Supplementary Material for
Controllable sealing of leaky alumina films on NiAl(100) surface by
catalytic oxidation
Kuan-Te Liu1,2 (劉冠德), Jian-Wei Chen,1,3 Yu-Wen Liao,1,2 Wen-Chin Lin,1,a) Chii-Bin
Wu,2 Chien-Cheng Kuo,3 Minn-Tsong Lin,1,2 and Ker-Jar Song1,b) (宋克嘉)
1 Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan, R.O.C.
2 Department
of Physics, National Taiwan University, Taipei 10617, Taiwan, R.O.C.
3 Department
of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, R.O.C.
Supplementary Material
Here we present some supplementary materials related to our experiment. Fig. S1 is STM image of 0.03 ML Co
deposited on Al2O3/NiAl(100) (striped oxide) at 300 K. Its size is 150 × 150 nm2. The sample preparation method is the
same as we mentioned in the main article. We can see Co nanoparticles (NPs) preferentially nucleate along the domain
boundaries (easy paths) in between the linear oxide stripes. The average width of oxide stripes is about 4 nm.
Fig. S2 shows the LEED patterns for a sample at different stages of a TPA experiment in which 12 ML of Co on
Al2O3/NiAl(100) is annealed up to 1000K. Fig. S2(a) is the characteristic LEED pattern of NiAl(100) clean surface,
which is due to existence of two mutually perpendicular type of domains of C( 2  3 2 )R45  reconstruction. Fig.
S2(b) is after growth of the striped oxide. The pattern now consists of two sets of mutually perpendicular parallel lines,
reflecting the existence of two types of mutually perpendicular domains of linear oxide stripes. The oxide stripes are well
ordered and in registry with the substrate along their length but only about 4 nm in width. Fig. S2(c) is LEED pattern
obtained after deposition of 12 ML of Co onto the striped oxide, the LEED pattern is a big blur, consistent with the STM
results indicating very high density of Co NPs (~0.06/nm2). Fig. S2(d) is after cooling down from the TPA experiment
which raised the temperature up to 1000 K. TPA curves in Fig. 1(a) indicate that most of the Co has diffused into the
bulk and the LEED pattern indicates the resulting surface consists of both Fig. S2(a) clean surface and S2(b) striped
oxide. Similar LEED patterns are observed not only after annealing Co films thicker than 1nm to 1000K, but also after
a)
Present address: Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan, R.O.C.
b)
Author to whom all correspondence should be addressed.
Electronic mail: kjsong@pub.iams.sinica.edu.tw
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annealing the oxide alone at 1400K. This strongly suggests that although the oxide itself tend to reorganize into thicker
oxide films and expose clean NiAl(100), the process has a high kinetic barrier. The existence of non-oxidized Co can
reduce that kinetic barrier and allow the reorganization to occur at a much lower temperature such that patches of clean
NiAl(100) surface big enough to form LEED spots (≥10nm) are exposed.
For “thickened oxide”, LEED indicates persistence of the stripe structure after annealing to 1000K, but the
broadened lines indicate increased disorder along the length of the stripe. The limited effect in blocking Co’s diffusion as
shown in Fig. 1(b) may thus be rationalized by existence of varied domain boundaries that provide paths with different
easiness to pass.
Figures and Figure captions
FIG. S1. STM image of 0.03 ML Co deposited on Al2O3/NiAl(100) (striped oxide) at 300 K.
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FIG. S2. These are LEED patterns at different stages of a TPA experiment for a sample with 12 ML of Co on Al 2O3/NiAl(100)
(hollow-blue triangle curve of FIG. 1). Incident energy is 90 eV for all LEED patterns shown. (a) is the LEED pattern of clean
NiAl(100) surface. (b) is after formation of the striped oxide. (c) is after deposition of 12 ML of Co on the striped oxide. (d) is after
heating up to 1000 K in the TPA experiment. (d) is approximately (a) plus (b). This means that after annealing to 1000 K not only the
whole striped oxide surface is exposed, but also large area of clean NiAl(100) surface is exposed.
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