Showing papers by "Stefan Vogt published in 2004"

Multilayer Laue lenses as high-resolution x-ray optics

Abstract: Using Fresnel zone plates, a spatial resolution between 20 nm for soft x-rays and 70 nm for hard x-rays has been achieved. Improvement of the spatial resolution without loss of efficiency is difficult and incremental due to the fabrication challenges posed by the combination of small outermost zone width and high aspect ratios. We describe a novel approach for high-resolution x-ray focusing, a multilayer Laue lens (MLL). The MLL concept is a system of two crossed linear zone plates, manufactured by deposition techniques. The approach involves deposition of a multilayer with a graded period, sectioning it to the appropriate thickness, assembling the sections at the optimum angle, and using it in Laue geometry for focusing. The approach is particularly well suited for high-resolution focusing optics for use at high photon energy. We present a theory of the MLL using dynamic diffraction theory and Fourier optics.

Evidence for strain compensation in stabilizing epitaxial growth of highly doped germanium

Abstract: We report on a study of the epitaxial phase diagram of Co- and Mn-doped Ge(001) magnetic semiconductors. Complementary doping using dopants from different groups of elements can compensate for the effects of lattice strain caused by the doping species. Reducing lattice mismatch with the Ge host has been shown to be the key to stabilizing epitaxial growth and suppressing phase separation at higher doping levels. Applying this approach to other multidopant systems opens new prospects for tailoring highly doped electronic materials.

Conceptual Design For A Beamline For A Hard x‐ray Nanoprobe with 30 nm Spatial Resolution

Abstract: The planned Center for Nanoscale Materials (CNM) at Argonne National Laboratory is aimed at the development and study of the properties of nanomaterials and nanodevices. As part of the characterization instruments at CNM, we are developing a new hard x‐ray nanoprobe beamline at the Advanced Photon Source. The beamline will provide microscopy and spectroscopy for photon energies from 3 keV to 30 keV. Hard x‐ray zone plates will be used to achieve a spatial resolution of 30 nm in the 3 – 10 keV region. Two operational modes will combine the speed of a transmission x‐ray microscope with the analytic capabilities of a hard x‐ray microprobe. The major operation mode will be a scanning probe mode, where spatially coherent radiation is focused into a diffraction‐limited spot to excite secondary signals in the specimen. This will allow elemental mapping and spectroscopy at high sensitivity using x‐ray fluorescence, or strain contrast imaging using x‐ray diffraction. A secondary mode will use partially coherent radiation to provide transmission imaging in absorption and phase contrast for photon energies between 3 – 10 keV.

Fast Differential Phase-Contrast Imaging and Total Fluorescence Yield Mapping in a Hard X-ray Fluorescence Microprobe

Abstract: We have incorporated differential phase‐contrast (DPC) detection in a hard x‐ray fluorescence microprobe at the Advanced Photon Source. We report a straightforward implementation of unidirectional DPC and demonstrate that it is highly advantageous for imaging low‐Z specimens with hard x‐rays (10keV). Phase‐contrast imaging of a specimen can be used to acquire fast overview images of samples that allow more precise targeting of time consuming fluorescence scans. In order to get an overview of the elemental content of a specimen in these fly‐scans, we have also implemented a fast detection of total fluorescence yield. Additionally, a DPC image of the specimen is obtained simultaneously with the fluorescence maps in normal step‐scanning mode, to facilitate a direct comparison and co‐registration with visible light micrographs.

The evolution of hard x-ray tomography from the micrometer to the nanometer length scale

Abstract: For several years efforts have been made to improve the resolution for imaging and tomography with hard X-rays. Recently we demonstrated sub-100 nm resolution at 13 keV with a microscope including a Kirkpatrick-Baez multilayer-mirror (KB) as a condenser followed by a micro-Fresnel Zone Plate (FZP) as an objective lens. We built since a new tomography station at UNICAT at the Advanced Photon Source integrating the KB-FZP microscope for 100 nm tomography.

Tapered tilted linear zone plates for focusing hard x-rays

Abstract: We introduce a new design of tilted linear zone plates, which are named tapered tilted linear (TTL) zone plates. The purpose of the design is to increase efficiency while at the same time keeping the focal plane perpendicular to the optical path. In order to accomplish this, the zone radius and number of zones must become a function of position along the structure. Simulation work described in this paper shows improved optical performance over regular tilted linear zone plates.

Workshop on biological applications of X-ray microscopy and imaging. Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA, 28-29 April 2003.

Abstract: A workshop on the biological applications of X-ray microscopy and imaging was held in conjunction with the 12th Users Meeting for the Advanced Photon Source (APS) at Argonne National Laboratory, Argonne, IL, USA, on 28–29 April 2003. The workshop was hosted jointly by the APS and Northwestern University Medical Center of Chicago, IL. Speakers from different institutions presented stateof-the-art lectures on electron microscopy, optical microscopy, microcomputerized tomography, diffractionenhanced imaging and magnetic resonance imaging to provide a context for X-ray microscopy-based imaging approaches. Imaging applications both in vitro and in vivo have received a new focus in recent years with the development of quantitative imaging techniques, computational approaches to image enhancement and real-time video imaging. Hard X-ray microscopy offers a complimentary technique that allows for elemental detection at high resolution (v150 nm) with subpart-per-million sensitivity. X-ray microscopy used alone or in concert with other imaging approaches can provide novel information on elemental concentrations and chemical states that cannot be obtained using other methods (Cholewa et al. 2001, Lai et al. 2002). Several lectures at the workshop were devoted to a description of on-going studies using X-ray microscopy at the Advanced Photon Source (ANL), National Synchrotron Light Source (BNL), European Synchrotron Radiation Facility (ESRF) and other sites. Applications discussed in detail included studies of intracellular metal distribution in bacteria and mammalian cells, use of X-ray fluorescence for detection of the anticancer drug cisplatin (Ilinski et al. 2003), iron in liver tissues from haemochromatosis patients and intracellular probes labelled with TiO2 nanoparticles (Paunesku et al. 2003a, b). Studies at ESRF and APS have compared the distribution of chromium (Cr) (III), which is not toxic, with Cr(VI), which is a carcinogen produced by industrial processing, using X-ray microscopy to determine the distribution and forms of Cr in mammalian cells as well as in bacteria (Ortega et al. 2001, Dillon et al. 2002). Experiments done at the APS examining iron distribution in vacuoles of macrophages infected with virulent and avirulent strains of mycobacterial species were reported. Other studies demonstrated that differentiation of precursor cells into macrophages is accompanied by changes in metal distribution. Applications of X-ray microscopy approaches to studies of human disease states including forensic medicine, disease pathology and disease diagnosis were described. In particular, studies from Australia have examined the fate of platinum (Pt) (IV) anticancer drugs in cancer cells and solid tumours, demonstrating that some Pt(IV)-containing drugs might be more inert than Pt(II)-containing drugs, possibly increasing the chance of reaching the DNA targets (Hall et al. 2003). Some new studies that have been initiated and are in their starting phases were also described including experiments on the elemental composition of sperm and differences in transition metals in human neurologic diseases such as amyotrophic lateral sclerosis and Parkinson’s disease (Szczerbowska-Boruchowska et al. 2003). These important areas are likely to provide exciting new information in the coming years. Studies have also investigated elemental distribution in various microbial populations (Twinning et al. 2003). Environmental applications included studies of trace element concentration in marine protists where elements like iron and silicon are present in limiting amounts in certain areas. Other reports described studies using spectral signatures to define the metabolic state of the microbe in a particular

Imaging and Quantifying Major/Trace Elemental Distribution

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Design for an x-ray nanoprobe prototype, with a sub-10-nm positioning requirement

Abstract: We are developing a new hard x-ray nanoprobe beamline with 30 nm resolution at the Advanced Photon Source (APS) Imaging and spectroscopy at this resolution level require staging of x-ray optics and specimens with a mechanical repeatability of better than 10 nm We have developed a prototype instrument with a novel interferometrically controlled scanning stage system The system consists of nine DC-motor-driven stages, four picomotor-driven stages, and two PZT-driven stages An APS-designed custom-built laser Doppler displacement meter system provides two-dimensional differential displacement measurement with subnanometer resolution between the zone-plate x-ray optics and the sample holder Also included is the alignment and stable positioning of two stacked zone plates for increasing the focusing efficiency The entire scanning system was designed with high stiffness, high repeatability, low drift, flexible scanning schemes, and possibility of fast feedback for differential motion Designs of the scanning stage system, as well as preliminary mechanical test results, are presented in this paper

Trace Element Imaging and Analysis in Biological Cells with Scanning X-ray Fluorescence Microscopy

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.