B. W. Yates

Preliminary Commissioning and Performance of the Soft X‐ray Micro‐characterization Beamline at the Canadian Light Source

The Soft X‐ray Micro‐characterization Beamline (SXRMB) is a medium energy, bending magnet based beamline, designed to cover an energy range of 1.7–10 keV using two sets of crystals—InSb(111) and Si(111). The design goal is to deliver a flux of 2×1011 photons sec−1/100 mA with a resolution up to 10,000 for X‐ray Absorption Spectroscopy. A KB mirror stage is designed to provide microprobe capability, with a spot size of 10×10 μm2 and a flux of >109 at the microprobe station. The beamline has been in the commissioning phase since 2008, and access to the X‐ray absorption endstation is now open to general users. The optical commissioning and performance of the beamline is presented with some early experimental results.

Calcium L-edge XANES study of some calcium compounds

The Ca L3,2-edge XANES spectra of six calcium salts have been measured in both total electron and fluorescence yields using a high-resolution spherical grating monochromator. The compounds investigated were; CaF2, CaCO3, CaCl2 x 2H2O, calcium phosphate, calcium glycerophosphate and calcium gluconate. We find that the fine structure of the Ca L3,2-edges for each compound is unique and relates to the local structure of the Ca atom. The implications of these results to the study of the structure of calcium binding sites in systems of biologically interest will be discussed.

Commissioning and performance of the variable line spacing plane grating monochromator beamline at the Canadian Light Source

The variable line spacing plane grating monochromator beamline at the Canadian Light Source (CLS) employs three grazing incidence variable line spacing gratings to cover a photon energy range of 5-250 eV. It uses a 185 mm period length planar permanent magnet insertion device as the photon source, sharing a straight section with another soft x-ray beamline at the CLS. The commissioning and performance of the beamline is reported. The high resolution photoabsorption spectra of Ar and PF(5) gases are reported. A resolving power of over 40,000 for photons in the low energy region and >10,000 for a wider energy range (8-200 eV) can be achieved. A photon flux of up to 2 x 10(12) photons/s per 100 mA with slit settings of 50 microm has been measured.

Soft x-ray excited optical luminescence: Some recent applications

X-ray excited optical luminescence (XEOL) studies of several classes of light emitting materials excited using soft x rays (photon energy ranging from 10 to 2500 eV) are presented. We show that XEOL with soft x rays (short penetration depths) is often site specific and is ideally suited for the study of light emitting thin films and devices. Several examples including porous silicon, organic light emitting diode materials, and CdS based nanostructures are used to illustrate the unique properties of XEOL and its applications in the soft x-ray energy region.

First results from the Canadian SGM beamline at SRC

The first experimental results obtained from the Canadian SGM beamline at SRC (Synchrotron Radiation Centre, University of Wisconsin-Madison, USA) are reported. The beamline is based on the Dragon-type design, with a constant deviation angle, using photons from a second-generation bending-magnet light source. The medium-energy grating on this beamline covers a photon energy range from 240 to 700 eV, with a ruling density of 600 lines mm(-1). A maximum resolving power of approximately 10000 is achieved at a photon energy of approximately 400 eV. Gas-phase absorption spectra collected at the N, O and C K-edges are presented to demonstrate the excellent performance of this beamline. High-resolution absorption spectra of some C- and Ti-containing solid-state samples are also reported.

Soft x-ray-excited luminescence and optical x-ray absorption fine structures of tris (8-hydroxyquinoline) aluminum.

Photoluminescence from tris (8-hydroxyquinoline) aluminum (Alq3) films has been observed using tunable soft x rays as an excitation source. The photons were tuned to energies above and below the K absorption edges of C, N, O, and Al. The luminescence was in turn used to monitor the absorption. It was found that the luminescence induced by soft x ray exhibits additional emission bands at shorter wavelengths compared to ultraviolet excitation. While all K edges exhibit optical x-ray absorption fine structures (XAFS) similar to those of total electron and fluorescence yield, the optical XAFS at the C K-edge resonance are enhanced for the C1s to π* transitions, indicating site specificity. These observations are attributed to the energetics of the process and the local electronic structure.

X-ray excited optical luminescence (XEOL) studies of CaF2 at the Ca L3,2-edge

We report a study of the optical response of CaF2 specimens (crystal and powder) with excitation photon energy tuned across the Ca L3,2-edge. The luminescence was in turn used to monitor the absorption across the Ca L-edge (optical XAFS). It is found that the photoluminescence yield produces an inverted spectrum. This observation is interpreted in terms of total absorption (thickness effect), the change in decay dynamics below and above the edge and the atomic origin of the luminescence. By comparing crystal and powder results, we find that the surface component of CaF2 exhibits a positive shift (∼0.15 eV) relative to the bulk at the p–d resonance at the Ca L3,2-edge. A DFT calculation has been carried out and it is in good accord with the experiment. The implications of these results are discussed.

The Role of Oxygen in the Photoluminescence of Porous Silicon: Some Recent Observations

The role of oxygen in the luminescence from porous silicon is examined using a synchrotron spectroscopic technique often known as XEOL (X-ray Excited Optical Luminescence) and associated optical XAFS (X-ray Absorption Fine Structures using photoluminescence yield). The tunability of synchrotron light permits the probing of the inner valence and the core levels of silicon and oxygen in porous silicon. These processes are associated with site specificity and probing depth variations depending on the absorption coefficient. Luminescence excited with photons in the inner valence region (15–40 eV) and at the oxygen K-edge are reported. From these results together with previous and new Si K-edge and L3,2-edge studies, a picture of the role of oxygen emerges.

Design and performance of the double crystal monochromator beamline at the Canadian Light Source

The medium energy x-ray double crystal monochromator (DCM) is currently being designed at the Canadian Light Source (CLS). Design goals for the DCM are to provide photons between 1750–5500 eV with a resolving power better than 3000 and photon flux better than 5×1010 photons/s/0.1% bandwidth for 500 mA beam current. A set of indium antimonide crystals [InSb(111)] will be used over the energy range of 1750–3700 eV, with resolution ranging from 0.52–1.05 eV. Although InSb allows one to probe the important silicon K edge at ∼1840 eV, it has the disadvantage of poor thermal conductivity. Exposure to high heat loads from the CLS synchrotron on the first crystal (∼56.5 W of power for 2 mrad of horizontal bending magnet radiation, ∼0.54 W/mm2 power density) will cause crystal distortion and thereby intensity/resolution degradation. A second set of silicon crystals [Si(111)] are proposed for the energy range of 3700–5500 eV. Resolution ranges linearly from ∼0.41 to ∼0.70 eV over this energy range. A harmonic filte...

A study of titanium nitride diffusion barriers between aluminium and silicon by X-ray absorption spectroscopy: the Si, Ti and N results

We report a multi-elment, multi-edge and multi-detection mode X-ray photoabsorption study of a series of Al/TiN(x)/Si(100) thin films as a function of the TiN(x) film thickness (100A-500A) and of the annealing temperature (400 degrees C-600 degrees C). The Si K- and L-edge results show that Si does not diffuse to the surface for all the films. The high resolution Ti L-edge and N K-edge spectra show that the TiN(x) layer undergoes a dramatic chemical reaction with the gradual increase in the annealing temperature. This chemical reaction stabilizes at 560 degrees C at which the TiN(x) film is known to fail to act as an effective diffusion barrier between Al and Si.