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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: [email protected]
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