Showing papers by "Tolek Tyliszczak published in 2006"

Comet 81P/Wild 2 under a microscope.

Abstract: The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Magnetic vortex core reversal by excitation with short bursts of an alternating field

Abstract: The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials(1-4) and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magneto-static and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres-the vortex core(5-7). The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position(8-10). The sense of gyration is determined by the vortex core polarization(11). Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy(12). We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.

Organics captured from comet 81P/Wild 2 by the Stardust spacecraft.

Abstract: Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.

Nanoscale detection of organic signatures in carbonate microbialites.

Abstract: Microbialites are sedimentary deposits associated with microbial mat communities and are thought to be evidence of some of the oldest life on Earth. Despite extensive studies of such deposits, little is known about the role of microorganisms in their formation. In addition, unambiguous criteria proving their biogenicity have yet to be established. In this study, we characterize modern calcareous microbialites from the alkaline Lake Van, Turkey, at the nanometer scale by combining x-ray and electron microscopies. We describe a simple way to locate microorganisms entombed in calcium carbonate precipitates by probing aromatic carbon functional groups and peptide bonds. Near-edge x-ray absorption fine structure spectra at the C and N K-edges provide unique signatures for microbes. Aragonite crystals, which range in size from 30 to 100 nm, comprise the largest part of the microbialites. These crystals are surrounded by a 10-nm-thick amorphous calcium carbonate layer containing organic molecules and are embedded in an organic matrix, likely consisting of polysaccharides, which helps explain the unusual sizes and shapes of these crystals. These results provide biosignatures for these deposits and suggest that microbial organisms significantly impacted the mineralogy of Lake Van carbonates.

Time-resolved imaging of spin transfer switching: beyond the macrospin concept.

Abstract: Time-resolved images of the magnetization switching process in a spin transfer structure, obtained by ultrafast x-ray microscopy, reveal the limitations of the macrospin model. Instead of a coherent magnetization reversal, we observe switching by lateral motion of a magnetic vortex across a nanoscale element. Our measurements reveal the fundamental roles played independently by the torques due to charge and spin currents in breaking the magnetic symmetry on picosecond time scales.

Speciation and Quantitative Mapping of Metal Species in Microbial Biofilms Using Scanning Transmission X-ray Microscopy

Abstract: A scanning transmission X-ray microscope illuminated with synchrotron light was used to investigate the speciation and spatial distributions of metals in a microbial biofilm cultivated from river water. Metal 2p absorption edge signals were used to provide metal speciation (through shapes of the absorption spectra) and quantitative spatial distributions of the metal species. This paper presents sample data and describes methods for extracting quantitative maps of metal species from image sequences recorded in the region of the metal 2p edges. Comparisons were made with biochemical characterization of the same region using images recorded at the C 1s and O 1s edges. The method is applied to detailed quantitative analysis of ferrous and ferric iron in a river biofilm, in concert with mapping Ni(II) and Mn(II) species in the same region. The distributions of the metal species are discussed in the context of the biofilm structure. These results demonstrate that soft X-ray STXM measurements at the metal 2p abs...

Motexafin-gadolinium taken up in vitro by at least 90% of glioblastoma cell nuclei.

Abstract: 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 develop- ment 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 spectromicro- scopic 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. Glioblastoma multiforme, the most common primary intra- cranial malignancy in the United States, has an annual

Nanometer-scale chemical heterogeneities of black carbon materials and their impacts on PCB sorption properties: soft X-ray spectromicroscopy study.

Abstract: Synchrotron-based soft X-ray spectromicroscopy was used to probe nanometer-scale chemical heterogeneities of black carbon (BC) materials, including anthracite coal, coke, and activated carbon (AC), and to study their impact on the partitioning of one type of polychlorinated biphenyls (PCB-166: 2,3,4,4‘,5,6 hexachloro biphenyl) onto AC particles. Various carbon species (e.g., aromatic, ketonic/phenolic, and carboxylic functional groups) were found in all of the BC materials examined, and impurities (e.g., carbonate and potassium ions in anthracite coal) were identified in nanometer-scale regions of these samples. We show that these chemical heterogeneities in AC particles influence their sorption of hydrophobic organic compounds (HOCs). PCB-166 was found to accumulate preferentially on AC particles with the highest content of aromatic functionalities. These new findings from X-ray spectromicroscopy have the following implications for the role of BC materials in the environment: (1) the functional groups ...

Scanning x-ray microscopy investigations into the electron-beam exposure mechanism of hydrogen silsesquioxane resists

Abstract: Electron-beam exposed hydrogen silsesquioxane cross-linking chemistry is investigated by scanning transmission x-ray microscopy (STXM) and atomic force microscopy (AFM). Using STXM, a maximum in the chemical contrast is obtained by measuring the x-ray absorption at 535.4eV, corresponding to the 1sK-edge transition in oxygen. An area-dependent and dose-dependent chemical conversion is observed for feature sizes between 150nm and 10μm and doses between 0.4 and 40mC∕cm2. The activated (cross-linked) regions extend beyond the exposure zones, especially for higher dosed exposures. With AFM, thickness changes in the latent images (e-beam exposed but undeveloped) are observed, which also display a dependence on exposed area. Potential mechanisms, involving chemical diffusion outside the exposure zone, are discussed.

Chemically Sensitive Tomography at 50 nm Spatial Resolution using a Soft X- ray Scanning Transmission X-Ray Microscope

Abstract: Previous very successful soft X-ray microscopy tomography experiments [1-3] have been performed at a single photon energy. They have provided high spatial resolution, density based 3D images, but with only limited chemical information. We are developing computed angle-scan tomography in a scanning transmission x-ray microscope (STXM) for chemical visualization of a 3D spatial volume. Our goal is not only to do x-ray tomography at ~50 nm spatial resolution, but also to utilize the capability of STXM to perform energy scanning at high spectral resolution in order to identify and quantitatively map the chemical composition of the sample in a 3D volume.

Chemically sensitive 3D imaging at sub-100-nm spatial resolution using tomography in a scanning transmission x-ray microscope

Abstract: Computed angle scan tomography has been implemented for the first time using sample raster scanning in a scanning transmission X-ray microscope. The experimental apparatus, acquisition and data analysis procedures, and first results from fully hydrated river biofilm samples measured from 528-534 eV are reported. The multiple energy images are processed to 3-dimensional quantitative chemical maps of major biological components, such as proteins, polysaccharides and lipids.