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Supporting Information
In Situ Determination of the Pore Opening Point
during Wet-Chemical Etching of the Barrier Layer
of Porous Anodic Aluminum Oxide (AAO): Non-
Uniform Impurity Distribution in Anodic Oxide
Hee Han†, &
, Sang-Joon Park‡, &
, Jong Shik Jang†, Hyun Ryu
†, Kyung Joong Kim
†, Sunggi
Baik‡, and Woo Lee
†,*
† Korea Research Institute of Standards and Science (KRISS), Yuseong, Daejeon, 305-340,
Korea
‡ Department of Materials Science and Engineering, Pohang University of Science and
Technology (POSTECH), Hyoja-dong, Pohang, 790-784, Korea
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Figure S1.
Figure S1. A photograph of H-cell with Pt-electrodes and Pt-resistance temperature detector
(RTD) loaded in cells for DI water and and an etchant (i.e., H3PO4), respectively.
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Figure S2.
Figure S2. Thickness of nanoporous AAO (black squares), the corresponding total charge
(blue circles) and the linear fits with respect to the anodization time.
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Figure S3.
Figure S3. Cross-section TEM images showing barrier oxide layers of 1h- (left) and 24 h-
anodized AAO (right).
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Figure S4.
Figure S4. Conductivity (squares) and pH (circles) of electrolytes as a function of anodization
time (tanodi).
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Figure S5.
Figure S5. Current-time transient curve during the etching of barrier layer (BL) of AAO
prepared by 23 h-anodization followed by additional 1 h-anodization by using fresh
electrolyte (i.e., 0.3 M H2C2O4). Insets are SEM images of bottom surfaces of AAO at etching
time of 15 min (left) and 50 min (right). Scale bars are 200 nm.
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Figure S6.
Figure S6. Current-time transient curve during second anodization of aluminum using 0.3 M
H2C2O4 (7 oC) at 40 V. The enlarged current-time curve at the early stage of anodization is
presented as an inset.
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Figure S7.
Figure S7. Current-time transient curves during the additional anodizations of second-
anodized AAOs using 0.3 M (red trace) and 0.03 M (black trace) H2C2O4 for 10 min and 35
min, respectively. The inset is charge-time curves of the respective anodizations.
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Figure S8.
Figure S8. SEM micrographs showing the morphological evolution of top surface of 24 h-
anodized AAO as a function of etching times (tetch) in 5 wt % H3PO4 at 29 ± 0.2 °C. Scale
bars are 200 nm for tetch = 0 ~ 80 min and 4 μm for tetch = 90 min.
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Figure S9.
Figure S9. SIMS depth profiles of the top (upper) and bottom part (lower) of AAOs
fabricated by 72 h-anodization. Al, O, and C elements are indicated as blue, black, and red
symbol, respectively. In order to exclude the inhomogeneity caused by morphological
characteristics of top and bottom surface, pre-sputtering was performed before depth profiling.
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Figure S10.
Figure S10. A schematic cross-section of AAO illustrating the variation of the relative
thickness of the outer and inner pore walls along the pore axes.
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Figure S11.
Figure S11. SEM images presenting the morphologies of opened barrier layers fabricated
through second anodization using 0.3 M H2C2O4 at 7 oC for (a) 24 h, (b) 48 h, (c) 72 h and (d)
120 h. The magnified images are shown as insets in the respective images. Scale bars are 200
nm.