🔬 The Winning Alliance: Technician and Microscopist
This informal guide has been created by Media System Lab for all electron microscopists. The objective is to help recognise and quickly resolve the most common problems encountered when using an SEM. This version can be improved, and we welcome your suggestions to do so; please send them to: info@m-s.it.
Media System Lab is the place for microscopists.
🤖 Interactive Assistant
✨ Problem Solving
Describe a problem you are observing in your SEM image. The assistant will analyse the description and suggest the most probable cause and a solution.
✨ Protocol Generator
Enter the sample type and the desired analysis to generate a basic preparation checklist.
1. Contamination
The Problem:
A dark veil of carbon, caused by hydrocarbons, covers the details and alters the chemical analysis. This is one of the most frequent problems, but also one of the most preventable.
The Solution:
- Cleaning: Meticulously clean samples and the stage.
- Pre-treatment: Use an airlock and, if possible, a plasma cleaner.
- Maintenance: A well-maintained vacuum system is your first line of defence.
Common Sources of Contamination
2. Charging
The Problem:
On insulating samples, the accumulation of charge deflects the beam, creating distorted, blurred, or excessively bright images, a phenomenon known as "charging".
The Solution:
The solution depends on the nature of the sample. Follow this decision flow to choose the best approach.
3. Beam Damage
The Problem:
The high-energy beam can irreversibly damage sensitive materials such as polymers or biological samples, altering their structure.
The Solution:
- Minimum Necessary: Use the lowest possible energy and current.
- Low-Dose Microscopy: Reduce the acquisition time.
- Cryogenics: A cooled stage stabilises the sample.
Relative Resistance to Beam Damage
4. Preparation Artefacts
The Problem:
Incorrect preparation can introduce deformations, contaminants, or chemical modifications that confuse the results. An artefact is not a real feature of the sample.
The Solution:
- Method: Be critical and follow standard operating procedures.
- Right Tools: Use FIB for hard materials, ultramicrotomy for biological ones.
- Final Cleaning: Always clean the sample after preparation (e.g., plasma cleaning).
5. Resolution
The Problem:
Focusing only on very high magnification can cause you to lose the overall view, making the analysis unrepresentative. It is like studying a single leaf without knowing the forest.
The Solution:
- From the Forest to the Leaf: Always start with a low-resolution map.
- Improve Analytical Resolution: Operate at low voltage for more precise EDS data.
Forest (Overall View)
Tree (Area of Interest)
Leaf (High Resolution)
6. EDS Analysis Limitations
The Problem:
Peak overlaps, spurious X-rays, and sample drift can distort the elemental analysis. Automatic results are not always reliable.
The Solution:
- Manual Verification: Do not blindly trust the identification software.
- Correct for Drift: Use your system's drift correction software.
- Maintenance: Calibrate the EDS detector regularly.
Impact of Spurious X-rays on Results
7. Aberrations and Alignment
The Problem:
Lens aberrations (spherical, chromatic, astigmatism) distort the image, making it blurred or elongated if the column is not perfectly aligned.
The Solution:
- Perfect Alignment: Practise using the stigmators ("wobble and stigmator").
- Column Cleaning: Periodic maintenance reduces astigmatism caused by deposits.
8. Vacuum System Issues
The Problem:
Leaks, pump failures, or dirty O-rings degrade the vacuum, causing image instability and contamination. A good vacuum is essential.
The Solution:
- Attention to Detail: Ensure that the O-rings are always clean.
- Monitoring: Regularly check the vacuum levels indicated by the sensors.
- Prevention: Preventive maintenance of the pumps is a worthwhile investment.
9. Interpretation and Competence
The Problem:
Without a solid understanding of the basic principles, you might misinterpret artefacts or fail to fully utilise the instrument's potential.
The Solution:
- Continuous Training: Learn what each "knob" does.
- Distinguish Contrasts: Learn to recognise topographic, compositional contrast, etc.
- Experiment: Every "mistake" is a learning opportunity.
3 Final Tips from Your Technician
Know your instrument
Read, experiment, and never stop learning the physics behind it.
Prepare with care
Good sample preparation solves half of the problems.
Do not be afraid to ask
Our collaboration is the key to extraordinary discoveries.