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In our paper(1) the N 1s core level energy as obtained by Al Kα excited X-ray photoelectron spectroscopy (XPS) of boron nitride on Ru(0001) is not correctly reproduced, it is 398.63 ± 0.15 eV and not 389.63 ± 0.15 eV. Table 1 reproduces the B 1s and N 1s binding energies and work functions for h-BN on Rh(111), Ru(0001), Ni(111), and Pd(111).(2)Figure 1 reproduces the corresponding core level data with the correct energy scale. We are grateful to W. Auwarter for spotting these inconsistencies.

We present the design and performance tests of a miniaturized pulsed low-energy electron gun. Electrons photoemitted from a gold cathode are accelerated over a distance of 75 μm and then collimated by a microchannel plate. According to calculations, this novel concept will allow the time spread of the electron pulses to be kept below 5 ps for kinetic energies as low as 100 eV. The achievement of a minimum angular beam divergence (≈1°) along with an energy resolution of 1.1 eV has to be paid for by low signal intensities. We demonstrate the performance of the gun and the high electron-beam coherence by presenting low-energy-electron diffraction images taken from a submonolayer of lead adsorbed on the germanium (111) surface. We anticipate that this electron gun will open up new possibilities for following structural changes on solid surfaces in real time.

The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2π solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level EF. At energies greater than EF+5kBT the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He Iα (21.2 eV). For He IIα (40.8 eV) the residual photoelectron background is lower and photoemission up to 6kBT above EF can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag (111) above the Fermi energy is quantified.

The structural sensitivity of x-ray photoelectron diffraction is greatly enhanced by the acquisition of a full hemispherical diffraction pattern of chemically shifted core levels. Complex systems can be studied resolving the local order per element and per chemical environment. This technique is applied to study the earliest stages of hydrogenated diamondlike carbon film deposition on Si(001). Effects of the sample temperature and ion dose on the structure of deposited layers are discussed.

Although significant insight into fullerene-substrate interactions has come from recent surface science studies, to date there has been no unambiguous way to determine the molecular orientation of adsorbed C 60 molecules. We show that photoelectron diffraction patterns from monolayer C 60 films are directly related to the intramolecular structure of C 60. This allows for the first time a direct and unambiguous identification of the molecular orientation of the adsorbed fullerenes with respect to the substrate. A variety of molecular orientations is observed on different substrates. [S0031-9007(96)00473-5]

X-ray photoelectron diffraction has been used to investigate the interfaces of Ni/diamond, Si/diamond and Au/diamond. These elements were evaporated in UHV on doped and undoped diamond (100) and (111) substrates at different temperatures. While Ni grows heteroepitaxially on the diamond surface no orientation was observed for Si and Au. The Si/diamond interface shows no carbide formation even when heating to 850 °C. However, the C 1s peak of the diamond substrate shifts to lower binding energy when evaporating Si. This could possibly be explained by band bending at the interface. Ni, Si and Au form islands at these low film coverages.

Angular distributions of x-ray-excited Na 1s photoelectrons and Na KVV Auger electrons emitted from c(2\ifmmode\times\else\texttimes\fi{}2)-Na/Al(001) have been measured over the full 2\ensuremath{\pi} solid angle above the Al(001) surface. A detailed study involving single-scattering cluster calculations and an R-factor analysis has been performed to determine the room-temperature adsorption site of Na on Al(001). The best agreement with experiment is obtained for a configuration in which domains of Na atoms adsorbed in the hollow site and in the substitutional site coexist on the surface. This unusual and unexpected behavior has not been observed for an alkali-metal-on-metal adsorption system up to now, but it can be understood on the basis of very recent results from first-principles density-functional theory [C. Stampfl, J. Neugebauer, and M. Scheffler, Surf. Rev. Lett. 1, 222 (1994)].

The full-solid-angle (2\ensuremath{\pi}) intensity maps of the carbon-KVV Auger-electron emission at 260 eV from diamond (111), diamond (100), and highly oriented pyrolitic graphite (HOPG) (0001) samples were collected and compared with spherical-wave single-scattering cluster calculations. In contrast to Mg K\ensuremath{\alpha} excited C 1s patterns the C-KVV patterns show weak direct real-space information. We performed a detailed angular momentum analysis taking into account different l characters of the emitted Auger electrons and show that in diamond the C-KVV emission has mainly a d-like character while graphite emits a mixture of p- and d-like electrons with a minor contribution of s-like electrons.

Using GaAs/AlAs/GaAs heterostructures we report measurements of complete hemispheric Auger-electron diffraction patterns originating from single well-defined subsurface sites within a crystal lattice. With this data set a detailed experimental analysis of multiple elastic-scattering effects is performed. We investigate the dependence of the forward enhancement factor along atomic chains on the length and on the internal structure of the chain. No randomization of the elastically scattered electrons is observed even for long traveling path lengths. The angle-dependent features related to elastic scattering as well as those originating from inelastic scattering are evaluated independently to obtain depth profiles of the electron-emitting atoms. Both types of depth profiles indicate a microscopic redistribution of Al and Ga in a surface region of one bilayer thickness.

Angular distributions of several photoelectron and Auger transitions have been measured above a Cu(001) single crystal at 16 different kinetic energies between 60 and 1740 eV. The results are presented as 2π full-solid-angle intensity maps-diffractograms-that permit a clear representation of the relative importance of various scattering processes at each energy and the evolution of intensity patterns with energy. The experiments are compared with single-scattering-cluster (SSC) simulations performed at corresponding energies

Angular distributions of Auger electrons and of photoelectrons emitted at high (>500 eV) and low (

A single crystal Bi 2 Sr 2 CaCu 2 O 8+ x ( T 0 =84 K has been studied by X-ray photoelectron diffraction (XPD). Nearly full-solid-angle intensity distributions of Bi4f, Sr3d, Ca2p, Cu2p and O 1s emission from a (001)-terminated surface (= c plane) show twofold symmetric patterns with mirror planes along the a and b crystal axes, although the directions of several dominant forward scattering peaks are positioned in a fourfold symmetric way. The results are consistent with the pseudotetragonal structure with a periodically modulated lattice along the b -axis. All diffraction patterns are very different from other, reflecting the different local geometries around different types of emitter atoms. Basically, the positions of the prominent diffraction peaks are well described by single scattering clusters (SSC) calculations with a tetragonal cluster which is terminated by a Bi-O layer. The discrepancy between the experiment and the simulation gives information about the interlayer mixing of atoms.

Ultrathin films of one monolayer (ML) or less of Au on Cu(001) have been prepared by in situ deposition at 300 K in order to investigate the formation of a surface alloy. The local order within these films was determined by X-ray photoelectron diffraction, measuring full solid angle Au4d 5 2 intensity distributions. For deposition of between 0.2 and 0.6 Ml we confirm that a surface alloy is formed, with a mixed c(2 × 2) Au/Cu layer on top. In contrast to earlier low-energy electron diffraction measurements we find a measurable amount of substitutional Au in the 2nd and 3rd layer. At a coverage of 1.2 ML all azimuthal structure in the angular distribution is lost, consistent with the growth of an incommensurate pseudo-hexagonal Au overlayer with no short-range orientational order. Still the presence of narrow rings of higher intensity reveals the presence of subsurface Au.

A method for a controlled change of the doping level of high-temperature superconductors with ultraviolet radiation is presented. With photoemission it is shown that the exposure of Bi2Sr2CaCu2O8+δ samples to the light of a He gas-discharge lamp causes oxygen desorption. From measurements of the Fermi surface, it is found that the oxygen desorption causes a decrease of the doping level of the superconductors. From the desorption cross sections that strongly depend on the photon energy, two different oxygen desorption channels are inferred. This procedure for decreasing the doping level has the advantage that the crystallinity of the sample is not altered and that the doping level can be simultaneously measured by photoelectron spectroscopy.

The local structure of p(2×2)-Na/Al(111) has been investigated using angle-scanned full hemispherical x-ray photoelectron diffraction. The resulting diffraction patterns allow a direct and unequivocal determination of the surface atomic structure. Even though Na and Al are completely immiscible in the bulk, the p(2×2)-Na/Al(111) phase consists of a composite double-layer surface alloy where Na atoms take substitutional and fcc hollow sites and Al atoms removed from the surface occupy hcp hollow sites.

Heteroepitaxial nucleation and growth of twin-free diamond on Ir(111) is reported. The bias enhanced nucleation (BEN) technique was applied in a microwave plasma chemical vapor deposition setup to induce diamond nucleation on the new multilayer stack Ir/YSZ/Si(111). We demonstrate that the gathering of the diamond nuclei in so-called “domains,” a pattern formation process unique for diamond nucleation on iridium, is also present on Ir(111). The 1–2 nm thick carbon layer deposited by BEN does not show any crystalline diamond structures in electron diffraction and high resolution lattice imaging microscopy. In contrast, x-ray photoelectron diffraction (XPD) measurements yield C 1s diffractograms with clear threefold symmetry. The main features are comparable to measurements on diamond (111) single crystal surfaces. The weaker fine structure in the XPD patterns of the BEN layers is attributed to some disorder due to the harsh ion bombardment. However, this ion bombardment did not induce any measurable amount...

Using a single crystal of AuCu 3 (001) as a test case, it is shown that x-ray-excited core-level-photoelectron-diffraction patterns of an ordered alloy can be employed to decompose the total alloy density of states of the valence band into the partial densities of states of the constituents. The results of this new method are in good agreement with earlier experiments and recent band-structure calculations. The ratios of core-level to valence-band cross sections of each constituent of the alloy are also determined and compared to those of the pure elements

On observe des anisotropies du photocourant de 73% et 65% dans des balayages azimuthaux des intensites des niveaux de cœur 1s et 2s comprenant la direction [011]. De plus on mesure les pics de perte des plasmons accompagnant les raies de cœur 2s

Azimuthal X-ray photoelectron diffraction (APD) experiments have been carried out on a sample of Hg0.78Cd0.22 Te (MCT) epitaxially grown by liquid phase epitaxy (LPE) on (111) CdTe. To our knowledge this is the first XPD study of the (111) face of a II-VI semiconductor. Reproducible diffraction features are seen for emission from core levels of Hg, Cd and Te both before and after minimum ion bombardment, with bombardment being done to remove the native oxide overlayer. Single scattering cluster (SSC) calculations have been carried out using a spherical wave (SW) model. From comparison between experiment and theory an absolute determination of the surface polarity is possible.

In an attempt to assess the relative importance of recent improvements in the theoretical description of X-ray photoelectron diffraction (XPD) data we consider an extensive set of Ni 2p3/2 azimuthal measurements from a clean Ni(001) surface, taken at a very high angular resolution of approximately ±1.0°. In particular, we discuss the sensitivity of the theory-experiment agreement to the variation of the following parameters: cluster size, electron inelastic attenuation length, substrate inner potential, photon polarization, angular broadening due to the finite acceptance of the electron analyzer, and the absolute accuracy in the experimental emission directions relative to the crystal axes. It is then demonstrated how different levels of scattering cluster theory, including single scattering (SS) of plane p-waves, SS of spherical p-waves, SS of spherical waves with proper angular momentum final states, and finally multiple scattering (MS) of spherical waves, affect the calculated XPD curves. Experiment and theory are compared by means of R-factors, and we are thus able to assess the reliability of structural information that one can expect at different levels of theory, thereby minimizing computational complexity.

The role of on-site correlation in the low-energy excitations of nickel is studied by comparing the results of high-angular and high-energy resolution photoemission spectroscopy with quasiparticle states calculated as a three-body scattering solution of a multiorbital Hubbard model. It is found that correlation effects modify the energy dispersion and spin polarization of electron states and are essential in order to get a quantitative agreement with experimental data.

We demonstrate multiple-wave-number reconstruction of experimental data for forward-scattering-photoelectron and Auger-electron-angular-diffraction distributions of Cu(001). Direct structural information of the nearest- and next-nearest-neighbor atoms is obtained. The structure so determined provides a useful starting point for refinement by diffraction methods, thus avoiding the cumbersome trialand-error process

We have studied the growth of Mg overlayers on Pd(111), a system with 16.6% misfit, by means of x-ray photoelectron diffraction. No long-range order is observed by low-energy electron diffraction. Pronounced forward-focusing maxima in Mg 1s emission indicate considerable short-range order. At coverages below 1 monolayer Mg is found to occupy fcc sites distributed over two layers. At higher coverages oriented clusters are formed, accommodating the misfit by alternatively occupying fcc and hcp sites. Comparison to single-scattering calculations suggests an average cluster size of less than 15 A

Experimental photoelectron distributions of Al 2s emission above Al(001) and Pt 4f emission above Pt(110) are presented, measured over much of 2\ensuremath{\pi} solid angle at high angular resolution. These intensity maps illustrate very clearly the relative importance of various scattering processes. In addition to forward scattering along high-density atomic chains, concentration of photoelectron flux along dense atomic planes is observed. Al 2s and Pt 4f exhibit very similar intensity patterns associated with equivalent low-index directions. Holographic information about atomic positions within the nearest-neighbor shell around emitter atoms is found to be contained in circular interference fringes in the vicinity of 〈011〉 forward-scattering directions.

We decompose the valence band photoelectron spectrum of LaNi5 (11–20) into its La and Ni contributions. This is achieved by comparison of valence band photoelectron diffraction with La 5p and Ni 3p core level photoelectron diffraction. The well-known satellite at 6 eV binding energy in LaNi5 valence band spectra is clearly attributed to Ni photoemission. In accordance with calculations we find the La VB emission centered around 1.4eV binding energy while the Ni 3d band has a maximum at 0.8 eV below the Fermi level.

X-ray-photoelectron diffraction has been measured from an Al(001) single crystal for the free-electron-like valence band and the well-localized 2s core level, using Mg Kα radiation. Both show the same high anisotropy of 65% in the azimuthal distribution of the photoemitted electrons at 45 o away from the surface normal. The similarity between intensity patterns provides evidence for a strong degree of hole localization in high-energy valence-band photoemission

In order to obtain microscopic information on the Ag/Bi2Sr2CaCu2O8+x and Au/Bi2Sr2CaCu2O8+x interfaces we have investigated the structure of Ag and Au films on Bi2Sr2CaCu2O8+x(001) single crystals with x-ray photoelectron diffraction. Although Ag and Au are very similar from a crystallographic and electronic point of view, we find considerable differences. Our results show that Ag forms islands on the Bi2Sr2CaCu2O8+x surface and that about 50% of the Ag is ordered in two (110) domains which are rotated by 109°. Au, however, wets the surface much better and about 20% of the deposited Au forms two (111) domains rotated by 180°.

We present a new method to study the formation of a metallic film on an insulator. During the deposition of a metal on an insulator we measure the capacitance C(t) of the forming metal insulator structure and monitor the metal deposition rate with a quartz-crystal microbalance. Ce was deposited with rates of around 4 ML min −1 on a thermally, dry-grown, SiO 2 layer on a Si substrate. From the C(t) curve of the forming metal-insulator-semiconductor (MIS) structure we can distinguish three stages of the Ce film growth. Up to 3 ML of Ce no capacitance change is observed. In the second stage, between 3 and 5 ML, a steep increase of the capacitance occurs. From 5 to 10 ML the capacitance saturates gradually to the maximum value. At coverages which correspond to the first stage, Ce diffusion into SiO 2 was observed with X-ray photoelectron spectroscopy (XPS). The analysis of the Si(2s), O(1s) and Ce(3d) core levels suggest a Ce diffusion into oxygen vacancy positions of SiO 2− δ at room temperature.

We present X-ray photoelectron diffraction (XPD) data from AuCu3(001) at 293 and 823 K. i.e. below and above the well known order-disorder transition of the bulk. Azimuthal XPD data of Au4f and Cu 3p show a rather weak dependence on temperature. They are compared with layer-type multiple scattering calculations and it is concluded that the first two layers do not mix up to 823 K. In agreement with other authors the ordered alloy is found to have 50% Au and 50% Cu in the first layer while the second layer contains 100% Cu.

Recent experimental results on the electronic structure of hydrides of palladium, the rare earths, niobium and magnesium, of the intermetallic compounds LaNi 5 , FeTi and Mg 2 Ni, of the zirconium-based Laves phase compounds and of a few glassy metals are reviewed and compared with results of band structure calculations. The review focuses on results obtained by photoelectron and X-ray spectroscopy methods. Emphasis is placed on missing data to stimulate further investigations.

The crystal and magnetic structures of polycrystalline CeDx(2.2 or=2.90 remains approximately cubic down to 1.5K, second-order phase transitions to ordered structures with tetragonal symmetry (basic translations at approximately ac, ct approximately 2ac, space group I4; in contrast to Titcomb and co-workers (1974)) occur at temperatures Tc=290(3) and 330(5)K for x=2.18 and 2.29 respectively. Between x=2.29 and x=2.96 the magnetic ordering changes from ferromagnetism (Tc=3.7(2)K, ordered magnetic moment mu (Ce3+)=1.1(1) mu B at 1.3K) to FCC II antiferromagnetism (TN=4.2(2)K, mu (Ce3+)=0.6(1) mu B at 1.3K, mu //(111)).

The use of x‐ray photoelectron diffraction (XPD) for the structural study of oxide growth on Ni(001) from c(2×2)O up to the saturated oxide of approximately two‐monolayers thickness is described. Some rather unique structural information is obtained from XPD. This includes the site type and position of the c(2×2) overlayer and the geometry and lattice parameters of the saturated oxide. The XPD data are also in excellent agreement with single‐scattering cluster calculations at the spherical wave level.

On recrystallized Eu2O3 we have measured the optical re-emission which is very sensitive to Eu2+ contamination. On this material we observed XPS core level and valence band spectra. Only Eu3+ peaks could be identified, thus neither in the bulk nor at the surface Eu2+ is stable. We conclude that neither shake down effects nor intermediate valence is present in Eu2O3.

Frequency modulation of GaAlAs double heterostructure injection lasers at microwave frequencies is reported for the first time. The lasers are operating at a 0.85 μm wavelength and have been modulated at frequencies up to 2.25 GHz with a modulation index of 2.4. The laser FM modulation is displayed by a high resolution spectral measuring setup comprising a monochromator and a Fabry-Perot interferometer. A simple laser model is presented which allows the static frequency shift of the laser resonance frequency to be calculated as a function of the bias current change. The results are compared with measured data.

We present UV isochromat spectra of polycrystalline CeH2.1 and CeH2.9. The intensity at EF is small in CeH2.1 and vanishes in CeH2.9 as it is expected from XPS, UPS and conductivity data. In both hydrides broad features (≈2 eV FWHM) appear between 4 and 5 eV above EF. This is in qualitative agreement with bandstructure calculations.

The interface of Yb on polycrystalline Al has been studied at 300 K. Between 0.03 and 5 monolayers of Yb have been investigated by means of core-level x-ray photoelectron spectroscopy. The influence of the substrate spreads within 5 Yb monolayers. From intensity ratios between the Yb 3{ital d}, Al 1{ital s}, and Al 2{ital s} core levels and from Yb 3{ital d}{sup 9}4f{sup 14} core-level shifts, we conclude a strong Yb contraction within the first monolayer. The contraction is substrate and adsorbate driven. Within an electrostatic valence-shell picture, which takes only the screening of the initial state into account, this contraction does not fully explain the Yb 3{ital d} core-level shifts. Relaxation effects would have to compensate a large portion of the initial-state screening. In the photoelectron spectra a weak shoulder appears on the higher-binding-energy side of the Yb 3{ital d}{sup 9}4f{sup 14} peaks. This shoulder may contain a Yb 3{ital d}{sup 9}4f{sup 13} multiplet, which would indicate a cracking of the Yb 4{ital f} shell, i.e., the occurrence of a mixed-valence behavior of Yb on Al.

We report the observation of spin-polarized photoelectron diffraction for antiferromagnetic MnO(001). Data at kinetic energies near 100 eV for the spin-split Mn $3s$ multiplet show abrupt changes in the $^{5}S:^{7}S$ intensity ratio at a temperature of 530\ifmmode\pm\else\textpm\fi{}20 K that is 4.5 times the N\'eel temperature. An additional temperature-dependent study done at higher electron kinetic energies, along with azimuthal diffraction measurements, support the conclusion that this abrupt change is due to a new type of high-temperature short-range-magnetic-order transition.

The saturated oxide formed on Ni(001) under UHV conditions has been studied by x-ray photoelectron diffraction (XPD) and low-energy electron diffraction. At ambient temperature and with a 1200-L exposure to oxygen, the saturation oxygen coverage is found to be 4.3\ifmmode\pm\else\textpm\fi{}0.4 monolayers (ML) as measured relative to the Ni(001) surface-atom density. [1 langmuir (L)${==10}^{\mathrm{\ensuremath{-}}6}$ Torr sec.] The oxide is furthermore found to grow primarily as NiO(001) in a highly strained superlattice for which the horizontal lattice constant is expanded by (1/6 compared to the underlying Ni(001). The XPD results are found to be very sensitive to the degree of short-range order in the oxide before and after light annealing, particularly when obtained with high angular resolutions of approximately \ifmmode\pm\else\textpm\fi{}1.0\ifmmode^\circ\else\textdegree\fi{}. Single-scattering calculations with spherical-wave scattering are found to give an excellent description of the XPD from the annealed and more-ordered overlayer. These results also suggest the general utility of high-resolution XPD for studying the degree of short-range positional order present in epitaxial overlayers.

Multiple-scattering effects in Auger electron and photoelectron spectroscopies are assessed using a new spherrical-wave multiple-scattering formalism which is based on a separable approximation to the scattering Green's functions.