Application I
Sample: Langmuir-Blodgett film (ethyl-2,3-dihydroxyoctadecanoate) on mica in air
Scan Range: 8.6 µm × 8.6 µm
Data Type: topography / Data Range: 25 nm
This highly sensitive sample surface could only be imaged
non-destructively with active Q-Control, whereas the periodic repulsive
contact with the probe in standard mode led to a significant
modification or destruction of the surface structure.
Data courtesy of L. F. Chi et al., University of Münster.
Application II
Sample: DNA ring structures on mica in air
Scan Range: 1 µm × 1 µm
Data Type: topography / Data Range: 8 nm
Even though non-destructive imaging of DNA ring structures in air was
also possible in standard mode, applying Q-Control resulted in a clear
improvement in resolution.
Sample courtesy of chimera biotec GmbH; data courtesy of L. F. Chi et al., University of Münster.
Application III
Sample: DNA on mica in buffer solution
Scan Range: 600 nm × 600 nm
Data Type: topography / Data Range: 2.3 nm
Being able to minimize the interactions forces during scanning is of
great relevance for imaging delicate biological samples in enviroments
such as water of buffer solution. The cross sections of the topographic
data reveal that the measured DNA height is significantly larger when
Q-Control is activated. The difference in the observed DNA height
indicates that the imaging forces were reduced by employing Q-Control.
Data courtesy of D. Ebeling et al., University of Münster.
Application IV
Sample: Langmuir-Blodgett film (DPPC double layer) on mica in H2O
Scan Range: 7 µm × 7 µm
Data Type: topography / Data Range: 6 nm
Each scan line was scanned twice - in standard tapping mode during the
first scan of the line (left data) and with Q-Control being activated
by a trigger signal during the subsequent scan of the same line (right
data). This interleave technique allows a direct comparison of the
results of the two modes obtained on the same surface area while
minimizing drift effects. The observed height of the DPPC layer is
significantly larger in case of imaging with Q-Control, i.e. the film
is compressed less by the probing tip.
Data courtesy of D. Ebeling et al., University of Münster.
Application V
Sample: harddisk with magnetic data structures
Scan Range: 5 µm × 5 µm
Left Data Type: topography / Data Range: 20 nm
Right Data Type: MFM phase / Data Range: 10 deg
The left image shows the surface topography of a computer harddisk
measured in tapping mode. The upper part of the right image shows the
magnetic data structures as they were recorded simultaneously in
standard mode, whereas in the lower part of the image Q-Control was
activated. It is clearly visible, that the application of Q-Control
leads to a significant improvement of the overall sensitivity and
thereby to an amplification of the magnetic contrast. Please note that
except for that Q-factor all parameters, e.g. oscillation amplitude,
lift height and scan speed, were kept constant during the entire scan.
Further investigations revealed, that in particular the signal-to-noise
ratio of such measurements on magnetic fields can be improved
significantly:
This analysis of measurements on a magnetic tape shows that the signal
amplitude (upper diagrams), i.e the image contrast, was increased by a
factor of 12.4 by Q-Control. However, in order to assess the
improvement in overall sensitvity it is more relevant to analyse the
signal-to-noise ratio. Just by looking at the cross-sections it is
already obvious that Q-Control leads to an significant improvement,
i.e. less noise. The detailed statistical analysis of averaged data
(lower diagrams) revealed an increase of the signal-to-noise ratio by a
factor of 2.3.
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