Phase transitions on clean and nickel containing vicinal Si(111) surfaces

Structure and reversible structural phase transitions on clean vicinal Si surfaces inclined from the (111) plane towards [2] and [11] poles and the effect of nickel on the structure and the structural transitions on these surfaces have been studied by LEED. The structures of clean surfaces inclined towards [2] and [11] are different. Phase transitions take place at about 870°C and 800° C, respectively. Above the transition temperatures these two surfaces consist of regular steps with heights equal to one interplanar distance d₁₁₁ (3.135 Å). The terrace width between steps is determined by the angle of inclination to the (111) plane. Below the transition temperatures the surfaces inclined to [2] contain steps with height 3d₁₁₁, those inclined towards the [11] pole consist of combinations of (111) facets and some other, apparently (133). The effect of nickel leads to the formation of regular steps with height 2d₁₁₁ on the surfaces inclined towards [2] and with height 2d₁₁₁ or 1d₁₁₁, depending on the nickel concentration, on the inclined towards [11]. On nickel-containing surfaces there also take place reversible structural transitions with varying temperature.