Our basic explanation is split into several steps
The picture on the right illustrates the core part of the microscope.
A solenoid creates a strong magnetic field. The solenoid is
surrounded by a ferromagnetic shield with an aperture on the axis.
A sample is placed in the magnetic field at the center of the
The sample is illuminated with x-ray photons, and a shower of
secondary electrons is emitted from the surface.
These electrons travel away from the sample down the magnetic
field lines in cyclotron orbits.
When the electrons exit the magnetic field through the aperture they
still have the momentum from the field. The momentum makes the
electrons move at an angle off the axis.
The final angle that an electron has with the axis depends on the
electron's original position in the magnetic field at the sample.
The result is that each x,y position on the sample leads to a different
exit angle, and this transforms the electron trajectories into an
angular image in to theta and phi.
Inside the magnet field the electrons move in cyclotron orbits. When
they exit the field they are deflected off at an angle
The magnetic field is terminated by the aperture. The angular image is
projected into field free space. The angular image is composed of many
electron energies across the secondary electron spectrum.
We now need to choose one energy window, and project the angular image
as a monochromatic x,y image (real image).
An important thing to understand is that the focus of the angular image is not
at the sample. The sample can move back and forward in the magnetic field.
It does not go out of focus. VPPEM has a very high depth of field.
|The NIST XPS microscope is based on a new imaging concept:
The momentum in a strong magnetic field is used to create the image.
Note: The momentum field of a magnetic field B is the vector potential A. Maxwell's equation is B=∇×A
More information on how it works