Tl/Ge(1 0 0) system: Phase formation and phase transitions

Using scanning tunneling microscopy, phase formation and temperature-driven phase transitions in Tl/Ge(1 0 0) system have been studied. Evolution of Tl overlayer structure has been considered for three temperature ranges, including around room temperature (RT), high-temperature (HT) (350-450 K) and low-temperature (LT) (20-100 K) ranges. Upon RT growth, a 2 × 1-Tl phase develops in submonolayer range and is completed at around 1 ML of Tl. Cooling of the RT-deposited Tl overlayer results in formation of a set of various LT structures. These are 1D chains, 5 × 4-Tl and “stroked” phases observed in submonolayer range and a long-period c(12 × 14)-Tl phase developed at around 1 ML. All transitions between these RT and LT structures are reversible. At doses beyond 1 ML, RT deposition of Tl onto Ge(1 0 0) leads to the growth of second-layer Tl stripes, forming arrays with a 1 × 4 periodicity. Meanwhile, structure of the first layer also changes and it displays a set of various reconstructions, c(2 × 8), c(10 × 6) and c(10 × 7). All these structures remain unchanged upon cooling to LT. Growth at HT as well as heating of RT-deposited Tl overlayer irreversibly produces 3 × 2-Tl phase whose rows become decorated by second-layer Tl stripes at prolonged Tl deposition.