When Si is cleaved along the (100) surface, the ideal diamond-like structure is interrupted and results in a 1×1 square array of surface Si atoms. Each of these has two dangling bonds remaining from the diamond structure, creating a surface that can obviously be reconstructed into a lower-energy structure. The observed reconstruction is a 2×1 periodicity, explained by the formation of dimers, which consist of paired surface atoms, decreasing the number of dangling bonds by a factor of two. These dimers reconstruct in rows with a high long-range order, resulting in a surface of filled and empty rows. LEED studies and calculations also indicate that relaxations as deep as five layers into the bulk are also likely to occur.