Interband Effects

A semi-quantitative description of magneto-optical spectra in terms of interband effects was given by Erskine and Stern (1973a,b). The interband transitions are governed by the following selection rules,... 

We have given a summary of Allen s excellent review article. We refer the reader to the original papers for further details. Allen clearly points out that it is important to include interband effects in the formalism. This also follows from experiments since saturation effects in the resistivity at high temperatures seem to occur in metallic compounds and alloys with unfilled d or f bands. Allen and Chakraborty s theory may therefore lead to the understanding of saturation effects if s-d(f) scattering and electron-phonon scattering effects are treated on... 

Used effects Phonon excitation (20 meV-1 eV) Plasmon and interband excitations (1-50 eV) Inner-shell ionization (A = ionization energy loss) Emission of x-ray (continuous/characteristic, analytical EM)... 

Linear absorption measurements can therefore give the first indication of possible alloy formation. Nevertheless, in systems containing transition metals (Pd-Ag, Co-Ni,. ..) such a simple technique is no longer effective as interband transitions completely mask the SPR peak, resulting in a structurless absorption, which hinders any unambiguous identification of the alloy. In such cases, one has to rely on structural techniques like TEM (selected-area electron diffraction, SAED and energy-dispersive X-ray spectroscopy, EDS) or EXAFS (extended X-ray absorption fine structure) to establish alloy formation. 

John O. Dimmock, Introduction to the Theory of Exciton States in Semiconductors B. Lax and J. G. Mavroides, Interband Magnetooptical Effects... 

B. O. Seraphin, Electroreflectance R L. Aggarwal, Modulated Interband Magnetooptics D. F. Blossey and Paul Handler, Electroabsorption B. Batz, Thermal and Wavelength Modulation Spectroscopy 7. Balslev, Piezopptical Effects... 

The second and perhaps most probable explanation is damping and broadening of the resonance, due to size dependent, single electron 5d- 6p,6s interband transitions. Their explanation is that the discrete level structure of the Au 55 cluster acts as an effective decay channel. In reducing the plasmon lifetime, it would also strongly increase the bandwidth of the resonance, washing out the resonance peak. 

In 1958, Franz [45] and Keldysh [46] independently theoretically predicted the absorption by a semiconductor, placed in an electric field, of light quanta which have an energy less than the width of the forbidden gap. The effect is connected with interband tunneling (Fig. 20). The valence band electron tunnels from point xl to point 3c, then it absorbs a quantum with a frequency lo < Eg (Eg is the width of the forbidden gap) and further tunnels to point x2. Using the law of conservation of energy and the law of conservation of imaginary momentum (see the previous section), it is easy to show that light absorption at point 3c, which lies exactly between points acj and x2, is optimal. Consequently... 

However, the existence of such an effect can be demonstrated by the application of a recently proposed technique for the study of interband transitions having energies greater than the "optical" band gap (11). Standard procedures exist for the extraction of band-gap information from measurement of the optical absorption coefficient, which has been shown to be proportional to the quantum efficiency (photocurrent density divided by the incident... 

One of the most important theoretical contributions of the 1970s was the work of Rudnick and Stern [26] which considered the microscopic sources of second harmonic production at metal surfaces and predicted sensitivity to surface effects. This work was a significant departure from previous theories which only considered quadrupole-type contributions from the rapid variation of the normal component of the electric field at the surface. Rudnick and Stern found that currents produced from the breaking of the inversion symmetry at the cubic metal surface were of equal magnitude and must be considered. Using a free electron model, they calculated the surface and bulk currents for second harmonic generation and introduced two phenomenological parameters, a and b , to describe the effects of the surface details on the perpendicular and parallel surface nonlinear currents. In related theoretical work, Bower [27] extended the early quantum mechanical calculation of Jha [23] to include interband transitions near their resonances as well as the effects of surface states. 

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