W. Yun

X-ray imaging and microspectroscopy of plants and fungi.

X-ray fluorescence microscopy and microspectroscopy with micrometre spatial resolution and unprecedented capabilities for the study of biological and environmental samples are reported. These new capabilities are a result of both the combination of high-brilliance synchrotron radiation and high-performance X-ray microfocusing optics and the intrinsic advantages of X-rays for elemental mapping and chemical-state imaging. In this paper, these capabilities are illustrated by experimental results on hard X-ray phase-contrast imaging, X-ray fluorescence (XRF) imaging and microspectroscopy of mycorrhizal plant roots and fungi in their natural hydrated state. The XRF microprobe is demonstrated by the simultaneous mapping of the elemental distributions of P, S, K, Ca, Mn, Fe, Ni, Cu and Zn with a spatial resolution of approximately 1 x 3 micron and with an elemental sensitivity of approximately 500 p.p.b. Microspectroscopy with the same spatial resolution is demonstrated by recording near-edge X-ray absorption (XANES) spectra of Mn at a concentration of approximately 3 p.p.m.

DEVELOPMENT OF A HARD X-RAY IMAGING MICROSCOPE

A hard x‐ray imaging microscope based on a phase zone plate has been developed and tested. The zone plate, with a 5 cm focal length and a 0.2 μm smallest linewidth, was used to image 8 keV x rays from the samples. The imaging microscope can be used to obtain nearly diffraction‐limited resolution over the entire imaging field, and its resolution is almost independent of source size and source motions. We have tested such an imaging microscope, and a resolution of about 0.4 μm was obtained. The images were obtained with an exposure time of less than 1 min, for a magnification factor of 30 in the x rays. The x rays were then converted into visible light, and another 7 times magnification were obtained by using a lens system coupled to a charge coupled device camera. The results from the imaging microscope, and possible applications, will be discussed.

Coherent hard x‐ray focusing optics and applications

Coherent hard x‐ray beams with a flux exceeding 109 photons/sec with a bandwidth of 0.1% will be provided by undulators at the third‐generation synchrotron radiation sources such as APS, ESRF, and Spring‐8. The availability of such high flux coherent x‐ray beams offers excellent opportunities for extending the coherence‐based techniques developed in the visible and soft x‐ray part of the electromagnetic spectrum to the hard x‐ray region. These x‐ray techniques (e.g., diffraction‐limited microfocusing, holography, interferometry, phase contrast imaging, and signal enhancement) may offer substantial advantages over noncoherence‐based x‐ray techniques currently used. For example, the signal‐enhancement technique may be used to enhance an anomalous x‐ray or magnetic x‐ray scattering signal by several orders of magnitude. Coherent x rays can be focused to a very small (diffraction‐limited) spot size, thus allowing construction of high spatial resolution microprobes. This paper will discuss the feasibility of e...

Beamline and exposure station for deep x-ray lithography at the Advanced Photon Source

The Advanced Photon Source (APS) is a third-generation synchrotron radiation source. With a characteristic x-ray energy of 19.5 keV and highly collimated beam (< 0.1 mrad), the APS is well suited for producing high-aspect- ratio microstructures in thick resist films (> 1 mm) using deep x-ray lithography (DXRL). The 2-BM beamline has been constructed and will be used for DXRL at the APS. Selection of the appropriate x-ray energy range is accomplished by a variable-angle mirror and various filters installed in the beamline. At the exposure station, the beam size will be 100 (H) X 5 (V) mm2. Uniform exposure will be achieved by a high-speed (100 mm/sec) vertical scanner. The scanner allows precise angular (approximately 0.1 mrad) and positional (< 1 micrometers ) control of the sample, allowing full use of the highly collimated beam for lateral accuracy and control of sidewall slopes during exposure of thick resists, as well as the generation of conicals and other profiles. For 1-mm thick PMMA, a 100 X 25 mm2 area can be fully exposed in about 1/2 hour, while even 10-mm thick PMMA will require only 2 - 3 hours.

APS undulator radiation—first results

The first undulator radiation has been extracted from the Advanced Photon Source (APS). The results from the characterization of this radiation are very satisfactory. With the undulator set at a gap of 15.8 mm (K=1.61), harmonics as high as the 17th were observed using a crystal spectrometer. The angular distribution of the third-harmonic radiation was measured, and the source was imaged using a zone plate to determine the particle beam emittance. The horizontal beam emittance was found to be 6.9 {plus_minus} 1.0 nm-rad, and the vertical emittance coupling was found to be less than 3%. The absolute spectral flux was measured over a wide range of photon energies, and it agrees remarkably well with the theoretical calculations based on the measured undulator magnetic field profile and the measured beam emittance. These results indicate that both the emittance of the electron beam and the undulator magnetic field quality exceed the original specifications.

Design of a dedicated beamline for x‐ray microfocusing‐ and coherence‐based techniques at the Advanced Photon Source

A dedicated insertion‐device beamline has been designed and is being constructed at the Advanced Photon Source (APS) for development of x‐ray microfocusing‐ and coherence‐based techniques and applications. Important parameters considered in this design include preservation of source brilliance and coherence, selectable transverse coherence length and energy bandwidth, high beam angular stability, high order harmonic suppression, quick x‐ray energy scan, and accurate and stable x‐ray energy. The overall design of this beamline layout and the major beamline components are described. The use of a horizontally deflecting mirror as the first optical component is one of the main features of this beamline design, and the resulting advantages are briefly discussed.

Precision white-beam slit design for high power density x-ray undulator beamlines at the Advanced Photon Source

A set of precision horizontal and vertical white‐beam slits has been designed for the Advanced Photon Source x‐ray undulator beamlines at Argonne National Laboratory. There are several new design concepts applied in this slit set, including a grazing‐incidence knife‐edge configuration to minimize the scattering of x rays downstream, enhanced heat transfer tubing to provide water cooling, and a secondary slit to eliminate the thermal distortion on the slit knife edge. The novel aspect of this design is the use of two L‐shaped knife‐edge assemblies, which are manipulated by two precision X‐Z stepping linear actuators. The principal and structural details of the design for this slit set are presented in this paper.

Performance comparison of hard x-ray plates fabricated by two different methods

Two types of fabrication methods have been developed to fabricate Fresnel zone plates for focusing x-rays in the 5 - 25 keV energy region. These two fabrication methods are discussed in terms of spatial resolution and focusing efficiency, which are two important parameters that characterize the performance of a Fresnel zone plate. Experimental characterization of the zone plates fabricated by the two methods are described and the results are discussed.

Beam size measurement of the stored electron beam at the APS storage ring using pinhole optics

Beam sizes of the stored electron beam at the APS storage ring were measured using pinhole optics and bending magnet x-rays in single-bunch and low-current mode. A pinhole of 25 {mu}m and a fast x-ray imaging system were located 23.8 m and 35.4 m from the source, respectively. The x-ray imaging system consists of a CdWO{sub 4} scintillation crystal 60 {mu}m thick, an optical imaging system, and a CCD detector. A measurement time of a few tenths of a second was obtained on a photon beam of E>30 keV produced in a bending magnet from a 7-GeV electron beam of 2mA current. The measured vertical and horizontal sizes of the electron beam were in reasonable agreement with the expected values.

Finite thickness effect of a zone plate on focusing hard x-rays

Spatial resolution and focusing efficiency are two important properties of a zone plate in x-ray focusing applications. A general expression of the zone plate equation describing its zone registration is derived from the interference of spherical waves emited from two mutually coherent point sources. An analytical expression of the focusing efficiency in terms of the zone plate thickness and x-ray refractive indices of the zones is also derived. Validity condition for using this expression is considered. Thickness required for obtaining adequate focusing efficiency is calculated as a function of x-ray energy for several representative materials. The spatial resolution of a finite thickness zone plate is worse than that of an infinetly thin zone plate which is approximately equal to the smallest zone width of the zone plate. The effect of the finite thickness on the spatial resolution is considered. This manuscript has been authored under contract number W-31-109-ENG-38 with the U. S. Department of Energy. Accordingly the U. S. Government retains a non-exclusive royalty-free license to publish or reproduce the published form of this contribution or allow others todo so for U. S. Government purposes. 146 / SPIE Vol 1345 Advanced X-Ray/EUV Radiation Sources andApplications(1990)