Atomic force microscopy investigation of the growth of different alkylsiloxane monolayers from highly concentrated solutions

The growth of self-assembled monolayers of alkylsiloxanes on silicon surfaces through adsorption of alkyltrichlorosilanes at various concentrations in toluene has been investigated. The influence of high alkylsilane concentrations up to 50 mmol/L on the ordering of the films has been studied. Characterization of the films has been performed with tapping mode atomic force microscopy and ellipsometry. Different alkylsilanes have been used in order to study both the effect of the chain length and the age of the precursor solution on the ordering of the molecules in solution as well as on the substrate surface. For freshly prepared solutions with a high concentration of octadecyltrichlorosilane (OTS, C-18), irregular rough films with a maximum surface coverage of 70% have been observed. For C-10, C-12, and C-16 alkylsilanes, comparatively flat films have been obtained under the same conditions. For OTS, such flat films can only be achieved after prolonged aging of the precursor solution. The results are discussed in terms of ordering depending on different experimental parameters.