Realtime Operation
38
Scanning Probe Microscope Training Notebook
Rev. F
Figure 16.2b
Scope Trace Demonstrating the Effect of Setting the Integral Gain Too Low
Set the Integral Gain as high as possible by increasing the gain until noise is seen, then reduce the
gain just lower than the value where the noise disappears.
16.3 Scan
Rate
The Scan Rate is the number of trace and retrace scan lines performed per second (Hz).
•
For example, with a scan rate set to 1Hz, the tip will scan forward and back (trace and
retrace) in 1 second.
Set this value so that the feedback loop has time to respond to changes in the sample topography.
Setting the scan rate too high will result in poor tracking of the surface, as shown below.
Figure 16.3a
Scope Trace Demonstrating the Effect of Setting the Scan Rate Too High
The actual
tip speed
or of the tip depends on two parameters:
Scan Rate
and
Scan Size
. Since the
Scan Rate units are lines per second (Hz), increasing the Scan Size without changing the Scan Rate
actually increases the scan velocity of the tip.
•
For example, if the Scan Rate is 1Hz and the Scan Size is 1µm, the scan velocity is
2µm/sec (since it performs the trace and retrace scans in 1 sec). By increasing the Scan
Size to 100µm, the scan velocity increases to 200µm/sec if the Scan Rate remains 1Hz.