Francesco DeCarlo

Optimizing synchrotron microCT for high-throughput phenotyping of zebrafish

We are creating a state-of-the-art 2D and 3D imaging atlas of zebrafish development. The atlas employs both 2D histology slides and 3D benchtop and synchrotron micro CT results. Through this atlas, we expect to document normal and abnormal organogenesis, to reveal new levels of structural detail, and to advance image informatics as a form of systems biology. The zebrafish has become a widely used model organism in biological and biomedical research for studies of vertebrate development and gene function. In this work, we will report on efforts to optimize synchrotron microCT imaging parameters for zebrafish at crucial developmental stages. The aim of these studies is to establish protocols for high-throughput phenotyping of normal, mutant and diseased zebrafish. We have developed staining and embedding protocols using different heavy metal stains (osmium tetroxide and uranyl acetate) and different embedding media (Embed 812 and glycol methacrylate). We have explored the use of edge subtraction and multi-energy techniques for contrast enhancement and we have examined the use of different sample-detector distances with unstained samples to explore and optimize phase-contrast enhancement effects. We will report principally on our efforts to optimize energy choice for single- and multi-energy studies as well as our efforts to optimize the degree of phase contrast enhancement.

X-ray lenses fabricated by deep x-ray lithography

Refractive x-ray lenses have been fabricated using deep x-ray lithography. Lenses were produced directly in 1- to 6-mm-thick sheets of polymethylmethacrylate (PMMA) with as many as 100 cylindrical lenses along the optical axis. The fabrication process consists of exposing the PMMA sheets to high-energy synchrotron radiation through a mask of 50-micron-thick gold on silicon, and subsequent development in ketone. The lenses are suitable for use in synchrotron radiation from a bending magnet at the Advanced Photon Source in the energy range of 8-16 KeV. Results of measurements of focus quality, flux density gain, and scatter are presented and discussed with regard to the quality of lens material and fabrication method. Means for improving the performance of the lenses is discussed.

Bending-magnet beamline for x-ray microtechniques at the Advanced Photon Source (abstract)

Beamline 2-BM at the Advanced Photon Source has been fully commissioned for a range of x-ray microtechniques including micromachining, microtomography, and microcharacterization by scattering and fluorescence. The beamline has been designed and constructed to provide a highly collimated beam with great flexibility in tuning the energy bandpass. To achieve this, the beamline incorporates two mirrors, filters, and two monochromators allowing selection of energy in the range of 3–33 keV with a bandpass in the range of 1–1000 eV. The endstation includes precision instrumentation for deep x-ray lithography, x-ray microtomography, x-ray imaging, x-ray optics characterization, and the development of techniques for high-throughput x-ray microcharacterization of libraries of samples. The various experimental systems are controlled and integrated in the station to allow for the flexibility of techniques, while improving efficiency of use. We describe in detail the beamline design, capabilities, and endstation instr...

Multiaxial analysis of dental composite materials

Dental composites are subjected to extreme chemical and mechanical conditions in the oral environment, contributing to the degradation and ultimate failure of the material in vivo. The objective of this study is to validate an alternative method of mechanically loading dental composite materials. Confined compression testing more closely represents the complex loading that dental restorations experience in the oral cavity. Dental composites, a nanofilled and a hybrid microfilled, were prepared as cylindrical specimens, light-cured in ring molds of 6061 aluminum, with the ends polished to ensure parallel surfaces. The samples were subjected to confined compression loading to 3, 6, 9, 12, and 15% axial strain. Upon loading, the ring constrains radial expansion of the specimen, generating confinement stresses. A strain gage placed on the outer wall of the aluminum confining ring records hoop strain. Assuming plane stress conditions, the confining stress (sigma(c)) can be calculated at the sample/ring interface. Following mechanical loading, tomographic data was generated using a high-resolution microtomography system developed at beamline 2-BM of the Advanced Photon Source at Argonne National Laboratory. Extraction of the crack and void surfaces present in the material bulk is numerically represented as crack edge/volume (CE/V), and calculated as a fraction of total specimen volume. Initial results indicate that as the strain level increases the CE/V increases. Analysis of the composite specimens under different mechanical loads suggests that microtomography is a useful tool for three-dimensional evaluation of dental composite fracture surfaces.

Hard x-ray monochromator with milli-electron volt bandwidth for high-resolution diffraction studies of diamond crystals

We report on design and performance of a high-resolution x-ray monochromator with a spectral bandwidth of ΔE(X) ≃ 1.5 meV, which operates at x-ray energies in the vicinity of the backscattering (Bragg) energy E(H) = 13.903 keV of the (008) reflection in diamond. The monochromator is utilized for high-energy-resolution diffraction characterization of diamond crystals as elements of advanced x-ray crystal optics for synchrotrons and x-ray free-electron lasers. The monochromator and the related controls are made portable such that they can be installed and operated at any appropriate synchrotron beamline equipped with a pre-monochromator.

A beamline for micromachining and micro-characterization at the APS

Beamline 2-BM at the Advanced Photon Source had been designed for developing micromachining techniques based on deep x-ray lithography and also for micro-characterization of optics and samples. With a critical energy of 19.5 keV and a highly collimated beam, the APS bending-magnet source is well suited for fabricating thick photoresist structures (>1 mm) with high precision. The 2-BM beamline was designed to exploit these source characteristics and to provide flexible spectral tuning in order to accommodate different mask/resist thicknesses and to study the effects of the x-ray energy on the lithography process. The beamline will also be used for developing micro-characterization techniques. This includes characterization of microfocusing optics such as zone plates and developing instrumentation for techniques such as x-ray microprobe and microtomography. For this purpose, two monochromators, one using crystals and one using multilayers, will be used to cover the 1-35 keV regime with different energy bandwidths. Beamline design, end-station layout, and recent results will be presented.

Exposure station with precision scanning stage for deep x-ray lithography

An exposure station with a precision scanning stage has been designed and constructed for use at the Advanced Photon Source for deep x-ray lithography. The precision scanning stage consists of four motion stages—two translations and two rotations. There is a theta rotation in the horizontal plane at the base, which allows precise setting of the angle of inclination of the x-rays to the substate for inclined, trapezoidal, and conical exposures. The horizontal X travel is mounted on the theta rotation and provides accurate positioning in the horizontal direction to allow field stitching and general alignment. The vertical Z travel is mounted on the X travel and is used to scan the mask and substrate through the x-rays repeatedly during exposure. The phi rotation is mounted on the Z travel and can be used for generating pyramidal and conical structures. Total absolute worst case angular error due to the sum of the stage motions including theta axis wobble, X axis pitch, yaw, and roll, and Z axis pitch, yaw, ...