nGauge AFM User Manual
13
beyond the range of the Fine Z control, the image will get clipped. To increase or decrease the Fine Z
scan range, click on the
Menu
, then under PGAs increase or decrease the Z Fine. For maximum imaging
resolution, the smallest Fine Z range should be used. It is also possible that the sample topology is not
centered around the middle of the Fine Z range, which could result in image clipping. The Approach tab
displays a graph with the Fine Z position. If it appears that most of the image data is at the lower or
higher end of the Fine Z range, you can click
Show Advanced Controls
and increase or decrease the
Coarse Z to center the data. In some cases, you may even need to
Disengage
and then re-
Approach.
There are several parameters that you can control to improve the imaging performance. The
Time spent at each point
is the number of microseconds that the tip will dwell above each data point.
As you decrease this value, the scan speed will increase and the controller will have less time to track
the sample topology, leading to poor image results. The
Set Point
is the tip oscillation amplitude that
the controller will try to maintain as the tip scans over the sample surface. It can be thought of as the
amount of force that the tip exerts as it taps the surface, where a lower setpoint exerts more force. A
lower setpoint can often give better results, but is also more likely to damage the tip or sample, and
when the setpoint gets too low the imaging performance may suffer. A PI controller is used to maintain
a constant tip oscillation amplitude throughout the scan by adjusting the Fine Z height. The
Proportional
and
Integral
control in the advanced controls section are used to adjust the response of the controller,
and can be tuned to give the best sample tracking performance. See section 6.0 Troubleshooting for
more details for PI tuning.
At any time you can click
Pause
and
Resume
to temporarily halt and then resume the current
scan, or you can
Pause
and then
Reset
to re-start the current scan at the beginning. When the scan is
complete, you will be able to click
Save
to save the image as a .gwy file which is native to Gwyddion (a
post-processing software), and as a .png image. You can also save the data as a .tsv file where the data
points are arranged in a 2-d tab and line separated table. The image will be saved in the folder specified
by
Path
, which you can click on to change. All 6 images (topo, phase, error forward/reverse) will be
saved, and a Unix timestamp will be appended to the file name.
To zoom into a region of interest, you can drag across the displayed image to select an area to
zoom in. Click
Scan
again after the selection has been made to scan the region of interest. To reset to
the original scan area, click
Reset Zoom
. If
Reset Zoom
button is disabled, the AFM will scan the default
area.
