Scanning Probe Microscopy
In order to resolve atomic resolution details beyond optical diffraction thresholds a physical probe can be placed on an x-y manipulated sample to map the topography and structure of the surface.
Different SPM implementations can also be used in temperature dependent experiments within cryogenic vacuum, benefiting from low noise, vibration isolation and highly clean sample vacuum.
Atomic Force Microscopy (AFM)
Focuses a laser on a probe tip placed onto the surface of the sample. This allows for height mapping of the sample by detecting changes in the laser as the tip moves and resonates.
Ref: Markus Raschke, University of Colorado (Paper Link)
Ref: RHK Technologies, Commercial Cryo-SPM’s
Scanning Tunnel Microscopy (STM)
A conductive probe tip is placed very close to the sample surface with a biased electrical signal run through the tip. As the sample’s surface and tip interact, the changes in current indicate the surface height at a given position.
Using ultra-low vibration Cryostats such as the Closed Cycle DMX-20B or Helitran LT-3 Flow system, single atom resolution can be achieved.
Ref: Dr. George Nazin, University of Oregon
Ref: Dr. Wilson Ho, UC Irvine
Scanning Electron Microscopy (SEM)
This form of microscopy directs an electron beam across the surface of the sample to measure electron interactions at different depths. A detector measures electron loss as the beam interacts with the surface, or deeper within the structure.
Cryogenic temperatures help to maintain structure for biological samples and Ice based samples while being scanned under the beam.
Ref: Dr. Dan Rich, Ben Gurion University (Paper Link)