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spring 1998 logo1998 MRS Spring Meeting & Exhibit

April 13 - 17, 1998 | San Francisco
Meeting Chairs: John A. Emerson, Ronald Gibala, Caroline A. Ross, Leo J. Schowalter

Symposium V—Application of Synchrotron Radiation Techniques to Materials Science


Susan Mini 
Dept of Physics 
Northern Illinois Univ 
DeKalb, IL 60115 

Dale Perry
Lawrence Berkeley National Laboratory
MS 70A-1150
Berkeley, CA 94750

Stuart Stock 
School of Materials Science & Engr 
Georgia Inst of Technology 
Atlanta, GA 30332-0245 L-357

Louis Terminello
Dept of Chemistry & Matls Science
Lawrence Livermore National Laboratory
Livermore, CA 94550

Symposium Support 
*Argonne National Laboratory (APS) 
*Blake Industries, Inc. 
*Brookhaven National Laboratory (NSLS) 
*Lawrence Berkeley National Laboratory (ALS) 
*Lawrence Livermore National Laboratory (Dept of MS&C) 
*Luxel Corporation 
*Physical Electronics 

1998 Spring Exhibitor 

Proceedings published as Volume 524 
of the Materials Research Society 
Symposium Proceedings Series.

* Invited paper

Chair: Dale L. Perry 
Monday Morning, April 13, 1998 
Salon 13
9:15 AM V1.1 HIGH-RESOLUTION X-RAY PHOTOEMISSION ELECTRON MICROSCOPY AT THE ADVANCED LIGHT SOURCE. Thomas Stammler, Simone Anders, Howard Padmore, Lawrence Berkeley National Laboratory, Berkeley, CA; Joachim Stohr, IBM Almaden Research Center, San Jose, CA. 

The combination of x-ray spectroscopy and microscopy opens a wide field of new applications in materials research and has proven to be a powerful tool to investigate simultaneously topological, elemental, chemical state, and magnetic properties of surfaces, thin films, and multilayers. Using synchrotron radiation as a tunable, polarized photon source allows near-edge x-ray absorption fine structure spectroscopy (NEXAFS/ XANES) and x-ray magnetic dichroism (XMD) experiments to be performed with high spatial resolution. As a full-field imaging technique X-PEEM is inherently fast and allows in situ imaging of microscopic surface structures and magnetic-surface imaging at video rates. With field strengths of the extraction field of the objective lens in the microscope higher than the onset field strength of high field emission yield samples we are able to study the nature of the emission sites of possible flat panel display materials. Examples of the application of X-PEEM to materials research in the fields of magnetic domain imaging of magnetic recording materials, elemental and bonding contrast imaging of hard disk coatings, and field emission studies will be presented. 

9:30 AM V1.2 
Abstract Withdrawn. 

9:45 AM V1.3 
ELECTRONIC VALENCE STRUCTURE OF SINGLE CRYSTAL GRAPHITE. C. Heske, Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA; R. Treusch, F.J. Himpsel, Dept of Physics, Univ of Wisconsin-Madison, Madison, WI; S. Kakar, Dept of Applied Science, Univ of California at Davis/Livermore, Livermore, CA; L.J. Terminello, Lawrence Livermore National Lab, Livermore, CA; H.J. Weyer, SLS Project, Paul-Scherrer Inst, Villigen PSI, SWITZERLAND; E.L. Shirley, National Inst of Standards and Technology, Optical Technology Div, Gaithersburg, MD. 

Despite a long history of experimental and theoretical investigations, several aspects of the electronic valence structure of graphite have still to be clarified. For example the valence band width, which constitutes the single most important quantity characterizing the electronic structure of a solid, shows a large scatter in published experimental and theoretical values. In particular, valence band widths derived from state-of-the art local density theory (about 19.5 eV) differ significantly from results obtained by quasiparticle calculations, where a band widening of 10 % is predicted (21.5 eV). We will present a detailed investigation of the valence electronic structure of single-crystal graphite by synchrotron-based, angle-resolved photoemission using an imaging photoelectron spectrometer at beamline 8.0 of the Advanced Light Source, Lawrence Berkeley National Laboratory. Photoelectron angular distribution images at a fixed kinetic electron energy were collected for a variety of photon energies. These images represent constant-energy contours in the graphite band structure, and a set of such images can be assembled into a complete band structure of graphite. The valence band width, as derived from a parabolic fit of the bottom of the band, was determined to 21.9 eV (+0.2/-0.4 eV), which is in good agreement with the recent quasiparticle calculations. The full set of constant-energy contours will be compared with theoretical simulations of the photoelectron angular distributions. The band structure will be discussed with respect to Brillouin-zone selection effects published earlier (E.L. Shirley et al., Phys. Rev B 51, 13614 (1995)). Furthermore, we will present an investigation of the Fermi surface of graphite by recording angular distribution images near the Fermi energy for a large range of final-state energies. The observed tubulation effects and their connection with interlayer coupling and dispersion perpendicular to the sample surface will be discussed. 

10:30 AM *V1.4 
SPECTROSCOPIC STUDIES OF LOW DIELECTRIC CONSTANT HYDRO- AND FLUOROCARBON FILMS. Yanjun Ma, Hongning Yang, Sharp Microelectronics, Camas, WA; J. Guo, C. Sathe, A. Agui, J. Nordgren, Uppsala University, Uppsala, SWEDEN. 

Materials with low dielectric constants (low-k) is one of the most active research areas in the semiconductor industry. Together with copper metallization, low-k materials are needed to reduce the interconnect RC delay in further scaling of integrated circuits towards deep sub-quarter micron dimensions. In this work, we report spectroscopic studies on PECVD prepared fluorinated amorphous carbon and vacuum deposited parylene-N films, two of the most promising materials for replacing SiO2 as the intermetal dielectric (IMD). High resolution carbon and fluorine K-edge x-ray absorption and emission spectra taken at the Advanced Light Source (ALS) using a state-of-the-art soft x-ray spectrometer from Uppsala University will be presented. They are compared with the spectra of amorphous carbon, graphite, and diamond. The electronic structures of these films will be discussed. 

11:00 AM V1.5 
RESONANT PHOTOEMISSION STUDIES OF THE 5f LEVEL IN URANIUM ALLOYS. Jonathan D. Denlinger, Yuxin Zhang, James W. Allen, Univ of Michigan, Dept of Physics, Ann Arbor, MI; See-Hun Yang, Se-Jung Oh, Seoul National Univ, Dept of Physics, Seoul, KOREA; En-Jin Cho, Chonnam National Univ, KOREA; W.P. Ellis, Los Alamos National Laboratory, Los Alamos, NM; Don A. Gajewski, Ricky C. Chau, M. Brian Maple, Univ of California, Dept of Physics, San Diego, CA. 

The valence f-electrons of rare-earth and actinide materials exhibit extreme examples of strongly correlated solid state electronic phenomena including mixed valence, heavy Fermions and Kondo effects. Direct electron spectroscopy measurements of the f-electrons in Ce and Yb materials have been modeled successfully with the single-impurity Anderson model and related to these low-energy transport properties. However, the understanding of actinide (i.e. uranium) spectra is much more primitive due to the general presence of diffuse spectral weight bunched near the Fermi level. Three uranium alloy systems, Y(1-x)U(x)Pd(3) , U(Pd(x)Pt(1-x))(3)and U(Pd(x)Cu(1-x))(5) , have been studied with core-level, valence and inverse photoelectron spectroscopies. At the Advanced Light Source synchrotron (Beamline 7.0), resonant photoemission at the 5d absorption edge with improved resolution (60 meV) and a finely focused beam spot (100 m) have revealed new structure in the U 5f spectra. Also, for the case of (Y,U)Pd(3), the high flux allowed measurement of weak uranium intensities down to 1% dilution of uranium atoms. In each of the three systems, newly observed is spectral weight transfer between two distinct peaks, a sharp peak right at E(F) and a second sideband at deeper binding energy, as the overall U 5f spectral weight approaches E(F) upon deviation of the stoichiometry away from the common endpoint alloy of UPd(3). The systematic variation of the U 5f spectral weight measured for (Y,U)Pd(3) is generically consistent with the Anderson impurity model and results of quantitative modeling of the spectra will be presented. 

11:15 AM V1.6 
ANGLE-RESOLVED PHOTOEMISSION STUDY OF PtGa2 AND AuA12L.-S. Hsu, Department of Physics, National Chang-Hua University of Education, Chang-Hua, TAIWAN and Randall Laboratory, University of Michigan, Ann Arbor, MI; J.D. Denlinger, J.W. Allen, Randall Laboratory, University of Michigan, Ann Arbor, MI. 

Angle-resolved photoemission spectroscopic (ARPES) study of the (111) face of PtGa2 and the (111) and (100) faces of AuAl2 were carried out at the beamline 7.0 of the Advanced Light Source. Low energy electron diffraction and x-ray photoelectron diffraction were first performed to show the orderliness of the sample surfaces and to check the crystal-axis directions, respectively. The ARPES data were compared with the band-structure calculations [1]. The 5d-band splittings were used to derive the spin-orbit and the crystal-field parameters of these intermetallic compounds. The Pt and Au 5d-band intensities modulated with photon energy and displayed solid-state effects. The Pt and Au s-p band crossing at the Fermi energy were resolved. The Fermi surfaces of these three faces were mapped and compared with the results obtained from the de Haas-van Alphen measurement on AuAl2 [2]. 

11:30 AM V1.7 
FERMI CONTOURS, CHEMICAL BONDING, AND SURFACE POTENTIAL GRADIENT FOR ALKALIS ADSORBED ONTO MO(110) AND W(110). E. Rotenberg, Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA; S.D. Kevan, Physics Department, University of Oregon, Eugene, OR.; J.W. Chung, Physics Department, POSTECH, Pohang, KOREA. 

Most of the enduring and interesting questions concerning alkali adsorption - the nature of the adsorbate chemical bond, the formation and screening of the adsorbate dipole layer, modification of surface chemical and physical processes, etc. - are directly impacted by surface electronic states near the Fermi level. We report new high resolution photoemission results for several alkalis adsorbed onto Mo(110) and W(110). The Fermi contours evolve systematically as a function of alkali coverage so that detailed information about the motion of charge into various bands can be deduced. The data also exhibit formation of alkali-induced bands having fairly well-defined Fermi contours. The appearance of these is directly correlated with the onset of emission of alkali core-valence-valence Auger peaks. These results both indicate initial occupation of a predominantly alkali-associated valence level near the work function minimum. Finally, we delineate an important role played by the spin-orbit interaction, which lifts the Kramerís degeneracy of certain bands. This provides a new and very useful local probe of the potential gradients in the vicinity of the surface as a function of alkali coverage. 

Chair: Susan M. Mini 
Monday Afternoon, April 13, 1998 
Salon 13
1:30 PM V2.1 
X-RAY ABSORPTION FINE STRUCTURES (XAFS) STUDIES OF COBALT SILICIDE THIN FILMS. S. J. Naftel, I. Coulthard, Y. Hu, T. K. Sham and M. Zinke-Allmang, University of Western Ontario, London, CANADA. 

Cobalt silicide thin films prepared on Si(100) wafers, have been studied by x-ray absorption near edge structures (XANES) at the Si K-, L2,3- and Co K-edges, utilizing both total electron (TEY) and fluoresence yield (FLY) detection, as well as extended x-ray absorption fine structure (EXAFS) at the Co K-edge. Samples made using DC sputter deposition on clean Si surfaces and MBE were studied along with a bulk CoSi2 sample. XANES and EXAFS provides information about the electronic structure and morphology of the films. It was found that the films studied have essentially the same structure as bulk CoSi2. Both the spectroscopy and materials characterization aspects of XAFS are discussed. 

1:45 PM V2.2 
ELECTRONIC EFFECTS AT INTERFACES IN Cu/TRANSITION METAL (Cr, Mo, W, Ta, Re, W3Re, Cr3C2) MULTILAYERS. A.F. Bello, T. Van Buuren, J.E. Klepeis, T.W. Barbee, Jr., Lawrence Livermore National Laboratory, Livermore, CA. 

Interfacial electronic effects between Cu and the transition metals Cr, Mo, W, Ta, Re, W3Re, Cr3C2 are investigated by determining the strength of the white line absorption resonances on the L3 and L2 edges of Cu in multilayers. X-ray absorption (XAS) was performed to study the white lines, which are directly related to the unoccupied states of Cu in the multilayers. The metallic multilayers are 2 nm in period and 200 nm in total thickness. Each period contains 5 monolayers of Cu and 5 monolayers of the transition metal. These immiscible material pairs are ideal structures to investigate electronic effects at the interface as approximately 40% of the atoms are at interfaces and these materials form no compounds and exhibit terminal solid solubility. In the L-edge XAS of bulk Cu metal, only weak white lines are observed since all the d-orbitals are filled. In the L-edge XAS of Cu in the Cu/transition metal multilayers, however, enhanced Cu white lines are observed. This is attributed to charge transfer from the interfacial Cu d-orbital to the transition metal layers. Analysis of the white line enhancement enables calculation of the charge transfer calculation from the Cu to the transition metal. Cu in Cu/Cr shows a charge transfer of about 0.04 electrons/interfacial Cu atom, while Cu in Cu/Ta transfers about 0.50 electrons/interfacial Cu atom. Charge transfer in the remaining samples has values between these two. Calculations of the Cu density of states in the multilayers are compared to the observed spectra. This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. TVB was supported by the Division of Materials Science, Office of Basic Energy Science, U.S. DOE. Part of this work was done at the ALS and at SSRL, which are supported by the DOE. 

2:00 PM V2.3 
EXTENDED X-RAY ABSORPTION FINE STRUCTURE STUDY OF Gd1-xCaxBa2Cu3O. C. L. Chang, H. Y. Tsay, Dept of Physics, Tamkang University, Tamsui, TAIWAN; J. F. Lee, Synchrotron Radiation Research Center, Hsinchu, TAIWAN. 

The substitution of Ca for rare earth in RBa2Cu3O (R=rare earth) generates excess holes in the 123 system, and Tc is supressed due to the over doping effect. On the other hand, it has been known that the Ca doping cointroduces oxygen vacancies which reduces the number of generated holes. However, there has been some controversy as to whether the Ca is introcuced into the R or Ba site, the oxygen vacacies are produced in the CuO2 plane or CuO chain sites. We present Ca K edge, Gd LIII edge and Cu K edge extended x-ray absorption fine structure data for a series of Gd1-xCaxBa2Cu3O samples with x=0, 0.1 and 0.2. Our data indicate that Ca is located in the R site, there is no observable change of oxygen content in the CuO2 plane and that the increased Ca concentration causes a higher disorder in the local environment around the rare earth site. 

2:15 PM *V2.4 
AXS AND DAFS STUDIES OF SHORT-AND INTERMEDIATE-RANGE ORDER IN GLASSES. David L. Price, Marie-Louise Saboungi, Pascale Armand*, Argonne National Lab., Argonne, IL; David E. Cox, Brookhaven National Lab., Upton, NY. *Present address: CNRS Montpellier, Lab. Physicochimie des Materiaux Solides, Montpellier, FRANCE. 

The "first sharp diffraction peak" (FSDP), the strong diffraction peak seen at low wave vector in oxide and chalcogenide glasses, is a signature of intermediate-range order in the glass network. Despite a substantial body of work with diffraction experiments and computer simulation, its nature and origins remain controversial. The Diffraction Anomalous Fine Structure (DAFS) technique combines the short-range selectivity of XAFS with the long-range structural analysis of x-ray diffraction, and provides structural information not available from these techniques alone or in combination. As such it should throw light on the question of what local atomic arrangements are involved in the scattering that gives rise to the FSDP. In a first experiment at X-7A at NSLS we have made DAFS measurements around the first two diffraction peaks in two typical glasses, GeSe2 and GeO2 . In the first case, partial structure factors are available from neutron diffraction with isotope substitution, and in the second, partial structure factor information is available from a combination of neutron and anomalous x-ray diffraction, so that considerable information is available to help interpret the DAFS data. We report results of this first experiment, conclusions that may be drawn about intermediate-range order in the glasses, and prospects for the future use of the DAFS technique in disordered systems. This work was supported by the U.S. Department of Energy, Materials Sciences, Basic Energy Sciences, under Contract No. W-31-109-ENG-38 

2:45 PM V2.5 
ELECTRONIC STRUCTURE OF GERMANIUM NANOCLUSTERS. S. Kakar1, T. van Buuren2, R. Treusch3, C. Heske4, F.J. Himpsel3, L.L. Chase2, and L.J. Terminello2,11Department of Applied Science, University of California at Davis/Livermore, Livermore, CA; 2Chemical and Materials Science Department, Lawrence Livermore National Laboratory, Livermore, CA; 3Department of Physics, University of Wisconsin, WI; 4Lawrence Berkeley National Laboratory, Berkeley, CA. 

There have been recent observations of efficient visible luminescence from nanometer sized germanium clusters. Alternative explantations ranging from the quantum confinement of electron-hole pairs to the presence of germanium oxide have been advanced to explain these observations. To shed light on this issue we have used photoelectron spectroscopy and x-ray absorption spectroscopy to study the electronic structure of germanium nanoclusters as a function of their size. The nanoclusters are produced by thermal evaporation of germaniun in an ambient atmosphere of argon and deposited on a substrate. The size-distribution and morphology of the clusters is varied by changing the evaporation temperature and argon pressure, and is characterized in-situ by scanning tunneling microscopy and ex-situ by atomic force microscopy. Our spectroscopic data probe the changes in electronic density of states in the valence and conduction band of nanoclusters and exhibit clear dependence on cluster size. For example, the valence band edge derived from the photoemission data shows a shift towards lower energy with decreasing cluster size. On the other hand, the x-ray absorption data reveal concomitant shift to higher energies. The resulting widening of the gap is discussed in view of quantum confinement effects as well as other competing hypotheses. 
Work supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract W-7405-ENG-48, and the NSF under contract DMR-9632527. 

3:30 PM V2.6 
MANGANESE PARTICULATE FROM VEHICLES USING MMT FUEL. Joe Wong, Steven Deutsch, Carlos Colmenares, John G. Reynolds, University of California, Lawrence Livermore National Lab, Livermore, CA; Joe Roos, I. Smith, Ben Fort, Ethyl Corporation, Richmond, VA. 

This paper presents results from an extensive test program commissioned by Ethyl Corporation (Ethyl) and conducted by Lawrence Livermore National Laboratory (LLNL) and other independent laboratories. The goal of the overall effort was to identify the basic characteristics, including species and size range, of manganese particulates emitted from vehicles operating on fuel containing methylcyclopentadienyl manganese tricarbonyl (MMT). Studies were conducted with fuel containing MMT at a concentration of 0.03125 gram manganese per gallon. The purpose of the test program reported here was to identify, in accordance with regulations established by the U. S. Environmental Protection Agency, under its fuel and fuel additive registration testing program (40 C.F.R. Part 79), which manganese particulate should be used in a combustion emission health testing program for MMT. The investigations at LLNL by XAS L-edge, K-edge, and ESCA, showed the following characteristics of particles in vehicle exhaust: (1) Respirable size particulate, those with a mass median aerodynamic diameter of 2.5 microns (mm) or less (PM2.5), contained manganese primarily in the form of a divalent manganese phosphate. (2) Manganese in total suspended particulate samples was divalent and continued phosphate (and/or sulfate) as well as other species. 

3:45 PM V2.7 
CHARACTERIZATION OF SILVER BINDING IN CRYPTOMELANE BY X-RAY ABSORPTION SPECTROSCOPY. R. Ravikumar, D.W. Fuerstenau, University of California at Berkeley, Dept of Materials Science and Mineral Engineering, Berkeley, CA; G.A. Waychunas, Stanford University, Center for Materials Research, Stanford, CA. 

Using silver K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, two different samples of silver-containing manganese oxide were analyzed in the fluorescence mode. For the first sample, silver ions from solution were sorbed onto a model manganese oxide phase, namely cryptomelane (KxMn8O16, where 1<x<2). The structure of cryptomelane is made up of [MnO6]8 octahedra in an edge and corner sharing geometry with regular holes or tunnels that are the sites for the potassium ions. Cryptomelane is quite widely present in silver-bearing ore bodies containing manganese oxides. The second sample was a silver-manganese oxide from Colorado. Theoretical phase and amplitudes between silver and the other atoms in the structure (silver, manganese, potassium and oxygen) were extracted from a calculation of the idealized lattice structure where silver is in the tunnel sites. From the EXAFS analysis, silver was found to occupy two different sites in the synthetic sample. The peaks in the radial distribution function correspond to distances of 2.23 Å, 2.87 Å, and 3.67 Å. The latter two correspond to the silver-silver distance in the tunnels and the silver-manganese distance in the lattice respectively. The first peak at 2.23 Å  corresponds to silver in a distribution of two and four-fold coordination sites with oxygen. The natural samples from Colorado also exhibited a very similar coordination distance as the synthetic samples. The two and four-fold coordinated oxygen sites may be on the surface of the manganese oxide or inside the tunnels where the silver could be occupying an off-center position. In the low temperature spectrum of the synthetic sample at 10 K, the 2.23 Å  peak was found to be missing and the amplitude of the 2.87 Å  peak was approximately three times larger than the corresponding room temperature sample. The large silver-silver back scattering could overwhelm the silver-oxygen back scattering, such that this 2.23 Å  peak may be buried under the broad 2.87 Å  peak. 

4:00 PM V2.8 
SYNCHRONTRON X-RAY ABSORPTION STUDIES OF ATOMIC-LEVEL ALLOYING IN IMMISCIBLE SYSTEMS. J.-H. He, P.J. Schilling and E. Ma, Center for Advanced Microstructures and Devices (CAMD) and Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA. 

An X-ray absorption beamline has been developed recently at the electron storage ring of the LSU Center for Advanced Microstructures and Devices. Using Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES), we have studied the local atomic environments in immiscible mixtures processed by high-energy ball milling, a mechanical alloying technique involving heavy deformation. By examining the local coordinations and bond distances, it is concluded that atomic-level alloying can indeed be induced between Cu and Fe through milling at room temperature, forming substitutional fcc and bcc solid solutions. In addition to single-phase regions, a two-phase region consisting of fcc/bcc solutions has been found after milling at both room temperature and liquid nitrogen temperature. An attempt has been made to extract phase compositions and fractions from XANES data. The local structure evolution of alloyed solid solutions upon prolonged milling has also been followed using EXAFS/XANES. In contrast to the Cu-Fe system, no solid solution formation is detectable in milled Ag-Fe and Cu-Ta mixtures. This work is a clear demonstration of the power of synchrotron EXAFS/XANES experiments in monitoring nonequilibrium alloying on the atomic level. At the same time, the results provide direct experimental evidence of the capability as well as limitations of high-energy ball milling to alloy immiscible elements. 

4:15 PM V2.9 
DIRECT CORRELATION OF SOLAR CELL PERFORMANCE WITH METAL IMPURITY DISTRIBUTIONS IN POLYCRYSTALLINE-SILICON USING SYNCHROTRON-BASED X-RAY ANALYSIS. Scott A. McHugo, A.C. Thompson, T. Stammler, S. Anders, Lawrence Berkeley National Laboratory, Berkeley, CA; H. Hieslmair, C. Flink, E.R. Weber, University of California at Berkeley, CA; B. Sopori, National Renewable Energy Laboratory, Golden, CO; M. Imaizumi, M. Yamaguchi, Toyota Technological Institute, Nagoya, JAPAN; I. Perichaud, S. Martinuzzi, LPSDO, Marselle, FRANCE; M. Werner, MPI-Halle, GERMANY; M. Rinio, H.J. Möller, University of Freiberg, GERMANY. 

Polycrystalline silicon solar cells can be made with moderate cell efficiencies and low cost, which makes the cells cost competitive for terrestrial power generation. However, this material typically has regions with high minority carrier recombination, which severely degrades cell performance. Past research has shown high rescombination regions possess a high density of dislocations or microdefects. In general, dislocations or other defect clusters in silicon can have a significant recombination activity when decorated with transition metals. The work presented here directly measures metal impurity distibutions and their chemical state (e.g. FeC or FeSi2...) in high carrier recombination regions of as-grown and fully processed polycrystalline silicon. Synchrotron-based x-ray fluorescence and near edge x-ray absorption spectroscopy mapping, with a spatial resolution of 0.3-1m, were used to determine impurity distributions and chemical state, respectively, in high recombination regions. We have detected iron, chromium, nickel and copper impurities in these regions and have identified their chemical state. The impurities were typically found at dislocations and grain boundaries. The distributions of these impurities directly correlated with high recombination regions in both as-grown and fully processed material. These results indicate impurities are the cause for high carrier recombination regions in polycrystalline silicon. Since the impurities remain after complete cell processing, the results also suggest the processing steps should be modified to ensure complete impurity removal and realization of maximum solar cell efficiency. 

4:30 PM V2.10 

Polynuclear iron(II) complexes of the composition FeL3A2 where L=1,2,4-triazole (trz), 4-amino-1,2,4-triazole (atrz), A = Br-, BF4-, NO3-, ClO4-, as well as magnetically diluted phases FexZn1-x (atrz)3(NO3)2 have been synthesized and characterized.