Tl/Ge(100) system: Phase formation and phase transitions

Using scanning tunneling microscopy, phase formation and temperature-driven phase transitions in Tl/Ge(100) system have been studied. Evolution of Tl overlayer structure has been considered for three temperature ranges, including around room temperature (RT), high-temperature (HT) (350–450K) and low-temperature (LT) (20–100K) ranges. Upon RT growth, a 2×1-Tl phase develops in submonolayer range and is completed at around 1ML 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 1ML. All transitions between these RT and LT structures are reversible. At doses beyond 1ML, RT deposition of Tl onto Ge(100) 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.