Bradley H. Frazer

The probing depth of total electron yield in the sub-keV range: TEY-XAS and X-PEEM

X-ray absorption spectra can be collected in multiple ways, each exhibiting a different probing depth. The total electron yield signal contains contributions from primary, Auger and secondary electrons. We present data on the total electron yield probing depth at core level energies ranging from 77 to 929 eV. By coating materials with chromium overlayers, we find that the maximum probing depth increases with core level energy from 15 to 141 A. We demonstrate that the Auger electron contribution to total electron yield intensity is negligible, therefore X-ray absorption spectra acquired in X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) are equivalent to spectra acquired by total electron yield. We find that the signal intensity decreases exponentially with coating thickness, and that total electron yield probing depth and Auger electron range (calculated in the continuously slowing down approximation) are similar at low energies, but diverge for kinetic energies above 400 eV.

Compensation of charging in X-PEEM: a successful test on mineral inclusions in 4.4 Ga old zircon.

We present a new differential-thickness coating technique to analyze insulating samples with X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM). X-PEEM is non-destructive, analyzes the chemical composition and crystal structure of minerals and can spatially resolve chemical species with a resolution presently reaching 35 nm. We tested the differential coating by analyzing a 4.4 billion-year-old zircon (ZrSiO(4)) containing silicate inclusions. We observed quartz (SiO(2)) inclusions smaller than 1microm in size that can only be analyzed non-destructively with synchrotron spectromicroscopies. With the removal of charging we greatly extend the range of samples that can be analyzed by X-PEEM.

Are gadolinium contrast agents suitable for gadolinium neutron capture therapy

Abstract Objective: Gadolinium neutron capture therapy (GdNCT) is a potential treatment for malignant tumors based on two steps: (1) injection of a tumor-specific 157Gd compound; (2) tumor irradiation with thermal neutrons. The GdNC reaction can induce cell death provided that Gd is proximate to DNA. Here, we studied the nuclear uptake of Gd by glioblastoma (GBM) tumor cells after treatment with two Gd compounds commonly used for magnetic resonance imaging, to evaluate their potential as GdNCT agents. Methods: Using synchrotron X-ray spectromicroscopy, we analyzed the Gd distribution at the subcellular level in: (1) human cultured GBM cells exposed to Gd-DTPA or Gd-DOTA for 0–72hours; (2) intracerebrally implanted C6 glioma tumors in rats injected with one or two doses of Gd-DOTA, and (3) tumor samples from GBM patients injected with Gd-DTPA. Results: In cell cultures, Gd-DTPA and Gd-DOTA were found in 84% and 56% of the cell nuclei, respectively. In rat tumors, Gd penetrated the nuclei of 47% and 85% of the tumor cells, after single and double injection of Gd-DOTA, respectively. In contrast, in human GBM tumors 6.1% of the cell nuclei contained Gd-DTPA. Discussion: Efficacy of Gd-DTPA and Gd-DOTA as GdNCT agents is predicted to be low, due to the insufficient number of tumor cell nuclei incorporating Gd. Although multiple administration schedules in vivo might induce Gd penetration into more tumor cell nuclei, a search for new Gd compounds with higher nuclear affinity is warranted before planning GdNCT in animal models or clinical trials.

X-ray absorption spectroscopy of silicates for in situ, sub-micrometer mineral identification

Abstract We present X-ray absorption near-edge structure (XANES) spectroscopy of 11 silicate and aluminosilicate minerals and two glasses at the SiK and SiL2,3, and OK edges. The similar nearestneighbor environments lead to similar spectral lineshapes at each edge, but the fine-structure differences allow individual and groups of structurally similar minerals to be distinguished. By combining spectra and their first energy derivative from three absorption edges, we show that every mineral studied is distinguishable with XANES. This background work, combined with X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM), allows non-destructive in situ, sub-micrometer (to 35 nm) X-ray analysis of materials, including silicate inclusions, which has not been possible previously. Images and spectra from a 7 μm × 3.5 μm quartz inclusion in zircon are presented as a test of this novel technique in geology.

Motexafin-Gadolinium Taken Up In vitro by at Least 90% of Glioblastoma Cell Nuclei

Purpose: We present preclinical data showing the in vitro intranuclear uptake of motexafin gadolinium by glioblastoma multiforme cells, which could serve as a prelude to the future development of radiosensitizing techniques, such as gadolinium synchrotron stereotactic radiotherapy (GdSSR), a new putative treatment for glioblastoma multiforme. Experimental Design: In this approach, administration of a tumor-seeking Gd-containing compound would be followed by stereotactic external beam radiotherapy with 51-keV photons from a synchrotron source. At least two criteria must be satisfied before this therapy can be established: Gd must accumulate in cancer cells and spare the normal tissue; Gd must be present in almost all the cancer cell nuclei. We address the in vitro intranuclear uptake of motexafin gadolinium in this article. We analyzed the Gd distribution with subcellular resolution in four human glioblastoma cell lines, using three independent methods: two novel synchrotron spectromicroscopic techniques and one confocal microscopy. We present in vitro evidence that the majority of the cell nuclei take up motexafin gadolinium, a drug that is known to selectively reach glioblastoma multiforme. Results: With all three methods, we found Gd in at least 90% of the cell nuclei. The results are highly reproducible across different cell lines. The present data provide evidence for further studies, with the goal of developing GdSSR, a process that will require further in vivo animal and future clinical studies.

The multidisciplinarity of spectromicroscopy: from geomicrobiology to archaeology

Abstract Synchrotron X-ray PhotoElectron Emission Microscopy (X-PEEM) is a useful tool to investigate the microchemical composition of a variety of different samples, including cells in culture, tissue sections, magnetic material, bacteria, rocks, materials science, tribology and archaeology specimens. The MEPHISTO X-PEEM, installed at the Wisconsin Synchrotron Radiation Center, reached a peak resolution of 20 nm, has been extensively used for the last 4 years to explore all of the above systems. The experiments reported here are some of the most unusual ones for this technique: ZnS precipitating bacteria, Mn and Fe oxide rocks and archaeological coins. The microchemistry of each one of these samples delivered new results.

The symmetry of the order parameter in highly overdoped Bi2Sr2CaCu2O8+x

We report results of an angle-resolved high-resolution photoemission study of strongly overdoped Bi2Sr2CaCu2O8+x single crystals with T-c similar to 60 K. We find a nonzero superconducting (SC) gap along all three high symmetry directions in the Brillouin zone, in contrast with a d-wave scenario of high temperature superconductivity. Our data indicate that both the maximum gap value and the gap anisotropy decrease with overdoping

XANES in Nanobiology

The combination of spectroscopy and microscopy enables unprecedented insights into the molecular and crystal structures of organic and inorganic materials, and their interfaces. This is relevant to the field of biomaterials in general and biominerals in particular. In this framework, we extensively analyzed various proteins, minerals and biominerals. Here we present two novel observations: x‐ray absorption near‐edge structure (XANES) spectroscopy at the carbon K‐edge is sensitive to protein misfolding and aggregation into amyloid fibrils, and to the polar and azimuthal rotation of the CaCO3 polymorph aragonite.

Current Status of the Synchrotron Radiation Center

The Synchrotron Radiation Center (SRC) operates the Aladdin electron storage ring at energies of 800 MeV or 1 GeV in support of a broad range of national and international research programs. A low emittance configuration is in routine operation during 800‐MeV shifts and offers improved photon flux density with about the same beam lifetime. An improved undulator compensation algorithm and new optical beam position monitors have been implemented improving beam stability and maintaining vertical beam size variations to < 2% peak‐to‐peak during undulator scanning. Instrumentation initiatives include construction of a modified Wadsworth beamline (7.8 – 50 eV) and a variable‐line‐spacing plane‐grating monochromator (VLS‐PGM, 75 – 2000 eV) to utilize radiation from a permanent magnet undulator. The Wadsworth beamline is being commissioned for photoelectron spectroscopy (PES) experiments using high‐resolution Scienta analyzers. The VLS‐PGM is being constructed for experiments that require higher photon energies a...

Electronic properties of layered oxides: Pulsed laser deposition of YBCO films for in-situ studies by photoemission spectroscopy

Due to imperfect surfaces of most cuprate samples, almost all photoemission studies in the past decade were performed on Bi2Sr2CaCu2O8+x, even though a large fraction of other studies and electronic applications was reported for YBa2Cu3O7-delta (YBCO) family of superconducting compounds. In order to systematically study the gap parameter and the Fermi surface variation in high symmetry directions of YBCO and related oxide films we have constructed a new facility at the Wisconsin Synchrotron Radiation Center. We use the pulsed laser ablation (PLD) system that is directly linked to the photoemission chamber. In our unique approach, the samples never leave the controlled ambient and we oxidize our films, either by molecular oxygen or by ozone. Tn this paper, we summarize some of the most relevant recent results on electronic properties of layered oxides and describe our new facility for the study of YBCO and related oxide films.