Silica films characterization techniques

To determine the success of synthesis efforts and to provide feedback on quality control, the mesoporous silica films are characterized by several techniques. The ability to determine the continuity and quality of the films must be quick and accurate. Owing to this fact, x-ray diffraction has proven the easiest way to resolve the film structure. However, phase identification by x-ray diffraction alone is not always conclusive (e.g., when only one peak is observed). Other techniques must be employed to fully determine the phase of the mesostructure. 

Borsacchi et al. (2008) studied BaS04 submicronic (0.20-0.25 im) particles (sample A), modified by a thin silica film (1 wt%) (sample B) and then treated with stearic acid (sample C), characterized by means of Si, and H MAS high-resolution techniques, and low-resolution H-FID analysis. 

Ikoma S., Kawakita K., Yokoi H. Characterization ofpolyamine copper(ll) complex-doped alumina gels prepared by the sol-gel technique. J. Non-Cryst Solids 1990 122 183-192 Ilharco L.M., Santos A.M., Silva M. J., Martinho J.M.G. Intramolecular pyrene excimer in probing the sol-gel process. Langmuir 1995 11 2419-2422 Innocenzi P., Kozuka H., Yoko T. Dimer-to-monomer transformation of rhodamine 6G in sol-gel silica films. J. Non-Cryst. Solids 1996 201 26-36... 

Figure 4-11 shows the evolution ofthe frequency ofthe TO peak, for silica and silica-titania sol-gel films, with the heat treatment temperature. There is a minimum in the frequency values for both compositions at about 400-500°C, followed by a peak frequency increase for higher treatment temperatures (Almeida et al., 1994 Primeau et al., 1997 limocenzi, 2003). This frequency minimum may be associated with a maximum in the porosity ofthe films. Indeed, with the help of other characterization techniques (DTA,... 

Thin films on substrates provide a characterization challenge the whole system must be measured at once and substrate properties can easily mask those of the thin film. Other techniques have been employed to study these complex systems. Fryer et al. used local thermal analysis to probe polystyrene (PS) and PMMA on two different substrates. These results were comparable to ellipsometry values establishing local thermal analysis as an effective technique. Again, PS did not have a favorable interaction with the polar or nonpolar silicon surface and both PS systems showed a decrease in Tg with decreasing film thickness. PMMA showed similar behavior on the nonpolar surface. However, on the polar substrate the Tg increased as the PMMA films became thinner. Porter saw similar effects measuring PMMA on silica with a differential scanning... 

The fullerenes, Cgo and C70, are produced in the laboratory by the contact arc-evaporation of 6 mm graphite rods (e.g. Johnson Matthey, spectroscopic grade) in 100 torr of helium in a water-cooled stainless steel chamber described previously [5]. The soluble material in the soot produced from the arc-evaporation is extracted with toluene using a Soxhlet apparatus. The pure fullerenes are obtained by chromatography on neutral alumina columns using hexanes as the eluant, or by the use of a simple filtration technique using charcoal-silica as the stationary phase and toluene as the eluant [5]. The fullerenes so prepared are characterized by UV/Vis spectroscopy and other techniques. FT-IR spectra of vacuum deposited fullerene films on KBr crystals also provide a means of characterization, just as do Raman spectra of films deposited on a silicon crystal. Ultraviolet and X-ray photoelectron spectra of fullerene films on... 

Infrared spectroscopy (IR) is also a very useful technique for characterizing stmcture. IR spectroscopy can be used for identification purposes as well as for monitoring the progress of a chemical reaction. Comparisons of the positions of absorptions in the IR spectrum of a sample with the characteristic absorption regions, leads to identification of the bonds and functional groups present in the sample. For example, the chemical stmctures of polyimide-silica hybrid films were confirmed by IR spectroscopy by the appearance of two absorptions at 1,100 and 830 cm indicating the formation of the Si-O bonds. 

Other techniques have been also used in oriented thin fim fabrication like shear technique (Meyler and Thakur (1985)) giving truly monocrystalline thin films. In this case, the film is grown from solution between two e.g. silica slides with a preorientation of monomers at low temperature by shearing and controlled solvent evaporation. It works for monomers characterized by a high ability for cristallization like diacetylenes TS and TCDU. 

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