Atomic grating

GD, 112-113,113(f) dark space, 112 Grimm source, 112 sputtering, 112 Glow discharge. See GD Graphite furnace. See Electrothermal atomizers Gratings. 

In the second step, both FW and BW probes are generated and frozen in the sample together with an absorptive and dispersive (atomic) grating when a perfect SW coupling is switched on. This... 

In the third step, the FW and BW probes are retrieved in an asymmetric way by switching on a FW coupling, which is accompanied by the death of the atomic grating composed of only spin... 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

The analogy of a crystal surface as a diffraction grating also suggests how surface defects can be probed. Recall that for a diffraction grating the width of a diffracted peak will decrease as the number of lines in the grating is increased. This observation can be used in interpreting the shape of RHEED spots. Defects on a crystal surfr.ee can limit the number of atomic rows that scatter coherendy, thereby broadening RHEED features. 

We are grateful to the Swedish Natural Science Research Council for financial support. The support by the Swedish Materials Consortium 9 is acknowledged. The Center for Atomic-scale Materials Physics is sponsored by the Danish National Research Foundation. Part of work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory, contract number W-7405-ENG-48. 

As one may infer from the quotation, W. L. Bragg realized that a crystal can act as an x-ray grating made up of equidistant parallel planes (Bragg planes) of atoms or ions from which unmodified scattering of x-rays can occur in such fashion that the waves from different planes are in phase and reinforce each other. When this happens, the x-rays are said to undergo Bragg reflection by the crystal and a diffraction pattern results. 

The author is indebted to Union Carbide Corp. for permission to quote unpublished results obtained during his association with its Sterling Forest Research Laboratory and to the Atomic Energy Commission for partial support of this research. We are deeply grateful to M. C. Sauer (Argonne National Laboratory) for transmitting unpublished results of his work on ethylene and for his encouragement to use it in this presentation. 

The authors are grateful to M. S. B. Munson, J. H. Futrell, and J. R. McNesby for samples of ND3, C3D8, and C2D6, respectively. This work was partially supported by the U.S. Atomic Energy Commission, Contract No. At(ll-l)-1116. 

In 1895, Rdntgen experimentally discovered "x-rays" and produced the first picture of the bones of the human hand. This was followed by work ty von Laue in 1912 who showed that solid crystals could act as diffraction gratings to form symmetrical patterns of "dots" whose arrangement depended upon how the atoms were arranged in the solid. It was soon... 

The authors sincerely appreciate the research carried out by former graduate students (now) Drs. C. Lo, M. Oskoole-Tabrlzl, H.J. Jung, and A.V. Prasad Rao, under the direction of one of us (LNM), during the past five years. We are grateful to various research associates/ collaborators, namely Drs. K.R.P.M. Rao (Bhabha Atomic Research Center, Bombay, India) and to Drs. B. Bernstein, R. Schehl,... 

This work was supported by a contract from the Atomic Energy Control Board of Canada. The co-operation of mine management and personnel is gratefully acknowledged. 

The relative importance of the two mechanisms - the non-local electromagnetic (EM) theory and the local charge transfer (CT) theory - remains a source of considerable discussion. It is generally considered that large-scale rough surfaces, e.g. gratings, islands, metallic spheres etc., favour the EM theory. In contrast, the CT mechanism requires chemisorption of the adsorbate at special atomic scale (e.g. adatom) sites on the metal surface, resulting in a metal/adsorbate CT complex. In addition, considerably enhanced Raman spectra have been obtained from surfaces prepared in such a way as to deliberately exclude one or the other mechanism. 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

The design of a conventional atomic absorption spectrometer is relatively simple (Fig. 3.1), consisting of a lamp, a beam chopper, a burner, a grating monochromator, and a photomultiplier detector. The design of each of these is briefly considered. The figure shows both single and double beam operation, as explained below. 

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