Structure of n‑Alkyltrichlorosilane Monolayers on Si(100)/SiO2

• Published in: Langmuir 2015-11, Vol.31 (43), p.11774-11780
• Main Authors: Steinrück, H.-G, Will, J, Magerl, A, Ocko, B. M
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.5b03091

The structure of n-alkyltrichlorosilane self-assembled monolayers (SAMs) of alkyl chain lengths n = 12, 14, 18, and 22 formed on the amorphous native oxide of silicon (100) has been investigated via angstrom-resolution surface X-ray scattering techniques, with particular focus on the proliferation of lateral order along the molecules’ long axis. Grazing incidence diffraction shows that the monolayer is composed of hexagonally packed crystalline-like domains for n = 14, 18, and 22 with a lateral size of about 60 Å. However, Bragg rod analysis shows that ∼12 of the CH2 units are not included in the crystalline-like domains. We assign this, and the limited lateral crystallites’ size, to strain induced by the size mismatch between the optimal chain–chain and headgroup–headgroup spacings. Analysis of X-ray reflectivity profiles for n = 12, 14, and 22 shows that the density profile used to successfully model n = 18 provides an excellent fit where the analysis-derived parameters provide complementary structural information to the grazing incidence results.