X-Ray Photoelectron Spectroscopy of Ferroelectrics

X-Ray Photoelectron Spectroscopy of Ferroelectrics

Jonas Grigas1), Ewa Talik2), and Valentinas Lazauskas3)

1)

Faculty of Physics, Vilnius University, Sauletekio Ave. 9/3, LT-10222 Vilnius, Lithuania, e

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2)_{Institute of Physics, Silesian University, Universytetska 4, 40-007 Katowice, Poland} 3)

Institute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, LT-01108 Vilnius, Lithuania

In this talk we discuss the X-ray photoelectron spectroscopy (XPS) of the valence band (VB) and core-levels (CL) form and electronic structure in ferroelectrics. The excitation source of the PHI 5700/660

Physical Electronics Spectrometer was

monochromatic Al Kα radiation (1486.6 eV). XPS were analyzed in the range 0 – 1400 eV. Experimentally obtained energies were compared with the results of theoretical ab

initio calculations by the Hartree-Fock method

for a molecular model of the crystal. Two kinds of phenomena are discussed: 1) The resolved splitting of the CL in the

incommensurate (IC) phase of TlInS2 (Fig. 1);

Fig. 1 Splitting of the Tl 4f spin-orbit doublet in the IC phase (195 - 210 K) of TlInS2 crystal.

2) Form and electronic structure of the VB and CL splitting in the quasi-one-dimensional SbSI [1] and SbSeI [2] crystals. The VB of SbSI and SbSeI are similar, and are composed from the s- and p-bands. The s-band is formed from Sb 5s, S(Se) 3s and I 5s states. The p-band is formed from S(Se) 5p, Sb 5p and I 5p states. The VB form depends on the population of energy levels of surface and bulk atoms. Conduction band (CB) edge is formed almost 100% by the Sb 5p surface states. The obtained theoretical density of states and the VB form is close to the experimental XPS (Fig. 2). Large CL splitting was obtained due

Fig. 2 Electronic structure of SbSI VB. D(ε) is the density of states. VB is approximated by the Gaussian broadening method for SbSI molecular clusters from 2 (bottom dotted) to 16 (top solid).

to different valence state of bulk and (001) surface atoms.

References

[1] J. Grigas, E. Talik, and V. Lazauskas, Lithuanian J. Phys. 44, 427 (2004).

[22] V. Lazauskas, V. Nelkinas, J. Grigas, E. Talik, and V. Gavryushin, Lithuanian J. Phys. 46, Nr.1 (2006). 203 K 210 K Tl 4f 195 K 206 K In te n s it y ( a .u .) 110 115 120 125 130 300 K