Optical absorption measurement

Optical absorption measurements give band-gap data for cubic sihcon carbide as 2.2 eV and for the a-form as 2.86 eV at 300 K (55). In the region of low absorption coefficients, optical transitions are indirect whereas direct transitions predominate for quantum energies above 6 eV. The electron affinity is about 4 eV. The electronic bonding in sihcon carbide is considered to be predominantiy covalent in nature, but with some ionic character (55). In a Raman scattering study of vahey-orbit transitions in 6H-sihcon carbide, three electron transitions were observed, one for each of the inequivalent nitrogen donor sites in the sihcon carbide lattice (56). The donor ionization energy for the three sites had values of 0.105, 0.140, and 0.143 eV (57). 

Electrical measurements on devices with different layer thickness have shown that the diode current depends on the applied field rather than the drive voltage. This is similar to what has been observed with our alternating PPV copolymers [68]. It indicates that field-driven injection determines the electrical characteristics. From Figure 16-39 it is evident that U-OPV5 has the lowest onset for both current and emission. By means of Fowler-Nordhcini analysis of the /-V -charac-teristics and optical absorption measurements, wc estimated the injection barrier for holes and the HOMO-LUMO gap, respectively [119]. The results of... 

The formation of the layers was also checked by optical absorption measurements and eUipsometry. After the reaction the absorption spectrum was blue-shifted with respect to the bulk spectrum of CdS, indicating the formation of very small particles. It was also possible to estimate their sizes using Rama Krishna and Friesner theory (Rama Krishna and Friesner 1991). After washing with chloroform, the blue shift became smaller (but still remained), indicating the aggregation of the particles in the layer (Facci et al. 1994a). 

Comparing the two optical transduction techniques (absorption or SPR) used in this work, we can conclude that SPR technique appears to be more suitable for gas sensing even if it presents some limitation regarding the suitable film thickness for SPR excitation. Moreover, the response and recovery times during the anal5fle/sensing layer interaction appears shortest in the case of optical absorption measurements. Further investigations are in... 

To summarize the various results which suggest the energy level diagram of Fig. 1, many authors have shown (24,26,28) that zinc oxide has interstitial zinc as a donor impurity. As determined by conductivity and Hall effect measurements, the energy level for single ionization of this interstitial zinc is of the order of several hundredths of an electron volt below the conduction band when the concentration of donors is of the order of 10 cm. . The energy level for double ionization, from optical absorption measurements, appears to be at about 3.2 e.v. below the con-... 

The life-time of the ionic intermediates in the liquid solutions is so short that it is difficult or impossible to observe them directly. One of the convenient ways to overcome this difficulty is to prolong the life-time by freezing the irradiated solution at low temperature. For convenience of measurement, organic substances frozen to a glassy state have been widely used as solvents for the study by means of optical absorption measurement at low temperature. A rigid glass matrix is preferably used also in the ESR study, because the experimental results are readily compared with those obtained by the optical study. 

Although the trapped electrons in 3-methylpentane glass irradiated at 77° K were studied by optical absorption measurements and reported on in 1966 by Guarino and Hamill (72), the first observation of their ESR spectrum was reported by Tsuji and the present authors in 1967 (13). The observation was difficult because of the very rapid disappearance of the trapped electrons at 77° K. The assignment of the spectrum was nicely reconfirmed by Shirom et al (14). 

From the viewpoint of the glass matrix, 2-methyltetrahydrofuran is useful to study the anionic reactions of solute monomers, while in n-butylchloride the cationic reactions are studied selectively. Such a selection of glass matrices was made in the study of radiation-formed ionic species by optical absorption measurements (24, 25). 

Polarized optical absorption measurements have been made for the bis (N,N-diethyldithiocarbamato)silver(II) complex also diluted in the zinc complex.544 Two spin-allowed transitions were observed ZA2— 2B1 (625nm) and 2A2— 2Bz (425 nm). 

Spectroscopic data (Ref 80) show that RDX force constants are similar to those of non-expi molecules. Thus the expl nature of RDX cannot be explained by the presence of weak bonds Optical absorption measurements have confirmed the reports of earlier workers that the solid forms of the cyclic polynitramines known... 

We have also calculated the absorption coefficient a (see Figure 37 bottom panel) that can be compared with optical absorption measurements performed on Si/CaF2 MQW s synthesized by molecular beam epitaxy [44,46] (see Figure 37 top panel). A striking resemblance between the two results is evident. In both results we observe a blue-shift of the onset and moreover a decrease of the optical absorption with decreasing Si layer thickness. The discrepancy in the absolute value of a(co) is a consequence of the use of the repeated slab scheme in the calculations. 

Design targets for the application were to have a total system volume < 1 cm3 and to achieve one sample throughput per minute [115]. The reaction time for the Berthelot reaction is about 40 s so that only 20 s are left for all other process steps. This involves the injection of the sample, mixing and an optical absorption measurement. Therefore, mixing has to be fast, requiring only a few seconds. 

The electronic control circuitry is situated in two levels below the MCB layer with the modules. It is based on a microcontroller system for the micro liquid handling and the chemical analysis data. Implemented in the electrical circuitry are driving circuits for the micro pumps, sensing circuits for the flow sensors, optical absorption measurement circuitry, power management and communications using an RS232 interface. 

In order to understand the change in the conductivity by irradiation, optical absorption measurement were carried out in the wavelength of 190-500 nm using a SHIMADZU UV-2200A. 

The optical absorption, measurable via the excitation spectra of secondary emissions (delayed fluorescence,143 phosphorescence,142 EPR triplet spectra,166 etc.). The absorption is the response of the crystal to an excitation spatially homogeneous at the microscopic scale ... 

Silicon films that were electron beam evaporated at a rate of 5 nm sec-1 on silica substrates at 440°C were subsequently irradiated with an Ar+ laser. The rapidly scanned Gaussian beam formed a smooth lateral temperature gradient in the film hence it provided a simple means to study the crystallization mechanism. The laser-heated track reveals two easily discernible areas. A 1 -//m-thick film showed color changes from black to deep red at the margins of the track to light yellow in the middle of the track. Despite the smooth fall of the laser intensity, the different boundaries are abrupt. Optical absorption measurements of the respective areas are also displayed in Fig. 1. The curve E440 represents the as grown evaporated film and is in... 

Equations (18)-(21) were given for the case of real susceptibilities. However, they have to be treated as complex quantities if the frequency is close to or within the region of an optical transition in the medium. An example in the domain of linear optics was given in (12) where the imaginary part of the first-order susceptibility, ft) w), was related to the absorption coefficient, of the medium. An example from non-linear optics is the technique of electro-optical absorption measurements (EOAM, p. 167) where the UV-visible absorption is studied under the influence of a static electric field. In EOAM, the imaginary part of the third-order susceptibility, w,0,0), is... 

Electrochromism of a liquid solution [lm (-a) a),0,0))] electro-optical absorption measurements (EOAM)... 

Optical transitions between the valence and conduction bands are responsible for the main absorption band and are the primary measure of the band gap energy. The optical data are also used to extract information about the band tail density of states. However, the absorption coefficient depends on both conduction and valence band densities of states and the transition matrix elements and these cannot be separated by optical absorption measurements alone. The independent measurements of the conduction and valence state distributions described in Section 3.1.1 make it possible to extract the matrix elements and to explore the relation between N E) and the optical spectrum. 

The energy levels of the anion states of naphthalene and styrene as determined from the gas phase studies are compared to those obtained from optical absorption measurements on the anions in organic matrices as well as with theoretical predictions. It is demonstrated that the effect of solvation on the energy of an anion state depends on its lifetime, with larger shifts being observed for the shorter lived anions. 

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