Structural model for Si(111)-(7×7)

A new structure is proposed for the Si(111)-(7×7) surface which is consistent with recent tunneling microscopy and ion-scattering data. It consists of 12 trimers which are located near the points (1,1), (3,1), (1,3), (5,1), (1,5), (3,3), (4,4), (6,2), (2,6), (6,4), (4,6), (6,6) of a (7×7) unit cell. The bonding of the trimers is similar to the $\pi$-bonded chain model for Si(111)-(2×1) but only half as many bond flips are required to reconstruct the surface. Broken bonds are eliminated by removing atoms along the boundaries between eclipsed and staggered structures.