A Statistical Approach to Optimize Parameters for Electrodeposition of Indium (III) Sulfide Films, Potential Low-Hazard Buffer Layers for Photovoltaic Applications

1. Maqsood Ali Mughal
Environmental Sciences Proposal Defense
Room No. : 153
12:30 PM
Arkansas State
University
“A Statistical Approach to Optimize Parameters for
Electrodeposition of Indium (III) Sulfide Films,
Potential Low-Hazard Buffer Layers for Photovoltaic
Applications”
November 14, 2014

2. Why Solar Cells??
Rapidly falling
prices and gains
in efficiencies
Federal/state tax
incentives, and
rebates
World carbon
emissions rate is
projected to
increase to 11.0
GtC/yr by 2050 [3]
Fossil fuels are
not renewable
energy
Social
responsibility
Economic goals Sustainability
Source: beyond1energy, LLC
Source: beyond1energy, LLC
Energy reserves on
earth equals energy
from just 20 days of
sunshine [2]
Increased energy
demand, 18 TW by
2050 [1]

3. SolarCellStructure
Source: http://www.circuitstoday.com/thin-film-solar-
cell
Source: Jackson, Philip, et al. March 2014

4. Role of Buffer Layer in Solar Cells
To form a junction with the absorber layer
while admitting a maximum amount of light
to the junction region and absorber layer.
To protect or passivate the junction material.
Provide layer of appropriate thickness and index of
refraction that will reduce the overall reflectance.
To absorb light energy from only the high-
energy end of the spectrum.
Must be thin enough and have a large enough
bandgap (2.3 eV or more) to let nearly all
available light through the interface
(junction) to the absorbing layer.
Photo taken by: John Hall

5. n-type
semiconductor
Large optical
bandgap of
(2.0-2.3) eV [4].
Stable, high absorption
coefficient, and
photoconductive [5][6].
Replacement for
hazardous CdS, as a
window layer in
solar cells [7].
Physical properties and structure of
In2S3 thin films
Structure Tetragonal
Color Yellow
Appearnce
Crystalline
solid
Melting Point 1050 oC
Density 4450 kg/m3
Lattice Parameters
a=b=7.619 Å
c=32.329 Å
Indium (III) Sulfide (In2S3)

6. Highest Efficiencies Achieved with In2S3-based Solar Cells Produced by
Various Deposition Methods
Buffer
Layer
Deposition
Method
Absorber
Layer
Efficiciency
[%]
Jsc
[mA/cm2
]
Voc
[mV]
FF
[%]
Area
(cm2
)
Reference Institution
In2S3
Sputtering CIGS 16.4 32.5 660 77.5 0.1 Naghavi N. et al. (2010) ZSW/HMI/WS
ALD CIGS 16.4 31.5 665 78 0.5
Naghavi N. et. al.
(2004)
ENSCP/ZSW
CBD CIGS 15.7 37.4 574 68.4 0.5 Allsop N.A. et al. (2005) IPE/ASC
PVD CIGS 15.4 33.7 628 72.7 0.528
Fraunhofe ISE
(2009)
Wurth Solar
ILGAR CIGS 14.7 37.4 574 68.4 0.5
Fischer C.-H. et al.
(2010)
HMI
ALE CIGS 13.5 30.6 604 73 N/A D. Lincot et al. (1995) LECA
USP CIGS 13.4 33.4 585 69 N/A Buecheler S. (2009) LTFP/SFLMTR
ED CIGS 9.5 29.3 535 61 N/A
Chassaing E. et al.
(2011)
IRDEP/IREM
CSP CuInS2 9.5* 48.2 588 33.5 N/A John T.T. (2005) CUSAT
Deposition
Method (Buffer
Layer)
Absorber
Layer
Buffer
Layer
Efficiency
[%]
Jsc
[mA/cm2]
Voc
[mV]
FF
[%]
Area
(cm2)
References
ALD
CIGS In2S3 16.4 31.5 665 78 0.5 A. Hultqvist, et al. 2007
CdTe CdS 16.7 32.8 671 75.8 0.5 Y. Yan, et al. 2012
CBD
CIGS In2S3 15.7 37.4 574 68.4 0.5
C. D. Lokhande, et al.
1998
CIGS CdS 20.8 39.6 581 60.3 0.5 P. Jackson, et al. 2014
PVD
CIGS In2S3 15.2 29.8 677 75.6 0.528 S. Gall, et al. 2007
CIGS CdS 14 31.4 613 73 0.5 U. P. Singh, et al. 2010
Sputtering
CuInS2 In2S3 12.2 31.5 665 78 0.1 N. Naghavi, et.al, 2003
CuInS2 CdS 9.4 20.3 671 68.9 0.5 A. Grimm, et al. 2008
USP
CIGS In2S3 11.9 30.2 543 73 0.3 N. Demirci, et al. 2012
CIGS CdS 12.5 30.3 576 73 0.3 Fella, et al. June 2010
Electrodeposition
CIGSe In2S3 10.4 29.3 535 61 0.5 N. Naghavi, et al. 2011
CdTe CdS 10.8 23.6 753 61 0.5 S. K. Das, et al. 1993
In2S3 vs. CdS

7. Electrodeposition 1) Straightforward scale-up to
larger areas.
2) Low cost, simple apparatuses
and reagents; no vacuum
required [8].
3) Relatively low hazard due to
non-gaseous nature.
4) Potential for stoichiometry
control through variation of
deposition voltage and current, and
in-situ monitoring of photocurrents.
5) Excellent material utilization
efficiency [9].
Three-electrode
Electrochemical Cell
Side View
Aerial View
Coated-glass
substrate
(cathode)Reference
electrode
Graphite
(anode)
Magnetic
stir bar
Teflon
cover
Temperature
probe
Glass Beaker

8. Experiment Details
 Solvent: ethylene glycol, 150 ml
 Solutes: 0.1 M NaCl, 0.1 M Na2S2O3. 5H2O, 0.05 M InCl3
(Sulfur concentration is 0.1 M and 0.15 M)
 Anode (counter electrode): graphite, 1.25 inch by 1.25 inch.
 Reference electrode: Ag/AgCl (filled with KCL & C2H6O2)
 Cathode (working electrode): molybdenum-coated glass, ITO, FTO
 Thickness: 0.12 inch
 Material: SiO2: Mo
 Target resistivity value of 2.5 – 30 ohms per square
 Size: 1 inch by 1 inch
 Wavenow digital potentiostat: Pine Research Instrumentation
 Digital hotplate from Fisher Scientific (Isotemp 11-400-49SHP)
was used to heat and stir the solution.
 Substrates ultrasonically (Cole Parmer 8890) cleaned with
acetone for 15 min
 Distilled water used for rinsing the films
* Samples are stored in air-tight plastic boxes/bags to protect the films.

9. 9

10. 10
MM-In2S3-06/16/11-1 MM-In2S3-06/14/11-2
MM-In2S3-06/8/2011-9
MM-In2S3-06/2/2011-6
MM-In2S3-04/19/2011-6
MM-In2S3-04/06/2011-9
MM-In2S3-03/30/2011-3
MM-In2S3-03/10/2011-8
MM-In2S3-03/09/2011-7
MM-In2S3-03/08/2011-5
MM-In2S3-03/07/2011-3 MM-In2S3-02/16/2011-4
MM-IIn2S3-03/03/2011-2MM-In2S3-02/15/2011-2

11. Voltage
Temperature
Time
Composition of
Solution
Stir Rate
Current
Density
Deposition Parameters
Solvent

12. Absorbance Optical
Bandgap
Stoichiometry
Crystalline
Structure
Morphology
Thickness
Performance Parameters

13. Why Taguchi Experimental Design?
Taguchi Methods are statistical methods developed
by Genichi Taguchi to improve the quality of manufactured
goods, and more recently have also been applied to
engineering, biotechnology, etc [10].
Two basic goals of Taguchi Methods:
 Quality Control
 Design of Experiments (DOE)
 To determine the “best” combination of factors and levels to produce
a high quality product.
 To measure the impact/sensitivity of factors and parameter levels on
the characterized performance of a product using statistical analysis
tools (Orthogonal Regression, ANOVA, etc.).

14. Analyzing
Experimental Data
 Once the design of experiments (DOE) has
been determined and the trials have been
conducted, the measured performance
characteristic from each trial can be used to
analyze the relative effect of the different
parameters.
 To demonstrate the data analysis procedure,
the following orthogonal design arrays (L18,
L27, etc.) will be used, but the principles can be
transferred to any type of array.
 The Taguchi Method allows for the use of a
noise matrix including external factors
affecting the process outcome rather than
repeated trials [11].
Software:
Minitab, Matlab, MS Excel
і = experiment number
u = trial number
Ni = number of trials for experiment i
S/N

15. Collected : 14-Sep-2011 06:15 PM
Livetime (s) : 37.16
Real time (s) : 38.30
Detector : Silicon
Window : SATW
Tilt (deg) : 0.0
Elevation (deg) : 45.0
Azimuth (deg) : 0.0
Magnification : 552 X
Accelerating voltage ( kV ) : 19.48
Process time : 4
EDS Elemental Peaks for In2S3

16. SEM/EDS Analysis
Spectrum 1
Spectrum 2
Spectrum 3
(a) (b)
Experiment No. 5 and Trial No. 2) (a) SEM image of In2S3 film at 1.21 kX (b) SEM image of
scratched-off film on an aluminum stub at 99 X with selected surface area (squares) for EDS
analysis

17. Sulfur to Indium (S/In) Ratios from Energy
Dispersive X-ray Spectroscopy (EDS)
Uniformity
Experiment
No.
Taguchi Orthagonal
L27 Array
Sulfur to Indium Ratio (S/In)
Trial 1 Trial 2 Trial 3 Mean
A B C D S/In S/In S/In S/In
■ 1 1 1 1 1 1.432 1.462 1.447 1.447
■ 2 1 1 2 2 1.459 1.468 1.464 1.464
■ 3 1 1 3 3 1.49 1.535 1.513 1.513
■ 4 1 2 1 2 1.473 1.35 1.411 1.411
■ 5 1 2 2 3 1.522 1.47 1.481 1.49
■ 6 1 2 3 1 1.432 1.482 1.457 1.457
■ 7 1 3 1 3 1.465 1.452 1.459 1.459
■ 8 1 3 2 1 1.374 1.43 1.402 1.402
■ 9 1 3 3 2 1.428 1.484 1.456 1.456
■ 10 2 1 1 2 1.381 1.44 1.411 1.411
■ 11 2 1 2 3 1.442 1.418 1.43 1.43
■ 12 2 1 3 1 1.393 1.454 1.424 1.424
■ 13 2 2 1 3 1.743 1.853 1.798 1.798
□ 14 2 2 2 1 1.547 1.238 1.393 1.393
□ 15 2 2 3 2 1.448 1.269 1.358 1.358
□ 16 2 3 1 1 2.886 2.051 2.468 2.468
□ 17 2 3 2 2 2.434 1.966 2.2 2.2
□ 18 2 3 3 3 2.478 2.014 2.246 2.246
□ 19 3 1 1 3 2.329 1.449 1.889 1.889
□ 20 3 1 2 1 2.507 2.398 2.452 2.452
□ 21 3 1 3 2 1.384 1.469 1.426 1.426
□ 22 3 2 1 1 1.344 1.371 1.340 1.354
□ 23 3 2 2 2 1.357 1.327 1.342 1.342
□ 24 3 2 3 3 2.722 2.237 2.48 2.48
□ 25 3 3 1 2 2.007 2.817 2.412 2.412
□ 26 3 3 2 3 1.448 1.509 1.478 1.478
□ 27 3 3 3 1 1.429 1.539 1.484 1.484

18. OutputResponseTable
Levels
A,
Deposition
Voltage
(V)
B,
Deposition
Time
(min.)
C,
Composition
of Solution
(COS)
D,
Deposition
Temperature
(o
C)
1 34.79 31.61 24.68 25.04
2 23.21 25.73 30.92 30.13
3 23.63 24.52 26.15 27.18
▲ 11.58 7.08 6.23 5.10
Rank 1 2 3 4
Output Response Table for Signal-to-Noise
Ratios

19. Optimized Electrodeposition Parameters
-0.8V-0.7V-0.6V
35
30
25
9min6min3min
321
35
30
25
170C160C150C
Deposition Voltage (E)
MeanofSNratios
Deposition Time (D-Time)
Composition of Solution (COS) Deposition Temperature (D-Temp)
Main Effects Plot for SN ratios
Data Means
Signal-to-noise: Nominal is best (10*Log10(Ybar**2/s**2))
(V)

20. Orthogonal Regression Analysis
(S/In vs. Deposition Voltage)
Plot of S/In Ratio vs. Deposition Voltage with Fitted Line
S/InRatio
Deposition Voltage (V)

21. Spectrum In stats. O Si S Mo In Total S/In
Spectrum 1 Yes 6.54 0.00 54.1 3.12 36.24 100.00 1.493
Spectrum 2 Yes 0.00 0.00 56.65 8.36 37.51 100.00 1.51
Spectrum 3 Yes 0.00 0.00 55.18 7.27 37.54 100.00 1.471
Spectrum 4 Yes 14.48 0.00 50.65 2.82 33.75 100.00 1.5
Spectrum 5 Yes 0.00 0.00 58.32 0.00 40.5 100.00 1.443
Spectrum 6 Yes 0.00 0.00 59.8 0.00 39.91 100.00 1.498
Spectrum 7 Yes 4.21 0.00 57.49 0.00 38.30 100.00 1.501
Spectrum 8 Yes 0.00 0.00 60.28 0.1 39.71 100.00 1.53
Mean 1.493
Max. 14.48 0.00 60.28 8.36 40.5
Min. 0.00 0.00 50.65 0.00 33.75
MM-In2S3-09/01/11-6
EDS Data for In2S3 Films Grown at Optimal Values Obtained
from Taguchi Analysis

22. Morphology- Scanning Electron Microscopy
(SEM)
Electrodeposited at -
0.685 V for 6 min. and at
-0.7 V for 40 min.
(repeated trials)
Pulse-plating (-0.8 V
with 10 sec. delay) at120
oC for 50 min. Mo
Pulse-plating (-0.685 V
with 10 sec. delay) at 70
o
C for 95 min. FTO
Pulse-plating (-0.7 V
with 15 sec. delay) at 150
oC for 48 min. FTO
Pulse-plating (-0.7 V
with 10 sec. delay) at 80
oC for 75 min. ITO
Indium sulfide ring
formation from sodium
thiosulfate as sulfur
source-ITO
Electrodeposited at -
0.685 V for 4 min with
ethylene glycol solvent
Current density:
0.75 mA/cm2
Electrodeposited at -0.7
V for 15 min. (sodium
thiosulfate as sulfur
source)
Electrodeposited at -0.7
V for 50 min. at 160 o
C
JH: Electrodeposited at -
0.8 V for 30 min in
formamide solvent
Current density:
1.25 mA/cm2
Current density:
1.5 mA/cm2
Current density:
1 mA/cm2
Low resistance substrate-
ITO at150 o
C
Electrodeposited at -0.7 V for
50 min. at 160
o
C
Indium sulfide ring formation
from sodium thiosulfate as
sulfur source-ITO
Electrodeposited at -0.7 V for
15 min. (sodium thiosulfate as
sulfur source)
Post-annealed
electrodeposition
Post-annealed
electrodeposition
(repeated trials)
Post-annealed electrodeposition Post-annealed electrodeposition
(repeated trials)
Horizontally positioned
substrate-Mo
Horizontally positioned substrate-
MoLow resistance substrate-ITO at150
o
C
Pulse-plating (-0.685 V with 10 sec.
delay) at 70
o
C for 95 min. FTO
Pulse-plating (-0.7 V with 15 sec.
delay) at 150 oC for 48 min. FTO
Pulse-plating (-0.7 V with 10 sec.
delay) at 80 oC for 75 min. ITO
Electrodeposited at -0.685 V for 6
min. and at -0.7 V for 40 min.
(repeated trials)
Electrodeposited at -
0.685 V for 4 min using
ethylene glycol solvent
JH: Electrodeposited at -0.8 V for 30 min
in formamide solvent
Current density:
0.75 mA/cm2
Current density: 1.25 mA/cm2Current density: 1.5 mA/cm2
Pulse-plating (-0.8 V with 10 sec. delay)
at120 oC for 50 min. Mo
Current density:
1mA/cm2

23. Reported Papers on Electrodeposition of Semiconductor
Thin Films with Crack Morphology
Semiconductor
Material
Electrolyte Potential Cause for Cracks Reference
CdS Organic Thickness and current density Fulp & Taylor, 1985
CdS DEG-water mixtures
Incorporation of solutes with solvent/addition
agent
Fulp & Taylor, 1985
Si Ionic Liquid Thickness, substrates, deposition voltage Oskam et. al., 2001
Bi2S3 Aqueous Solvents A. Begum, et al. 2011
CIGS Aqueous % composition of precursor chemicals V. S. Saji, et al. 2011
CdS Organic Solvent and piezoelectric effect
M. N. Mammadov, et al.
2012
Cu-Ga-Se Aqueous
Incorporation of solutes with solvent/addition
agent and % composition of precursor
solutions
Y. Oda, et al. 2008
Cu Aqueous Surface contamination
H. Lou & Y. Huang,
2006
CdSe Aqueous Substrates
R. I Chowdhury, et al.
2011

24. Crack Morphologies from Solution-Based Deposition
Techniques
Cu-Ga-S (Y. Oda, et al.
2008)
CZTS(M. Jiang and X. Yan
2008)
TiO2 (A. R. Santos, et al.
2013)
ZnO (C. Liehiran, et al.
2007)
Ƴ-Fe2O3 (AT. Ngo, et al. 2013)
ZnO:Cl on CIGS/In2S3 (J.
Rousset, et al. 2011)
TiO2 (G. Xue, et al. 2012)
In2S3 (K. Otto, et al. 2011)In2S3 (E. Aydin, et al.
2012)

25. Control Deposition Parameters and Levels
Levels “A”
Bath Composition
“B”
Current
Density
(mA/cm2)
“C”
Substrate
“D”
Deposition
Time
(min)
“E”
Deposition
Temperature
(oC)
1 0.1M S + 0.05M InCl3 +
0.1M NaCl
0.75 Mo 5 140
2
0.1M S + 0.1M
Na2S2O3.5H2O +0.05 M
InCl3 + 0.1M NaCl
1.25 ITO 10 150
3 ----- 1.75 FTO 15 160

26. Digital Imaging Analysis: Fracture and Buckling
Analysis Software for Crack Density Calculation
(Area of interest = 2100.69 µm2)

27. Deposition Parameters
Levels
A,
Bath
Composition
B,
Current
Density
(mA/cm2
)
C,
Substrate
D,
Deposition
Time (min)
E,
Deposition
Temperature
(o
C)
1 0.1989 0.0684 0.16 0.1880 0.1284
2 0.1772 0.2847 0.2721 0.2002 0.2232
3 --- 0.1916 0.1758 0.1754 0.2005
▲ 0.0218 0.2162 0.1121 0.0247 0.0948
Rank 5 1 2 4 3
Output Response Table for Means
(Mean Crack Density)

28. Optimized Electrodeposition Parameters

29. EDS Data for Indium Sulfide Films
Electrodeposited at 0.75 mA/cm2
As-deposited
Annealed
200oC
Annealed
300oC
Annealed
400 oC
Element Atomic%
Carbon (C) 24.3 8.93 0 19.36
Oxygen (O) 19.99 32.34 17.85 58.17
Aluminum
(Al)
0 0 0 0.19
Sulfur (S) 32.33 34.05 49.21 11.21
Indium (In) 23.38 24.68 32.94 11.08
S/In Ratio 1.38 1.37 1.49 1.01

30. Optical Bandgap Plots (ITO)

31. X-Ray Diffraction Pattern

32. Future Work
i. Study and improve the crystalline structure of In2S3 films as a function of heat treatment
and then compare the results from conventional oven-based heating versus laser
annealing, and intense pulse light annealing.
ii. Use the X-ray mapping feature on the EDS to study elemental distributions over the
surface area of the electrodeposited In2S3 films.
iii. Study the effect of performance parameters as a function of thickness of In2S3 films.
iv. Prepare/complete three potential papers for publication:
- Effect of different heat treatments on the crystalline structure of electrodeposited In2S3
films.
- Indium Sulfide: A Review
(The paper will feature all of the In2S3-based solar cells with record efficiencies produced
with various deposition techniques).
- Life Cycle Assessment (LCA) of In2S3-based solar cells.

33. 1) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al.,
"Statistical analysis of electroplated indium (III) sulfide (In2S3) films, a potential
buffer material for PV (heterojunction solar cell) systems, using organic
electrolytes," Nanotechnology 2013: Bio Sensors, Instruments, Medical,
Environment, and Energy,3. Technical Proceedings of the 2013 NSTI
Nanotechnology Conference, Washington, DC, pp. 523-527, May 12-16, 2013.
2) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al.,
“Morphological and compositional analysis of electrodeposited In2S3 Films”
Proceedings of the 40th IEEE Photovoltaic Specialists Conference (PVSC),
Denver, CO, pp. 1322-1326, June 07-14, 2014.
3) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al.,
“Optimization of the electrodeposition parameters to improve the stoichiometry
of In2S3 films for solar applications using the Taguchi Method, Journal of
Nanomaterials, vol. 2014, pp. 1-10, 2014.
4) Paper submitted (October, 2014) to IEEE Journal of Photovoltaics (under review)
on “Morphological and compositional analysis of electrodeposited In2S3 films”.
Scholarly Publications

34. Publication: Journal of Nanomaterials

35. 1) Poster presentation at Fourth Annual Renewable Energy Conference (Sep., 2014) on “Update on Semiconductor Film
Electrodeposition Research at Arkansas State University”, Arkansas State University-Jonesboro, AR.
2) Posterl presentation at ASSET Initiative Annual Meeting (Sep., 2014) on “Update on Semiconductor Film
Electrodeposition Research at Arkansas State University ”, Little Rock, AR .
3) Poster presentation at 40th IEEE PVSC Conference (June, 2014) on “Morphological and Compoitional Analysis of
Electrodeposited In2S3 Films”, Denver, CO.
4) Poster presentation at TechConnect Conference (May, 2013) on “Statistical Analysis of Electroplated Indium (III) Sulfide
(In2S3) Films, a Potential Buffer Material for PV (Heterojucntion Solar Cells) Systems, using Organic Electrolytes”,
Washington, DC.
5) Poster presentation at Create@State (Apr., 2013) on “Innovations in Semiconductor Electrodeposition”, Arkansas State
University, Jonesboro, AR.
6) Poster presentation at Arkansas State Capitol (Feb., 2013) on “CdTe/In2S3 Solar Cells by Electrodepostion and
Evaporation”, Little Rock, AR.
7) Oral presentation at ASSET Initiative Annual Meeting (Aug., 2012) on “Progress and Challenges in Electrodeposition of
Indium (III) Sulfide (In2S3) Films from Organic Electrolytes for Potential Solar Cell Use”, Springdale, AR.
8) Oral presentation at Arkansas Academy of Science ( Apr., 2012) on “Taguchi Analysis and Characterization of
Electrodeposited Indium Sulfide Films for Use as Potential Buffer Layers in Solar Cells”, Magnolia, AR (Third prize in the
graduate physics category).
9) Oral presentation at Create@State (Apr., 2012) on “Rest Potential-Based Electrodeposition of Metal Sulfide Films”,
Arkansas State University, Jonesboro, AR.
10) Poster presentation at Arkansas State Capitol (Feb., 2012) on “Progress in Electrodeposition of Indium Sulfide and Copper
Indium Disulfide”, Little Rock, AR.
11) Poster presentation at ASSET Initiative Annual Meeting (July, 2011) on “Research at Arkansas State University
Optoelectronic Materials Research Laboratory”, Heber Springs, AR.
12) Oral presentation at Electronic Materials Conference EMC (June, 2011) on “Electrodeposition of Indium Sulfide Films
from Organic Electrolyte”, University of Santa Barbara, Santa Barbara, CA.
13) Oral presentation at Create@State (Apr., 2011) on “Electrodeposition of Indium Sulfide from Organic Electrolytes”,
Arkansas State University, Jonesboro, AR.
14) Oral presentation at Arkansas Academy of Science ( Apr., 2011) on “Elemental Sulfur-based Electrodeposition of Indium
Sulfide Films”, Monticello, AR (First Prize in graduate category).
Scholarly Activities

36. I acknowledge the gracious support provided by Arkansas State University,
National Science Foundation grant EPS-1003970 administered by the Arkansas
Science and Technology Authority, and NASA grant NNX09AW22A
administered by the Arkansas Space Grant Consortium. Dr. Alan Mantooth,
Kathy Kirk, Dr. Greg Salamo, Dr. Omar Manasreh, Dr. Alex Biris, Dr. Tansel
Karabacak, Dr. Hyewon Seo, and other collaborators at the University of
Arkansas (Fayetteville, Little Rock, and Pine Bluff campuses) are also thanked,
as are Dr. Keith Hudson and Laura Holland at ASGC, and Dr. Gail McClure, Cathy
Ma, and Marta Collier at ASTA. The authors are also grateful for the ongoing
support provided by Arkansas State University, particularly Dr. David Beasley,
Dr. Rick Clifft, Dr. Paul Mixon, Dr. William Burns, Dr. Tom Risch, Dr. Tanja McKay,
Dr. John Pratte, and Dr. Andrew Sustich.
Thanks also go to Dr. Richard Segall and Dr. Ilwoo Seok for an introduction to
the Taguchi Method, and Dr. Trauth for the use of the SEM/EDS unit.
Particular thanks go to my advisor, Dr. Robert Engelken, my student research
colleagues, and all of you, my Ph.D. committee members.
Thank You !
Acknowledgements

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Institution of Oceanography (scrippsco2.ucsd.edu/). Available at:
http://www.esrl.noaa.gov/gmd/ccgg/trends/
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