Quartz reflection

Near the bottom of the profile, more tridymite forms than quartz, reflecting the former mineral s larger rate constant and specific surface area. 

Siebert C, McManus J, Bice A, Poulson R, Berelson WM (2006b) Molybdenum isotope signatures in continental margin sediments. Earth Planet Sci Lett 241 723-733 Sime NG, De la Rocha C, Galy A (2005) Negligible temperature dependence of calcium isotope fractionation in 12 species of planktonic foraminifera. Earth Planet Sci Lett 232 51-66 Simon K (2001) Does 5D from fluid inclusions in quartz reflect the original hydrothermal fluid Chem Geol 177 483 95... 

If quartz is analyzed by X-ray diffraction and the presence of an interfering peak is suspected, it may be possible to cross check the X-ray diffraction by petrographic examination of particles picked from the sample membrane. Quartz reflects light in a characteristic way also. The parlodian film which may be used in X-ray diffraction tends to interfere in petrographic examination. 

Fig. 4.15. uv reflectance spectra of crystalline and fused quartz. Reflectivity values for fused quartz have been reduced by 5% to separate spectra (after Philipp, 1971 reproduced with the publisher s permission). 

UV microscopes are supplied mainly by two optical companies, Zeiss and Leitz, in the Federal Republic of Germany. The major difference between the Zeiss and the Leitz instruments lies in their optical systems. The Leitz microscope uses quartz reflecting objectives, while Zeiss uses quartz refractive objectives. Both objectives are achromatic for a wide portion of the UV and visible light range, with no shift in focus accompanying the change of wave-... 

Table 4.10 Quartz reflections after PDF 46-1041 (20obs)- 20caic was calculated with the above lattice constants and >.= 1.5405981 A (both values at 25 °C). Only the stronger reflections with Aei > 1 are reported.

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

Interplanar Spacings. Diffractometer alignment procedures require the use of a well-prepared polycrystalline specimen. Two standard samples found to be suitable are silicon and a-quartz (including Novaculite). The 26 values of several of the most intense reflections for these materials are listed in Table 7.6 (Tables of Interplanar Spacings d vs. Diffraction Angle 26 for Selected Targets, Picker Nuclear, White Plains, N.Y., 1966). To convert to d for Ka or to d for Ka2, multiply the tabulated d value (Table 7.6) for Ka by the factor given below ... 

An additional advantage to neutron reflectivity is that high-vacuum conditions are not required. Thus, while studies on solid films can easily be pursued by several techniques, studies involving solvents or other volatile fluids are amenable only to reflectivity techniques. Neutrons penetrate deeply into a medium without substantial losses due to absorption. For example, a hydrocarbon film with a density of Ig cm havii a thickness of 2 mm attenuates the neutron beam by only 50%. Consequently, films several pm in thickness can be studied by neutron reflecdvity. Thus, one has the ability to probe concentration gradients at interfaces that are buried deep within a specimen while maintaining the high spatial resolution. Materials like quartz, sapphire, or aluminum are transparent to neutrons. Thus, concentration profiles at solid interfaces can be studied with neutrons, which simply is not possible with other techniques. 

Typically specimens for reflectivity measurements are prepared on flat, smooth, rigid substrates. For example, these substrates can be polished fused silica, quartz, or silicon. It is important, however, that the substrates be thick to avoid distonions of the specimen when mounted in the reflectometer. Any curvature or bowing will increase the divergence of the incident beam and result in a deterioration of the resolution. 

Langmuir-Blodged films have been deposited on many different substrates. The substrates used include different types of glass (such as quartz for UV-visible spectroscopy) CaF2 plates for transmission infrared spectroscopy silicon, germanium, and ZnSe plates for internal reflection infrared spectroscopy. For electrochemical applications, LB films... 

The Fe-B nanocomposite was synthesized by the so-called pillaring technique using layered bentonite clay as the starting material. The detailed procedures were described in our previous study [4]. X-ray diffraction (XRD) analysis revealed that the Fe-B nanocomposite mainly consists of Fc203 (hematite) and Si02 (quartz). The bulk Fe concentration of the Fe-B nanocomposite measured by a JOEL X-ray Reflective Fluorescence spectrometer (Model JSX 3201Z) is 31.8%. The Fe surface atomic concentration of Fe-B nanocomposite determined by an X-ray photoelectron spectrometer (Model PHI5600) is 12.25 (at%). The BET specific surface area is 280 m /g. The particle size determined by a transmission electron microscope (JOEL 2010) is from 20 to 200 nm. 

Similar reflection plates are used for recording ultraviolet-visible and Raman spectra of matrix isolated molecules, although the traditional beam path passing through transparent quartz windows is more frequently used in UV spectrometers. Sapphire rods, which are placed in the spectrometer cavity, are applied as targets in matrix esr studies. 

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