Chemistry and Physics of Nanoscale Materials Energy Spintronics - - PDF document

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Song Jin

Department 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 Spintronics

magnetic semicond. nanomaterials

Silicide Nanowires Thermoelectrics

CrSi2, MnSi1.8 nanowires; Magnetic Fe1-xCoxSi and silicon-based spintronics Biomimetic Assembly

• f 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

Chalcogenide Nanomaterials

EuS, EuO nanocrystals and nanowires

Energy 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.

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Nanowires for Solar Energy Conversion

photovoltaics, photoelectrolysis,

Other applications in energy: thermoelectrics, battery electrodes

Caltech JACS 2007 Science 2010 PSU JACS 2007 Harvard Nature 2007 Berkeley JACS 2008

Caltech PEC PV

Vapor-Liquid-Solid Nanowire Growth

gold nanocatalyst

1-d growth nucleation

reactant

Vapor-Liquid-Solid growth

reactant

SiH4 Si + 2 H2 Δ

AuSi nano-alloy AuSi nano-alloy Supersaturation SiNW Nucleation Gold 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

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Jin Research Group

jin.chem.wisc.edu

A New Twist on Nanowire Formation

See 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.

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A Primer on Dislocations

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 Edge dislocation

Dislocation&Crystal Growth: Frank’s Mechanism

Idealized layer-by-layer crystal growth on perfect crystals

1930s 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

• n crystal faces

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Dislocation & 1-D Anisotropic Crystal Growth

a 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

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“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

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R b π α =

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

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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

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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

Morin, Bierman, Tong &Jin submitted B, C F

lattice continuous across tube

• Single-crystal hollow nanotubes!

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2

) ln( 4 b r R E π μ =

Hollow Nanotubes: Open Core Dislocations

Dislocations 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

γ π μ

2 2

8 b r =

“Dislocation micropipes” in solid crystals and thin films (SiC, GaN, etc) R r μ -- shear modulus γ -- 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( 4 2

2 2 2 2 2 2

r R r R b r R b r E + − − + = π μ π μ πγ

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − + = − = 1 8

2 2 2 2 2

r R r R r b b b

TUBE TOTAL TWIST

μ γ π

2 2 2 2 2

* 8 r R r R r b dr dE

TOTAL

− + = → = μ γ π Energy Minimization b= 1.3 nm Direct Measurement b= 1.9 nm Two pathways to relieve strain energy: Morin, Bierman, & Jin in press Science, 2010.

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Complex Nanowires for Solar Energy Conversion

20 µm

D

20 µm 20 µm

Epitaxial growth on TiO2, NaCl, mica Lau, …, & 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

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Significance of the Discoveries

a “new” nanowire growth mechanism driven by screw dislocations Clear demonstration of the Eshelby twist Spontaneous formation of single-crystal nanotubes driven by screw dislocations 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.

Used classic crystal growth theory to conclusively prove dislocation-driven growth Complex NW structures useful for solar energy conversion

• 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.