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Figure 3.28. Dependence of the semiconductor energy gap of CdSe nanocrystais (Ncs), in the form of a glass (□) and a coUoidai suspension 0> on the mean particie radius. The colloidal nanocrystai spectral data are presented in Fig. 3.27. The soHd curve gives the fit to the data using a parabolic band model for the v&rational potential. [From V. I. Kliniov in Nalwa (2000), Vol. 4, Chapter 7, p. 465.)

The photoelectron spectrometer sketched in Fig. 3.29 shows, at the lower left side, X-ray photons incident on a specimen. The emitted photoelectrons then pass through a velocity analyzer that allows electrons within only a very narrow range of velocities to move along trajectories that take them from the entrance slit on the left, and allows them to pass through the exit slit on the right, and impinge on fee detector. The detector measures the number of emitted electrons having a given kinetic energy, and this number is appreciable for kinetic energies for which Eq. (3.11) is satisfied.

The energy states of atoms or molecular ions in the valence band region have characteristic ionization energies that reflect perturbations by the surrounding lattice environment, so this environment is probed by fee measurement Related spectroscopic techniques such as inverse photoelectron spectroscopy (EPS), Bremsstrahlung isochromat spectroscopy (BIS), electron energy-loss spectroscopy (EELS), and Auger electron spectroscopy provide similar information.

As an example of fee usefulness of X-ray photoemission spectroscopy, fee ratio of Ga to N in a GaN sample was determined by measuring the gallium 3d XPS peak at 1.1185keV and fee nitrogen Is peak at 0.3975 keV, and fee result gave fee average composition Gao 95N. An XPS study of 10-nm InP provided fee indium 3<i5/.2 asymmetric line shown in Fig. 3.30a, and this was analyzed to reveal fee

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