Scanning Tunneling Microscopy (STM)
Spectroscopy with the STM
Rev. D
Dimension 3100 Manual
187
Head Offset
The value of the head preamplifier offset can be measured and corrected with the
Offset
command
in the
Realtime
>
Microscope
menu. The procedure is as follows:
•
Withdraw the tip from the sample surface.
•
Invoke the
Offset
command to observe the offset current of the preamplifier in
nanoamps.
11.4 Spectroscopy with the STM
The NanoScope STM performs limited spectroscopic operations under the two scanning tunneling
spectroscopy STS modes of operation. The variation of the tunneling current due to variations of
the bias voltage or tip-to-sample separation can be tested and recorded at a single point with the
View
>
STS Plot
modes.
STS Plot Modes
In the
STS Plot
modes, the tip is positioned at a point on the surface, and a spectroscopic plot is
acquired and displayed in a scope format. Between plots, the feedback is run to establish the
tunneling current to the setpoint value. The different types of STS Plots that can be acquired are:
STS i(v)
— The tunneling current as a function of the bias voltage is displayed. The tip height is
held constant while the I-V plot is being acquired. In addition to I vs. V, F(d i,dv), F(d ln(i),dv), or
F(d ln(i),d ln(v)) vs. V can be plotted.
STS i(s)—
The tunneling current as a function of the tip height is displayed. The bias voltage is
held constant while the I-S plot is being acquired. In addition to I vs. S, ln(I) vs. S can be plotted.
11.4.1 Operation of STS
In the following sections, the operation of the spectroscopic functions of the NanoScope STM will
be discussed. Additional information can be obtained from the
Command Reference Manual
.
STS Plot
There are several items that you should be aware of when using the NanoScope to acquire
spectroscopic plots with the
STS Plot
commands. The spectroscopic capabilities can provide
information that can help to distinguish different species although exact species identification is
difficult, especially in air. The spectroscopic plots should aid in comparative studies between
samples or between different regions on a sample, but they will not reveal the precise make-up of
that sample.
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