The photochemical conversion of 200-500 nm layers of perhydropolysilazane --(SiH2-NH)n-- (PHPS) in the presence of oxygen into an SiOx network was studied. Different UV sources in the wavelength range of 160-240 nm, that is, 172 nm Xe2* and 222 nm KrCl* excimer, and 185 nm Hg low-pressure (HgLP) lamps were used for these purposes. The role of both ozone and O(1D) as well as of catalytic amounts of tertiary amines in the degradation process of PHPS and the formation of SiOx were studied. In this context, the kinetics of the entire reaction were elucidated and allowed both a continuous and discontinuous process to be established for the production of fully transparent, flexible barrier coatings. Barrier improvement factors (BIFs) of 400 were achieved with one single layer on 23 microm poly(ethyleneterephthalate) (PET), which translated into oxygen transmission rates (OTRs) of 0.20 cm3 m(-2) day(-1) bar(-1). Double layers prepared by this technique allowed the realization of OTRs of or=800.

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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 x ) 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 x 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 (H e ) of 2.3 J cm −2 led to almost carbon-free amorphous layers with a composition close to stoichiometric titanium dioxide (TiO 2 ) 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.

The vacuum-UV (VUV)-induced conversion of commercially available poly(1,1-dimethylsilazane-co-1-methylsilazane) into methyl-Si-O-Si networks was studied using UV sources at wavelengths around 172, 185, and 222 nm, respectively. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS), X-ray photo electron spectroscopy (XPS), and Fourier transform infrared (FTIR) measurements, as well as kinetic investigations, were carried out to elucidate the degradation process. First-order kinetics were found for the photolytically induced decomposition of the Si-NH-Si network, the subsequent formation of the methyl-Si-O-Si network and the concomitant degradation of the Si-CH(3) bond, which were additionally independent of the photon energy above a threshold of about 5.5 eV (225 nm). The kinetics of these processes were, however, dependent on the dose actually absorbed by the layer and, in the case of Si-O-Si formation, additionally on the oxygen concentration. The release of ammonia and methane accompanied the conversion process. Quantum-chemical calculations on methyl substituted cyclotetrasilazanes as model compounds substantiate the suggested reaction scheme. Layers <100 nm in thickness based on mixtures of poly(1,1-dimethylsilazane-co-1-methylsilazane) and perhydropolysilazane (PHPS) were coated onto polyethylene terephthalate (PET) foils by a continuous roll to roll process and cured by VUV irradiation by using wavelengths <200 nm and investigated for their O(2) and water vapor-barrier properties. It was found that the resulting layers displayed oxygen and water vapor transmission rates (OTR and WVTR, respectively) of <1 cm(3) m(-2) d(-1) bar(-1) and <4 g m(-2) d(-1), respectively.