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Growth and Structure of Thin Fe Films on the Ti-Al Interface

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Growth and Structure of Thin Fe Films on the Ti-Al Interface C. V. Ramana Montana State University http://www.physics.montana.edu/Ionbeams/ionbeams.html – PowerPoint PPT presentation

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Title: Growth and Structure of Thin Fe Films on the Ti-Al Interface


1
Growth and Structure of Thin Fe Films on the
Ti-Al Interface
  • C. V. Ramana
  • Montana State University
  • http//www.physics.montana.edu/Ionbeams/ionbeams.h
    tml

2
Stabilizing Metal-Metal Interfaces
  • Metal thin film devices have layers nm
    thickness
  • Diffusion occurs frequently interface nm thick
  • Need to stabilize the interface, provide a
    template for epitaxial growth, minimize
    interdiffusion
  • Applications magnetoresistive devices, spin
    electronics
  • Surface energy (broken bonds)
  • Chemical formation energy
  • Strain energy

Smith et al, Appl. Surf. Sci. 219 (2003) 28
3
Experiment
  • Substrate Al(100)
  • Metal overlayers
  • Fe
  • Ti
  • Surface energy gt Al surface energy
  • Form Al compounds with ?Hform lt 0
  • Use resistively heated wires ( ML/min)
  • Deposition at room temperature

4
Techniques and Goals
  • Rutherford backscattering and channeling (RBS/c)
  • Low-energy electron diffraction (LEED)
  • Low-energy ion scattering (LEIS)

5
Overview of Rutherford Backscattering and
Channeling
  • MeV He ions
  • Yield Q ? ? (Nt)
  • Fe (Ti) peak for coverage
  • Al peak for structure

6
Fe Growth on Al(100) Does Ti Interlayer Makes
Any Difference?
Ramana et al, Phys. Rev. Lett. 90 (2003) 66101
7
Fe-Fe Shadowing
8
Angular Ion Yield Curves
0o
If it is fcc Fe
9
Angular Ion Yield Curves Cont
If it is bcc Fe
10
Structure of Fe Off-Normal Ion Channeling
Measurements
11
Structure of Fe contd..
?min 54.55o
12
Lattice Parameters Calculations
Lattice Parameters
a) Fe bcc 2.8665 Å
b) Al fcc (4.0496) 2.8635 Å
c)TiAl Tetragonal a 4.0155 Å c 4.0625 Å
2.8560 Å
13
Unrelaxed bcc Fe
Volume is conserved VFe CFe A CFe X2 CFe
(2.8665)3/X2
14
Fe (bcc) relaxed to Al substrate
Volume is conserved VFe CFe A CFe X2 CFe
(2.8665)3/X2
? tan-1(X / CFe )
15
Fe (bcc) relaxing to Ti-Al interface
16
Calculations cont.
X CFe ?
Fe 2.8665 - 54.74
Al 2.8635 2.8725 54.65
TiAl 2.8560 2.8876 54.44
17
Why does it work?
  • Bimetallic Formation Energies (kJ/mole-atom)
  • Fe/Al 25 Ti/Al 38 Fe/Ti 20
  • Ti-Al bond stronger than Fe-Al or Fe-Ti so Ti
    prefers to stay near the Al interface
  • Lattice matching bcc Fe (100) unit cell has a
    2.86 Å
  • fcc Al (100) has Al-Al distance
    2.86 Å
  • hcp Ti (0001) has Ti-Ti distance 2.95 Å
  • Fe (small atom) more easily accommodated by
    Al(100) than Ti (larger atom). Formation of
    Ti-Al interface stiffens the
  • surface, restrains movement of Fe into the
    substrate.

18
Summary and Conclusion
  • Demonstrated the use of a metallic interlayer to
    stabilize a metal-metal interface and promote
    epitaxial growth
  • Fe growth occurs in slightly distorted bcc
    structure on the Al(100) surface with Ti
    interlayer at the interface.

19
Acknowledgements
  • Prof. Richard J. Smith
  • Prof. Bum-Sik Choi (Korea)
  • Ion Beamers
  • NSF (DMR-0077534)
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