X-ray Reflection Phase-Contrast Microscopy (XRIM)

Observation of Subnanometre-High Surface Topography with X-Ray Reflection Phase-Contrast Microscopy

Schematic of an X-ray reflection interface microscope (XRIM), using Fresnel zone plate (FZP) optics to image an interface.

XRIM image of an orthoclase (001) surface. The white box indicates a region with a 0.65 nm-high monomolecular step (seen as a dark line).

The ability to image interfaces in complex environments is strongly limited. Scanned probe microscopies (e.g., atomic force microscopy) are widely used but require the use of a probe tip which can be invasive. X-ray-based techniques have mostly relied on laterally averaging approaches (e.g., x-ray scattering and spectroscopy). X-ray microscopy has so far been limited to studying objects that are larger than the ~20 nm resolution of state-of-the-art x-ray optics.

• The ability to observe subnanometer-high interfacial topography using X-ray microscopy has been demonstrated for the first time.
   
• Molecular-scale interfacial topography is imaged as changes in the reflected intensity, in this case, due to destructive interference of X-rays reflected near steps. This novel use of interfacial phase contrast allows objects to be observed that are substantially (~300x) smaller than the experimental spatial resolution.
   
• The use of full-field imaging allows large areas of the surface to be imaged rapidly (~1 minute) so that real-time observations of interfacial dynamics are possible.
   
• This capability opens up a number of new possibilities for interfacial science:
  • Observation of interfacial dynamics in aggressive chemical environments
  • High-resolution structural studies of surfaces on small-grained materials
  • Direct observations of buried interfaces

Reference

P. A. Fenter, C. Park, Z. Zhang, and S. Wang, “Observation of Subnanometre-high Surface Topography with X-ray Reflection Phase-Contrast Microscopy,” Nature Physics 2(10) (2006).