Hard X-ray imaging
This is a nondestructive way of visualizing samples, often their internal parts. The applications are virtually limitless. There are two basic techniques employed:
- Imaging: A full field image, similar to a traditional x-ray image is recorded
- Scanning: The full image is constructed by scanning an extremely focused ray over the sample.
In any case, the contrast in the image stems from physical differences in the sample. These can be in absorption, elemental composition or refractive index.
Although the resolution is not as good as in an electron microscope, x-ray imaging allows studying more than just the surface of a sample, e.g. buried interfaces or wet biological samples.
Includes: radiography; phase contrast imaging; scanning micro/nanoprobe; full-field microscopy; DEI; x-ray tomography; topography
Soft X-ray imaging
The wavelength of soft x-rays (1-15 nm) is well suited to probe the interior structure of biological cells and inorganic mesoscopic systems, e.g. in the study of:
- Cell biology
- Nanomagnetism
- Environmental Science
- Soft matter, polymers
Soft x-ray microscopy employs photon or electron optics to achieve the necessary high resolution.
- Fresnel zone plates are employed as photon optics in scanning transmission x-ray microscopy (STXM) to build up the image by scanning through the illuminated spot.
- In photoelectron emission microscopy (PEEM), the generated photoelectrons are passed through an electron microscope column to generate the magnified image.
Again, the tunability is important, in this case for reaching the photon energies where different contrast mechanisms can generate an image. Cell biology uses radiation around 300-500 eV, while nanomagnetism studies need 600-900 eV.
One technique unique to synchrotron light sources is phase contrast micro-tomography. Here the light is split up in two rays. The one which passes through the sample experiences slightly differing phase shifts depending on minute differences in material density. After recombining the rays, the resulting interference pattern enables researchers to detect much smaller changes in density than with regular tomography techniques. Essential is the synchrotron radiation’s near-coherence.
Includes: PEEM; STXM; XDI; CAT scans; full-field microscopy; x-ray tomography
Infrared imaging
By measuring absorption of radiation in the IR region of the spectrum (<1 eV) when the beam is focused through or reflected from a very small spot on a sample it is possible to investigate the sample with high accuracy. The absorption peaks correspond to vibrational frequencies and generate a molecular fingerprint for each point of the sample, which together make up the complete image.
The intensity of SR sources is greater than that of ordinary laboratory sources. This allows more accurate, though still non-destructive analysis of a sample. Applications are in:
- Chemistry in biological tissues
- Chemical identification and molecular conformation
- Mineral phases in geological and astronomical specimens
- Forensic studies
Includes: IR; microspectroscopy; infrared microprobe
