Article

Fabrication of diffraction gratings for hard X-ray phase contrast imaging

Paul Scherrer Institut, CH 5232 Villigen-PSI, Switzerland
Microelectronic Engineering (Impact Factor: 1.2). 05/2007; 84(5-8):1172-1177. DOI: 10.1016/j.mee.2007.01.151

ABSTRACT

We have developed a method for X-ray phase contrast imaging, which is based on a grating interferometer. The technique is capable of recording the phase shift of hard X-rays travelling through a sample, which greatly enhances the contrast of low absorbing specimen compared to conventional amplitude contrast images. Unlike other existing X-ray phase contrast imaging methods, the grating interferometer also works with incoherent radiation from a standard X-ray tube. The key components are three gratings with silicon and gold structures, which have dimensions in the micrometer range and high aspect ratios. The fabrication processes, which involve photolithography, anisotropic wet etching, and electroplating, are described in this article for each of the three gratings. An example of an X-ray phase contrast image acquired with the grating interferometer is given.

Download full-text

Full-text

Available from: Ana Diaz
    • "However, since hard x-rays have good penetrating power, the gratings should also be deep enough to substantially modulate the beam, particularly for absorption gratings. New UV and x-ray lithography techniques have been developed to make hard x-ray absorption gratings of 2.0 μm periods[21] [22] [23], although for smaller periods, it becomes difficult to maintain the thickness of the gratings due to the extreme aspect ratios of the vertical structures. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe the design and fabrication trials of x-ray absorption gratings of 200 nm period and up to 100:1 depth-to-period ratios for full-field hard x-ray imaging applications. Hard x-ray phase-contrast imaging relies on gratings of ultra-small periods and sufficient depth to achieve high sensitivity. Current grating designs utilize lithographic processes to produce periodic vertical structures, where grating periods below 2.0 μm are difficult due to the extreme aspect ratios of the structures. In our design, multiple bilayers of x-ray transparent and opaque materials are deposited on a staircase substrate, and mostly on the floor surfaces of the steps only. When illuminated by an x-ray beam horizontally, the multilayer stack on each step functions as a micro-grating whose grating period is the thickness of a bilayer. The array of micro-gratings over the length of the staircase works as a single grating over a large area when continuity conditions are met. Since the layers can be nanometers thick and many microns wide, this design allows sub-micron grating periods and sufficient grating depth to modulate hard x-rays. We present the details of the fabrication process and diffraction profiles and contact radiography images showing successful intensity modulation of a 25 keV x-ray beam.
    No preview · Article · Oct 2012 · Journal of Micromechanics and Microengineering
  • Source
    • "The period g 2 of grating G2 was 2 μm, which is equal to the interference fringe period caused by grating G1. The source grating G0 has a period of g 0 = g 2 × L/d = 14 μm, ensuring that the interference patterns from neighboring source lines will overlap at G2 (David et al 2007a). The sample should be located immediately in front of G1, and the detector should be immediately behind G2. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the first experimental soft-tissue phase-contrast tomography results using a conventional x-ray tube source, with a millimeter-sized focal spot. The setup is based on a Talbot-Lau grating interferometer operated at a mean energy of 28 keV. We present three-dimensional ex vivo images of a chicken heart sample, fixated in formalin. The results clearly demonstrate the advantageous contrast attainable through phase-contrast imaging over conventional attenuation-based approaches.
    Full-text · Article · May 2009 · Physics in Medicine and Biology
    • "(Orange graph) Spectrum w(E ) considering anode self-absorption, 1 mm Be window and 1689 mm air in the beam path, only; (black graph) effective spectrum w eff (E ) according to Eq. (18), which also comprises the detection efficiency of the 600 µm thick CsI scintillator and beam hardening due to the two 280-µm-thick Si wafers of the gratings, a 1-µm-thick gold layer on the analyzer grating (cf. David et al., 2007) and the 0.5-mm-thick amorphous carbon scintillator substrate (absorption coefficients from Hubbell & Seltzer, 1995). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of different physical parameters, such as the source size and the energy spectrum, on the functional capability of a grating interferometer applied for phase-contrast imaging is discussed using numerical simulations based on Fresnel diffraction theory. The presented simulation results explain why the interferometer could be well combined with polychromatic laboratory x-ray sources in recent experiments. Furthermore, it is shown that the distance between the two gratings of the interferometer is not in general limited by the width of the photon energy spectrum. This implies that interferometers that give a further improved image quality for phase measurements can be designed, because the primary measurement signal for phase measurements can be increased by enlargement of this distance. Finally, the mathematical background and practical instructions for the quantitative evaluation of measurement data acquired with a polychromatic x-ray source are given.
    No preview · Article · Nov 2008 · Journal of Microscopy
Show more