in press Science, 2010.
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Kinetics of Crystal Growth
Experimentally determined growth rates vs. rate laws predicted by theory:
Prove screw dislocation driven crystal growth!
Morin, Bierman, Tong & Jin in press Science, 2010.
Dislocations in ZnO Nanowires/Nanotubes
• Diffraction contrast TEM show dislocation
with screw component along (001)
• Axial dislocations in NWs drives growth
• Single-crystal hollow nanotubes!
Morin, Bierman,
Tongtube
&Jin
lattice continuous
across
submitted
B, C
F
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Hollow Nanotubes: Open Core Dislocations
Dislocations contain elastic energy proportional to b2:
E=
R
μ
ln( )b 2
4π
r
r
a large value of b lead to a “hollow core dislocation”
(F. C. Frank, Acta Crystallogr. 1951, 4, 497)
• Core materials removed to alleviate the strain energy;
• Balanced by surface energy of the new internal surface:
R
μb 2
r= 2
8π γ
μ -- shear modulus
γ -- surface energy
Guggenheim Museum, New York
“Dislocation micropipes” in solid crystals and thin films (SiC, GaN, etc)
To Twist or Not to Twist: Re-Examine the
Energy Equations
Two pathways to relieve strain energy:
E = 2πγr +
μb 2 R μb 2 ( R 2 − r 2 )
ln( ) −
4π
r
4π ( R 2 + r 2 )
8π 2 γr R 2 + r 2
dE
* 2
= 0 → bTOTAL =
μ
dr
R − r2
• New energy minimization:
hollowing out at small b;
Eshelby twist at large b.
bTWIST = bTOTAL − bTUBE =
⎞
8π 2γr ⎛ R 2 + r 2
⎜
− 1⎟
μ ⎜⎝ R 2 − r 2 ⎟⎠
• Twist vs. hollow at different r/R:
thick tubes have little twist,
thin-walled tubes have twist.
Energy Minimization Æ b= 1.3 nm
Direct Measurement Æ b= 1.9 nm
Morin, Bierman, & Jin in press Science, 2010.
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Complex Nanowires for Solar Energy Conversion
1) Complex branching structures
potentially useful for solar energy
harvesting and carrier collection
•
Dendritic structures good for solar
energy harvesting and carrier collection
Nanoscale heterostructures allow more
diverse materials
•
Bierman & Jin,
(invited perspective) 2009, 2, 1050.
D
20 µm 20 µm
20 µm
Epitaxial growth on TiO2, NaCl, mica
Lau, …, & Jin J. Mater. Chem. 2009, 19, 934.
Solution Grown Nanomaterials of Inexpensive
Semiconductors for Solar Energy Conversion
Dislocation-driven nanowire growth has
advantages over VLS growth for large scale
applications of nanomaterials for energy.
– No metal catalysts,
– vapor or solution phase growth
– Aqueous solution growth better for large scale
synthesis!
– Heterojunctions by simple solution synthesis?
e.g. Fe2O3 - TiO2
Solution grown ZnO nanotube
For example, solar energy from Fe2O3 NWs?
•
•
•
•
Hematite is a poor semiconductor (Eg= 2.1 eV)
Cheap, stable in aqueous solutions, promising
for photocatalysis
Nanowires might circumvent the problems
How to construct solar devices with rust
nanowires?
On going – Mark Lukowski, Miguel Caban, Fei Meng, Matt Faber
Fe2O3 nanowires
2 μm
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Significance of the Discoveries
9 a “new” nanowire growth mechanism driven by screw
dislocations
9 Clear demonstration of the Eshelby twist
9 Spontaneous formation of single-crystal nanotubes driven
by screw dislocations
9 General to 1-D growth of many materials, vapor or
solution growth, such as:
‰ ZnO, PbQ (we have proven herein)
‰ InN, GaN, Te, SnO2, etc (seen in literature)
‰ SiC, CdS, CdSe, etc.
9 Used classic crystal growth theory to conclusively prove
dislocation-driven growth
9 Complex NW structures useful for solar energy conversion
9 Large scale, low cost synthesis of NW materials
Unanswered questions and future work:
•
•
How does the screw dislocation originate?
The perfect platform for investigating the effects of a single
dislocation on material properties.
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