Formation of nanoclusters on silicon from carbon deposition

Changes in the structure of silicon surfaces can be induced by adsorption of carbon-containing molecules followed by thermal treatments. Clean Si(1 11) surfaces, prepared in vacuum and exposed to different adsorbants such as methanol or carbon monoxide, change their structures with the formation of self-organised nanostructures (15-50 nm diameter) after suitable UHV annealing procedures. Evolution of the size and density per unit area over different heating periods indicates that the structures are nucleated by carbon atoms present on the surface while their growth derives from mobile surface silicon atoms during the annealing process. Methanol adsorbs dissociatively on silicon at room temperature thus leading to a high density of nucleation centres, but when the process is applied to partially oxide-masked silicon surfaces using CO as adsorbant the nanostructures form preferentially at the Si/SiO2 interface around the mask border thus offering the possibility to grow more ordered self-organised nanoscale patterns. Monte Carlo simulations of this process correlate well with STM measurements.