FlexSEM-EDS FAQs

A: Not always! The FlexSEM is a variable-pressure SEM, meaning it can operate at a lower vacuum level. The small amount of atmosphere around the sample surface creates positive ions that help to neutralise surface charge. This means you can image insulators without the need for coating!

That said, you will generally always obtain higher performance at high vacuum, so a coating will still give better results if it will not interfere with the results you are trying to achieve.

A: Loose samples, like powders and fibres, need to be adhered to a substrate to minimise the likelihood that these particles will become loose inside the chamber, and potentially contaminate or damage the instrument.

Adhesive tape (carbon tape) is a simple method to securely hold your powder sample. Place a small piece of tape on a pin stub, remove the white backing cover from the tape, then carefully place a small amount of your sample onto the tape. If possible, spread it thinly and evenly across the tape, then tap the stub on its side to dislodge any loose particles.

You can also use drop-casting from solution (nanoparticles for example) directly onto a substrate.

A: This will require two things: preparation of your sample to enable the cross-section to be viewed, and mounting at a pre-tilted angle.

Preparation of a suitable cross-section will depend on your sample. Simple methods for this can be cutting with a sharp blade (for soft materials), or mechanical fracturing of the sample (for hard/brittle materials). For some soft materials like polymers or membranes, you can also consider freezing the sample in liquid nitrogen, then snapping it to expose the cross-section.

It is usually preferable to mount your sample at an angle before inserting it into the SEM, rather than using the stage tilt function. This will allow you to maintain a short working distance and therefore obtain better results. Use one of the 45/90° mounts to position your cross-section upwards for imaging.

Remember to ensure the correct height of your sample before it goes into the instrument!

A: If your samples are conductive, or you have a coating applied to your sample, you should choose the SEM (high vacuum) mode.

If your samples are non-conductive, and you do not wish to apply a coating to your sample, you should choose the VP-SEM (variable-pressure) mode. Note that you will not be able to use the SE detector in this mode.

A: Yes! The EDS will work fine in both SEM and VP-SEM modes. You may notice a reduction in signal intensity in the VP-SEM mode, but given the flexibility this enables it is a small trade-off.

A: This can vary depending on what you want to achieve. Remember that in general a higher accelerating voltage (V_acc) will give you better resolution, but it may make surface charging worse. Low voltages will reduce charging and increase surface sensitivity, but you will achieve poorer resolution.

Spot intensity controls the size and brightness of the beam. A low spot intensity (e.g. 20-40) will give you better resolution but at the expense of signal, so you will need to scan slower. High spot intensity (like 60-80) will make your images brighter, but not as sharp, and may also lead to increased charging.

It is always a balance!

A: This depends on the results you want to obtain.

SE (secondary electron) will give you topographic information, like edges and roughness. It will also give the best sharpness. It can only be used the SEM mode (high vacuum). SE should not be used for polished mineral samples as there is minimal topography to see.

BSE (back-scattered electron) will give you compositional contrast, highlighting regions that are composed of different elements or materials. It is not so sensitive to topography. The BSE detector can be used in SEM and VP-SEM modes. It can also be less sensitive to small amounts of charging.

UVD (ultra-variable detector) is only for use in the VP-SEM mode, and will give an SE-like signal that is sensitive to topography. Under special conditions it can be used for cathodoluminescence (CL).

This can be caused by a few things depending on the circumstances.

Image is grey when using the BSE detector - check if the chamberscope is on (the camera that looks inside the chamber). It has an IR light that blinds the BSE detector. If it is on, turn it off, then perform an auto brightness-contrast adjustment.

Image is black or there is no signal - ensure you have pressed the Start button to power up the beam. If the beam is on, is it indicating the filament needs replacing? Check the emission current in the electron beam settings dialog, it will usually be around 80uA. If all looks ok, try going to an area you know should be conductive, like a bare part of the holder, then perform an auto brightness-contrast, and auto focus. If you cannot resolve the issue, contact the manager.

Image is blurry - go to a known conductive location/feature on your sample, such as bare sample holder, check your magnification and go to a low value (e.g. ×100), perform an auto focus and an auto brightness-contrast.

This happens when you try to use the Specimen Exchange button but the stage is positioned lower than the 5.0mm exchange position (e.g. after performing EDS at WD=10mm). The stage needs to be at 5.0mm for the image capture to be in focus, and to ensure the sample is mounting safely at the correct height.

Using the HEIGHT dial on the front of the instrument return the stage position to 5.0mm, then try pressing the Specimen Exchange button again.

This occurs when the software believes the stage tilt angle is not perfectly level at zero degrees, even if the dial on the front of the instrument may suggest that it is.

To resolve this, turn the TILT dial on the front of the instrument in the direction it needs to bring the value in the error message to zero.

For example, if the message reads Current values: -0.6°, turn the dial counter-clockwise (i.e. + tilt). The value should not increase further, and the message should clear. If it remains and the value increases, then turn the opposite direction.

This means that the tungsten filament in the source has blown and needs to be replaced. This is a consumable part and happens regularly.

Please contact the instrument manager to let them know the source needs replacing.

This can happen during sample mounting, or stage motion inside the chamber, and indicates that the sample stage has made contact with something inside the system. It will often happen during sample mounting, where there is minimal risk. If this has happened during your session while imaging and moving your sample, it can be more dangerous for the system and you should contact the instrument manager to investigate.

Follow the on-screen instructions. It will ask you to turn the HEIGHT (Z) dial left, i.e. counter-clockwise until it reaches 15mm. The stage will then reinitialise, and then it will ask you to return it to 5.0mm.

If this error persists, contact the instrument manager.