Impurities technique-oriented

The lead precursor in PbSe film deposition was lead acetate complexed with triethanolamine. The growth rate for PbSe was 0.18-0.16nm/cycle. The films were polycrystalline (i.e., cubic) without preferred orientation. The stoichiometry of SILAR-grown PbSe was found to be 1 1 within the limits of the RBS technique. Impurities detected were 5 at.% of oxygen and 8 at.% of hydrogen.103... 

Platinum surfaces Mith (111) and (100) orientations treated in this May have been checked by using LEED characterization on as received" samples, both shoued the characteristic LEED pattern Hith their respective (lxl) surface symmetry. The non observation of the (5x20) symmetry for the (100) orientation Mas due to the presence of residual adsorbed impurities at the surface of as received samples. Simply this confirms the crystalline surface quality of the platinum samples prepared according to this technique (10). 

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

For iron oxides, IR spectroscopy is useful as a means of identification. Hematite crystals in films that were too thin (<70nm) to be characterized by XRD were shown by IR to be oriented with the c-axis perpendicular to the surface of the film (Yubero et al. 2000). This technique also provides information about crystal morphology, degree of crystallinity and the extent of metal (especially Al) substitution because these properties can induce shifts in some of the IR absorption bands. It is also widely used both to obtain information about the vibrational state of adsorbed molecules (particularly anions) and hence the nature of surface complexes (see Chap. 11) and to investigate the nature of surface hydroxyl groups and adsorbed water (see Chap. 10). Typical IR spectra of the various iron oxides are depicted in Figure 7.1. Impurities arising either from the method of preparation or from adsorption of atmospheric compounds can produce distinct bands in the spectra of these oxides -namely at 1700 cm (oxalate), 1400 cm (nitrate) and 1300 and 1500 cm (carbonate). 

Trace impurities in noble metal nanoclusters, used for the fabrication of highly oriented arrays on crystalline bacterial surface layers on a substrate for future nanoelectronic applications, can influence the material properties.25 Reliable and sensitive analytical methods are required for fast multi-element determination of trace contaminants in small amounts of high purity platinum or palladium nanoclusters, because the physical, electrical and chemical properties of nanoelectronic arrays (thin layered systems or bulk) can be influenced by impurities due to contamination during device production25 The results of impurities in platinum or palladium nanoclusters measured directly by LA-ICP-MS are compared in Figure 9.5. As a quantification procedure, the isotope dilution technique in solution based calibration was developed as discussed in Chapter 6. 

To assess about the quality and purity of the synthesized membranes, several experimental techniques and procedures are available many of those are commonly employed in catalyst characterization. Thus, XRD (x-ray diffraction) analysis of the supported samples is conventionally used to identify the type of zeolite, the proportion of amorphous material and impurities, and the preferential orientation of the crystals (XRD-pole figure). However, for the vast majority of the synthesis procedures described, the XRD spectra of the scrapped membrane or the resulting powder from the liquid phase is supplied to avoid the support contribution. 

The dip resulting from the implanted sample is shallower compared with that of the pure sample, indicating a small fraction of the impurity atoms not being shadowed. In the <10> direction we get even an increased yield in comparison with the random orientation, this being a sign for a position almost in the middle of the channel. Details of this technique and its application may be found in. ... 

An alternative technique for producing clean surfaces of any orientation of III—V compounds and alloys is to grow a thin epitaxial film (> 2000 A) in situ from molecular beams of the elements generated from Knudsen sources inside the UHV system. The growth process has become known as molecular beam epitaxy or MBE [111]. Any impurities remain at the film—substrate interface and the freshly created surface is very clean. A more detailed account of this process will be given in Sect. 5. 

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