Specular-reflection spectra

Different features are stressed to specify the most basic type of reflection when referring to it as 

The last denomination implies that the sample is thick enough so that virtually no radiation having been reflected on a deeper interface or even the back surface of the sample, interferes with the one reflected at the front surface. This is quantified by the penetration 

A set of s-polarized spectra of a polymer slab obtained with different angles of incidence is shown in Fig. 6.4-10 the small dispersion-like features are centred at the oscillator frequencies and follow the shape of the refractive index. With closely neighboured or even overlapping resonances, the anomalies are difficult to resolve since a dispersion curve extends over a wider spectral interval than the related absorption band does. This impedes e.g. the compilation of band tables to be used for searching in conventional spectral libraries. By no means an automatic peak-locating routine designed for absorption bands in transmission spectra must be applied the bands would appear to be shifted. In order to convert reflectance spectra into absorption-proportional ones. 

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When the Specular Reflectance spectra in Figures 3A and 3B are compared to the PAS spectrum in Figure 1, the Reflectance spectra show somewhat better spectral detail because of a higher resolution (2 cm—1 versus 4 cm—1, and a higher number of data collections, 8,192 versus 1000). 

Compared to the PAS spectra of cotton cloth, in the Specular Reflectance spectra, the signal-to-noiae is higher and any noise is low enough to show clearly the spectral features described here. Even though there are differences due to the change in sampling conditions, the spectra can be compared for a one-to-one comparison and identification of absorption bands. Mote however that in the PAS spectrum relative intensities are displayed and that the Specular Reflectance spectra show an absolute response and measurement which leads to a better possibility for quantification and a more rigorous treatment of the data. 

Fig. 8.21. Specular reflectance spectra of a natural sample of bornite ( ) after exposure to oxidation in air for increasing lengths of time and of a second, heavily tarnished sample (V) (after Vaughan et al., 1987).

Table 2 lists the known crystallographic data for the systems studied. Of the phenylurethane series, only TCDU has complete structural information in the literature (17). Apparently, more recent structural data for TCDU exists but it has yet to be published (10). While a drawing relevant to the crystal structure of HDU is published (18), no quantitative crystallographic parameters have been located in the literature. No structural information is available for POD. The specular reflection spectra for ETCD and TCDU have been published elsewhere (3,19). 

Coupling in PDA Crystals. The polarized specular reflection spectra for the most highly reflective principal directions are shown in Figure 1. For the first three members of the series, the characteristic LT spectrum is observed. Backreflection was a severe problem because of the thinness of the crystals and, in the case of the less reflective principal direction, structure was altered sufficiently to render the spectra unuseable. Thus, direct measurement of exciton splitting, if present, was not possible. In the spectra reported, the backreflection in the intensely reflecting principal directions was corrected using a curve fitting procedure described elsewhere (21). 

Figure 2. Piezomodulated specular reflection spectra of PTS at 17K with light polarized along the b and a (b) axes. The uniaxial stress was along the b-axis.

Fig. 13. Specular reflectance spectra at different incident angles for a colloidal crystal made of TPM-modified Au Si02 particles with 15 nm core diameter and 150 nm total diameter. The particle volume fraction in this sample was 15.8 vol%, corresponding to 0.31 wt% Au content. The inset shows the fit of the experimental Bragg peak positions with Eq. (28)...

To study the PBG properties of synthesized composites, we measured the specular reflection spectra from the (111) lattice planes of opal-V02. To avoid any contribution of the opal polydomain structure and structural defects to the signal being measured, we used the so-called light microscopic technique [9]. It allowed investigation of a fragment of the sample surface within a single domain. To study the phase transition effect on the PBG properties, the samples were heated by a resistance microheater. 

Fig. 5 shows experimental specular-reflection spectra for a domain of the inverted VO2 photonic crystal synthesized in this study. It can be seen that the reflection pehk, corresponding to PBG, is shifted by 38 nm upon the semiconductor-metal phase transition to shorter wavelengths. Fig. 5(b) presents temperature hysteresis loops of the peak position in the reflection spectra of an inverted composite (VO2 photonic crystal). 

FIGURE 51.14 Specular reflectance spectra of a concentrated Au-Si02 dispersion with increasing volume fractions from 0.15 up to 0.40. 

Reflectance spectroscopy has the advantage that can be used both, in solid materials, and/or in concentrated dispersions. Although Uv-Vis reflection techniques have been used in some applications, " they have not been extensively tested for monitoring emulsion polymerization reactions. Yu et al used reflectance to monitor imidization reactions. Specular reflection spectra from polarized light combined with a Kramers-Kroning transformation were used to assess the surface orientation of PET sheets. NIR with monochromatic laser light has been used to monitor the particle size distribution. The main problem for the interpretation of... 

Figure 1.6 shows the specular reflectance spectra of A1 coated and uncoated surfaces of the film 1. A1 coated surface reflected 100% of the infrared rays since the absorbance values were very close to zero. Uncoated surface had the characteristic spectrum of polypropylene. However, there were other peaks observed called fringes due to reflection of light from both surfaces of the thin film. 

SPECULAR REFLECTANCE SPECTRA OF COMMERCIAL AL COATED POLYPROPYLENE FILM 2... 

The specular reflectance spectra of the surfaces of the commercial film 2 are seen in Fig. 1.8 curve 1 show the specular reflectance spectrum of the polypropylene side of the film and curve 2 show the specular reflection spectrum of the A1 side of the film. While the polypropylene surface has the spectrum of polypropylene, the A1 coated surface reflected the infiared rays. The absorWce values close to zero indicated that the light was not absorbed but reflected by the A1 surface. 

FIGURE 1.8 Specular reflectance spectra of the film 2 (1) polypropylene surface (2) A1 coated surface of the film 1. 

SPECULAR REFLECTANCE SPECTRA OF MAGNETRON SPUTTERED FILMS... 

The specular reflection spectra of uncoated and coated surfaces of polypropylene film prepared by Ozmihci et al. [5] are seen in Fig. 1.9. Both... 

FIGURE 1.9 Specular reflection spectra of (a) uncoated surface (b) A1 coated surface of cast film. 

COMPARISON OF ABSORBANCE VALUES IN SPECULAR REFLECTANCE SPECTRA OF PACKING MATERIALS... 

TABLE 1.1 Absorbance Values of Specular Reflectance Spectra of Uncoated and A1 Coated Surfaces of Packing Materials... 

A quantitative treatment of the specular reflection spectra obtained from the surface of uniaxially drawn PETP samples was performed. A procedure for correcting for the effect of surface irregularities is presented, and an overall orientation function based on the orientation and content of trans-conformers is calculated. The results are correlated with mechanical modulus and crystallinity values. In addition, an unconventional dichroic ratio parameter based on a combination of two major bands is proposed. Results obtained from the Kramers-Kronig analysis and directly from the reflection spectra are discussed. Both are compared with the overall orientation function obtained before. 21 refs. 

K. Krishnan, Applications of the Kramers-Kronig Dispersion Relations to the Analysis of FTIR Specular Reflectance Spectra, Fl lR/IR Notes 51, Biorad Digilab Division, Cambridge, MA, August 1987. 

Specular reflectance Pure specular reflection spectra may be recorded directly from the surfaces of flat, nonscattering, optically thick (opaque) samples from which the absorption index spectrum may be extracted by application of the Kramers-Kronig algorithm. This is sometimes a useful approach for generically fingerprinting intractable or heavily filled polymer samples. An example is shown in Figure 9. 

Specular reflectance spectra Specular reflectance accessory (SRA) ... 

Figure 13.9. Optics for measuring specular reflection spectra with varying incidence angles. (Reproduced from [9], by permission of Wiley-Interscience copyright 1998.)...

In summary, the measurement of specular reflection spectra allows a very wide variety of samples, from partial monolayers on metallic and dielectric substrates to bulk liquids and polymer films, to be characterized. 

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