TRU Analytical Chemistry
Scanning Electron Microscope Activity
(marked out of 10, counts as a short laboratory report)
For the last laboratory experience of the term, you are going to work in groups to
compare two paint samples using scanning electron microscopy (SEM). We do
not have a SEM at TRU, but are fortunate that we can access one remotely at
Western Washington University in Bellingham through the British Columbia
Integrated Laboratory Network (BC-ILN).
SEM is a technique which is often used to examine surfaces. It allows samples
to be viewed under high magnification by probing the surface with an electron
beam. When the beam scans the surface of the sample, emission from the
surface occurs producing secondary electrons and x-rays. The secondary
electrons can be detected and converted in to an electrical signal which produces
an image of the surface. The x-rays produced can be detected if the SEM is
connected to an energy dispersive spectrometer (EDS). EDS allows for nondestructive elemental analysis to occur for sodium and heavier elements.
Case Scenario:
A van used to transport equipment by the department of Natural Resource
Science (NRS) went missing from TRU late Sunday night. A series of small paint
chips were collected from the van’s parking spot. Early Monday morning, a
partially burnt van was recovered at the Kenna Cartwright Park parking lot. The
vehicle cannot be identified as belonging to TRU, but paint samples were taken
from the rear door of the van that was not damaged in the fire. Your goal today
is to examine the two samples using SEM-EDS. Your laboratory instructor will
guide you in the use of the instrument and provide you with the co-ordinates of
the two paint samples. Your goal is to collect a detailed image of each surface
and visually compare them, as well as collect a series of EDS spectra from points
on each sample that you choose.
The samples have been prepared by coating them with a palladium/gold mixture
to ensure the sample does not build up a negative charge which would
destabilize the image. If possible, the paint samples have been mounted so you
can access the top, bottom and cross section.
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We will be running the activity remotely, which means we will be operating the
WWU SEM-EDS via the internet. When you arrive in the lab for your session you
will be running four different windows on two computers:
1. WWU network camera – used so you can view the WWU laboratory
2. oovoo – Voice Over Internet Protocol (VOIP) used for communication with
WWU Technician Erin Macri
3. SEM control through Vega Remote Client – used to enter sample coordinates, control beam parameters and magnification
4. EDAX Genesis – used to control the EDS spectrometer and obtain the
spectra
Using the SEM control, enter the co-ordinates of the first sample. Under
guidance from your instructor you may adjust position, magnification and
brightness until you are satisfied with your image.
Choose EXT on the SEM control. This gets you ready to work on the EDAX.
Decide if you are going to select an area of the sample to scan or if you want to
obtain a spectrum of the entire window. You may do multiple runs on a sample
so keep track in your laboratory notebook of what you are running.
When you are ready ensure that the previous spectrum is cleared, and start to
collect the spectrum. You may click on peak id at any time.
When you are satisfied with the spectrum, stop collection.
To obtain a report of the elemental analysis click on Q.
To save your image, click on print (print to file Snagit) and type in the file name.
When Snagit opens, click on finish and type the file name.
You may repeat the process to collect another spectrum of the same image.
When you are done with that image, return to the SEM control, click on EXT and
enter the new co-ordinates of the next sample.
Repeat the EDAX process.
When you are done, you will need to transfer your files to your flaskdisk using the
VNC file transfer protocol.
This work is licensed under the Creative Commons Attribution-Share Alike 2.5 Canada License. To view a
copy of this licence, visit http://creativecommons.org/licenses/by-sa/2.5/ca/ or send a letter to Creative
Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.
magnification
working distance
Figure 1: SEM control window
The SEM is controlled from this
screen, instrument parameters
may also be recorded from here:
probe current
brightness
to enter
coordinates
to exit to
EDAX
This work is licensed under the Creative Commons Attribution-Share Alike 2.5 Canada License. To view a
copy of this licence, visit http://creativecommons.org/licenses/by-sa/2.5/ca/ or send a letter to Creative
Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.
Figure 2: EDAX control window
transfer files at end of session
whole image or select area
Collect image
Collect spectrum
Print
(set to Snagit
printer)
Clear spectrum
The report of your laboratory activity should include:
1. A list of spectra acquired from specific samples including locations.
3 points
2. A paragraph summarizing your findings (did the paint samples match or not?)
and explaining how you came to your conclusions.
5 points
3. Labeled EDAX spectral printouts.
2 points
This work is licensed under the Creative Commons Attribution-Share Alike 2.5 Canada License. To view a
copy of this licence, visit http://creativecommons.org/licenses/by-sa/2.5/ca/ or send a letter to Creative
Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.