Epitaxial Electrodeposition of Metal Oxide Thin Films and

Superlattices for Energy Conversion and Storage

Jay A. Switzer, Elizabeth Kulp, Rakesh Gudavarthy, and Guojun Mu

Department of Chemistry Materials Research Center

Missouri University of Science & TechnologyRolla, MO 65409, USA

Email: jswitzer@mst.edu

Outline• Electrodeposition of ceramic films

• Tilted ZnO nanospears on Si(001) – photovoltaics & solid-state lighting

• Superlattices based on Fe3O4 – sensors & RRAM memory– Defect-chemistry superlattices based on Fe3O4

– Zn-doped Fe3O4 superlattices

• Electrodeposition of nanostructured lithium battery materials

Electrodeposition of metal oxides

Deposition methods

I. Redox Change

3Fe2+ + 4H2O Fe3O4 + 8H+ + 2e-

II. Base Generation: 2H2O + 2e- H2 + 2OH-

Zn2+ + 2OH- Zn(OH)2 ZnO + H2O

Ca2+ + HCO3- + OH- CaCO3 + H2O

III. Acid Generation: 2H2O O2 + 4H+ + 4e-

Zn(OH)42- + 2H+ ZnO + 3H2O

Cu(OH)42- + 2H+ CuO + 3H2O

Electrodeposited Epitaxial Oxide Films

ZnO on Au(110) AgO on Au(111)

CuO on Au(100)Cu2O on InP(111)

Applications of ZnO films and nanowires

Huang et al. Science 292, 1897-1899 (2001). Dietl et al. Science 287, 1019-1022 (2000).

D. Andeen et al. Adv. Funct. Mat. 16, 799-804 (2006).Tsukazaki et al. Science 315, 1388-1391 (2007).

CBD of Epitaxial ZnO(203) on Si(100)

ZnO(002) pole figureSEM image of ZnO nano-spears on Si(100)

Speciation and solubility of Zn(II) at 70 oC

X-ray 2θ scan

0.0

0.3

0.6

0.9R

elat

ive

con

c.lo

g [

So

lub

ility

]

Zn

(OH

) 42-

Zn(OH)2

Zn

(OH

) 3-

Zn

(OH

)+Zn2+

6 8 10 12 14

-6.0

-4.5

-3.0

-1.5

*Zn(OH)2

ZnO

pH

Epitaxial relationships: ZnO(203)[010] // Si(100)[010], ZnO(203)[010] // Si(100)[001],ZnO(203)[010] // Si(100)[010], and ZnO(203)[010] //Si(100)[001]

Tilted ZnO Nanospears on Si(001)

Magnetite – Fe3O4 (a = 8.394 Ǻ)

Inverse spinel = B(AB)O4

Fe(III)↓Td

[Fe(II)↑Fe(III)↑]OhO4

Fe(III) antiferromagnetically coupledNet ferrimagnetism due to Fe(II) 100 % spin polarization at Fermi levelCurie temperature = 860K

Octahedral sites: Fe2+ + Fe3+

Tetrahedral sites : Fe3+

8.00 Angstroms

Magnetite-Based Magnetoreception

Bacterial Magnetoreceptors

Homing Pigeon Magnetoreceptors

Johnsen and Lohmann Physics Today 61, 29-35 (2008).

Fe3O4 on Au(111)

LowResistance

Parallel Spins

Antiparallel Spins

HighResistance

Tunnel Barrier or

Nonmagnetic Layer

Spin-Dependent TransportMagnetoresistance

Ag wire iout

Ag wire

iin

Glass

HSuper Glue

Fe3O4

Resin

Substrate

a

b

a

b

a

b

a

b

Schematic of a Superlattice

Science 247, 444 (1990) Chemistry of Materials 9, 1670 (1997)Science 258, 1918 (1992) Chemistry of Materials 14, 2750 (2002)Science 264, 1505 (1994) Science, submitted (2009)

Solution: 0.043 M Fe2(SO4)3 hydrate 0.1 M triethanolamine (TEA)

2M NaOH

Temperature: 60 to 90oC

Potential: -1.0 to -1.2 V vs. Ag/AgCl

Proposed Mechanism:

Fe(TEA)3+ + e- Fe2+ + TEA

2Fe(TEA)3+ + Fe2+ + 8OH- Fe3O4 + 4H2O + 2TEA

Cathodic Deposition of Fe3O4

Scan rate = 50 mV/s

J. Mater. Res. 21, 293 (2006)Science, submitted (2009)

Using Applied Potential to Control Stoichiometry

Measured iV curve

Calculated surface concentrations

Zn conc. as function of potential Lattice parameters as function of potential

Fe3O4 superlattices produced by pulsing between -1.01 V and -1.05 V

= λ (N+ - N-)/ (2 (sin θ+ - sin θ-))

•N+ and N- are satellite orders•λ is the x-ray wavelength•θ+ and θ- are the positions of the high angle and low angle satellites on the 2θ scan.

Transient of a superlattice produced by pulsing potential between -1.01 V (3 s) and -1.05 V (1 s)

X-ray Analysis of a Superlattice ( = 12.5 nm) on Au(111)

(311) superlattice pole figure

(311) azimuthal scans at 30o

Rocking curves

(444) superlattice

(111) Au

X-ray 2 scansuperlattice

Au

Zn-Fe3O4 superlattices produced by pulsing between -0.99 V and -1.05 V

FIB Cross Section of a ZnxFe3-xO4 Superlattice = 78 nm

Magnetoresistance of Zinc Ferrite Superlattice (12.2 nm) at 45 K

Resistive Switching in Zinc Ferrite Superlattice (12.2 nm) at 77 K

100 mV/s scan rate 10 mA/s scan rate

Resistive Random Access Memory RRAM ?

Electrodeposition of Nanostructured NaMnO2 for Li Battery Cathodes

Electrodeposition of NaMnO2 from Mn(II)-TEA in strong base

NaMnO2 is a precursor to LiMnO2

Electrical continuity

Nanostructured material has high surface area

Potentially high capacity

Does not revert to LiMn2O4 spinel on cycling

Functions as supercapacitor

Electrodeposition of Nanostructured NaMnO2 for Li Battery Cathodes

CV in Mn-TEA solution SEM of electrodeposited NaMnO2

Acknowledgements

Students/Postdocs

Elizabeth KulpRakesh GudavarthyEric BohannanHiten KothariSteven LimmerShuji NakanishiShaibal SarkarNiharika Burla

Guojun Mu

Financial Support National Science Foundation CHE-0437346 CHE-0243424 DMR-0504715 DMR-0076338 Department of Energy - DE-FG02-08ER46518