Dresden 2014 – scientific programme

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DS: Fachverband Dünne Schichten

DS 6: Thin Film Characterization: Structure Analysis and Composition (XRD, TEM, XPS, SIMS, RBS,...)

DS 6.14: Talk

Monday, March 31, 2014, 18:45–19:00, CHE 89

Partial Crystallinity in Alkylsilanes Monolayers — •Hans-Georg Steinrück¹, Moshe Deutsch², Ben Ocko³, and Andreas Magerl¹ — ¹1Lehrstuhl für Kristallographie und Strukturphysik, Universität Erlangen Nürnberg, Germany — ²Bar-Ilan University, Ramat- Gan, Israel — ³Brookhaven National Laboratory, Upton NY, USA

Alkylsilane (denoted as Cn, n = 12, 14, 18, 22, 30) self-assembled monolayers (SAMs) on the amorphous oxide of silicon are vertically aligned and densely packed as shown by X-ray reflectivity. A new 3-slab model simulating the electron density profile was developed yielding only four free fit parameters (roughnesses of each interface and the density of one slab). All other parameters for the alkyl chain were fixed to the values in the rotator phase [1] and to the chemical bond length in the linker group region. For all Cn, expect C12, a hexagonal ordering with a lattice constant of a = 4.82 Å is revealed by X-ray grazing incidence diffraction. Interestingly, the analysis of the intensity distribution along q_z (Bragg rod) reveals that crystalline phase is less than the length of the molecule. We argue that this reflects gauche defects at the chain ends [2] as well as steric hindrance in the linker group region [3]. The percentage of the surface normal crystalline part of the alkyl chain increases up to   60% for C18 and linearly drops down to 40% for C30.

[1] Ocko, B.M. et al., PRE 1997, 55, 3164-3182.

[2] Allara, D.L. et al., Langmuir 1995, 2357-2360.

[3] Prasad, S. et al., A. PRL 2008, 101, 065505-065505.