Electron%20probe%20microanalysis%20-%20Scanning%20Electron%20Microscopy%20EPMA%20-%20SEM

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Electron probe microanalysis - Scanning Electron
Microscopy EPMA - SEM
UW- Madison Geoscience 777

• Preface
• Whats EPMA and SEM all about?
• How does Geology 777 work?
• What can you learn?

Updated 1/21/18
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Why?
UW- Madison Geology 777
You are taking this class because you need to be
able to intelligently use an electron beam
instrument the Hitachi S3400 SEM, the CAMECA
SX51 or SXFive FE electron microprobe. These
instruments work on the same physical principles,
but have differences.
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EPMA - what is it?
UW- Madison Geology 777
EPMA is a tool to get precise and accurate
quantitative chemical analyses of micron-size
domains of our samples. A focused beam (spot)
of high energy electrons interact with the atoms
in the sample, yielding X-rays (and other
signals), which we quantify and compare with
counts from standards. It is nominally
non-destructive.
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SEM - what is it?
UW- Madison Geology 777
SEM is a tool to produce images -- pictures -- of
our samples. A rastered (scanned) beam of high
energy electrons sweeps across the surface,
interacting with the atoms in the sample,
yielding backscattered electrons, secondary
electrons, auger electrons, and in some cases
photons in the visible light range (CL). It is
nominally non-destructive.
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SEM - is it for me?
UW- Madison Geology 777

• This technique is rather simple and one can learn
  the essentials in a short time.
• It provides images easily, though one needs to
  understand the various parameters (e.g. working
  distance, resolution, etc) to not make mistakes
  compromising image quality.
• Samples may be imaged with little or no
  preparation (coating, mountingpolishing), though
  this may complicate detailed examination.
• It is very easy to make mistakes using the easy
  EDS software, especially for attempts to get
  chemistry of small particles.

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EPMA - is it for me?
UW- Madison Geology 777
Traditionally EPMA has meant using a dedicated
electron microprobe (also known as electron probe
microanalyzer.. EPMA) ? to do quantitative
chemical analysis at the micron level. EPMA
traditionally has meant an instrument with
wavelength dispersive spectrometers (WDS) and a
rigorous calibration procedure, using
standards. However, there are many people who
attempt to also do quantitative chemical analysis
at the micron level in SEMs using a different
type of detector (EDS). One key theme of the
class is to understand the similarities and the
differences between WDS and EDS.
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EPMA - is it for me?
UW- Madison Geology 777

1. It uses standards (reference materials)
2. It is a micro-technique, and for multiphase
   samples provides discrete compositions, not the
   bulk composition.
3. Under normal operating conditions, it samples
   volumes (widths-depths) on the order of 1-3 um,
   limiting its usefulness for smaller inclusions or
   thin films.
4. It provides major and minor element
   quantification, and has limited capacity for
   trace element analysis. (What do you mean by
   trace?)
5. Despite being non-destructive, samples need to be
   mounted and polished they can be reanalyzed many
   times.
6. It is relatively inexpensive and accessible
7. Some degree of complexity there can be a sharp
   learning curve

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Goal of this course
UW- Madison Geology 777
The goal is to provide useful background
information to make SEM and EPMA less a black
box for you and to help you make better
decisions about how to analyze your samples, and
to understand when data is good and when it is
not. This class will provide the basic
instructions for the use of our Hitachi SEM and
Oxford AZTec EDS. It will point out errors that
can occur with EDS spectral interpretation. This
course provides some directed exercises with our
CAMECA SX51 probe. The electron probe is more
complicated than the SEM and experience has shown
that individualized training is the best way to
go. This happens when the student has his/her
samples ready to analyze do we set up a 4-8 hour
appointment.
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How this course is structured
UW- Madison Geology 777
Weekly class meetings 1.5 hours, discussion of
assigned materials (PPT presentations, possible
readings) Instructional materials will be
provided as PPT slides and reprints, all on class
web page www.geology.wisc.edu/johnf/g777/ W
eekly quiz at start of each class, on the
assigned material (emphasis on previous weeks
lecture) Weekly labs 2 hours. Complete lab
report and turn in following week Weekly
assignments Calculations and computer
exercises. Each student do some literature
searching and write a brief paper
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Use for Reference--In Library on Reserve
UW- Madison Geology 777
Goldstein et al, 3rd Edition. 2003

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Also On Reserve in Geo Library
UW- Madison Geology 777
Reed (1996) 201 pages
Reed (1993)