Tip Shape Issues
56
Scanning Probe Microscope Training Notebook
Rev. F
19.1 Resolution
Issues
The resolution of AFM images can be thought of in terms of
lateral
(X,Y)
resolution and
vertical
(Z)
resolution.
Lateral Resolution Issues
Tip Shape
:
•
As discussed in the previous section on tip shape effects, the radius of curvature of the
end of the tip will determine the highest lateral resolution obtainable with a specific tip.
The sidewall angles of the tip will also determine its ability to probe high aspect ratio
features.
Pixelization
:
•
The
Samples/ line
parameter in the Realtime menu determines the number of data
points present in the image in the X and Y scan direction. These data points are
commonly called “pixels.” Available choices are 512, 256, and 128.
•
Pixelization affects resolution in that you cannot resolve features smaller than the pixel
size of the image.
•
For example, if you are acquiring a 50µm x 50µm image with the
Samples/ line
parameter set to 512, then the pixel size is 98nm (50µm÷512=0.098µm or 98nm). Thus,
you will not be able to resolve features smaller than 98nm at a 50µm scan size.
•
If you want to be able to see 10nm sized features, you will need to choose a scan size
<5.12µm (preferably 1 or 2µm) since 5.12µm÷512 = 0.010µm or 10nm.
•
Regardless of the pixel size, the feedback loop is sampling the topography many times
at each pixel. The data displayed at each pixel is the average of the sampling iterations
by the feedback loop over the pixel area.