Reflectivity curves

These aspects of the optical spectra of solids are illustrated in the upper portion of Figure 1, which displays the reflectance curve (R) at room temperature for a typical semiconductor, GaAs. The fundamental absorption edge around 1.4 eV produces only a weak shoulder. Some structure is apparent in the two features around 3 eV and the large, broad peak near 5 eV. However, the dominant aspect of the line shape is the slowly varyii background. The derivative namre of Modulation Spectroscopy suppresses the uninteresting background effects in favor of sharp, deriva-... 

Fig. 4 Explanation of the fluorescence-quenching effect [2]. — (A) chromatograms of the same quantities of saccharin and dulcin observed under UV 254 light, (B) schematic representation of fluorescence quenching, (C) spectral reflectance curves of saccharin and dulcin.

Fig. 1 Reflectance curve of a blank track (A) and a chromatogram (B) with 80 ng prostaglandin El (1), -front (2).

Fig. 10. X-ray reflectivity curves of polystyrene (PS)/poly-p-bromostyrene (PBrS) on a glass substrate before (solid line) and after annealing for 13 h at 130 °C (dashed tine) [191]. The width of the interface changes from 1.3 nm to 2.0 nm due to interfacial mixing of components. The X-ray wavelength is 0.154 nm and films have a thickness of 37.8 nm (PS) and 45.0 nm (PBrS), respectively...

Fig. 12. Interface width a as a function of annealing time x during initial stages of interdiffusion of PS(D)/PS(H) [95]. Data points are obtained by a fit with error function profiles of neutron reflectivity curves as shown in Fig. 11. Different symbols correspond to different samples. The interface width a0 prior to annealing is also indicated (T) and is subtracted quadratically from the data (a = [

X-ray measurements were carried out with a small-angle diffractometer with a linear position-sensitive detector. Cu Ka radiation (X = 0.154 mn) was used (Mogilevski et al. 1984). The samples were rotated with respect to the incident beam, while the intensity was registered by linear position-sensitive detector. The angular resolution of the detector was 0.01°. The curves were acquired in the 20 range of 0.3-2.0°. X-ray reflection curves are presented in Figures 22 and 23 for wild-type and recombinant proteins, respectively. The... 

In recent years, high-resolution x-ray diffraction has become a powerful method for studying layered strnctnres, films, interfaces, and surfaces. X-ray reflectivity involves the measurement of the angnlar dependence of the intensity of the x-ray beam reflected by planar interfaces. If there are multiple interfaces, interference between the reflected x-rays at the interfaces prodnces a series of minima and maxima, which allow determination of the thickness of the film. More detailed information about the film can be obtained by fitting the reflectivity curve to a model of the electron density profile. Usually, x-ray reflectivity scans are performed with a synchrotron light source. As with ellipsometry, x-ray reflectivity provides good vertical resolution [14,20] but poor lateral resolution, which is limited by the size of the probing beam, usually several tens of micrometers. 

The oscillations in the reflectivity curves arise from interference between the X-rays reflected from the various interfaces. The frequency of the oscillations is proportional to layer thickness and the amplitude depends on the interface roughness. 

Figure 3.6 Reflect vity-potential curve (top) and corresponding cu r rent-poten tial c y clic volta m -mograms (bottom) for a platinum electrode in 1.0M H2S04. The reflectivity curve was taken at 546 nm using S-poiarised light at a 701 angle of incidence. The potential limits for both the reflectivity and cyclic voltammetry experiments were + 0.535 V and —0.006 V vs. NHF, and the scan rate was 26.46 Vs-1. From Bewick and Tuxford (1973).

Although a great deal of data analysis is needed to obtain a value of the optical nonlinearity from this measurement, we can estimate the order of magnitude of the value. The estimate comes from a comparison of this data with that taken on a similar experiment using Si as the nonlinear material. (15) The two experiments used approximately the same laser power and beam geometry, and the linear reflectivity curves were similar in shape and size (the minimum value of reflectivity). Neglecting differences... 

Two objects with different spectral properties, i.e., variation in the slope of spectral reflectance curve of two bands, can be separable with the help of ratio images (Lillesand et al. 2007). In this study standard reflectance data of USGS Spectral Library and John Hopkins University spectral library (Available in ENVI) have been used. To enhance the dissimilarity between different rock types in the scene, plots with a higher reflectance were kept in the numerator and plots with low reflectance were kept in the denominator, while taking the band ratios. Using this approach, a ratio of 5/3 was taken for basalt, 7/3 for peridotite, and 4/2 for vegetation. 

The shade of a product is another parameter which is influenced by the particle size (Sec. 1.6.1.2). This is easy to see by comparing the reflection curves of two Pigment Yellow 83 white reductions in an alkyd-melamine resin system. The electron photomicrographs in Fig. 65 and the particle size distribution histograms in Fig. 66 represent these samples. At equal pigment concentration, curve 1 of the two remission curves in Fig. 67 reflects the behavior of the pigment with the smaller... 

The double-crystal rocking curve is symmetric, though the plane wave reflectivity curve is not. This is a consequence of the autocorrelation, since the autocorrelation of any function is an even fimction. 

For the Eikonal theory to be valid, the distortions must be suffieiently small that the eoneept of a ray is retained. The criterion is that the radius of curvature of the reflecting planes does not exceed a critical value R. approximately equivalent to an angular rotation of the Bragg planes by half the reflecting curve width in an extinction distance. The critical radius of curvature is thus... 

At the initial recording stage, for t < Ioptim, the depth of the etched groove is approximately proportional to the etching time t, and for t > roptim the relief depth tends to a limit (curve 3 in Fig. 22). The profile of the relief is quite close to the sinusoidal one but at the same time there is undesirable random etching of the surface that leads to a decrease in its reflectivity (curve 2 in Fig. 22). 

Relaxation of CT samples also depends strongly on Sn content. For the most Sn-abundant sample x-ray analysis showed the presence of almost completely oriented Sn crystallites of 100-500 nm size, and electronic microscopy revealed that metal particles were separated by distances less than their size. It means that in this case we have practically metal film. The time response of such a sample appeared to be the same as that for pure Sn film. We attribute pulsewidth-limited rise of negative transmission and reflection (curves 10,11) to excitation of electrons in metal. Subsequent 5 ps rise reflects electron-phonon relaxation and further long decay is due to lattice cooling. Contribution of this dynamics is observed for the... 

Figure 3. Spectral reflectance curves of some inorganic pigments in paints...

Pigments and coatings may be unambiguously characterized by their spectral reflectance curves q (A) or spectral reflectance factor curves / ( ) (Fig. 3). The reflectance spectrum q (A) or R (A) and hence the color properties can be almost completely derived from physical quantities [1.15] (Fig. 4) ... 

A modem well-equipped color measurement laboratory can use the principle of spectral evaluation described above [1.38] to simulate this procedure with a computer. The thickness of the hiding film can then be calculated in advance from the reflectance curves of a single film on a black/white substrate at a known film thickness. 

Figure 19. Spectral reflectance curves of barium sulfate and zinc sulfide a) Barium sulfate b) Zinc sulfide (Codoped)...

Figure 28. Reflectance curves of cadmium pigments (pigment volume concentration 10%)...

The use of zinc yields greenish yellow pigments due to the lower lattice constants mercury and selenium lead to expansion of the lattice. With an increasing content of selenium, or especially mercury, the shades of the pigments change to orange, red, and ultimately to deep red (bordeaux). The brilliant colors of cadmium pigments are primarily due to their almost ideal reflectance curves with a steep ascent (Fig. 28). 

The reflectivity within the halo is not constant one observes a maximum close to the radioactive source with a decrease outwards. The tracing of reflectivity curves with a photocell, recorder, and moving stage has shown that the decrease curves are smooth but sometimes stepwise (Figure la, b). The width of the halos is difficult to estimate by a subjective method, and our instrumental measurements are still too few to allow, definite interpretation. However, the width generally varies between 20 and 50 microns. Preliminary observations suggest that the intensity of the halos is proportional to the quantity of uranium (Figure 4c). 

Figure I. Reflectivity curves of halos around uranium inclusions (a) in Temple Mountain asphalt, (b) in St. Hippolyte Coal Ordinate axis (R) gives reflectivity in arbitrary linear units. Recordings were made along the white line drawn on the photographs. Notice the step-wise shape of the curves and their asymmetry...

The hydrogen content is higher where the reflectance values noticeably decrease. This break in the uniform reflectance curve occurs where there is a greater concentration of coked carbonaceous material, without a large admixture of igneous material. 

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