Certain samples are tricky to image. Sometimes, even the best sample preparation will be of no help in finding the results you need. Surface roughness and features on top of the sample might hide the specific area of interest, which could contain crucial information about surface defects or characteristics of the imaged material. In cases like this, you need a new point of view. Read this blog to discover how you can get just that.
When performing a failure analysis on a computer chip, a wire or other object might cover the bad connection that is causing the item to malfunction. Or maybe the count of specially designed alloy particles, which will boost the performances of the latest engine components or micro-medical tools, could be inaccurate due to surface roughness hiding some of them.
Fig. 1: SEM image showing broken parts hidden by connecting cables
Fig. 2: After tilting and rotating thesample,you have a better view of the broken edge
Pre-tilted clamping devices allow you to position the sample at a fixed angle (generally 30° or 45°). But these instruments still only allow sample imaging from one point of view. Slightly more advanced designs feature a system of screws that enable you to set the preferred angle for imaging. Therefore, it is possible to image the sample, unload it from the SEM, tilt and rotate the pin stub in the clamper, and then load it again.
Although this solution might seem simple and immediate, there are several problems involved:
Loading and unloading can take a very long time, making the analysis extremely time-consuming;
It is difficult to find the same spot that was imaged previously, especially after tilting the sample and consequently losing all the reference points. In fact, the surface will look totally different when imaged from a new perspective;
Ejecting the sample from the microscope for repositioning involves a high chance of contamination, compromising the reproducibility of results.
How motorized stages that allow sample tilting and rotation help users retrieve more accurate results
To help users retrieve more accurate results — and to save precious time — SEM suppliers have designed highly sophisticated motorized stages that allow sample “tilting and rotation”. These operations are performed while the sample is inside the SEM and users can monitor the movements on the screen.
During the development of a tilt and rotation sample holder for a desktop scanning electron microscope(SEM), a central aspect needs to be considered: the small amount of space available within the device.
Commonly used devices for floor models feature an IR camera to observe the sample while being tilted. It is then up to the user to finely and accurately tune the movement of the stage to avoid hitting — and potentially damaging — internal components of the microscope.
Contact sensor solutions are also available, but they will not prevent the sample from hitting something. A smarter and more user-friendly approach is gaining popularity. It is based on recreating a 3D model of the sample and the sample holder for a real-time display of what is happening inside the device. The system integrates software that will prevent any stage movement that could compromise the safety of internal components, so that no damage can be done to the instrument.
An example of real-time 3D visualization
When dealing with features in the nanoscale, a very small movement of the sample translates into a huge difference in terms of the imaged spot. Consequently, extreme accuracy is required when moving the sample. As basic tilting might still not be enough to keep the area of interest within the field of view, eucentric tilting is required. You can find out more about this technique by downloading this eucentric sample holder information sheet.
Luigi Raspolini is an Application Engineer at Phenom-World, the world’s leading supplier of desktop scanning electron microscopes. Luigi is constantly looking for new approaches to materials characterization, surface roughness measurements and composition analysis. He is passionate about improving user experiences and demonstrating the best way to image every kind of sample.