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A 5f-like photoemission feature in normal emission from UN(100) appears for T N e el = 53 K . It arises from band states that are modified due to a halving of the Brillouin zone in the antiferromagnetic phase. This is the first observation for f electrons and proves their itinerant character in UN.

Recently, spin-polarized photoemission from gadolinium films was interpreted in terms of a 4f → 5d resonant scattering mechanism. In view of our photoemission data, we believe that this mechanism is very unlikely. Instead, the spin-polarization data can be explained in a straightforward manner taking into account the Gd band structure and simple photoemission escape cone rules.

Angle‐resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy‐vs‐momentum s‐ and d‐band dispersions, show that ferromagnetic nickel can be described by a spin‐split itinerant band model with an exchange splitting. An experimental one‐electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin‐polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)

We have measured unoccupied surface and interface states on Ga‐ and In‐derived III–V semiconductors with momentum‐resolved inverse photoemission. The position of the surface states is found to be unrelated to the fundamental band gap. Instead, a connection with the gap of p‐like states can be made. This finding is discussed in the context of theories of Fermi level pinning and band lineup, which use (virtual) gap states as a reference energy. Unoccupied metal‐induced gap states are found for transition metals (Y, Ti, V, Mn, Pd) on GaAs(110) and InP(110). Their energy tracks the Fermi level pinning position, suggesting that these states are connected with the pinning process. A tentative assignment in terms of nonbonding metal d states is given.

Auger electron spectroscopy (AES), combined with thermal desorption mass spectroscopy (TDS), work function (Δφ) measurements and energy-dependent angular resolved UV photoemission using synchrotron radiation were used to investigate the geometric and electronic properties of submonolayer and monolayer copper films grown by vapor deposition on a clean Ru(0001) substrate. A pronounced influence of the deposition temperature on the morphology of the Cu films was established in that lower temperatures favor an island growth mechanism (Stranski-Krastanov or Volmer-Weber type), whereas higher deposition temperatures lead to a more uniform spreading and a layer-by-layer growth (Frank-van der Merwe type). For Cu films grown under the latter conditions angular resolved photoemission reveals the existence of two-dimensional Cu bands even before the monolayer has reached completion; the experimentally determined band dispersions agree quite well with recent theoretical calculations.

Inverse photoemission is shown to be complementary to photoemission in probing unoccupied electronic states. The momentum of delocalized valence states can be measured as well as their energy if low electron (photon) energies in the 10–40 eV range are used: Thus, energy band dispersions are obtained for bulk, surface, and adsorbate states which cannot be determined by other techniques. Applications are demonstrated for Si, GaAs, SiO 2 and metal-semiconductor interfaces.

Structure-dependent $\mathrm{Si}(2p)$ surface core-level shifts and $2p$ photothreshold spectra which yield new surface geometry information are reported. For Si(100)-(2\ifmmode\times\else\texttimes\fi{}1), \ensuremath{\sim}0.5 monolayer of surface atoms are found shifted to smaller binding energy (-0.5 eV) relative to the bulk; this rules out symmetric pairing models. Si(111)-(7\ifmmode\times\else\texttimes\fi{}7) and Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) show different surface $2p$ core-level spectra (e.g., $\frac{1}{6}$ layer shifted -0.7 eV versus \textonehalf{} layer shifted - 0.4 eV), suggesting different geometries. Si(111)-(1\ifmmode\times\else\texttimes\fi{}1)H exhibits first-layer (+ 0.26 eV) and second-layer (+ 0.15 eV) shifts.

Using angle-resolved photoemission with single-crystal Fe(111) and Co(0001), we have determined accurate exchange-split energy-band dispersions $E(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ along symmetry lines. For Fe, Co, and Ni, respectively, occupied $d$-band widths are 3.1 eV ($P$), 3.8 eV ($L$), and 3.4 eV ($L, X$), while exchange splittings are \ensuremath{\sim}1.5 eV ($P$), \ensuremath{\sim}1.1 eV ($\ensuremath{\Gamma}$), and 0.3 eV (near $L$). Comparison with theory shows that state-of-the-art ab initio calculations describe the strong ferromagnets Fe and Co much better than Ni.

High resolution core level spectroscopy, polarization‐dependent near edge x‐ray absorption fine structure and angle‐resolved photoemission have been used to study CaF2 grown by molecular beam epitaxy on Si(111). It is found that both Ca and F bond to Si at the interface and that both Ca and F‐derived interface states are created. A new radiation induced ordered structure is also reported.

The relation of surface states and surface core levels to the surface geometry is discussed for Si(111) surfaces by comparing photoemission and inverse photoemission results with calculations for different geometries. It is shown that several sets of recent angle-resolved photoemission data for Si(111)-(2 × 1) and Si(111)-(7 × 7) are very similar to each other despite the fact that they have been interpreted in terms of different geometries. This indicates that no unique conclusions about the surface geometry can be drawn from the surface electronic structure. At present, only the traditional ionic buckling models can be ruled out rather safely. New information about unoccupied urface states in the gap of Si(111)-(7 × 7) is obtained from inverse photoemission data. The quenching behavior of occupied surface states under hydrogen exposure shows an unexpected band narrowing which helps identify the origin of surface state bands from the energy level of a localized state at 0.2 eV below the valence band maximum.

High resolution soft X-ray photoemission spectra of Si(111) surfaces subjected to steady-state etching are reported. The reaction is shown to proceed via the formation of a thick, highly fluorinated reaction layer, dominated by trifluorosilyl moieties. In addition, SiF4, the major reaction product has been observed in the spectra, indicating that it may be trapped within the reaction layer. The implications of these measurements for previously proposed reaction mechanisms are discussed.

New synchrotron radiation results are reported for adsorption of oxygen at room temperature on Si(111)-7×7 surfaces in the 1–10 4 L exposure range. Core-level Si 2p spectra measured at 150 eV are confronted to O 1s spectra measured at 590 eV with high surface sensitivity and high energy resolution. The main finding is the presence, within the whole adsorption range, of two O 1s components separated by 1.5 eV with an intensity ratio of about 1:4. The main component at lower binding energy is defined with bridging oxygen atoms whereas the component with smaller intensity is related to surface atomic non-bridging oxygen atoms which are converted into bridging oxygen atoms upon heating. These results show that chemisorbed oxygen and oxide-like bridging oxygen coexist and that oxidation dominates at coverages as low as 0.2 monolayer.

Photoemission spectra of 3d core levels excited with synchrotron radiation reveal a multicomponent substructure which increases in complexity with oxygen exposures over the range 106–1014L (langmuir). Spectral changes are already evident for Ga at 104 L, and for As near 106 L. Two oxide components shifted by 0.45 and 1 eV relative to the bulk Ga‐3d core level are evident throughout the exposure range, but shift to 0.8 and 1.4 eV for 1014 L. With increasing exposure the As‐3d core level develops a sequential set of shifted components at 0.8, 2.3, 3.2, and 4.2 eV relative to the bulk position in GaAs, which are attributed to single through fourfold coordinated bond formation to oxygen. Both surface and bulk‐sensitive core spectra reveal a nearly equally intense oxide substructure, which indicates that contrary to previous notions subsurface oxidation is the dominant mechanism throughout the exposure range. The core spectra furthermore indicate preferential Ga oxidation—which suggests that separate Ga and As...