The Si (111) structure, by comparison, exhibits a much more complex reconstruction. Cleavage along the (111) surface at low temperatures results in another 2×1 reconstruction, differing from the (100) surface by forming long π-bonded chains in the first and second surface layers. However, when heated above 400 °C, this structure converts irreversibly to the more complicated 7×7 reconstruction. In addition, a disordered 1×1 structure is regained at temperatures above 850 °C, which can be converted back to the 7×7 reconstruction by slow cooling.