Correlating Morphology with Electronic and Photoluminescence Properties in Oxidized Silicon Nanoclusters
Professor John Carlisle
Department of Physics, Virginia Commonwealth University, Virginia, U.S.A.
Quantum size effects in nanostructured materials are of increasing interest in both basic science and applications. The dependence of quantum size effects on bonding structure and morphology in oxidized silicon nanoclusters is established by correlating photoluminescence data with photon-yield electronic structure measurements (SXF and NEXAFS) at the Advanced Light Source. After removal from the growth chamber, our photoluminescence (PL) results indicate that as the nanoclusters oxidize, the main PL peak moves from 1.83 eV to 1.94 eV in energy. Our finding is that the as-synthesized nanoclusters consist of a pure, crystalline Si core within a nearly pure SiO₂ shell. Very few suboxides are present, and the oxidation process does not lead to an increase in the amount of suboxides present within the particles. As the nanoclusters oxidize, the radius of the crystalline core decreases in size, which gives rise to the change in the position of the PL signal.

Main Group K- and L-Edge and Transition Metal L-Edge Spectroscopy of Solid and Gaseous Inorganic Compounds – Soft X-ray Spectroscopy from 100 to 2000 eV
Professor Ronald Cavell
Chemistry Department, University of Alberta, Alberta, Canada
The development of soft X-ray beamline facilities at the Canadian Synchrotron Radiation Facility (CSRF) on the Aladdin ring at the Synchrotron Radiation Center (SRC) in Stoughton, Wisconsin and the development of HRMON at Aladdin has provided the necessary instrumental capacity for the measurement of X-ray absorption spectra of compounds of the main group elements - phosphorus, sulphur (both K and L edges), nitrogen and oxygen (K edges). In addition, L edges of the first row transition metals (Ti-Mn) are presently accessible. The instrumentation spans the energy scale from 100 to approximately 3500eV. We have measured X-ray absorption spectra of a wide collection of compounds containing these listed elements.  The molecular species span the range of valence states and molecular geometries. Both gaseous and solid state measurements have been performed, dictated by the properties of the compounds. Our emphasis has been on the exploration of highly oxidized compounds of phosphorus and sulphur (e.g. OPF₃,  NSF₃,  PF₅,  OSF₄,  SF₅Cl etc.) and on the study of transition metal compounds and complexes of the elements from Ti to Mn. Examples will be drawn from selected groups of measurements to illustrate the character and trends in the XANES spectra and the chemical information that can be derived therefrom. In many cases all edges of a molecular system have been explored (e.g. nitrogen and oxygen edges in NO₂, all sulphur and oxygen edges in SO₂  etc.)  and the contrasts in the spectral character which derives from the dipole selection rules associated with each core level are revealed.

New methods for studying surface reaction kinetics, compositional heterogeneity, and interface properties with x-ray photoelectron spectroscopy
Professor Charles Fadley
Department of Physics, University of California, Davis, and Lawrence Berkeley National Laboratory, U.S.A.
Three new aspects of soft x-ray photoelectron spectroscopy (XPS) making use of third-generation synchrotron radiation will be discussed: time- and chemical state-resolved XPS, which permits following surface reactions in real time; multi-atom resonant XPS, which permits directly determining near-neighbor atomic identities and other bonding and magnetic properties; and XPS excited by x-ray standing waves from synthetic multilayer substrates, which permits probing species at surfaces and at buried interfaces.  First applications of these methods to metal oxidation, metal oxides, metal alloys, and metallic bilayers will be considered, and likely future directions of development will be discussed.

Soft X-ray Spectromicroscopy: Quantitative chemical analysis of functional materials at high spatial resolution
Professor Adam Hitchcock
Chemistry Department, McMaster University, Ontario, Canada
Chemical analyses of laterally and vertically structured polymeric systems are being performed with sub-100 nm spatial resolution using synchrotron- based scanning transmission x-ray microscopy (STXM) at the Advanced Light Source, Berkeley, CA. Novel methods for converting image and spectral information to quantitative component maps will be described. The capabilities will be illustrated by applications to nano-structured polymer encapsulation materials, to self- organized, confined multi-layer polymer films, and to engineered polymeric biomaterials.

Theory of the angular distributions of electrons photoejected from matter by x-ray photons: Inferences for complex materials from studies of fixed-in-space and randomly oriented polyatomic molecules
Professor Peter Langhoff
Department of Chemistry, Indiana University, Bloomington, Indiana, and San Diego Supercomputer Center, University of California, La Jolla, California, USA
New theoretical descriptions are reported of the dynamics of electrons photoejected from matter by x-ray photons. The formalism provides explicit expressions for photoionization cross sections differential in electron ejection angles for both anisotropic materials and an ensemble of randomly oriented molecules in simple closed forms which distinguish between geometrical, dynamical and target structural aspects of the photoejection process. Applications of the formalism are given in dipole and nondipole limits for photoejection from adsorbate or fixed-in-space molecules of arbitrary point-group symmetry as a vehicle for addressing related processes which can probe the vibronic degrees of freedom of nanostructures, clusters, surfaces and complex materials more generally.

Electronic Band Shift Measurements of Nanoclusters using Soft X-ray Spectroscopies
Dr. Louis Terminello
Lawrence Livermore National Laboratory, California, U.S.A.
We have used third generation synchrotron radiation to perform X-ray Absorption Spectroscopy (XAS), Photoelectron Spectroscopy (PES), and Soft X-ray Fluorescence (SXF) experiments on a variety of nanostructured materials. The reduced dimensional materials characterized include diamond, Si, Ge, and MoS2 nanoclusters ranging is size from 1 – 12 nM.  In each case we have exploited the element selectivity of the soft x-ray methods to probe the electronic structure, bonding, and morphology of these materials as a function of particle size. In particular, we use soft x-ray probes to determine band-shift and surface effects in our nanocluster samples. For many of these material systems, knowledge of band gap widening with quantum confinement, band alignment, and surface effects is critical to rational design and utilization of these novel materials in diverse applications.
         We present data obtained from the IBM/U. of Tennessee/Tulane U./LLNL/LBNL beam line at the Advanced Light Source, Lawrence Berkeley National Laboratory.  The spectral range of 70-1200 eV covers the sharpest core levels of all elements with optimum element and chemical environment sensitivity and resolution. The soft x-ray probes employed in our studies reveal structural information that would be difficult, if not impossible to uncover using conventional probes. The high brightness of this new facility has made possible the element specific probing of dilute materials such as nanoclusters and thin and buried layers that were previously undetectable. We will report our results on the nanocluster structures mentioned above, plus additional self-assembled and thin-film material systems.