Monitoring of the Degree of Condensation in Alkoxysiloxane Layers by NIR Reflection Spectroscopy

This paper introduces a novel analytical approach for monitoring the degree of condensation of thin siloxane films, which is potentially suitable for in-line process control during the deposition of such layers, e.g., to polymer films. Near-infrared (NIR) reflection spectroscopy in combination with chemometric methods was used as a process monitoring tool. The state of the formation of the inorganic Si–O–Si network in partially condensed 3-methacryl­oxypropyl­trimeth­oxysilane batches was analyzed by inverse gated ²⁹Si NMR spectroscopy. Results were expressed in terms of different relative ratios of the Tⁱ species (i.e., structures with different numbers of Si–O–Si units per Si atom). These data were used for calibration of the NIR method, which was applied to thin layers printed on a polymer foil with a thickness of ∼2.2 g m^–2. The root-mean-square error of prediction (RMSEP) for the determination of the ratio of the Tⁱ species from the NIR spectra was found to be less than 3%. The error of the reference data from ²⁹Si NMR spectroscopy is 4%, which results in an overall error of 5%. Moreover, the thickness of siloxane layers was determined by this method in a range from 2.5 to 5.5 g m^–2 using gravimetry for calibration (prediction error ∼0.3 g m^–2)

Low-Temperature Photochemical Conversion of Organometallic Precursor Layers to Titanium(IV) Oxide Thin Films

Thin layers of titanium­(IV) ethoxide [Ti­(OEt)₄] as a metal–organic precursor were spin-coated onto silicon wafers under inert conditions and subsequently photochemically converted to thin titanium­(IV) oxide (TiO_<i>x</i>) films employing vacuum ultraviolet (VUV) radiation from a xenon excimer lamp. The photochemical conversion was performed below 35 °C and at ambient pressure in a nitrogen atmosphere with an optimized content of oxygen. Ti­(OEt)₄ decomposition and its kinetics were monitored and analyzed by gas chromatography and infrared spectroscopy. Precursor layers with a thickness between 270 and 1060 nm could be converted into much thinner TiO_<i>x</i> films (40–165 nm). The decrease in thin film thickness was found to coincide with the removal of organic side chains and densification to a compact oxide network. For precursor layers with a thickness of up to 550 nm, VUV irradiation with a moderate radiant exposure (<i>H</i>_e) of 2.3 J cm^–2 led to almost carbon-free amorphous layers with a composition close to stoichiometric titanium dioxide (TiO₂) having a density of ∼2.95 g cm^–3 determined by X-ray photoelectron spectroscopy and X-ray reflectometry, respectively. In turn, crack-free thin films exhibiting high UV–visible transparency and smooth surface topography were obtained. The highlighted example of Ti­(OEt)₄ shows that photochemically initiated decomposition of a metal alkoxide is a powerful approach for the generation of thin metal oxide layers at normal pressure and near ambient temperatures