A highly detailed x-ray photoelectron diffraction data set has been acquired for crystalline Cu(001). The data set for bulk Cu 3p emission encompasses a large k-space volume (k=3–10 Å-1) with sufficient energy and angular sampling to monitor the continuous variation of diffraction intensities. The evolution of back-scattered intensity oscillations is visualized by energy and angular slices of this ‘volume’ data set. Large diffractyyion data sets such as this will provide rigorous experimental tests of real-space reconstruction algorithms and multiple-scattering simulations.

Angle-resolved photoemission extended fine structure (ARPEFS) was used to determine the structure of c(2×2)P/Fe(100) for the first time. P 1s core-level photoemission data were collected normal to the (100) surface and 45° off-normal along the [011] direction at room temperature. A close analysis of the auto-regressive linear prediction based Fourier transform and multiple-scattering spherical-wave calculations indicate that the P atoms adsorb in the high-coordination four-fold hollow sites. The P atoms bond 1.02 Å above the first layer of Fe atoms and the Fe-P-Fe bond angle is 140.6°. Additionally, it was determined that there is no expansion of the Fe surface. Self-consistent-field Xα scattered wave calculations were performed for the c(2×2)P/Fe(100) and the c(2×2)S/Fe(100) systems. These independent results are in excellent agreement with this P/Fe structure and the S/Fe structure previously published, confirming the ARPEFS determination that the Fe1-Fe2 interlayer spacing is contracted from the bulk value for S/Fe but not for P/Fe.

We have investigated the unreconstructed (0001) surface structure of sapphire (α-Al2O3) by Grazing Incidence X-ray Scattering. Modulations along the crystal truncation rods were analyzed in order to determine the chemical nature of the terminating plane, and the structural relaxations of the first few atomic planes below the surface. The most likely model yields a single Al layer termination with relaxations of the first four planes of -51%, +16%, -29% and +20% respectively. These results compare well with the most recent theoretical calculations on this surface.

The interfacial structure of room-temperature MBE-grown Cu thin film on c-plane sapphire has been studied by measuring the substrate crystal truncation rod (CTR) using synchrotron radiation. One substrate was annealed in air at 1500°C for 3 hours followed by an anneal in UHV at 1200°C for 30 minutes prior to Cu deposition. CTR from a clean sapphire substrate without Cu coverage was measured as a reference. The annealed substrate showed higher diffracted intensity along the CTR due to changes in surface structure. The terminating sequence of the substrate surface layers have been obtained from intensity profile analysis.

We have measured polarization-dependent Fe K-edge XAFS spectra from an epitaxially-grown Al/Fe/Al/ZnSe/GaAs(001) sample using synchrotron radiation. The Fourier-transformed XAFS spectra were fit up to four coordination shells simultaneously using theoretical spectra generated with FEFF 6. Our results reveal a small tetragonal distortion of the bcc α-Fe film lattice towards a contraction in the film growth direction (c=2.863 Å and a=2.874 Å; bulk a=2.867 Å). The anomalous tetragonal distortion is consistent with a model involving substantial interdifussion of Fe and Al, leading to Fe1−xAlx alloy formation localized in the interface regions.

We have used Grazing Incidence X-ray Diffraction to study the structure of a liquid crystal (LC) at the buried LC-glass interface in micrometer size LC films. This measurement is done in reflection mode through the glass substrate, which consists of a grating photolithographed onto a 0.2mm slide. This experiment was performed in beamline X22B of the National Synchrotron Light Source at Brookhaven National Laboratory, using 1.3776Å X-ray radiation. We have used both the glass and LC absorption properties to control the penetration depth of the beam into the LC film bulk. The ability to measure LC interfaces in this manner is essential to study any LC device, arid its response to applied fields.

We present measurements of the evolution with film thickness of the 3d electronic states at the Fermi energy of ultrathin Ni films. The morphology and thickness of the films is determined from x-ray photoelectron spectroscopy. x-ray photoelectron diffraction and x-ray magnetic linear dichroism using synchrotron radiation. Photoelectron angular distributions were measured using an ellipsoidal mirror analyzer. Even at submonolayer Ni coverages, the 3d electronic states exhibit bulk-like properties. This is attributed to the short screening length of electrons in metals, the localization of the 3d electrons, the similarity of the Ni and Cu ion cores, and finally the interaction with the underlying fcc periodic potential.

The electronic states at the Fermi surface determine diverse properties such as magnetism, chemical bonding, and phonon-electron coupling. Using a conventional hemispherical analyzer at the ultraESCA beamline 7.0 of the Advanced Light Source, we have measured Fermi contours of the bulk and surface states of Cu(001) and Ag(001). For bulk states, we used uniform sampling in k-space by varying both the electron takeoff angle as well as the photon energy. Three-dimensional plots (in k-space) of bulk and surface states at the Fermi level can easily be achieved within one or two synchrotron shifts. Surface states, whose momentum is independent of k-perpendicular, are easily mapped if sufficiently dense angular sampling is performed. The states crossing the Fermi level at X in the surface Brillouin Zone of Cu(100) and Ag(100) are presented as examples.

A marked resonance enhancement of the 3d photoemission intensity in angle-integrated electron-distribution curves from Ni3Al has been observed 6.6 eV below the Fermi level for photon energies in the vicinity of the Ni 2p absorption threshold. Soft x-ray L-edge absorption spectra were measured to determine the Ni 2p excitation threshold. The Fano asymmetry parameter and the effective Coulomb interaction for Ni3Al are 2.2 and 4.8 eV, respectively, as derived from the experimental data. Differences between the 2p→3d and the 3p→3d resonance effect are discussed, and comparisons with Ni, NiAl, and NiGa are made.

We have begun a program to characterize magnetic alloy overlayers using both magnetic x-ray circular dichroism (MXCD) and magnetic x-ray linear dichroism (MXLD). This will allow a direct comparison of MXCD-absorption and MXLD-photoelectron emission. First results from the Advanced Light Source will be presented.

XAFS analysis of the local structure about Pt and Co in PtxCo1−x, for x ˜ 0,7 revealed that the local coordination of Co and Pt is similar to that found in cubic L12 Pt3Co. In the plane of the films, significant Co-Co bonding was found- a feature not present in ordered L12 Pt3Co. The presence of Co-Co bonds, preferentially in-plane, suggest that clustering of Co into “sheets” or “chains” is the source of PMA in these films.

The experimental program at the Advanced Light Source to produce and characterize circularly polarized x-rays is described. A number of beamlines are either operating or under construction which produce circularly polarized light. Bend magnets, multilayer phase retarders, and insertion devices which directly produce circularly polarized radiation are described. These beamlines will have capabilities for both microscopy and high resolution spectroscopy. Measurements of the linear and circular polarization of these beamlines are also described.

While Magnetic X-ray Circular Dichroism (MXCD) has been applied extensively to the extraction of elemental magnetic moments in various magnetic multilayers, the configuration of actual devices imposes certain constraints on the application of MXCD to devices. Using a set of real, thin-film spin valve devices with varying Cu spacer layer thicknesses, we demonstrate the correlation between MXCD and magnetoresistance measurements on those devices as well as the restrictions on the interpretation of MXCD data imposed by both the device topology and the formulation of realistic error estimates.

We report the results of temperature dependent, Mn K-edge X-ray Absorption measurements: Magnetic X-ray Circular Dichroism (MXCD) for local magnetic properties and X-ray Absorption Near Edge (XANES) for electronic and structural properties of Mn-based oxide magnetoresistive compounds La1−xSrxMnO3. This is the first report of an MXCD signal of the Mn K-edge in Mn oxide systems. By studying the integrated peak intensity of the first peak in the MXCD signal, it can be determined that the magnetic properties of the system are independent of temperature in the range 94 to 223K.

An energy dispersive spectrometer is used to measure the temperature dependence of the Magnetic Circular X-ray Dichroism (MCXD) effect at the gadolinium (Gd metal) LIII absorption edge from 94 K to 335 K. In ferromagnetic Gd, the MCXD spectrum consists of the main positive peak with pre- and post-edge features. Only the main positive peak exhibits a temperature dependence similar to that of Gd magnetization. All other features decrease as the temperature increases and vanish slightly above the transition temperature (293 K). Well above the ordering temperature (paramagnetic Gd), the MCXD consists only of the positive peak, with a post-edge background that slowly decays away from it over a range of 90 eV.

We have utilized the scanning transmission x-ray microscope at Brookhaven National Laboratory to acquire high energy resolution spectra of various polymers and to investigate the bulk characteristics of multiphasic polymeric materials with chemical sensitivity at a spatial resolution of about 50 nm. We present studies ranging from phase separated liquid crystalline polyesters and polyurethanes to various polymer blends. Improvements in the NEXAFS imaging and spectral acquisition protocol in the recent past provide much improved spectral fidelity and include in situ energy calibration with CO2.

Synchrotron White Beam X-ray Topography (SWBXT) has been applied to the characterization of marked growth interfaces in Ga doped Ge single crystals. The techniques employed in interface demarcation include modifications of the cold zone temperature, mechanical pulsing and Peltier pulsing. As revealed by our observations, the visibility of growth interfaces is a sensitive function of diffraction conditions. A combination of the correct orientation of the active reciprocal lattice vector with respect to the interface plane and the necessary strain sensitivity controlled by the rocking curve width of the reflection are proved to be important for interface visibility. This can easily be achieved by using synchrotron radiation since the tunability of the synchrotron source provides great flexibility in the choice of proper diffraction conditions. Structural defects such as small-angle tilt boundaries and dislocation cell structures were also observed. The formation mechanism of these defects will be discussed. Direct evidence of dislocations present in the seed crystal propagating into the as-grown crystal through the melt-back interface during crystal growth was also obtained.

The fluorescence x-ray microprobe beamline at the Advanced Light Source (ALS) provides a technique to study almost any sample with excellent trace element sensitivity, high spatial resolution and minimal sample damage. During the last two years, the focused spot size has been improved from 2 μm × 4 μm to 1.6 μm × 1 μm using a pair of elliptically-bent multilayer mirrors. Two sets of mirrors have been produced for operation at 8.5 keV and 12.5 keV with a bandpass (ΔE/E) of 4 %. The intensity has also increased by a factor of 20 to over 1 × 1010 photons/sec by linearly grading the multilayer coating on the mirrors and by operation of the ALS at 1.9 GeV rather than 1.5 GeV.

A wide variety of samples have been studied. Some of the materials science samples that have been studied include gallium nitride samples, polycrystalline silicon solar cells, the liner material of a rocket motor and the central germanium core of an optical fiber.

Experimental observations of ice single crystals strained under uniaxial tension using synchrotron X-ray topography have shown that there is far more dislocation activity around notches at high temperature, -7.8°C, than at lower temperatures (-40°C and -60°C).

In order to understand the macroscopic response of polycrystalline structural materials to loading, it is frequently essential to know the spatial distribution of strain as well as the variation of micro-texture on the scale of 100 μm. The methods must be nondestructive, however, if the three-dimensional evolution of strain is to be studied. This paper describes an approach to high resolution synchrotron x-ray diffraction tomography of polycrystalline materials. Results from model samples of randomly-packed, millimeter-sized pieces of Si wafers and of similarly sized single-crystal Al blocks have been obtained which indicate that polychromatic beams collimated to 30 μm diameter can be used to determine the depth of diffracting volume elements within ± 70 μm. The variation in the two-dimensional distribution of diffracted intensity with changing sample to detector separation is recorded on image storage plates and used to infer the depth of diffracting volume elements.