Band-edge peak

Nanopartide Synthesis in Microreactors, Fig. 5 Reproducibility of CdSe nanoparticle properties (a) band-edge peak location, (b) photoluminescence wavelength, and (c) photoluminescence intensity... 

In Modulation Spectroscopy, which is mosdy used to characterize semiconductor materials, the peak positions, intensities and widths of features in the absorption spectrum are monitored. The positions, particularly the band edge (which defines the band gap)> are the most useful, allowing determination of alloy concentration. 

It must be noted that the prerequisite to see distinct peaks in a TSC experiment is a sleep onset of the density of stales at the band edges. This is fully fulfilled... 

Bolis et al (43) reported volumetric data characterizing NH3 adsorption on TS-1 that demonstrate that the number of NH3 molecules adsorbed per Ti atom under saturation conditions was close to two, suggesting that virtually all Ti atoms are involved in the adsorption and have completed a 6-fold coordination Ti(NH3)204. The reduction of the tetrahedral symmetry of Ti4+ ions in the silicalite framework upon adsorption of NH3 or H20 is also documented by a blue shift of the Ti-sensitive stretching band at 960 cm-1 (43,45,134), by a decrease of the intensity of the XANES pre-edge peak at 4967 eV (41,43,134), and by the extinction of the resonance Raman enhancement of the 1125 cm-1 band in UV-Raman spectra (39,41). As an example, spectra in Figs. 15 and 16 show the effect of adsorbed water on the UV-visible (Fig. 15), XANES (Fig. 16a), and UV-Raman (Fig. 16b) spectra of TS-1. 

The spectrum of melanin components in Figure 9.7 is different from that of methyl viologen in Figure 9.4. The latter spectrum has a clear, symmetrical peak. We call it an optical band. By contrast, the spectrum of melanin components increases but never quite reaches a peak. In fact, the spectrum only shows the side of a huge optical band. We sometimes say that spectra like Figure 9.7 contain a band edge. 

Fig, 26. Experimental dispersion curve of the Kr monolayer and measured line width broadening As of the Kr creation phonon peaks. The solid line in the dispersion plot is the clean Pt(lll) Rayleigh phonon dispersion curve and the dashed line the longitudinal phonon bulk band edge of the Pt(l 11) substrate, both in the r Mn azimuth which is coincident with the r Kk, azimuth. 

The lowest-energy-resolved features in the absorption spectrum of M0S2-type semiconductors are the A and B excitons, shown in Fig. 3 for the case of M0S2 [30]. The dissociation limit of peaks built off of the A exciton correspond to the direct band edge. Calculations indicate that these transitions are at K and that the A and B excitons correspond to K4 K5 and K1 K5, respectively [25,26]. The lowest-energy direct-transition excited states have considerably different orbital character than the band-edge state. K1 and K4 correspond to 84% and 82% dyy, respectively corresponds to 77%... 

UPS spectra of clean Ar+ sputtered and in Vacuo carbon-contaminated surfaces are shown in Figure 4. On the clean, sputtered surface a filled state due to Ti3+ lies 0.6 eV below the conduction band.(22) Carbon-induced filled states lie in a broad peak with considerable intensity between the valence band edge and the Ti + peak. Frank et al.lQ) reported evidence that a state lying about 1.2 eV above the valence band mediates electron transfer from Ti02 electrodes. Although these carbon states are as of now poorly defined and have not been directly implicated in any aqueous photochemistry, their nearly ubiquitous presence should be considered in discussions of charge transfer at real oxide surfaces. 

Figure 9 (A) Typical TEM image of a CdSe nanoparticle synthesized by the direct reaction of Se and CdO (see main text). (B) Typical emission spectrum of a CdSe nanoparticle. The spectrum exhibits two main features (1) a sharp Gaussian-shaped peak due to band-edge emission and (2) a broad feature at lower energies due to defect emission. (C) The size-dependence of the peak wavelength for CdSe nanoparticles, determined using data provided in Murray et al. (1993).

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