T. A. Callcott

First experimental results from IBM/TENN/TULANE/LLNL/LBL undulator beamline at the advanced light source

The IBM/TENN/TULANE/LLNL/LBL Beamline 8.0 at the advanced light source combining a 5.0 cm, 89 period undulator with a high‐throughput, high‐resolution spherical grating monochromator, provides a powerful excitation source over a spectral range of 70–1200 eV for surface physics and material science research. The beamline progress and the first experimental results obtained with a fluorescence end station on graphite and titanium oxides are presented here. The dispersive features in K emission spectra of graphite excited near threshold, and found a clear relationship between them and graphite band structure are observed. The monochromator is operated at a resolving power of roughly 2000, while the spectrometer has a resolving power of 400 for these fluorescence experiments.

Observation of intermixing at the buried CdS/Cu(In, Ga)Se2 thin film solar cell heterojunction

A combination of x-ray emission spectroscopy and x-ray photoelectron spectroscopy using high brightness synchrotron radiation has been employed to investigate the electronic and chemical structure of the buried CdS/Cu(In, Ga)Se2 interface, which is the active interface in highly efficient thin film solar cells. In contrast to the conventional model of an abrupt interface, intermixing processes involving the elements S, Se, and In have been identified. The results shed light on the electronic structure and interface formation processes of semiconductor heterojunctions and demonstrate a powerful tool for investigating buried interfaces in general.

Photo‐oxidation of electroluminescent polymers studied by core‐level photoabsorption spectroscopy

The C 1s and O 1s core‐level photoabsorption spectra of poly[2‐methoxy,5‐(2′‐ethyl‐ hexoxy)‐1,4‐phenylene vinylene] (MEH‐PPV) before and after exposure O2 and broadband visible light were recorded to determine the degradation pathway for this polymer. The change in the O 1s spectra as a function of exposure demonstrates that the O adds to the polymer chain to form a carbonyl group. Exposure to only O2 or only light causes no change in the C 1s or O 1s spectra. In the C 1s spectra, the change in the dependence on the photon angle of incidence after exposure demonstrates that O attacks the polymer at the double bond in the vinyl group thereby altering the extended conjugation of the polymer.

High‐efficiency soft x‐ray emission spectrometer for use with synchrotron radiation excitation

A new soft x‐ray spectrometer designed for use with photon excitation from synchrotron light sources is described and characterized. Special design features, including a close‐spaced input slit, large toroidal gratings, and a two‐dimensional charge‐coupled‐device array based detector system, provide exceptional measuring efficiency in a 5‐m Rowland circle design. Descriptions are given of the spectrometer’s mechanical and detector design, and of calibration and alignment procedures. The beam line providing photon excitation from a synchrotron light source is described. Typical electron beam and/or photon excited emission spectra of Al, Si, and LiF are presented and compared with those produced by other instruments.

Stoichiometry reversal in the growth of thin oxynitride films on Si(100) surfaces

Synchrotron‐based O 1s and N 1s photoabsorption spectroscopy, O 1s, N 1s, Si 2p, and valence‐band photoelectron spectroscopy (PES), and medium energy ion scattering (MEIS) have been used to determine the composition and thickness of oxynitride films grown in N2O on a Si(100) surface. Core‐level photoabsorption spectroscopy is shown to be a very sensitive probe capable of measuring surface coverages lower than 0.1 monolayers of N (6.5×1013 N atoms/cm2). Film composition was monitored as a function of growth to demonstrate the stoichiometry reversal from primarily N‐terminated surfaces in thin films to nearly pure SiO2 in films thicker than ∼20 A. A sample with a 60 A oxynitride film was depth profiled by etching in HF and was shown, via N 1s absorption spectroscopy, to have N segregation within 10 A above the Si/SiO2 interface. Core‐level PES and MEIS were used to study the growth mechanisms of oxynitrides on Si(100) and these data were used to create a schematic phase diagram showing three distinct region...

Experimental and theoretical investigation of the electronic structure of transition metal sulphides: CuS, and

Results of measurements of sulphur x-ray emission spectra of CuS and , excited by synchrotron radiation near the sulphur 2p threshold, are presented. An excitation energy dependence of the sulphur XES is only observed for CuS, and is attributed to the presence of inequivalent sulphur atoms in CuS. Two thirds of the sulphur atoms form dimers (as in ) while the remaining ones are single (as in ). This conclusion is confirmed by XPS measurements and LMTO band structure calculations for CuS, and . It is shown that selective excitation of x-ray emission valence spectra can be used to determine the atom-decomposed partial density of states for inequivalent sites in solids, occupied by chemically identical species.

Soft-x-ray spectroscopy measurements of the p-like density of states of B in MgB[d2] and evidence for surface boron oxides on exposed surfaces - art no. 132504

Soft-x-ray absorption and fluorescence measurements are reported for the K edge of B in MgB{sub 2}. The measurements confirm a high density of B p{sub xy}({sigma}) states at the Fermi edge and extending to approximately 0.9 eV above the edge. A strong resonance is observed in elastic scattering through a core exciton derived from out-of-plane p{sub z}({pi}{sup *}) states. Another strong resonance, observed in both elastic and inelastic spectra, is identified as a product of surface boron oxides.

LOCALIZATION OF NA IMPURITIES AT THE BURIED CDS/CU(IN, GA)SE2 HETEROJUNCTION

We demonstrate a general approach to identify and locate minority species at buried interfaces which are of fundamental interest in many fields of solid state research. The approach combines soft x-ray emission for bulk and photoelectron spectroscopy for surface sensitivity. In the present study, the interface between a thin CdS layer and a Cu(In, Ga)Se2 thin film solar cell absorber has been investigated, showing that Na impurities are localized at the buried CdS/Cu(In, Ga)Se2 heterojunction.

Soft X-ray emission spectroscopy of early transition metal compounds

Abstract Soft X-ray emission studies for several early transition metal compounds, such as Sc, Ti and V compounds, have been studied. Raman scattering was found at the 2p→3d excitation in the transition metal compounds. The elementary excitation of the Raman spectrum is mainly elucidated by the d–d transition within the 3d bands, as well as the interband transition from the O 2p valence band to the conduction band, which consists mainly of transition metal 3d states. The charge transfer transition due to the localized electron picture is dominant in the soft X-ray spectra of Sc compounds. Raman scattering is a powerful tool in the study of the electronic structure of transition metal compounds.

Electronic structures of the tungsten borides WB, W2B and W2B5

Abstract The electronic structures of the tungsten borides WB, W 2 B and W 2 B 5 were studied experimentally and theoretically. Using monochromatic synchrotron radiation as the excitation source, soft X-ray emission and absorption spectroscopic techniques were employed to probe the occupied and unoccupied states of the valence band, respectively. The linear muffin-tin orbital method was used to calculate the ground state electronic properties of these compounds. The experimental spectroscopic data and the calculated angular momentum- and site-projected densities of states yielded new useful information regarding bonding and hybridization in these materials.