Elemental impurity survey

It is important to emphasize that GDMS provides an essentially complete elemental impurity survey to very low detection limits in a timely, cost effective manner. Although this level of analysis requires long signal integration times, the Ga measurement requires only a few hours to obtain an accurate, confirmed analysis to 7N levels. Except for the presence of rather high In in the Ga, the remaining impurities are at sub ppmw levels. Detection limits in the Ga are clearly adequate for 7N qualification. 

H. Kramer, S. Semel J.E. Abel, Trace Elemental Survey Analysis of Trinitrotoluene , PATR 4767 (1975) (An evaluation of the applicability of spark source mass spectrometry and thermal neutron activation for the detn of origin-related trace elemental impurities in TNT) 10) C. Ribando J. Haber-man, Origin-Identification of Explosives Via Their Composite Impurity Profiles I. The... 

At present time the use of oxide single erystals sueh as bismuth germanate (Bi Ge O, ) and pai atellurite (TeO,) as deteetors in opto-eleetronies stimulate produetion of high purity Bi, Te, Ge and their oxides Bi O, GeO, TeO,. This requires development of analytieal teehniques for purity eontrol of these materials. For survey traee analysis atomie emission speetrometry (AES) and mass speetrometry (MS) with induetively eoupled plasma (ICP) is widely used. However, the deteetion limits of impurities aehievable by these methods for the analysis of high purity solids are limited by neeessity of sample dissolution in pure aeids and dilution up to 5 10 times for ICP-MS and 50-100 for ICP-AES. One of the most effeetive ways to improve the analytieal performanees of these methods is pre-eoneentration of miero-elements. 

A mass scan is acquired in cases when a survey of all impurities present in a volume of material is needed. Rather than measuring the secondary ion count rates of preselected elements as a fimction of sputtering time the count rates of all secondary ions are measured as a fimction of mass. Because a mass scan is continuously acquired over a mass range, no depth profiling or lateral information is available while operating in this mode. Figure 4 shows a mass scan acquired from a zirconia... 

A ZnSe-on-GaAs epitaxial layer required a sensitive survey of near-surface contamination. PAI was selected for ZnSe analysis because its major constituents and many of the expected impurities are elements that have poor ion yields in conventional LIMS. Figures 8 and 9 are two mass spectra acquired from the ZnSe epitaxial layer. 

Of course, the most reliable and accurate method of quantitative analysis is to calibrate each element with standards prepared in matrices similar to the unknown being analyzed. For a survey technique that is used to examine such a wide variety of materials, however, standards are not available in many cases. When the technique is used mainly in one application (typing steels, specifying the purity of alloys for a selected group of elements, or identifying impurities in silicon boules and... 

NAA cannot be used for some important elements, such as aluminum (in a Si or Si02 matrix) and boron. The radioactivity produced from silicon directly interferes with that ftom aluminum, while boron does not produce any radioisotope following neutron irradiation. (However, an in-beam neutron method known as neutron depth profiling C3J be used to obtain boron depth profiles in thin films. ) Another limitation of NAA is the long turn-around time necessary to complete the experiment. A typical survey measurement of all impurities in a sample may take 2-4 weeks. 

I.r. and radioactive tracer studies have shown that Se and Sb trace impurities in AsCl, are in the form of SeOCl2 and SbCls, respectively. The literature concerning the stereochemical behaviour of Se oxides, fluorides, and oxy-fluorides has been surveyed.Several other elements, including l e were also dealt with. 

SURVEY/HYDROBURN (Ref. 5) An optional subroutine in SURVEY which calculates the oxidation of fuel element graphite and the hydrolysis of failed fuel particles by coolant impurities, particularly water vapor. Transport of water vapor through the graphite web of the fuel element is modelled as a combination of diffusion and convection due to cross-block pressure gradients. The effects of catalysts and burnoff on the graphite oxidation kinetics are modelled. 

A survey XPS scan on a material can provide a qualitative analysis of the elemental eomposition on the surface. The XPS survey scan spectra of Pt/MWCNT nanocomposites before and after reduction treatment are shown in Figure 10.15(e). Elements of Pt, Cl, C, and O existed in flie Pt/MWCNT nanocomposite before the reduetion treatment. However, the Cl 2p peak vanished after the reduction, indicating removal of chloride ions in the reduced sample. The removal of halide ion impurities sueh as Cf ean improve the activities of the catalyst for CO oxidation and also direct methanol oxidation reactions in fuel cells [136,137]. 

The accuracy of an analysis can approach these values when Standard Reference Materials of the same matrix are available or when a synthetic standard can be applied. In the absence of standards, concentrations can be estimated to within a factor of 3-10 of the true value. This method of analysis is ideal for a general survey covering all possible trace elements. The results of such survey analyses can then be used to assign the analysis of specific impurities to other trace techniques when more accurate values are required. 

X-ray spectroscopy can also be employed for survey analysis of impurities and has the advantage of being nondestructive. Lower limits of detection are rarely better than 10-100 ppm, unless preconcentration is used, and the elements of the first period cannot be detected at low concentrations. 

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