Offline Operation
46
Scanning Probe Microscope Training Notebook
Rev. F
There are a wide variety of measurements made in Roughness. The roughness parameters which
are displayed are chosen under the Screen Layout menu.
The measurements made on the entire image are displayed under “Image Statistics.” Roughness
measurements of a specific area may be determined by using the cursor to draw a box on the image.
After selecting “Execute,” the measurements within the selected area are displayed under “Box
Statistics.”
The most common measurements are the following:
1.
RMS (Rq)
: The Root Mean Square (RMS) Roughness is the standard deviation of the Z
values within a given area.
•
Z
ave
is the average Z value within the given area, Z
i
is the current Z value, and N is the
number of points within a given area.
•
R
a
: The Mean Roughness (R
a
) represents the arithmetic average of the deviations from
the center plane.
•
Z
cp
is the Z value of the center plane, and Z
i
is the current Z value, and N is the number
of points within a given area.
Note:
The above equations for RMS and R
a
are presented for ease in understanding.
The formulas used by the NanoScope software to compute these numbers are
found in the manual.
2.
R
max
: The difference in height between the highest and lowest points on the surface relative
to the Mean Plane
3.
Surface Area
: The three-dimensional area of a given region. This value is the sum of the
area of all of the triangles formed by three adjacent data points.
4.
Surface Area diff
: The percentage increase of the three dimensional surface area over the
two dimensional surface area.
RMS
Z
i
Z
ave
–
2
i
1
=
N
N
-------------------------------------
=
R
a
Z
i
Z
cp
–
i
1
=
N
N
-------------------------------
=