Electrodeposition of rare earth-transition metal alloy thin films and nanostructures

151 Pages·2017·9.53 MB·English

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LSU Doctoral Dissertations Graduate School
2007
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Rohit Mishra
Louisiana State University and Agricultural and Mechanical College
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Mishra, Rohit, "Electrodeposition of rare earth-transition metal alloy thin films and nanostructures" (2007).
LSU Doctoral Dissertations. 1694.
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ELECTRODEPOSITION OF RARE EARTH-TRANSITION METAL ALLOY
THIN FILMS AND NANOSTRUCTURES

A Dissertation

Submitted to the Graduate Faculty of the
Louisiana State University and
Agricultural and Mechanical College
in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy

in

The Department of Chemical Engineering

By
Rohit Mishra
B.S. Kakatiya University, India, 1999
May, 2007
DEDICATION

To my parents……

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ACKNOWLEDGEMENTS
I would like to sincerely thank my advisor, Dr. Elizabeth J. Podlaha, for her
guidance and patient support. Without her steadfast commitment, this research would not
have been possible. I would also like to show my appreciation to my advisory committee,
Dr. Karsten Thompson, Dr. David Young, Dr. John Flake and Dr. Jaye Cable for their
time and positive advice towards my research.
I would like to thank the Chemical Engineering Department at LSU for giving me
this opportunity to be here. A special thanks is due to the chemical engineering staff and
the machine shop personnel, especially Paul Rodriguez for their continued help and
support.
Finally I want to extent my gratitude to Dr. Xiaogang Xie, Ms. Cindy Henk and
Dr. Dongmei Cao for their help with SEM, TEM and XPS respectively. I would also like
to thank Dr. Monica Moldovan and Amar Karki for their help in measurement of
magnetic properties. Last but not the least; I acknowledge the support of my fellow
colleagues, Yutong Li, Despina Davis and Maoshi Guan.
This work was funded by NSF/NIRT and the Coates Memorial Fellowship at
Louisiana State University.

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TABLE OF CONTENTS
DEDICATION....................................................................................................................ii
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ACKNOWLEDGEMENTS...............................................................................................iii
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LIST OF TABLES.............................................................................................................vi
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LIST OF FIGURES..........................................................................................................vii
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ABSTRACT ...................................................................................................................xii
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CHAPTER I. INTRODUCTION......................................................................................1
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1.1 References...........................................................................................................4
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CHAPTER II. ELECTRODEPOSITION OF RARE EARTH-TRANSITION METAL
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THIN FILMS .....................................................................................................................9
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2.1 Literature Review................................................................................................9
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2.1.1 Aqueous Electrolytes................................................................................10
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2.1.2 Organic Electrolytes..................................................................................13
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2.1.3 Molten Salt................................................................................................18
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2.2 Experimental Setup...........................................................................................19
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2.3 Results and Discussion.....................................................................................24
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2.3.1 Macro-electrode Analysis.........................................................................24
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2.3.2 Microelectrode Analysis...........................................................................38
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2.4 Summary...........................................................................................................42
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2.5 References.........................................................................................................44
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CHAPTER III. TEMPLATE DEPOSITION OF RARE EARTH-CO ALLOYS ...........48
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3.1 Literature Review..............................................................................................48
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3.1.1 Introduction to Template Deposition........................................................48
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3.1.2 Electrochemical Aspect of Template Deposition.....................................51
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3.1.3 Fabrication of Nanotubes..........................................................................52
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3.1.4 Applications of Nanowires and Nanotubes...............................................56
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3.2 Experimental Setup...........................................................................................58
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3.3 Experimental Results........................................................................................61
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3.3.1 Composition..............................................................................................62
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3.3.2 Morphology...............................................................................................70
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3.3.2.1 Effect of pH...........................................................................................74
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3.3.2.2 Effect of Deposit Material....................................................................77
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3.3.2.3 Effect of Pore Diameter........................................................................79
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3.3.2.4 Effect of Deposition Time....................................................................80
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3.3.2.5 Effect of Duty Cycle.............................................................................82
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3.3.3 Characterization........................................................................................86
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3.4 Summary...........................................................................................................94
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3.5 References.........................................................................................................95
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CHAPTER IV. SIMULATION OF RARE EARTH-COBALT ALLOY
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ELECTRODEPOSITION...............................................................................................101
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4.1 Introduction.....................................................................................................101
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4.2 Deposition Mechanism...................................................................................104
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4.3 Model Development........................................................................................106
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4.4 Results.............................................................................................................114
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4.5 Summary.........................................................................................................125
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4.6 References.......................................................................................................126
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CHAPTER V. CONCLUSION.......................................................................................129
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APPENDIX A. LIST OF SYMBOLS............................................................................132
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APPENDIX B. THIN FILM DEPOSITION TECHNIQUES........................................133
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APPENDIX C. CYCLIC VOLTAMMETRY................................................................134
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APPENDIX D. PROPERTIES OF RARE EARTH ELEMENTS.................................135
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APPENDIX E. LETTER OF PERMISSION..................................................................136
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VITA .................................................................................................................137
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LIST OF TABLES
Table 2.1 Composition of the electrolyte........................................................................22
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Table 3.1 Composition of rare earth-transition metal alloys deposited under DC
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condition in 200 nm polycarbonate membrane...............................................63
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Table 3.2 Coercivity and squareness ratio of CoGd, CoTb and CoSm nanotubes
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deposited by pulsed deposition in 200 nm pore diameter polycarbonate
membranes......................................................................................................91
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Table 4.1 Steady state diffusion equations in the boundary layer................................109
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Table 4.2 Diffusivity values used in the model for the reacting species......................110
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Table 4.3 Boundary layer boundary conditions............................................................111
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Table 4.4 Boundary conditions at x=0..........................................................................111
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Table 4.5 Kinetic rate expressions and the kinetic constants obtained by fitting the
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experimental data set for 0.2 M Co(II) electrolyte in the model..................112
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Table D.1 Physical properties of rare earth elements....................................................135
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LIST OF FIGURES
Figure 2.1 A typical electrochemical setup...................................................................20
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Figure 2.2 Beaker type electrochemical cell used to deposit rare earth-cobalt alloys..21
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Figure 2.3 Microelectrode used for cyclic voltammetry...............................................22
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Figure 2.4 EIS of CoTb electrodeposition at -2 V vs. SCE on copper foil...................23
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Figure 2.5 Partial current densities of cobalt, terbium and side reactions during alloy
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electrodeposition, at pH 2.15, 0.2 M Co and corrected for ohmic drop:
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⎯♦⎯ total current density, --■-- cobalt partial current density, --▲--
terbium partial current density, --●—side reaction partial current density.25
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Figure 2.6 Composition of the deposited alloy at pH 2.15: ⎯●⎯ 0.3 M Co2+, --▲--
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0.2 M Co , …■… 0.1 M Co ....................................................................26
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Figure 2.7 Deposit composition reproducibility for (a) 0.3 M Co (II), (b) 0.2 M Co (II)
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and (c) 0.1 M Co (II) electrolyte at an applied potential of -3 V vs. SCE...27
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Figure 2.8 Partial current densities of (a) total (b) cobalt (c) terbium and (d) side
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reaction at pH 2.15: ⎯●⎯ 0.3 M Co2+, --▲-- 0.2 M Co2+, …■… 0.1 M
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Co ..............................................................................................................29
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Figure 2.9 Current efficiency at pH 2.15: ⎯●⎯ 0.3 M Co2+, --▲-- 0.2 M Co2+, …■…
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0.1 M Co ...................................................................................................32
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Figure 2.10 Comparison of (a) rare earth partial current density and (b) cobalt partial
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current density in cobalt-terbium, cobalt-gadolinium and cobalt-samarium
electrodeposition: --∆-- TbCo, …x… GdCo, ⎯o⎯ SmCo.......................33
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Figure 2.11 Comparison of rare earth content in cobalt-terbium, cobalt-gadolinium and
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cobalt-samarium electrodeposition: ---∆--- TbCo, .…x…. GdCo,
⎯⎯o⎯⎯ SmCo.........................................................................................34
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Figure 2.12 Comparison of current efficiency in cobalt-terbium, cobalt-gadolinium and
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cobalt-samarium electrodeposition: ---∆--- TbCo, .…x…. GdCo,
⎯⎯o⎯⎯ SmCo.........................................................................................35
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Figure 2.13 Transient current responses for various applied potentials..........................36
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Figure 2.14 Effect of charge on alloy composition with electrolyte pH 2.15 at 0.2 M
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Co2+: --■-- cobalt, ⎯●⎯ terbium.............................................................37
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2+
Figure 2.15 Effect of pH on alloy composition at 0.2 M Co , and applied potential -3 V
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(uncorrected for ohmic drop).......................................................................38
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2+
Figure 2.16 Cyclic voltammogram for (a) 0.2M Co /0.5M boric acid electrolyte (b)
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2+ 3+
0.2M Co /0.2M Tb /0.5M boric acid electrolyte, pH 2.15.......................39
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3+
Figure 2.17 Cyclic voltammogram for (a) 0.5 M boric acid electrolyte (b) 0.2 M Tb /0.5
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M boric acid electrolyte, pH 2.....................................................................41
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Figure 2.18 XPS result of cobalt terbium alloy prepared at applied potential -3.5 V vs.
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SCE and after 20nm surface sputter.............................................................43
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Figure 3.1 Outline of nanowire deposition process using template based deposition..50
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Figure 3.2 Typical current transient response for template deposition.........................51
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Figure 3.3 Boundary layer in recessed nanoelectrodes at (a) short time (b) intermediate
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time (c) long time.........................................................................................52
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-1/2
Figure 3.4 Current density vs. t showing the three different mass transport regimes53
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Figure 3.5 Sketch of E-t curves for (a) step potential (b) pulse potential and (c)
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potential rectangular wave...........................................................................59
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Figure 3.6 Current response for CoGd alloy deposition in 200 nm polycarbonate
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membrane at an applied potential of -2.5 V.................................................62
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Figure 3.7 Effect of duty cycle on composition of cobalt gadolinium deposits prepared
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in 200 nm pore diameter alumina and polycarbonate templates..................65
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Figure 3.8 EDS spectrum of the (a) top section and (b) bottom section of cobalt
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gadolinium nanotubes deposited in 200 nm polycarbonate membrane.......66
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Figure 3.9 Transient current response in electrodeposition of cobalt-gadolinium alloy in
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polycarbonate and alumina membranes at a duty cycle of 0.8....................68
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Figure 3.10 A Cottrell plot for CoGd alloy deposition in 200 nm alumina membrane at
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an applied potential of -2.5 V......................................................................69
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Figure 3.11 Effect of (a) cobalt (b) gadolinium electrolyte concentration on the
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composition of cobalt-gadolinium deposit in 200 nm pore diameter
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polycarbonate membrane prepared by pulse deposition at an on-potential of
-2.5 V...........................................................................................................69
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Figure 3.12 SEM micrograph of CoGd nanowires deposited by DC deposition at -2.5 V
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using 200 nm pore diameter polycarbonate membrane...............................71
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Figure 3.13 SEM micrograph of CoGd nanotubes deposited by DC deposition at -2.5 V
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using 200 nm pore diameter polycarbonate membrane...............................72
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Figure 3.14 SEM micrograph of CoGd nanotubes deposited using 200 nm pore diameter
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polycarbonate membrane at a duty cycle of 0.8..........................................73
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Figure 3.15 SEM micrograph of CoGd nanotubes deposited using 200 nm pore diameter
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polycarbonate membrane at a duty cycle of 0.8..........................................75
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Figure 3.16 SEM image of Co nanowires deposited by pulse plating at a duty cycle 0.8
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in (a) 200 nm polycarbonate membrane and (b) 200 nm alumina
membrane.....................................................................................................77
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Figure 3.17 SEM micrograph of (a) CoTb, and (b) CoSm nanotubes deposited using 200
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nm pore diameter polycarbonate membranes at a duty cycle of 0.8............78
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Figure 3.18 TEM image of CoGd nanowires deposited by pulse plating in (a) 20 nm
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alumina and (b) 50 nm polycarbonate membrane at a duty cycle of 0.8.....79
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Figure 3.19 (a) SEM and (b), (c) TEM image of CoGd nanowires/tubes deposited by
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pulse plating in 200 nm alumina membrane at a duty cycle 0.8 and
Q=100 C.......................................................................................................81
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Figure 3.20 A sketch of deposition time effect on deposit morphology.........................82
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Figure 3.21 SEM image of CoGd nanowires deposited by pulse plating in 200 nm (a)
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polycarbonate membrane and (b) alumina membrane at a duty cycle
of 0.25..........................................................................................................83
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Figure 3.22 SEM image of CoGd/Co multilayer in polycarbonate membrane deposited
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by pulsing plating between -0.85 V for 60 s and -2.5 V for (a) 240 s
(b) 15 s.........................................................................................................84
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Figure 3.23 Thin film growth inhibition in CoGd alloy thin film deposition from
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aqueous sulfamate bath, pH 1.8 on copper foil............................................86
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Figure 3.24 Effect of deposition time on current efficiency in CoGd alloy thin film
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deposition from aqueous sulfamate bath, pH 1.8 on copper foil.................87
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