Magnetic Resonance Force Microscopy (MRFM) is a relatively brand new imaging technique. It was theorised in 1991 by J. A. Sidles in his paper "Noninductive detection of single-proton magnetic resonance" published in Applied Physics Letters. His idea was put into practice and the first image produced using MRFM was made in 1993.
How MRFM Works
MRFM uses equipment that is very similar to that used for Atomic Force Microscopy (AFM). The main difference is that for MRFM the microscope tip is magnetic. A coil in the instrument applies a radio-frequency (RF) magnetic field that changes the ‘spin’ of electrons and protons in the sample. Each flip of the spin causes the cantilever attached magnetic tip to move resulting in vibration as it moves across the sample surface. A laser and optical detector is able to read these vibrations and produce a picture of the individual atoms in the sample.
Figure 1. Schematic diagram for an MRFM
The application of different RF fields results in difference responses in the cantilever tip for different atoms. With further work it is expected that MRFM will be able to identify the exact location of individual atoms and identify which element they are.
Atomic Scale 3D Images
One of the most exciting promises offered by MRFM is that due to such high resolution and the fact that it can detect atoms below the surface, MRFM can show three dimensional images at an atomic level. Although yet to be achieved, 3D imaging in this manner has been proved theoretically possible.