Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) is an important tool in the field of materials science and can be used to examine the structure and composition of a wide range of samples. It enables advanced surface analysis, having use in multiple areas such as product failure investigation and contaminant identification.
SEM/EDS offers several key advantages. This technique is versatile, accurate, and usually non-destructive. What’s more, it can provide qualitative analysis of all but two elements in the periodic table (hydrogen and helium), so it may be applied in a range of materials science applications.
How SEM/EDS works
SEM/EDS is a combined technique that uses a scanning electron microscope and energy-dispersive X-ray spectroscopy to analyze materials. SEM provides the imaging component, while EDS is used for detection. While traditional microscopy uses light to create an optical signal, a scanning electron microscope uses electrons. EDS is then used for detection and analysis.
SEM/EDS offers several key advantages. This technique is versatile, accurate, and usually non-destructive.
The microscope works by generating a beam of electrons from an emitter-cathode within an electron gun. This beam is then accelerated and focused by an anode and a series of electromagnetic lenses. It is scanned across the surface of the sample, interacting with the atoms in the sample and causing secondary electrons to be emitted from the surface. The emitted electrons then reach the EDS detector.
“EDS is a technique used with electron microscopes to determine the chemical composition of materials,” explains Chris Stephens, an applications scientist at Thermo Fisher Scientific, specializing in EDS, WDS (wavelength-dispersive x-ray spectroscopy), and EBSD (electron backscatter diffraction). “EDS works by measuring the energy of X-rays emitted when the electron beam strikes the specimen surface and then uses this information to determine which elements are present and at what concentration.”
Stephens adds that since the electron beam is highly localized, EDS is used to provide high-resolution chemical composition maps and give a clear understanding of processes occurring within a material. “EDS is widely used in application specific packages, for example, to get detailed particle classifications reported to industry standards,” he says.
Applications of SEM/EDS in materials science
The versatility and high-resolution capabilities of SEM/EDS lend its use in a variety of applications. “EDS is commonly used across materials science fields, including geology, metallurgy, microelectronics, ceramics, coatings, cements, soft materials, and everything in between,” says Stephens. “It is used to characterize every aspect of a material’s life cycle through development, process control, and failure analysis.”
SEM/EDS is typically used as an investigative approach and can be tailored to specific applications. A broad range of industries find use for this technique, including automotive supplies, plastics manufacturing, pharmaceuticals, and electronics manufacturing, to name a few.
One of the most common uses for SEM/EDS is surface characterization. The technique can be used to study the surface topography and morphology of materials such as metals, composite, polymers, and ceramics. This information is helpful in understanding things like the effects of the manufacturing process and the degradation and wear of materials. For example, it enables manufacturers to investigate failure mechanisms or characterize defects in devices like transistors or integrated circuits.
Not only can SEM/EDS provide information about the surface structure of various materials, but it can also measure their elemental composition. This makes it particularly useful for applications such as studying nanoparticles or examining corrosion layers. Moreover, SEM/EDS can be used to study organic as well as inorganic materials. Other common uses for SEM/EDS include contaminant identification in various manufacturing processes and forensic analysis—to analyze trace evidence such as gunshot residue, paint fragments, and explosives.
SEM/EDS applications are further enhanced through the use of advancing technologies such as machine learning and 3D imaging. SEM/EDS processes often produce large datasets, which can be labor-intensive to analyze manually. Machine learning algorithms can be used to identify correlations between material properties and speed up analysis. Meanwhile, electron tomography can be used alongside EDS to develop 3D images of materials. This has a variety of uses in applications such as process control and technical cleanliness.
Advantages and limitations of SEM/EDS
As with all analytical techniques, SEM/EDS has its own set of advantages and drawbacks. A key quality is that it can provide precise chemical information about samples on very small scales. “The main benefit of EDS is its versatility, providing specimen information over tens of nanometers through to tens of centimeters,” says Stephens, adding that the technique is also accurate, sensitive to low concentrations, and non-destructive in most situations.
Not only can SEM/EDS provide information about the surface structure of various materials, but it can also measure their elemental composition.
EDS is also relatively simple to execute and may be used alongside additional investigative methods. “EDS requires minimal sample preparation to get qualitative information and can be readily combined with other techniques,” says Stephens. One such example is EBSD. In addition to secondary electrons, backscattered electrons are emitted from the surface of the analyzed sample. Unlike secondary electrons that come from the sample, the backscattered electrons are incident electrons from the emission source. EBSD is used to determine crystallographic data that EDS alone cannot provide.
A limitation of EDS is that it can’t be used to analyze hydrogen and helium. The nuclei of these elements each have only one neutron, so there are no free electrons to emit. In addition, X-rays produced by lithium, beryllium, and other low-atomic number elements may be insufficient for measurement. Carbon also represents issues as it is often present as a surface contaminant.
Another drawback is that SEM involves subjecting the sample to high-vacuum conditions. As such, the technique is generally not used to analyze liquid samples, although special preparation techniques have been developed for select cases. As with other techniques, there are also limitations in terms of sample size and element concentration. Some of these may be overcome by adjusting sample preparation techniques, although opting for an alternative technique might be necessary.
SEM/EDS is considered a vital tool for many applications. With many advantages, few drawbacks, and the potential for combination with other detection methods, SEM/EDS is an exciting and promising technique for high-resolution imaging and chemical analysis within materials science research.