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Analysis of Specimen Orientation
Methodology for Energy Dispersive
X-Ray Spectroscopy
Writer: Alexander Huey
Advisor: Dr. Chunfei Li

Abstract: When using a scanning electron microscope (SEM) equipped
with a spectrometer, it is difficult to know if the specimen being observed is
in the optimal position to get the best readings from the equipment.
Previous data collected by my advisor, the Principal Investigator (PI), and
Clarion University (CU) has determined a method of specimen orientation
through rotation and tilt of the specimen table to determine its optimal
positioning. This was done by constructing a macroscale copy of the
equipment found inside a SEM and using it to measure the ratio of the
specimen’s projected lengths versus the rotation of the specimen table. To
confirm the methodology and interpretations of data developed in previous
experiments, new data has been collected to test against previous trials. The
newest trial has found evidence in support of previous findings, with similar
data being produced. This is an indication that the developed method of
orienting a specimen inside a SEM may fill a gap in research dedicated to
the use of lab equipment. Suggestions for further research and apparatus
redesign will be offered along with the conclusions.

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1. Introduction:
What is the function of a scanning electron microscope? A SEM allows for
the topological analysis of a specimen down to the order of a few micrometers,
that is, 1/1000000 of a meter. In the figure to the right, a breakdown of a SEM
can be seen along with an example of the
type of image that can be achieved.
Inside of an SEM, it is
possible to equip a spectrometer.
This allows for the spectral
analysis of an object in tandem
with the topological analysis.
While the topological analysis
provides a clear image of a
specimen, the spectral
analysis, known as Electron
Dispersive Spectroscopy
(EDS), provides a clear
elemental composition of the
specimen.
Both of these functions are commonplace in labs across
the globe, but there can be issues with their effectiveness that depend upon
the orientation of the analyzed specimen. The goal of this research is to
analyze the method of specimen orientation, proposed by PI, that may be
completed on site and will ensure the effectiveness of the equipment.

2. Importance:
This area of research is relatively untouched, however its benefits
can be appreciated by every scientist that uses this equipment on a regular
basis. One major benefit of EDS is that it is non-destructive. This means
that a very small amount (< 1/1000000000 grams) of material is required
and the material will not be altered or harmed after its use inside the SEM.
In years preceding spectral analysis, to determine the composition of a
material, it would have been burned or submerged in a chemical bath that
would give the same results as EDS, but leave the specimen chemically
altered or destroyed altogether. This can be beneficial, for example, in the
case of jewelry. EDS can be used to check the authenticity of

jewelry without rendering it useless in the process. The non-destructive3
nature of EDS makes it indispensable to agencies like NASA that often deal
with materials from outer space that are not easily obtainable but must be
studied to understand their place in the cosmos.

3. Predetermined Method
PI and CU have determined a
method of specimen orientation that
they tested theoretically and
experimentally before this trial. The
main idea behind getting an effective
reading from a SEM/EDS is that the
surface of the specimen being
analyzed must be perpendicular to
the electron beam emitted from the
SEM. The top image shows an
example of how a “specimen” (in our
case a 10 cm wedge) may be
oriented in such a way to achieve this
goal. The electron beam, denoted by
the red arrow, can be made
perpendicular to the surface of the
specimen by using the rotation and
tilt functions available in the SEM.
The steps taken can be seen in parts
a, band c. From a to b, the table is
rotated so that the interception line of
the Specimen is parallel to the tilting
Axis.
From here, the table may be rotated to bring the specimen’s surface
perpendicular to the electron beam, as can be seen from b to c. However,
not all specimens will be as uniform as a wedge and a set of steps must be
designed to guarantee that the surface of the specimen can be brought
perpendicular to the beam. To do this, a method of specimen orientation
was created by PI to determine a “special rotation angle.” This SRA is
where the specimen is in position to be tilted so that it is in the optimal spot
for EDS (part b of the top figure). The method to determine the SRA relies
on the projected lengths of two points on the specimen, and how these
projected lengths change based on tilting the specimen. The bottom left
figure shows how the distances between the same two points can change
based on tilting the specimen. Part b of the figure shows the distance
between two points on the specimen without any tilting inside the SEM.

Parts a and c show how the projected lengths can either be lengthened or 4
shortened depending on which direction the specimen is tilted. The figure
on the bottom right helps to demonstrate why these lengths change. In the
image, the true length (A to B) is not what is seen from the top-down view
inside the SEM. Instead, the projected length (A’ to B’) is seen. As the
specimen is tilted, the true length does not change, however the projected
length does. This is a key point of the research, as the method of specimen
orientation must be completed with only the functions found inside the
SEM. This means that only tilt and rotation can be used to orient the
specimen, and it must be completed only with information derived from the
top down view, as would be the case when using a SEM.
The two new figures on
the right show the theoretical
results based on simulations ran
by PI (top) and experimental
results used by gathering actual
data in a SEM (bottom). The
first graph is a comparison of
ratios of the projected lengths
versus the stage rotation angle.
The importance of this graph is
that the local minimum values
(found at 0, 180 and 360
degrees) are where our SRA
lies. So, if we have our wedge
set at 0 degrees or 180 degrees
rotation, its interception line will
be parallel to the tilting axis and
therefore can be oriented so that
it is in the optimal position for
the imaging functions of the
SEM or EDS analysis.
The bottom graph detailing the experimental results tell a similar
story, but they do not necessarily guarantee the results that are hoped for by
the method of orientation. To examine the method closer, an apparatus was
designed on the macroscale to imitate the functions found inside the SEM.
Using the macroscale apparatus, it is possible to mimic these functions and
take data that could help confirm the orientation methodology.

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4. The Experiment

The apparatus used in the experiment is pictured above.
It consists of a rotary table (equipped with rotation and tilt
functions similar to those found in the SEM), our “specimen”
placed on top of the rotary table, and two wires pinned to the
specimen that hang down and allow a measurement of the
projected distances between two points on the specimen. The
idea of the experiment is to take a measurement of the
projected length between the two points at 0 degrees rotation
and 0 degrees tilt, then measure the projected length again at 0
degrees rotation and 10 degrees tilt. From there, the apparatus
is lowered back to 0 degrees tilt and moved to 20 degrees
rotation. From there, the process is repeated again until
projected lengths at 0 and 10 degrees tilt are measured at 0
degrees rotation, 20 degrees rotation, 40 degrees rotation and
so on until the specimen has been rotated a full 360 degrees
back to its original position. At this point, the measurements at
each rotation angle and tilting position can be graphed to show
similar results to the experimental and theoretical results found
by PI.

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5. Results
The top graph to the right
shows the data points of the
experiment. The x-axis is the
rotation angle of the rotary table,
and the y-axis is the ratio of the
projected lengths of the points
on the specimen [(Tilt at 0
degrees - Tilt at 10) / Tilt at 0
degrees]. This is very similar to
the data found by PI in the
initial experiment done inside
the SEM. The bottom graph
shows the same data, but
applied in a way that can
resemble results produced from
the theoretical interpretation of
the experiment. Both graphs
determine the same thing, that a
“special rotation angle” exists at
0 degrees, 180 degrees, and 360
degrees.
Looking back at the first figure in part 3, it makes sense that this will be the
case. Zero degrees rotation and 180 degrees rotation place our specimen at
a point where it can be tilted to be perpendicular to the electron beam. 360
degrees rotation will obviously work as well, because at that point the
specimen has been brought back to what is considered its starting point,
zero degrees rotation, and it has been established that this is one of the
special rotation angles.
This confirms that the method of specimen orientation did in fact
determine the special rotation angle. Two things should be noted. First,
these results were achieved only by using the information available as it
would be when using a real SEM. This is important because the goal of the
experiment is to successfully orient a non-uniform specimen inside a SEM
using only the functions and views available inside the equipment. Second,
these findings do not represent every specimen, only ours in particular.
However, this method should be applicable to all specimens, even those not
as uniform as the wedge used in this experiment.

6. Conclusions and Recommendations
The methodology determined by PI and CU provide
clear and comprehensible results that allow a specimen to be
placed in its optimal positioning for SEM imaging and EDS
analysis. To further research, another experiment should be
conducted in which digital imaging techniques could be
applied to a more sophisticated apparatus. This will further the
idea of “mimicking” the functions found inside the SEM and
give more exact measurements regarding how the projected
lengths change based on rotation and tilt.

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