5-118
TMPM5200-2
Obse
de is larger than that in the STM observation
(for a conductive specimen). If the bar graph displayed in the Status window exceeds
scale, reduce the set value of Preamp Gain in the Advanced
rving a contact current image
•
The current measured in the contact mo
the maximum on the
Control window.
Signal value for
current image
Signal value
for topograph
image
nm nA
y
The maximum detectable current for each preamplifier gain is shown below.
Preamp gain
Maximum detectable
current
0.01 V/nA
1
µ
A
0.1 V/nA
100 nA
1 V/nA
10 nA
•
If the specimen has low conductivity like an insulating material, or the surface of the
specimen is oxidized, the current changes little and the image contrast is poor.
•
Linear current instead of Log current can be used to observe a current image. When
the contrast does not increase with Log current, the apparent sensitivity can be
increased with Linear current.
•
In order to correctly observe a current image, a topography image must be acquired
correctly. If the feedback filter setting is too slow, the cantilever response to the
specimen surface topography becomes very slow, thus resulting in incorrect current
measurement.
Cantilever
Distance between
specimen sur face
and cantilever tip
is constant.
Distance between
specimen sur face
and cantilever tip
varies with positions.
Specimen
Too slow feedback speed
Appropriate feedback speed
