## 3 Uncertainties, Limitations, and Sources of Error in SEM Measurements
### Sample Preparation and Related Issues
It also helps in enhancing images of thin sections and provides crystal clear information about crystal faces, surface roughness, and other textural attributes, which is essential for understanding the formation of minerals and digging deep into the geological history of minerals. Figure 11 shows wollastonite samples mounted on three stubs, as described in Table 3. Figure 12 shows the effects of layers and sputter coating on SEM analysis by comparing wollastonite samples A, B, and C for three magnifications, i.e., 5k\(\times\), 60k\(\times\), and 250k\(\times\). In the sample preparation stage, sample C was left uncoated to investigate the effect of sputter coating, while samples A and B were coated with gold-platinum coating. It is clearly illustrated in Figure 12 that all SEM images of sample C are fuzzy and dark with few very bright spots and lines, making it difficult to visualize the sample morphology. This is the charging effect, logically occurring due to the absence of a conductive material coating. Another important aspect can be found by comparing the 60k\(\times\) and 250k\(\times\) SEM images of sample C with its 5k\(\times\) image. While charging effects are prominent in all SEM images, that with lower resolution provides better visualization of features when compared to the ones at higher resolution. This suggests that for samples that are difficult to coat with conductive materials, it is useful to capture SEM images at lower resolution. When comparing the SEM images of samples A and B, it is observed that the morphology of the sample can be well studied with single-layered samples compared with multilayered samples. \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & **Layer** & **Sputter Coating** \\ \hline A & Multiple & Applied \\ B & Single & Applied \\ C & Single & Not Applied \\ \hline \end{tabular}
\end{table} 
Table 3: Wollastonite samples prepared for SEM analysis. To ensure that the stigmator is well adjusted for taking quality SEM images, the SEM instrument should be allowed to stabilize and warm up, which will ensure that the electron source and other components of the instrument are at steady state before any adjustment. There are usually two stigmation modes in SEM, i.e., objective lens stigmation and condenser stigmation. The specific requirement of the imaging task will require the selection of an appropriate stigmation mode. Misalignment in electron columns and detectors can adversely affect SEM image quality, which is why it is important to ensure  
Figure 11: Wollastonite samples prepared for SEM analysis: (A) multilayer, coated; (B) single layer, coated; and (C) single layer, uncoated. Figure 12: SEM images of wollastonite samples **A**, **B**, and **C** captured at 5k\(\times\), 60k\(\times\), and 250k\(\times\) magnifications. proper alignment of these components before starting the imaging process. Some of the latest SEMs include automated alignment features. The sample preparation stage is also important for avoiding any contamination and charging effects hindering image quality. Dry, clean, and well-mounted samples provide a foundation for high-resolution SEM imaging. While focusing the electron beam on the sample, it is necessary to adjust the astigmatism controls to obtain a sharp image at low magnification. It is considered good practice to select a well-defined edge or feature on the investigated sample as a reference point for stigmation control adjustments. Astigmatism is usually indicated by distortions in the SEM image, such as asymmetrical or elliptical features. In the SEM imaging process, it is important to observe such biases. The X- and Y-stigmation (representing horizontal and vertical stigmation, respectively) need to be adjusted to eliminate any distortions. The focus of the electron beam should be rechecked and adjusted, if necessary, for proper and clear imaging. For optimal SEM imaging, several iterative adjustments might be needed.