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Imaging of hydrogen‐induced Si(111) surface with the scanning tunnelling microscope

We have directly observed the hydrogen‐induced changes of the Si(111)7times7 surface using a scanning tunnelling microscope (STM). The 7times7 reconstructed atomic structure was formed on a clean surface of Si(111). But when the clean surface was dosed with typically 1–2 L [1 L (Langmuir) = 1·33 times 10−4 Pa. sec] hydrogen, the 7 times 7 image was gradually smeared out and then a 1 times 1 unreconstructed pattern appeared. After dosing with 5–10 L hydrogen, the STM image exhibited a new long‐periodic structure together with the 1times1 structure underneath. These experimental results may be ascribed to the chemisorption of hydrogen atoms on clean Si surfaces.