Silanol density

Support silanol density ( i-OH per nm ) wt% Ti Ratio of NpH Ti evolved Consumption (% SiOH) Ratio 2a 2b... 

The hybrid mesoporous material has some silanol groups corresponding to the T2 type Si species. The peak intensity ratio of the T2/T3 signals of the hybrid mesoporous material is almost equivalent to the Q3/Q4 signals of siliceous MCM-41 material. This indicates that silanol density is almost same to the siliceous MCM-41 material. Adsorption isotherm of water vapor showed that the hybrid mesoporous material has more hydrophobic surface than siliceous MCM-41. This fact supports that the organic fragments are exposed on the surface and increased the surface hydrophobicity. 

R-values as a function of the different Al-concentrations with respect to the silanol density on the PCH (x %) ... 

Silicagel is also called silica or bare silica. Its adsorptive properties depend on the hydroxyl groups attached to surface silicon atoms. Silicagel has a maximum silanol density of 8.0 yumolcs/ m2. Many of these silanols are buried deep in the porous structure and are available only to the smallest analytes. Silanols are either isolated, geminal, or vicinal they can be distinguished by means of Si solid-state nuclear magnetic resonance (NMR). The surface also contains siloxane bonds (Si-O-Si), which are considered hydrophobic. 

Table II. Silanol Density on A-150 and P-150 Determined by Different Methods...

From silanol densities measured between 4.2 and 5.7 OH per square nanometer, Zhuravlev (39) found a mean value of 4.9 OH per square nanometer at 180-200 °C under vacuum for 100 samples of different, fully... 

A comment on these silanol densities is necessary. A value of about 4.5-5.0 OH/nm is generally accepted for fully hydroxylated silicas, although there is considerable scatter in the literature data [1,2,20,21]. Fumed silicas that... 

From silanol densities measured between 4.2 and 5.7 OH per nm, Zhuravlev [47] found a mean value of 4.9 OH per nm at 180-200°C under vacuum for 100 samples of different, fully hydroxylated, amorphous silicas. Thermogravimetry of silica A showed that the silanol density that must be compared to these values, in the same conditions, is about 3.3 OH per square nanometer. As received, silica A is thus not completely hydroxylated. Other results corroborate this conclusion the D2 Raman band decreases under a further exposure to water vapor (Figure 26.8, curve a, 40), and the meth-oxyl density of 4.9 per nm observed after reaction with methanol at 460°C is larger than the initial OH density (Table 26.1). 

Samples G and P display a very large apparent silanol density (12-14 OH per nm with Ar or N2 specific surface area). Most of these hydroxyls can be deuterated and many are engaged in H-bonded aggregates larger than pairs. Thus, for these samples the sites Sp-Gp... 

Modeling of cation packing density as a function of distance z to the Si-OH and the Si-H surfaces is shown in Figure 7.17. Water molecules on the surface initiate complex interaction mechanisms since water affects the surface silanol density and... 

Table 5. Surface area, percentage SiOj, and surface silanol density of fibrous silicates (from Ghio et al. 1994) ...

Silicate Surface area (mVg) Percentage SiOj Surface silanol density (groups/nm )... 

The hydrophilic surface was obtained by a treatment with a piranha solution (H2SO4/H2O2). This treatment was aimed to produce a high-surface silanol density. 

Analogous to the electrical conditioning, the characteristics can be improved by a thermal treatment prior to the deposition of the source/drain metallization. On the basis of XPS measurements it could be shown that a heat treatment of the SiOa/Ca double layer results in a promoted interface reaction reducing the interfacial silanol density and the metallic fraction in the Ca overlayer. The former results in a reduction of the electron trap density and the latter in a reduction of screening effects by the metallic Ca. Since a cyclic electrical stress of an already annealed transistor does not yield a significant additional improvement in device performance, it was concluded that the observed OFET improvement for both device treatments, have the same origin. This implies that the oxidation of the metallic fraction in the Ca overlayer is promoted by the electrical cyclic stress as well as by the heat treatment. 

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