One very powerful way to create nanostructures in a well-controlled manner is to use stepped silicon surfaces as templates. To obtain such stepped surfaces Si crystals are cut at a small angle with respect to a highly stable crystal plane (in this case Si(111) plane). The surface then attempts to maintain the preferred orientation, but is forced by miscut to form atomic steps every so often. These steps are separated by atomically flat terraces and the width of these terraces is determined by the miscut angle.
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Shown above is a 3 dimensional representation of an STM image of silicon stepped
surface. Each one of the steps on this "atomic staircase" is approximately 0.3 nm
high. The area shown is about 400x400 nm2, so the vertical axis was stretched
by a factor of 15 to show the steps. Flat terraces are on average 15-17 nm wide. Note
how straight the steps are - this can be seen better on the image on the left. The image on the left is basically a top view of the surface shown above. Or rather the top view with illumination from the left (STM image in the derivative mode). Downhill is to the right and steps appear as dark lines. Note that there's one kink (close to the center of the image) in the whole area, the rest of the steps are in fact atomically straight. It turns out that the 7x7 reconstruction of this surface is responsible for the straightness of the steps. |
Si(111) Surface & 7x7 Reconstruction
Main Nanowiz Page
Univ of MD site with stepped Si(111) info
This page was created with 1st Page 2000, last updated on August 8, 2000.