Structure of n-Alkyltrichlorosilane Monolayers on Si(100)/SiO2
H-G Steinrück1,2, J Will1, A Magerl3
1Crystallography and Structural Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany.
Langmuir : the ACS Journal of Surfaces and Colloids
|October 6, 2015
Summary
Self-assembled monolayers (SAMs) of n-alkyltrichlorosilanes on silicon show crystalline domains but limited lateral order. Strain from spacing mismatches restricts domain size and order in these alkyl silane SAMs.
Area of Science:
- Surface science
- Materials science
- Nanotechnology
Background:
- Self-assembled monolayers (SAMs) are crucial for modifying surface properties.
- Understanding the structural ordering of SAMs is key to controlling their function.
- Alkyltrichlorosilanes form SAMs on silicon oxide surfaces, but their detailed structure is complex.
Purpose of the Study:
- To investigate the structural organization of n-alkyltrichlorosilane SAMs on silicon.
- To determine the extent of lateral order and domain formation.
- To understand the factors limiting structural perfection in these SAMs.
Main Methods:
- Angstrom-resolution surface X-ray scattering techniques were employed.
- Grazing incidence diffraction was used to analyze in-plane structure.
- X-ray reflectivity profiles provided information on vertical density distribution.
- Bragg rod analysis assessed the inclusion of alkyl chains within ordered domains.
Main Results:
- Hexagonally packed crystalline-like domains (∼60 Å lateral size) were observed for longer alkyl chains (n=14, 18, 22).
- A significant portion (∼12 CH2 units) of the alkyl chains were found outside these ordered domains.
- Strain, arising from spacing mismatches, was identified as the cause for limited domain size and order.
- A consistent density profile model, derived from n=18, successfully described data for other chain lengths (n=12, 14, 22).
Conclusions:
- The structural ordering in n-alkyltrichlorosilane SAMs is imperfect due to intrinsic strain.
- Surface X-ray scattering provides detailed insights into both lateral and vertical structure.
- The findings offer a deeper understanding of SAM formation and limitations on silicon oxide surfaces.
