Nanosurf easyScan 2 AFM, Operating Instructions Manual

Page: 60 / 164

I
MPROVING MEASUREMENT QUALITY
60
Improving measurement quality
Removing interfering signals
Interfering signals can be recognised because they have a fixed frequency,
usually a multiple of the local mains frequency (50 or 60 Hz) throughout
the image. Thus, they are manifested by straight lines that run throughout
the image.
Possible interference sources are:
• Mechanical vibrations from machines or heavy transformers in the envi-
ronment (e.g. pumps).
• Infrared light sources (light bulbs, sample illumination in an inverted
microscope).
• Electrical interference (in the electronics, or in electrical forces in the tip-
sample interaction).
Mechanical vibrations
Measure the frequency of the vibrations to find out if the interference is due
to mechanical vibrations. These vibrations have a frequency that is (a mul-
tiple of ) the rotation frequency of the source. This frequency is usually not
a multiple of the local mains frequency, and may change slightly over time.
Try the following to find out if the interfering signal is due to mechanical
vibrations:
- If possible, turn off all rotating machines (i.e. pumps) in the room.
- Change the vibration isolation by putting the Scan head directly on the
table, instead of on the Sample stage.
To reduce the influence of these vibrations, either improve the isolation of
these machines, or improve the isolation of the instrument by using a vibra-
tion isolation table (e.g. the optional TS-150 active vibration isolation
table).