Silicon oxidation thick-oxide case

Fig. 16. Influence of the ionic strength in the prevention of readhesion phenomenon in the case of a positive particle on a negative substrate (alumina slurries on silicon oxide layer) a high-ionic-strength limit the double layer thickness. Particle and substrate are therefore electrically masked at a closer particle-substrate distance. (The double layer of the substrate is not represented here.)...

The -propanol adsorption from the gas phase significantly decreases the adhesion force between the silicon oxide surfaces measured with AFM. Fig. 7 illustrates the adhesion force measured with a single tip (2.2 N/m) at various partial pressures of n-propanol. The adhesion force decreases 40% compared with the dry Ar case upon initial introduction of n-propanol partial pressure. This reduction is not as drastic upon further increase of the n-propanol partial pressure. A sudden change in adhesion with only 10% partial pressure indicates that a few monolayer thick n-propanol film, as shown in Fig. 4, is sufficient to reduce the adhesion between the silicon oxide surfaces. This behavior is in sharp contrast to the relationship between the adhesion force and the water adsorption isotherm. In the case of water, the adhesion force increases several fold when the relative humidity increases from zero to... 

Infrared Spectroscopy. An inspection of the infrared spectra of dry or hydrated pure Nafion in the sulfonic add or various cationic salt forms reveals a multiplidty of bands (28, 30, 31) some of which are inconveniently located in close proximity to the aforementioned peaks characteristic of silicon oxide strudures. The Nafion contribution to the composite spectra was subtracted in each case using the 2860 cm band (combination 1140 + 1720 cm, both CF,CF,) as an internal thickness standard. While this band appears weak and may not be an ideal internal standard (Membranes were not available to test absorbance vs. thickness linearity.), it is backbone-related, lies in a region of peak noninterference and the resultant subtractions do appear effective. 

At 20 nm, the SiOa layers are practically homogeneous, and the ratio f ii6o/f i25o is independent of the thickness. For a thinner SiOa layer, the band at 1250 cm is broader, its maximum is shifted toward lower frequencies, and the ratio Rim/Rnso is increased. These effects are all a result of an oxygen deficiency at the initial stages of thermal silicon oxide formation, as in the case of anodic oxides, which leads to the appearance of a nonstoichiometric SiO layer, as observed in the IRRAS spectra [23]. 

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

In fabrication of the catalysts by laser electrodispersion, thermally oxidized silicon wafers with a thickness of Si02 oxide layer of 1 pm were used as a substrate. A substrate with so thick an oxide layer can be regarded as an insulator. In some cases, wafers of crystalline (1 0 0) Si were used, which had on their surface only a thin (l-2nm) layer of a natural oxide. This layer is tunnel-transparent for electrons, and, therefore, charge exchange between supported nanoparticles and silicon is possible. 

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