Fine structure origin

Generally, all band theoretical calculations of momentum densities are based on the local-density approximation (LDA) [1] of density functional theory (DFT) [2], The LDA-based band theory can explain qualitatively the characteristics of overall shape and fine structures of the observed Compton profiles (CPs). However, the LDA calculation yields CPs which are higher than the experimental CPs at small momenta and lower at large momenta. Furthermore, the LDA computation always produces more pronounced fine structures which originate in the Fermi surface geometry and higher momentum components than those found in the experiments [3-5]. 

The dependence of the PL spectra on temperature is again quite complicated. The change from a Gaussian-shaped PL spectrum at RT to a multi-peak spectrum at 5 K for low excitation energies was initially interpreted in terms of an interference effect in the thin porous layer [Ho3]. Later work, however, showed that the peak positions are independent of PS layer thickness, excitation wavelength and sample rotation [Ke3]. The spacing of the peaks is about 61 meV. The origin of this fine structure is still controversial [Ro4],... 

The spectrum of titanium metal foil is in Fig. 23. The foil, originally of 12/t thickness, was reduced by etching in HF to about 4/. A corresponding spectrum of titanium metal powder (not shown here) contained the same peaks but with only about half the amplitude, and with greater scatter of data points. This is an illustration of the advantages of having uniformity of thickness, which is especially difficult to achieve with metal powders. The titanium metal spectrum appears to be Kronig type fine structure. 

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