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

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.

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.

Figure S3.

Figure S3. Cross-section TEM images showing barrier oxide layers of 1h- (left) and 24 h-

anodized AAO (right).

Figure S4.

Figure S4. Conductivity (squares) and pH (circles) of electrolytes as a function of anodization

time (tanodi).

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.

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.

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.

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.

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.

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.

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.