We report the results of a real-time synchrotron x-ray scattering study of the growth of TiN thin films on Si(001) substrates by RF sputtering. Our experiemnts show that the morphology of the TiN films strongly depends on growth conditions. After the nucleation and growth takes place with random crystallographic orientation at the very early stage, the films grow with a preferred orientation. Such preferred orientation was found to depend on both the sputtering power and the carrier gases used in the sputtering. Generally, the final morphology assumes either (111) or (002) crystallographic orientation. Using Ar sputtering, a cross-over effect from (002) to (111) was observed at intermediate time. The nature of the observed morphological changes is discussed.

Thin amorphous films (t=200Å) of Fe80B20 were annealed at temperatures ranging from 473K–823K and studied using extended X-ray absorption fine structure to investigate the evolution of local structure around the Fe atoms during crystallization. Modeling of the local environment around Fe using empirical standards was employed to determine the relative fraction of the crystalline phases present in annealed samples. Results illustrate the sensitivity of EXAFS in detecting the onset of crystallization in thin amorphous films and its ability to quantitatively measure the relative fraction of crystalline phases present in partially crystallized thin film samples.

We are using resonant soft x-ray fluorescence at the Advanced Light Source to probe the electronic and geometric structure of novel materials. In the resonant process, a core electron is excited by a photon whose energy is near the core binding energy. In this energy regime the absorption and emission processes are coupled, and this coupling manifests itself in several ways. In boron nitride (BN), the resonant emission spectra reflect the influence of a “spectator” electron in an unoccupied excitonic state. The resonant emission can be used to distinguish between the various bulk phases of BN, and can also be used to probe the electronic structure of a monolayer of BN buried in a bulk environment, where it is inaccessible to electron spectroscopies. For highly-oriented pyrolytic graphite (HOPG) a coherent absorption-emission process takes place in the resonant regime, whereby crystalline momentum is conserved between the core excited electron and the valence hole which remains after emission

Extended x-ray absorption fine structure measurements of a Co78Cr22 film were performed using normal and glancing incident radiation in order to investigate, respectively, the in-plane and out-of-plane local structure and chemistry. The Fourier transformed EXAFS data of the in-plane and out-of-plane structures around the Co and Cr atoms illustrates the presence of an anisotropy. Analysis of the local environments around Co for the two sample orientations indicates the presence of Co-enriched clusters, while similar studies of the Cr environments indicate preferential ordering parallel to the film plane. Quantitative analysis of the higher order Fourier transform peaks shows a greater amount of disorder perpendicular to the film plane beyond that expected for a textured hcp film. These results are consistent with earlier reports of a high density of stacking faults or twinning planes perpendicular to the growth axis, supporting the interpretation that a platelet-like texturing exists within the columnar microstructure.

Extended x-ray absorption fine structure (EXAFS) techniques have been used to investigate the local structures in Inl-xMnxAs films grown by molecular beam epitaxy (MBE) under different processing conditions. For samples grown at low substrate temperatures (near 200°C) or with a low Mn concentration (about 1 atomic%), the Mn atoms can substitute for In in the InAs host, thus indicating that III-V diluted magnetic semiconductors (DMS) can indeed be prepared by substitutional doping of magnetic impurities. On the other hand, substitution dose not take place in high Mn concentration (above 10%) samples grown at high substrate temperatures (around 300°C); these samples contain a large amount of MnAs clusters and become ferromagnetic

The magnetic properties of MnZn-ferrite are greatly affected by the distribution and valence state of the magnetic and nonmagnetic metallic ions on the tetrahedral (A) and octahedral (B) sites in the spinel ferrite unit cell. A primary factor which can affect the distribution and valence state of the metallic ions is the stoichiometry of the ferrite. In this paper we report on the results of the site occupancy of the transition metal ions in a series of MnZn-ferrite films using extended x-ray absorption fine structure (EXAFS). The EXAFS data are correlated with the film composition and those magnetic properties which are sensitive to the ionic distribution (e.g., magnetic anisotropy field and magnetization) in order to confirm the use of EXAFS as a technique for the investigation of metallic ion distribution in spinel ferrites.

The interaction of synchrotron radiation (SR) emitted from a polarizing undulator with SiO2 gel films was investigated by ellipsometry and infrared spectroscopy. The photon energy in SR was varied in the range of 6.4−17.8 eV using an Onuki-type undulator in order to study the energy dependence of the interaction. We found that an increase of refractive index, a decrease of thickness of the films and a loss of OH groups were induced by photons with energies above ˜9 eV although any changes were not observed with photons below ˜7 eV. These results suggest that SiO2 gel films are densified through electronic processes stimulated by the energetic photons.

Amorphous alloys of the binary system CaAl are known to have highly unusual electron transport properties with resistivities up to 450μΣcm and a Hall coefficient that deviates from free electron values at Ca concentrations higher than 45 atomic percent. For amorphous CaMg alloys, on the other hand, the resistivity is very much less and this great difference between the two sets of alloys is not fully understood.

We report on the correlation of photoemission and transport measurements made on two sets of amorphous CaAl and CaMg alloys prepared by magnetron sputtering in such a way that we could carry out both sets of measurements within the same UHV system. A special feature of the measurements was that the electrical resistivity was also measured in-situ using a specially designed 4-point probe to check for amorphicity and to compare with transport experiments carried out elsewhere.

Photoemission studies were carried out in the energy range 15–50 eV with tuneable synchrotron radiation enabling us to examine the Ca 3p-3d photoemission resonance in detail. The main result from the present series of experiments was that whereas in the CaAl alloys the Fermi edge developed a shoulder at high concentrations of Al, this feature was completely absent in CaMg. At the same time the intensity of the Ca 3p-3d photoemission resonance revealed the presence of d-states in both sets of alloys, indicating that the presence of these dstates cannot, by itself, explain the high resistivity of CaAl.

Chemical Vapor Deposition of Si1-x Gex – films on Si (100) and of polycrystalline Si1-x Gex, layers on SiO2 – coated substrates have been performed at a pressure of 200 Pa in the temperature range of 500°C – 800°C, correspondingly. To observe the growth process and to characterize the growing thin films at deposition conditions an optical reflection interferometer (PYRITIERS) has been used. Comparing the data obtained at growth temperature with ex- situ measurements by spectroscopic ellipsometry the temperature dependence of optical constants of SiGe films have been evaluated. The reflectivity measurements during the deposition process allow to study the quality of the heteroepitaxial film, even in the initial stage of epitaxial growth.

Soft-x-ray magnetic circular dichroism (MCD) is the difference between the absorptivity or reflectivity of left and right circularly polarized soft-x-rays at the magnetically interesting L2,3- edges of 3d transition metals or the M4,5-edges of the 4f rare earth elements. Thanks to its large absorption cross-section and strong MCD effect, this technique has become a powerful new means for probing, in an element- and site-specific manner, the magnetic properties of ultra-thin films and multilayers. Soft-x-ray MCD experiments, recently conducted at the Dragon beamline, are utilized to demonstrate the recent progress in this technique and its applications in the research of magnetic thin films.

Magnetic circular dichroism in x-ray absorption is used to investigate the in-plane, remnant magnetization of well-characterized Ni0.48/Au0.52 multilayers. Large superlattice strains are found in this multilayer system for samples with a 2nm layer pair spacing. A larger dichroism is found in the Ni 2p absorption edge for a 1.8nm than for a 4.4nm layer pair sample. The larger dichroism is consistent with a larger magnitude of in-plane strain for the Ni layers and a larger total magnetic anisotropy energy as previously shown from magnetization curves.

The effects of ferromagnetic capping layers on the perpendicular magnetic anisotropy of Ni/Cu(001) have been studied. X-ray magnetic circular dichroism was used to obtain element specific magnetic information, including hysteresis loops for both in-plane and perpendicular magnetization. A 15 ML Ni/Cu(001) film maintains its perpendicular magnetic orientation after the addition of a 2.5 ML Fe capping layer. The Fe capping layer reduces the area of the Ni hysteresis loop by a factor of 2.0. A 2.0 ML capping layer of Co on 15 ML Ni/Cu(001) switches the easy axis of magnetization from perpendicular to in-plane.

We have utilized Ginzberg-Landau mean field theory to analyze the branching ratio and soft X-ray magnetic circular dichroism measurements of the L3 and L2 adsorption edges of thin Mn overlayers on ferromagnetic fcc Co(001) at room temperature. We have determined a short range magnetic correlation of 4.25Å and that the long range magnetic magnetic order has a decay length of 1.29Å. These results indicate that the first monolayer of Mn ferromagnetically couple with the Co substrate. The paramagnetic Mn layer exhibits short range magnetic order, but lacks long range magnetic order. Due to the exponential decrease of both the branching ratio and dichroism signals, we have concluded that the magnetization of the Mn overlayer is substrate induced.

The results of magnetic circular x-ray dichroism (MCXD) measurements and extended x-ray absorption fine structure measurements (EXAFS) of the Fe K-edges of textured Fe(110)/Pd(111) multilayers are reported. The EXAFS results indicates that the iron in the system goes from bcc to a more densely packed system as the thickness of the iron layer is decreased. The magnetic properties were measured by SQUID magnetometry from 5 - 350 K. For all the samples, the saturation magnetization was significantly enhanced over the bulk values indicating the interface Pd atoms are polarized by the Fe layer. The enhancement corresponds to a moment of ≈2.5μB per interface Pd atom.

Soft X-Ray Magnetic circular dichroism (SX-MCD) can be used to obtain element-specific magnetic hysteresis curves and to elucidate the two- and three-dimensional magnetization reversal processes for each constituent magnetic element of a heteromagnetic system. As a demonstration, two systems which exhibit in-plane magnetization reversal are studied: a thin Fe (100) singlecrystal film and a Fe1-xCox/Mn/Fel-xCox trilayer. The results for both systems show that the magnetic moment vector reverses via a combination of coherent rotation toward the nearest in-plane magnetically easy axis followed by the formation of orthogonal <100> domains which rapidly sweep across the sample. In the case of the trilayer, the moment reversal process is significantly more complex due to a strong ∼90° coupling between the magnetic moments of the two FeCo layers. By using element-specific vector magnetometry (ESVM), the details of this reversal process are revealed. Furthermore, the results of the SX-MCD for Mn show that Mn possesses a ferromagnetically aligned net magnetic moment which depicts a 2D magnetization behavior different than that for either Fe or Co.

The first structural determination with spin-polarized, energy-dependent photoelectron diffraction using circularly-polarized x-rays is reported for Fe films on Cu(001). Circularly-polarized x-rays produce spin-polarized photoelectrons from the Fe 2p doublet, and intensity asymmetries in the 2p3/2 level are observed. Fully spin-specific multiple scattering calculations reproduce the experimentally-determined energy and angular dependences. A new analytical procedure which focuses upon intensity variations due to spin-dependent diffraction is introduced. A sensitivity to local geometric and magnetic structure is demonstrated.

Using a recently developed spin-polarized, fully relativistic, multiple scattering approach based on the layer KKR Green function method, we have reproduced the Fe 3p angle-resolved soft x-ray photoemission spectra and analyzed the associated large magnetic dichroism effects for excitation with both linearly and circularly polarized light. Comparison between theory and experiment yields a spin-orbit splitting of 1.0 – 1.2 eV and an exchange splitting of 0.9 – 1.0 eV for Fe 3p. These values are 50 – 100 % larger than those hitherto obtained experimentally.

Quantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The H/Si ratios, as large as 1.2, were independently confirmed by ir-absorption and α-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 Å. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.

X ray standing wave measurements were undertaken to study the bonding position of Sb adatoms on the Sb-saturated Si(001)−(2×1) surface. Using the (004) and (022) Bragg reflections, we find that the Sb atoms form dimers, and that the center of the Sb ad-dimers lies 1.64 Å above the bulk-like Si(004) surface atomic plane. This work describes the extraction of structural parameters for a dimerized surface from in-plane measurements. Our results are compared to two structural models consisting of dimers whose bonds are parallel to the surface plane and whose centers are either shifted or unshifted (parallel to the dimer bond direction) relative to the underlying substrate planes. We thus find two special cases consistent with our data: one with symmetric (unshifted) dimers having a dimer bond length of 2.81 Å, and the other with midpointshifted dimers, having a bond length of 2.88 Å and a lateral shift of 0.21 Å.

Soft x-ray photoelectron spectroscopy (SXPS) from the S 2p core level has been used to study adsorbate induced reconstruction, identify reaction intermediates and study reaction kinetics on the Ni(111) surface. The S 2p binding energy is affected by the nature of the surface adsorption site. It has been determined from the number of S 2p states and their relative binding energies that adsorbed S induces a reconstruction of the Ni(111) surface and that the S adsorbs in fourfold sites on terraces and in troughs. S 2p SXPS has also been used to identify adsorbed species during the thermal decomposition of methanethiol on Ni(111). CH3SH adsorbs as CH 3S- at low temperatures. Above 200 K, the CH3S- changes adsorption site and the C-S bond begins to cleave. The relative concentrations of CH3S- in the two different sites and of atomic S have been monitored as a function of temperature and initial coverage. As a result of the sensitivity and resolution available in SXPS, reactions rates and kinetic parameters have been obtained for the decomposition of benzenethiol on Ni(111) by monitoring the changes in the surface composition continuously as a function of temperature and time.