Scanning electron microscope (SEM) is a powerful analytical tool that is widely used in materials science, biology, medicine, semiconductor materials, and chemical engineering. SEM is capable of providing high-resolution images of surface topography, making sample preparation a critical step in obtaining accurate, clear images. In this paper, the requirements and methods of SEM sample preparation are analyzed in detail.

A. SEM sample requirements

1. The sample does not contain water

Vapor from wet samples can reduce the vacuum, affect image clarity, and may cause the electron beam to react with water vapor, shortening the life of the device. As a result, most biological samples and all wet samples need to be dried.

2. The sample does not contain volatiles and pollutants

Volatiles and contaminants can contaminate equipment components, reducing imaging signals and detector efficiency. Therefore, these substances need to be removed during sample preparation to ensure that the sample surface is clean.

3. The sample is electrically conductive

SEM imaging relies on secondary electrons and backscattered electron signals. Excess electrons or free particles can accumulate on the surface of non-conductive samples, affecting signal transmission. Therefore, non-conductive samples need to be electrically conductive, such as gold or carbon plating.

B. SEM sample preparation method

According to the sample type, morphology, conductivity and observation requirements, the appropriate sample preparation method is selected.

1. Bulk samples

Bulk samples should be kept as small as possible to avoid exceeding the size of the EM stage. Use conductive adhesive to bond the sample to the sample stage. For samples that are not conductive or have poor conductivity, a coating treatment is required.

2. Powder sample

Glue the conductive tape to the sample stage, sprinkle the powder sample evenly on the conductive adhesive, and blow off the unstuck sample with compressed air. For samples that are not conductive or have poor conductivity, a coating treatment is required.

3. Liquid samples

Using a thin copper sheet as a carrier, the conductive adhesive is glued to the sample stage, and the liquid sample is dropped on the copper sheet, and the solvent is allowed to evaporate and dry before sputtering and SEM testing.

4. Biological samples

Biological sample preparation is complex and includes sampling, washing, fixation, dehydration, drying, stickiness, and conductive treatment. Appropriate drying methods need to be selected to ensure that the surface topography of the sample is not damaged.

C. Precautions

1. Ensure that the surface of the sample is free of contamination, wrinkles, obvious artificial damage and additional structures.

2. When plating heavy metal films, control the thickness of the film to ensure that the film layer does not mask the structure of the sample itself.

3. When EDS quantitative analysis is required, the metal film should not be coated so as not to affect the X-ray absorption.

4. The thickness of the powder sample should be uniform, and the amount should not be too much, so as to avoid affecting the effect of gold spraying.

SEM sample preparation is the key to obtaining accurate, clear images. Understanding the sample requirements and preparation methods, as well as following the precautions, will help improve the effectiveness of SEM analysis.

ZEPTOOLS ZEM18 Benchtop Scanning Electron Microscope

ZEPTOOLS is a scientific instrument company with fully independent intellectual property rights. Since the 1990s, our R&D team has been committed to providing excellent instruments for nanoscience research. At present, the company has a number of product lines including PicoFemto series of in-situ TEM measurement system, in-situ SEM measurement system, ZEM series of benchtop scanning electron microscope, JS series of step profiler, nano-displacement stage, two-dimensional material transfer stage, probe stage and cryogenic system, grating Ruler etc., which have gained a high degree of attention at home and abroad, and filled the gaps of the country's high-end precision instruments in the field of a number of blank.