Energy distribution curves EDC

Figure 10. Energy distribution curves of photoelectrons (EDCs) excited by AlKa radiation. The curves (a), (b), and (c) were obtained after the same sputtering as in Figure 9. (Reprinted from Ref [171], 2002, with permission from Elsevier.)...

Two variables of a PES experiment are readily altered the input photon energy (hv) and the output photoelectron kinetic energy (KE). In a classical energy distribution curve (EDC) operation mode, one scans KE only and obtains information on the energy level manifold. While this is the only mode possible with fixed-energy VUV photon sources, SR permits two further combinations a constant final-state (CFS) mode where one scans hv and a constant initial-state (CIS) mode with both hv and KE scanned in such a way that their difference remains constant. CIS and CFS modes permit separate studies of the initial (ground electronic states, ionization probabilities) and final (photoelectron perturbed by the molecular ion) stages of photoionization events. 

Figure I shows representative energy distribution curves (EDCs) for Cso taken at Av 65, 170, and 1486.6 eV additional spectra acquired from 20 to 200 eV in 2-eV increments will be discussed elsewhere. Figure 2 shows an EDC acquired at 50 eV with an experimental resolution of 0.2 eV. The zero of energy is the emission maximum of the highest occupied feature. Calculations for neutral C6o, Cso, and C6o indicate that the removal or addition of one electron would displace these levels rigidly. With account of the position the Fermi level...

In a photoemission experiment monochromatic photons at uv or X-ray frequency are incident upon a clear surface of the solid. The number of emitted electrons in a specific energy range is counted. With incident photon energy hv the number of photoelectrons in the energy interval (E, E -I- AE) is denoted by AT(E, hv)AE, and the quantity N(E, hv), named energy distribution curve (EDC),... 

Fig. 13. Energy distribution curves along the FS symmetry line. Identifiable quasiparticle peaks are indicated by circles, with the k value of each EDC given as a fraction of the total distance between high symmetry...

Fig. 3. Construction of an electron energy distribution curve (EDC) from a density of states. The top panel depicts a parabolic density of states with structure centered around E-,. For simpUcity, we show photoexcitation of three initial state levels by a photon energy hv with no account taken of dipole matrix element effects. p is the Fermi energy, Vo is the inner potential,

Fig. 5. The origin of energy distribution curves (EDCs), of constant initial state spectra (CISs), and constant final state spectra (CFSs). For the EDC, the photon energy is fixed and the electron energy is scanned. For the CIS, the photon and the electron energies are scanned synchronously. For the CFS, the electron energy is fixed while the photon energy is scanned. Matrix element and escape effects will distort all these spectra.

Experimental results are always crucial for any theory which aims to formulate basic physics behind observed phenomenon or property. However, an experiment always cover much wider variety of different influences which have impact on results of experimental observation than any theory can account for, mainly if theory is formulated on microscopic level and some unnecessary approximations and assumptions are usually incorporated. On the other hand, interpretation of many experimental results is based on particular theoretical model. This is also the case of ARPES experiments at reconstruction of Fermi surface for electronic structure determination of high-Tc cuprates. Interpretation of experimental results is based on band structure calculated for particular compound. Methods of band structure calculations are always approximate, with different level of sophistication. Calculated band structure, mainly its topology at EL, is a kind of reference frame for assignment of particular dispersion of energy distribution curve (EDC) or momentum distribution curve (MDC) to particular band of studied compound at interpretation of ARPES. This is in direct relation with theoretical understanding of crucial aspects of SC-state transition in general. 

In Fig. 2 the correlation between the electron distribution curve (EDC) of the solid sample and the distribution of kinetic energies is sketched. The binding energies of the electronic levels can be calculated from the kinetic energy by... 

Fig. 2. Projection of electron distribution curve EDC of a sample onto kinetic energy distribution measured by the analyzer.

With the same sample, we performed micro-photoelectron spectroscopy (p-PES) at selected positions in the channel. With this technique a built-in spectrometer is used to record an electron distribution curve (EDC) with an iris aperture limiting the area of the detected photoelectrons to a range of about 30 pm. The spectra represent the integrated energy distribution of the photo-eleetrons. 

When the measured ESP moment is aligned parallel to the total magnetization, the spin polarization is designated as positive. Because the ESP technique suffers from low measurable intensities of polarized photoelectrons, the usual electron energy distribution (EDC) curves are not measured for polarized electrons. 

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