Comment on “oscillatory indirect interaction between adsorbed atoms — Non-asymptotic behavior in tight-binding models at realistic parameters” by K.H. Lau and W. Kohn

A sensitive infrared reflectance accessory suitable for the study of surface films on medium size single crystals is described. Oxide films formed on the (100), (110) and (111) crystal faces of aluminum in air, at room temperature, display nearly identical behavior with films approximately 10 Å thick absorbing as a single band near 940 cm^?. After 10⁴ sec at 570 °C, in oxygen, films formed on these crystals begin to display differences in band characteristics and growth kinetics. Between 10⁴ and 4 × 10⁴ sec the rates of growth on the (110) and (111) crystal faces are much greater than on the (100) face. Beyond 4 × 10⁴ sec the growth rate on the (100) face increases while the (110) and (111) growth rates approach zero. Limiting thicknesses reached after 4 × 10⁵ sec approach 3.4 × 10², 2.1 × 10² and 2.2 × 10² Å for (100), (110) and (111) faces, respectively. Oxide compositional differences were reflected by the number and form of the infrared bands after 10⁴ sec of oxidation. After 5 × 10⁴ sec the (100) face oxide was composed of two and possibly three oxide species as evidenced by several bands. Differences in bandwidth and frequency were observed between the (110) and (111) oxide films. The significance of such differences is discussed.