The project was initiated by a request for proposal from NIST for a high
spatial resolution XPS microscope in 2006. The project was started as a
Phase I SBIR in 2007.
The initial design concepts for the current instrument were based on the
MicroESCA instrument at Stanford University (1) which used the same
operating principle as the Turner microscope (2). In this instrument the
sample was held in a strong magnetic field and illuminated with x-ray
photons. The photoelectrons are entrained along the lines of force and as
the magnetic field decreased away from the center field the expanding lines
of force magnify the photocurrent distribution. The photocurrent was energy
filtered using a high pass filter in the form of a retarding field grid in front of
the image detector.
Stanford attempted to take the idea forward by proposing to add a band
pass filter by adding magnetic grids in from of a CHA. However, this
approach ultimately proved unsuccessful, and work on the instrument was
However, the concept of adding a band pass filter was a good one.
It was clear from the literature that slowly allowing the photoelectrons to
leave the magnetic field at a low magnetic field strengths produced only a
swirling and confused distribution. But, our calculations showed that
suddenly terminating the magnetic field using an aperture in a
ferromagnetic shield prevented any swirling, and instead produced a
rotated but perfect two dimensional angular image.
It was later that we realised that the angular image formation was directly
due to the momentum change in the two dimensional vector potential field
as it went to zero.
Operating principle of the micoESCA
The NIST project benefited from the discontinued Stanford project when the
SLAC group kindly loaned the NIST project the hardware from the
microESCA instrument. This equipment included the superconducting
magnet and CHA.