XRay Imaging

in an Electron Microscope



The X-ray ultraMicroscope (XuM) from XRT Limited provides X-ray images to be recorded with resolution better than 120 nm. X-ray images from the XuM exploit both absorption and phase contrast to reveal fine internal structure and edge detail.
Images are formed using projection X-ray microscopy as shown below:

Principle of operation

A point-like X-ray source needed to form high-resolution images is obtained using the scanning electron microscope (SEM) and a suitable target. Moving the sample position between the source and the detector varies magnification and phase contrast, with magnification at the detector being given by (R1+R2)/R1. To achieve the required magnification range R1 is varied from tens of microns to tens of millimeters.

The XuM can be fitted to a range of host SEM instruments to dramatically expand their imaging capability. In comparison with existing microscopy techniques, X-ray ultraMicroscopy offers:

  • Ability to form images showing internal sample structure.
  • Enhanced image detail using both absorption and phase contrast data.
  • Large depth of field, providing micro-tomography and stereo imaging capacities.
  • A reduced requirement for sample preparation.
  • X-ray image manipulation and enhancement (phase retrieval and resolution improvement) using proprietary processing software, X-TRACTTM.

The XuM has four main components, which are integrated into the host SEM to provide the unique XuM facilities:

  1. Advanced Target Positioner (ATP).
  2. Specialized sample holders.
  3. X-ray detector (CCD).
  4. Host PC with XuM CONTROL software for target positioning, sample positioning, image acquisition and pre-processing and X-TRACT software for advanced X-ray image processing, stereo imaging and microtomography.

Advanced Target Positioner and chamber arrangement

Advanced Target Positioner:

The Advanced Target Positioner uses a Nanorobotics manipulator with three stages including a Position Measurement System in three axes to position the target with nanometer accuracy over a total translation range of 20 mm. The target holder holds up to five targets, each designed to optimize X-ray energy distribution and intensity while minimizing source size.

Maximum sample thickness is limited by the energy of X-rays that can be generated efficiently using the SEM and the density and atomic number of the sample. Maximum thickness can range from a micron or so for dense metal samples to many hundreds of microns for low density samples. Samples that may be suitable for imaging with the XuM include semiconductors, MEMS, powders and granules, thin ceramics or metal samples, fibers, plastics and polymers, paper and solid foams composed of carbon, silicon or silicates.

This application describes how a Nanorobotics manipulator is used as Advanced Target Positioner to form an X-ray ultraMicroscope out of an Electron Microscope.
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