Fluctuations and phase separation in Br/Pt(1 1 0)

The quasi-one-dimensional system c(2 × 2)-Br/Pt(1 1 0) is investigated by low-energy electron diffraction (LEED) spot-profile analysis and by variable-temperature scanning tunnelling microscopy (VT-STM). An order–disorder transition is found at 375 K. For 250 K < T < 375 K a long-range ordered c(2 × 2) phase is observed, but the spot profiles reveal strong correlated fluctuations along the close-packed row direction. At T = 50 K three different phases coexist in a glassy state: c(2 × 2), (2 × 1), and (3 × 2). The loss of long-range order and transition into a phase-separated state is a common feature predicted for strongly correlated systems. Some inconsistencies between theory and experiment in our previous interpretation of the (3 × 1)-Br/Pt(1 1 0) phase as a charge density wave (CDW) are resolved by identifying it as a fluctuating (3 × 2) CDW phase.