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\u2550CH 12(CH2)9 12O 12CH2 12 and R = CH2\u2550CH 12(CH2)7 12, have been investigated. After deprotection, the two ligands are well-suited receptors for anchoring molecular functionalities, such as Fe4 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\u2550CH 12 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 Fe4 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

Eu-Doped Titania Nanofibers: Processing, Thermal Behaviour and Luminescent Properties

Undoped and Europium-doped titania nanofibers have been fabricated by electrospinning technique, using a single multielement Titanium/Europium source. In this communication we present the synthesis, structural and spectroscopic characterisation of Eu-doped TiO2 nanofibers starting from polyvinylpyrrolidone, titanium tetraisopropoxide (Ti(O/Pr)(4)) and Eu(hfa)(3)center dot diglyme (Hhfa = 1,1,1,5,5,5-hexafluoroacetyacetone, diglyme = CH3O(CH2CH2O)(2)CH3). The chosen system allowed to investigate a wide compositional range, i.e., from 3 to 10 %mol of Eu3+. Microstructure was studied by means of scanning electron microscopy (SEM), thermal behaviour followed by thermogravimetric and differential thermal analysis (TG-DTA). Phase analysis was performed by means of X-ray diffraction (XRD) and high temperature X-ray diffraction analysis (HT-XRD) up to 1100 degrees C. Luminescence properties were investigated by means of luminescence spectroscopy, using a laser excitation source at 395 nm. All electrospun materials consisted of randomly oriented nanofibers of fairly uniform diameter. The average fiber size was 80-100 nm and 40 nm for, respectively, Eu-doped and undoped TiO2 calcinated at 500 degrees C. The presence of Europium shifted toward higher values either the crystallization temperature of anatase and the anatase to rutile phase transition, the latter being accompanied by the formation of the Eu2Ti2O7 phase. The doped samples showed a strong luminescence of Eu3+ ions. The emission spectra were dominated by the D-5(0) -> F-7(2) emission, suggesting a notable distortion around the Eu3+ ions. The broadening of the bands pointed to the presence of a relevant inhomogeneous disorder around the Eu3+ sites. The Eu3+ doped TiO2 nanofibers showed a higher emission intensity with respect to the PVP/TiO2 one