Reflection measurements

Willey R R 1976 Fourier transform infrared spectrophotometer for transmittance and diffuse reflectance measurements Appl. Spectrosc. 30 593-601... 

Figure C2.10.1. Potential dependence of the scattering intensity of tire (1,0) reflection measured in situ from Ag (100)/0.05 M NaBr after a background correction (dots). The solid line represents tire fit of tire experimental data witli a two dimensional Ising model witli a critical exponent of 1/8. Model stmctures derived from tire experiments are depicted in tire insets for potentials below (left) and above (right) tire critical potential (from [15]).

Color. The visual color, from white to dark brown, of sugar and sugar products is used as a general indication of quaUty and degree of refinement. Standard methods are described for the spectrophotometric deterrnination of sugar color that specify solution concentration, pH, filtration procedure, and wavelength of deterrnination. Color or visual appearance may also be assessed by reflectance measurements. 

The single most severe drawback to reflectivity techniques in general is that the concentration profile in a specimen is not measured directly. Reflectivity is the optical transform of the concentration profile in the specimen. Since the reflectivity measured is an intensity of reflected neutrons, phase information is lost and one encounters the e-old inverse problem. However, the use of reflectivity with other techniques that place constraints on the concentration profiles circumvents this problem. 

Figure 1 Schematic diagram of the neutron reflectivity measurement with the neutrons incident on the surface and refiected at an angle 6 with respect to the surface. The angie 62 is the angle of refraction. The specimen in this case is a uniform film with thickness d, on a substrate.

For specimens where gradients in the ms etic moment are of interest, similar arguments apply. Here, however, two separate reflectivity experiments are performed in which the incident neutrons are polarized parallel and perpendicular to the surfiice of the specimen. Combining reflectivity measurements under these two polarization conditions in a manner similar to that for the unpolarized case permits the determination of the variation in the magnetic moments of components parallel and perpendicular to the film surface. This is discussed in detail by Felcher et al. and the interested reader is referred to the literature. 

Neutron reflectivity measures the variation in concentration normal to the surface of the specimen. This concentration at any depth is averaged over the coherence length of the neutrons (on the order of 1 pm) parallel to the sur ce. Consequendy, no information can be obtained on concentration variadons parallel to the sample surface when measuring reflectivity under specular conditions. More imponantly, however, this mandates that the specimens be as smooth as possible to avoid smearing the concentration profiles. 

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. 

In situ quantitation Reflectance measurements were carried out at a wavelength of A = 429 nm. The detection limit lay at 50 to 200 ng per chromatogram zone (Fig. 1). 

An interesting special application has been proposed by Schlichthorl and Peter.31,41 It aims at deconvolution of electrochemical impedance data to separate space charge and surface capacitance contributions. The method relies on detection of the conductivity change in the semiconductor associated with the depletion of majority carriers in the space charge region via potential-modulated microwave reflectivity measurements. The electrode samples were n-Si(lll) in contact with fluoride solution. 

Intensity-modulated photocurrent spectroscopy has been used in combination with microwave reflectivity measurements to investigate hydrogen evolution at a p-type silicon45 and an n-type silicon.46 The measurement of amplitude and phase under harmonic generation of excess carriers, performed by Otaredian47 on silicon wafers in an attempt to separate bulk and surface recombination, should also be mentioned here. 

Fig. 4. Spectral reflectance measurements in copper telluride halides. (Redrawn from A. Rabenau, H. Rau, and G. Rosenstein, Solid State Commun. 7, 1281 (1969), Fig. 1,...

The network is implemented by the participating countries through WHO. Sulfur Dioxide (SO,) and suspended particulate matter (SPN) data are routinely reported from each of the participating countries to WHO for entry into the global data base, which is maintained by the United States Environmental Protection Agency (U.S. EPA) at Research Triangle Park, North Carolina. Methods of collection and analysis varies by country. SPN is reported either as a gravimetric or a photometric (transmittance or reflectance) measurement converted to mass units. Since the accuracy of the conversion of the photometric measurement to mass units is... 

Handley, L.L., Austin, A.T., Robinson, D., Scrimgeour, C.M, Raven, J.A., Heaton, T.H.E., Schmidt, S., Stewart, G.R. (1999). The 15N natural abundance(815N) of ecosystem samples reflects measures of water availability. Australian Journal of Plant Physiology, Vol. 26, pp.185-199. 

The infrared spectra for various aluminum oxides and hydroxides are shown in Figure 3. Figure 3a is a-alumina (Harshaw A13980), ground to a fine powder with a surface area of 4 m /g. The absorption between 550 and 900 cm is due to two overlapping lattice modes, and the low frequency band at 400 cm is due to another set of lattice vibrations. These results are similar to those obtained by reflection measurements, except that the powder does not show as... 

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

Reflectance measurements involve measurements of the intensity of light reflected from a flat specular surface of an electrode in a spectroelectrochemical cell. The incident light is polarized either parallel (p) or perpendicular s) to the plane of incidence, as shown in Fig. 27.24. A detector monitors the intensity of the reflected beam. The light is monochromatic, but the spectrometers usually can be tuned over large wavelength ranges. There are excellent reviews of reflectance by McIntyre (1973) and Plieth et al. (1992). 

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