Lake Shore Cryotronics Measure Ready M91 FastHall, Руководство пользователя

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6 CHAPTER 1: Introduction
MeasureReady™ M91 FastHall™ Measurement Controller
Resistivity (

) is used to derive Hall mobility, but it is also an important transport
property. Resistivity (

) is the shape independent expression of resistance (R) derived
by canceling the area (A) through which the current flows, and the length (L) along
which the current flows.
In the figure below, the area is the width (w) times the thickness (t), so the equation
for resistivity becomes:
FIGURE 1-2
Resistivity
Following Ohm’s Law, resistance (R) is the ratio of voltage (V) to current (I).
Sheet resistivity (

sheet
) can be calculated even when the thickness of a sample is
unknown at the time of the measurement. If the resistance (R) of the sample is
measured, then sheet resistivity is the resistivity divided by thickness.
The SI units of (

sheet
) are
V
/ A. It is not
V
/square meter or any other length, but simply
the resistance of any size square (w = L in the above equation) of the material when
the current is flowing uniformly along the length of the sample.
Sheet Hall coefficient (R
Hsheet
) can also be calculated even when the thickness of a
sample is unknown at the time of the measurement.
Voltage measurement notation (V
ij
,
kl
): four lead measurements are used to measure
resistance (for resistivity), or Hall voltage. The most common measurement is to
apply a current through two leads and measure the voltage difference between the
other two leads.