Shape & Structure
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Shape & Structure Growth Approach Molecular Beam Epitax y & Shuttered RHEED Composition Growth of Self-Assembled BaTiO 3 Nanodots using Tensile Strain Timothy A. Morgan, Zhaoquan Zeng, Robert J. Sleezer, Gregory J. Salamo Department of Physics, University of Arkansas, Fayetteville, Arkansas Institute for Nanoscale Materials and Engineering, University of Arkansas, Fayetteville, Arkansas Motivation Summary RHEED: The Transition to Nanodots a b d c MgO [110] MgO [100] BTO [100] BTO [110] Ti 2p 1/2 2p 3/2 O 1s Ba 3d 5/2 TiO 2 layer starts BaO layer starts Growth Mechanism • Tensile Strain (+5.5% Mismatch) • BTO stretches laterally • Strain Builds Up • BTO relaxes into islands • Riber MBE32 • Addon Oxygen Plasma • DCA Titanium Cell • RHEED • kSa BandiT Tempearture Monitoring Only Ba & O Cells Open Only Ti & O Cells Open Ferroelectric materials has found application in non-volatile especially FeRAM. Theoretical investigation (Bellaiche, Nature, 2004) of Ferroelectric nanostructures has found the possibility of exploiting polarization vortex states to increase the density of FeRAM to 60 Tbit/in 2 . The pursuit of creating material to exploit this phenomenon is the goal of this work. • Reflection High Energy Electron Diffraction (RHEED) monitoring during layer by layer growth • Kikuchi lines on MgO indicate clean, flat surface (Figures a, b) • Spotty RHEED pattern at 15 monolayers of BTO growth indicates nanodot formation (Figures c,d) • Atomic force microscopy (AFM) revealed dots • Avg. height 1.3 nm, Avg. radius 18 nm, Avg. Volume 3,1457 nm 3 , Density 5 x 10 11 cm -2 • The volume of the dots only accounts for ~1 monolayer deposited • Cross-sectional transmission electron microscopy (XTEM) confirms a layer ~14 monolayers (5.6 nm) thick exists beneath the dots • X-ray photoelectron spectroscopy (XPS) revealed BTO stoiciometry to be 1:1:3 for Ba:Ti:O Molecul;ar beam epitaxy has been used to grow self- assembled barium titanate (BTO) nanodots on MgO (001). This is shown by: • RHEED confirms the tensile strain allows the BaTiO3 to transition from a two dimensional (2D) film to three dimensional (3D) islands • AFM confirms BTO nanodots and reveals an average height and diameter of 1.3 nm and 36 nm, respectively • XPS confirmed the stoichiometry of the grown material as 1:1:3 for Ba:Ti:O • XTEM revealed a layer between 4-6 nm thick lies beneath the dots ACKNOWLEDGEMENTS: Department of the Army, Army 0.4 1.2 2 2.8 3.6 4.4 0 5 10 15 20 25 30 Height (nm) Frequency 14 18 22 26 30 34 38 42 46 50 54 58 62 0 2 4 6 8 10 12 14 16 18 Radius (nm) Frequency
description
Growth of Self-Assembled BaTiO 3 Nanodots using Tensile Strain . Timothy A. Morgan, Zhaoquan Zeng, Robert J. Sleezer, Gregory J. Salamo. Department of Physics, University of Arkansas, Fayetteville, Arkansas - PowerPoint PPT Presentation
Transcript of Shape & Structure
Shape & Structure
Growth Approach
Molecular Beam Epitax y & Shuttered RHEEDComposition
Growth of Self-Assembled BaTiO3 Nanodots using Tensile Strain Timothy A. Morgan, Zhaoquan Zeng, Robert J. Sleezer, Gregory J. Salamo
Department of Physics, University of Arkansas, Fayetteville, ArkansasInstitute for Nanoscale Materials and Engineering, University of Arkansas, Fayetteville, Arkansas
Motivation
Summary
RHEED: The Transition to Nanodots
a b
dc
MgO [110] MgO [100]
BTO [100]BTO [110]
Ti 2p1/2 2p3/2
O 1sBa3d5/2
TiO2 layerstarts
BaO layerstarts
Growth Mechanism• Tensile Strain
(+5.5% Mismatch)
• BTO stretches laterally
• Strain Builds Up• BTO relaxes into
islands
• Riber MBE32• Addon Oxygen Plasma• DCA Titanium Cell• RHEED• kSa BandiT Tempearture
Monitoring
Only Ba & O Cells Open
Only Ti & O Cells Open
Ferroelectric materials has found application in non-volatile especially FeRAM. Theoretical investigation (Bellaiche, Nature, 2004) of Ferroelectric nanostructures has found the possibility of exploiting polarization vortex states to increase the density of FeRAM to 60 Tbit/in2. The pursuit of creating material to exploit this phenomenon is the goal of this work.
• Reflection High Energy Electron Diffraction (RHEED) monitoring during layer by layer growth• Kikuchi lines on MgO indicate clean, flat surface (Figures a, b)• Spotty RHEED pattern at 15 monolayers of BTO growth indicates nanodot formation (Figures c,d)
• Atomic force microscopy (AFM) revealed dots• Avg. height 1.3 nm, Avg. radius 18 nm, Avg. Volume 3,1457 nm3, Density 5 x 1011 cm-2 • The volume of the dots only accounts for ~1 monolayer deposited• Cross-sectional transmission electron microscopy (XTEM) confirms a layer ~14 monolayers (5.6 nm) thick exists beneath the dots
• X-ray photoelectron spectroscopy (XPS) revealed BTO stoiciometry to be 1:1:3 for Ba:Ti:O
Molecul;ar beam epitaxy has been used to grow self-assembled barium titanate (BTO) nanodots on MgO (001). This is shown by:• RHEED confirms the tensile strain allows the BaTiO3 to transition from a two dimensional (2D) film to three dimensional (3D) islands• AFM confirms BTO nanodots and reveals an average height and diameter of 1.3 nm and 36 nm, respectively• XPS confirmed the stoichiometry of the grown material as 1:1:3 for Ba:Ti:O• XTEM revealed a layer between 4-6 nm thick lies beneath the dots
ACKNOWLEDGEMENTS: Department of the Army, Army Research Lab, Contract No: W911NF-08-2-0006
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