Epitaxial titanium silicide islands and nanowires

The growth of titanium silicide islands formed by reactive deposition of Ti on Si(1 1 1) at T ∼ 850 °C has been studied using atomic force microscopy and transmission electron microscopy. The predominant shape is very long and narrow, and can be considered to be a nanowire (NW). Other flat-topped structures coexist with the NWs, including small equilateral triangles and large rectangular plates. Most NWs are oriented along Si〈220〉 directions, with typical dimensions 20 nm wide, 10 nm high and several microns long. A minority of NWs are oriented along Si〈224〉. These latter tend to break up into chains of small segments with regular size and spacing. Growth at lower temperature or higher deposition rate results in smaller and more numerous NWs. Length appears to be limited by intersection with other NWs oriented 120° apart. The junction between NWs appears to be incoherent in most cases. The triangular islands are positively identified as fully relaxed C54 TiSi₂, while the chains are relaxed C49 TiSi₂. The dominant NW structure is incommensurate and is tentatively identified as C49 TiSi₂.