Mapping of conduction bands in GaAs by angle-resolved photoemission

Using angle-resolved photoemission spectra in the photon energy range 12 ? hv ? 20 eV, we have mapped selected conduction bands for the (110) direction in GaAs using a simple direct-transition analysis. At higher energies the spectra suggest a one-dimensional density of states interpretation. The two mechanisms are discussed.     

Repeated zones and Mahan cones in the angular dependence of photoemission

The intensity of photoemission from the Ta-derived d states in the layer compound 1T-TaS₂ has been measured as a function of both polar and azimuthal angle of emission at the photon energy $\text{h}\text{?}\text{ω=21.2}\text{eV}$. The light source was a high intensity He resonance lamp employing an aluminum window in place of the more conventional differentially pumped capillary system. The azimuthal dependence of the d emission displays three kinds of lobes which we refer to as “heads, chins and ears”. The heads and chins are oriented along directions close to the bifurcated lobes observed previously at $\text{h}\text{?}\text{ω=10.2}\text{eV}$. The ear lobes, however, are oriented quite differently and appear only at high polar angles, corresponding to larger relative values of the parallel wavevector. The results can be understood in terms of a repeated zone scheme in which the ears and chins (not necessarily at the same polar angle) correspond to different Mahan cones of the same optical transitions.     

Polarization and angular dependencies in the photoemission from gold

An elementary calculation of the polarization and angular dependencies of photoemission from the valence band of gold is presented. The results are applied to experiments using synchrotron radiation as a light source. We show that use of a cylindrical energy analyzer could result in modulations of the relative peak heights in the d-bands. Simple experimental tests of our conclusions are suggested.     

Electron energy loss spectroscopy and ultraviolet photoemission of TmSe

Intraionic Tm²⁺ and Tm³⁺ ? → d and p → d charge transfer transitions are identified in the energy loss spectra of 100eV electrons of TmSe by comparison with X-ray photoemission data. In contrast the ultraviolet photoemission spectra with photon energies up to 21.2 eV do not show any evidence for the intermediate valence character of TmSe due to matrix element effects.     

Special features in photoemission from the s-p bands of copper

Angle-resolved photoemission (ARPES) studies of the (100) face of clean copper using He I radiation reveal two distinct peaks with binding energies between 0 and 2 eV. These peaks have the opposite dispersion with emission angle and have very different widths, one peak in particular being unusually sharp. We show that both of these peaks are associated with the upper part of the s-p band and that their behaviour can be qualitatively explained by an examination of the bulk band structure for finite values of k_∥ away from the Δ-symmetry direction. We also show that rather good quantitative agreement with the experimental spectra can be obtained by performing realistic photocurrent calculations which include a proper treatment of the surface electronic structure, matrix elements and lifetime effects. Finally, the significance of a sharp peak arising from the s-p band for ARPES studies of random alloys and chemisorption systems is briefly discussed.     

Angle-resolved ultraviolet photoemission study of first stage alkali-metal graphite intercalation compounds

The electronic band structure of the first stage alkali-metal graphite intercalation compounds (C₈K, C₈Rb and C₈Cs) was determined by angle-resolved ultraviolet photoelectron spectroscopy. The dispersive feature of the ^* bands at point in the Brillouin zone was clearly observed in all the compounds. The electron occupancies in the ^* band of C₈K, C₈Rb and C₈Cs were estimated to be 0.5±0.05 e (e; unit electronic charge), 0.45±0.05 e and 0.4±0.05 e, respectively. This strongly suggests that another half of the unit electronic charge is accommodated in the three-dimensional band at point, which forms a spherical Fermi surface at the center of the Brillouin zone. The character of the three-dimensional band at point was also discussed.He died on 27th of September, 1986     

Phenomenological electronic energy bands in graphite intercalation compounds

The electronic energy bands near the Fermi level for both donor and acceptor graphite intercalation compounds are modelled using a k_z-axis zone folded form of the SWMcC bands for pristine graphite. The effect of intercalation is included through terms for the intercalant and for the interaction between intercalant and graphite layers. Graphitic π-bands appropriate to both donor and acceptor compounds are presented.     

Spin polarized photoemission from La-doped EuO in the vacuum ultraviolet

The spin polarization of photoelectrons emitted form La doped EuO was measured as a function of light energy up to hv = 11 eV, together with the quantum yield. The spectrum of spin polarization can be understood in terms of the energy level diagram of bulk EuO.     

Excitation energy dependence of Raman bands in multiwalled carbon nanotubes

Vertically aligned multiwalled carbon nanotubes (MWCNTs) were grown on 1‐ and 3‐nm cobalt (Co) films, at various growth times by microwave plasma enhanced chemical vapor deposition technique and their microstructural properties were analyzed with the help of Raman spectra that were obtained from different sources of laser excitation energies (E_L: 2.41, 1.96 and 1.58 eV). The variation of D and G band positions in MWCNTs grown on 1‐ and 3‐nm Co films follows a similar behavior, and an anomalous behavior was observed in the E_L dependence of the D′‐band wavenumber. In the second‐order spectra, the G′ band varied strongly according to structure with the laser excitation energy (E_L). The I_D/I_G ratio decreased with the increase of E_L for all MWCNTs; however, for a fixed E_L, the I_D/I_G dispersion is higher at lower E_L. The crystallite sizes were estimated using I_DI_G and E_L. We have shown that, for all MWCNTs, I_D/I_G ratio is inversely proportional to . Copyright © 2010 John Wiley & Sons, Ltd.     

Spin-orbit splitting in the valence bands of PbSe from angle-resolved uv photoemission

Angle-resolved photoelectron spectra of single-crystal PbSe have been measured employing 16.85 eV and 21.22 eV photon energies. Characteristic double peaks in the valence band spectra are attributed to the effect of spin-orbit interaction. The dependence of peak intensities on the photon incidence angle furnishes an additional justification for this interpretation. Experimentally obtained values of the spin-orbit splitting agree well with the prediction of band structure calculations.     

Parity- and spin-mixng in relativistic energy bands observed by vector analysis of spin-polarized photoemission

The polarization vector of momentum selected photoelectrons from Pt(1 1 1), excited by circularly polarized synchrotron radiation, has been measured outside high symmetry lines. Substantial spin polarization and a strongly varying vector orientations are found. The orientation of the polarization vector for various initial bands reveals strongly varying parity- and spin-mixing in the ΛLUX mirror plane.     

Magnetic linear dichroism in the angular dependence of core-level photoemission from (Ga,Mn)As using hard x rays

We report a study of the electronic properties of the ferromagnetic semiconductor (Ga,Mn)As using magnetic linear dichroism in the angular dependence of Mn 2p photoemission under hard x-ray excitation. Bulk plasmon loss satellites demonstrate that the probed Mn ions are incorporated deep within the GaAs lattice, while the observed large dichroism indicates that the spectra originate from ferromagnetic substitutional Mn. Simulations of the spectra using an Anderson impurity model show that the ferromagnetic Mn 3d electrons of substitutional Mn in (Ga,Mn)As are intermediate between localized and delocalized.     

Energy dependence of electron energy loss processes in Ge 2s photoemission

Deep core Ge 2s photoelectron spectra from polycrystalline Ge films induced by monochromatic synchrotron radiation, of 4, 6 and 8 keV were measured and analysed using two different methods, the partial intensity analysis and the extended Hüfner method to determine the spectral contributions from different electron energy loss processes due to bulk extrinsic, intrinsic and surface excitations. The obtained photon energy dependence of the ratio of these contributions was compared as a function of the photoelectron kinetic energy. It was found that the relative contribution of intrinsic excitations increase with the photon energy.     

Bombarding energy dependence of angular momentum transfer in deep inelastic collisions

Measurements of first and second moments of γ-ray multiplicity distributions from deep inelastic collisions of ⁸⁶Kr + ¹⁵⁴Sm are reported. A global systematics of the angular momentum distributions from deep inelastic reactions with projectile masses ? 40 is presented. The average angular momentum is found to depend linearly on the incident channel average angular momentum, while no simple systematics for the second moment appears obvious. In order to illuminate the question whether the angular momentum transfer process reaches statistical equilibrium in deep inelastic collisions, numerical calculations have been performed on two models: a two-sphere classical model including the collective modes of twisting, bending, wriggling and tilting, and a statistical equilibrium Fermi-gas model. The two-sphere classical model is not able to account for the observed second moments, and neither does the Fermi-gas model give an explanation of the deep inelastic multiplicity data.     

Gap emission in ultraviolet photoemission experiments

It is shown that the gap emission observed in ultraviolet photoelectron spectra of metals takes place via a wavevector conserving excitation in the surface region localized on bulk Brillouin zone boundaries. Thus gap emission correspond to direct transitions between bulk initial statesE _i(k =k _BZ,k ) and evanescent statesE _f(k =k _BZ,k ) which are made possible by the existence of the surface. This fact can be used to map occupied bulk energy band dispersions. Examples for Silver, Copper, Gold and Platinum are given.