XPS, FTIR-ATR, and AFM Structural Study of Silicon-Grafted Triol Monolayers for Controlled Anchoring of Single Molecule Magnets

The structures of monolayers on Si(100) made up of two acetyl-protected triol ligands, derived from 2-hydroxymethyl-propane-1,3-diol, namely, R-C(CH2OAc)(3) with R = CH2=CH-(CH2)(9)-O-CH2- and R = CH2=CH-(CH2)(7)-, have been investigated. After deprotection, the two ligands are well-suited receptors for anchoring molecular functionalities, such as Fe-4 single molecule magnets, to the Si surface through OH groups. Monolayers were obtained by the hydrosilylation reactions between H-terminated Si(100) and the CH2=CH- end groups and were prepared in pure form or diluted with inert 1-alkenes to achieve an accurate control over the concentration and concerted orientation of the receptors on the surface. Subsequent anchoring of a Fe-4 cluster, especially designed for a vertical atom sequence, has been expedient to clarify the influence of ligand mole fraction on the ordering of molecular receptors. We have achieved insight into the related structures and morphologies by combining angle-resolved X-ray photoelectron spectroscopy (AR-XPS), FTIR-attenuated total reflection (ATR) spectroscopy, and atomic force microscopy (AFM), including force lithography experiments. There is evidence that steric hindrances of apical groups are crucial for surface concentrations and, in turn, for geometrical orientation of the tethering units. Aging effects on monolayer structures and possible recovery processes have also been evaluated.