How the Gatan X-ray Ultra Microscope (XuM) works
- The electron beam of the SEM is used to create a cone of X-rays by focusing the beam onto a metal target (usually platinum).
- The sample, which is off-set to one side of the beam, is placed within the X-ray cone.
- The resulting X-ray absorption image is projected onto a charge-coupled device (CCD) behind the specimen. This CCD output is essentially a 2D X-ray image where differences in grey-scales reflect changes in density of the specimen:
- lighter areas indicate that the X-rays are less absorbed and therefore consist of a material of low-density
- darker areas indicate that the X-rays are more absorbed and therefore consist of a material of high-density
- A full 3D CT dataset is created by collecting 2D images over 360 degrees at 1º increments of rotation.
- These data are then reconstructed to produce ‘virtual slices’ through the specimen and a virtual 3D volume can be visualised.