The Partially Chlorinated/Hydrogenated Si(111) Surface as a Template for the Formation of Nanopatterns

E. M. PATRITO; F. A. SORIA; P. PAREDES OLIVERA

Boston, MA

Congreso; 2013 MRS Fall Meeting; 2013

Materials Research Society

In this work we show that the different reactivities of SiH and SiCl surface groups in partially chlorinated silicon surfaces open pathways for the selective functionalization of flat Si(111) surfaces, therefore allowing the formation of nanopatterns on such surfaces. We also show that the high reactivity of the step edges of fully chlorinated surfaces could also be used for the selective functionalization of vicinal surfaces. Using density functional theory and a slab model of the surface (1), we investigated the reactivity of the partially chlorinated Si(111) surface towards reactants with N, O and S head groups (NH3, H2O, H2S, CH3NH2, CH3OH, and CH3SH) in relation to the development of selectively functionalized surfaces. The reactivities of the fully hydrogenated and halogenated Si(111) surfaces are also considered as a reference. The results show that the perfect H−Si(111) and Cl−Si(111) surfaces are unreactive at room temperature. However, the decrease of steric factors on partially chlorinated surfaces, increase the reactivity of the SiCl group towards NH3, CH3NH2 and H2O to such extent that they could react at room temperature. As the reactivity of SiH and SiCl groups is very different (2), surfaces with a partial coverage of chlorine atoms may allow a selective functionalization of the surface by a chemistry route. Therefore, by controlling the initial chlorine surface coverage during the chlorination procedure, the surface density of molecules grafted to the silicon surface could be controlled as well. The concept of selective functionalization thus relies upon the presence of reactive SiCl groups embedded in a matrix of unreactive SiH groups. Once steric factors around a SiCl group are liberated by the appearance of adjacent SiH groups, the reactivity of SiCl greatly increases, whereas the reactivity of SiH remains unaltered. Unlike the fully chlorinated Si(111) surface, the SiCl groups on the reconstructed step edges are very reactive showing the lowest activation energy barriers. Fully chlorinated vicinal silicon surfaces seem to offer an opportunity to build molecular lines along the highly reactive step edges. We envisage a two step procedure in which the step edges are first functionalized via the formation of Si−N or Si−O bonds and then the Cl−Si(111) terraces are passivated via the formation of Si−C bonds by reaction with alkyl Grignards.