JEOL JSPM-5200 Instructions Manual page 181

５ MEASUREMENT OPERATION
Obse rving a contact current image
• The current measured in the contact mo
(for a conductive specimen). If the bar graph displayed in the Status window exceeds
the maximum on the
Control window.
The maximum detectable current for each preamplifier gain is shown below.
• 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.
Appropriate feedback speed
5-118
scale, reduce the set value of Preamp Gain in the Advanced
Signal value
for topograph
image
Preamp gain
0.01 V/nA
0.1 V/nA
1 V/nA
Distance between
specimen surface
and cantilever tip
Cantilever
is constant.
Specimen
de is larger than that in the STM observation
Signal value for
current image
y
nm nA
Maximum detectable
current
1 µ A
100 nA
10 nA
Distance between
specimen surface
and cantilever tip
varies with positions.
Too slow feedback speed
TMPM5200-2