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IRRAS optimum conditions

One common problem when examining ultrathin films on various surfaces and at various interfaces by IR spectroscopy is that of selecting both the best IR method [transmission, IR reflection-absorption spectroscopy (IRRAS), ATR, DT, or DR] and the best experimental geometry (optical configuration) for this method. For films on plane substrates, this can be done using the optical theory introduced in Chapter 1 (Sections 2.1-2.6). In the case of powdered substrates, the optimum conditions are chosen based on the general theoretical and empirical regularities (Section 2.7). [Pg.79]

Thus, for both metallic and transparent snbstrates, p-polarization, angles of incidence above cpc, and water layers thinner than 1-2 p,m are preferable. Under these conditions (p > (pc and t/2 < dp, where dp is the penetration depth), the cell windows act as IREs. In other words, the in situ IRRAS geometry under the optimum conditions is in fact the ATR geometry in Otto s configuration (Fig. 236d). [Pg.117]

Fignre 2.47 allows comparison of the spectra from DRIFTS and IRRAS of an organic monolayer (dodecylamine) on crystalline quartz in the region of the vCH vibrations. Optimum conditions for IRRAS (70° angle of incidence and s-polarized radiation) were chosen as described in Section 2.3.1. The resolution is higher in the spectrum collected by IRRAS, since the polished substrate surface is more uniform. However, the SNR is substantially higher in DRIFTS, which can be explained, in addition to the optical effects, by a higher surface density of the surfactant adsorbed on a fine powder than on a polished surface (Section 7.4.3). As can be concluded from the spectra reported in Ref. [174], the sensitivity threshold for the vCH bands in the DRIFTS is about 0.1 monolayer (ML). [Pg.128]

Optimum conditions in the case of Ag films on the Si or ZnSe IREs and the ATR geometry were found [403] to be the film thickness of 9 nm and the angle of incidence of 30°-40°. As in ordinary spectra obtained by transparent IRRAS (Section 2.3.1), the j-polarized IRRAS-SEIRA bands are negative, independent of the angle of incidence, while the / -polarized bands are negative at and positive at (pi > cpB, where (Pb is the Brewster angle of the substrate [384]. The maximum band intensity is observed at small and oblique angles of incidence in s- and p-polarization, respectively [384], However, the maximum absorption of 5-polarization is always smaller than that for p-polarization, independent of the metal film thickness and the optical properties of the substrate [359, 360, 384]. The enhancement factor increases as the refractive index of the substrate decreases [350, 384],... [Pg.241]

Although the optimum conditions for a number of simple systems are known (e.g., for ultrathin films on metals reflection-absorption (IRRAS) at grazing angles of incidence is commonly used, and for ultrathin films on transparent substrates, multiple internal reflection (MIR) is most suitable in many cases), the spectral contrast can be further enhanced by employing additional special technical approaches. [Pg.738]

InP(lll) substrates by anodic, chemical, and thermal oxidation was studied [55]. The anodization was carried out in an aqueous solution of ammonium citrate and propylene glycol at an applied potential of 120 V. Concentrated nitric acid was used for the chemical oxidation at 80°C for 15 min, and the thermal oxidation occurred in a flow of wet oxygen, Tq = 450°C, ThjO = 95°C. The oxide thickness was 80-150 nm. The effect of a thermally deposited metallic coating (Au or Al, d = 0.2-0.3 xm) on the oxide chemical composition was studied by IRRAS. Conditions of optimum and degraded electrophysical characteristics of the MOS structures were achieved by annealing at 300 and 530°C, respectively, for 1 h in a mixture of N2 and O2. [Pg.489]


See other pages where IRRAS optimum conditions is mentioned: [Pg.95]    [Pg.115]    [Pg.277]    [Pg.283]    [Pg.544]    [Pg.738]    [Pg.200]    [Pg.232]    [Pg.90]    [Pg.107]    [Pg.120]    [Pg.315]    [Pg.284]   
See also in sourсe #XX -- [ Pg.84 , Pg.85 , Pg.86 , Pg.87 , Pg.90 , Pg.110 , Pg.164 , Pg.165 , Pg.166 , Pg.316 ]




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