Scanning electron microscopy (SEM) is a powerful tool for imaging and analyzing materials at the nanoscale. However, artifacts can arise during imaging, leading to misinterpretation of data if not properly addressed. Common artifacts include charging, edge effects, and contamination, each of which can distort image quality and analytical results. Understanding these artifacts and implementing strategies to mitigate them is critical for accurate SEM analysis.

Charging occurs when a non-conductive or poorly conductive sample accumulates electrons from the electron beam, creating an electrostatic field that deflects incoming electrons. This results in bright or dark regions, streaking, or image distortion. Charging is particularly problematic in insulating materials like ceramics, polymers, or biological samples. To minimize charging, samples can be coated with a thin conductive layer of gold, platinum, or carbon. Alternatively, reducing the accelerating voltage or using a low-vacuum mode can help dissipate charge. In one case study, researchers analyzing a polymer composite misinterpreted bright spots as filler particles when they were actually charging artifacts. Subsequent energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the absence of additional elements, highlighting the need for complementary techniques to verify SEM observations.

Edge effects arise when secondary electron emission is enhanced at sharp edges or rough surfaces due to increased electron escape probability. This creates artificially bright edges that can be mistaken for compositional variations or topographical features. Edge effects are common in fractured samples or those with pronounced surface roughness. To mitigate this, tilting the sample or adjusting the detector position can reduce edge brightness. A notable example involved a study of fractured metal alloys, where edge effects led researchers to incorrectly conclude that grain boundaries were enriched with precipitates. Cross-sectional TEM analysis later revealed uniform composition, demonstrating how edge effects can mislead interpretations.

Contamination is another common artifact caused by hydrocarbon deposition on the sample surface due to electron beam interaction with residual gases in the chamber. Contamination appears as dark, growing regions that obscure surface details. Prolonged beam exposure exacerbates contamination, particularly in organic or biological samples. To prevent contamination, samples should be cleaned thoroughly before imaging, and the microscope chamber should be maintained at high vacuum. Pre-irradiating areas adjacent to the region of interest can also reduce contamination buildup. In one instance, a study on carbon nanotubes reported unusual surface modifications that were later attributed to hydrocarbon contamination rather than actual structural changes. Repeating the experiment with stricter contamination controls confirmed the initial findings were erroneous.

Accurate SEM image interpretation requires a systematic approach to distinguish artifacts from real features. First, varying imaging parameters such as accelerating voltage, beam current, and working distance can help identify artifacts. Charging artifacts often change in appearance with beam conditions, whereas real features remain consistent. Second, combining SEM with other techniques like EDS or AFM provides additional validation. For example, a study on semiconductor nanowires initially reported diameter variations due to edge effects, but AFM measurements confirmed uniform dimensions. Third, comparing multiple regions of the sample ensures observed features are reproducible and not localized artifacts.

Case studies further illustrate the consequences of misinterpretation. In one example, researchers studying a layered ceramic material observed alternating bright and dark bands, which they attributed to phase segregation. However, the contrast was later found to result from differential charging between layers of varying conductivity. Coating the sample eliminated the contrast, proving the initial interpretation incorrect. Another study on nanoparticle dispersions reported agglomeration based on SEM images, but TEM analysis revealed the particles were well-dispersed, with SEM contrast arising from surface contamination.

Strategies for minimizing artifacts include optimizing sample preparation, selecting appropriate imaging conditions, and corroborating findings with additional analytical methods. For insulating samples, conductive coatings or low-voltage imaging should be standard practice. Rough samples may require careful tilt adjustment to reduce edge effects. Contamination can be mitigated by minimizing beam dwell time and ensuring a clean vacuum environment. Training and experience are also crucial, as familiarity with artifact signatures helps prevent misinterpretation.

In summary, SEM artifacts such as charging, edge effects, and contamination can significantly impact data accuracy if not properly addressed. Recognizing these artifacts and employing strategies to mitigate them ensures reliable image interpretation. Case studies demonstrate how misinterpretations can lead to incorrect conclusions, emphasizing the need for a rigorous, multi-technique approach. By understanding and controlling these artifacts, researchers can maximize the utility of SEM in materials characterization.