HOW THE KELVIN PROBE SYSTEM WORKS
-
The Kelvin Probe consists
of a vibrating reference electrode in plane-parallel orientation to the
sample, creating a capacitor. The sample and probe are connected via a
voltage source called the "backing potential" (Vb).
When Vb is set to zero, a contact potential
difference (Vcpd) equal to the difference
in the probe and sample work functions appears across the probe/sample
faces. The change in work functions is detectable because
wf
= eVcpd where
e is the electronic charge. At the unique point where Vb=-Vcpd
the circuit is balanced, and the electric field between the plates vanishes
resulting in a null output signal. This null condition, and deviations
from it, can be detected with high precision, thereby directly measuring
the changing sample work function. -
The
Kelvin Probe System measures work function changes in electron volts and
needs no calibration. The Kelvin Probe does not run the risk of desorbing
weakly bound adsorbates. This method provides a mean work function value
of the sample and is not biased towards low work function patches as is
the case in thermionic emission, photoemission and field emission. - The Kelvin Probe uses a computer controlled backing potential operating in a scanning mode. This has a significant advantage by reducing shielding problems. The signal-to-noise ratio is dramatically increased even with long connecting cables or reduced probe dimensions (i.e., micro-tips) due to the remote preamplifier and produces very high accuracy measurements.
-
Historically,
many problems have arisen when the null condition is detected using a lock-in
amplifier. The Kelvin Probe System uses a digital oscillator and digital
trigger which eliminate the need for a lock-in amplifier. This allows data
to be recorded at a variety of frequencies and amplitudes. This ability
to acquire data off resonance eliminates the subtle, but significant, resonant
frequency shifts that plague other probes. These features are unique
to the Kelvin Probes from this company
DEPENDABILITY
AND VERSATILITY
In addition to UHV use,
the Kelvin Probe System can operate in air, gas and even
some liquid environments. This allows in situ measurements under
real-world conditions as well as the laboratory environment.
INCREASED SIGNAL-TO-NOISE RATIO
NO LOCK-IN!