In far-field microscopes, the spatial resolution is ultimately limited by the wavelength of the radiation used. While near-field and related microscopes can improve upon this, they can only do so with thin specimen regions. Thin specimens can also be studied at atomic resolution using electron microscopes. To achieve improved resolution on micrometer-thick specimens, another alternative is to use significantly shorter photon wavelengths. We discuss here the use of soft x-rays for microscopy and their resolution limits.
Image formation requires resolution and contrast. by using soft x-rays with a photon energy between the K absorption edges of carbon and oxygen, one is able to image hydrated biological specimens with high contrast. The contrast is such that no addi-tional staining is required, while efforts are also underway to utilize gold and luminescent probes for selective labeling. In addition, x-ray sources have high spectral resolution and good signal-to-background relative to electron microscopes which allows for elemental and chemical state mapping of major constituents.