This document summarizes research on self-organized porous alumina templates and their applications in nanofabrication. It describes the experimental techniques for synthesizing porous alumina templates through anodization of aluminum foils. Factors that influence the pore size and spacing are discussed, such as applied voltage, aluminum purity, and etching time. Various deposition methods are also summarized, such as electrodeposition of nickel and sputtering of cobalt through the templates. Finally, potential applications of these templates in areas such as carbon nanotube growth and their optical properties are mentioned.

1. Self-Organized Porous Alumina Templates
and Their Applications
S. K. Yadav
Materials Science Programme,
Indian Institute of Technology Kanpur
,
RAIM08-NIT Hmairpur

2. Contents
 Introduction
Nanofabrication techniques
Template-assisted synthesis
 Experimental techniques: PAA synthesis
 Anodization kinetics
 PAA templates
 Commercial Aluminium foil
 Pure aluminium foil
 Highly pure aluminium foil
 Nickel deposition
 Cobalt deposition
 Conclusions
 Acknowledgment

3. Introduction
Nanofabrication techniques
 E-beam and nano-imprint fabrication
 Epitaxy (MBE, MOCVD)
 Scanning probe technique
 Self-assembly and template synthesis
Approach
 Top-Down- Size and distribution can be controlled.
Limitation- Small area fabrication < 100μm x100μm
 Bottom-up- Direct growth of smallest structures : Starting with building
blocks, difficult to control size and locations.
Synthesis of nanostructures by template synthesis technique is combination of
above two: Template by top-down then nanostructures by bottom-up

4. • Ion track-etched Polymer membranes
• Porous anodic alumina (Al2O3)
• Nano-channel glass (NCG)
 Simple and intuitive way to fabricate nanostructures.
 Cheaper (cost effective), quick, effective over large area
fabrication.
Template-assisted synthesis
Two stage
synthesis
Fabrication of
nanostructures using
templates
Template synthesis
1. J. Y. Ying, Sci. Spectra 18 , 56 (1999).
2. C. R. Martin, Science 266,1961(1994).

5. Experimental techniques
Synthesis techniques of porous alumina templates
 Single step anodization
 Double step anodization
Single step anodization
 Pretreatment of aluminium foil (annealing and cleaning)
( 5000C for 1hrs, sonicate in acetone for 5minutes )
 Electro-polishing
(2:2:4 H2SO4:H3PO4:H2O ,16V, 3A, 30-180 secs)
 Anodization
(oxalic acid at different voltages an temperatures)
 Dissolution of back side aluminium
( 5wt% Cupric chloride, saturated solution of HgCl2)
 Etching and washing
( H3PO4)
K. N. Rai and E. Ruckenstien, Journal of Catalysis 40, 117 ( 1975)

6. Double step anodization
 Pretreatment of aluminium foil(annealing and cleaning)
( 5000C for 1hrs , sonicated in acetone for 5minutes )
 Electropolishing
(2:2:4 H2SO4:H3PO4:H2O ,16V, 3A, 30-180 secs)
 1st step Anodization
(oxalic acid, sulfuric acid, at different voltages and temperatures)
 Removal of anodized layer
( H3PO4)
 2nd step Anodization
(oxalic acid , sulfuric acid, at different voltages and temperatures)
 Dissolution of back side aluminium
( 5wt% Cupric chloride, saturated solution of HgCl2)
 Etching and washing
( H3PO4)
1. H.Masuda and M. Satoh, Jap. J. Appl. Phys. 35 L126 (1996).
2. H. Masuda and K. Fukuda, Science 268,1 466 (1995).

7. Current-time curve
0 100 200 300 400 500
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Currentdensity(A/cm
2
)
5432
Time(sec)
1
I-t at 40V in 0.3M oxalic acid at 100C
0 50 100 150 200 250 300 350 400 450 500
0.00
0.01
0.02
0.03
0.04
1
st
Step
2
nd
Step
Currentdensity(A/cm
2
)
Time(sec)
 Current decreases rapidly due to the
formation of thin barrier-type layer (40V- 44
nm) .
 Growth of highly resistive oxide layer
stops further current flow and hence
increases field.
This leads to field enhance dissolution in
the formed oxide and thus to the growth of
pores .
 Due to competition among pores the
current decreases again since some pores
stop growing.
From region 5 we can extract information
about the film growth with time.
Anodization kinetics
Y. Du, W. L. Cai, C. M. Mo, J. Chen, L.D. Zhang and X.G. Zhu, Appl. Phys. Lett. 74, 2951 (1999).

8. Fabrication of PAA using commercial aluminum foil
Average pore size : 49 nm
Average interpore distance: 99nm
Pore density : 210
/cm101.1
Al foil~150 µm (commercial)
Electro polished
Applied voltage- 40V
Electrolyte- 0.3M oxalic acid
T~ 100C,
Pore widening in H3PO4
35 40 45 50 55 60 65 70
0
5
10
15
20
Counts
Pore diameter(nm)
70 80 90 100 110 120 130 140
0
2
4
6
8
10
12
14
Counts
Interpore distance(nm)

9. Al foil~100 µm (99%)
Average pore size : 57 nm
Average inter-pore distance:103nm
Pore density:
Al foil~20 µm (99.99%)
Average pore size : 53 nm
Average inter-pore distance:105nm
Pore density:
Purity Dp
(nm)
Dip
(nm)
Pore density
N/ cm2
commercial 49 98
99 % 57 103
>99.99% 53 105
10101.1
9109.5
9107.08
2/cm9109.5
9107.08
Fabrication of PAA using pure aluminum foils

10. Effect of applied voltage
S. No. Applied voltage (V) Pore diameter
(nm)
Interpore distance
(nm)
Pore density
Number/cm2
1 30 36 78 1.52x1010
2 40 49 99 1.09x1010
3 50 58 123 6.16x109
4 60 68 136 8.16x109
5 80 103 203 1.81x109
30 40 50 60 70 80
40
60
80
100
120
140
160
180
200
40
60
80
100
120
140
160
180
200
Interporedistance(nm)
Porediameter(nm)
Applied voltage(V)
Extrapolated both curves
At V=0
pore diameter ~0
pore to pore distance =16nm
(close to the reported value of
18nm).
Dip = mV + C
m=2.2nm/V
K. N. Rai and E. Ruckenstien, Journal of Catalysis 40, 117 ( 1975)

11. Double step anodization
130micron, purity >99.99%
1st step: 1hrs
2nd step: 20hrs
30 minute in 5 wt% H3PO4 RT
No etching
30 +15minute in 5 wt% H3PO4 RT
30 minute etching in 5 wt% H3PO4
at 350C-400C
Etching Pore size
(nm)
Interpore
distance(nm)
Pore desnity
/cm2
Top without etching 31 79 1.75x1010
Bottom without etching 98 110 8.50x109
Top 30minute 32 82 2.31x1010
Bottom 30minute 77 117 9.27x109
Top 30+15minute 34. 89 1.73x1010
Bottom 30+15minute 24 113 9.7x109
Top 30minute ~35-40oC 36 83 1.16x1010
Bottom 30minute ~35-
40oC
30 113 8.04x1010

12. 1st step: 3hrs
15,30,45 and 60 minute etching in 5wt% H3PO4 at 35-400C
Etching
time
(minute)
Pore
diameter
(nm)
P-P
distance
(nm)
15 50 107
30 52 104


Double step anodization

13. PAA synthesized at low temperature~2C
Cross sectional view
Cross sectional viewCross sectional view Top view
Top view

14. Nickel electrodeposition
Electrolyte-300g/l NiSO4.7H2O, 45g/l NiCl2.H2O and 40g/l H3BO3
Current density~10mA/cm2
20 sec 120 sec
poresofnumberTotal
nickelbycoveredporesofNumber
ratioFilling 
1. K.R. Pirota, D. Navasa, M. Hernández, K. Nielsch, M. Vázquez Journal of Alloys and Compounds 369,18 (2004)
2. G. Meng, A. Cao, J. Cheng, A.Vijayaraghavan, Y. Jung, M. Shima, and P. M. Ajayan Journal of Applied Physics 97, 064303 (2005)

15. Through templates Size=82nm separation=500nm
Direct deposition for
20second and annealing
at 8000C
Base Pressure ~10-7 mbar
Substrate Silicon (100)
Buffer layer Titanium ~(500 Å)
Inter electrode distance 5 cm
H2 flow rate during pretreatment
60 sccm
H2 flow rate during CNT growth
80 sccm
C2 H2 flow rate during CNT
growth 20 sccm
O2 flow rate during post
treatment 40 sccm
Growth time interval 10 minutes
H2 plasma pre-treatment 10
minutes
DC bias voltage -600 Volts
Substrate Temperature 800 C
Size=380nm

16. Cobalt deposition (sputtering)
Base Pressure~10-6mbar
Argon gas pressure~4x10-2mbar
T~3000C
Voltage~480V
Current~0.15A
Time~61secs
Co on titanium coated silicon substrate
Size-171nm
Co on PAA of 42nm diameter
100nm pore to pore distance
Co on PAA of 230nm diameter
394nm pore to pore distance
-10000 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 10000
-0.0008
-0.0006
-0.0004
-0.0002
0.0000
0.0002
0.0004
0.0006
0.0008
Perpendicular to pores
Parallel to pores
M(emu)
H(Oe)

17. Conclusions
 Pores of diameter ranging from 30-100nm are fabricated having inter pore distance
in the range of 80-200nm by changing anodizing voltage in 0.3M oxalic acid.
 We also observed the difference in average pore size, pore spacing and their
distribution as a function of film purity.
 Ni nano dots have been electro-deposited on titanium coated silicon substrate
through PAA as mask.
 CNTs have been grown on nickel electrodeposited titanium coated silicon
substrates.
 Cobalt have been sputtered through PAA templates on Ti coated silicon substrate
 Further work is in progress to explore the optical properties of these templates.

18. Acknowledgment
• Thanks CSIR for financial support
• Thanks RAIM08
• Thanks Shyam, D. N. Patel, Durgesh and Dibyendu.

19. 30V 50V
60V 80V

20. Optical properties
200 300 400 500 600 700 800
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
3
4
5
1
2
%Transmittance
(nm)
B107
C94
D102
E91
F
Sample No. Eg (eV) Pore Size(nm)
1 3.56 53
2 3.46 32
3 3.61 35
4 3.43 36
5 3.27 31
200 300 400 500 600 700 800
0
2
4
6
8
10
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
%Transmittance(a.u.)
 nm)
Before Annealing
After Annealing 500
0
C
350 400 450 500 550 600 650 700
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.1
0.2
0.3
0.4
0.5
Counts(a.u.)x10
4
(nm)
437414
Sulfuric acid
Oxalic acid
PL peak at 2.83eV