1

Song JinDepartment of Chemistry

University of Wisconsin – Madison, Madison, WI 53706, USA

e-mail: jin@chem.wisc.edu Group webpage: jin.chem.wisc.edu/

Dislocation-Driven Nanomaterial Growth: Nanowire Trees, Nanotubes, and Their Potential Applications

in Solar Energy Conversion

US-Korea Nano Workshop, April 5, 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,

The Jin Research Group March 2010

Energy Spintronicsmagnetic semicond.

nanomaterials

SilicideNanowires

ThermoelectricsCrSi2, MnSi1.8 nanowires;

Magnetic Fe1-xCoxSi and silicon-based spintronics

Biomimetic Assembly of nanomaterials

Overview of Research Interests:Chemistry and Physics of Nanoscale Materials

JACS 2007, 129, 14296.JACS 2007, 129, 13776.J. Mater. Chem. 2008,18, 3865.Angew. Chemie. 2009, 48, 2135.

Chem. Mater. 2007, 19, 3238.Nano Lett. 2007, 7, 1649.JACS 2008, 130, 16086.J. Solid State Chem. 2008, 181, 1565.

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.

J. Mater. Chem. 2010, 20, 223.Nano Lett., 2007, 7, 965.APL 2007, 90, 173122.

Science 2008, 320, 1060.JACS 2009, 131, 16461.

Dislocation-Driven Growth mechanism of 1-D nanomaterials

Solar Energy PbSe, PbS nanowires

ChalcogenideNanomaterials

EuS, EuO nanocrystalsand nanowiresEnergy Environ. Sci., 2009, 1050. (Perspective)

Nano Lett. 2007, 7, 2907. J. Mater. Chem. 2009, 19, 934.

Adv. Mater. 2007, 19, 2677. (EuO)APL 2009, 95, 20251. (EuS XMCD)

Nano Lett. 2008, 8, 2356.

2

Nanowires for Solar Energy Conversion

photovoltaics, photoelectrolysis,Other applications in energy: thermoelectrics, battery electrodes

Caltech JACS 2007Science 2010 PSU JACS 2007

Harvard Nature 2007

Berkeley JACS 2008

Caltech

PECPV

Vapor-Liquid-Solid Nanowire Growth

gold nanocatalyst

1-d growth nucleation

reactant

Vapor-Liquid-Solid growthreactant

SiH4 Si + 2 H2Δ

AuSi nano-alloy AuSi nano-alloy Supersaturation

SiNWNucleationGold

Nanoparticle

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).

Using Silicon nanowires as examples

SEM image

10 μm

TEM image HRTEM image

5 nm

3

Jin Research Groupjin.chem.wisc.edu

A New Twist on Nanowire FormationSee Science 2008, 320, 1060 for details.

100 μm

Forest of PbS Nanowire “X-mas Trees”

These nanowire tree structures demonstrate an entirely different nanowire growth mechanism

that is driven by screw dislocations.

4

A Primer on Dislocations

Burgers vector (b): The displacement vector to close a lattice circuitEdge dislocation: Burgers vector ⊥ line of cutScrew Dislocation: Burgers vector // line of cut

Edge dislocation

Dislocation&Crystal Growth: Frank’s MechanismIdealized layer-by-layer crystal growth on perfect crystals1930s Kossel, Stranski, Becker & Doring, Gibbs

Burton, Cabrera & Frank, Philos. Trans. R. Soc. London A, 1951, 243, 299.

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

5

Dislocation & 1-D Anisotropic Crystal Growtha self-perpetual step for adding new layers for crystal growth at low

supersaturation!

1-D anisotropic crystal growth! --whiskers, nanowires…

√

× ×

Tree Nanowires – combination of fast dislocation-driven trunk NW growth and slower VLS growth of branch NWs

DCTEM Observation of Screw Dislocations in PbS X-mas Tree NWs

Bierman, Lau, … & Jin Science 2008, 320, 1060.

A

B C D E F

6

“Eshelby Twist”

Screw dislocation, if no opposite torque is applied at its ends

J.D. Eshelby. Screw dislocations in thin rods. J. Appl. Phys. 24, 1953, 176-179.

Strain associated with screw dislocation

2Rb

πα =

Bierman, Lau & Jin Science 2008, 320, 1060.

II. Screw dislocation driven growth of 1D nanomaterials is general to both vapor

phase and solution phase growth

7

Aqueous Solution Growth of ZnO Nanowires/tubes

Most popular route:Aqueous hydrolysis of zinc nitrate with hexamethylenetetramine (HMT)Generates low aspect ratio nanowires/rods.

We overcome this problem by targeting low supersaturation growth conditions that promote dislocation driven growth.

10 μm

1 μm

2 μm

High density, high aspect ratio, thin ZnO nanowires

Morphology Change with Supersaturation

Morin, Bierman, Tong & Jin in press Science, 2010.

c Axis Growth

8

Kinetics of Crystal GrowthExperimentally 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

Morin, Bierman, Tong &Jinsubmitted

B, C

F

lattice continuous across tube

• Single-crystal hollow nanotubes!

9

2)ln(4

brRE

πμ

=

Hollow Nanotubes: Open Core DislocationsDislocations contain elastic energy proportional to b2:

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:

Guggenheim Museum, New York

γπμ

2

2

8br =

“Dislocation micropipes” in solid crystals and thin films (SiC, GaN, etc)

Rr

μ -- shear modulusγ -- surface energy

To Twist or Not to Twist: Re-Examine the Energy Equations

• New energy minimization: hollowing out at small b; Eshelby twist at large b.

• Twist vs. hollow at different r/R:thick tubes have little twist, thin-walled tubes have twist.

)()(

4)ln(

42 22

2222

rRrRb

rRbrE

+−

−+=π

μπ

μπγ

⎟⎟⎠

⎞⎜⎜⎝

⎛−

−+

=−= 1822

222

rRrRrbbb TUBETOTALTWIST μ

γπ

22

222

*80rRrRrb

drdE

TOTAL −+

=→=μγπ

Energy Minimization b= 1.3 nmDirect Measurement b= 1.9 nm

Two pathways to relieve strain energy:

Morin, Bierman, & Jin in press Science, 2010.

10

Complex Nanowires for Solar Energy Conversion

20 µm

D

20 µm 20 µm

Epitaxial growth on TiO2, NaCl, micaLau, …, & Jin J. Mater. Chem. 2009, 19, 934.

Bierman & Jin, (invited perspective) 2009, 2, 1050.

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

Solution Grown Nanomaterials of Inexpensive Semiconductors for Solar Energy Conversion

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?

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

2 μm

Fe2O3 nanowires

Solution grown ZnO nanotube

On going – Mark Lukowski, Miguel Caban, Fei Meng, Matt Faber

11

Significance of the Discoveriesa “new” nanowire growth mechanism driven by screw dislocationsClear demonstration of the Eshelby twistSpontaneous formation of single-crystal nanotubes driven by screw dislocationsGeneral 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.

Used classic crystal growth theory to conclusively prove dislocation-driven growthComplex NW structures useful for solar energy conversionLarge 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.