Angle and spin resolved Auger and photoelectron spectroscopy on Rb-layers by means of circularly polarized VUV radiation

Abstract

Abstract. Normal incidence circularly polarized VUV radiation with energies around 23 eV creates spin polarized photoelectrons from thick layers of Rb on Pt(ll 1) and thus excites oriented 4p hole states. The preferential spin direction of the Auger electrons and its dependence upon the emission angle has been measured and is compared with the corresponding angular dependence of the primary photoelectron spin polarization also measured. Since the CVV Auger decay relates to a s a pair of valence electrons, the cross comparison of results for photoelectrons and Auger electrons studies the questions on whether photoemission and Auger decay Occur in sequence, assuming an independent two step model, and whether the valence s-electrons couple to a singlet state configuration. PACS:79.20.Fv; 79.60.Bm a singlet state configuration or also partially to a triplet state configuration. Figure 1 shows the spin polarization of the Auger electrons averaged across the Auger peak measured [4] at rubidum thick layers on Pt(111) in normal emission versus the energy of the exciting circularly polarized VUVradiation in normal incidence, after having subtracted the unpolarized inelastic background in the spin-resolved Auger electron spectra. Figure 1 also denotes the thresholds for p_~ and pa hole creation by the photons. The p½ hole states excitect above the p± threshold decay via a Koster-Kronig transition into p] hole states [6,7]. Since 2 * • at higher photon energies phototransltlons into d states are more probable, the creation ofp~ holes with magnetic sublevels mj = +½ and ms = +~ Is preferred against creation of p~ holes with ms = -½ and rn; = -3, resultPhoton impact on solids often creates core level holes with subsequent valence electron Auger decay. In Auger spectroscopy usually the energetic position and the shape of Auger lines in spin-independent intensity spectra are studied [ 1 ]. Spin-dependent effects have been investigated experimentally in most cases with ferromagnetic material [2,3], where the electrons to be emitted are highly spin oriented in the ground state. Very recently first experimental results of spin dependent Auger emission from non-magnetic Rb-layers [4] as well as from free unoriented Ba-atoms [5] exposed to circularly polarized radiation have been reported. The spin polarized radiation creates spin polarized primary photoelectrons and thus spin oriented hole states whose decay results in spin polarized Auger electrons. It is worth noting that the Auger electrons from the CVV decay of metallic Rb-layers could not be observed for an isolated Rb atom since the alkalis only have one outermost s electron. The second s electron for the decay has to be supplied in the condensed matter by the Rb neighbours via the joint valence band. This gives rise to the question on whether they only couple to

Spin–orbit-induced photoelectron spin polarization in angle-resolved photoemission from both atomic and condensed matter targets

“…Figure 19 additionally shows the angular dependences of the photoelectron as well as the Auger electron spin polarization of a thick rubidium layer condensed on a platinum single crystal. The data can be fitted within the atomic model not only for the primary photoemission process but also for the subsequent Auger decay process emitting spin polarized Auger electrons due to the decay of a spin polarized photohole state [47]. Photoelectron emission of inner core (111)] at different photon energies [46].…”

“…Figure 19. Measured angular dependences of the spin polarization component in the direction of the radiation helicity for photoelectrons as well as for Auger electrons emitted by circularly polarized radiation of 23 eV energy from a thick rubidium layer adsorbed on a platinum single crystal[47]. Upper part: photoelectrons leaving a p 3/2 or p 1/2 hole state of opposite spin polarization with a fit using the atomic model (curves).…”

“…The two curves describe the upper and lower limits in application of the atomic model predicted using the data of the photoelectron spin polarization of the upper part under the assumption of a singlet coupling of the Auger decay. From[47].…”

Band symmetries of GaSe(0001) studied by spin-resolved electron spectroscopy using circularly polarized radiation

“…In these studies the symmetry of unoccupied states with energies below the vacuum level was determined. [15][16][17] In this paper we extend the studies of the layered semiconductors to GaSe, a material which shows similarities with InSe but very different band symmetries just above the vacuum level. As with InSe the electronic structure of the semiconducting III-VI compound GaSe is interesting from a fundamental point of view: GaSe also crystallizes in a layered structure with strong covalent bonding within the layer, but only weak van der Waals bonding between adjacent layers and shows quasi-two-dimensional properties.…”

“…With an Auger decay of the excited hole states the core hole orientation is transferred to the outgoing Auger electrons. [12][13][14][15][16][17] Therefore, the Auger-electron spin polarization ͑measured as a function of the photon energy͒ is suitable for probing the symmetry of the unoccupied final states being reached by the primary photoexcitation. This is of special interest for unoccupied states below the vacuum level, e.g., with energies between the conduction band minimum and the vacuum level in the case of semiconductors.…”