Secondary thin film processing

One way of implementing the UV disinfection process at existing activated sludge plants involves suspending the UV lights (in the form of low-pressure mercury arc UV lamps with associated reflectors) above the secondary clarifiers. The effluent is exposed to the UV radiation as it rises over the wire in a thin film. 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

Figure 7.7 Schematic set-up for measuring X-ray fluorescence with an energy-dispersive detector as in EDX. Irradiation of a bulk sample activates a pear-shaped volume from which X-rays are emitted. The chance of secondary processes is considerable and requires correction of the measured X-ray yields secondary effects are much less important if the sample is a thin film.

The sample surface is bombarded with a beam of around 1 keV ions of some gas such as argon and neon. The action of the beam sputters atoms from the surface in the form of secondary ions, which are detected and analyzed to produce a characterization of the elemental nature of the surface. The depth of the analysis is usually less than a nanometer, making this process the most suitable for analyzing extremely thin films. 

In contrast to SIMS, in SNMS - where the evaporation and ionization processes are decoupled -the matrix effects are significantly lower, because the composition of sputtered and post-ionized neutrals corresponds more closely to the composition in the solid sample (compared to the sputtered secondary ions in SIMS), which means the RSCs of elements vary by about one order of magnitude. Consequently, a semi-quantitative analysis by SNMS can also be carried out if no suitable matrix matched CRM is available. This is relevant for thin film analysis, especially for the determination of elemental concentration profiles in depth, for studying the stoichiometric composition of thin films and interdiffusion effects. 

We studied two families of compounds and explored their ability to give VN thin films on silicon or steel substrates. One of these families were the chloromido vanadium (V) compounds (Table 15.2, compounds 20-25). The presence of a V = N double bond strengthens the core of the molecule and should facilitate the elimination of the secondary substituents.40 Compounds 20 and 23 appeared to be too stable they decomposed in multistep processes that ended at temperatures higher than 1173 K. On the contrary, compound 22 at normal conditions was too unstable versus hydrolysis and too light-sensitive to be considered further for CVD applications. 

Electron impact ionization of the parent molecule is only one of several important ion formation processes in nonthermal plasmas. Secondary processes such as electron impact ionization of neutral fragments produced by dissociation of the parent molecule and ion-molecule reactions are other mechanisms contributing to the formation of plasma ions. It is interesting to compare ion abundances in a realistic plasma with the ion abundances predicted from electron impact ionization cross sections measured under single-collision conditions. Although mass spectrometry of plasma ions is a known and well-developed diagnostic method (Osher, 1965 Drawln, 1968 Schmidt et al., 1999), its application to plasmas for thin-film deposition is not very common. The main reasons are deleterious effects of insulating deposits on the ion collection orifice (which connects the mass spectrometer to the plasma) and on the ion transfer optics, which render it... 

But in spite of all the advantages of the SEFS method as compared to both diffraction and spectroscopic methods of structure analysis, this technique has not yet been applied to analyze the local atomic structure of surfaces and thin films. This is explained by the diversity and complexity of the processes forming the secondary electron spectrum and the corresponding fine structures, and the resulting difficulties in their theoretical description and in the mathematical formalization of the problem of determining local atomic structure parameters from the experimental data. 

Another widely used approach in this area is a sol-gel process. In order to create surface roughness after deposition of thin films, a secondary component is included in the sol-gel deposition process which can be removed later by dissolution in hot water or sublimation. The removal of the secondary components gives porous structures. Subsequent lluorinated silane coating can render these sol-gel processed films superhydrophobic [81-83]. Microporous structures can be created through phase separation of organic polymer solutions and then used as a template for sol-gel processing of porous silica substrates. Ruorosilane treatment of these substrates produces superhydrophobic surfaces [84]. 

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