Advances in microscopy techniques based on x-rays have opened unprecedented opportunities in terms of spatial resolution, combined with chemical and morphology sensitivity, to analyze solid, soft and liquid matter. The advent of ultrabright third and fourth generation photon sources and the continuous development of x-ray optics and detectors has pushed the limits of imaging and spectroscopic analysis to structures as small as a few tens of nanometers. Specific interactions of x-rays with matter provide elemental and chemical sensitivity that have made x-ray spectromicroscopy techniques a very attractive tool, complementary to other microscopies, for characterization in all actual research fields. The x-ray penetration power meets the demand to examine samples too thick for electron microscopes implementing 3D imaging and recently also 4D imaging which adds time resolution as well. Implementation of a variety of phase contrast techniques enhances the structural sensitivity, especially for the hard x-ray regime. Implementation of lensless or diffraction imaging helps to enhance the lateral resolution of x-ray imaging to the wavelength dependent diffraction limit.

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Transmission and emission x-ray microscopy: operation modes, contrast mechanisms and applications.

Principles and Applications of Zone Plate X-Ray Microscopes

High energy X-ray micro-optics

The development of 3rd generation synchrotron radiation sources like European Synchrotron Radiation Facility (ESRF) in parallel with recent advances in the technology of X-ray microfocusing elements like Kirkpatrick–Baez (KB) mirrors, diffractive (Fresnel zone plates, FZP) and refractive (compound refractive lenses, CRL) optics, makes it possible to use X-ray microscopy techniques with high energy X-rays (energy superior to 4 keV). Spectroscopy, imaging, tomography and diffraction studies of samples with hard X-rays at micrometre and sub-micrometre spatial resolutions are now possible. The concept of combining these techniques as a high-energy microscopy has been proposed and successfully realized at the ESRF beamlines. Therefore a short summary of X-ray microscopy techniques is presented first. The main emphasis will be put on those methods which aim to produce sub-micron and nanometre resolution. These methods fall into three broad categories: reflective, refractive and diffractive optics. The basic principles and recent achievements will be discussed for all optical devices. Recent applications of synchrotron based microanalytical techniques to characterise radioactive fuel particles (UO2) released from the Chernobyl reactor are reported.

X-Ray microanalytical techniques based on synchrotron radiation

X-ray computed tomography (XCT) is a powerful nondestructive 3D imaging technique, which enables the visualization of the three dimensional structure of complex, optically opaque samples. High resolution XCT using Fresnel zone plate lenses has been confined in the past to synchrotron radiation centers due to the need for a bright and intense source of x-rays. This confinement severely limits the availability and accessibility of x-ray microscopes and the wide proliferation of this methodology. We are describing a sub-50nm resolution XCT system operating at 8 keV in absorption and Zernike phase contrast mode based on a commercially available laboratory x-ray source. The system utilizes high-efficiency Fresnel zone plates with an outermost zone width of 35 nm and 700 nm structure height resulting in a current spatial resolution better than 50 nm. In addition to the technical description of the system and specifications, we present application examples in the semiconductor field.

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High-resolution x-ray tomography using laboratory sources

Development of microfocusing optics for scanning microscopy and image forming optics for imaging microscopy are now in progress in SPring-8 by using varieties of optical devices: refractive lens, total reflection mirrors. Fresnel zone plates, and sputtered-sliced Fresnel zone plates. Spatial resolution of 100 nm has been achieved in scanning microscopy using highly coherent X-ray beam at a 248 m-long beamline 20XU and F2P' focusing optics. Recent results on development of optical systems are described.

Hard X-ray microscopy activities at SPring-8

Zone plates for high energy X-rays with an outermost zone width as small as ∼0.1 μm and thickness with 10∼50 μm have been fabricated using sputtered-sliced technology. With the brilliant x-ray beam from the undulator at the SPring-8 the minimum focal spot size attained was 0.7 μm at 27.5 keV. The light collecting efficiency was determined to be ∼15%. We have also succeeded to focus much higher energy x-rays as 80 keV with these zone plates.

M. Yasumoto

Papers

Hard X-ray microscopy activities at SPring-8

Fabrication of high energy X-ray Fresnel phase zone plate