SCANNING
With the cantilever mounted and thelaser alignment optimized, the system isready to begin imaging. Minimum user
input is required prior to engaging, andin most cases the default parameters
can be used. The parameters available tothe user at this stage include:
1) Scan Size
Scan size(s) can be entered to allow theAFM to collect either single or multiple
images from the same sample.
2) Cantilever Type
Select the cantilever type in order torestrict the frequency range used during
the autotune process. This signiﬁcantly
speeds up the search for the cantilever’s
resonant frequency.
3) Imaging Force
The imaging force is controlled by boththe cantilever oscillation amplitude andthe amount by which that amplitude is
reduced once the tip is on the surface.
4) Image Quality
The image quality is given by the numberof lines and the number of samples
per line in the ﬁnal image. Throughout
the Easy AFM imaging process, square

pixels are maintained regardless of thequality setting. This square-pixel setting
ensures a more consistent off-line
image analysis.
Once these parameters have beenset, the system is ready to image. The
imaging process is initiated by simply
clicking on the green GO button (seeﬁgure 1).
Once the imaging process is started, thesystem will tune the cantilever, engage
on the sample and optimize the scanparameters with no further user input
required.
IMAGE OPTIMIZATION

Easy AFM® starts with a set of default
engage parameters that are calculated
from the imaging force and cantilevertype user inputs. Default engage
parameters are designed to allow thesystem to engage successfully for thevast majority of samples. Once engaged
on the surface with a zero scan size,
the system will proceed to increase
the scan size while optimizing the scanparameters to ones more appropriate
to the topography of the sample being
imaged. This is done in several stages.

The RMS amplitude of the cantileverat zero scan size as a function of thefeedback gains is an indicator of thenoise on the system and is cantilever
speciﬁc. Hence, continuously monitoring
the RMS amplitude of the cantilever as
the feedback gains are increased will
help determine the gain levels required
for the chosen cantilever type. Once theRMS amplitude reaches a predetermined
limit, the system is switched to image
mode at 105% of the requested scansize. The software now obtains a lowresolution topography image at this scansize in order to determine the heightvariation of the sample.
From the initial survey scan, imaging
parameters are calculated using themeasured height variation. These
parameters are subsequently used
for the ﬁnal high-resolution scan. The
derived scan parameters are functionsof the measured sample roughness,
imaging force selected by the user, andscan size.
The variables are set using thefollowing algorithms:• Scan rate (Hz)The scan rate is initially set based on
the sample roughness with an additional
factor to account for the scan size andimaging force.
The scan size correction factor reduces
the scan rate as the scan size increases
in order to limit the tip velocity relative tothe sample. This ensures that the tip will
track surface topography regardless ofscan size.
The correction is only applied for scansizes above 1μm. For scan sizes of 1μm
or less, the correction factor is set to
1.0, and hence, from equation 1, as thesample roughness tends to zero themaximum scan rate tends to 2.65Hz (seeequation 1).

Figure 2. Animated guides help the new user with fundamental tasks such as changing the cantilever andaligning the laser.

PAGE 2Easy AFM• Set-point reduction
The amplitude set-point is reduced,
which creates a higher tip/sample force
and enables the feedback loop to better
track the sample topography. The setpoint reduction factor is further modiﬁed
to ensure that set-point reduction isscaled appropriately when imaging
samples with light forces. The setpoint reduction factor is calculated byequation 2.
• Gain scalar
The initial feedback gains set tocapture the initial low-resolution scan
are modiﬁed based on the measured
roughness of the sample. Samples withlittle topography require lower gains forthe feedback loop to track the surface,whereas samples with rougher surfaces
require a higher feedback gain at thesame scan rate.
The corrections given by these equations
allow the feedback loop to better follow
the surface topography for a sample witha given roughness.
Finally the Z-limit is reduced to a value
appropriate for the measured roughness
in order to maximize the resolution inthis axis.
With the calculated scan parameters forthe ﬁnal high-resolution image set, thesystem will attempt to optimize themfurther in order to ensure the highest
possible image quality. Optimization of
the scan parameters for the ﬁnal image
is measured by the ability of the tip tocorrectly track the surface topographyusing both trace and retrace data.
Variations in measured trace versus
retrace data will cause the system totake the following actions:

Scan Rate = 2.65 exp –6x10–4(rms amplitude)4
scan size (μm)

x1Reduction Factor =exp5–6x10 (rms amplitude)(equation 1)(equation 2)
x1
Setpoint Delta

Gain Scalar = [0.35 1n (rms amplitude)] – 1(equation 3)

Equations used to calculate image parameters are based on the measured sample roughness.

• Reduce the scan rate
The scan rate is reduced to 90%
enabling the system to better track thetopography with the existing tapping
force and gain settings.
• Increase the drive amplitude
The drive amplitude is increased bya factor of 1.15. This has the effectof increasing the tapping force while
preventing the set-point from becoming
too low when imaging with light tapping
forces and low drive amplitudes.
Between each of these four adjustments,
tracking is remeasured. Hence, only
those actions necessary for good
image quality are carried out. Once thescanning parameters are ﬁnalized thescan is started from the top of the frame
and the system is set to capture theresultant data.

OPTIMIZED DATA

Once the optimization process has
determined the ﬁnal scan parameters,
the AFM will capture the resultantimage. Following capture, the “TrackingFactor” is measured and compared tothat recorded before the image wasacquired. The ﬁrst value is taken at thetop of the image, while the second ismeasured at the bottom. If tracking inboth of these regions was not optimum
then a warning is shown allowing theuser to decide whether or not to rescan
the sample.
For the majority of samples imaged
with Tapping Mode® in air, the resulting
data will be in the form of high quality
images. These images will contain bothheight and amplitude data and may
be processed in the usual way using
NanoScope’s off-line functionality.

• Increase the tapping forceThe amplitude set-point is reduced to
90% resulting in an increase in the tip/sample interaction force. Increased
tip/sample forces generally allow thesystem to track surface
topography better.
• Increase the feedback gains
The integral and proportional gains
are increased by a factor of 1.2 and 1.4
respectively, which increases the abilityof the AFM to track topography.

Figure 3. Data before (left) and after (right) the optimization process shows an improvement in the ability totrack surface topography.

Easy AFM.

PAGE 3