We present structural characterizations of a series of sputtered Fe/Nb and V/Nb superlattices by high-angle x-ray diffraction. Diffraction scans were performed with the scattering vector at various angles (χ) with respect to the layers. χ=0° diffraction spectra (normal to the layers) were fitted to a general structural model to determine the (110) lattice strains, interfacial disorder and interdiffusion. χ>0° spectra probe the lattice strain of the individual layers and the in-plane interfacial coherence. Both systems form incoherent interfaces above a critical modulation wavelength (ΛC). At ΛC, the Fe/Nb system undergoes a crystalline-to-amorphous transition while the V/Nb forms in-plane coherent interfaces.

A systematic investigation of the adsorption properties of several organometallic compounds on silicon surfaces is reported. In this framework, a new method to deposit thin metal films on silicon surfaces is described, which is based on a synchrotron radiation induced photodecomposition reaction. The precursors are metal carbonyls adsorbed on single-crystal Si surfaces in ultrahigh vacuum conditions. Irradiation of these adsorbatesubstrate systems with unmonochromatized synchrotron radiation (“white light”) induces a chemical reaction leading to a thin metal film on the surface. This process has been monitored in situ by photoemission. The fingerprint for the film formation is the appearance of a clear Fermi edge in the valence band. We have been able to deposit thin films of Mo, W and Fe on Si(111) surfaces. This method offers several advantages over traditional techniques, and namely the mild conditions and the limited number of process steps. An intriguing future development under testing is the possibility of creating ordered patterns on the surface.

A new technique of obtaining layer thickness and internal strains in multilayer structures and quantum wells from the rocking curve data is described and analytically proved. This method consists of Fourier transform of the experimental intensity profile multiplied by the wave vector deviation squared. It is shown that peaks of the Fourier transform correspond to distances between boundaries in the specimen. The (400) reflection curves of a quantum well in InP/InAs and a superlattice structure made up of latticematched GaAs/Ga0.49 In0.51P layers were measured with 8 KeV radiation at beamnline X-18A, National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The results of above procedure were used to reduce a number of degrees of freedom in a computer simulation of reflecting curves. It is shown that it is possible to extract layer thicknesses with the accuracy of about 15 Å for thick layers to as low as 1 Å for superlattices. Interplanar distances can be obtained with an accuracy of 0.0001 Å.

Co EXAFS data for these Co/Ag multilayers exhibit no changes in basic form and obey a simple scaling with Co thickness down to 6Å. Over this same thickness range the giant magnetoresistance and the manner in which magnetization approaches saturation change substantially. These results indicate that local structural changes do not play a significant role in altering the magnetic properties of this multilayer system.

Soft x-ray synchrotron radiation has been utilized as the excitation source in a high-resolution photoemission experiment designed to investigate the chemisorption and subsequent reaction of diethylsilane on the technologically important Si(100) surface. We have found that diethylsilane chemisorbs dissociatively to form Si-CH2CH3 surface species on Si(100) following a room temperature exposure. These species are identified by two very sharp peaks observed in the valence band spectra positioned at 17.9 and 14.3 eV binding energy. In addition, C Is core level spectra, measured following exposures of Si(100) substrates as a function of surface temperature, show that carbon, in some form, exists on the Si surface following exposures at every temperature from room temperature to about 600°C. While only -CH2CH3 ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate at 300°C, producing a mixture of -CH2CH3 groups and other intermediate carbonaceous species. At a growth temperature of about 400°C the intermixing of elemental carbon with Si begins. At higher temperatures, we observe the continued degradation of diethylsilane to produce a Si + C alloy on the surface at 600°C. Our results indicate that diethylsilane has potential as a molecular precursor for SiC formation by chemical vapor deposition techniques.

Grazing incidence x-ray scattering has been used with a synchrotron source to characterize the stress gradients during thermal cycling in 1.0 μm thick Al-0.5%Cu films passivated with silicon nitride. The films were cycled between room temperature and 400°C. The stress-temperature behavior is quantitatively similar to that measured for unpassivated films. The presence of an inhomogeneous strain is documented at low temperatures. The dissolution and precipitation of Al2Cu is suggested as an explanation for the gradients and asymmetric x-ray peak broadening.

We report the first application of Soft X-ray Photoelectron Spectroscopy (SXPS) to probe the bonding at epitaxial, bi-metallic interfaces with atomic-layer spatial selectivity. Specifically, we have measured the W(4f)7/2 levels of interfacial tungsten atoms for (1×1)Fe/W(110), (1×1)Ni/W(110), and (1×1)PtW(110). For clean W(110), the surface atoms exhibit a W(4f)7/2 peak at -320 meV binding energy with respect to the bulk W(4f)7/2 peak. Upon formation of the metallic overlayers, the interfacial tungsten atoms contribute W(4f)7/2 peaks at -225 meV (Fe/W), -140 meV (Ni/W), and +70 meV (Pt/W) with respect to the bulk W(4f)7/2 peak. The systematic reduction in the binding energy difference between interfacial and bulk tungsten atoms for Fe, Ni, and Pt correlates with increasing heats of adsorption on W(110), as determined by Temperature Programmed Desorption. This suggests that SXPS, in combination with first principles calculations and Born-Haber thermochemical cycle analyses, can be used as a non-destructive probe of bi-metallic interfacial bonding energies.

This paper describes x-ray absorption measurements made on 10 to 16-μm-thick films of ZnO, which contained 5 mol% CuO, and were grown by reactive sputtering. We compare our experimental near-edge and XAFS results to models for Cu-O phases and Cu incorporation into the ZnO lattice, and we conclude that roughly half of the Cu atoms are substitutional for Zn on the wurtzite lattice and the other half is in a highly disordered phase, which has an XAFS signature which is similar to disordered CuO. Our results are compared to other structural studies of Cu-doped ZnO materials.

We have synthesized dilute magnetic semiconductor (DMS) thin films of CdMnTe and ZnMnSe using the ion beam technique. High doses of Mn ions (∼2–5×1016/cm 2) were implanted into single crystal CdTe and into ZnSe epilayers on GaAs, forming subsurface layers of Cdl.xMnxTe and Znl-xMnxSe alloys, respectively, with x∼0.15–0.22. Fluorescence extended x-ray absorption fine structure (EXAFS) measurements on these materials reveal that the Mn atoms in the CdMnTe and ZnMnSe layers, both as-implanted and annealed, have local environments similar to their corresponding bulk-grown DMS alloys. While the anion-cation distances (Ra-c) in the annealed samples are equivalent to those in the corresponding bulk-grown DMS, the Ra-c in the asimplanted samples are slightly larger (∼0.01Å) than those in the bulk-grown DMS. This is most likely due to the implantation damage in the as-implanted materials. Our results on the Ra-c of the ion beam synthesized layers deviate significantly from Vegard's law, but are consistent with the bimodal distribution model. The EXAFS results are corroborated with results from ion beam analysis and Raman spectroscopy.

The near-EF electronic structure and Fermi surface of Bi2212 has been mapped out with ARPES. A key feature of our measured bandstructure is the existence of an extended region of flat CuO2-derived bands at EF. Comparative analysis of this data with that from NdCeCuO and YBCO7 suggests that many of the anomalous (normal) physical properties of Bi2212 and YBCO7 (NdCeCuO) may be related to the existence (absence) of such bands at EF. Superconducting gap anisotropy at least an order of magnitude larger than that of the conventional superconductors has been observed in the a-b plane of Bi2212 in ARPES. For samples with Tc of 88K, the gap size reaches a maximum of approximately 20 meV along the Cu-O bond direction, and a minimum of much smaller or vanishing magnitude 45° away. The experimental data is discussed within the context of various theoretical models. In particular, a detailed comparison with what is expected from a superconductor with a dx2-y2 order parameter is carried out, yielding a consistent picture.

The materials and electronic properties of the new cuprate superconductors are critically dependent upon both the oxygen stoichiometry and annealing history of the material. Improving Jc, Tc, and determining the underlying mechanism of superconductivity depend on a better understanding of these effects. In the study of Bi2Sr2CaCu2O8-δ we have combined standard material characterization techniques with high resolution angle resolved photoemission spectroscopy and resonant photoemission spectroscopy to illuminate these issues. Specifically, we make high quality single crystals of BSCCO and then anneal in different atmospheres and pressures. We correlate this with c-axis resistivity, a, b-plane resistivity, and resonant photoemission spectroscopy. In this way we can explain the macroscopic transport properties in terms of the electronic properties of the material determined from photoemission. We find that we can change the c-axis resistivity from non-metallic to metallic by adding oxygen and that this correlates with increased oscillator strength in the c-axis direction at the Fermi level.

Monochromatized synchrotron radiation has been employed as the excitation source for soft x-ray emission spectroscopy. In the present paper changes in the emission spectra that occur as the excitation energy is varied near the core-absorption threshold are discussed. In the case of crystalline silicon, strong variations are seen in the L2,3 emission for excitation energies up to 30 eV above threshold. These variations are shown to be dependent on the crystalline order of the material and can be interpreted in terms of restrictions on the crystal momentum that arise in an inelastic scattering description of the combined absorption and emission. On the other hand this description is less relevant to the excitation-energy dependence of ionic insulators, in which strong phonon coupling removes these restrictions on crystal momentum. In the insulators B2O3 and BN strong variations in the emission are observed at threshold, upon creation of a core exciton: the exciton affects the emission through its influence on the phonon coupling as well as on the initial and final-state screening.

The electronic structure of single-crystal Cr2O3 has been studied by Cr 2p core-level XPS and valence-band UPS spectroscopies. A cluster configuration-interaction analysis was applied to investigate the nature of the satellite in the Cr 2p core-level photoemission spectrum. It is argued that the satellite can be understood as a charge-transfer satellite, and Cr2O3 is found to be situated at the boundary between the Mott-Hubbard and the charge-transfer regimes. The values of the charge-transfer energy, Δ, the Coulomb correlation energy, U, and the ligand 2p-cation 3d hybridization energy, T, found from fitting the Cr 2p XPS spectrum were also used to analyze the valence-band UPS spectrum. The comparison between the experimental spectrum and the spectrum from theoretical fitting is fair.

A review of the technique of White Beam Synchrotron X-ray Topography is presented along with some examples of its applications in materials science. Among the topics covered are: the characterization of growth defects in KTiOPO4, ZnTe, and SiC single crystals; studies of phase transitions in perovskite-like crystals; and studies of rapid thermal processing damage in semiconductors. Methodologies for analyzing dislocations, twins (rotational, mirror and inversion twins), precipitates and other crystallographic defects, will be reviewed.

Real-time studies of the deformation behavior of a-brass bicrystals were conducted via in-situ synchrotron white beam X-ray topography (SWBXRT). The object of this work was to understand the role of internal interfaces such as grain boundaries, in controlling the mechanical behavior of materials. A brass bicrystal, in which the two grains made 5° of tilt and 11° of twist with respect to each other was grown by the Bridgman method. Observations were performed by straining the bicrystal in a microtensile stage while stop-action X-ray diffraction topographs were taken. Slip initiated in the grain with the most favorable Schmid factor at a stress level of 1.4MPa which was 5% of the macroyield stress. Since the grain boundary acted as a barrier to slip, the next grain did not slip until the dislocation pile-up at the grain boundary reached a critical value.

Synchrotron white beam x-ray topography has been used to study dislocation configurations induced in InSb single crystals by three point bending at temperatures above the brittle to ductile transition point. Semi-hexagonal dislocation loops with one long screw segment and two outcropping 60° segments, single 60° B(g) dislocation kinks on screw dislocations, and screw dislocation dipoles were observed. The relationship between these observed defect structures and the mobilities of A(g), B(g), and screw dislocations in InSb, which appear to control the plastic behavior of crystals with the sphalerite structure, is discussed. Dislocation interactions and their role in the plastic deformation process are also addressed.

Synchrotron white beam X-ray topographic studies of damage induced during the R-F electromagnetic breakdown of bi-polar diodes on silicon have been carried out. Filaments associated with damage processes in reverse bias, have been observed close to the surface of the Si epilayer, using the surface sensitive grazing Bragg-Laue technique. Ray-tracing experiments have enabled us to determine the exact lateral location of the filament to be at the edge of the metallization region, at the junction between it and the metallic contact. The influence of these results on hardening technologies is discussed.

Defect structures in large, high quality flux-grown KTP single crystals have been studied by using synchrotron white beam X-ray topography. Growth dislocations, inclusions, growth sector boundaries, growth bands and surface micro-scratches were imaged. A number of planar defects in the dislocation-free region are imaged and determined to be inversion twin lamellae (lamellar ferroelectric domains) which have never been previously reported in KTP crystals. These inversion twin lamellae were also studied by section topography. Detailed analysis of observed contrast revealed that the domain walls bounding the lamellae are faulted with a fault vector of ½[0±1±1]. This fault vector seems to be consistent with the atomic structure of KTP. A detailed analysis is presented and discussed.

Synchrotron white beam X-ray topography has been used to characterize defect structures in 6H-SiC wafers grown on (0001) seeds. Two major types of defects are observed: super screw dislocations approximately perpendicular to the basal plane and dislocation networks lying in the basal plane. The super screw dislocations, which have open cores, are growth dislocations. These dislocations act as sources and/or sinks for the glide dislocation networks. Detailed analysis and discussion of dislocation generation phenomena and Burgers vectors will be presented.

We have utilized a scanning photoemission spectromicroscope with sub-micron spatial resolution to observe microscopic Fermi level pinning on the cleaved GaAs(110) surface. We present micrographs which identify pinning that is highly localized to the vicinity of a single linear cleavage step. This extends previous work utilizing scanning Kelvin probe and imaging photoelectron microscopy conducted at lower spatial resolution. A sub-monolayer coverage of In uniformly pins the surface, thus allowing us to observe only the image contrast mechanism resulting from topography. From this one can determine the spatial extent of defects near a cleavage step. Initial observations indicate that Fermi level pinning can extend from a cleavage step over the range of 2 μm. This indicates the additional presence of defects at the adjacent surfaces of the step.