Spin-resolved inverse photoemission of ferromagnetic surfaces

Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism.     

Comparing inverse photoemission and X-ray absorption spectroscopies

The comparison of inverse photoemission with X-ray absorption spectra is possible. We discuss some of the similarities and differences that must be considered in both techniques. Two examples of such comparison are given: the NiMnSb half-Heusler alloy and the La_0.65Pb_0.35MnO₃ perovskite. We briefly present the dipole and symmetry selection rules which can be used for the interpretation of inverse photoemission as well as the absorption spectra. Due to the symmetry constraints imposed by the initial state, the selection rules in inverse photoemission are more restrictive than in the case of X-ray absorption.     

Photoemission and inverse photoemission spectroscopy of NiO

Photoemission (UPS) and inverse photoemission (BIS) spectra of NiO grown as a thin film on metallic Ni are reported. The data are discussed with respect to the electronic structure of the occupied and empty states in NiO.     

Theory of satellites in photoemission and inverse photoemission spectra of 4 f materials

We present calculations of the relative intensities and peak separations of the f derived spectral density for the, integer valent, light rare earths. We consider both f derived photoemission and inverse photoemission spectra. In these types of experiments, the final states has either an excess or a deficiency of charge residing on the screened by the conduction electrons. If the screening interaction is This may give rise to the appearance of satellites in both photoemission and inverse photoemission spectra. However, the calculations indicate that the relative intensity of the f derived satellite in the inverse photoemission spectrum should be extremely weak, when compared to the intensity of the satellites in the photoemission experiment.     

Effects of short-range magnetic order on photoemission and inverse photoemission spectra in iron

The dependenc of spin-resolved photoemission and inverse photoemission spectra on short-range magnetic order below and aboveT _c is investigated within a bulk interband transition model. The spectra are calculated in a 2000-atom cluster of bcc-Fe with local exchange field configurations, which are random subject to an assumed spin-correlation function. The model continuously bridges the gap between the disordered-local-moment picture (no short-range order) and a local-band picture (massive short-range order). Special emphasis is given to the analysis of factors like group velocity and the symmetry of the wave function by investigating special points in the Brillouin zone. Comparison with experimental data reveals a short-range order of at least 4 Å (corresponding to a nearest-neighbour correlation of about 0.4) nearT _c .     

UV inverse photoemission from cerium and its hydrides

Isochromate spectra of polycrystalline Ce, CeH_2.1 and CeH_2.9 were measured at a photon energy of 9.7 eV. The intensity at E_F is 4 to 5 times lower on CeH_2.1 than it is on the metal, and it vanishes on CeH_2.9. This is in accordance with XPS, UPS and conductivity data. In both hydrides broad features ( ～2 eV FWHM) appear, centered between 4 and 5 eV. From cross section arguments and from comparison with a CeRu₂ spectrum taken at the same photon energy, we conclude that we do not see any 4f contribution in our spectra. A signal at 7 eV on the CeH_2.9 spectrum is assigned to the ²Σ⁺_u shape resonance of the H₂^? ion, formed by desorbed H₂ molecules.     

Photon polarization effects in inverse photoemission from Cu(001)

A study of the polarization of Bremsstrahlung emitted from a Cu(001) single crystal surface helps to identify surface states and allows to determine the parity of bulk final states involved in a particular radiative transition if the angle of electron incidence is varied in a mirror plane of the crystal. In case of overlapping peaks with different polarization, a polarization dependent light detection increases in addition the apparent experimental resolution considerably.     

Design of an efficient monochromatic electron source for inverse photoemission spectroscopy

A design for an efficient monochromatic electron source for Inverse Photoemission Spectroscopy(IPES)apparatus is described. The electron source consists of a Ba O cathode, a focus electrostatic lens, a hemispherical deflection monochromator(HDM), and a transfer electrostatic lens. The HDM adopts a "slit-in and slit-out" structure and the degradation of first-order focusing is corrected by two electrodes between the two hemispheres, which has been investigated by both analytical methods and electron-ray tracing simulations using the SIMION program. Through the focus lens, the HDM, and the standard five-element transfer lens, an optimal energy resolution is estimated to be about 53 MeV with a beam flux of 27 μA. Pass energy(P.E.) of 10 eV and 5 eV are discussed, respectively.     

Structure of adsorbate inverse photoemission spectra: A model hamiltonian study

We present an Anderson-Newns Hamiltonian model of inverse photoemission spectra (IPES) of adsorbates on metals. We find that besides image screening, another screening mechanism may operate in IPES when intra-adsorbate electron correlation is strong and the adsorbate has filled levels near the Fermi energy of the metal. While image screening results in spectral shifts and the appearance of plasmon satellites, this new screening mechanism gives a doublet structure to the IPES. We also find that the hybridization of the adsorbate affinity levels with the unoccupied metal levels plays a crucial role in determining both the width and energy of the spectra.     

Momentum-resolved bremsstrahlung isochromat spectroscopy of silver surfaces

Angle-resolved bremsstrahlung isochromat spectra of the Ag(100), Ag(110) and Ag(111) surfaces have been measured. Our work extends and complements several earlier investigations of other authors. The data are summarized in the form of final state dispersionsE(k ). Comparison is made to the available theoretical and experimental information. The results for the bulk as well as for the surface-specific features are in excellent to reasonable agreement among each others and with recent calculations.     

Unoccupied electronic levels and conduction-band structure of Xe(111) probed by inverse photoemission

Inverse photoemission spectra from Xe(111) crystals grown on an Ag(111) substrate show features which are interpreted in terms of density-of-states emission from the conduction bands of Xe along the-L direction. The energies of critical points determined by this method show good agreement with recent spin-polarised photoemission band mapping. A peak which is located in the fundamental band gap is tentatively assigned to surface emission, on the basis of an experiment in which this peak is quenched by covering the Xe crystal with one monolayer of krypton.