We present the experimental results of the electronic band structure study of the PbGdTe surface - pure and covered by gadolinium. The substitution of rare earth (RE) ions for some of the lead cations modifies their band structure parameters and brings about many magnetic, magneto-optical and magneto-transport properties.
The valence band and shallow core levels of ultrathin Gd overlayer on PbGdTe have been investigated. Resonant photoemission spectroscopy was applied as an experimental method. The Fano-type Gd 4d-4f resonance photoemission spectra have been taken for photon energies 130-152 eV. The photoemission measurements were performed at the FLIPPER II system in HASYLAB (Germany).
The PbGdTe layers were grown on BaF2 (111) substrates by an MBE method with use of PbTe, Te2 and Gd solid sources. Before the growth process the substrate was preheated at the temperature about 500oC. The sample surface was protected against interaction with ambient atmosphere by a layer of amorphous tellurium.
The photoemission spectra were measured for the clean surface of PbGdTe (the protecting Te layer removed) and after subsequent stages of Gd evaporation (Gd layer thickness: 0.4 and 1 nm). The Gd/PbGdTe structure were finally annealed at 600 K for 3.5 hours. After each deposition of Gd on PbGdTe and annealing of such a structure the photoemission spectra were taken. The comparison of the collected photoemission spectra enabled us to reveal Gd related features in PbGdTe substrate for each stage of sample treatment in a case of low Gd content (the solubility of Gd in PbTe was very weak). The maximum occurring at the binding energy of about 8 eV was ascribed to Gd 4f. Analysis of the collected photoemission spectra made it possible to reveal two Gd 4f - related features in the emission from Gd/PbGdTe. One of them was ascribed to the emission from Gd atoms built into the substrate, the second - to Gd deposited on the surface. The feature that can be ascribed to Gd 5d were revealed at the edge of the valence band. Analysis of the changes in its intensity enabled us to draw conclusions about population or depopulation of the Gd 5d state in the system.
We acknowledge support by MSHE (Poland) grants N202 101 31/0749 and 1 P03 B053 26