1. Determination of the Dielectric Function of Nickel Ferrite Thin Films
Luis A. Barrera1, Khadijih N. Mitchell1, Lina S. Abdallah1, Stefan Zollner1, Arunava Gupta2
1Department of Physics, New Mexico State University, Las Cruces, NM, 88003
2Center for Materials for Information Technology, University of Alabama, Tuscaloosa, AL, 35487
Background
5 mm x 5 mm substrate
1 micron thick
Single side polished
NiFe2O4 has a crystal structure of inverse spinel
MgAl2O4 has a crystal structure of normal spinel
NiFe2O4 is an indirect band gap system
Face-centered cubic oxygen lattice
Results
Conclusions
NiFe2O4 exhibits one indirect band gap (minority channel) and two
different direct band gaps (minority and majority channels)
The increase of Fe leads to cation disorder, thus broadening the
lattice vibration
The metallic properties are 1000 times weaker than actual metal
Characterized the optical properties of nickel ferrite thin films
Modeled data using Tauc-Lorentz oscillator
Found approximate band gaps
Plotted the absorption coefficient
This characterization will allow…
Stoichiometric
Fe-rich
2 srough Å
1 genosc Å
0 spinel vuv tabulated (1) mm
2 srough Å
1 genosc Å
0 spinel vuv tabulated (1) mm
MSE: 2.569
MSE: 3.845
Applications
Fiber-optic thermometers
Electronics
Data Storage
Spintronics
Objective
Precision measurements of the optical constants for NiFe2O4 with MgAl2O4 substrate in stoichiometric and Fe-rich samples using variable-angle spectroscopic ellipsometry.
References
C. Himcinschi, I. Vrejoiu, G. Salvan, M. Fronk, A. Talkenberger, D. Zahn, D. Rafaja, J. Kortus, J. Appl. Phys. 113, , (2013).
A Gupta et al. (need specifics)
H. Fujiwara, Spectroscopic Ellipsometry: Principles and Applications (Wiley, Chichester, England, 2007).
Method
Ellipsometry is a non-invasive optical technique that measures the change in polarization state of a light beam reflected from or transmitted through the sample under study.
Some basics:
n: index of refraction (real value)
k: extinction coefficient (imaginary value)
MSE: mean-squared error
ε~= ε1+ i ε2 : complex dielectric function
n~=n+ik: complex index of refraction
ε 1=n2-k2
ε 2=2nk
Measurements:
eV by 0.02 eV steps slow scan
65-75°with alignment detector
Linearly polarized light reflects off the sample surface at an oblique
angle, resulting in elliptically polarized light
Tauc-Lorentz oscillator models were used to fit the data in the
transparent region
Atomic Force Microscopy measurements (AFM) were conducted
to compare with WVASE32 generated models
AFM
Image rms: 22.0 Å
Image rms: 24.4 Å
Acknowledgements
We are grateful to Dr. Peter Cooke for guidance on performing atomic force microscopy measurements.
This work was supported, in part, by the National Science Foundation under grant numbers DMR (MRI), HRD (New Mexico AMP), and DMR
NSF HRD #