1. Electron Probe Sample Preparation The Hebrew University of Jerusalem
Revised on July 10, 2016 at the Hebrew University of Jerusalem.
Based on work by the University of Wisconsin, Geology Department.

2. Why is sample preparation necessary?
1. If your sample doesn’t fit in the probe we can’t analyze it.
2. If your sample isn’t properly polished the chemical analysis will be wrong.
3. If your epoxy isn’t dried properly it will damage the probe.
4. If your sample isn’t properly coated (and therefore not conductive) your chemical analysis will be wrong.

3. Sample preparation Sample preparation does make a difference:
Proper sample preparation is critical to the success of your EPMA work.
Your experiment may be successful but your EPMA results may be nonsensical if your sample was not properly mounted, polished and coated.
We are happy to answer any and all questions.

4. Identify your goals before you start working.
1. Identify your goals before you start working. What would you like to learn from your samples? Make sure your sample preparation is appropriate. Do some “dry run” preps before you waste your precious experimental materials.
2. Recognize that there are several different ways to prepare samples for the probe.
-Sometimes “normal” sample preparation is an inefficient for your analysis in the probe. This can include sample mounting, sample preparation and the handing of your sample in between these two steps.
3. Understand that sometimes reaching your goal in the probe may take time. You may have to fine tune your method until you reach an ideal work protocol.

5. Sample Mounts
90% of the samples used in an EPMA are 1” (outside diameter) rounds or geological thin sections.
-Epoxy mounts in the probe measure 1 inch in outside diameter and 1 inch in depth.
-Thin sections should measure 4.5 cm long by 2.6 cm wide. Three thin sections of this size can be inserted into the probe at once
-Large flat samples can measure 7.5 cm long by 3.5 cm wide and 2 mm thick.
There are a few other sample sizes that can be accepted by the probe; ask if you have questions.

6. Advice for Mounting grains
Separate out the grains to be probed.
Determine what size holder they will need to be mounted in.
Place the grains on sticky tape, within the required perimeter.
Place the round holder over them, sticking firmly to the tape.
Pour the epoxy over the grains, without creating air bubbles.
Wait for hardening
Remove and polish.

7. Mounting Media
Most samples need to be encapsulated for ease of mounting in the probe or SEM and for polishing.
Only use epoxies created for metallographic/microscopic applications (high vacuum, low degassing). There are several options available.
Before you start using a new epoxy (or an epoxy of an indeterminate age), mix up a small batch and make a dummy mount to test it. Never use an unlabeled epoxy on a precious sample without first testing it out.

8. Mounting Media - devil in the details
Epoxy mixing and curing- It is very critical when mixing epoxy that you adhere to the following procedure.
Use FRESH epoxy. Old epoxy will not harden properly. If you are not sure how old your epoxy is, mix up a small batch and make a dummy mount to test it. (Always write the opening date on new epoxy.)
Use CORRECT proportions. (Always use a scale or syringe to measure the ingredients, and mix well. Pay attention to the epoxy mixing ratio. Some epoxies are measured by volume and some are measured by weight.)
Wear gloves while working with epoxy and use a hood.

9. Cutting, Grinding, Polishing
Your goal is to prepare the specimen so that the surface is polished to an optic scale (at least 1 micron) to minimize errors in the matrix correction (path length).
Cutting, coarse grinding and then polishing with finer abrasives can introduce various artifacts, which may or may not affect your investigation (i.e. plucking of grains; preferential removal of ‘softer’ phases; imparting chemical change and/or deformation to the surface of the sample)

10. Cleaning
After polishing, samples must be cleaned and degreased, to minimize outgassing and contamination of the probe vacuum. Regardless of how or who makes your sample mounts, you are responsible for cleaning and drying.
Gently wipe the surface of your sample with ethyl alcohol (not acetone).
Rinse gently with distilled water. Shake off the excess water and blot dry with a clean kimwipe to minimize water marks on the surface.
Do not blow water off with compressed air (oil is in the lines). Do not use canned air (it leaves hydrocarbons on the surface).

11. Carbon Coating Non-conductive samples (e.g,.
rock thin sections) will need to be
carbon coated. They should be
coated in the EPMA Lab’s
evaporator. This will be done by a
probe operator.
Experience has shown that coating
elsewhere with carbon sputtering does not yield favorable quantitative results on our probe.
Samples that were coated in any other material cannot be analyzed quantitatively in the probe. (We will only be able to image your sample.)
Old samples that were coated many years ago must be finely polished and then recoated.

12. Carbon Coating —Thickness
Variation in the carbon thickness between standard and unknowns can create additional uncertainty and error.
The electrons entering the specimen lose energy passing through the coating, reducing the x-ray intensity produced within the specimen.
Emergent x-rays are absorbed by the carbon as they leave the sample on their way to the detector. These effects are largest for the “light” elements, but also higher Z elements.
Uncoated sample
Coated sample
** Armstrong, J.T. (1993) Effects of carbon coat thickness and contamination on quantitative analysis: a new look at an old problem, in Proceedings of the 27th Annual MAS Meeting, S13-14

13. NOT IN THE PROBE!
There are occasions where thin sections are stained to distinguish various phases (carbonates, feldspars). Samples that have been stained ARE NOT ALLOWED IN THE ELECTRON MICROPROBE.
Organic samples cannot be analyzed in our EPMA
Magnetic samples are VERY problematic and lead to beam deflection. Please consult a probe operator.
Powders and unpolished samples will not yield reliable quantitative results. Please consider this carefully and discuss your options with a probe operator.

14. DIFFICULT TO ANALYZE IN A PROBE!
Samples with carbon like calcite are very difficult to analyze in the probe because C and O are hard to measure and there is always a low total. Beam currents of nA immediately cause changes to the surfaces (either a hole or build up of contamination).
Samples that are chemically identical but crystallographicaly different cannot be chemically distinguished in the probe. (i.e. calcite and aragonite)
Minerals with water cannot be fully analyzed in the probe.
Some samples are beam-sensitive (i.e. alkali feldspar (albite) and apatite)
Oxidation states in iron cannot be accessed in the probe

15. Storage Protect your specimen mounts!
Avoid touching surface with fingers, use gloves if possible. Oils on your skin become dangerous hydrocarbons in the probe.
Do not wrap in kleenex (paper fibers); if necessary, use a kimwipe or cotton
Keep in containers, specifically plastic boxes
Label the boxes with your name, so if you leave them in the lab they can find their way back to you. Samples cannot be left in the lab for more than two weeks. We are not responsible for your samples.
We are not a storage facility

16. Documentation - Navigation
If your samples have any ambiguities or complexities, make maps or drawings beforehand, showing orientations (e.g., North arrow) and regions of interest.
It is difficult to find a 100 micron grain in a micron forest without landmarks.
We now can scan mounts, import the images to the Probe for EPMA software, “register” the image with actual stage coordinates, and then click on the image to move to that area.

17. How do I get my EPMA reports
You must bring a USB key to every session in the EPMA.
DO NOT INSERT YOUR USB INTO THE PROBE’S COMPUTER!
You cannot directly remove your data from the probe. Only insert your USB into the second computer console in the lab which is intended for data reduction.
We will NOT send you your data electronically.
There is some data reduction processes that you can only perform on the second computer console in the lab.
It is your responsibility to retrieve and process your data.

18. Probe Calibration
If you plan to do quantitative analysis, the elements to be analyzed need to be previously calibrated. You must understand that not all elements are calibrated at any given time.
The calibration process is twofold. There is the primary stage which the probe operator performs. The calibration process is extensive and must be constantly updated.
The second stage, secondary calibration and matrix correction, is based on your specific samples. This will take place one day before you start your analysis. Please be patient-every individual sample needs a secondary calibration. IT’S NOT JUST YOU!