Growth dynamics of low-dimensional CoSi 2 nanostructures revisited: Influence of interface structure and growth temperature

Abstract

The growth of cobalt silicide nanostructures on clean Si(001) was studied using scanning tunnelling microscopy and transmission electron microscopy. Two types of CoSi 2 nanostructures, flat and ridge-type islands, were formed when 0.1 ML Co was deposited onto clean Si(001) between 500 °C and 800 °C. These islands form elongated islands along [110] directions and grow into the Si-substrate within the temperature range. The formation of the two types of islands arises primarily due to the type of CoSi 2{111}- Si{111} interface formed between the island and the substrate. Flat islands are bound by CoSi 2{111}-Si{111} Type-A interfaces such that CoSi 2(001)//Si(001) and CoSi 2[001]//Si[001]. Ridge islands, on the other hand, are bound by a "twinned" CoSi 2{111}- Si{111} Type-B interface such that CoSi 2(221)//Si(001) and CoSi 2 [11̄0] //Si[11̄0]. This leads to the formation of three less energetically-favourable interfaces: CoSi 2(1̄1̄1̄ )-Si(115̄), CoSi 2(1̄1̄2̄)-Si(112̄), and CoSi 2(1̄1̄5̄)-Si(111̄). Analysis of the interfacial energies through dangling bond counting per interfacial area for each interface shows that the formation of the Type-B interface is energetically more favourable compared to the rest of the interfaces. As a result, the island elongates preferentially along the Type B interface leading to the formation of long nanowires with large length-width aspect ratio of 20:1. However, this formation is only achieved at high growth temperatures due to the presence of corner-barriers constraining the growth at low temperatures. Conversely, flat islands are slightly elongated at low growth temperatures with aspect ratio reaching 7:1 at 650 °C. As temperature increases towards 760 °C, they are brought closer to equilibrium and hence become less elongated with aspect ratio reduced to 1.6:1. © 2012 Elsevier B.V. All rights reserved.