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SEM-EDS Analysis
Correlative microscopy, Filter-Handling, PSE operating modes, Spectra and material databases

JOMESA PSE: Material analysis with SEM-EDS

Requirements for Filter Preparation

To be able to investigate filter membranes in the optical microscope (JOMESA HFD) as well as in the scanning electron microscope (JOMESA PSE), several requirements have to be met.

The filter must be – due to the limited depth of focus - sufficiently flat.
Methods like covering with glass plates must be excluded because glass is intransparent for electrons and so an investigation in the SEM-EDX is impossible.

The particles must be affixed onto the filter membranes because charged particles may be kicked out of place in the SEM-EDX. Furthermore during the transport of the filter membrane from the optical microscope to the SEM-EDX it must be ensured that particles will not change their position or orientation. This is very critical for large (>500 mm) particles.
A fixation may not affect the light optical nor the electron optical image; otherwise a correct judgement of the particle origin may be hindered. The fixation must not cover the particle; the EDX analysis may be limited or even impossible. Glue-based solutions which cover particles – even when optical transparent - must be excluded.
A manual picking of particles from the filter onto a sticky carbon tape may not be considered just because of time and cost reasons in serial analysis.

Due to the non-conductivity of the filter membranes we often observe charging effects in the SEM-EDX which make it nearly impossible to obtain good SEM images and so it´s hardly possible to face the correct area of the EDX analysis – even if the particle is properly fixed.
The use of so called „low-vacuum“ or „variable pressure“ conditions in the SEM is a compromise only: the charging effects are reduced, but the quality of the EDX spectra is severely degraded. The coating of the sample (with e.g. gold or carbon) is not an option: the metallic coating affects the analysis of filters in the optical microscope. There is a risk that all particles are detected as metallic. Also the EDX-spectra are overlayed by the signal of the coating layer. Additionally the process and the equipment necessary for coating is time consuming and expensive.
The use of conductive, ionic liquids in the SEM-EDX is established, the application and the conditions for particle analysis on filter membranes is not state of art yet.

The filter should have markers to synchronize the motion of optical microscope and SEM-EDX. The marker should be permanently fixed and the filter should be asembled in a low-priced mount. The marker must be visible in the optical microscope as well as in the SEM; so simple printed markers can be excluded.

The optical analysis is much faster and cheaper then the SEM-EDX analysis, so the filter should be covered and protected from contamination.

It should be possible to archive the analyzed filter to allow a repetition or cross-check of the analysis.

As a consequence of these issues JOMESA developed a handling procedure for PET and Polyamide (Nylon) filter membranes (patent pending).

Step 1: JOMESA SEM filter mount SM60x60

SEM60x60 filtermount consists of a bottom part (left pricture), onto the outer side information about the filter can be written. On the inner side, where the filter is placed there is a small copper platelet on the right top corner. This will be used for a precise correlative alignment of the filter in the HFD and the PSE. Furthermore it can be used to calibrate the EDX detector of the PSE. There is space on the SM60x60 to attach a QR code for sample identification.

The upper part of the filtermount contains a "spacer", which ensures, that the particles on the filters do not touch the glass cover.

Step 2: The JOMESA Fixation Solution: Secure fixation of the particles on the filter

The JOMESA Fixation Solution is a monomer solved in acetone. The filter membrane will be placed onto the the filtermount, wetted with the solution. The acetone will evaporate. The polymerisation will take place between the particle and the filter membrane. The particles will be fixed by the polymerisation. The upper side of the particles will not be covered; the results of the analysis are unaltered.

JOMESA Fixation Solution:

  • the particle will be fixed at the bottom side

  • save fixation

  • no influence on the analysis results

Conventional fixation glues

  • will be applied from the top

  • particles do not really stick on the filter

  • covered particles: bad analysis results

How will the JOMESA Fixation Solution applied?

0.2 ml of the JOMESA Fixation Solution FS-ACR1will be drawn into a syringe.

The JOMESA Fixation Solution FS-ACR1 will be distributed equally inside the circular mark.

The filter will be placed into the solution. Let it dry.

To protect the filter from dust, it may be covered with the glass.
In this condition the filter may be measured in a special holder under the optical microscope HFD.

Step 3: Measuring the filter under the optical microscope (JOMESA HFD)

The filter under the optical microscope (JOMESA HFD). Before starting the scan the system will move to the alignment marker top right automatically.

The alignment mark in the image of the HFD: the Cu disc has a small hole in the center. This hole will be centered in the image automatically. It is the reference for the coordinate system of this filter.

Step 4: JOMESA Conductivity Solution CS-IL1
The JOMESA Conductivity Solution is an organic liquid to make particles and filter conductive. This ionic liquid contains only the elements C, O, N and H.
Using the Conductivity-Solution CS-IL1 is optional. It is recommended if electrostatic charging in the high-vacuum worsens the image quality and perfect SEM images are required. It is not necessary if only EDX spectra should be acquired. It is highly recommended when the exact place of the EDX spectrum must be determined.

Without JOMESA Conductivity Solution

With JOMESA Conductivity Solution

JOMESA PSE works in high vacuum. The arguments are:
"... X-ray microanalysis in the VPSEM and ESEM can be a useful tool to complement SEM imaging, but the analyst must recognize the inevitable limitations that result from gas scattering compared to the level of analytical performance achieved in a conventional high vacuum SEM. … While it is usually possible to achieve useful results for major constituents, minor and trace constituents are likely to be severely compromised. … Quantitative analysis of areas with micrometer dimensions is severely compromised.... ."
Dale E. Newbury, National Institute of Standards and Technology:in: Journal of research of the National Institute of Standards and Technology 2002 Nov-Dec; 107(6): 567–603.

How will the JOMESA Conductivity Solution be applied?

0,2 ml JOMESA Conductivity Solution CS-IL1 will be drawn into a syringe.

The JOMESA Conductivity Solution CS-IL1 will be equally dropped over the filter with the particles affixed. Let it dry.

Step 5: Measuring the filter with the scanning electron microscope (JOMESA PSE)

The SEM-filter mount can be analyzed directly in the PSE electron microscope. A special holder will be used.

As in the HFD light microscope the Cu alignment marker will be used for the correlation of the filter position.

Components Overview:

SEM filter mounts
Packing Unit: 16 pcs.
Article Code: SM60x60

Fixation solution FS-ACR1
Volume: 25 ml
Article Code: FSACR1

Advantages JOMESA Fixation Solution:

  • Secure fixation of the particles on the filter membrane.

  • Save handling and storage of the filter.

  • Save shipment of the filter.

  • Simple and fast application.

  • Reproducible results.

  • No impact on the analysis quality.

  • Works in light and in electron microscope.

  • Particles can not „jump“ in the electronen microscope (SEM).

Conductivity solution CS-IL1
volume: 25 ml
article code: CSIL1

Advantages JOMESA Conductivity Solution:

  • Simple and fast application.

  • Good conductivity of the filter.

  • Fast results in the SEM: working in high vacuum - no charging.

  • No need for a time consuming search for the right pressure.

  • Imaging with the SE detector: better images – more detail can be recognized.