Peierls instability in Pt chains on Ge(0Â 0Â 1)

We have studied the structural and electronic properties of atomic Pt chains on a Pt modified Ge(0 0 1) substrate. Using scanning tunneling microscopy we show that these Pt chains undergo a phase transition from a 2× periodicity at room temperature to a 4× periodicity at low temperature. The coupling between the atomic chains turns out to be of essential importance, since isolated Pt chains and chains located at the edge of an array of chains maintain their 2× periodicity at temperatures as low as 4.7 K. The 2× to 4× transition is accompanied by an opening of an energy gap and is interpreted in terms of a Peierls instability.