A new type of surface phase in Si(110) was discovered and analyzed by scanning tunnelling microscopy and low-energy electron diffraction. When the Si(110) surface was flashed at 1200C followed by annealing at 330C for 1 h, a superstructure with two equivalent domains forms. From scanning tunnelling microscopy and low-energy electron diffraction analysis, the structure was revealed to be a 5 x 8 superstructure. On the basis of high-resolution scanning tunnelling microscopy images, a possible structural model of the 5 x 8 structure was proposed. Moreover, since this structure eventually returns to the clean so-called 16 x 2 structure by prolonged annealing at the same temperature, the 5 x 8 structure was believed to be a metastable phase of a clean Si(110) surface. Metastable Phase of Si(110) Surface - 5 x 8 Reconstruction. Y.Ohira, M.Yoshimura, K.Ueda: Japanese Journal of Applied Physics, 2007, 46, 5652-4