Scanning Electron Microscope (SEM) Various Applications and Case Studies

Scanning Electron Microscope (SEM) is an electron microscope that serves as a tool for microstructure observation, bridging the gap between transmission electron microscopy and optical microscopy. It enables the microscopic imaging of materials by utilizing the surface properties of the sample. SEM is an indispensable tool in modern research and finds wide applications in various fields such as materials science, physics, biology, geology, archaeology, and more. This article will demonstrate the significant role of SEM in research through case studies in some common application areas.

1.Nanomaterials

SEM is used to analyze the structure of nanomaterials, particle size, distribution, uniformity, and agglomeration. Combined with energy-dispersive X-ray spectroscopy (EDS), SEM can also analyze the micro-area composition of nanomaterials to determine material composition.

Case Study 1:

As shown in Figure 1, the Mg/MOF-74 nano-composite consists of MOF-74 metal-organic framework material intertwined with columnar and needle-shaped magnesium nanoparticles. The overall particle size is on the order of micrometers. The active metal sites in the MOF-74 are magnesium, hence the EDS elemental distribution map shows only C, O, and Mg.

Figure 1. FE-SEM Image and EDS Elemental Distribution Map of Mg/MOF-74 Nano-composite

2.Polymer Materials

Observing the microstructure of polymer materials, as well as the aging, fatigue, tensile, and torsional fracture and diffusion during the process.

Case Study 2:

As shown in Figure 2a, the fracture surface of the fiber and matrix is relatively smooth and perpendicular to the fiber axis, and there are no matrix cracks or fiber fractures below the fracture surface. Figures 2b and 2c reveal numerous cracks in the reaction layer near the fracture surface. Although the fracture surface of SiCf/Ti-200 composite material is irregular, it can be regarded as composed of several small flat regions based on the relative height of the matrix fracture surface.

Figure 2. SEM Image of Longitudinal Fracture Surface of SiCf/Ti-200 Composite Material

3.Metal Materials

SEM is used to analyze the microstructure, fracture modes, surface wear, corrosion, and deformation of metal materials. It can also analyze the quality and defects of steel products (such as bubbles, microcracks, micropores, etc.). Combined with energy-dispersive X-ray spectroscopy (EDS), SEM can determine the element segregation of metals and alloys, observe phases, and identify compositions.

Case Study 3:

Due to the XRD results, the content of reverse austenite is highest at 620°C. Therefore, the tempering time was further increased to 32h and 64h based on this tempering temperature. Figure 3 shows the metallographic structure and SEM images of these two tempering times. As shown in Figure 3, with the increase of tempering time, the new α phase continues to increase, and the volume of this phase gradually increases.

Figure 3. Optical Microscope (OM) Image and Scanning Electron Microscope (SEM) Image of Sample Tempered at 620°C

4.Ceramic Materials

Analysis of the microstructure and defects of ceramic materials, observing the crystal phases, crystal sizes, impurities, distribution of pores and voids, grain orientation, and grain size in ceramic materials.

Case Study 4:

From Figure 4, it can be observed that all ceramics exhibit a dense structure. With the addition of MgO, the average grain size of ceramics decreases significantly from 30-40 μm (SYT14) to 3-4 μm (SYT14-9M), and the average grain size is comparable to that of pure ST ceramics. Combining with the EDS spectrum, it can be clearly seen that the material mainly composed of Mg oxide forms a second phase at the grain boundaries of the ceramics, which inhibits the growth of grains. The inset shows that the ST and SYT14-9M ceramic samples appear yellow, while the SYT14 and SYT14-7M ceramic samples appear dark blue. This indicates that there are fewer Ti3+ ions in the ST and SYT14-9M ceramics. This is mainly because the introduction of MgO can stabilize the valence state of Ti4+ ions, primarily due to the occurrence of defect chemical reactions when Mg2+ ions are introduced into ST.

Figure 4. SEM Image of Ceramics, with insets showing the EDS spectra of SYT14-7M and SYT14-9M ceramics.

5.Physics Applications

Observing the Effect of Surface Treatment on Material Hardness, Optical, and Other Physical Properties; Also, Observing Surface Morphology after Coating and Photolithography Etching.

Case Study 5:

From Figure 5, it is evident that the untreated carbon fiber surface appears smooth and flawless, while the surface of the carbon fiber after sizing shows the presence of a sizing film along with various-sized particles. Moreover, it can be observed that the microstructure of the carbon fiber surface undergoes changes with different sizing concentrations. This is primarily due to the fact that at lower concentrations, the sizing forms a complete film on the fiber surface, thereby improving micro-pores and cracks on the fiber surface. Conversely, excessively high concentrations result in the formation of granular particles on the fiber surface, leading to a relatively rough and uneven surface. The impact of sizing agents on the morphology of carbon fiber surfaces is a complex process. Generally, variations in surface roughness significantly affect the interfacial bonding of carbon fiber composites. Even minor changes in roughness can greatly influence the interfacial adhesion between the fiber and the matrix resin.

Figure 5. SEM Image of the Surface of Sized Carbon Fiber

6.Applications in Biology

Studying the surface morphology of bioactive materials and bioceramics, as well as cell growth conditions; also used to observe the pore structure of hydrogels, the fiber structure of collagen, the pore distribution of artificial bones, the scale and coating of magnetic bioimaging materials, etc.

Case Study 6:

From Figure 6, it can be seen that cells adhere to PGS/PLLA, but the quantity is relatively low and the arrangement is sparse. On the surface of PGS/PLLA-PDA, the number and density of cells increase compared to PGS/PLLA, with pseudopodia extending and cells exhibiting a polygonal shape with good morphology. On PGS/PLLA-PDA-CoⅡ, the cell growth density significantly increases, with a more dense arrangement, cell fusion, and a larger spreading area. There are more pseudopodia and lamellipodia, with increased length and number of cell synapses. There are more dendritic protrusions interconnecting between cells and between cells and material pores, indicating that PGS/PLLA-PDA-CoⅡ material is more conducive to cell adhesion and growth.

Figure 6. SEM image of co-cultured sheep temporomandibular joint disc cells with scaffolds before and after surface treatment for 2 days.

7.Microelectronics Industry Applications

It can be used for failure analysis of semiconductor devices, observation of microstructures, and identification of failure points and defects.

Case Study 7:

From Figure 7, it can be observed that the Sb2Se3 crystal is composed of some large micron-sized grains. After chemical etching, the distribution of grains in (Sn0.05Sb0.95)2Se3 crystal is clearly displayed, with an average grain size of about 15μm. Furthermore, the spatial distribution of each element in the crystal can be observed through the EDS elemental distribution map. Sb and Se are evenly distributed throughout the crystal, while the doping element Sn shows enrichment at the grain boundaries after chemical etching. For the (Sn0.10Sb0.90)2Se3 crystal with higher Sn doping concentration, the Sn enrichment region becomes more pronounced, as shown in Figure 7c. Point 1 in Figure 7d is taken from Figure 7b, while point 2 is taken from Figure 7c. The atomic ratios of Sn:Sb:Se at these two points are 14.54:23.74:61.72 and 15.39:22.22:62.39, respectively. It can be seen that the Sn enrichment regions in (SnxSb1-x)2Se3 crystals with different chemical compositions exhibit similar element compositions, and the specific atomic ratios are close to the stoichiometric ratio corresponding to Sn2Sb4Se8, which is 2:4:8.

Figure 7. SEM images of the surfaces of Sb2Se3 crystal (a), (Sn0.05Sb0.95)2Se3 crystal (b), and (Sn0.10Sb0.90)2Se3 crystal (c) after chemical etching with NaOH solution, along with the EDS spectra of two points tested (d).