Microanalysis crystal

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Stoichiometric variations in compositions of a material and of surface layers can be revealed by AEM. Because a relatively small amount of scattering occurs through a thin HRTEM specimen, X-rays are generated from a volume that is considerably less than in the case of electron microprobe analysis (EPMA). For quantitative microanalysis, a ratio method for thin crystals (57) is used, given by the equation ... 

Storey R, Thomson WW. An x-ray microanalysis study of the salt glands and intracellular crystals of Tamarix. Ann Bot 1994 73 307-313. 

Petrographic data consist of light photomicrographs, electron micrographs, x-ray microanalyses, and observations on size and distribution of pyrite crystals. Light microscopy was carried out on all 57 sections, while electron microscopy and x-ray microanalysis were carried out on two sections, one from the Avery site (depth 210 cm) and one from the Barataria site (depth 106 cm). Micrographs and x-ray microanalysis of iron sulfides are shown in Figures 9 and 10, respectively. 

Cation Site Distribution, Thin-film EDS analysis can also be used to quantitatively determine the site occupancy of atoms in a known crystal structure. Atom Location by Channeling Enhanced Microanalysis (ALCHEMI) is a technique which utilises electronchanneling enhanced X-ray emission for specific atoms in a crystal when appropriately oriented relative to the incident beam [43]. The method involves no adjustable parameters, can be used on relatively small areas of sample and provides fractional occupancies of atom positions [44] Unlike X-ray diffraction which has had limited success with adjacent elements in the periodic table [e.g. 45], ALCHEMI can provide site occupancies for adjacent elements and is relatively insensitive to sample thickness or the precise electron beam orientation [44] ... 

Si MASNMR spectrum of a sample of synthetic Na-Y which had crystallized slowly (over a period of 17 years) at room temperature. Using the equation given in the text we calculate the (Si/Al) framework to be 2.28. This does not correspond to a unique composition, so that the framework must consist of patches or domains of different local composition (e.g. of Si/Al = 16/8, 17/7, 18/6 etc.) Detailed electron microscopic analyses (using microdiffraction and microanalysis) may clarify the nature of the Si,Al disorder. It is clear, however, from results obtained to date that there is no strong tendency for Si,A1 ordering otherwise a ratio of 2.28 would not have been obtained. 

For the higher beam currents necessary for microanalysis in a reasonable time, mass-loss damage at analysis points is likely to occur. For zeolite crystals with low Si Al ratios, mass loss was evident as holes in the specimen at high beam currents (see Figure 2). For such specimens very low beam currents were required for analysis. However, even in cases where mass loss is evident, the trends in compositional variations across particles will still be valid. 

Alternate work-up The filtered tetrahydroturan solution is concentrated under reduced pressure (20°C, 50 mm) to a volume of 80 mL. Dry hexane (KF < 50 pg/mL, 600 mL) is slowly added with stirring. The product should begin to crystallize during the addition seed if necessary. The mixture is stirred at 20-25°C for 1 hr, then filtered. The cake is washed with dry hexane (2 x 25 mL). Filtration is performed in an enclosed, medium-frit Schlenk funnel, under an atmosphere of nitrogen (with careful exclusion of moisture). The cake is dried under reduced pressure (30°C, < 100 mm) for 2 hr to yield 70.5 g (95%) as a free-flowing white crystalline solid, mp 51.5-52°C. The product should be stored cool, protected from moisture. By microanalysis, the product contains 1-4 wt% of triethylammonium hydrochloride. It is also possible to concentrate the THF to precipitate the product as a white solid. 

X-Ray diffraction examination and electron probe microanalysis showed that the initial film was amorphous and contained an excess of sulphur. When the film was heated in vacuum at 400°C for one hour, the excess of sulphur decreased, and the X-ray diffraction pattern showed peaks possibly indicating the presence of molybdenum disulphide crystals. They inferred that the excess of sulphur initially... 

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