1. Electron probe microanalysis - Scanning Electron Microscopy EPMA - SEM
UW- Madison Geoscience 777
Electron probe microanalysis - Scanning Electron Microscopy EPMA - SEM
Preface:
What’s EPMA and SEM all about?
How does Geology 777 work?
What can you learn?
Updated 12/6/18

2. UW- Madison Geology 777
Why?
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.

3. UW- Madison Geology 777
EPMA - what is it?
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.

4. UW- Madison Geology 777
SEM - what is it?
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.

5. UW- Madison Geology 777
SEM - is it for me?
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, mounting+polishing), 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.
Relatively cheap ($25/hr)
Hydrothermal worm
Campo del Cielo meteorite

6. UW- Madison Geology 777
EPMA - is it for me?
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.
10 µm
Al Kα X-ray map of volcanic rock
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.
EDS
WDS

7. EPMA - is it for me? It uses standards (reference materials)
UW- Madison Geology 777
EPMA - is it for me?
It uses standards (reference materials)
It is a micro-technique, and for multiphase samples provides discrete compositions, not the bulk composition.
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.
It provides major and minor element quantification, and has limited capacity for trace element analysis. (What do you mean by “trace”?)
Despite being nominally non-destructive, samples need to be mounted and polished and coated if not conductive; they can be reanalyzed many times.
It is accessible and relatively inexpensive ($35-50/hr) .
Some degree of complexity; there can be a sharp learning curve.
Phase identification of volcanic rock
10 µm
ZrO2 15 kV
1 µm

8. UW- Madison Geology 777
Goal of this course
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 or SXFive FE 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.

9. How this course is structured
UW- Madison Geology 777
How this course is structured
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:
Weekly quiz: at start of each class, on the assigned material (emphasis on previous week’s 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

10. Traditional Reference: on Reserve in Geology Library
UW- Madison Geology 777
Traditional Reference: on Reserve in Geology Library
Goldstein et al, rd Edition

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

12. New Kid on the Block: electronic copy free to download
UW- Madison Geology 777
New Kid on the Block: electronic copy free to download
Goldstein et al, rd Edition