We investigated the Si(1 0 0) 1 x 1:2H dihydride surface using the noncontact atomic force microscopy (NC-AFM). NC-AFM images showed that the pattern of the dihydride surface changed depending on the distance between the tip and the sample surface. The image with 1 x 1 structure appeared when the tip was a little far from the sample surface. When the tip became close to the surface, 2 x 1 structure where the bright lines and the dark lines were alternately located appeared. This 2 x 1 image was stable for retracting the tip from the surface. Furthermore, when the tip became close to the surface, 1 x 1 structure reappeared. It turned out that the structures of the dihydride surface changed due to the attractive force between the tip and the sample under NC-AFM measurement. (C) 2002 Published by Elsevier Science B.V.